![Maximum freeboard exceedance data. (a) Comparison of freeboard exceedance time series between VWPs measured before (VWPw0-Hst, x = −0.005 m) and after (VWPd0, x = 0.005 m) the bow edge of the deck (C1, EXP1, CAM1); see also [24]. η0 and η0,out represent the maximum freeboard exceedance for VWPd0 and VWPw0, respectively. (b) Ratios of maximum freeboard exceedances η0,out/η0, considering η0,out obtained at different positions from the deck edge (x/Lst, where Lst is the structure length) for all the study cases. (c) Ratios of time of occurrence of the maximum freeboard exceedances (í µí±¡ í µí¼ 0,í µí±í µí±¢í µí±¡ /í µí±¡ í µí¼ 0 ), considering η0,out obtained at different positions from the deck edge for all the](https://www.researchgate.net/profile/Jassiel-Fontes/publication/337812710/figure/fig25/AS:837741818433536@1576744622350/Maximum-freeboard-exceedance-data-a-Comparison-of-freeboard-exceedance-time-series_Q320.jpg)
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Green Water on A Fixed Structure Due to Incident Bores: Guidelines and Database for Model Validations Regarding Flow Evolution
Water
Abstract and Figures
This paper presents a two-dimensional experimental study of the interaction of wet dam-break bores with a fixed structure, regarding the evolution of the incident flows and the resultant green water events on the deck. The study employs image-based techniques to analyse flow propagation from videos taken by high-speed cameras, considering five different shipping water cases. The features of small air-cavities formed in some green water events of the plunging-dam-break type were analysed. Then, the spatial and temporal distribution of water elevations of the incident bores and green water were investigated, providing a database to be used for model validations. Some guidelines for the selection of the freeboard exceedance, which is of relevance for green water simulations, were provided. Finally, the relationship between the incident bore and water-on-deck kinematics was discussed. The proposed study can be used as a reference for performing simplified and systematic analyses of green water in a different two-dimensional setup, giving high-resolution data that visually capture the flow patterns and allow model validations to be performed.
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Supplementary resource (1)
... The present study uses the wet dam-break method to generate isolated shipping water events on a fixed cuboid structure. Details of this method can be found in [20,46,57]. The present numerical research reproduces the experimental setup by Hernández-Fontes et al. [14,57] and therefore experimental data from these works were used to validate the numerical results regarding water elevations [57] and loads over the deck [14]. ...
... Details of this method can be found in [20,46,57]. The present numerical research reproduces the experimental setup by Hernández-Fontes et al. [14,57] and therefore experimental data from these works were used to validate the numerical results regarding water elevations [57] and loads over the deck [14]. Figure 1 shows the experimental setup. ...
... Details of this method can be found in [20,46,57]. The present numerical research reproduces the experimental setup by Hernández-Fontes et al. [14,57] and therefore experimental data from these works were used to validate the numerical results regarding water elevations [57] and loads over the deck [14]. Figure 1 shows the experimental setup. ...
Shipping water events that propagate over the decks of marine structures can generate significant loads on them. As the configuration of the structure may affect the loading behaviour, investigation of shipping water loads in different structural conditions is required. This paper presents a numerical investigation of the effect of deck roughness and deck length on vertical and horizontal loads caused by shipping water on a fixed structure. Systematic analyses were carried out of isolated shipping water events generated with the wet dam-break method and simulated with OpenFoam Computational Fluid Dynamics toolbox. The numerical approach was validated and then the shipping water loads were examined. It was found that, as roughness increased, the maximum vertical and horizontal loads showed a delay. As the deck length reduced, the vertical backflow loads tended to increase. These results suggest it may be worthwhile examining the behaviour of shipping water as it propagates over rough surfaces caused by fouling, corrosion, or those with small structural elements distributed on them. Moreover, the effect of deck length is important in understanding the order of magnitude of loads on structures with variable deck lengths, and those which have forward and backflow loading stages.
... The main difference between the DB and the PDB types of green water is that an air cavity is often formed at the deck's edge in the latter. As water propagates over the deck, this cavity is entrapped and fragments inside the flow, producing bubbles that tend to escape when the water travels along the deck [19]. In the HF type, no cavities are formed; instead, a block of water remains almost suspended at the beginning of the deck, as a fluid-arm [9]. ...
... Regarding the research of green water evolution, in terms of water elevations, recent investigations have been performed using image-based measurements in simplified experiments, providing useful information [17,19,30,31]. From these works, Hernández-Fontes et al. [31] employed the concept of Virtual Wave Probes (VWP, [32]) in green water research to investigate the distribution of water-on-deck through binary image processing and analysis. ...
... In green water research, the time series of water elevation measured at the start of the deck are known as freeboard exceedance [1,20,42] and are important in the application of analytical and numerical models used in ocean engineering to analyze the water-on-deck behavior, such as [16,19,43]. In this research, the measurements given by sensor d2 defined in Figure 4 (positive measurements from the deck level), are considered as the freeboard exceedance of the green water events. ...
Green water events may present different features in the initial stage of interaction with the deck of a structure. It is therefore important to investigate the evolution of different types of green water, since not all the events interact with the deck at the same time. In this paper, the evolution of three types of green water events (dam-break, plunging-dam-break, and hammer-fist) are studied. The water surface elevations and volumes over the deck in consecutive green water events, generated by incident [wave trains in a wave flume, were analyzed using image-based methods. The results show multiple-valued water surface elevations in the early stage of plunging-dam-break and hammer-fist type events. Detailed experimental measurements of this stage are shown for the first time. The effect of wave steepness on the duration of the events, maximum freeboard exceedance, and volumes were also investigated. Although the hammer-fist type showed high freeboard exceedances, the plunging-dam-break type presented the largest volumes over the deck. Some challenges for further assessments of green water propagation are reported.
... Digitized surface profiles showed a horizontal jet in dry bed and a special mushroom-like jet in wet bed conditions at the initial stage of propagation. Based on the previous research of unbroken [27,28] and partially broken waves [29] generated by wet dam-break on a fixed structure, Hernández-Fontes et al. [30] developed and investigated this interaction via fully developed broken incident flow. In the experiment, a high-speed camera, water elevation, and force sensors were applied to record the overtopping behaviors, patterns, and loads. ...
This paper presents the results of an experimental investigation on the impact of dam-break-induced surges on a vertical wall. The instantaneous surge height and dynamic pressure on a vertical wall were measured for surges with different reservoir depths of H = 200 mm, 250 mm, and 300 mm. The time-histories of horizontal pressure on the wall were measured using the miniaturized pressure transducers, and the surge heights were recorded with an ultrasonic sensor. The relationships between dynamic pressure and surge height on the vertical wall and during the impact were obtained from recorded raw data. The experimental results highlighted detailed processes on the variation of impact pressure during the surge propagation, impact on the wall, runup, falling, and breakup of the turbulent flow. The time-histories of surge height and dynamic pressure were analyzed, and the results were compared with the hydrostatic pressure on the wall to study wave breaking mechanism of tsunami waves on the wall. Dynamic pressures at the impact instant were found to be approximately three times the corresponding static pressure in the bed, in good agreement with previous research Moreover, the maximum surge runup heights on the wall were between 2.1 and 2.3 times the corresponding initial reservoir depths. The vertical distributions of impact pressure were divided into two hydrodynamic regimes. Based on the impact duration, the first regime occurred less than 0.1 s after the impact with highly non-linear pressure distributions, and the second regime showed a semi-hydrostatic pressure distribution from 0.5 s to 0.7 s. The results presented in this study are suitable for the design of coastal infrastructures and can be used to validate numerical models.
... Recently, alternative and simplified methods based on the concept of virtual water surface measurements at specific locations in wave flume experiments have been proposed for hydraulic applications [11] and ocean engineering research [12,13]. To the best of the authors' knowledge, Kocaman and Ozmen-Cagatay [11] introduced the concept of virtual wave probe (VWP) measurements evaluating the flow from wet dam-break experiments. ...
This paper presents the use of virtual level (VL) probes as an alternative image-based approach to investigate the interaction of waves with coastal structures in wave flume experiments. These probes are defined as regions of interest located at specific positions along the horizontal domain of the images, in which edge interfaces are detected and, thus, their vertical motions can be obtained. To demonstrate the use of the methodology, a critical condition of breaking waves interacting with a Cubipod homogeneous low-crested structure (HLCS) in a two-dimensional framework was selected. With the video recorded from the experiments, image calibration, processing, and analysis stages were implemented to analyze the performance of the HLCS in reducing wave elevations and to study the stability of the armor units. The present approach can be extended to a wide range of coastal structures applications where the interface detection between components of the scene is useful to observe the behavior of coastal structures, increasing effectiveness and alternatives to acquire precise data in 2D experimental tests.
Studies on wave and structure interaction are essential to design safe and sustainable marine structures for various applications. Specifically, the occurrence of green water phenomenon in marine structures can result in significant hydrodynamic loads. However, no systematic analyses have been undertaken to assess the loads produced by water interacting with sloped decks, due to different types of green water events. This paper describes an experimental and numerical analysis to investigate the impact of deck inclination and length on the overall loads caused by green water on a fixed structure. Wet dam-break methodology was used to generate the green water events, while OpenFOAM software was used for hydrodynamic modelling. The investigation examines three kinds of green water situations, namely dam-break and plunging-dam-break with minor and significant hollows formed at the deck periphery. Validation of the numerical approach was carried out using the results from experiments obtained with a horizontal deck, considering water elevations and loads over the structure deck. Then, numerical simulations were performed to provide a systematic analysis on how the slope and length affect total green water loads. The total loads assessed were those acting perpendicularly on the deck and on a vertical wall that limits the deck length. Experimental results obtained from the three types of green water showed different patterns, mainly distinguished by the features of the breaking wave, the size of the air cavity formed at the edge of the deck, and different amounts of water over the deck. The numerical results show that negative deck slopes and longer deck lengths notably increase the water-on-deck peak loads, while positive deck slopes decrease the loading time. Two main peak forces were consistently seen throughout the majority of the time series data, with their appearance being influenced by deck pitching. Considering the case of a horizontal deck with a vertical wall as reference, and the incident flows of this research, it was discovered that negative deck slopes may increase the peak loads acting on the deck by approximately 150%, and by five times more the ones acting on the wall. Further research is suggested to determine the maximum peak loads to be used for design purposes in different types of deck configurations. The simplified methodology described in this paper can enhance our understanding of the patterns of green water loads on inclined decks of fixed structures or ships with angular movements.
This paper presents an experimental and numerical investigation of the interaction of wet dam-break flows with a fixed structure. These flows presented breaking features and caused bow run-up and shipping water events on the deck of the structure. Wet dam-break experiments were performed using high-speed video to capture the stages of wave generation, interaction with the structure and propagation on its deck. Two different incoming flows were generated, varying the freeboard, and keeping the same wet dam-break ratio. These were numerically simulated using Moving Particle Semi-implicit (MPS) method. The purpose was to compare MPS numerical simulations based on two surface tension models previously proposed in the literature and a geometric-based surface tension model proposed in this work, this to improve free surface performance to represent breaking wave features more realistically. First, the different approaches were compared with experimental results. Then, the proposed model was implemented to analyze the effect of the velocity applied to gate opening on the water surface during wave generation, wave-bow interaction and water propagation over the deck. The distribution of particles, pressure and velocity fields was presented in this analysis. Results showed that the proposed surface tension model performed well in representing the free surface. It was seen that surface tension effects can be relevant during the wave formation effects. Furthermore, it was verified that variating the gate opening velocity, dynamic interactions of the resulting waves with the structure was affected, causing energetic processes variations. It is recommended to consider this velocity for validation purposes.
Shipping water events (SWE) occur when incident waves flood and propagate over the deck of maritime structures, usually during extreme wave climate. SWE can cause structural damage, unexpected overloading, human losses or even spills of products that are harmful to the environment. Therefore, the estimation of variables that help to predict the evolution of these events is highly helpful to lessen catastrophic consequences. In this regard, this work proposes a model-based approach to describe the spatiotemporal evolution of SWE on a fixed structure with a horizontal propagation domain. The approach is based on a model expressed as an advection-difussion equation with space-dependent nonlinear coefficients. To explore the suitability of the model, for characterizing the SWE evolution, its numerical response is compared with elevation data of SWE generated in a channel by incident regular wave trains. For the comparison, the model coefficients were estimated from an experimental data set with the use of an adaptive observer. The results of the comparison show that the response of the model allows to represent the physics of the analyzed SWE in an acceptable way. The advantage of using an adaptive observer for the estimation is that it can be used in further applications where the actual values of varying coefficients could be required in a reasonable computational time.
An experiment that investigates the interactions between dam-break flow and a floating box is reported in this paper. The interaction processes are described in detail, and the effects of reservoir depth, clearance between the structure and vertical wall, and structure motion on the observed interactions are discussed. Results indicate that interactions are mild if the reservoir depth is relatively small and most of the water flows through under the structure. However, as the reservoir depth increases, the interactions intensify, and overtopping and wave splashing occur. The incident wave is divided into two parts by the structure: 1) a jet generated by wave impact and 2) the water flowing through under the structure. The water flowing through under the structure is the main factor influencing the motion of the structure. The phenomenon of secondary slamming is observed in all of the test cases, and the relative motion of the structure and free surface explains the occurrence of secondary slamming.
Understanding the interaction between waves and maritime structures (IWMS) has been a primary concern for humans since ancient times, when they started sailing oceans and defending land from flooding and erosion [...]
Shipping water (SW) events occur when waves, usually during extreme weather conditions, overtop the deck of vessels or structures. Since SW events take place independently but close enough in time to interact with one another, their simulation requires strong non-linear equations to achieve an appropriate precision. To avoid using equations with high complexity and computational cost, we blueexplore the use of the time fractional diffusion equation (TFDE) for modeling SW events. The idea behind this proposal is to keep the simplicity of the widely used standard diffusion equation, but employing a generalized derivative of order . This order can be used to describe an intermediate behavior between diffusion and wave propagation. For the time derivative, we adopted the Caputo fractional derivative. To demonstrate that the TFDE is a suitable model to describe SW events, we present its results compared against data sets of water free surface elevation recorded during SW experiments carried out in a wave flume. The best agreement was found for a fractional order derivative between 1.69 and 1.75.
The mesh-free particle method is the latest method in the computational fluid dynamics field. It has become well-known due to its application for simulating any kind of interface deformation and fragmentation, including large disturbance on the interface. In this study, the moving particle semi-implicit (MPS) method has been developed for multi-phase to simulate mobile (erodible)-bed under violent flows such as a dam break. In order to develop the MPS method, multi-phase particle interaction models including self-buoyancy and surface tension models were employed. All of the newly adopted particle interaction models were modified by the author. When fluids collide with the soil bed, the erodible bed can be liquefied. In this regard, polyethylene oxide (PEO) solution was used as a mobile bed. The water column captured by the gate collapsed after opening the gate, and it then propagated over a mobile bed. The mobile bed has various thicknesses based on corresponding experiments. Moreover, the dam break on an inclined tank was also simulated to investigate the swash uprush problem. The maximum velocity and height of mixed flows were measured at a certain point, which aligned with the corresponding experiment. All of the simulation results were compared with those obtained from some experimental work.
Liquid dispersion in chemical processes is significant for increasing mass or heat transfer. A particle-based method, the moving particle semi-implicit (MPS) method, was employed in this study to simulate the process of liquid dispersion by mesh packing. The computational framework includes a designed inlet flow model, hydrophilic/hydrophobic surface boundary conditions, and a surface tension model. This study mainly focuses on the effect of hydrophobic/hydrophilic mesh packing on liquid dispersion performance. The mechanism of liquid dispersion is systematically investigated in basic situations as a liquid passing through a single wire, an orthogonal wire and a single aperture. The results indicate that hydrophobic and hydrophilic mesh packing have different effects on the formation of the free surface, which is the key to the mechanism of the liquid dispersion process. Hydrophobic mesh packing can disperse a liquid into several fine columns with detected droplets, which further develop into fine droplets, whereas hydrophilic mesh packing will guide a liquid to converge into a column at the bottom of the mesh packing. In addition, the surface area density and dispersion range of a liquid are quantitatively analyzed to illustrate liquid dispersion performance.
A 3-dimensional large-scale Fluid-Structure Interaction (FSI) framework is developed for the simulation of strength of the coastal structures to withstand tsunami. One-way coupling is used in this framework. Moving Particle Simulation (MPS) is adopted for fluid computations involving free surface flow and Finite Element Method (FEM) is adopted for structural computations. To achieve high parallel efficiency and reduce development costs, the open parallel source named ADVENTURE_Solid is used as the structural analysis solver and LexADV_EMPS is used as fluid analysis solver. Since our proposed framework combines two different numerical methods: FEM and MPS, and distribution of physical values in their methods are differently expressed; therefore interpolation related to fluid forces on fluid-structure interface is required. Accuracy of the interpolation directly affects reliability of result obtained by the FSI simulation. In this study we propose three interpolation methods and quantitatively evaluate their accuracies by solving a benchmark test case. In addition, using an interpolation method that achieves highest accuracy among the three methods, we perform a large-scale parallel FSI simulation of a nuclear power station subjected to a tsunami wave to demonstrate applicability of our proposed framework.
The mechanism of a ripple formation process under swash zone, which is shallower than surf zone, has not yet been fully investigated due to the difficulty of a precise measurement or of an implementation of accurate numerical simulation, under complex boundary conditions caused by wave breakings or bores. To simulate the formation process of the ripples resulting from a sediment transport around swash seabed, the enhanced MPS (moving particle semi-implicit) is employed, which enable simulating wave breakings with a high degree of accuracy. On the other hand, the DEM (distinct element method) is adopted for simulating the ripple formation from tracking individual sand particle. This DEM–MPS coupling model based on particle method will have a high potential to accurately simulate violent flow and its induced sediment transport. The interaction between fluid flow and sediment particles in the formation process of ripples on the swash zone has been numerically examined from the spatial profiles of the flow field and interparticle forces. In this study, the effect of pore water on the formation process of rolling grain ripples is discussed, in particular. Numerical results indicate that the pore water plays an important role in fluidization of sediment DEM particles and contributes development of the ripple formation.
The shipping of water is a problem that affects naval and offshore structures. Estimating its propagation on the decks of these structures by using analytical methods has been a main concern of projects. However, classical approaches disregard the decay tendency of water elevation time series and tend to overestimate the resultant water on deck. This paper is concerned with estimating the evolution of water along the deck of a fixed structure due to shipping water events. An analytical convolution model is proposed to estimate water elevations. The model considers the freeboard exceedance time series and the mean shipping flow velocity as inputs and the frictional effects of the bottom by resistance coefficients, which enables an approximated representation of the water elevation time series over the deck. It was validated with experiments of isolated shipping water events that were generated with the wet dam-break approach. The results obtained with the proposed model captured the experimental results, approximating the peak values and the decay trend of time series. Improvement of the proposed approach over classical models to represent shipping water elevations was demonstrated by comparing the results obtained with those of the dam-break model of Stoker.
Sediment scouring is a common example of highly dynamic sediment transport. Considering its complexities, the accurate prediction of such a highly dynamic multiphase granular flow system is a challenge for the traditional numerical techniques that rely on a mesh system. The mesh-free particle methods are a newer generation of numerical techniques with an inherent ability to deal with the deformations and fragmentations of a multiphase continuum. This study aims at developing and evaluating a multiphase mesh-free particle model based on the weakly compressible moving particle semi-implicit (WC-MPS) formulation for simulation of sediment scouring. The sediment material is considered as a non-Newtonian viscoplastic fluid, whose behavior is predicted using a regularized μ(I) rheological model in combination with pressure-dependent yield criteria. The model is first validated for a benchmark problem of viscoplastic Poiseuille flow. It is then applied and evaluated for the study of two classical sediment scouring cases. The results show that the high-velocity flow currents and the circulations can create a low-viscosity region on the surface of the sediment continuum. Comparing the numerical results with the experimental measurements shows a good accuracy in prediction of the sediment profile, especially the shape and dimensions of the scour hole.
Estimation of loads derived from shipping water events in naval and offshore structures is of importance to improve their structural design or to predict changes in their dynamics. For the case of vertical loads on deck of a fixed structure, it is possible to estimate analytically their evolution in time by considering the distribution of shipping water elevations. However, the classical approach to estimate this distribution (i.e., dam-break method) tends to overestimate the amount of water on deck and does not follow the generated decay trends observed experimentally. In the present work, the time evolution of the vertical loads due to shipping water events was studied analytically and experimentally. The validation of the use of a convolution model to estimate the time evolution of vertical loads is presented, aiming to improve the results obtained with classical approaches. A systematic experimental study has been conducted using the wet dam-break method to generate isolated shipping water events, measuring the slow-varying vertical loads on a rectangular fixed structure. A force balance and a high-speed camera have been used at the same sampling rate to monitor the vertical loads and the shipping water evolution on the deck. Results demonstrated that the use of the convolution model improved the representation of the time series of loads compared with the traditional dam-break approach. With this new method, it was possible to capture the peaks and the decay tendencies observed in the experimental data in an approximated way.
A novel multiphase mesh-free particle numerical model is developed and applied for modeling of sub-aerial (dry) and submerged (underwater) landslides. The model is based on the weakly-compressible moving particle semi-implicit method (WC–MPS), and treats the multiphase system of water and granular materials as a multi-density multi-viscosity continuum. The viscous behaviour of the granular material is predicted using a visco-plastic rheological model (i.e. μ(I)) with a dynamic inter-grain mechanical pressure. The model is validated and evaluated for the rigid, sub-aerial and submerged landslides in comparison with the available experimental measurements and past numerical results. The granular surface profile and the evolution of the granular mass are compared. Comparisons show a good agreement between the results of the developed model and those of the experiments, and also a better accuracy comparing to the past numerical studies. The results also show the capability of the model in dealing with the shape evolution and the deformation and fragmentation of granular interface. Complementary experiments on the sub-aerial landslide are also conducted to study the relevant physics and validate the model. The role of the rheological model is also investigated. Comparing the μ(I) rheology with the widely–used Herschel–Bulkley model shows a slightly more accurate granular profiles for the μ(I) rheology, for both sub-aerial and submerged landslides.
Green water occurs when an incoming wave exceeds the freeboard and propagates onto the deck of naval/offshore structures, such as floating production storage and offloading units and platforms. This water can affect the integrity of facilities and equipment that are installed on the deck, compromise the safety of the crew, and affect the dynamic stability of the structure. Traditionally, wave trains have been used to study the green water problem, which is a good approach to analyzing consecutive green water events. However, to carry out systematic studies that allow local details to be identified for different types of green water, an alternative method is to study isolated events generated by a single incoming wave. The purpose of this paper was to experimentally investigate the generation of different types of isolated green water events using the wet dam-break (DB) approach as an alternative to generating the incoming wave. Tests were carried out in a rectangular tank with a fixed internal structure. Different freeboard conditions were tested for two aspect ratios of the wet DB (h0/h1=0.40 and 0.6). Conventional wave probes were used to measure the water levels in the tank, and a high-speed camera was set to capture details of the generated green water events. The results demonstrated the ability of this approach to represent different types of green water, similar to those obtained with unbroken regular waves in barge-shaped fixed structures, including DB, plunging-dam-break (PDB) and hammer-fist (HF).
Available for free-access until May 30th, 2018 in the next link:
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This paper presents an alternative and open-source methodology based on binary image analysis to measure water elevations in two-dimensional hydrodynamic experiments. The proposed methodology considers the three main stages of an artificial vision system: image digitalization, processing and analysis. In the image processing stage, binary images were obtained by intensity modulation and pseudo-color-based segmentation. The image analysis stage employs simplified morphological operations to measure water elevations at specified regions of interest in the binary images. The image processing and analysis stages were developed in scripts for the ImageJ open-source software. The applicability of the proposed methodology was verified by comparing measurements of water elevations obtained using the proposed approach and conventional wave probes during experiments of shipping water on a fixed structure. The experiments included cases where single-valued and double-valued water surfaces were observed. For all the test cases, the water elevation time series obtained using the proposed approach were in good agreement with the experiments before three-dimensional effects on flow were significant. For the case in which a double-valued water surface was observed, it was confirmed that the proposed procedure possesses the capability to measure the effective water height at specified regions of interest.