No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Hydraulic modeling: Concepts and practice
Abstract
Hydraulic modeling is a form of physical modeling used to investigate design and operation issues in hydraulic engineering. It entails the use of a scaled model for replicating flow and fluid-transport processes in diverse natural flow systems and for evaluating the performance of hydraulic structures and hydraulic machines. An advantage of hydraulic model is its potential capacity to replicate many features of a complicated flow situation. The manual is intended to be a useful reference for the hydraulic engineering conducting a hydraulic model study and for the sponsor or client of a hydraulic model study wishing to become conversant with the concepts supporting model design and operation.
... A water flume, which is a water trough with moving water, is used in hydraulic studies as an analog of a fluvial system, but at a smaller, more manageable scale (Franco 1978;Ettema et al. 2000). The validity of water flume studies relies on the theory of similarity between the model and the real-world example. ...
... The validity of water flume studies relies on the theory of similarity between the model and the real-world example. Flumes were used to develop the theoretical background of fluvial hydraulics, chiefly the underlying principles of complex flows on and by the channel bed, bed topography, sediment transportation, and various obstacles such as weirs, bridge abutments, piers, dams, and other structures (e.g., Boguchwal and Southard 1990;Southard and Boguchwal 1990;Ettema et al. 2000Ettema et al. , 2006Smith and Foster 2005;Euler et al. 2017). The results of flume studies are used to interpret or predict real-world events (e.g., Ashmore and Parker 1983;Ettema et al. 2000), and have become increasingly important to understand probable impacts of proposed river restoration projects (e.g., Zhou and Endreny 2013;Pagliara and Kurdistani 2017). ...
... Flumes were used to develop the theoretical background of fluvial hydraulics, chiefly the underlying principles of complex flows on and by the channel bed, bed topography, sediment transportation, and various obstacles such as weirs, bridge abutments, piers, dams, and other structures (e.g., Boguchwal and Southard 1990;Southard and Boguchwal 1990;Ettema et al. 2000Ettema et al. , 2006Smith and Foster 2005;Euler et al. 2017). The results of flume studies are used to interpret or predict real-world events (e.g., Ashmore and Parker 1983;Ettema et al. 2000), and have become increasingly important to understand probable impacts of proposed river restoration projects (e.g., Zhou and Endreny 2013;Pagliara and Kurdistani 2017). However, scaling does have problems because some physical effects, such as gravity and water density, cannot be scaled (Ettema et al. 2000;Heller 2011). ...
Laboratory water flumes are artificial troughs of moving water widely used in hydraulic studies of fluvial systems to investigate real-world problems at smaller, more manageable scales. Water flumes have also been used to understand bone transportation sorting and bone orientation found in the fossil record using actual bones. To date, these studies have not involved scaled bones. A 1/12 scale model of a 21.8-m long skeleton of Apatosaurus, a long-necked sauropod dinosaur from the Late Jurassic, was used to explore three problems at Dinosaur National Monument (USA) that cannot be explained by tradition bone flume studies: (1) why there is an abrupt bend in articulated vertebrae, (2) why articulated dorsals are inverted relative to the pelvis, and (3) how bone jams form. The flume experiments established that (1) bed friction with the wing-like transverse processes of vertebrae resists the force of the water flow, whereas those vertebrae lacking the processes are free to pivot in the flow; (2) elevation of the dorsal vertebrae by the transverse processes subjects the vertebrae to the energy of the flow stream, which causes the vertebrae to flip. Computation fluid dynamics (CFD) software shows this flip was due to differential pressure on the upstream and downstream sides. (3) The formation and growth of bone clusters or jams (analogous to log jams in rivers) occur as transported bones pile against an initial obstruction and jammed bones themselves become obstacles. These preliminary studies show that scale models can provide valuable insights into certain taphonomic problems that cannot be obtained by traditional bone flume studies.
... Two clarification notes. In the literature on scale modelling there are mentions of "principles of similarity" (Rouse 1950;Robinson 1992;Ettema et al. 2000;Sterrett 2006;, "laws of similarity" (Rouse 1950;U. S. Army Corps 1963), "criteria of similarity" (Rouse 1950;Hughes 1993;Ettema et al. 2000;Sterrett 2006; and "requirements of similarity" (Rouse 1950;Hughes 1993;Ettema et al. 2000;Sterrett 2009). ...
... In the literature on scale modelling there are mentions of "principles of similarity" (Rouse 1950;Robinson 1992;Ettema et al. 2000;Sterrett 2006;, "laws of similarity" (Rouse 1950;U. S. Army Corps 1963), "criteria of similarity" (Rouse 1950;Hughes 1993;Ettema et al. 2000;Sterrett 2006; and "requirements of similarity" (Rouse 1950;Hughes 1993;Ettema et al. 2000;Sterrett 2009). Although it could seem that referring to "laws" has stronger implications than referring to "requirements" of similarity, they should be considered synonymous. ...
... In the literature on scale modelling there are mentions of "principles of similarity" (Rouse 1950;Robinson 1992;Ettema et al. 2000;Sterrett 2006;, "laws of similarity" (Rouse 1950;U. S. Army Corps 1963), "criteria of similarity" (Rouse 1950;Hughes 1993;Ettema et al. 2000;Sterrett 2006; and "requirements of similarity" (Rouse 1950;Hughes 1993;Ettema et al. 2000;Sterrett 2009). Although it could seem that referring to "laws" has stronger implications than referring to "requirements" of similarity, they should be considered synonymous. ...
The thesis proposes an account of the means of scientific representation focused on similarity, or more specifically, on the notion of “creative similarity”. I first distinguish between two different questions regarding the problem of representation: the question about the constituents and the question about the means of representation (following Suárez 2003; van Fraassen 2008). I argue that, although similarity is not a good candidate for constituent of representation, it can satisfactorily answer the question about the means of representation if adequately characterized. To motivate this position, I dispute the main arguments offered against similarity as means of representation, namely the arguments from variety, vagueness, and misrepresentation, and contend that similarity plays a central epistemic role in practices of representing in science. The study of the role of similarity in scientific practice, I argue, requires the analysis of the uses of judgments of similarity in the construction of scientific models. I examine the cases of the Mississippi Basin Model and the San Francisco Bay Model to illustrate how judgments of similarity are directly involved in the production of epistemically fruitful models. Informed by the practical investigation developed throughout the thesis, I finally outline what I call the creative similarity account of the means of representation. The notion of “creative similarity” helps to capture the way in which similarity, as means of representation, intervenes in actual practices of representing, namely, in the form of a productive interplay of judgments of similarity and distortions (i.e. idealizations, abstractions, simplifications), which is employed by resourceful agents with the aim of understanding aspects of the natural world.
... LITERATURE REVIEW Size-scale effects are attributed to the inability to maintain geometric, kinematic, and dynamic similitude between the prototype and model scale. To model a perfect representation of the prototype, the Froude (gravity to inertia forces), Reynolds (viscous to inertia forces), and Weber (surface tension to inertia forces) numbers must be identical at the model and prototype scales (Ettema 2000). Equations 1, 2, and 3 present the definitions of the Froude, Reynolds, and Weber numbers, respectively. ...
... Table 1 summarizes minimum head recommendations from the reviewed literature. Ettema (2000) 0.025 Rating curve Ettema (2000) 0.06 Nappe shape Hager and Schwalt (1994) 0.05 Broad-crested Johnson (1996) 0.001-0.028 Flat-top Johnson (1996) 0.014 Sharp-crested Krischmer (1928) 0 ], where p is water pressure, γ is specific weight of water, z is water level elevation, and V is upstream velocity). ...
... Table 1 summarizes minimum head recommendations from the reviewed literature. Ettema (2000) 0.025 Rating curve Ettema (2000) 0.06 Nappe shape Hager and Schwalt (1994) 0.05 Broad-crested Johnson (1996) 0.001-0.028 Flat-top Johnson (1996) 0.014 Sharp-crested Krischmer (1928) 0 ], where p is water pressure, γ is specific weight of water, z is water level elevation, and V is upstream velocity). ...
Experimental physical model studies of hydraulic structures are often conducted to replicate flow behavior that may occur at the prototype scale. Geometric similitude is most often maintained between the prototype and model when studying reservoir and open channel hydraulic structures to account for the dominant gravity and inertia forces while other fluid forces (e.g., viscosity,surface tension) are assumed negligible. However, as model size and/or upstream head decreases, other fluid forces can exceed the negligible level and influence model flow behavior. This phenomenon is referred to as size-scale effects and is one potential origin of error in predicting the prototype behavior through testing geometrically similar models.
To extend the existing research of size-scale effects on nonlinear weirs half-and quarter-round trapezoidal labyrinth weirs and piano key weirs were fabricated at length ratios of 1, 2, 3, 6, and 12. The largest weir model for each weir type (i.e., a weir height of 36 in for labyrinth weir models and a weir height of 33 in for piano key weir models) served as the corresponding prototype.Weir models were hydraulically tested to assess differences among head-discharge relationships and flow behavior.
Limiting criteria were recommended to avoid size-scale effects depending on the weir type and model size. The results of this study will help hydraulic modelers determine what limiting criteria should be met to avoid size-scale effects.
... where φ is another functional symbol, and R = ρVd/μ and W = V(ρd/σ) 0.5 are the Reynolds and Weber numbers of the approach flow, respectively (Figure 1 presents V and d as dependent parameters). Since the viscosity effects are insignificant (turbulent flow with R > 25000), R is eliminated from Equation (3) [47,48]. In lower values of the flow depth, surface tension may affect Froude-scaled models [49]. ...
... where ϕ is another functional symbol, and R = ρVd/µ and W = V(ρd/σ) 0.5 are the Reynolds and Weber numbers of the approach flow, respectively ( Figure 1 presents V and d as dependent parameters). Since the viscosity effects are insignificant (turbulent flow with R > 25000), R is eliminated from Equation (3) [47,48]. In lower values of the flow depth, surface tension may affect Froude-scaled models [49]. ...
This paper focuses on Piano Key Weirs (PKWs) as an effective solution for improving the discharge capacity of spillway systems. The flow behavior in inlet and outlet keys is experimentally studied to analyze the discharge capacity of PKWs with different plan shapes (i.e., rectangular, trapezoidal, and triangular). The results show that in outlet keys, the flow aeration regimes extend to higher values of headwater ratios (Ho/P) by increasing the length magnification ratio (B/w) and apex width ratio (A/w). In addition, the local submergence length is a decreasing function of A/w, especially in high flow heads. While the total interference length enlarges by reducing A/w in lower Ho/P values (Ho/P < 0.5), a reverse trend is observed in higher headwater ratios. PKW performance may also be impacted by the flow contraction and recirculation zone in inlet keys, which intensify in higher values of Ho/P, B/w, and A/w. According to the obtained results, while the discharge coefficient is a decreasing function of A/w in Ho/P > 0.4, it may have a reverse trend in lower head conditions. In addition, a trapezoidal PKW has the highest discharge efficiency in a wide range of the studied domain (Ho/P > 0.25 and B/w ≥ 2). It can improve the discharge efficiency by around 5%, while its body volume is almost 7% smaller than the traditional rectangular PKW. However, for low-length and high-head conditions (B/w = 1 and Ho/P > 0.5), the efficiency a rectangular PKW exceeds that of the other shapes.
... Therefore, a relatively large value of e H is used to limit the extent of the laboratory setup while keeping relatively high flow depths thanks to a smaller value of e V (Figure 1). This strategy is expected to improve the accuracy and representativeness of the measurements (Arndt et al., 2000;Li et al., 2019). ...
... 2. A flooding scenario is defined here at the prototype scale, by setting the value of the characteristic discharge Q 0 , flow depth h 0 , and roughness height k s for a given urban geometry (with a typical street width b). Based on these values and the properties of water (viscosity, surface tension), it is hence possible to set the value of the five dimensionless numbers introduced in Equation 1: h 0,p /b p , F 0,p , R 0,p , k s,p /h 0,p , and W 0, p , where subscript "p" refers to the real-world prototype scale.As detailed by Li et al. (2019) and Heller (2011), as well as in textbooks (Arndt et al., 2000;Chanson, 2004), laboratory-scale modeling of free surface flow is generally based on Froude similarity. This means that the scaling of flow velocity is related to the geometric scaling, by considering F 0,m = F 0,p , with subscript "m" referring to the model scale. ...
Geometrically distorted scale models have been a valuable tool for physical modelling of urban flooding in a network of streets. However, little is known so far about the bias induced in such cases by the model geometric distortion. Here, we use 2D computational modelling to provide a first systematic quantification of this bias in the case of a synthetic urban layout. The bias is found to be generally small, with the maximum deviations of the upscaled flow depth and discharge partition from the corresponding values of the undistorted model being around 10 % in the case of relatively rapid and shallow flow conditions. When the geometric distortion is increased, the computations reveal a non-monotonous pattern of the flow variables (depth, discharge partition, size of flow separation zones), which results from a competition between declining frictional losses and growing local losses in the model. These findings may guide the design of distorted scale models of urban flooding and assist the interpretation of laboratory observations for assessing flood protection measures, for process understanding or for validating computational modelling.
... Certainly, observing a functioning scaled version of a proposed design is reassuring to those involved in the project where success impacts public safety, performance, longevity, and monetary expenditures. Explicitly following geometric, kinematic, and dynamic similarity is the ideal for simulating a full-size structure (Montes 1998;Ettema et al. 2000;Novak et al. 2010). This is often unachievable, however, when a common fluid (e.g., water) is used for both the model and prototype. ...
... An uncertainty analysis following ASME PTC 19.1 (ASME 2006) was performed to quantify confidence levels of experimental results, as discussed in the following section. Sarginson (1972) 50 Linear Cylindrical weir Hager and Schwalt (1994) 50 Linear Flat Johnson (1996) 1 -28 Linear Flat Bollrich and Aigner (2000) 4 0 -60 Linear Half-round Ettema (2000) 25 Linear Flat, rounded Castro-Orgaz and Hager (2014 ...
Using similitude relationships, laboratory-scale models have been used for decades to predict and confirm prototype hydraulic structure performance. For free-flow weir discharge conditions, gravity and inertia typically represent the dominant forces, and the Froude number scales the head-discharge performance between model and prototype. Under low-head flow conditions, other forces (e.g., viscous and surface-tension forces) can become relevant, resulting in differences between the model and prototype performance. In this study, the head-discharge relationships for 15 different nonlinear weirs (labyrinth and piano key) with prototype-to-model length ratios of 2, 3, 6, and 12 (based upon Froude modeling) were evaluated, with the largest weirs (∼1 m tall) serving as prototypes. This study found differences in the head-discharge performance between prototype and model that exceeded what could be explained solely by model and measurement effects, confirming the presence of scale effects. The range of small upstream heads influenced by scale effects, in general, increased with decreasing model size. The minimum dimensionless head above which scale effects were negligible increased with decreasing model size. As such, model size and geometric scale appear relevant because no single minimum upstream head limit was found that characterized a scale effects limit for all nonlinear weirs tested herein.
... A general rule applies to unsteady flow experiments: When fully rough flow occurs in a river; it is enough to assure that scaled flow is also fully rough to satisfy the Reynolds number criterion. Then the Froude number becomes the main criterion to calculate scaling between the model and the prototype [43]. The similitude of boundary shear stresses is usually obtained by applying the Shields number to satisfy the similarity of forces acting on sediment particles in a prototype and a model [43]. ...
... Then the Froude number becomes the main criterion to calculate scaling between the model and the prototype [43]. The similitude of boundary shear stresses is usually obtained by applying the Shields number to satisfy the similarity of forces acting on sediment particles in a prototype and a model [43]. Mao [24] used Froude scaling to prepare a model that represents a narrow gravel-bed river. ...
Recent advances in understanding bedload transport under unsteady flow conditions are presented, with a particular emphasis on laboratory experiments. The contribution of laboratory studies to the explanation of key processes of sediment transport observed in alluvial rivers, ephemeral streams, and river reaches below a dam is demonstrated, primarily focusing on bedload transport in gravel-bed streams. The state of current knowledge on the impact of flow properties (unsteady flow hydrograph shape and duration, flood cycles) and sediment attributes (bed structure, sediment availability, bed composition) on bedload are discussed, along with unsteady flow dynamics of the water-sediment system. Experiments published in recent years are summarized, the main findings are presented, and future directions of research are suggested.
... Due to the incompressible flow in weirs, the effect of changes in the specific mass (ρ) can be neglected. The influence of viscosity and surface tension can be disregarded if the flow is turbulent and the flow height over the weir, according to the recommendation of Ettema et al. (2000), is not less than 0.5 cm. Considering that the acceleration due to gravity and the channel width is constant for all experiments, they can be neglected in the analysis. ...
This study focuses on the experimental investigation of an inclined circular labyrinth weir with angles of inclination of 60, 70, 80, and 90 degrees. Additionally, the influence of different weir diameters (15, 20, 25, and 30 cm) under various flow rates on hydraulic performance and the discharge coefficient of the weirs were examined. Experimental results revealed that the flow over the weir initially exhibited a free flow type, transitioning to submerged flow as the flow rate increased. No air infiltration into the flow was observed. Moreover, an increase in the dimensionless ratio of the total hydraulic head to the inclined labyrinth weir's height led to a decrease in the discharge coefficient. The inclined weir with an angle of inclination of 60 degrees exhibited the highest discharge coefficient, while the vertical weir had the lowest coefficient. The analysis of weir diameter showed that although the initial highest discharge coefficient occurred at a 15 cm diameter, further variations in the discharge coefficients among different diameters were minimal, indicating an insignificant effect of weir diameter on the discharge coefficient. Overall, this study provides insights into the hydraulic behavior and discharge coefficient of inclined circular labyrinth weirs, contributing to the understanding and optimization of their performance in water management systems.
... After reviewing the available technical literature, it is recommended to ensure thorough turbulence (Re > 2000) to eliminate scale effects during the conduct of single-phase tests related to weirs. Additionally, to minimize the effects of surface tension force, it is recommended to maintain a Weber number higher than 100 and a flow depth of more than 0.03 m at the crest [19]. Considering these points, the minimum and maximum values of the Reynolds number are 20382 and 124014, respectively. ...
The performance of semi-cylindrical weirs (SCWs) is evaluated and modified by considering a downstream ramp. Modified semi-cylindrical weirs (MSCWs) were constructed in 12 variations, with 4 different slopes (θ) and 3 radii (R), and were tested through laboratory experiments. Additionally, numerical studies were conducted to examine the performance of the MSCW models. The findings suggest that the θ significantly affects the hydraulic characteristics downstream of the MSCWs. In the traditional SCW (θ = 90°), the flow downstream of the weir is turbulent and irregular, and the flow depth increases with aeration. However, reducing θ decreases turbulence in the flow downstream of the weirs. The discharge coefficient (Cd) of the MSCWs is dependent on R (negative correlation) and independent of θ. When the ratio of the upstream flow depth (yup) to R changes from 0.306 to 1.36, the value of Cd varies within the range of 1.1–1.45. Examination of bed pressure distribution on the MSCW models reveals that reducing θ effectively controls the negative pressure on the crest surface.
... These latter comments remind us that, to date, most of the research about spillway flows has been conducted based on observations and measurements of flow on scale physical models [51]. Because the fluid properties are not scaled, scale models suffer scale effects, whose impact on flow properties may be important but depends on which specific parameter is considered [52][53][54][55][56]. Experimental studies using large-scale models [57][58][59] or even on prototypes [60][61][62] need to be performed to complement traditional research and enable the validation of the current knowledge at the scale to which it is applied. ...
Over the past decades, significant advances have been achieved in hydraulic structures for dams, namely in water release structures such as spillway weirs, chutes, and energy dissipators. This editorial presents a brief overview of the eleven papers in this Special Issue, Advances in Spillway Hydraulics: From Theory to Practice, and frames them in current research trends. This Special Issue explores the following topics: spillway inlet structures, spillway transport structures, and spillway outlet structures. For the first topic of spillway inlet structures, this collection includes one paper on the hydrodynamics and free-flow characteristics of piano key weirs with different plan shapes and another that presents a theoretical model for the flow at an ogee crest axis for a wide range of head ratios. Most of the contributions address the second topic of spillway transport structures as follows: a physical modeling of a beveled-face stepped chute; the description and recent developments of the generalized, energy-based, water surface profile calculation tool SpillwayPro; an application of the SPH method on non-aerated flow over smooth and stepped converging spillways; a physical model study of the effect of stepped chute slope reduction on the bottom-pressure development; an assessment of a spillway offset aerator with a comparison of the two-phase volume of fluid and complete two-phase Euler models included in the OpenFOAM® toolbox; an evaluation of the performance and design of a stepped spillway aerator based on a physical model study. For the third topic of spillway outlet structures, physical model studies are presented on air–water flow in rectangular free-falling jets, the performance of a plain stilling basin downstream of 30° and 50° inclined smooth and stepped chutes, and scour protection for piano key weirs with apron and cutoff wall. Finally, we include a brief discussion about some research challenges and practice-oriented questions.
... Then, it must be checked to make sure that the flow is in the "wholly rough" regimethe condition for which energy losses become independent of Reynolds number. This requirement is enumerated by Ettema et al. (2000) as: has some impact on model scale selection. ...
A physical model of Deadmans Run and a pair of railroad bridges was constructed to assess the impacts of the bridges on flood flows. Lower Platte South Natural Resources District is planning a series of improvements to Deadmans Run to improve flood conveyance capacity and remove approximately 500 homes and businesses from the floodplain. The rail bridges are located less than a mile from the confluence of Deadmans Run and Salt Creek, meaning the bridges present a significant bottleneck to the planned improvements. The physical model was used to characterize the drag effects caused by the bridges, which was used to improve computer models. Drag coefficients were determined from tests with individual bridges, then combined to predict losses for both bridges. These predictions aligned well with results from tests with both bridges. The model was modified with a flume to assess alternative designs to improve conveyance under the bridges. The addition of the flume caused a hydraulic jump to form at low tailwater depths, but the jump was drowned out for higher tailwaters. The addition of pier extensions and elliptical entrances to the spur bridge and flume, respectively, had similar effects: small benefits at high tailwaters and small detriments at low tailwaters. However, observed changes were only on the order of about 0.1 feet at prototype scale. On the other hand, removing the spur bridge completely provided substantial benefits to flume performance, with head reductions approaching nearly 1.0 ft upstream of the bridge. Advisor: David M. Admiraal
... 원형(prototype)의 수리현상을 모형(model)에서 재현하기 위해서는 두 흐름 사이에 수리학적 상사성(similitude)을 근 거로 실행되어야 유의미하다 (1) . 이를 위하여 필요한 세 가 지 조건은 다음과 같다 (2) (Figure 10(a)). ...
In this study, waterway modeling experiments were conducted by incorporating the information obtained by analyzing accident sites to prevent frequent accidents of firefighters that occur during water rescue operations conducted near water pipes in rapid flow waterways. Based on the conducted experiments, it was observed that the flow velocity increased with decreasing distance from the water pipe. Furthermore, the maximum flow velocity was found to be 3.99 times higher at the posterior end than at the anterior end of the water pipe, and the flow velocity was found to be higher at the lower side than at the upper side of the water pipe’s anterior end. The maximum flow velocity was measured to be 1.65 m/s at a distance of 10 cm from the entrance to the pipe, 2.63 m/s at a distance of 5 cm from the entrance to the pipe, 7.12 m/s within the pipe, and 5.33 m/s at a distance of 5 cm from the pipe’s exit. The average flow velocity was measured to be 0.94 m/s at a distance of 10 cm from the entrance to the pipe, 5.53 m/s within the pipe, and 4.64 m/s at a distance of 5 cm from the pipe’s exit. Furthermore, in this study, relevant standard operating procedures and regulations were taken into consideration. Based on the results obtained from this study, recommendations and guidelines were then accordingly devised for preventing accidents of firefighters that occur during water rescue operations.
... Although various debris scenarios are possible in nature e.g. a single piece of drifting debris or 108 accumulated multiple floating debris (Ettema et al., 2000), the single discrete floating debris 109 scenario, as seen in Fig. 1, forms the focus of the present study. Special attention was also devoted 110 to assessing the effect of debris orientation by examining detailed pressure-time histories in the 111 vicinity of the front spandrel wall and the arch barrel. ...
This paper explores flood-induced hydrodynamic and debris impact forces on masonry arch bridges using the numerical method smoothed particle hydrodynamics (SPH). Masonry arch bridges make up a significant proportion of the bridge stock in many parts of the world, including the UK and US. Although the masonry arch is a durable bridge form, those spanning watercourses can be vulnerable to the effects of flooding. Where fast flood flows impinge on the bridge superstructure, highly transient behavior is observed, which can lead to violent interactions, especially where debris is carried by the flow. This paper investigates flood-induced impact pressures on a typical single-span masonry arch bridge subject to hydrodynamic action and discrete floating debris. Different debris orientations relative to the bridge span are considered. Results revealed that the presence of the debris can lead to impact pressures an order of magnitude greater than the hydrodynamic conditions alone. Furthermore, the influence of debris orientation at impact was significant, with the 90° orientation resulting in higher peak impact pressures with shorter impact duration compared with the 0°.
... Both approaches must respect the design rules and represent certain specifics of the results presentation. The paper presents the results obtained by physical modelling [1,2,3,4] of water pollution transport. This approach is very time-consuming, it requires the background of a laboratory [5] with pumping equipment with distribution circuits and sufficient water capacity, measuring equipment and knowledge and experience of the operator, both in terms of craft, technical and scientific. ...
Water pollution is one of the most significant problems in the world today and is a global problem. Surface water pollution in streams and reservoirs is reflected in the deterioration of the quality of aquatic ecosystems, including those that occur in their vicinity or follow them. Lack of quality drinking water is one of the main causes of various diseases, which can lead to death, especially in developing countries. Therefore, it is important to detect water pollution in time and anticipate how it could develop and be transported in the stream. Measurements on a physical model are time-consuming and economically demanding, but for a given locality it can provide comprehensive information, including the proposal of possible measures and their verification. It is also a suitable approach for calibration and verification of mathematical models. One of the main tasks in the physical modelling of the spread of pollution in the stream was to find a suitable substance that would simulate the pollution without being aggressive towards the water pumping circuit. The method of electrical impedance spectrometry was chosen for its detection in the stream.
... A way to overcome the problem of extremely small flow depths in the laboratory, and to attain a flow regime close to that of the prototype, is the utilization of geometrically distorted physical models. Such physical models have different horizontal and vertical scale factors (Arndt et al., 2000;Kobus, 1984), with the former typically being larger than the latter in the context of shallow flow. Geometrically distorted models have been successfully applied in river hydraulics, with some representative examples being the physical model of the Mississippi River (Chanson, 1999) with horizontal and vertical scale factors equal to 2,000 and 100, respectively, and the physical model of Dargle River in Ireland (Novak et al., 2018) with horizontal and vertical scale factors equal to 100 and 50, respectively. ...
Laboratory studies of urban flooding often use geometrically distorted scale models due to the multi‐scale nature of these specific flows. The possible bias induced by geometric distortion has never been thoroughly investigated with dedicated laboratory experiments. In this study, we combine experimental and computational modeling to systematically assess the influence of the distortion ratio, that is, the ratio of horizontal to vertical scale factors, on upscaled flow depths and discharge partition between streets. Three flow configurations were considered: a street junction, a street bifurcation, and a small synthetic urban district. When the distortion ratio is varied up to a value of about 5, the upscaled flow depths at the model inlets decrease monotonously and the flow discharge in the branch that conveys the largest portion of the flow is greatly enhanced. For equal flow depths at the model outlets and depending on the configuration, the distortion effect induces a variation of the upstream flow depth approximately from ∼4% to ∼17% and a change in outlet discharge partition up to 24 percentage points. For a distortion ratio above 5, both upscaled upstream flow depths and outlet discharge partition tend to stabilize asymptotically. Our study indicates the direction and magnitude of the bias induced by geometric distortion for a broad range of flow cases, which is valuable for offsetting these effects in practical laboratory studies of urban flooding.
... For a more in-depth treatise on hydraulic scale models and associated scale effects, the reader is referred to the literature, e.g. Ettema et al. (2000) and Heller (2011). ...
This book presents the advancements made in applied metrology in the field of Urban Drainage and Storm water Management over the past two decades in scientific research as well as in practical applications. Given the broadness of this subject (measuring principles, uncertainty in data, data validation, data storage and communication, design, maintenance and management of monitoring networks, technical details of sensor technology), the focus is on water quantity and a sound metrological basis. The book offers common ground for academics and practitioners when setting up monitoring projects in urban drainage and storm water management. This will enable an easier exchange of results so as to allow for a faster scientific progress in the field. A second, but equally important goal, is to allow practitioners access to scientific developments and gained experience when it comes to monitoring urban drainage and storm water systems. In-depth descriptions of international case studies covering all aspects discussed in the book are presented, along with self-training exercises and codes available for readers on a companion website.
Numerous detailed examples are given in the book, with corresponding open-source codes and training files available to download here.
ISBN: 9781789060102 (Paperback)
ISBN: 9781789060119 (eBook)
... For a more in-depth treatise on hydraulic scale models and associated scale effects, the reader is referred to the literature, e.g. Ettema et al. (2000) and Heller (2011). ...
This book presents the advancements made in applied metrology in the field of Urban Drainage and Storm water Management over the past two decades in scientific research as well as in practical applications. Given the broadness of this subject (measuring principles, uncertainty in data, data validation, data storage and communication, design, maintenance and management of monitoring networks, technical details of sensor technology), the focus is on water quantity and a sound metrological basis. The book offers common ground for academics and practitioners when setting up monitoring projects in urban drainage and storm water management. This will enable an easier exchange of results so as to allow for a faster scientific progress in the field. A second, but equally important goal, is to allow practitioners access to scientific developments and gained experience when it comes to monitoring urban drainage and storm water systems. In-depth descriptions of international case studies covering all aspects discussed in the book are presented, along with self-training exercises and codes available for readers on a companion website.
Numerous detailed examples are given in the book, with corresponding open-source codes and training files available to download here.
ISBN: 9781789060102 (Paperback)
ISBN: 9781789060119 (eBook)
... The discharge Q was measured with a magnetic inductive flow meter ( 0.5% at full span). The surface tension effect on the rating curve is negligible if the flow depth exceeds some 0.025 m (Ettema et al., 2000) and 0.02 m particularly for standard ogee spillways (Breitschneider, 1978). Pfister, Battisacco, et al. (2013) state that a head of 0.015 m generates an error of 5% only in terms of discharge coefficient at a piano key weir. ...
Large wood increases the morphological and hydraulic complexity of rivers, yet it may block and modify the flood discharge capacity of hydraulic structures. To assess the related risk, blockage probability estimation for hydraulic structures such as reservoir spillways is needed. This work presents unstudied parameters for blockage of large wood with a reservoir-type approach flow, where the inflow velocity has a negligible magnitude. Experiments were conducted in a channel with an ogee crested spillway equipped with piers, representing a commonly used hydraulic structure. Artificial stems were used to systematically evaluate the influence of stem length and stem draft on the blocking process. Different hydraulic conditions were evaluated by changing the water level in the reservoir. The head at the spillway crest with respect to stem draft was found to be a key parameter for blockage probability estimation at a spillway. Additionally, stem length was related to the bay width in the estimation of blockage. Larger heads tend to reduce the blocking probability of large wood, for a given stem draft, while increasing the relative stem length tends to increase the blocking probability. A logistic regression model is provided to estimate large wood blockage probability at ogee crested spillways with piers. Finally, recommendations for engineering practice are presented.
... The above considerations are among the most popular research questions in the field of flood inundation modeling and mapping [22,23]. Applying hydraulic modeling for flood inundation at a large scale has been addressed by few researchers through coupled hydrologic and hydraulic models [24][25][26][27][28][29]. ...
Fluvial floods are one of the primary natural hazards to our society, and the associated flood risk should always be evaluated for present and future conditions. The European Union’s (EU) Floods Directive highlights the importance of flood mapping as a key stage for detecting vulnerable areas, assessing floods’ impacts, and identifying damages and compensation plans. The implementation of the EU Flood Directive in Greece is challenging because of its geophysical and climatic variability and diverse hydrologic and hydraulic conditions. This study addressed this challenge by modeling of design rainfall at the sub-watershed level and subsequent estimation of flood design hydrographs using the Natural Resources Conservation Service (NRCS) Unit Hydrograph Procedure. The HEC-RAS 2D model was used for flood routing, estimation of flood attributes (i.e., water depths and flow velocities), and mapping of inundated areas. The modeling approach was applied at two complex and ungauged representative basins: The Lake Pamvotida basin located in the Epirus Region of the wet Western Greece, and the Pinios River basin located in the Thessaly Region of the drier Central Greece, a basin with a complex dendritic hydrographic system, expanding to more than 1188 river-km. The proposed modeling approach aimed at better estimation and mapping of flood inundation areas including relative uncertainties and providing guidance to professionals and academics.
... The hydraulic dynamics are modeled based on the cylinder extension movement (positive to the right), in which the nonlinear parts are neglected. Therefore, the dynamic model of the valve-controlled asymmetric cylinder system Ph(s) = Da / I can be approximated as follows [57]: ...
Series elastic actuator (SEA) is a promising compliance device due to its lower output mechanical impedance, and it is widely applied to ensure safe human-robot interaction. Although some efforts have been made to achieve accurate stiffness tracking, the time-delay issue in SEA control has still not been well investigated. However, the time delay can cause an inaccurate response and increase the risk of injury. To overcome this problem, this article proposes a fast-response admittance control method for SEAs. First, an admittance control scheme considering the external force estimation is developed for a hydraulic SEA. Then, a parallel adaptive time-series (ATS) (P-ATS) compensator is proposed and further adopted in the admittance control scheme to compensate for the time delay and tracking error. The P-ATS compensator is a modification of the ATS compensator, which is enhanced with a unique parallel mechanism. Such a mechanism can save more computational resources on locating better parameters the for P-ATS compensator, thus improving its performance. Moreover, the parameter setting is converted to an optimization task, which is solved by the whale swarm algorithm (WSA) to achieve higher accuracy. The newly located parameters are compared to the current parameters based on a proposed evaluation criterion, thus guaranteeing the quality of the updated parameters. All the above strategies are employed to improve the SEA admittance control performance. The results obtained from both simulation and real-world experiments validate that, compared to conventional methods, the proposed method achieves a better performance in SEA stiffness tracking with lower time delay and tracking error.
... The structure had a prototype length of 12 m and a log diameter of 1 m. The resulting model structure had a 1:40 geometric scale, and flow conditions were selected to satisfy dynamic and kinematic similarity while limiting the applied bed shear stresses to ensure only clear water scour occurred (Ettema 2000). To prevent effects of ionic forces (cohesion), the loose bed material was not scaled, and consisted of poorly graded medium sand (D g ¼ 0.94 mm, and σ g ¼ 1.27). ...
... For instance, it can be used in the early design stages, where numerical modeling can provide boundary conditions for physical models, or in later stages, as a design tool to explore several solution alternatives. This kind of modeling is referred to by some authors as hybrid modeling or composite modeling (Kamphuis 1995, Kamphuis 1996and Ettema et al. 2000. A common factor to this approach is the need to validate CFD models with the data collection of the physical models (Hager & Boes, 2014). ...
Velocity measurements with Acoustic Doppler Velocimeter (ADV) in the collector channel of Ancoa Reservoir's physical model are contrasted with LES numerical simulation results. In order to evaluate the accuracy and applicability of the numerical model in highly turbulent flows, times series of velocity fields, Reynolds stress (′ ′ ̅̅̅̅̅̅) and energy spectral density are compared. LES calculations were developed in OpenFOAM free software and a wall adapting local eddy viscosity (WALE) model was used. The ADV data have been filtered in order to get rid of the spikes in the velocity signal due to the air bubble presence. The analysis was carried out for a constant discharge of 761 m 3 /s in prototype, corresponding to floods with a return period of 1.000 years. The results show that LES numerical model predicts well the average turbulent flow variables, but those associated with turbulent fluctuations are not satisfactory. 1 INTRODUCTION In the field of hydraulic design, complex situations are usually validated through physical models. However, due to the high cost of laboratory experiments and the current computational advance, researchers have attempted to use numerical simulation along with physical modeling (Dehdar-behbahani & Parsaie, 2016). Recently, the tendency to use physical and numerical models jointly can be applied in different ways. For instance, it can be used in the early design stages, where numerical modeling can provide boundary conditions for physical models, or in later stages, as a design tool to explore several solution alternatives. This kind of modeling is referred to by some authors as hybrid modeling or composite modeling (Kamphuis 1995, Kamphuis 1996 and Ettema et al. 2000). A common factor to this approach is the need to validate CFD models with the data collection of the physical models (Hager & Boes, 2014). In this context of hybrid modeling, the National Institute of Hydraulics in Chile (INH) and the University of Chile, have developed a study to improve the design of the spillway of the Ancoa reservoir, located almost 300 km south of Santiago. To do this, a physical model of the existing structure was built at 1:40 Froude scale. Also, a numerical model was used to test different alternatives in order to decrease the high flow agitation in the collector channel. To implement the numerical model, the open source OpenFOAM software was used. In particular, the solver interFoam can handle incompressible two-phase flow problems by applying an interface capturing technique based on a modified volume of fluid (VoF) approach. On the treatment of turbulence, the Reynolds average equations (RANS) were initially used, but early comparisons between the physical and numerical model showed that the free surface in the collector channel was not well reproduced by RANS, making it necessary to improve the numerical model. For this reason, an increase in the grid resolution and a different treatment of the turbulence was implemented. In this case, the idea was to capture the flow separation in the lateral spillway in a better way than RANS, using a Large Eddy Simulation (LES) approach (Spalar 2009, Rodi et al. 2013 and Thorsten 2014). Finally, the numerical model was in agreement with the punctual values of the surface elevation (Negrete et al., 2015). Later, a more rigorous analysis of time series of hydrodynamic parameters, surface elevation and pressure, was made to evaluate and validate the numerical model. The results showed a good agreement, in particular, the free surface showed a better result than the pressure, which had a range of error in the average pressure of 3-18% (Negrete et al., 2016). Similar results are obtained by other authors in similar cases, for example, Sánchez-Cordero et al. (2018) who used OpenFoam for the analysis of a dam-break in a 3D numerical model, using VOF method and LES. In similar applications, there are no results related to the velocity in order to make a comparison. In this study, a comparison between velocity measurements taken with an Acoustic Doppler Velocimeter (ADV) and the results of the numerical model with LES and WALE subgrid model is shown. ADV is an instrument
... Due to the extreme complexity of the hydraulic problem in practical engineering and the impossibility of a general solution for the N-S equation, hydraulic model testing satisfying a gravity similarity criterion is an effective and frequently used method. In order to obtain a structural vibration response induced by flood discharge excitation in engineering practice, Ettema et al. [21] suggest that the hydro-elastic model experiment can be applied, but the similarities for mass and stiffness of the structures in model and prototype are difficult to satisfy without using a specially customized material. In the 1980s, a hydro-elastic model experiment technique was presented by Cui et al. [22]. ...
Ground and environmental vibrations induced by high dam flood discharge from the Xiangjiaba hydropower station (XHS) has significant adverse effects on nearby building safety and the physical and mental health of surrounding residents. As an effective approach to simulate the flow-induced vibration of hydraulic structures, the hydro-elastic experiment approach has been extensively applied and researched by Chinese scholars, but the relevant systematic research is rarely reported in international journals. Firstly, the hydraulic and structural dynamic similarity conditions that should be satisfied by the hydro-elastic model are briefly reviewed and derived. A hydro-elastic model of the XHS was further constructed using self-developed high-density rubber, and the vibration isolation system (including open trenches and flexible connects) was applied to avoid the external disturbances of pump operation, vehicle vibration and other experiments in the laboratory. Based on the data of model and prototype dynamic tests, a back propagation (BP) neural network was established to map the acceleration of the physical model to the ground in the prototype. In order to reduce the ground vibration, experiments were carried out to meticulously evaluate the ground vibration intensity under more than 600 working conditions, and the optimal operation scheme under different discharge volumes is presented here in detail. According to the prototype test data in 2013, 2014, and 2015, ground vibrations were significantly reduced by applying the presented optimal operation principle which indicates that the presented hydro-elastic approach and the vibration attenuation operation scheme were effective and feasible.
... The similarity between the model and the prototype was realised by dynamic similarity based on the Froude number (Fr). The lateral scale and the vertical scales were taken as 1:120((Lr) H = 120) and 1:40 ((Lr) V = 40), respectively (Ettema et al. 2000). The prototype's transport pattern was observed for a 100-m distance using 'Domba' (Calophyllum inophyllum) seeds (diameter ∼ 25 mm) released at the centre of the straight reach, and in the physical model, plastic beads (diameter 3 mm) were used. ...
Three representative earthen canals from urban, peri-urban, and rural-urban fringe of Sri Lanka were studied for a 2-year period against different seasons to capture insights important in ecological rehabilitation. Only the canal from rural-urban fringe showed a better water quality in wet season; elucidating, the impact of contaminated catchment runoff in the other canals. At a given sampling session, one or two peaks (relative maxima) were observed in urban and peri-urban canals for pollution representative parameters such as nitrate nitrogen and soluble reactive phosphorus. Those peaks were highly localised, an indication of poor advection. In general, two-dimensional variations of electrical conductivity and turbidity in dry season were uniform in urban and peri-urban canals, an indication of dominant molecular diffusion. This was further evidenced via physical models for different flow stages (low, high, and bankfull). Therefore, fate of contaminants had to be mainly governed by assimilation via sediments. However, grey water footprint analyses showed urban and peri-urban canals have over utilised the natural assimilation capacity of many water quality parameters by several folds. This study proved the importance of inducing attenuation by instream physical heterogeneity similar to natural streams or naturalised canals such as the canal from the rural-urban fringe of this study.
... In this study, criteria for the similitude of sediment movements were required to assess coarse sediment for modeling the permeable barrier and to assess cohesive sediment for the dredged material placed in the replenishment area. For coarse sediment, we could adopt the Shields diagram for the condition involving incipient riverbed particle motion [29]. ...
Dredging is a commonly used sedimentation management strategy to remove mechanically deposited sediment from reservoirs. However, dredged sediment disposal is costly. Dredged sediment can be considered a beneficial resource and used for riverbed replenishment to prevent downstream riverbed degradation and improve aquatic habitats. This study investigated the feasibility of using dredged deposits with cohesive sediment for replenishment at the Shihmen Reservoir. Using the criterion of critical scour velocity, we conducted hydraulic assessments and identified the feasible replenishment area as the experimental domain. A physical model was developed to mimic the scouring process in the replenishment area. By applying dynamic similarity for scouring fine replenished sediment, we derived the regression relationship between flow-critical velocity and sediment-dry density, and used it for model ratio scaling of the grain size, dry density, and concentration in the physical model. Scoured sediment concentrations were measured to study the scour ratio at various flood discharges. Experimental results indicated that the scour ratio was related to factors such as flood discharge, flood duration, and water content of the replenished sediment. The reduction ratio of the concentration of sediment scoured from the replenishment area to the concentration of sediment at the downstream water intake was approximately 90% in the present study.
... Hydraulic engineers have studied weirs for centuries and frequently incorporated weirs in hydraulic structures. Discrepancies between data sets (e.g., similar models from different laboratories, prototype weirs and their scaled models) may come from three types of sources: model effects (Novak 1984), scale effects (Heller 2011, Ettema 2000 and measurement effects (Yalin 1971). ...
Though weir flow has been studied for centuries, there still remains some nuances of weir flow that are not well understood. Therefore, an international study was conducted in which 20 different hydraulics laboratories from around the world built and tested two linear weirs (quarter-round and half-round crested weirs) of common geometry. The only unconstrained dimension was the weir length, which could be adjusted to match the width of the test flume. Participating laboratories used the instrumentation and data collection methodologies of their choosing for head and discharge measurements.
The experimental results found significant variability in the discharge coefficients as a function of dimensionless upstream head, as well as in the head-discharge relationships (as much as 50% in some cases). Potential sources contributing to the scatter may have included head meter instrumentation, flow meter instrumentation, approach flow length (flume length upstream of weir), head measurement location, nappe behavior, laboratory measurement methods and experimental setup, and the care and skill of the investigator (human error). Analyzing the data as a function of instrumentation types, approach length, and head measurement location did not provide any insight regarding the variations. Nappe behavior (e.g., aeration), which could be influenced by laboratory-specific conditions, varied among the datasets primarily for the half-round crested weir (about 20%).
... Modeling of Hydraulic structures has received much attention in recent years due to these effect on the increasing the hydro system performance. 1 Weirs are the common structure which uses in the most of water engineering projects such as hydropower systems, irrigation and drainage networks and sewage networks. Side weir has many possible uses in the hydraulic engineering field and has also been investigated as an important structure in hydro systems. ...
... Model of computational fluid dynamic in three dimensional (3D-CFD), however a 3D physical hydraulic model is more intuitive and direct feedback on pre-trial changed on the model could be obtained. Three dimensional hydraulic physical model is constructed based on the flow regime which will be modeled and significant dimensional flow parameter involved in the flow (Ettema et al., 2000). ...
Limitation of space for spillway constructions leads to application of side spillway design. Side spillway reduces space requirement through aligning the crest of spillway along side of the spillway channel. Three-dimensional flow due to abrupt change of flow direction for almost 90 degrees together with incremental lateral discharge is very difficult to be defined clearly during design stage. In this situation, a scale-model test is useful to investigate flow pattern to obtain optimal design. A physical hydraulic model tests will shows possible deficiencies of an original design. Deficiencies were usually observed at approach section, stilling pool downstream the spillway, transition reach and downstream energy dissipater. The deficiencies may be due to inherent flow characteristics of side spillway or unaccounted three-dimensional feature during design process. Results from scale-model tests shows that improvement of the design were obtained in terms of smooth flow toward spillway section, improved energy dissipation at just downstream of spillway before transition reach, reduction of surface disturbance and enhanced energy dissipater performance.
... Full dynamic similarity requires all these force ratios to be identical: While it is possible to ensure that some of the ratios are constant, for there to be full dynamic similarity the gravity and atmospheric pressure would need to be scaled which is not realistically possible in most cases (Ettema et al., 2000). ...
It has been suggested that biofuels produced from microalgae may be a more sustainable alternative to other types currently produced, although currently the production of microalgae for this purpose has the potential for the overall energy balance to be negative. Microalgae are today cultivated in oval ponds of up to 10 m width and 500 m length, with water depths of 200 to 300 mm. The water must be kept in motion to avoid sedimentation. This is usually done with paddlewheels which have 6 to 8 blades, and a typical diameter of around 1.20 m. The energy demand for the continuously running wheels is one of the main cost factors, whilst the wheel efficiency is typically estimated as only 10 %. Very little is known about the effect of blade number or rotational speed on wheel efficiency. This research aimed to improve the paddlewheel as a propulsion mechanism in order to reduce the energy required.
Theoretical work and 1:5 scale physical model tests were conducted to analyse the parameters affecting paddlewheel performance, to develop a consistent and improved model of the hydraulics of algae ponds, to define optimum configurations and to develop appropriate design tools. The results indicate that the number of blades, rpm and immersion depth have a great effect on the efficiency, with optimum values of over 60 % being achieved with higher blade numbers and lower rpm. Using an insert to reduce the backflow around the blades increased the efficiency and discharge of a 12-bladed wheel especially for the lower rotational speeds tested.
A new theoretical equation to calculate the efficiency of the wheel was derived and validated against the physical model. It was found that the leakage of the fluid beneath the blades was the main loss factor in the efficiency of the wheel and should be minimised by using the insert where possible.
... 3) Dynamic similarity exists between two systems when forces at corresponding points are similar. In fluid mechanics, to achieve dynamic similarity all the non-dimensional numbers relevant to the flow must be preserved between the two systems, such as Reynolds, Grashof, and other numbers (Ettema, 2000). This is extremely limiting since in practice at most one or two non-dimensional numbers of the flow can be preserved. ...
This textbook explains turbulent flows using an introductory but fundamental approach to teaching the core principles, striking a balance between theoretical and practical aspects of the topic without overwhelming the reader with mathematical detail. It is aimed at students in various engineering disciplines—mechanical, civil, environmental—and the geosciences. It is divided in five parts. Part 1 provides the fundamentals of turbulence, main hypotheses, and analysis tools; Part 2 illustrates various measurement techniques used to study turbulent flows; Part 3 explains the modelling and simulation frameworks to study turbulent flows; Part 4 describes brief applications of turbulence in engineering and sciences; and Part 5 presents basic statistical, mathematical, and numerical tools.
Elucidates the theory behind turbulence in a concise yet rigorous manner;
Combines theoretical, computational, experimental, and applied aspects of the topic;
Reinforces concepts with practice problems at the end of each chapter.
... Dimensional analysis provides methods for reducing the number of phenomena describing variables by classifying them into dimensionless groups (Dey, 2014;Ettema, 2000). This classical method was applied to find the relationships for bedload transport in other studies as well (Ahanger et al., 2008;Sinnakaudan et al., 2006). ...
Two sets of triangular hydrographs were generated in a 12-m-long laboratory flume for two sets of initial bed conditions: intact and water-worked gravel bed. Flowrate ranging from 0.0013 m³ s⁻¹ to 0.0456 m³ s⁻¹, water level ranging from 0.02 m to 0.11 m, and cumulative mass of transported sediment ranging from 4.5 kg to 14.2 kg were measured. Then, bedload transport rate, water surface slope, bed shear stress, and stream power were evaluated. The results indicated the impact of initial bed conditions and flow unsteadiness on bedload transport rate and total sediment yield. Difference in ratio between the amount of supplied sediment and total sediment yield for tests with different initial conditions was observed. Bedload rate, bed shear stress, and stream power demonstrated clock-wise hysteretic relation with flowrate. The study revealed practical aspects of experimental design, performance, and data analysis. Water surface slope evaluation based on spatial water depth data was discussed. It was shown that for certain conditions stream power was more adequate for the analysis of sediment transport dynamics than the bed shear stress. The relations between bedload transport dynamics, and flow and sediment parameters obtained by dimensional and multiple regression analysis were presented.
... The model scale was selected to ensure that an appreciable frequency range could be captured by the dynamic instruments. Although the Strouhal number, which dictates the frequency of say the vortex shedding, is directly relatable given Froude similitude, smaller models may have a limited capability to generate certain higher frequency behaviours (Phillips & Lesleighter 2013, Ettema 2000. This means that even though such frequencies may be present in the prototype, their scaled counterparts may not appear in the physical model unless its scale is large enough. ...
The roughness Froude number is a relatively new dimensionless parameter that began appearing in the hydraulic engineering literature in the late 1970s, first for the analysis of aeration inception in smooth chutes, and then later in connection with stepped chutes. This article reviews its foundations, historical development, alternative forms, present-day applications, and physical significance, which has received little attention previously. In addition to its empirically demonstrated connection to aeration inception, this paper shows that one form of a roughness Froude number has a strong relation to the transition between nappe and skimming flow regimes of stepped chutes, while another combines the dimensionless flow friction factor and the relative submergence of roughness elements.
This chapter introduces the transport equations of motion without the consideration of turbulence. Continuity, momentum, passive scalar, and vorticity transport equations are discussed. In the development of the transport equations, the concept of fluid element deformation is defined, where each parcel of fluid in the flow can be understood as being deformed via a combination of translation, linear strain, shear strain, and rotation mechanisms. Finally, the idea of similitude and non-dimensional transport equations is presented, where the transport equations are non-dimensionalized for characterizing their general behaviour. The concept of similarity for two systems involves geometric, kinematic, and/or dynamic similarities between them.
This chapter introduces compressible flows, which are flows at very high velocities comparable to the speed of sound or flows influenced by temperature-driven buoyant forces. Transport equations are developed for continuity, momentum, and temperature, which link various non-constant flow properties such as density, velocity components, pressure, and temperature. The similitude analysis is performed, and non-dimensional transport equations are derived. Boundary layer equations are developed for a two-dimensional case of a compressible turbulent flow. Finally, the Mach number is defined, which characterizes the flow regimes in relation to the speed of sound, concerning subsonic, transonic, supersonic, hypersonic, and re-entry flows.
The water flow rates through a 2D model of a tainter-gate are calculated. The geometric computer-aided design (CAD) model is created as parametric one, allowing thus simple and efficient variations of the model dimensions, compatible with automatic update of the solution domains and generation of computational meshes. The problem of water flow is considered as fluid flow with free-surface, which is computed using a computational-fluid dynamics (CFD) method based on Volume-of-Fluid (VoF) approach. The flow rates and their corresponding discharge coefficients are calculated for a number of different values of the water level in reservoir, the gate opening size and the intake depth.
For underwater observation and exploration, the accurate measurement
of few basic parameters is very important. During measurement process underwater
noise plays an adverse effect, so noise measurement is essential to refine the result of
other parameters. Sound, distance, and fish population measurements are common
activities in oceanography. Finding proper instrumentation in this field is quite challenging
due to the uncertain environment. This chapter describes the construction,
operation, and performance of the different measurement system with different techniques
for specific underwater applications. In addition, advances in sensors and
processors with proper design ensure accurate measurement.
Wet scrubber systems have inherent advantages over other air pollution control devices as they have the ability to absorb gaseous pollutants, remove flammable and explosive dust particles safely. Though various types of wet scrubbers systems exist, spray towers based are preferred due to their simplicity in design, least energy consumption, cheaper to construct and maintain, less space requirements and operation with slight pressure drop, ability to handle a large volume of gases as well as engaged for the dual purpose of absorbing gaseous pollutants while removing particle contaminants. The mechanisms for the separation of the particle pollutant from the gas stream include impaction, interception, and diffusion, an inertia impaction mechanism is used in the spray tower wet scrubber system. This mechanism limits the size of particle contaminants control to Particle Matter (PM) size ≥ 5 μm, whereas PM10 and PM2.5 ≤ 5 μm pollutants from industrial sources constitute a great danger to human health. Consequently, several attempts have been made to improve the performance of spray tower wet scrubber for the pollutant control of PM10 and PM2.5 ≤ 5 μm. Two approaches for improving the design of wet scrubber systems, namely, similitude model design and computational fluid dynamics approaches have been discussed in this chapter. A pilot scrubber system for PM2.5 and PM10 control has been designed using PM data obtained from Ashaka cement industry in Gombe State, Nigeria. A Hydraulic Similitude approach has been employed to design a scaled model of the scrubber system. The airflow velocity and pressure fields within the scrubber system were simulated using ANSYS Fluent software to obtain optimum design of the system, improve efficiency, shorten experimental period, and avoid dead zone. Some simulated results are presented to justify the essence of the designed approaches.
“Colligation”, a term first introduced in philosophy of science by William Whewell (1840), today sparks a renewed interest beyond Whewell scholarship. In this paper, we argue that adopting the notion of colligation in current debates in philosophy of science can contribute to our understanding of scientific models. Specifically, studying colligation allows us to have a better grasp of how integrating diverse model components (empirical data, theory, useful idealization, visual and other representational resources) in a creative way may produce novel generalizations about the phenomenon investigated. Our argument is built both on the theoretical appraisal of Whewell’s philosophy of science and the historical rehabilitation of his scientific work on tides. Adopting a philosophy of science in practice perspective, we show how colligation emerged from Whewell’s empirical work on tides. The production of idealized maps (“cotidal maps”) illustrates the unifying and creative power of the activity of colligating in scientific practice. We show the importance of colligation in modelling practices more generally by looking at its epistemic role in the construction of the San Francisco Bay Model.
Hydraulic structures are critical for water management. Yet many structures continue to be neglected, in poor condition, and inadequate in adapting to evolving societal challenges associated with shifting climatic events and population growth. In this context, hydraulic structures engineering should be moving from traditional design considerations toward sustainability, that is, continuing to meet current and future social, environmental, and economic needs. This requires this community to embrace and help advance global and multidisciplinary perspectives. Therefore, this article presents the authors' point of view on current trends, concerns, and needs related to hydraulic structures engineering. Furthermore, the authors propose a new, forward‐looking framework for the consideration of the hydraulic structures community that is grounded on the evolution of interconnected research tools and methodologies in addition to emphasizing and bolstering strong links between academia and industry. The evolution of this framework has naturally originated from the pervasive challenge of validating the design and operation of hydraulic structures in the field for frequent and extreme conditions. The authors suggest that future developments of hydraulic structures engineering require (a) continuous updating of complementary tools and methodologies following technological developments, (b) addressing the lack of detailed field observations, (c) increasing interactions of hydraulic specialists with other scientific disciplines and water experts, and (d) restoring a strong collaboration between academia and industry. It is anticipated that in this way the hydraulic structures community, and all of society, will make a new step toward more sustainable and resilient interactions with nature and between communities in water management.
This article is categorized under: Engineering Water > Engineering Water
An oval recycling flume with live-beds (moveable) of medium and very coarse grained sands were used to explore the process of bone burial as a precursor to fossilization. Two-dimentional computation fluid dynamics was used to visualize and interpret the flow turbulence around bones. Results show that a water mass approaching and passing a static bone (obstruction) is subjected to flow modification by flow separation, flow constriction, and flow acceleration producing complex flow patterns (turbulence). These complex patterns include an upstream high-pressure zone, down flows, and vortices (with flow reversal near the bed) causing bed shear stress that produce bed erosion. Downstream of the bone, the water mass undergoes flow deceleration, water recirculation (turbulence eddies), flow reattachment, low-pressure zone (drag), and sediment deposition. Scour plays a crucial role by undercutting bone on the upstream side and may cause the bone to settle into the bed by rotation or sliding. Scour geometry is determined by bone size and shape, approaching flow velocity and angle to flow, flow depth, bed topography, and bed friction. Drag on the downstream side of the bone causes scoured sediment deposition, but burial by migrating bed forms is the most important method of large bone burial. Bone may be repeatedly buried and exposed with renewed scour. However, each episode of scour may lower the bone deeper into the bed so that it essentially buries itself. No difference in these effects were noted between experiments using fine or coarse grain sizes. This experimental work is then used to interpret the possible history of bone burial in the Upper Jurassic Morrison Formation on the bone wall inside the Quarry Exhibit Hall at Dinosaur National Monument, Utah.
Groundwater is the main source of potable water for more than 1.5 billion people throughout the world, including arid and semi-arid regions like Iran. Literature review showed that there is no use of the dimensional similitude and physical modelling for estimating seepage from channels and its effect on the groundwater, yet. Thus, in order to better understand this phenomenon, the current study aimed at investigating the effects of infiltration and seepage on the groundwater recharge at different water level depths. Numerous studies have been conducted to assess the groundwater recharge, such as Yin et al. (2011) that utilized some methods such as the water table fluctuation method and the Darcian flux and water balance method in China. Similarly, using data from some irrigation projects and piezometric level data, Ochoa et al. (2013) evaluated the effects of seepage on the groundwater recharge in New Mexico. Moreover, Demlie (2015) compared the water balance method and the chloride mass balance method to quantify and investigate the groundwater recharge in Ethiopia. In the current research, the earth channel of Boldaji with loamy soil, located in Borujen city, Chaharmahal and Bakhtiari province, was chosen as the prototype. The dimensions of such a channel were transmitted to laboratory models at soil mechanics lab at Shahrekord University. Using dimensional similitude equations, 9 discharges (40-161 l/s) and 4 water-table depths (0.75, 0.8, 0.85 and 0.9 m from soil surface) were converted to the applicable discharges of the model. The results of the laboratory physical model showed that the infiltrated water raised the groundwater 3.5-11 cm. The values of recharged groundwater were, in turn, calculated by means of water balance method and the results showed no suitable estimates of such a method for the trapezoid and triangle cross-sections.
Ongoing development in variable speed technology for hydraulic power plants improves the flexibility and allows new manoeuvres. In this context, the present work investigates a fast transition from pump mode to generating mode in a reversible pump-turbine by means of CFD and one-dimensional plant dynamic analysis. Calculations are carried for a transition at model scale and finally for a transition in an existing power plant. At model scale, simulation is compared to data measured in the framework of the HYPERBOLE project. For the simulation of the transition at model scale, experimental data for rotational speed and flow rate are prescribed as boundary conditions. To include interaction with the pipe system, the open-source code OpenFOAM® is subsequently coupled to an in-house code for one-dimensional system analysis based on the Method of Characteristics. The coupled method is validated by a comparison to the reference simulation at model scale, and applied to the existing power plant. Results include the evaluation of pressure values and fluctuations at various locations in the machine and the description of different flow phenomena. Furthermore, results for steady operating conditions are compared to the results from transient calculations to identify dynamic effects.
Personalised medicine (PM) has been discussed as a medical paradigm shift that will improve health while reducing inefficiency and waste. At the same time, it raises new practical, regulatory, and ethical challenges. In this paper, we examine PM strategies epistemologically in order to develop capacities to address these challenges, focusing on a recently proposed strategy for developing patient-specific models from induced pluripotent stem cells (iPSCs) so as to make individualised treatment predictions. We compare this strategy to two main PM strategies—stratified medicine and computational models. Drawing on epistemological work in the philosophy of medicine, we explain why these two methods, while powerful, are neither truly personalised nor, epistemologically speaking, novel strategies. Both are forms of correlational black box. We then argue that the iPSC models would count as a new kind of black box. They would not rely entirely on mechanistic knowledge, and they would utilise correlational evidence in a different way from other strategies—a way that would enable personalised predictions. In arguing that the iPSC models would present a novel method of gaining evidence for clinical practice, we provide an epistemic analysis that can help to inform the practical, regulatory, and ethical challenges of developing an iPSC system.
Three-dimensional laser-induced fluorescence (3D LIF) was applied to visualize and quantitatively analyze hydrodynamics and mixing in a multichamber ozone contactor, the most widely used design for water disinfection. Results suggested that mixing was characterized by extensive short-circuiting between chambers, internal recirculation within the chambers, and dead zones at the chamber centers. Because of these nonideal mixing behaviors, the hydrodynamics in the entire reactor showed greater dispersion than a series of completely mixed reactors. These flow patterns could be diminished by decreasing the channel width, whereas the effects of the flow rate and baffle gap were negligible within the range investigated. Accordingly, reactive transport model simulations suggested that overall reactor performance could be significantly improved by preventing these flow behaviors. The 3D LIF technique developed and presented in this study is expected to provide a novel tool for reactor diagnosis, retrofitting to improve performance, and new reactor design.
The concept of similar systems
arose in physics and appears to have originated with Newton
in the seventeenth century. This chapter provides a critical history of the concept of physically similar systems
, the twentieth century concept into which it developed. The concept was used in the nineteenth century in various fields of engineering (Froude
, Bertrand, Reech
), theoretical physics (van der Waals
, Onnes
, Lorentz
, Maxwell
, Boltzmann
), and theoretical and experimental hydrodynamics (Stokes
, Helmholtz
, Reynolds
, Prandtl
, Rayleigh
). In 1914, it was articulated in terms of ideas developed in the eighteenth century and used in nineteenth century mathematics and mechanics: equations, functions, and dimensional analysis. The terminology physically similar systems was proposed for this new characterization of similar systems by the physicist Edgar Buckingham
. Related work by Vaschy
, Bertrand, and Riabouchinsky
had appeared by then. The concept is very powerful in studying physical phenomena both theoretically and experimentally. As it is not currently a part of the core curricula of science, technology, engineering, and mathematics (STEM
) disciplines or philosophy of science, it is not as well known as it ought to be.
Design studies are described for two recently completed large scale hydroacoustic test facilities (one of which is the world's largest). These recirculating water tunnels have a different configuration than conventional tunnels, and special hydrodynamic design studies were required to evaluate and optimize the performance of some critical components. This paper considers the flow quality in the test section as influenced by the design of the contraction and the turbulence management system. Numerical modeling and experimental work were used to arrive at an acceptable nonsymmetrical nozzle design. Studies were also made of a turbulence management system using honeycombs rather than screens as typically used. Although design goals for turbulence levels were met, this study indicated that additional research in the area of turbulence management is necessary before there is a complete understanding of the overall process of turbulence attenuation.
Experiments to determine the length, height and steepness of bed forms generated by wave action have been conducted in a laboratory wave flume and an oscillating water tunnel. The effects of a wide range of oscillatory flows were examined on polystyrene (specific gravity 1.05, diameter 1.54 mms), bakelite (specific gravity 1.60, diameter 0.52 mms), bakelite (specific gravity 1.51, diameter 0.67 mms) and sand (specific gravity 2.68, diameter 0.36 mms). From the results of the experiments design curves were plotted which make it possible to predict the length and height of bed form that will develop on any specified sediment bed for given conditions of fluid oscillation.
Shear stress measurements on both smooth and sand roughened beds were carried out in an oscillating water tunnel using a flexurally supported shear plate. The range of simulated wave boundary layers covered practically any situation possible in the field or laboratory. In the laminar range good agreement is obtained with the theoretical shear stress calculated from first order wave theory. However, in the turbulent flow regimes the experimental data indicates that theory results in an overestimate of the shear force by 20-50%. Limits of laminar, smooth turbulent and rough turbulent flow regimes are determined and it appears that the rough turbulent flow regime may itself be subdivided into two sections, each having different turbulence characteristics.
A model law for two-dimensional, laboratory beach profiles assumed to be at equilibrium is considered. An experimental program was performed and the extensive laboratory beach profile data indicate a relationship or model law between the four basic scale ratios; the horizontal scale, vertical scale, sediment size ratio, and the relative specific weight ratio. Graphical forms of the experimentally derived model law are presented. Recommendations to optimize the practical application of scale model technology to coastal movable beds.
An example of coastal pollution modelling relates to one objective in the design of small boat harbours or marinas on salt water: that of achieving tidal flushing in the harbour basin that will minimize potential water quality problems. Questions addressed in the design and project permit-granting process might range from qualitative comparisons of flushing of alternative plan-form geometries to the quantitative prediction of circulation patterns and tidal exchange with ambient waters. This note emphasizes a type of low cost, essentially single-purpose physical model employing tracer concentration sought. Three-dimensional mathematical models for accurate simulation of currents and flushing of small harbours, and applicable to widely available computers, are still being developed. Physical models then still serve a useful purpose. They allow complex bathymetries and shoreline configurations to be modelled without schematic simplification, and allow observation of local flow features important in the internal hydraulics of a small harbour, thus providing a mechanism for investigating design details and changes. Basins considered are essentially enclosed, relatively shallow, and have no significant freshwater inflow. The number of openings connecting basin and ambient waters is limited, and opening widths are small relative to other plan-form dimensions of the marina, so that tidal currents are dictated primarily by entrance(s) configuration and basin plan-form geometry. Wind effects are negligible. Typical parameters for such basins partially enclosed by breakwaters are lengths of 250-1000m, widths of 100-300m, mean low water depths of 2-4m, and tidal ranges of 1-4m. (A)
The 'Pilatus' high-velocity cavitation facility simulates cavitation in the form of an attached cavity by means of a step venturi. Extensive erosion tests with resistant steel specimens and soft substitute materials establish the influence of flow velocity and average cavity length on the loss of material. The erosion model yields the correlation between eroded material and the determinant flow and operating parameters.
Hydraulic model studies of pumping pits will continue to be an important part of the design process. Even though many studies have been completed, design criteria are not available that insure trouble-free operation of the pump. The paper discusses the role of modeling in the design of pumping pits and suggests methods for making them more effective. Included is a description of the various hydraulic problems uncovered by past studies and successful solutions that have been developed. The article is not a technical state-of-the-art paper but does include several references to recent papers on the subject. 28 refs.
The designs of pump sumps for seven different projects, as developed through hydraulic model testing, are compared with published design standards. Modifications to the sump designs, in addition to the basic sump dimensions recommended by the published standards, are required to achieve satisfactory hydraulic performance. It is theorized that performance criteria applied in developing the standards are not as stringent as those required for present day large capacity pumps. Typical sump modifications and dimensions presented may provide a basis for developing conceptual designs for sumps for large capacity pumps. Final designs should be proven through hydraulic model testing. (A)
A model is set up for the determination of possible evolution in time and space of variables characteristic of the biotope and biocenoses of the algae in the Tunis Lake. The model of water quality is coupled with a physical model simulating the hydrodynamics, salinity and temperature of the environment. The model is calibrated on the basis of the measurements taken in situ prior to developments and validated from initial observations carried out after the developments which consisted mainly of the construction of a dike and management of the exchanges with the sea as well as the deepening of certain zones.
Two physical model studies were conducted to evaluate the thermal patterns produced in the Hudson River by the condenser cooling water discharge from the Indian Point Nuclear Generating Station. Model similitude criteria are developed and applied to the Indian Point site to determine model scale ratios. Model construction, verification, and operation techniques are described. Typical results show surface temperature rise patterns near the plant discharge and within a 15 mile reach of the river. Sensitivity of thermal patterns to variations in freshwater runoff, plant load, and discharge structure geometry are illustrated. Model results are evaluated with respect to scale effects, and limitations due to inability to simulate certain phenomena occurring in the field. Model results are compared to an extensive field survey program and one-dimensional time averaged mathematical model.
The simultaneous occurrence of vaporous and gaseous cavitation on hydrofoils is considered. The experimental results show that gaseous cavitation occurs at much higher ambient pressures than that for the vaporous cavitation resulting in desinent-cavitation numbers twice the minimum-pressure coefficient of the hydrofoil. The analysis indicates that the difference between the desinent-cavitation number for the gaseous cavitation and that for the vaporous cavitation is proportional to the dissolved air content and inversely proportional to the square of the velocity.
The method of combining a physical model with a mathematical model is described to study the concentration profile of pollutant dispersion in the Yangtze Estuary. the Experiments are described regarding a jet in a tidal physical model and two-dimensional calculations of diffusion using momentum and mass conservation equations of unsteady flow. The feature of dispersion in the tidal flow, which is different from that in the steady flow such as rivers, is explained. Dilution and dispersion mainly depend on the volume of runoff and tidal range. The results of the measurement and calculation are presented, and it can be seen that they are in good agreement.
The measurement of cavitation nuclei has been the goal of many cavitation research laboratories and has resulted in the development of many methods. Two significantly different approaches have been developed. One is to measure the particulate-microbubble distributions by utilizing acoustical, electrical or optical methods. The other approach measures a liquid tension and a rate of cavitation events for a liquid in order to establish a cavitation susceptibility. Comparisons between various methods indicate that most methods are capable of giving an indication of the nuclei distribution. Measurements obtained in the ocean environment indicate an average of three bubbles per cubic centimeter are present; whereas, water tunnel bubble distributions vary from much less than one to over a hundred per cubic centimeter.
The cooling performance of a shallow cooling pond can be determined in a hydraulic model where the residence-time distribution function of a passive tracer is measured at the intake. It is shown that within a range of discharges, i. e. , of Reynolds numbers where the flow characteristics in the lake remain similar, the lake performance for a given effluent discharge can be obtained from the results obtained for a different effluent discharge. An example of application of the method is presented.
Treatment performance of waste stabilization ponds is a function of both the hydraulic transport and the biological and chemical transformation processes within the pond. Both the efficient hydraulic design of these ponds and the appropriate mathematical models for describing the hydraulic transport process are identified. A model consisting of a dispersed flow active zone and a fully-mixed return flow zone is developed and calibrated. Dye tracer studies and model simulations are utilized to illustrate the treatment efficacy of various pond geometries and inlet and outlet configurations. Recommendations are made for optimum design. For certain of the ponds analyzed, treatment efficiency predicted by the completely-mixed flow model compares well with that determined by analysis of dye tracer studies. The plug flow assumption seriously overestimates treatment efficiency.
Vertically downward slug flow of air-water mixtures was experimentally investigated in circular pipes of diameter D equals 2. 80, 10. 16, and 14. 0 cm. The terminal velocity of descending, stationary, and ascending bubbles in downward flows was measured and correlated with the air and water volumetric flux densities. Except for very small pipe diameters, bubbles in downward flow are unstable and eccentrically located off the pipe axis in regions of lower fluid velocities. Consequently, the value of the flow distribution parameter C//0 is less than unity for downward flow, compared to C//0 equals 1 for rising bubbles in quiescent liquid, and C//0 equals 1. 2 for ascending bubbles in upward flow. Above a certain pipe diameter stable Taylor bubbles are not possible for downward flows. The terminal velocity coefficient C//1 is no longer 0. 35 for downward flows in relatively large pipes because the unstable bubbles ride the pipe wall, resulting in a higher value of C//1.
An earlier laboratory investigation by the author led to the acquisition of quantitative data on natural dispersion due to breaking waves, in terms of dispersion rate, droplet size distribution, and intrusion depth of the droplets in the water column. The present paper demonstrates that the relationships derived and empirical data can be applied to other dispersion sources as well. As found with breaking waves, these other dispersion sources must consist of a short-duration plunging process hitting the surface oil parcel. The following dispersion sources which apparently fulfill the requirement are discussed: flow over a dam, a cataract with a hydraulic jump, fast flow around an obstacle, and a ship sailing through an oil slick.
Laboratory models made of sand, water, and small amounts of cement (“weak mortar”) are shown to be practical, inexpensive alternatives to standard porous media models made from sand epoxy resins, glass geads, or sand only. By varying proportions of the weak mortar mix, one can fashion complex layered models with hydraulic conductivities ranging from 1.4 × 10 ⁻⁸ m/s to 3.7 × 10 ⁻⁴ m/s. Dispersion tests using Rhodamine dye were performed on a 2.4 m × 1.14 m × 0.15 m rectangular weak mortar model; the results compared favorably with the analytical predictions, with longitudinal dispersivities on the order of 10 cm. Anticipated applications of weak mortar models are for verification of mathematical models, hydraulic scaled models and laboratory demonstrations.
A systematic investigation of the circulation, pollutant transport and residence time in a distorted scale model of the Windermere Basin was undertaken by using a numerical approach. A numerical hydrodynamic model was developed to simulate the circulation pattern in the basin. The experimentally validated flow circulation was used as input to the pollutant transport model to imulate the transport of a pollutant Continuous Iy introduced at the inlet of the basin. The simulated re utt were found to be in good agreement with the experimental measurements. With the aid of the validated model, the influence of the wind, recirculation and dead zone, and construction of dikes on the residence time distributions in the basin were examined.
INTRODUCTION Recent increases in recreational and small commercial craft activities have resulted in the construction of many new marinas. Local, state and federal government must evaluate applications for marina construction permits. Little information exists on ecological impacts of marinas or of construction events such as dredging and spoil disposal. This report concerns one aspect of the marina permit evaluation process: water quality impacts related to marina circulation and flushing efficiency. These physical properties vary with the wind, tide range, water density and physical dimensions of a marina. Water quality is affected by the degree of flushing, and sediment redistribution by currents. Detrimental water quality can determine, e.g., the fate of migrating juvenile fish and benthic organisms (5,7). Ecological studies of marinas are few. The most comprehensive have been performed on Marina del Rey, California (3, 15, 16, 17, 22). Slotta and Noble (21) discussed the use of berithic sediments as indicators of marina flushing in several Pacific Northwest marinas.
AIR is often entrained naturally by flowing water-for example, in the plunging waters of mountain streams, waterfalls, bores, breakers, hydraulic jumps and subterranean siphons-and, in these and similar situations, appears generally to be beneficial. The quality of the water, certainly, is improved by air entrainment and very few hazards tend to arise with these naturally occurring flows.
The engineers of Chimor built canals to carry water from rivers to fields as much as 70 kilometers away. In the end they were defeated by relentless geologic forces. This article reviews this work.
THE RATE OF CAVITATION IN LIQUID FLOW APPEARS TO BE LINKED TO THE CONCENTRATION AND SIZE DISTRIBUTION OF GAS BUBBLES AND ″ WEAK ″ NUCLEI IN THE LIQUID USED, AS WELL AS TO THE DISSOLVED GAS CONTENT. CONSEQUENTLY, THE ONSET OF CAVITATION IS RELATED TO THE TENSILE STRENGTH OF THE LIQUID, RATHER THAN THE VAPOR PRESSURE. THE TENSILE STRENGTH OF THE LIQUID DEPENDS ON THE AMOUNT OF GAS IN GAS POCKETS (I. E. , GAS BUBBLES AND GAS ABSORBED AT SOLID PARTICLES) SUSPENDED IN THE LIQUID AND THE SHAPE OF THESE GAS POCKETS. AN INSTRUMENT IS DESCRIBED WHICH MEASURES THE TENSILE STRENGTH IN A DIRECT WAY. IN THIS METHOD A SAMPLE OF LIQUID IS MADE TO PASS THROUGH A PRESSURE WELL, THE MINIMUM PRESSURE OF WHICH CAN BE ADJUSTED.
This paper deals with pumps and turbines of radial to semi-axial flow (nq^ = 20÷70), as frequently used in water power and pump-storage plants. The described sealing process is based on previous publications [1, 2, 3] and is presented here in an abridged form in an easily intelligible way. To simplify practical application, use is made of clearly set out diagrams permitting a quick determination of efficiency scaling. For a better understanding the fundamental laws are briefly reviewed with reference to the relevant bibliography. Of particular interest is the relation between the efficiency loss due to roughness and an economically justifiable extent of surface finishing of flow passages. Another important criterion is the surface roughness characterized by the term “hydraulically smooth”. Relevant numerical data can easily be determined on the basis of suitable diagrams.
The principles of seawater intrusion and purging of seawater out of deep tunnelled outfalls are well known. Purging using a relatively low sewage water discharge requires high hydraulic head loss, which conflicts with the requirement for minimum head loss in the diffuser to reduce energy consumption. The hydraulic modelling of purging processes for the Hong Kong outfall and diffuser system was performed in order to optimize the discharge and head loss requirements for purging. Special attention is paid to two different purging methods: two-layer purging and salt-assisted purging.RésuméLes phénomènes d’intrusion saline et de purge de l’eau saumâtre par un émissaire profond sont bien connus. La purge avec un débit relativement faible exige une perte de charge importante, ce qui est en contradiction avec l’impératif de perte de charge ininimale dans le diffuseur alin de réduire la foumiture d’énergie. La modélisation hydraulique du système de purge de l’émissaire de Hong-Kong avec son diffuseur a été réalisée dans le but d’optimiser le débit et les contraintes de perte de charge pour la purge. Une attention particulière a été portée à deux méthodes différentes de purge: purge avec un système bi-couche et purge renforcée par l’eau saline.
In this study a maximised cross-correlation technique is applied to two very different experiments. The first is a laminar, slowly developing experiment where the main scales of the motion are comparable to the image size. Here extensive use of multiple passes with the technique and various filters are applied to replace erroneous measurements. The second experiment has both laminar and turbulent regions of flow, and in addition, many of the scales of motion are smaller than the correlation window size. Mean velocities are resolved in this application, as well as a qualitative impression of the turbulent fluctuations.
Flow and mixing in a wastewater dechlorination basin are investigated by tracing dye concentrations in a 1:12 scale sectional model and in a fullscale installation. The injection of an S02 solution that neutralizes residual chlorine is simulated by dye. Time series measurements of dye concentrations are obtained in the model and in the full-scale basin. Mean dye concentrations and standard deviations of concentration fluctuations measured throughout the model and the full-scale basin compare favorably. Both show incomplete mixing of S02 solution and residual chlorine. The model is then used to develop a substantially improved basin design by relocation of S02 injection and addition of a columnar wall to redistribute the flow and create small-scale turbulence. The modifications can be implemented without interruption of wastewater treatment. The performance of the improved design is again validated in the full-scale operation. The study shows that existing problems of mixing and flow processes can be explored and corrected efficiently and effectively using a scale model. It is recommended that this method be used for the study of novel designs before construction.
Sampling in an incompletely mixed effluent was studied with the aid of a hydraulic model. The effluent was the discharge from a major wastewater treatment facility. Residual chemicals from the chlorination/dechlorination process were of concern. Concentration time-series data obtained in a 1:12 scale model were used to determine the best sampling location and duration and to predict expected sampling errors relative to spatially and temporally averaged concentration values. Some general concepts for sampler placement in not fully homogeneous streams were derived. Spatial concentration gradients have to be determined to select number and location of multiple sampling points. When concentrations fluctuate in time due to process controls, the flow patterns and velocity distributions have to be known to select representative sampling points. For example, representative sampling within a separated flow region requires carefully selected probe placement and long sampling durations. Physical model simulations can provide the information on flow and concentration time series that are necessary to select the sampling strategy.
The mechanism of seawater purging in a tunneled outfall is studied using a 1:83 hydraulic scale model of Boston's proposed wastewater outfall. Purging requires high rates of effluent flow. which is particularly problematic for Boston because of the wide range of expected flow rates caused by combined sewers and seasonal ground-water infiltration. This study explores some potential solutions to this problem. Model results show riser purging at flows of 5 - 10% less than predicted for risers (Munro criterion) and tunnel purging at flows about 20% less than predicted (full pipe flow criterion based on riser section invert slope), suggesting that the theoretical criteria arc conservative. Construction of a tunnel constriction (Venturi section) just upstream from the risers substantially reduces seawater penetration in the tunnel by creating a condition of densimetric critical flow. Theoretical calculations of the minimum flow rate without tunnel penetration are consistent with observations when downstream mixing is considered. Further tests show that, in combination with the Venturi section, a short-term increase in effluent flow caused by intermittent dumping of the chlorine contact tanks could significantly reduce the riser purging requirement as well.
Failure to purge seawater from the diffuser section of ocean outfalls can cause seawater to circulate through the diffuser section of the outfall. Tunneled outfalls with their long risers are particularly susceptible to this problem. Seawater circulation reduces the hydraulic efficiency of an outfall and there is a possibility that the diffuser may ultimately be blocked by accumulated sediments and marine growth. Purging capability is therefore a fundamental design consideration for ocean outfalls with long risers. While theoretical models can provide upper bounds to the purging flow, the details of the purging process are complex and not amenable to theoretical analysis. Consequently, hydraulic models are a valuable aid to the design process for these types of outfall. The paper develops the model scaling laws appropriate to high riser outfalls. These are based on the various physical interactions involved in the purging process and it is shown that fluid inertia, buoyancy, friction and entrainment all play a role in defining the scaling laws.
The development of a fish-diversion system to be used in the turbine intakes of the Wanapum and Priest Rapids developments on the Columbia River, in the state of Washington, is described. The system uses a passive-bar screen, installed through the emergency gate well, to produce a flow pattern that deflects downstream-migrating juvenile salmonids into the gate well for subsequent removal and bypass to below the dam. The system is based on laboratory model studies and field tests. The model studies provide data on the hydraulic performance of the system and result in an understanding of the hydraulic features of the technique, which can be a guide for future designs. The studies also serve as a guide to development of the structural design of the system. The design, field tested in 1986, 1987, and 1988, attains a fish-guidance efficiency of about 68% with a minimal of descaling (removal of fish scales by abrasion).
Scale effects are always a major concern in mobile-bed hydraulic-model studies. These scale effects can be minimized by using large models (i.e., almost prototype size), but large models require large and costly modeling facilities. Several large ''super flumes'' have been built for two-dimensional (2D) testing, but right now a comparable large ''super basin'' does not exist. Thus, beach processes can be tested in large 2D models, but not yet in three-dimensional (3D) models. The research in super flumes assumes that 2D-wave-flume experiments are representative of the 3D prototypes. Two aspects of that assumption are tested in this paper. Six sets of parallel tests were performed in both a 3D wave basin and a 2D wave flume. It was found that the time scales for morphological development are adequately modeled in the 2D flume, and that there are some differences in the resulting beach profile shapes. The 3D profiles correspond closely with the prototype observations; the 2D profiles are affected by exaggerated turbulence generated when the incoming wave and the downrush of the previous waves meet head-on. The use of the term equilibrium for fluid flow, sediment flow, and profile formation is also discussed in this paper.
A simple-shear box was used to study the shear strength characteristics of floating layers of vertically unconstrained ice rubble comprised of parallelpiped ice blocks. A comparative set of experiments was also performed using floating layers of parallelpiped plastic blocks in order to determine the origin of cohesion in ice rubble. Experiments were also performed using mushy ice. However, the shear-box proved not to be useful for determining the shear testing of mushy ice.The shear strength of a layer of ice rubble was found to depend on normal stress, which in turn was found to depend on rubble thickness, layer porosity, and shear rate. The dependence on shear rate of normal stress and, as a consequence, of shear strength of a layer of floating ice rubble is attributed to the development of freeze-bonds between the ice blocks comprising the rubble layer. It is argued that, at slower shear rates, more and stronger freeze-bonds develop than at higher shear rates, thus enabling the layer to withstand larger normal stresses and, consequently, shear strengths that increase with decreasing shear rates. If the influence of freeze-bonding on normal stress is taken into account, and if a Mohr-Coulomb failure criterion is used to characterize shear strength, it is found that a floating layer of ice rubble undergoing continuous-shear deforms as a cohesionless material; or at least as a material with unique cohesive properties.
The primary purpose of this study was to validate, by comparing corresponding model and prototype data, small-scale model testing of mechanical draft cooling towers as a reliable means of plume prediction. Tests were also conducted to investigate the effects of plume buoyancy and ambient (wind) velocity, and plant-building location on plume trajectories, tower recirculation, plume downwash, and plume merger. Modeling requirements and limitations are summarized. Small-scale models of two existing plants for which sufficient field data were available to permit meaningful comparison were tested in the Environmental Flow Facility (EFF) of the Iowa Institute of Hydraulic Research. The EFF is a recirculatig water flume with a working section 19.8-m long, 3-m wide, and 2.3-m deep. Laboratory testing techniques were developed and modified as needed to bring field and laboratory data into conformity. Particular attention was directed to the role of the velocity distribution in the boundary layer of approach flow; vortex generators and floor roughness were installed in the upstream section of the flume to produce a velocity distribution corresponding to the 1/6 power law. The boundaries of prototype visible plumes were delineated from laboratory data on the stack-effluent concentration distributions. The boundaries of the visible plumes obtained from the scale models were in satisfactory agreement with those obtained in the prototype.
Turbulent transverse mixing is studied in an open channel flow in which
the frictional resistance comes primarily from vertical metal strips.
Analytically we obtain that the mixing coefficient ɛ = kau,
where a is the strip width and u is the mean velocity. The analysis
yields k = 0.08 as a minimum. An experiment in a laboratory flume
verifies the form of the result and yields as an average k = 0.11.
A three-dimensional scale model was designed and built to simulate ground-water solute transport at the Savannah River Site in east-central South Carolina. The site is 0.75 km2 in surface area, and averages 35 m in depth. Liquid wastes have been continuously disposed of on the site for about 30 years. The model was built to an undistorted geometric length scale of 1/500. Model materials of sand, cement, and water, blended in varying proportions to achieve different hydraulic conductivities and effective porosities, allowed simulation of four geologic formations in the prototype. The organic dye Rhodamine 6G was used to represent the prototype solute, tritium. Using scaling laws developed for advection, dispersion, chemical interaction, and making adjustments for the radioactive decay of the tritium, the model plume favorably compared with the carefully mapped plume at the prototype. Capillary forces were not scaled. The writers cautiously recommend more widespread use of scale models in ground-water research.
Winter operation of the New York Power Authority's and Ontario Hydro's hydropower generating stations on the Niagara River is affected by the possibility that ice jams might occur in the vicinity of the hydropower plant intakes. In this study, a two dimensional numerical model was used to study the ice transport and jamming processes in the vicinity of hydropower intakes in the upper Niagara River. The model was also used to analyze the effectiveness of several possible structural and operational measures that might be used to mitigate the occurrence of ice jams and improve winter power production.
The near field plume dilutions from ocean outfall line diffusers consisting of evenly spaced risers with clusters of two to eight ports per riser have been measured in a two‐dimensional sectional hydraulic model. Tests were run under both idealized and measured ocean current and stratification conditions. A mathematical model was successfully correlated with tests not involving ambient currents, thus providing a useful design tool. The laboratory results show that, for the cases studied, the initial dilution is at most a weak function of whether the discharge ports are clustered or evenly distributed along the diffuses and that the minimum dilution increases with decreasing port size (limited, ultimately, to that of a line source). Therefore, the most cost effective design for riser equipped ocean wastewater diffusers may involve the smallest port diameters permitted by other design considerations, and clustering many ports per riser to decrease the number of risers needed.
Cavitation is something hydro plant owners can't afford to ignore. A new technique using acoustic emissions can detect and monitor cavitation in its early stages, and thus serve as a guide for maintenance scheduling and operational changes. In the mid-1980s, the Electric Power Research Institute (EPRI) sponsored a feasibility study in which full-wave rectification spectral analysis was applied to two Kaplan turbines to process the sound emanating from cavitating blades. (In full-wave rectification spectral analysis, the system electronically manipulates the sound signal in order to bring out certain frequencies - in this case, those associated with cavitation. It is based on a phenomenon similar to the amplitude modulation in an AM radio signal, where a high frequency carrier wave is modulated by the lower frequencies of the sounds being broadcast). The study showed the approach to be a viable means of detecting the onset and severity of cavitation. The Institut de Recherche d'Hydro-Quebec (IREQ) also explored the potential of full-wave rectification spectral analysis in monitoring cavitation in hydroturbines in the mid-1980s. Its study, sponsored by the Canadian Electrical Association, focused on model and full-scale Francis turbines. The IREQ researchers confirmed the applicability of the method used in the EPRI study to large-scale Francis turbines.
Scaled physical model experiments have provided insight into the mechanism by which carbon dioxide recovers crude oil left behind after waterflooding. The efficiency of the process appears to depend primarily on the displacement of the mobile water to expose the occluded oil to the CO/sub 2/. Solution and swelling then restore mobility to the residual oil, which can then be immiscibly displaced by CO/sub 2/ or water. The large quantities of CO/sub 2/ required to recover a barrel of crude oil reported in field trials in which it was injected continuously are shown to be expected values. In order to achieve an economic CO/sub 2//oil ratio, it is necessary to use optimum-sized slugs of CO/sub 2/ followed by water, or by a gas in dipping reservoirs, and to maintain an adequate back pressure on the production well. Close spacing and high injection rates are indicated to be necessary in order to overcome gravity segregation and, because of viscous fingering and channelling, only a fraction of the crude in place can be targeted for recovery. Simple estimates of the incremental cost of a barrel of oil to be recovered by CO/sub 2/ are dangerous because at current interest rates the time gap between CO/sub 2/ injection and oil production will result in a significant increase in the effective cost of the CO/sub 2/.
Trashracks in pumped storage systems with high flow rates can develop fatigue failures due to excessive vibration excited by the flow past the rods in the rack. An experimental study of trashrack vibration was made on a half-scale model of a prototype rack design for the TVA Raccoon Mountain pumped storage system. The natural frequencies and loss factors of the first dozen natural modes of the rack were determined in air before placing the rack in a water channel. Under normal flow rates the rack developed “locked-in” pure tone vibrations of sufficient amplitude to cause early fatigue failure. Unexpectedly, the frequency of the vibration was not close to the vortex-shedding frequency and the motion of the rods was not transverse to the flow. The “locked-in” modes were identified as modes in which the bending displacements of the rods were parallel to the flow. Further investigation showed that the excitation mechanism involved synchronization between the fluctuating drag involved in vortex shedding and the fore-and-aft motion of the rods in sharply resonant modes. Modifications of the original design were introduced to defeat the identified mechanism. In order to completely eliminate the “lock-in” phenomenon it was necessary to change the bar cross-sectional shape and to introduce additional damping into the rack structure. A half-scale model of the modified design was built and tested to verify the absence of destructive vibrations.
A one-dimensional, vertically stratified, thermal simulation model was developed for prediction of temperature within and downstream from Dickey-Lincoln School Lakes. Two physical hydraulic models were used to obtain an improved understanding and description of the hydrodynamic response of the lakes to pumped-storage hydropower. An undistorted, 1:200-scale model of the Dickey Lake intake structures and local topography was used to determine the steady-state selective withdrawal and pumpback flow characteristics for various conditions. A highly distorted-scale model (1:3600 horizontal, 1:180 vertical) was used to simulate the entire dual reservoir system and to determine the response to dynamic, unsteady-state, density stratified flow. Information from the two physical models was used to modify existing algorithms and to develop new algorithms for the mathematical model. The mathematical model allows simulation of the hydrodynamic and heat exchange characteristics so that the thermal regimes within and downstream from the two lakes can be determined for various hydrologic and meteorologic conditions and various pumped-storage hydropower operations. (Author)
A model test series has been performed to investigate the dynamic ice loads on a bridge pier of the Great Belt Link, Denmark. Two models were constructed at a geometric scale factor of 30. Each model consisted of a bridge pier with two separate bridge shafts. The ice loads were measured on the shafts as a function of interaction rate and ice attack direction for three different values of foundation stiffness: rigid in both horizontal directions, rigid in one horizontal direction but flexible in the other, and flexible in both horizontal directions. The experimental techniques and results of the test series are discussed and presented in tabular form.
This paper presents the set-up and results of an extensive research programme concerning the erosion of coastal dunes during storm surges. A large number of two-dimensional and three-dimensional mobile-bed model tests has been carried out to investigate the process of dune erosion. The state of art after a series of small-scale tests is summarized. Attention is focussed on large-scale tests carried out in the Delta Flume with random waves up to 2 m significant height. Sediment concentration and orbital velocity measurements are discussed. The large-scale tests have confirmed the validity of a modelling technique based on the dimensionless fall velocity parameter H/Tw. The model results are being applied to check the safety of existing coastal dunes as a water-retaining structure that has to protect the major part of the Netherlands from inundation during storm surges.