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Abstract

The analysis of the dynamics of wing-in-ground-effect vehicles provides data for assessing the stability of motion, controllability, and ride comfort of the craft under development.

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... The abrupt end of GEV development in the late 1980s led to a small amount of available relative research work, as none of these concepts ever reached serial production phase. This fact presents a conceptual design challenge; however, some literature research could be used as an initial point in the design [1,3,4]. The term ground effect (GE) is understood as an increase in the lift-to-drag ratio (L/D) of a wing, at cruise altitudes of less than the chord length of the wing, preferably less than 25% [3]. ...
... This fact presents a conceptual design challenge; however, some literature research could be used as an initial point in the design [1,3,4]. The term ground effect (GE) is understood as an increase in the lift-to-drag ratio (L/D) of a wing, at cruise altitudes of less than the chord length of the wing, preferably less than 25% [3]. As the wing nears the sea surface boundary, the free stream air is not allowed to expand under the wing, further increasing the static pressure and thus increasing the lift [4]. ...
... The proposed novel UGEV combines the advantages of a blended wing body (BWB) platform, i.e., a tailless design that integrates wings and a fuselage, with the corrective additions of a box wing (BXW) platform, i.e., a closed box-like wing formation with no wing tips ( Figure 2). The greatest advantage of The term ground effect (GE) is understood as an increase in the lift-to-drag ratio (L/D) of a wing, at cruise altitudes of less than the chord length of the wing, preferably less than 25% [3]. As the wing nears the sea surface boundary, the free stream air is not allowed to expand under the wing, further increasing the static pressure and thus increasing the lift [4]. ...
Article
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In this study, the conceptual design of an unmanned ground effect vehicle (UGEV), based on in-house analytical tools and CFD calculations, followed by flow control studies, is presented. Ground effect vehicles can operate, in a more efficient way, over calm closed seas, taking advantage of the aerodynamic interaction between the ground and the vehicle. The proposed UGEV features a useful payload capacity of 300 kg and a maximum range of 300 km cruising at 100 kt. Regarding the aerodynamic layout, a platform which combines the basic geometry characteristics of the blended wing body (BWB), and box wing (BXW) configurations is introduced. This hybrid layout aims to incorporate the most promising features from both configurations, while it enables the UGEV to operate under adverse flight conditions of the atmospheric boundary layer of the earth. In order to enhance the performance characteristics of the platform, both passive and active flow control techniques are studied and incorporated into the conceptual design phase of the vehicle. For the passive flow control techniques, the adaptation of tubercles and wing fences is evaluated. Regarding the active flow control techniques, a wide range of morphing technologies is investigated based on performance and integration criteria. Finally, stability studies are conducted for the proposed platform.
... The effect of ground proximity is not accounted for in Theodorsen's original work. Rozhdestvensky's expansive collection of research on lifting wings in ground effect, primarily relating to Wing-in-Ground (WIG) effect vehicles, contains extensive approximations for the various configurations and operating conditions such craft encounter, including sinusoidal and pitching oscillation [14]. ...
... Figure 7 and compared to the Lifting Line Theory [33]. Here, we observe that the distribution closely follows the theoretical prediction for a finite aspect ratio wing in unbounded flow out to 90% of the half-span and approaches uniform distribution in extreme ground effect for h/c < 0.1 [14]. In the tip region 2y/b > 0.9, the lift coefficient is never lower than 50% of the center plane lift. ...
... Further examination of the literature on extreme ground effect craft led to the collection of research by Rozhdestvensky [14]. From two-dimensional potential flow analysis, for a flat plate at a given angle of pitch, the lift coefficient can be represented by Equation (5). ...
Article
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An inverted single element was subjected to a sinusoidal heaving motion in both free flight and extreme ground effect, with the ground effect simulations oscillating in various states of interaction with the peak lift ride height of the wing. Peak negative lift during the heaving cycle was greater than the static values at the same ground clearances, time and ensemble averaging showed an overall reduction in the lift coefficient of 10-22%. An analytical model combining potential flow lift predictions and a new variation of the Goman-Khrabrov state-space model predicts the lift behavior of the wing in ground effect based on reduced frequency and ground clearance.
... Most of physical phenomena in ground effect aerodynamics have been already described in various papers and monographs [5][6][7]. In this introduction, we would like to mention just three facts which are often not sufficiently interpreted in the literature. ...
... Most detailed description of the dynamics, stability, and control of the WIG craft is given by Zhukov [11] and Diomidov [12] who made serious contribution to the design of all famous Soviet ekranoplans. An overview of some results can be found in the book of Rozhdestvensky [6] and in the SNAME handbook [3]. In fact, WIG crafts designed by Russian and German specialists were thoroughly proved using the linear stability theory and nonlinear motion simulations. ...
... This problem is addressed in Section 2.1 of the present paper. Representation (6) was widely used in the Russian WIG community. It is based on the assumption of linear representation of forces caused by unsteady effects. ...
Article
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The paper presents the analysis of unsteady forces and their influence on the aerodynamics and motion of a wing-in-ground (WIG) effect craft. Two-dimensional and three-dimensional aerodynamic models based on the potential flow are coupled with time domain simulations in the longitudinal plane. A special attention is paid to the explanation of the dynamic ground effect on both the sink and pitching motions. The influence of unsteady and quasi-steady forces on the dynamic ground effects and the craft motion is analyzed for different heights of flight.
... Applications have included aircraft in landing or takeoff modes or aircraft designed specifically to fly in ground effect (Wing-in-ground-effect, or WIG vehicles). In these cases, proximity to the ground serves to enhance the lifting performance of the wing, and often the aerodynamic efficiency (lift/drag, L/D) as well (1)(2)(3) . The principal effect of the ground is to move the stagnation point downwards as the wing experiences a reduction in velocity and an increase in pressure on the lower surface, accompanied by an increase in local velocity at the upper surface suction peak near the leading edge (1,2) . ...
... Therefore, the overall efficiency (L/D) of the wing can be greatly improved as ground clearance is decreased. A much-improved understanding of the aerodynamic influence of compressible ground effects and of shock/ground interaction is timely, particularly given recurring interest in high-speed subsonic (freestream Mach number, M ∞ ≥ 0·4) WIG aircraft (3) , as well as magnetic-levitation space vehicle launch systems (4) , and high speed rail vehicles increasingly pushing towards the midsubsonic Mach number range (5) . An example of shock/ground (in this case, water) interaction is shown in Fig. 1, where a US Navy Blue Angel performs an extremely low-level pass in San Francisco and generates a series of shockwaves, some of which influence the water surface. ...
... Although the incidence here is high enough to promote large-scale separation on the upper surface, the flow between the aerofoil and ground is closer to the 'ram' effect that can be achieved at lower incidence for a more flat-bottomed aerofoil section (3) , as the profile is fairly parallel with the ground from the point of minimum ground clearance to the trailing edge. In this scenario, the region under the aerofoil is almost exclusively a high pressure zone, and features relatively little local acceleration due to curvature. ...
Article
The potential positive effects of ground proximity on the aerodynamic performance of a wing or aerofoil have long been established, but at transonic speeds the formation of shock waves between the body and the ground plane would have significant consequences. A numerical study of the aerodynamics of an RAE2822 aerofoil section in ground effect flight was conducted at freestream Mach numbers from 0.5 to 0.9, at a range of ground clearances and angles of incidence. It was found that in general the aerofoil's lifting capability was still improved with decreasing ground clearance up until the point at which a lower surface shock wave formed (most commonly at the lowest clearances). The critical Mach number for the section was reached considerably earlier in ground effect than it would be in freestream, and the buffet boundary was therefore also reached at an earlier stage. The flowfields observed were relatively sensitive to changes in any given variable, and the lower surface shock had a destabilising effect on the pitching characteristics of the wing, indicating that sudden changes in both altitude and attitude would be experienced during sustained transonic flight close to the ground plane. Since ground proximity hastens the lower surface shock formation, no gain in aerodynamic efficiency can be gained by flying in ground effect once that shock is present.
... Some aspects of aero-hydrodynamics, stability and dynamics of other aerodynamically assisted marine craft were considered by Nangia (1987), Collu et al. (2010), Gu et al. (2011), andMatveev (2012). To calculate aerodynamic lift on a platform moving above but close to the water surface, the extreme-ground-effect theory can be applied (Rozhdestvensky, 2000). Previously, Chaney and Matveev (2012) utilized a steady quasi-one-dimensional formulation of that theory. ...
... where m and I are the boat mass and moment of inertia, respectively, U is the boat horizontal speed, x T is the horizontal thrust component, D F is the total drag force, cg y is the vertical position of the center of gravity, L F is the total lift force, g is the gravity constant, M is the sum of all moments with respect to the center of gravity (CG), and t is the time. In the Extreme-Ground-Effect (EGE) theory approximation (Rozhdestvensky, 2000), i.e., when the clearance between the platform and surface is much smaller than the platform length, the aerodynamic lift is predominantly caused by increased pressure underneath the platform. The governing continuity equation for the under-platform quasi-two-dimensional airflow under inviscid and incompressible assumptions is ...
... The aerodynamic extreme-ground-effect theory is relatively new and only a few validation cases can be found in the literature (Rozhdestvensky, 2000;Soderlund and Matveev, 2010). Here, a comparison with another experiment is demonstrated. ...
Article
Full-text available
High-speed marine vehicles can take advantage of aerodynamically supported platforms or air wings to increase maximum speed or transportation efficiency. However, this also results in increased complexity of boat dynamics, especially in the presence of waves and wind gusts. In this study, a mathematical model based on the fully unsteady aerodynamic extreme-ground-effect theory and the hydrodynamic added-mass strip theory is applied for simulating vertical-plane motions of a tunnel hull in a disturbed environment, as well as determining its steady states in calm conditions. Calculated responses of the boat to wind gusts and surface waves are demonstrated. The present model can be used as a supplementary method for preliminary estimations of performance of aerodynamically assisted marine craft.
... The summary was a translation from a French author, M. L. Sueur, who had suggested using ground effect (GE) for economic and rapid transport especially over water. Rozhdestvensky (2000) noted that T.J. Kaario of Finland had been the first engineers involved in the development of GE craft from 1935. These were sledges which utilize the GE. ...
... This book is possibly the most authoritative text on the subject at present. Other reviews include those of Rozhdestvensky (2000Rozhdestvensky ( , 2006, Halloran & O'Meara (1999). This review focuses only on the reverse delta "Lippisch" WIG craft and begins with the early development of Lippisch WIG craft and concludes by summarizing its development till the end of 2014. ...
Article
Full-text available
A 4-seat Wing in Ground effect craft was designed informed by an extensive literature review of past efforts in WIG craft engineering. Several designs were considered during concept evolution. The review identified a reverse delta configuration as best meeting the design requirements. A one-fifth scale of the craft was modelled using blue polystyrene foam and flown using an electric motor in pusher configuration. The flight test verified the design concept, and the effectiveness of the design. A key consideration for effective flight is undercambered airfoils to reduce take-off distance. The model was flyable in sea-state 1. It is estimated the full-size craft can get airborne in sea-state 2. A full-scale model is envisaged.
... When flying in the proximity of the ground, the flow around an aircraft is forced to be parallel to the ground due to ground effect; thus, the aerodynamics in ground effect is significantly different from that in out of ground effect in unbounded flow. The aerodynamic analysis requires an additional bounday condition to simulate the effect of the ground [2,3]. In the realm of ground effect aircraft, most studies have focused on two kinds of ground effect-the steady ground effect (SGE) wherein the flying altitude does not vary with time and the dynamic ground effect (DGE) wherein the flying altitude varies continuously with time [4][5][6][7][8][9][10][11]. ...
... Generally, crossover is implemented by choosing a crossover point on each individual and swapping alleles-or vector elements as illustrated in Figure 1. Step (2). Convergence occurs after a certain number of generations when the shape of the optimized airfoil does not change from one generation to next. ...
Article
Full-text available
This paper employs a multiobjective genetic algorithm (MOGA) to optimize the shape of a widely used wing in ground (WIG) aircraft airfoil NACA 4412 to improve its lift and drag characteristics, in particular to achieve two objectives, that is, to increase its lift and its lift to drag ratio. The commercial software ANSYS FLUENT is employed to calculate the flow field on an adaptive structured mesh generated by ANSYS ICEM software using the Reynolds-Averaged Navier-Stokes (RANS) equations in conjunction with a one equation Spalart-Allmaras (SA) turbulence model. The results show significant improvement in both the lift coefficient and lift to drag ratio of the optimized airfoil compared to the original NACA 4412 airfoil. It is demonstrated that the performance of a wing in ground (WIG) aircraft can be improved by using the optimized airfoil.
... Mechanism of WIG effect creation [1] As it was written before, the most important factor, next to the angle of attack, is the height of flight. K.V. Rozhdestvensky [2] determines height coefficient for WIG crafts, this coefficient is the ratio of the height of flight above the sea level and length of airfoil chord. Moore N. [3], in his article about WIG effect wing geometry investi-gate that best value of height coefficient for WIG flight is 0,1; equation (1) shows height coefficient dependency: ...
Article
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The main purpose of this article was to point out causes of reduced fuel consumption in aircraft jet engine when aircraft is in ground effect influence. Wing in ground effect occurs in the direct proximity of ground. The paper presents wing in ground effect description, with the numerical analysis of NACA M8 airfoil in three different conditions of flight. Numerical analysis was conduct in Ansys Fluent 17.2 software. The paper shows results of simulations which describes wing in ground effect influence on NACA M8 airfoil with two cases of jet engine exhaust gasses usage, first with exhaust gasses stream turns on upper airfoil surface, and second with exhaust gasses stream turns under lower airfoil surface. Results allow to define characteristics of NACA M8 airfoil in the influence of wing in ground effect which are lift coefficient, drag coefficient, drop of fuel consumption usage by the jet engine when lift force remains still in the wing in ground effect. The paper shows that in the wing in ground effect aircraft energy usage for flight in ground effect is smaller than for free air flight.
... The concept of the Ground Effect Vehicle (GEV) was materialized from the '60s up to the '80s. The term ground effect is understood as an increase in the Lift to Drag (L/D) ratio of a wing, at distances from the ground less than the chord length of the wing, preferably even less than 25% of the chord length [2]. This increases the static pressure at the pressure side of the wing and therefore the L/D ratio [3]. ...
Article
Full-text available
In this work, a methodology for the conceptual design of a combined Box-wing and Blended-Wing-Body unmanned aerial platform, which exploits the ground effect, is presented. Ground Effect Vehicles (GEVs) are aircrafts or aerial vehicles capable of flying very close to the surface of water areas, being a promising alternative to ships and seaplanes operating in closed seas. In order to exploit the air cushion that is formed underneath, GEVs have low Aspect Ratio wings. Thus, the Blended-Wing-Body (BWB) layout configuration is an appealing choice due to the large available body surface. On the other hand, a tailless vehicle having the BWB layout is facing challenging stability issues, especially in a turbulent and highly volatile environment as the one close to the sea level. Therefore, the addition of the Box wing configuration, namely a continuous-surface nonplanar wing formation with no wing tips, is deemed beneficiary as a way to overcome the stability challenges and eliminate the wingtip vortices. The combination of these two prominent platforms leads to improved aerodynamic performance and eventually, a reduced fuel consumption. The design methodology starts by the estimation of the most important design parameters, such as aspect ratio, sweep angle, and taper ratio, which are continuously refined in an iterative computational framework during the conceptual design phase. In an initial approach, the flight scenario with no ground effect interference is studied, with the use of both analytical calculations and computational fluid dynamics simulations. The results from the conceptual design phase indicate that the UGEV configuration has a considerable potential as an alternative to ships or seaplanes, based on its ability to carry larger payload than seaplanes and deliver it faster than ships.
... Ground effect was initially observed for flying birds and fish near the surface. It is a phenomenon with a positive influence on the aero-hydrodynamics performance of a body flying close to the ground [Blockley and Shyy, 2010;Rozhdestvensky, 2010]. This effect leads to the distortion of the airflow between the body and ground and, in turn, changes the vortex structure [Hsu and Ye, 2015]. ...
Article
Examination of the flat and curved plates flying close to the ground is an appropriate approach in understanding the complexity of flow behavior near a solid or liquid surface. When a body flies close to a surface, the vortex structure behind the body is changed; therefore, the resultant lift force is more than zero. This phenomenon is named “ground effect”. In this study, flat and curved plates submerged in the ground boundary layer were numerically investigated under the ground effect. After validating the desired numerical code, the influences of adding porous layer to the plates with [Formula: see text] attack angle were examined on vortex structure and flow separation behind the plate under the ground effect. The obtained results revealed that using a porous zone significantly reduced the separation zone and changed the vortex shedding structure downstream of the plates.
... The difference between an airplane and the Aerotrain is the WIG effect. The WIG effect happens when an airfoil or wing-like object is close to the ground as shown in Figure 2 when the altitude h is less than 25% of the wing chord c [6], a high-pressure air cushion will be created for the stagnation of the air which generates a greater lift force and a greater lift-drag ratio (L/D) than the airfoil at higher altitude. When travelling, the pitching and rolling motion of the vehicle are controlled through the control surfaces on the levitation wings. ...
Article
Full-text available
A new generation electric high-speed train called Aerotrain has levitation wings and levitates under Wing-in-Ground (WIG) effect along a U-shaped guideway. The previous study found that lacking knowledge of the design makes the prototype unable to regain stability when losing control. In this paper, the nonlinear three-dimensional dynamic model of the Aerotrain based on the rigid body model has been developed to investigate the relationship between the vehicle body design and its stability. Based on the dynamic model, this paper considered an Aerotrain with a horizontal tail and a vertical tail. To evaluate the stability, the location and area of these tails were parameterized. The effects of these parameters on the longitudinal and directional stability have been investigated to show that: the horizontal tail gives its best performance if the tail area is a function of the tail location; the larger vertical tail area and (or) the farther vertical tail location will give better directional stability. As for the lateral stability, a dihedral front levitation wing design was investigated. This design did not show its effectiveness, therefore a control system is needed. The obtained results are useful for the optimization studies on Aerotrain design as well as developing experimental prototypes.
... The ocean surface can be rough, so that can be taken into account for points close to the surface, while the ocean surface can be considered as flat in the far field (also, see [14], [15], [16]). Another example of the Neumann problem appears in aerodynamics, where the effects of ground should be taken into account to determine correctly the lift force for objects flying close to the ground [17]. For flat surfaces the Neumann problem can be also solved using the method of images, which causes the same problems as for the Dirichlet problem described above. ...
Preprint
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The Green's functions for the Laplace equation respectively satisfying the Dirichlet and Neumann boundary conditions on the upper side of an infinite plane with a circular hole are introduced and constructed. These functions enables solution of the boundary value problems in domains where the hole is closed by any surface. This approach enables accounting for arbitrary positive and negative ground elevations inside the domain of interest, which, generally, is not possible to achieve using the regular method of images. Such problems appear in electrostatics, however, the methods developed apply to other domains where the Laplace or Poisson equations govern. Integral and series representations of the Green's functions are provided. An efficient computational technique based on the boundary element method with fast multipole acceleration is developed. A numerical study of some benchmark problems is presented.
... The model design starts from calculations based on idealized or semi-empirical theories for PAR systems. [5][6][7] Since these calculation methods involve advanced fluid mechanics, they are carried out by a faculty advisor. In discussions with a faculty advisor, students gain understanding of the basic theoretical results and the expected system behavior in various operational conditions. ...
... Dihedral angles tend to help in rolling an aircraft back to its position whenever they are banked, that they can be used to control rolling moment, as the resulting rolling moment is approximately proportional to the dihedral angle as stated by Raymer (2012). In ground effect where the wing is placed near the ground, induced drag is reduced due to span dominated ground effect, meanwhile, an increase in lift takes place as a result of chord dominated ground effect as stated by Rozhdestvensky (2000). Through WIG vehicle design phase, wing geometrical parameters have important contribution in the vehicle performance integrity. ...
Book
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The aerodynamic performance of a 3-D NACA 6409 wing in ground effect was examined numerically with different wing configurations. The influence of changing twist angles, anhedral angles, taper ratios, and sweep angles on the aerodynamic performance was examined and compared with based model. Structured mesh domains were built, and RANS turbulence model Spalart-Allmaras was solved with a commercial solver. Base model numerical results show good agreement with available experimental data. The results show that wash-in twist has a positive effect on wing aerodynamic performance near ground proximity, as well as anhedral angles. Although swept wings have a negative effect on aerodynamic efficiencies compared with non-swept wings, an optimum swept twisted wing configuration was proposed to achieve higher aerodynamic efficiency, while applying wing sweep. Tapered wings produced a slight increase in aerodynamic efficiency in a narrow range of taper ratios. Speed variation has no drastic or abrupt effect on results.
... The ground effect (or the ground clearance effect), as an important aspect of vehicle aerodynamic research, has been studied for various bluff bodies to passenger cars, racing cars and aircraft (Bearman, 1980;Anderson, 1977;George, 1981;Fackrell, 1975;Morel, 1978;Garry, 1996;Zhang et al., 2004;Zhang et al., 2006;Rozhdestvensky, 2000Rozhdestvensky, , 2006. Considering trains, few studies related to the ground effect have been conducted in the latest years, mostly focusing on the relative motion between the vehicle and the ground. ...
Article
The effect of lowering the ground clearance, on train aerodynamics is investigated using IDDES. The high speed train geometry with its full underbody complexity is used in the investigation. The clearance is reduced by installing extra panels on the track. The numerical results are verified and validated by a grid independence study and experimental data. This work shows that, when lowered the clearance, the underbody velocity at the head car decreases, while the underbody velocity at the middle and tail car increases. The reduced clearance barely affects the time-averaged slipstream at 3 m away from the center of track. However, at a closer distance to the train body, the difference in velocity is observed to reach up to 50% between the two clearance configurations and the clearance has an opposite effect on the trackside and platform slipstream. Based on the analysis of ensemble-averaged slipstream, lowering the underbody clearance, the characteristic air speed at the trackside and platform height increases by 2.0% and 6.7%, respectively. The total drag is almost unaffected by the clearance, but the changed distribution of the drag indicates a larger drag depends on the bogie structure if longer grouped train is used. The total lift decreases 25.9% after the clearance is reduced. Specifically, 4.1% of the negative lift is increased at the head car, while the positive lift decreases 92.7% and 1.8% for the middle and tail car, respectively. Overall it is shown that reducing the underbody clearance barely affect the slipstream at standard positions , but affects more aerodynamic loads of the train.
... Wing in ground effect has some features, which provide to increase in lift force, and in a decrease in drag force. With lower fuel consumption [5] and without the need of regular airports, wing in ground effect crafts could be future of aviation. Due to the low altitude of the flight, the choice of this kind of transport may be suitable for people who are afraid of flying aircraft. ...
Article
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The article presents a comparison of the wing in ground effect magnitude of conceptual WIG craft model main characteristics for a wing with and without endplates which are also known as winglets in regular aircraft. In article, the author describes WIG effect with and WIG craft, which operates on low altitude, smaller than the length of wing chord, mostly above the water reservoir. WIG effect phenomenon is simple. The first aircraft needs to fly at adequate altitude, with a smaller distance between lower airfoil surface and ground static pressure rises, leading to rising of lift force. The main advantage of the wing in ground effect craft on regular aircraft is a much higher lift to drag ratio, also this phenomenon provides to drop in specific fuel consumption of aircraft and allows flying with heavier cargo due to higher lift force. Characteristics present in the article were designated from simulations, which were conducted in Ansys Fluent software. Results obtained for a wing with endplate in numerical analysis shows the superiority of this approach. Endplates provide to increase WIG effect by a decrease in induced drag through the move out vertices from the wing tips, which are made by differential pressure above and under the wing. As winglets in regular aircraft, endplates provide to save fuel. WIG craft does not need airports so it could be a cheap alternative for modern aircraft.
... • The wing-in-ground effect is well understood (see for example Rozhdestvensky [2000]), but never studied in relation to DWTs. DWT installation on building tops can take advantage of the ground effect, where the additional air pressure underneath the annular duct would increase the thrust force generated by the turbine. ...
Thesis
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Ducted Wind Turbines (DWTs) are one of the many concepts that have been proposed to improve the energy extraction from wind in comparison to bare wind turbines. In reviewing the DWT studies, investigations based on the combined use of theoretical, computational, and experimental techniques have been presented. Although indicated in these studies that the power output of wind turbines can be significantly increased by using surrounding ducts, the factors influencing this power increase, like the duct shape, augmentation add-on’s and yawed inflow conditions, need further investigation. These topics have been addressed in this doctoral thesis.
... Smaller height gives higher downforce, what is shown in Fig. 3. [Katz, 2006] A. Rojewski,J. Bartoszewicz 50 For the positive influence of wing in ground effect for planes, what means increasing of lift force, there is a specific coefficient (1) h [Rozhdestvensky 2000], which is the ratio of the height of fly and chord length. For best results, this coefficient value should be near 0.1 [Moore, Wilson, Peters 2002]. ...
... The Wing-in-Ground (WIG) effect vehicle is a promising means of transportation since it utilizes the favorable ground effect (Rozhdestvensky, 2000;Yun et al., 2010;Yang and Yang, 2009). It lies between a sea-going ship and an aircraft in terms of its characteristics. ...
Article
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Unlike conventional airplane, a WIG craft experiences righting moment and adverse yaw moment in banked turning in ground effect. Numerical simulations are carried out to study the aerodynamics of banked wing in ground effect. Configurations of rectangular wing and delta wing are considered, and performance of endplates and ailerons during banking are also studied. The study shows that righting moment increase nonlinearly with heeling angle, and endplates enhance the righting. The asymmetric aerodynamic distribution along span of wing with heeling angle introduces adverse yaw moment. Heeling in ground effect with small ground clearance increases the vertical aerodynamic force and makes WIG craft climb. Deflections of ailerons introduce lift decrease and a light pitching motion. Delta wing shows advantage in banked turning for smaller righting moment and adverse yaw moment during banking.
... The GE is a phenomenon where aerodynamic, aero elastic and aero acoustic impact on a body that cruises while keeping very close distance to a surface [2]. If relative ground clearances is less or equal than 10% of the chord of the main wing then it is known as extreme ground effect (EGE) [3]. A wing-in-ground (WIG) effect craft is heavier than air craft that is using GE efficiently by operating just above an underlying surface. ...
Conference Paper
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Analysis of dynamic stability is practically very important where the critical condition might occur during take-off of a Wing in Ground (WIG) craft. The change of hull resistance from the water to the air can make a sudden reduction in resistance. It is also strongly influenced by the pressure on the lower wing boundary layer which becomes greater due to air pressure reflections from the ground or water surface to the wings. The change of the pressure and resistance influenced the stability of the WIG significantly. In this research, dynamic stability of WIG craft during cruise and time domain analysis during take-off are conducted to study the WIG performance. A mathematical model was developed in time-domain (incorporating heave, pitch and surge motions) with varying parameters to analyze the WIG responses at the critical situation during take-off. Key words: WIG craft, Panel Method, Stability, Time domain.
... According to [18], to evaluate the influence of ground effect on aerodynamic coefficients the variation of either angle of attack (α), or downwash angle (ε) or aspect ratio (A) due to flight altitude have been modeled by using classical methodologies [13], [19] by: (1) where: ...
Article
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Taking ground effect into account a longitudinal automatic landing system is designed. Such a system will be tested and implemented on board by using the Preceptor N3 Ultrapup aircraft which is used as technological demonstrator of new control navigation and guidance algorithms in the context of the " Research Project of National Interest " (PRIN 2008) by the Universities of Bologna, Palermo, Ferrara and the Second University of Naples. A general mathematical model of the studied aircraft has been built to obtain non–linear analytical equations for aerodynamic coefficients both Out of Ground Effect and In Ground Effect. To cope with the strong variations of aerodynamic coefficients In Ground Effect a modified gain scheduling approach has been employed for the synthesis of the controller by using six State Space Models. Stability and control matrices have been evaluated by linearization of the obtained aerodynamic coefficients. To achieve a simple structure of the control system, an original landing geometry has been chosen, therefore it has been imposed to control the same state variables during both the glide path and the flare.
... Numerous models have been proposed in the literature for this phenomenon seen on various aircrafts. For helicopters, [78] has proposed a ground effect theory appearing when the altitude is less than the main blade length. In this approach, an additional thrust inversely proportional to the distance to the ground is considered. ...
Article
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The theme of "low-cost navigation", characterized by transferring performance from sensors to data fusion and control algorithms, is a central theme for many military applications, in particular those related to light troops. Using inertial or magnetic sensors from the MEMS category, along with civilian GPS, optimizes weight, size and energy consumption. As will be demonstrated, this approach requires application-specific guidance navigation and control algorithms to compensate for the relatively poor quality of the sensor signals. In this thesis, we consider three scenarios of interest and develop innovative techniques for guidance and navigation. First, we consider the case of a ground vehicle equipped with proximity sensors, a gyroscope, odometers and a GPS. Experimentally, we implement an algorithm for obstacle avoidance for which we establish a proof of convergence, and an offline path-planning algorithm that is complemented by a dynamic feedback controller and a non-linear state estimator. Then, we investigate the case of an unstable helicopter. We develop and implement algorithms within a real-time control system that we designed specifically for computational and estimation tasks. The state estimator includes a model of the flight dynamics, and uses data from inertial sensors, a barometer, and a GPS to serve as input for a closed-loop controller. The parameters of the model are identified accurately by using data obtained during experimental flights. Eventually, we shall perform autonomous hovering flights, which stress the performance of the system. Finally, we consider the problem of a pedestrian walking inside buildings. The heading estimation errors observed using various platforms (both ground and aerial) suggest a new use of the magnetic field, and we propose to derive information by inspecting its gradients. We explain how to use (unknown) disturbances of the magnetic field to improve the position estimate in inertial navigation. Experimental results emphasize the relevance of the approach.
... Research into the influence of ground effect on streamline around the wings began in the 1920s [9,10]. Rozhdestvensky [11] described the flow of air over the airfoils at different edges including the leading, trailing, and side edge. Airflow can be streamlined by reducing the downwash angle that causes the efficient angle of attack to rise. ...
Article
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... A IRCRAFT wings typically generate a higher lift in proximity of the ground at moderate angles of attack, which is known as the positive ground effect. Thus, wing-in-ground-effect (WIG) crafts are designed to fly near ground using the positive ground effect [1][2][3][4]. Compared to a ship, a WIG craft has lower drag, higher speed, and lower fuel consumption, and its cruising speed is less affected by the sea states. Compared to an airplane of comparable size, a WIG craft has a higher lift-to-drag ratio, lower propulsive power, wider flight range, and larger load. ...
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... T HE ground imposes an additional boundary condition on the flow around an aircraft when it is in the proximity to the ground: for example, during takeoff and landing. Thus, the flowfield around the aircraft and the aerodynamic forces in ground effect are significantly different from those without ground effect [1,2]. ...
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... Researchers began studying on the influences of ground effect on streamlines around wings from the 1920s [13,14]. Rozhdestvensky [15] described the streamline of flow over airfoils at different edges such as leading edge, trailing edge, and side edge. The streamline can be improved by reducing the downwash angle, which causes the efficient angle of attack to rise. ...
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Для расчета параметров вибрации трубопроводов (амплитуды смещений, внутренних усилий и опорных реакций) разработаны модель, алгоритм и программа. Модель – квазиодномерная конечноэлементная система. Алгоритм расчета построен на базе метода парциальных откликов в его дискретном варианте. Выведены формулы для парциальных откликов и парциальных параметров, необходимые при реализации предложенного алгоритма. Влияние протекающей жидкости учтено приложением дополнительной инерционной нагрузки, которая, в свою очередь, учитывается коррекцией и модификацией инерционно-жесткостных характеристик модели трубопровода. В качестве примера рассмотрена задача о вибрации прямого трубопровода постоянного поперечного сечения, опирающегося на две опоры. Выполнено исследование влияния составляющих инерционной нагрузки на параметры вибрации, значения собственных частот и величину критической скорости жидкости. Оценена сходимость процесса в случае необходимости применения метода последовательных приближений. To analyze vibration parameters of the pipeline (displacement amplitudes, internal forces, and support reactions) the model, algorithm, and program were created. The model is a quasi-one-dimensional (quasi-1D) finite element system. The calculation algorithm is based on the discrete version of the partial responses method. Formulas for partial responses and partial parameters necessary for the implementation of the proposed algorithm were derived. The influence of the flowing liquid is compensated by applying an additional inertial load, which, in turn, is taken into account by correcting and modifying the inertia-stiffness characteristics of the pipeline model. The problem of the vibration of a straight pipeline of a constant cross-section with two points of support is given as an example. The influence of inertial load components on vibration parameters, own frequency values, and the critical velocity of the liquid were studied. The convergence of the process in case of using method of successive approximations was estimated.
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В работе рассматривается влияние размерности математической модели движения судна на параметры движения, характеризующие его управляемость, к которым относятся курсовой угол, угловая скорость рыскания, продольное и боковое смещение. Указанное влияние определяется путем имитационного моделирования движения судна посредством математической модели плоского движения в плоскости невозмущенной поверхности воды, модели бокового и пространственного движения. Тестовым маневром является полная циркуляция судна на тихой воде и волнении различной балльности. В качестве опорного результата принимается картина движения, доставляемая пространственной моделью, как наиболее отвечающая условиям реального плавания. В результате тестирования 6 судов различных классов установлено, что соотношение между результатами прогнозирования поворотливости посредством моделей различной размерности существенно зависит от гидродинамических характеристик объекта исследования. The paper considers the influence of the dimension of the mathematical model of the ship's motion on the motion parameters characterizing its controllability, which include the heading angle, angular yaw rate, longitudinal and lateral displacement. This influence is determined by simulating the movement of the vessel using a mathematical model of plane movement in the plane of the undisturbed water surface, a model of lateral and spatial movement. The test maneuver this is the full circulation of the vessel in smooth water and on the varying conditions wave. The picture of movement, delivered by the spatial model, is taken as a reference result, as the most measure up for the conditions of real swimming. As a result of testing 6 vessels of various classes, it was found that the relationship between the results of predicting turnability by means of models of different dimensions significantly depends on the hydrodynamic characteristics of the research object.
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В работе изучается движение профиля над экраном на различных относительных высотах. Рассмотрены следующие методы его моделирования: условие неподвижного экрана и метод зеркального отображения для моделирования обращённого движения и условие экрана, движущегося со скоростью профиля, что моделирует прямое движение. Целью работы является выбор метода моделирования экрана, при котором обтекание профиля соответствует действительности и оценка разницы между рассмотренными методами. Задача решена в открытом пакете OpenFOAM методом контрольного объёма, где совместно решены уравнения Навье-Стокса и неразрывности, осреднённые по Рейнольдсу. Произведена верификация и валидация математической модели и найдено сеточно-независимое решение. Выбраны два профиля в плане: сегментный и симметричный. Рассмотрены несколько относительных высот. В работе построены эпюры скоростей под профилем, представлены картины обтекания профилей, исследованы их основные эксплуатационные характеристики: коэффициент подъёмной силы и коэффициент сопротивления в зависимости от относительной высоты. Построено распределение коэффициента давления по поверхности рассматриваемых профилей в зависимости от граничных условий и относительных высот. В результате анализа показано различие происходящих физических процессов при обтекании профилей в прямом и обращённом движении. Данная работа позволяет сделать вывод о том, каким образом проводить физический эксперимент для различных профилей, показывает преимущество использования метода зеркальных отображений или подвижного экрана при проведении эксперимента. In this article the movement of the profile above the screen at different relative heights is reviewed. The following methods of its modeling are considered: the condition of a stationary screen and the method of images for simulating reverse motion and the condition of a screen moving with the profile speed that simulate forward motion are considered. The aim of the work is to select a screen simulation method for a physical experiment. An open-source packet OpenFOAM based on finite-volume method is used to solve the Navier-Stokes and continuity equations averaged by Reynolds method. The mathematical model is verified and validated, and a grid-independent solution is found. Two profiles are selected: segmental and symmetrical. Several relative heights are considered. The velocitiy profiles under the airfoil are constructed, the patterns of the flow around the airfoils are presented. The dependences of coefficients on the studied parameters and the distribution of the pressure coefficient over the profile are studied and analyzed. As a result of the analysis, the difference between the physical processes when flowing around the airfoils is in forward and reverse motion is shown. This work allows us to make a conclusion about how to conduct a model experiment for various profiles, shows the advantage of using the method of images or a movable screen in the experiment.
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В статье рассматривается подход к решению задачи оптимизации характеристик корабля на ранних стадиях проектирования. Задача оптимизационного проектирования формулируется как многокритериальная. Дается краткий обзор подходов к решению задач математического программирования такого класса. Рассматривается такой метод многокритериальной оптимизации, широко используемый в экономических задачах, как оптимизация по Парето. Для решения задач, связанных с созданием технических систем, характерно большое количество частных критериев эффективности, выраженных, как правило, нелинейными функциями, а иногда описанными алгоритмическими процедурами. Следовательно, поверхность эффективных точек Парето, на которой ищется наилучший вариант проекта, представляет собой сложный геометрический объект в n- мерном пространстве частных критериев. Выбор наилучшего решения предлагается путем использования предпочтения проектанта, сформулированными в виде функции ценности. Функция ценности также является сложной поверхностью в n-мерном критериальном пространстве. Аналитическое решение, дающее координаты точек касания этих поверхностей, представляет сложную математическую проблему. В статье предлагается численный метод решения задачи оптимизации по Парето для сложной технической системы, каковой является корабль. The article considers an approach to solving the problem of optimizing the ship's characteristics at the early stages of design. The optimization design problem is formulated as a multi-criteria one. A brief overview of approaches to solving mathematical programming problems of this class is given. We consider such a method of multi-criteria optimization, widely used in economic problems, as Pareto optimization. To solve problems related to the creation of technical systems, a large number of specific performance criteria are characteristic, expressed, as a rule, by nonlinear functions, and sometimes described by algorithmic procedures. Consequently, the surface of effective Pareto points, on which the best variant of the project is sought, is a complex geometric object in the n-dimensional space of partial criteria. The choice of the best solution is proposed by using the preferences of the designer, formulated in the form of a value function. The value function is also a complex surface in the n-dimensional criterion space. The analytical solution that gives the coordinates of the points of contact of these surfaces is a complex mathematical problem. The paper proposes a numerical method for solving the Pareto optimization problem for a complex technical system, such as a ship.
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Снятие осадки судна – одна из ключевых операций на большинстве морских судов. Значение осадки используется при определении массы груза на судах типа балкер, а также при планировании перехода и обеспечении безопасности на всех других судах. Однако, если при планировании перехода погрешность в пять – десять сантиметров не играет существенной роли, то при определении загрузки судна каждый сантиметр ошибки может стоить компаниям тысячи, а то и десятки тысяч долларов США. Для определения осадки судна существует несколько способов, однако, несмотря на их наличие, в большинстве случаев измерения проводятся исключительно визуальным способом. Связано это с низкой точностью существующих методов, особенно в условиях волнения. В качестве направления исследования предлагается способ определения осадки судна при помощи алгоритмов компьютерного зрения и машинного обучения по видеозаписи. Обработка видео проводится покадрово. Общее исследование предполагает наличие трех частей – выделение марки углубления на изображении, сегментацию водной поверхности на изображении и снятие замеров с их последующей обработкой методами математической статистики и линейной фильтрации. В данной работе описана первая часть исследования, целью которой является выявление марки углубления. Каждый кадр подвергается бинаризации при помощи порогового разделения, затем после проведения ряда морфологических операций проводится определение связных областей на кадре. На основании полученных областей строится координатная прямая, по которой и будет в дальнейшем производится снятие осадки судна. В настоящее время, аналоги данной технологии отсутствуют на рынке. Также, исследование позволяет достичь высокой точности измерений даже при неблагоприятных погодных условиях. Ship's draft marks reading is a key procedure in cargo operations on bulk carriers, as well it`s significant part of passage planning and ensuring safety of navigation on all other ships. Though, whereas an error of five – ten centimeters doesn`t affect too much on passage planning, it is weighty while talking about cargo operations, as each centimeter of error can cost companies thousands, or even dozens of thousands of US dollars. There are several ways to determine the ship's draft, nevertheless, visual readings are still the primary manner of carrying out mentioned procedure. That`s caused by the reason of low accuracy of existing methods, especially in case of swell. In general, it is considered to describe alternative method for determining the ship's draft by using fundamentally new method, based on computer vision and machine learning technologies applied to video recording. Video processing is carried out frame by frame. Full research assumes the presence of three parts - highlighting the draft mark`s numerals on the image, segmentation of the water surface and taking measurements with their subsequent processing by methods of mathematical statistics and linear filtering. This paper describes the first part of research, so, there are threshold and morphological computer vision algorithms were applied. Thus, draft marks numerals segmentation was carried out. On the basis of the obtained areas, a coordinate line is constructed, along which the vessel`s draft will be measured in the future. The are no analogues of this method on the market. Besides, the high level of measurement accuracy is expected to be achieved even in adverse weather conditions.
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В работе исследуются структура и физико-механические характеристики наполненного эпоксидного клея ДМ-5-65, применяемого для сборки составных электроакустических преобразователей гидроакустических систем. Особенностью исследования служит использование в качестве дисперсных неорганических наполнителей порошков пьезокерамических материалов системы цирконата-титаната свинца (ЦТС): ЦТСтБС-2 и ЦТБС-3. Приведены результаты морфологического исследования, определены краевой угол смачивания и свободная поверхностная энергия отвержденного клея ДМ-5-65, содержащего указанные наполнители. Определены плотность, деформационно-прочностные и термомеханические свойства отвержденного клея ДМ-5-65. Механическими испытаниями на отрыв установлена прочность соединения эпоксидного клея ДМ-5-65 с металлом. Показано, что химическая природа наполнителей определяет характер их распределения в связующем клея. Установлен преимущественно полярный характер взаимодействий клея ДМ-5-65, содержащего в качестве наполнителя материал ЦТСтБС-2, в отличие от дисперсионной природы взаимодействий клея ДМ-5-65 с наполнителем ЦТБС-3. This paper studies the structure and physical-mechanical properties of filled epoxy glue DM-5-65 used to build a composite electro-acoustic transducers hydroacoustic systems. A special feature of the study is the use of powders of piezoceramic materials of the lead zirconate-titanate (PZT) system as dispersed inorganic fillers: PZTSrB-2 and PZTB-3. The results of morphological research are presented, the wetting angle and free surface energy of the cured DM-5-65 glue containing the specified fillers are determined. The density, strain-strength and thermomechanical properties of the cured DM-5-65 glue were determined. Mechanical separation tests established the strength of the connection of the DM-5-65 epoxy glue with metal. It is shown that the chemical nature of fillers determines the nature of their distribution in the glue binder. The predominantly polar nature of the interactions of DM-5-65 glue containing PZTSrB-2 material as a filler is established, in contrast to the dispersion nature of the interactions of DM-5-65 glue with PZTB-3 filler.
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В статье представлены результаты математического моделирования процессов топливоподачи судового дизеля при работе по винтовой характеристике при использовании дизельного топлива и водотопливной эмульсии с водосодержанием 30% в качестве аль­тернативного топлива. В результате исследования выявлены особенности процессов топливоподачи и влия­ние альтернативного топлива на рабочие характеристики впрыскивания серийной топлив­ной аппаратуры при работе на номинальном и частичных режимах. При оценке качества работы топливной аппаратуры учитывались: изменение характеристики подачи топлива; особенности распыливания топлива в начальной и конечной фа­зах впрыскивания; повышение стабильности последовательных циклов впрыскивания за счет увеличения активного хода плунжера; колебания остаточного давления в трубопро­воде высокого давления при последовательных циклах впрыскивания. При применении водотопливной эмульсии возможно существенное повышение каче­ства работы судового дизеля, расширение диапазона стабильных подач серийной топлив­ной аппаратуры как за счет возможности снижения скоростных режимов при малых подачах топлива, так и обеспечения форсированных подач топлива вследствие отсутствия повторных впрыскива­ний. The article presents the results of the mathematical modeling of marine diesel’s fuel supply processes during the screw characteristic while using diesel fuel and water-fuel emulsion with 30% water content as alternative fuel. As a result of the research, the features of the fuel supply processes and the effect of alternative fuel on the serial fuel equipment injection characteristics during operation in nominal and partial modes were identified. Considering the quality of fuel equipment operation the following features were taken into account, they are: changing fuel supply characteristics; features of fuel atomization in the initial and final phases of injection; increasing stability of the injection in sequential cycles by increasing plunger active stroke; residual pressure oscillations in the high pressure line during injection consecutive cycles. Using the water-fuel emulsion it is possible to significantly increase a quality of marine diesel engine operation, to extend the stable fuel supply range of the serial fuel equipment both from the possibility of speed modes reducing during fine fuel feed and providing forced fuel feed due to absence of repeating injections.
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Рассматривается динамический крен судов, расположенных лагом к фронту волнения, под действием порывов ветра и шквалов. Путем имитационного моделирования пространственного движения оценивается выполнение основных допущений, используемых при нормировании остойчивости в рамках критерия погоды. Показано, что первое динамическое наклонение судна на подветренный борт может быть максимальным, если длительность порыва ветра или шквала не превышает полупериода собственных бортовых колебаний. При более длительных шквалах максимальным будет второе или третье наклонение. Оценивается влияние хода судна и постоянно действующего ветра на динамический крен. Подтверждено, что для малых судов, для которых волнение высокой балльности приближается к резонансному, опасность воздействия шквалистого ветра наиболее велика. Результаты показывают, что, несмотря на существенную упрощающую схематизацию реальных процессов, критерий погоды является вполне эффективным средством прогнозирования безопасности штормового плавания судов. Reviewed the dynamic heel of ships disposed broadside to the wave front under the influence of wind gusts and squalls. By means of simulation of spatial motion, the fulfillment of the basic assumptions used in the normalization of stability within the framework of the weather criterion is evaluated. It is shown that the first dynamic inclination of the vessel to the leeward side can be maximal if the duration of a wind gust or squall does not exceed the half-period of natural side vibrations. With longer squalls, the second or third inclination will be maximum. The influence of the ship's course and the constantly acting wind on the dynamic heel is estimated. It has been confirmed that for small vessels, for which high-intensity waves are approaching resonance, the danger of the impact of squally wind is greatest. The results show that, despite the significant simplifying schematization of real processes, the weather criterion is a quite effective means of predicting the safety of stormy navigation of ships.
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در این مقاله به بررسی اثر سطح وتر حاکم پراخته شده و اثرات شکل مسیر (شکل بین سطح زیرین ایرفویل و زمین) بر مشخصات آیرودینامیکی و عملکردي ایرفویلها مورد آنالیز قرار گرفته است. معادلات ناویر-استوکس میانگین گیري شده رینولدز با مدل آشفتگی اسپالارت-الماراس توسط رهیافت حجم محدود حل شدهاند. چهار ایرفویل مختلف جهت ایجاد شکل مسیرهاي مختلف طراحی گردید. براي قابل مقایسه کردن ایرفویلها سطح بالایی آنها کاملاً یکسان طراحی شدند. نتایج نشان داد که مسیر واگرا فشار روي سطح زیرین و همچنین لیفت را افزایش داده، مرکز فشار را به سمت لب فرار حرکت داده و در نتیجه ضریب گشتاور حول لبه حمله کاهش پیدا میکند. مسیر موازي تغییر بسیار اندکی در توزیع فشار ایجاد میکند. مسیر همگرا فشار روي سطح زیرین ایرفویل و همچنین لیفت را کاهش داده، مرکز فشار را به سمت لبه حمله جابجا کرده و در نتیجه ضریب گشتاور حول لبه حمله را افزایش میدهد. ساکن شدن جریان هوا بین ایرفویل و سطح فشار روي سطح زیرین ایرفویل را افزایش داده و درگ فشاري را کاهش میدهد. بنابراین لیفت و بازده آیرودینامیکی همزمان با هم بهبود پیدا میکنند. اما بازده آیرودینامیکی و پایداري در تضاد با یکدیگر قرار دارند. در نهایت میتوان گفت از لحاظ آیرودینامیکی ایرفویل با پروفیل نازك در نزدیک لبه فرار ارجح است و ایرفویل با پروفیل ضخیم در نزدیکی لبه فرار از دیدگاه پایداري مناسبتر است.
Conference Paper
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هدف از انجام اين تحقيق بررسي اثر تغيير شکل سطح بالايي ايرفويل بر پايداري استاتيکي طولي در اثر سطح است. با توجه به اينکه ايرفويل مناسب اثر سطح بايد کمبر S شکل و سطح زيرين تخت داشته باشد، پنج ايرفويل با اين ويژگي¬ها که تنها سطح بالايي آن¬ها تفاوت دارد طراحي گرديد. لذا کاملاً قابل مقايسه با يکديگر در اثر سطح هستند. شرايط جريان مشابه شرايط پرواز يک پرنده اثر سطحي در فاز کروز انتخاب گرديد. جريان تراکم ناپذير، زاويه حمله دو درجه و ارتفاع بي بعد 2/0 است. عدد رينولدز بر مبناي سرعت ورودي و کرد ايرفويل تقريباً 106×7/2 است. شرايط پايداري ايرودوف، معيار پايداري قرار گرفته است. بر اساس اين معيار، ايرفويل پايدار در اثر سطح علاوه بر داشتن مشتق ضريب گشتاور نسبت به زاويه حمله منفي و مشتق ضريب ليفت نسبت به ارتفاع منفي بايد مرکز ارتفاع آن جلوتر از مرکز آيروديناميکي پيچ (pitch) واقع شده باشد. نکته مهم اين است که با جابجايي مرکز جرم نمي¬توان پرنده اثر سطحي با ناپايداري استاتيک طولي ارتفاع را پايدار کرد. نتايج حاصل بيانگر اين است که افزايش ضخامت و جابجايي محل بيشترين ضخامت به سمت لبه فرار هر دو سبب کاهش سطح پايداري پيچ مي¬شوند. علاوه بر اين مشتق ضريب ليفت نسبت به ارتفاع نيز افزايش يافته که به معني کاهش سطح پايداري است. با افزايش ضخامت مرکز ارتفاع به سمت لبه حمله حرکت مي¬کند که نرخ حرکت آن افزاينده است. با اين وجود محل مرکز پيچ تغييرات کمي را نشان مي¬دهد. بنابراين به طور کلي سطح پايداري ارتفاع افزايش پيدا کرده اما پايداري پيج کاهش مي¬يابد. جابجايي محل ضخامت بيشينه به سمت لبه فرار باعث حرکت مرکز ارتفاع به طرف لبه فرار شده در حالي¬که مرکز پيچ تقريباً ثابت است. در نتيجه حاشيه استاتيکي افزايش يافته و پايداري کاهش مي¬يابد. با وجود تغيير ضخامت و جابجايي محل ضخامت بيشينه مکان مرکز آيروديناميکي پيچ همه ايرفويل¬هاي مورد بررسي بسيار به هم نزديک بودند.
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The paper presents motion simulations in time domain of a WIG craft with a Lippisch configuration under wind and wave perturbations. The aerodynamic characteristics were obtained using the vortex lattice method. The motion is considered in the longitudinal plane. A novel approach is proposed to generate artificial wind turbulence with prescribed kinetic energy and spectra. The wave surface is modeled by a plane performing linear and angular oscillations. Motion simulations were performed to show the limitations of flight safety analysis based on the classic stability theory. Simulation of the take-off motion was carried out to determine the conditions for safe transition from the skimming to flare mode. It was shown that the application of the flight control is necessary for safe flight in the proximity of the ground.
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