共查询到20条相似文献，搜索用时 31 毫秒
1.
This study gives a new analytical solution for wave reflection and transmission by a surface-piercing porous breakwater. Velocity potential decompositions in the breakwater are used to obtain the solution. Different from traditional solutions, the new solution needs no complex dispersion relations (complex wave numbers) for wave motion through porous media. Thus, difficult procedures in traditional solutions for solving complex dispersion relations and handling non-self-adjoint eigenvalue problem are avoided. The calculated results of the new solution are in very good agreement with those of traditional solutions and multi-domain boundary element method solutions. 相似文献
2.
A numerical model is presented in this study to investigate the wave transformation over a submerged permeable breakwater on a porous slope seabed. For this purpose, the time-dependent mild-slope equation is newly derived for waves propagating over two layers of porous medium. This new mild-slope equation involves the parameters of the porous medium, and it is a type of hyperbolic differential equation, therefore numerically efficient. The validity of the present model is verified based on the comparisons with the previous experiments. The effects of the permeable properties of both the porous seabed and the submerged permeable breakwater are discussed in detail. The geometry of the submerged permeable breakwater to the wave transformation is also investigated based on the numerical solutions. 相似文献
3.
This paper presents numerical solutions for the wave reflection from submerged porous structures in front of the impermeable vertical breakwater. A new time-dependent mild-slope equation involves the parameters of the porous medium including the porosity, the friction factor and the inertia coefficient, etc. is derived for solving the boundary value problem. A comprehensive comparison between the present model and the existing analytical solution for the case of simple rectangular geometries of the submerged structure is performed first. Then, more complicated cases such as the inclined and trapezoidal submerged porous structures in front of the vertical breakwater with sloping bottom are considered. This study also examines the effects of the permeable properties and the geometric configurations of the porous structure to the wave reflection. It is found that the submerged porous structure with trapezoidal shape has more efficiency to reduce the wave reflection than that of triangular shape. The numerical results show that the minimum wave reflection is occurred when the breakwater is located at the intermediate water depth. 相似文献
4.
A uniformly valid asymptotic theory for water waves is presented, which accounts for the combined effects of refraction due to slowly varying water depth and diffraction by a semi-infinite thin break water. The present theory is more rigorous and generical than the approximate solution developed by Liu and Mei, which becomes invalid near the edge and the tip of the breakwater. The effects of wave breaking are ignored. 相似文献
5.
6.
A three-dimensional (3D) large-eddy-simulation model with macroscopic model equations of porous flow is proposed to investigate solitary waves interacting with permeable breakwaters. The major objective of this paper is twofold. First, we seek to evaluate the present model through the comparison with available simulated and measured data in the literature. The second aim, given the 3D nature of flow past a permeable breakwater, the variations of permeable breakwater modeled on both macroscopic and microscopic scales are examined. First validation is carried out with experiments on solitary wave propagation in a 3D wave basin and then runup on a vertical permeable breakwater with a gap in the lateral direction. A satisfactory agreement on the free surface elevation time series is obtained between model and measured results. Second, we replicate the experiments on a solitary wave interaction with a submerged permeable breakwater in a two-dimensional narrow wave flume. The porous medium is composed of spheres with a uniform size and arranged in a non-staggered regular pattern such that the porous medium can thus be modeled on macroscopic and microscopic scales. The numerical calculations indicate that the results obtained with macroscopic and microscopic modeling both fit the measurements fairly well in terms of the free surface elevations and velocity fields. Specifically, the microscopic modeling better simulates detailed phenomena such as flow injection from the porous medium and the initial stage of the formation of the main vortex in the leeward face of the obstacle. After the solitary wave completely propagates over the permeable object, the discrepancies between macroscopic and microscopic model results are insignificant. More accurate 3D results are used to determine the trajectories of fluid particles around the porous object to help understand the possible sediment movements in suspensions. 相似文献
7.
Simplified analytical solutions are presented to model the interaction of linear waves with absorbing-type caisson breakwaters, which possess one, or two, perforated or slotted front faces which result in one, or two, interior fluid regions (chambers). The perforated/slotted surfaces are idealized as thin porous plates. Energy dissipation in the interior fluid region(s) inside the breakwater is modelled through a damping function. Under the assumption of potential flow and linear wave theory a boundary-value problem may then be formulated to describe wave interaction with the idealized structure. A solution to this simplified problem may be obtained by an eigenfunction expansion technique and an explicit analytical expression may be obtained for the reflected wave height. Using the experimental work of previous authors, damping coefficients are determined for both single and double chamber absorbing-type caisson breakwaters. Based on the damping for a single perforated-wall breakwater, a methodology is proposed to enable the estimation of the damping coefficients for a breakwater with two chambers. The theoretical predictions of the reflection coefficients for the two-chamber structures using the present model are compared with those obtained from laboratory experiments by other authors. It is found that the inclusion of the damping in the interior fluid region gives rise to improved agreement between theory and experiment. 相似文献
8.
In this study,we investigated wave transformation and wave set-up between a submerged permeable breakwater and a seawall.Modified time-dependent mild-slope equations,which involve parameters of the porous medium,were used to calculate the wave height transformation and the mean water level change around a submerged breakwater.The numerical solution is verified with experimental data.The simulated results show that modulations of the wave profile and wave set-up are clearly observed between the submerged breakwater and the seawall.In contrast to cases without a seawall,the node or pseudo-node of wave height evolution can be found between the submerged breakwater and the seawall.Higher wave set-up occurs if the nodal or pseudo-nodal point appears near the submerged breakwater.We also examined the influence of the porosity and friction factor of the submerged permeable breakwater on wave transformation and set-up. 相似文献
9.
In this study, we investigated wave transformation and wave set-up between a submerged permeable breakwater and a seawall. Modified time-dependent mild-slope equations, which involve parameters of the porous medium, were used to calculate the wave height transformation and the mean water level change around a submerged breakwater. The numerical solution is verified with experimental data. The simulated results show that modulations of the wave profile and wave set-up are clearly observed between the submerged breakwater and the seawall. In contrast to cases without a seawall, the node or pseudo-node of wave height evolution can be found between the submerged breakwater and the seawall. Higher wave set-up occurs if the nodal or pseudo-nodal point appears near the submerged breakwater. We also examined the influence of the porosity and friction factor of the submerged permeable breakwater on wave transformation and set-up. 相似文献
10.
This is a theoretical study of a breakwater-seawall wave-trapping system. The breakwater, being flexible, porous and thin beam-like, is held fixed in the sea bed and idealized as one-dimensional beam of uniform flexural rigidity and uniform mass per unit length. The seawall, being vertical, rigid and impermeable, is located behind the breakwater by a distance of L. The velocity potentials of the wave motion are coupled with the equation of motion of the breakwater. Analytical solutions in closed forms are obtained for the reflected and transmitted velocity potentials together with the displacement of the breakwater. The free-surface elevation, hydrodynamic forces acting on both the breakwater and the seawall are determined. It is found that the values of L, at which the minimum reflected-wave amplitudes reach, are in the range of
λ to
λ for breakwaters with different rigidity and permeability. It is shown that, when the spacing L maintains values in the range of
λ to
λ, the resultant amplitudes in both regions can be reduced to a favorable amount for any wave and structural parameters. It is also shown that the hydrodynamic forces on the breakwater decrease as the structural flexibility and porosity increase. However, with increases of the structural porosity and flexibility, the seawall experiences an increase of the hydrodynamic forces. Various results are presented in this paper to illustrate the effects of the structural and perous parameters together with the spacing on the response and efficiency of the breakwater-seawall wave-trapping system. 相似文献
11.
Oblique wave diffraction by segmented offshore breakwaters 总被引：3，自引：0，他引：3
This paper presents a theoretical model to examine oblique wave diffraction by a detached breakwater system consisting of an infinite row of regularly-spaced thin, impermeable structures located in water of uniform depth. The fluid is assumed incompressible and inviscid and to undergo irrotational motion. Wave heights are assumed to be sufficiently small such that linear wave theory is applicable. The eigenfunction expansion solution of Dalrymple and Martin (1990) for normal wave incidence on this breakwater geometry is modified herein to study oblique wave effects. Numerical results, in the form of contour maps of the relative wave height behind the structure, or complex reflection coefficients, are presented for a range of wave and breakwater parameters. The accuracy of the present model is verified by a comparison with existing results for the limiting cases of an isolated detached breakwater, and a breakwater with a single gap. Also, for the multi-gap breakwater, the present solution is further verified for both normal and oblique wave incidence with results in the open literature. 相似文献
12.
In this work, we carried out an asymptotic analysis, up to the second order in a regular expansion, of the interaction of linear long waves with an impermeable, fixed, submerged breakwater composed of wavy surfaces. Below the floating breakwater, there is also a step with a wavy surface. The undulating surfaces are described by sinusoidal profiles. The effects of three different geometric parameters — the amplitude of the wavy surfaces and the submerged length and width of the structure — on the reflection and transmission coefficients are analyzed. The hydrodynamic forces are also determined. The governing equations are expressed in dimensionless form. Using the domain perturbation method, the small wavy surfaces of the breakwater are linearized. The wavy surfaces of the breakwater generate larger values of the reflection coefficient than those obtained for breakwaters with flat surfaces, and the largest values of this coefficient are obtained when the length of the breakwater is of the same order of magnitude as the wavelength. The asymptotic solution is compared with the theoretical solutions that have been reported in the specialized literature and with a numerical solution. The present mathematical model can be used as a practical reference for the selection of the geometric configuration of a submerged floating breakwater under shallow flow conditions. 相似文献
13.
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
14.
E.V. Koutandos 《Ocean Engineering》2011,38(1):34-48
In the present study, wave interaction with a fixed, partially immersed breakwater of box type with a plate attached (impermeable-permeable) at the front part of the structure is investigated numerically and experimentally. The large scale laboratory experiments on the interaction of regular waves with the special breakwater were conducted in the wave flume of Laboratori d’Enginyeria Marνtima (LIM) at Universitat Politecnica de Catalunya (UPC) in Barcelona. Experimental results are compared with numerical results obtained with the use of the Cornell breaking Wave and Structures (COBRAS) wave model. The effects of an impermeable as well as a permeable plate attached to the bottom of the breakwater on its hydrodynamic characteristics (wave transmission, reflection, dissipation, velocity and turbulence kinetic energy) are investigated. Computed velocities and turbulence kinetic energy in the vicinity of the structure indicate the effects of the breakwater with the attached (impermeable/permeable) plate on the flow pattern and the turbulence structure. The attached impermeable plate at the front part of the breakwater enhances significantly the efficiency of the structure in attenuating the incident waves. The permeable plate reduces the efficiency of the structure since wave energy is transmitted through the porous body of the plate. Based on the hydrodynamic characteristics it is inferred that the breakwater with an impermeable plate attached to its bottom is more efficient. The comparison of horizontal and vertical forces acting on the breakwater for all cases examined reveals that plate porosity influences slightly vertical force and severely horizontal force acting on the structure, reducing maximum values in both cases. 相似文献
15.
The aim of this paper is to develop an offshore breakwater, for which coefficients of both the wave reflection and transmission have low values. The breakwater is suggested to compose of n layers of porous materials with different porosities. A complex eigen function method is used in the theoretical analysis. Continuities of both mass flux and fluid pressure are assumed at interfaces between every two adjoining porous materials and at the interface between end materials and water region. Following a series of mathematical processes, the coefficients of the wave transmission and reflection along with the wave energy loss are calculated. The porosity of materials is varied in computations; and results are compared among structures composing of different layers of porous materials. A single layer offshore breakwater is shown to reduce simultaneously the coefficients of transmission and reflection only when the structure is very wide in the direction of wave propagation, and the structure material has a high porosity. A multilayer breakwater, however, can function well in reducing both coefficients at a much narrower width; structure having more layers can be more effective at narrower width. Finally, several experiments are conducted; theoretical computations and experimental results agree well. 相似文献
16.
应用椭圆余弦波的绕射理论,推导了V形防波堤的浅水波浪绕射解析解,从而对现有的Airy微幅波理论进行了有效拓展。据此理论对V形防波堤的浅水波绕射作用进行了解析计算,并与几何形状相近的圆弧型防波堤结果加以了对比。结果表明：椭圆余弦波理论计算的V形防波堤最大波浪力和最大绕射波面明显大于微幅波理论的对应值。本方法适用于张角180°的有限长直立薄壁防波堤的浅水波绕射作用计算,从而将无限长直立薄壁堤的反射波理论加以有效拓展。张角同为120°的V形堤与圆弧堤的堤后防浪效果相近,而180°圆弧堤的堤后防浪效果优于张角90°的V形堤。 相似文献
17.
Waves impinging on rubble mound breakwaters and seawalls induce a mean flow within the breakwater, analogous to the so-called undertow within the surf zone. Here, using a plane wave approximation (kh<1.5), a second-order problem is solved for an idealized breakwater with a rectangular cross-section to show the origin and the nature of the mean flow within the porous structure. The mean flow is expressed in terms of a mean stream function analytically derived, obtained based on the mass flux balance between the incident, reflected and transmitted waves. Furthermore, the evolution of other second-order magnitudes such as mean water level and mass flux is analyzed under different incident wave conditions, structure geometry and porous material characteristics. Results show that the evolution of the different mean quantities is controlled mainly by reflection and consequently depends highly on structure geometry and porous material characteristics. Furthermore, it is shown that the return flow is stronger with increasing mass flux decay. Some qualitative experiments to show the described mechanism are also presented. 相似文献
18.
The interaction of linear water waves with a semi-porous cylindrical breakwater surrounding a rigid vertical circular cylinder mounted on a storage tank is investigated theoretically. The cylindrical breakwater structure is porous in the vicinity of the free-surface, while at some distance below the water surface it becomes impermeable. Under the assumptions of linearized potential flow, the coupled problem of flow in the interior and exterior fluid regions is solved by an eigenfunction expansion approach. Analytical expressions are obtained for the wave motion in both the interior and exterior flow regions. Numerical results are presented which illustrate the effects of the various wave and structural parameters on the hydrodynamic loads and interior and exterior wave fields. It is found that for certain parameter combinations the semi-porous, cylindrical breakwater may result in a significant reduction in the wave field and hydrodynamic forces experienced by the interior structure. 相似文献
19.
Lao Guosheng Feng Hong Associate Professor Dalian University of Technology Dalian Postgraduate Dalian University of Technology Dalian 《中国海洋工程》1992,(4)
- In this paper, the theoretical calculation of floating breakwater performance in regular waves with arbitrary wave direction is discussed. Under the hypothesis of linearized system and applying the strip theory, we can solve the boundary condition problems of diffraction potential and radiation potential. Introducing the asymptotic expression of the wave velocity potential at infinity and using wave energy conservation, we can separately calculate the transmitted waves generated by the sway, heave and roll motion of the floating breakwater and by the fixed breakwater. Finally, we define the amplitude ratio of the transmitted wave to the incident wave as the transmitted wave coefficient CT which describes the floating breakwater effectiveness. Two examples are given and the theoretical results obtained by the present method agree well with experimental results. 相似文献
20.
This study examines the hydrodynamic performance of a modified two-layer horizontal-plate breakwater. The breakwater consists of an upper submerged horizontal porous plate and a lower submerged horizontal solid plate. By means of the matched eigenfunction expansion method, a linear analytical solution is developed for the interaction of water waves with the structure. Then the reflection coefficient, the transmission coefficient, the energy-loss coefficient and the wave forces acting on the plates are calculated. The numerical results obtained for limiting cases are exactly the same as previous predictions for a single submerged horizontal solid plate and a single submerged horizontal porous plate. Numerical results show that with a suitable geometrical porosity of the upper plate, the uplift wave forces on both plates can be controlled at a low level. Numerical results also show that the transmission coefficient will be always small if the dimensionless plate length (plate length versus incident wavelength) exceeds a certain moderate value. This is rather significant for practical engineering, as the incident wavelength varies over a wide range in practice. Moreover, it is found that the hydrodynamic performance of the present structure may be further enhanced if the lower plate is also perforated. 相似文献