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1.
The motion of a point vortex along a rectilinear boundary with a circle cavity, which models the coastline of a bay, and associated fluid particle advection are studied within a model of barotropic inviscid fluid. Using an analytical expression for the complex potential through which the velocity field is determined, we show that fluid particles start moving irregularly when the vortex is passing the cavity due to the nonstationarity of the velocity field generated by the vortex. Some of the fluid particles which were initially inside the vortex atmosphere leave it due to the irregularity and remain within the cavity vicinity. Depending on the initial position of the vortex and a parameter that determines the cavity size, the fraction of these fluid particles can differ significantly from fluid particles initially uniformly distributed within the vortex atmosphere. The escape of fluid particles from the vortex atmosphere is shown to be most efficient in the case of a relatively closed cavity under the condition that the initial vortex atmosphere area should be significantly smaller than the cavity area.  相似文献   

2.
By a model bay with a mouth and a narrow, an experiment on long period waves is carried out to discuss the behavior of the tsunamis and storm surges. Emphasis is placed on the analysis of the characteristics of the current velocities associated with the long period waves incoming through the mouth in terms of Ursell's parameter.  相似文献   

3.
This paper is concerned with the vibrations of a thin plate resting on a fluid-layer subjected to a moving point force. The frequency is assumed to be low and the fluid is deep. Both the fluid and the point force are always in contact with the plate. Hankel Transform and complex integration techniques are used to calculate the lateral displacements withrespect to a moving coordinate system and a coordinate transformation is used to achieve the results with respect to a fixed point. Numerical results are discussed with respect to the velocity of the moving force, its direction of movement and the fluid depth.  相似文献   

4.
Paolo Boccotti   《Ocean Engineering》2007,34(5-6):799-805
With an additional vertical duct at the wave-beaten side, an OWC is expected to give some much better performances. This is, essentially, due to two reasons. First, an OWC with the additional vertical duct (U-OWC) has an eigenperiod greater than the eigenperiod of a conventional OWC. Second, the amplitude of the pressure fluctuations on the opening of a U-OWC is greater than the amplitude of the pressure fluctuations on the opening of a conventional OWC (the greater the smaller the wave period is). For the first reason, a U-OWC can give performances better than those of a conventional OWC both with swells and large wind waves. For the second reason, a U-OWC can give performances better than those of a conventional OWC also with small wind waves.  相似文献   

5.
Linear stability of a barotropic jet on a sloping bottom with and without a side boundary is examined. When a sloping bottom and a side boundary are absent, a symmetric jet generally has two unstable modes: a symmetric mode and an antisymmetric mode. In the presence of a sloping bottom or a side boundary, they are modified and lose their symmetry.The presence of a side boundary does not produce substantial change in the stability characteristics, except that it stabilizes the flow to some degree. In the presence of a sloping bottom, the following features are noted; 1) when the direction of the jet is opposite to the propagation direction of topographic Rossby waves, the change of a preferred mode occurs at a certain slope, 2) when the direction of the jet is opposite to 1), with a side boundary, the dispersion relations change from unstable mode type to shelf wave type at a certain slope, accompanied by kissing.  相似文献   

6.
Didenkulova  I. I.  Pelinovsky  E. N. 《Oceanology》2019,59(4):478-481
Oceanology - Abstract—The nonlinear problem of run-up of a long wave on a plane beach in presence of a tide is solved within nonlinear shallow water theory using the Carrier–Greenspan...  相似文献   

7.
Using a vertically two-dimensional, two-layer model, we have analytically examined the generation mechanism of a nonzero Eulerian residual flow by strong tide-topography interaction in a narrow channel where the frictional effect is not included. In this case, tidally generated baroclinic disturbances are forced non-uniformly in space and time while being advected by a strong tidal flow over the non-uniform slope of the bottom topography. Consequently, nonzero Eulerian residual flow results when averaged over one tidal period. Although the time average of the velocity field is thus nonzero, the associated Eulerian residual transport in each layer is compensated by a Stokes transport so that no Lagrangian residual transport results in both layers. This warns us that simple time averaging of the velocity data obtained at a fixed mooring station might lead to a spurious material transport. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

8.
S. H. Rhee  S. -E. Kim  H. Ahn  J. Oh  H. Kim 《Ocean Engineering》2003,30(16):2117-2136
A jet-controlled high-lift hydrofoil with a flap is investigated using both experimental and computational methods. Experiments were carried out in a cavitation tunnel to measure forces and moment acting on the hydrofoil, and surface pressure distribution. The measured data show the feasibility of such a device for marine applications. Computational studies have also been carried out in parallel with the measurements. The computational results are analyzed in terms of global and local quantities using available experimental data. The present computational results compare well with the well-known experimental data for circulation control flows. The results for flow around a hydrofoil with a blown flap further validate the concept behind the proposed device. The results of the study demonstrate the applicability of the technology to the design of practical control surfaces.  相似文献   

9.
数据稀缺生态系统中多种类质量谱模型的构建   总被引：1，自引：0，他引：1  
多种类生态模型已经被广泛应用于渔业活动影响应预测和管理措施效果评估。质量谱模型是一种基于生理过程构建的生态模型,该模型为描述鱼类群落在个体摄食变异和随个体发生的生态位迁移提供了一个可行的方法。尽管生态模型在增进生态系统认识上具有重要意义,其应用在数据稀缺的渔业中受到很大限制。作为实践基于生态系统渔业管理(EBFM)的第一步,本研究构建了海州湾鱼类群落的质量谱模型。本研究详述了数据收集和模型参数化的过程,以促进该模型在数据稀缺的生态系统中未来的应用。作为一个范例,研究展示了不同捕捞努力量对生态系统的影响,并采用一套生态指标监测其动态。群落生物量、多样性指数、W指数,大鱼指数(LFI),平均体重和群落质量谱斜率对捕捞压力的响应呈非线性,最大的捕捞强度并非总是对鱼类群落产生最强的影响。本文强调了构建谱模型在生态研究中的的价值和可行性,并讨论了模型的局限性和改进的可能。本研究旨在促进质量谱模型的广泛应用以更好地支持基于生态系统的渔业管理。  相似文献   

10.
K. I. Matveev   《Ocean Engineering》2002,29(10):1283-1293
Experimental results of hydrofoil singing on a full-scale passenger ship are reported. It is proposed that hydrodynamic generation of a tone is caused by self-excited oscillation of a foil trailing edge. The natural frequency of the vibrating structure as well as the frequency of the external force are estimated. A lift-oscillator model is applied for modeling purposes. One effective method of eliminating the hydrofoil singing is discussed.  相似文献   

11.
During maneuvering, towed array beamforming degrades if a straight array is assumed. This is especially true for high-resolution adaptive beamforming. It is experimentally demonstrated that adaptive beamforming is feasible on a turning array, provided that array shape is estimated. The array shape can be inferred solely from the coordinates of the tow vessel's Global Positioning System (GPS) without any instrumentation in the array. Based on estimated array shape from the GPS, both the conventional beamformer and the white noise constrained (WNC) adaptive beamformer are shown to track the source well during a turn. When calculating the weight vector in the WNC approach, a matrix inversion of the cross-spectral density matrix is involved. This matrix inversion can be stabilized by averaging the cross-spectral density matrix over neighboring frequencies. The proposed algorithms have been tested on real data with the tow-vessel making 45/spl deg/ turns with a 500-m curvature radius. While turning, the improvement in performance over the assumption of a straight array geometry was up to 5 dB for the conventional beamformer and considerably larger for the WNC adaptive beamformer.  相似文献   

12.
《Coastal Engineering》2001,42(2):163-172
Applying the Green's theorem and a moving oscillating source as the Green's function, an integral equation method is developed for predicting wave height over a shoal in a weak current. The integral equation is discretized by a higher order element method and a numerical code is implemented. To validate the numerical code, comparison is made on wave run-up around a vertical cylinder with McCamy and Fuchs' analytic solution in the still water and the results in currents from numerical wave tanks. Computation has also been carried out for the wave diffraction over a parabolic shoal in a current, and numerical results are given at many sections. The numerical results from the calculation can be used for benchmark test for other methods on wave diffraction in current.  相似文献   

13.
A method of formulating the scattered acoustical field for certain types of hard bodies through the use of well-known exact solutions for the simple semi-infinite wedge and/or corner is presented. The method yields a representation of the total sound field for all frequencies and satisfying all boundary conditions. Relevant hard-wedge solutions for harmonic line sources and for plane waves are reviewed. Such solutions, which are rigorous, represent the total sound field as a superposition of directional line sources and sinks at the wedge vertex. A method of representing multiple scatter from combinations of wedges, allowing the explicit solution of the case of a truncated wedge, is introduced. This method uses the classic self-consistent algorithm for multiple scatter, together with a rigorous representation of vertex-diffracted fields  相似文献   

14.
近壁圆柱绕流水动力特性数值模拟与实验研究   总被引：3，自引：0，他引：3  
通过数值模拟和物理模型实验,对距壁面一定高度的圆柱绕流水动力特性进行了研究。数值模拟采用有限体积法对标准k-ε模式方程进行离散,采用SIMPLE算法进行求解,模拟绕流流场。在物理模型实验中,将PVC圆管制作的实验模型安放在水槽内,在圆管的跨中沿表面周向均匀布置水下压力传感器,用于测量绕流圆柱体表面动水压力分布。通过改变Re数和间隙比来分析它们对近壁圆柱绕流水动力特性的影响。基于数值流动显示技术,给出了近壁绕流流场的尾流流态分析。通过数值结果与实验结果的对比,对近壁绕流圆柱体的升力系数及其表面动水压力分布进行了研究,对比结果显示了较好的一致性。  相似文献   

15.
An inviscid zone of influence is postulated from a physical model to occur when a steady homogeneous fluid flows by a two-dimensional corrugated wall with small slopes. The thickness of the influence zone is calculated to be a constant times the wave length of the wall. The method used involves balancing pressure differences between extreme points along the wall and between the wall and the outer edge of the influence zone but does not involve the irrotational assumption. An influence zone forms because the curvature of the boundary induces cross-stream accelerations and pressure gradients in the fluid. The result for the thickness of the influence zone agrees qualitatively with the exponential decay scale of an available potential flow solution to a similar problem, which suggests that the influence zone may occur in some rotational (as well as irrotational) flows.  相似文献   

16.
In this paper, a numerical model based on the potential flow theory is established to simulate the interaction of a gas bubble with a nearby wall. The time-integration boundary integral method is used to solve the dynamics of a gas bubble. With this method the numerical calculations show an excellent agreement with the experimental data. Employing the numerical code based on the presented algorithm, the dynamics of a gas bubble close to a rigid wall is investigated systematically, especially the relationship between various characteristic parameters and the Bjerknes effect due to the presence of a nearby wall. It is found that Blake's criterion, which is usually used to predict the direction of the bubble jet, has a great degree of accuracy for the bubble relatively far away from the wall and bubble near a wall, there is a significant error, attributed to its simplifications and assumptions. Further studies show that an oblique jet will be formed when a bubble close to an inclined wall collapses, direction and width of which have a close relationship with the characteristic parameters used to characterize the bubble. For the bubble near a horizontal wall, a liquid jet pointing directly to the wall is developed generally when the Bjerknes attraction and buoyancy are in the same direction; and at the same time, if the Bjerknes attraction is in the opposite direction of buoyancy, the direction of the jet will depend on a criterion. Then the interaction of gas bubble between complicated walls of some a submarine is also studied, which shows the most dangerous induced loading condition of structure in water, and the evidently effects of bubble jet on loading. The special phenomena mentioned above have a great significance for the further study on the interaction of the bubble with its boundaries.  相似文献   

17.
Von Kármán first proposed a method of calculating the force on a vertically impacting wedge in 1929. Starting with Wagner (1931, 1932), quite a number of authors have suggested “improvements” to the theory. One purpose of this present note in to suggest that many of the proposed changes are actually incorrect and that the original theory is superior to most of its successors. The other purpose is to suggest a way in which the rigor of the Von Kármán theory can be improved and how the maximum pressure away from the keel can be calculated. Where comparison is possible, both the keel pressure and the maximum pressure predictions agree well with measurements by Chuang (1966).  相似文献   

18.
The transformation of a nonlinear wave in shallow water is investigated analytically and numerically within the framework of long-wave theory. It is shown that the nonlinearity parameter (the Mach number), which is defined as the ratio of the particle velocity in the wave to the propagation velocity, can be well above unity in a deep trough and that a jump appears initially in the trough. It is demonstrated that shockwave amplitudes at large times change in accordance with the prediction of weakly nonlinear theory. The shock front generates a reflected wave, which, in turn, transforms into a shock wave if the initial amplitude is large enough. The amplitude of the reflected wave is proportional to the cube of the initial amplitude (as predicted by weakly nonlinear theory) over a wide range of amplitudes except for the case of anomalously strong nonlinearity. When there is a sign-variable sufficiently intense initial perturbation, the basic wave transforms into a positive shock pulse (crest) and the reflected wave turns into a negative pulse (trough).  相似文献   

19.
A two-dimensional analytical solution is presented to study the reflection and transmission of linear water waves propagating past a submerged horizontal plate and through a vertical porous wall. The velocity potential in each fluid domain is formulated using three sets of orthogonal eigenfunctions and the unknown coefficients are determined from the matching conditions. Wave elevations and hydrodynamic forces acting on the porous wall are computed. Reflection and transmission coefficients are presented to examine the performance of the breakwater system. The present analytical solutions are found in fairly good agreement with the available laboratory data. The results indicate that the plate length, the porous-effect, the gap between plate and porous wall, and the submerged depth of the plate all show a significant influence on the reflected and transmitted wave fields. It is also interesting to note that the submerged plate plays an important role in reducing the transmitted wave height, especially for long incident waves.  相似文献   

20.
A storm moves with a constant speed parallel to a stationary geostrophic current which flows only in the upper layer of a two-layer, infinite ocean. It is assumed that the lower layer is motionless. The quasi-geostrophic approximation is valid for a moving speed less than 4 ms–1 for a storm radius of 100 km. The primary change of the upper layer thickness is caused by the wind stress divergence and the time integral of the wind stress curl. A cyclonic storm generates upwelling in its wake. The effect of the stationary flow similar to a western boundary current is minor by an order of magnitude and noticeable only on the left edge of the flow. Scaling of equations of motion and continuity for a more general upper geostrophic flow leads to expansion with a parametera 2=gH m(fL)–2, whereg is reduced gravity,H m is the maximum thickness of the upper layer,f is Coriolis' parameter andL is the storm radius. The zeroth order perturbations of transport and thickness do not include the stationary flow which appears only in the first order perturbations ina 2. When there is a coast, the change of the interface near the coast is dependent on the time integral of the wind stress component parallel to the coast, thus leading to upwelling or downwelling according to the center being to the left or right of the coastline.  相似文献   

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