Analysis of Wave Action Through Multiple Submerged Porous Structures

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Mohamin B. M. Khan ◽  
Harekrushna Behera
Keyword(s):  
Wave Energy ◽  
Structural Parameters ◽  
Wave Interaction ◽  
Expansion Method ◽  
Wave Theory ◽  
Rigid Wall ◽  
Porous Structures ◽  
Wave Trapping ◽  
Linear Water Wave Theory ◽  
Multiple Structures

Abstract Wave interaction with multiple bottom-standing rectangular porous structures of different structural parameters is numerically modeled using the multidomain boundary element method and the matched eigenfunction expansion method, while assuming linear water wave theory. The sensitivity of wave reflection and transmission to the wave and structural parameters is analyzed with the objective to maximize wave energy attenuation. Different configurations of multiple structures are tested for maximizing the efficiency of dissipation. Furthermore, wave trapping by multiple porous structures near a sloping rigid wall is studied. Bragg resonance is observed in the case of wave scattering by multiple structures irrespective of wave and structural parameters and is found as proportional to the number of structures deployed. In addition, the study reveals that in the presence of multiple structures, due to more wave energy dissipation, wave transmission in the lee side of the structures is reduced significantly when compared with that observed for a single structure.

Gravity Wave Trapping by Series of Horizontally Stratified Wave Absorbers Away From Seawall

2020 ◽  
Vol 142 (6) ◽  
Author(s):  
V. Venkateswarlu ◽  
D. Karmakar
Keyword(s):  
Dynamic Pressure ◽  
Vertical Wall ◽  
Expansion Method ◽  
Wave Theory ◽  
Middle Layer ◽  
Bottom Layer ◽  
Rigid Wall ◽  
Wave Trapping ◽  
Chamber Length ◽  
Eigenfunction Expansion Method

Abstract The fluid oscillation between the rigid wall and stratified wave absorber is analyzed in the context of the linearized water wave theory. The stratified wave absorber is composed of multiple horizontal layers considering higher porosity in the surface layer, moderate porosity in the middle layer, and zero porosity in the bottom layer. The study examined the wave motion through multiple horizontally stratified wave absorbers on solving the multilayer dispersion relation. The eigenfunction expansion method is used to form the system of analytical equations using the property of orthogonal mode-coupling relation with continuity of dynamic pressure and velocity at each of the interfaces. The free spacing available between leeward porous wave absorber and the rigid wall is termed as “trapping chamber.” The effect of the trapping chamber on wave reflection and fluid force experienced by a rigid wall is discussed. The analytical results formulated for the physical problem are validated with the available experimental and numerical results. The wave trapping is examined and compared for three types of seawalls such as vertical wall, permeable wall, and stepped wall. The change in trapping chamber length shows the harmonic peaks and troughs in the trapping coefficients and the harmonic oscillations help in the design and development of the stratified porous wave absorbers for the protection of marine infrastructure.

scholarly journals Trapped modes around a row of circular cylinders in a channel

1999 ◽  
Vol 386 ◽  
pp. 259-279 ◽  
Author(s):  
T. UTSUNOMIYA ◽  
R. EATOCK TAYLOR
Keyword(s):  
Expansion Method ◽  
Wave Theory ◽  
Multipole Expansion ◽  
Circular Cylinders ◽  
Large Radius ◽  
Trapped Modes ◽  
Resonant Phenomenon ◽  
Trapped Mode ◽  
Linear Water Wave Theory ◽  
Multipole Expansion Method

Trapped modes around a row of bottom-mounted vertical circular cylinders in a channel are examined. The cylinders are identical, and their axes equally spaced in a plane perpendicular to the channel walls. The analysis has been made by employing the multipole expansion method under the assumption of linear water wave theory. At least the same number of trapped modes is shown to exist as the number of cylinders for both Neumann and Dirichlet trapped modes, with the exception that for cylinders having large radius the mode corresponding to the Dirichlet trapped mode for one cylinder will disappear. Close similarities between the Dirichlet trapped modes around a row of cylinders in a channel and the near-resonant phenomenon in the wave diffraction around a long array of cylinders in the open sea are discussed. An analogy with a mass–spring oscillating system is also presented.

The Spring-Like Air Compressibility Effect in OWC Wave Energy Converters: Hydro-, Thermo- and Aerodynamic Analyses

2018 ◽  
Author(s):  
António F. O. Falcão ◽  
João C. C. Henriques
Keyword(s):  
Wave Energy ◽  
Process Model ◽  
Wave Theory ◽  
Theoretical Models ◽  
Irregular Waves ◽  
Power Performance ◽  
Floating Structure ◽  
Wells Turbine ◽  
Compressibility Effect ◽  
Linear Water Wave Theory

The oscillating-water-column (OWC) wave energy converter consists of a hollow (fixed or floating) structure, open to the sea below the water surface. Wave action alternately compresses and decompresses the air trapped above the inner water free-surface, which forces air to flow through a turbine coupled to a generator. The spring-like effect of air compressibility in the chamber is related to the density-pressure relationship. It is known to significantly affect the power performance of the full-sized converter, and is normally not accounted for in model testing at reduced scale. Three theoretical models of increasing complexity are analysed and compared: (i) the incompressible air model; (ii) the isentropic process model; (iii) and the (more difficult and rarely adopted) adiabatic non-isentropic process model in which losses due to the imperfectly efficient turbine are accounted for. The air is assumed as a perfect gas. The hydrodynamic modelling of wave energy absorption is based on linear water wave theory. The validity of the various simplifying assumptions, especially in the aero-thermodynamic domain, is examined and discussed. The validity of the three models is illustrated by a case study with numerical results for a fixed-structure OWC equipped with a Wells turbine subject to irregular waves.

Wave motion over stratified porous absorber combined with seaward vertical barrier

2020 ◽  
Vol 234 (4) ◽  
pp. 830-845
Author(s):  
Valliboina Venkateswarlu ◽  
Debabrata Karmakar
Keyword(s):  
Wave Reflection ◽  
Single Layer ◽  
Expansion Method ◽  
Wave Theory ◽  
Wave Trapping ◽  
Eigenfunction Expansion Method ◽  
Vertical Barrier ◽  
Friction Factors ◽  
Structural Configurations ◽  
Analytical Relations

The oblique wave reflection by horizontally stratified porous absorber having two horizontal porous bars of different porosities and friction factors placed on step-type bottom is studied using eigenfunction expansion method based on linearised wave theory. The present study examines several structural configurations such as porous absorber consisting of finite and semi-infinite thickness with/without seaward vertical barrier. The present study derived the direct analytical relations to determine wave reflection by each of the structural configuration for plane-wave assumption using potential flow theory. Initially, the porous absorber considering uniform porosity and friction factor is examined and validated with available numerical results, and the direct analytical relations are also validated with available relations of possible structural configurations. In addition, the present study reported wave reflection performance of submerged single-layer and double-layer porous absorbers with/without seaward vertical barrier. The effect of bottom rigid bar, surface porous bar, middle porous bar depth, multiple porosities, friction factors, incident wave angle and porous effect parameter on wave reflection coefficient is presented in detail for various structural configurations. The significance of seaward vertical barrier on wave reflection and wave trapping is reported. The point of wave trapping, critical angle of impinging, resonating peaks and troughs due to various structural configurations are presented against structural thickness.

Wave Trapping Efficiency of a Flexible Membrane Near a Partially Reflecting Seawall

2021 ◽  
Vol 143 (5) ◽  
Author(s):  
V. Venkateswarlu ◽  
K. G. Vijay ◽  
R. Raja Pandi ◽  
Chandra Shekhar Nishad
Keyword(s):  
Domain Boundary ◽  
Wave Interaction ◽  
Cost Effective ◽  
Wave Theory ◽  
Trapping Efficiency ◽  
Maximum Deflection ◽  
Wave Regime ◽  
Flexible Membrane ◽  
Wave Trapping ◽  
Submergence Depth

Abstract The gravity wave interaction with a flexible membrane placed at a finite distance from the partially reflecting seawall is analyzed under the framework of linear water wave theory using the multi-domain boundary element method (BEM). The flow through a flexible membrane is assumed to follow Darcy’s law in addition to membrane displacements. As a viable alternative to the existing wave dampers, the flexible membrane is examined for the effective dampening of incident waves. The correctness of the numerical results is affirmed with the known results available in the literature. The effect of membrane tension, submergence depth, membrane width, porosity, angle of inclination, and confined chamber spacing on hydrodynamic coefficients is discussed as a function of dimensionless wavenumber. The partially reflecting harbor wall diminishes the wave reflection coefficient in the long-wave regime. The increase in the flexible membrane width does not necessarily ensure the ideal wave capturing performance. A shift in the peak of the maximum deflection is observed with the increase of membrane width while there is a shift in peak outward for the increase in the submergence depth. Moreover, the maximum deflection is found to decrease with the increase in porosity, and it is 62% reduction for membrane porosity b = 1 due to the significant wave damping. The wave run-up and the wall force coefficients are found to be minimum when the relative plate width is B/h = 1. The present study is expected to be useful for the design of cost-effective wave attenuating systems.

scholarly journals Radiated Force due to Surge Motion by a Pair of Submerged Cylinder in Water

2019 ◽  
Vol 8 (10) ◽  
pp. 3205-3210
Keyword(s):  
Water Wave ◽  
Expansion Method ◽  
Wave Theory ◽  
Finite Depth ◽  
Added Mass ◽  
Damping Coefficient ◽  
Hydrodynamic Coefficients ◽  
Linear Water Wave Theory ◽  
Eigenfunction Expansion Method ◽  
Submerged Cylinder

Evaluation of hydrodynamic coefficients due to surge of submerged structure is great significant to designing a device which can be consider as a device of wave energy. In the present work, a theoretical approach is developed to describe radiation of water wave by fully submerged cylinder placed above a submerged circular plate in water of finite depth which is based on linear water wave theory The radiation problem due to surge motion by this pair of cylinders have investigated with the suspicion of linear water wave theory. To determine the radiated potentials in every area, we utilize the eigenfunction expansion method and variables separation method. Finally, we derived the analytical expressions of Hydrodynamic coefficients i. e. added mass and damping coefficient due to surge and associated unknown coefficients are calculated by utilizing the matching conditions between the physical and virtual boundaries. A set of added mass and damping coefficient have presented graphically for various radius of the submerge cylinder.

Wave Interaction With Floating Elastic Plate Based on the Timoshenko–Mindlin Plate Theory

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
K. M. Praveen ◽  
D. Karmakar ◽  
C. Guedes Soares
Keyword(s):  
Dispersion Relation ◽  
Elastic Plate ◽  
Plate Theory ◽  
Wave Interaction ◽  
Bending Moment ◽  
Expansion Method ◽  
Wave Theory ◽  
Mindlin Plate ◽  
Floating Elastic Plate ◽  
Mindlin Plate Theory

In the present study, the wave interaction with the very large floating structures (VLFSs) is analyzed considering the small amplitude wave theory. The VLFS is modeled as a 2D floating elastic plate with infinite width based on Timoshenko–Mindlin plate theory. The eigenfunction expansion method along with mode-coupling relation is used to analyze the hydroelastic behavior of VLFSs in finite water depth. The contour plots for the plate covered dispersion relation are presented to illustrate the complexity in the roots of the dispersion relation. The wave scattering behavior in the form of reflection and transmission coefficients are studied in detail. The hydroelastic performance of the elastic plate interacting with the ocean wave is analyzed for deflection, strain, bending moment, and shear force along the elastic plate. Further, the study is extended for shallow water approximation, and the results are compared for both Timoshenko–Mindlin plate theory and Kirchhoff’s plate theory. The significance and importance of rotary inertia and shear deformation in analyzing the hydroelastic characteristics of VLFSs are presented. The study will be helpful for scientists and engineers in the design and analysis of the VLFSs.

Wave scattering by a fixed submerged platform over a step bottom

2017 ◽  
Vol 233 (1) ◽  
pp. 93-107 ◽  
Author(s):  
Ramnarayan Mondal ◽  
Ken Takagi
Keyword(s):  
Water Wave ◽  
Wave Scattering ◽  
Rectangular Cross Section ◽  
Vertical Wall ◽  
Expansion Method ◽  
Wave Theory ◽  
Geometrical Parameters ◽  
Linear Water Wave Theory ◽  
Expansion Formulae ◽  
Submerged Body

This study deals with oblique and normal water wave scattering by a fixed submerged body of rectangular cross section which is infinite in length and finite in width. The fluid domain is considered as infinite as well as semi-infinite in nature. The study is carried out under the assumption of small amplitude linear water wave theory. It is considered that the bottom has a step and the submerged body is considered in shallower water depth region. The velocity potential is derived using the eigenfunction expansion method. The unknown constants, which appear in the expansion formulae, are obtained using orthogonal relation along with the boundary conditions at the interfaces. The wave-induced hydrodynamic forces acting on the submerged body and vertical wall are computed for different geometrical parameters. The wave reflection coefficient and the free surface motion are also calculated to see the wave phenomena around the submerged body.

Irregular wave interaction with an offshore OWC wave energy converter

2021 ◽  
Vol 222 ◽  
pp. 108619
Author(s):  
Milad Zabihi ◽  
Said Mazaheri ◽  
Masoud Montazeri Namin ◽  
Ahmad Rezaee Mazyak
Keyword(s):  
Wave Energy ◽  
Wave Interaction ◽  
Wave Energy Converter ◽  
Energy Converter ◽  
Irregular Wave

Comparisons of Simulation Methods for Motions of a Moored Body in Waves

1985 ◽  
Vol 107 (1) ◽  
pp. 34-41
Author(s):  
M. Takagi ◽  
K. Saito ◽  
S. Nakamura
Keyword(s):  
Wave Theory ◽  
Simulation Methods ◽  
Convolution Integral ◽  
Linear Water Wave Theory ◽  
Initial Stage ◽  
Constant Coefficients ◽  
Exciting Forces ◽  
Linear Differential ◽  
Experimental Values ◽  
The Time Domain

Based on the linear water wave theory, numerical simulations are carried out for motions in waves of a body moored by a nonlinear-type mooring system. Numerical results obtained by using the equation of motion described in the time domain with a convolution integral (C.I. method) are compared with those of the second-order linear differential equation with constant coefficients (C. C. method). These results are also compared with experimental values measured from the initial stage when the action of exciting forces starts and the validity of C.I. method is discussed.

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