Faculty Publications
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Item Wave transformation due to a submerged porous block associated with a vertical barrier(Springer, 2020) Krishna, K.R.A.; Venkateswarlu, V.; Karmakar, D.In the present study, the combination of vertical porous barrier along with the porous block is proposed for wave energy damping. Three types of vertical barriers such as (a) fully extended barrier (b) bottom-standing barrier and (c) surface piercing barrier away from the porous structure are analysed for wave trapping. The finite spacing in between vertical barrier and the porous structure is proposed for better wave trapping. The continuity of velocity and pressure at the interfaces of vertical barrier and porous structure are considered and the eigenfunction expansion method is adopted to determine the wave transformation characteristics due to the presence of submerged vertical barrier and porous block. The resistance and reactance offered by the porous structure are taken into account using the complex dispersion relation proposed by Sollitt and Cross (1972). The effect of structural porosity, width of the structure and angle of incidence on wave transformation due to the vertical barrier away from the porous structure are examined in detail. The results are compared and validated with the available literature for specific configurations as in Sollitt and Cross (1972) and Mallayachari and Sundar (1994). The study suggests that the increase in the structural porosity enhances the wave energy damping and global minima is achieved in the wave reflection coefficient due to the formation of standing waves by the breakwater system. The proposed structure can be adopted in leeward, port and harbour regions to achieve the tranquillity condition. © Springer Nature Singapore Pte Ltd. 2020.Item Wave scattering by vertical porous block placed over flat and elevated seabed(Springer Science and Business Media Deutschland GmbH, 2019) Venkateswarlu, V.; Karmakar, D.The present study addresses the hydrodynamic characteristics of the incident wave through porous structure for both finite and shallow water depth. The oblique wave transformation due to the porous block over flat and elevated seabed and the submerged rigid block is presented. Analytical direct formulae are proposed to determine the wave reflection and transmission coefficient for the porous structure considering different configurations like porous block, porous block backed by wall, vertical wall away from the porous block and semi-infinite porous block at flat and elevated seabed. The analytical results for wave interaction with porous structure are presented considering the mode-coupling relation and eigenfunction expansion technique. Further, the significance of the semi-infinite porous block placed on the flat and elevated seabed is studied in detail. The analytical results obtained in the present study are validated with the numerical results available in the literature for specific cases. The significance of the critical angle and skin depth for the semi-infinite structure is explored in the wave structure interaction problems. The comparative study between various structural configurations suggests that, if the ratio of wavelength and width of the structure is greater or equal to unity (d/??1), then the structure can be regarded as semi-infinite porous block for flat and elevated seabed. The derived analytical formulae will be helpful in the preliminary design and analysis of the porous blocks. © 2019, Sociedade Brasileira de Engenharia Naval.Item Significance of seabed characteristics on wave transformation in the presence of stratified porous block(Taylor and Francis Ltd. michael.wagreich@univie.ac.at, 2020) Venkateswarlu, V.; Karmakar, D.The wave transformation due to the presence of stratified porous structure lying on flat seabed, elevated seabed, and stepped seabed is analyzed under the oblique wave incidence. The stratified porous structure in the absence and presence of the leeward wall along with the confined region is examined using the matched eigenfunction expansion technique. The direct analytical relations are obtained to examine the wave transformation for the case of long-wave approximations for multilayered porous structure lying on various types of seabed. The wave reflection coefficient, transmission coefficient, energy damping, and wave force on the vertical wall in the presence of stratified porous block are analyzed with variation in the sea-bed characteristics, porosity, friction factor, structural width, and water chamber length. The study shows that the energy damping increases with the increase in the porosity of the seaside porous layer due to the presence of high void spaces. Further, the stratified porous structure shows a considerable impact in decreasing the resonating peaks and troughs for the wave force acting on the seawall. In addition, the stepped seabed is observed to reduce the wave force on the leeward wall as compared with the uniform and elevated seabed in the presence of stratified porous block. © 2019, © 2019 Japan Society of Civil Engineers.Item Wave transformation due to barrier-rock porous structure placed on step-bottom(Taylor and Francis Ltd. michael.wagreich@univie.ac.at, 2020) Venkateswarlu, V.; Karmakar, D.The oblique wave transport through barrier-rock porous structure for different structural configurations are examined considering impermeable uniform/step-bottom topography. The numerical study is performed on using the linearised wave theory and mode-coupling relation at seaward/leeward structural interfaces. The wave reflection, transmission, energy absorption, wave force on the rigid wall, the wave force on seaward and leeward barriers is reported considering various ranges of porosity, friction factor, structural thickness, trapping chamber spacing and angle of impinging. The analytical relations for calculating the wave reflection and transmission coefficients are reported for plane-wave approximation and the effectiveness of present analytical results are verified with the available literatures for specific structural configurations. The fluid resonance plays a vital role in the design of trapping chamber thickness, and resonating troughs in wave scattering suggest an effective structural configuration for better wave damping. © 2019 Informa UK Limited, trading as Taylor & Francis Group.Item Surface gravity wave scattering by multiple energy absorbing structures of variable horizontal porosity(Taylor and Francis Ltd., 2020) Venkateswarlu, V.; Praveen, P.; Karmakar, D.The oblique wave scattering by fully-extended two-layered, three-layered and submerged two-layered porous structures occupying finite width is reported using an analytical model based on the eigenfunction expansion method. The fully extended two-layered structure is composed of two porosities and friction factors in the surface porous layer and the bottom porous layer. In addition, the three-layered energy-absorbing structure is composed of two-porous layers along with the bottom rigid layer to replace the natural seabed variation. Further, the study is extended for multiple energy-absorbing structures to report the impact of free spacing available between the two subsequent structures on fluid resonance. The two-layered porous structure dispersion relation is derived and solved using step approach and Newton-Raphson method. The derived analytical results are validated with the published results of notable authors. The effect of the surface and bottom layers porosity, friction factor, free spacing, structural width, number of structures, and angle of contact on the wave scattering is reported. Finally, the comparative study between the single and multiple energy absorbing structures of multiple horizontal layers is discussed. Further, the significance of the critical angle of contact and fluid resonance for better wave blocking is presented precisely, which is essential for the coastal engineers to design offshore structures. © 2020 Japan Society of Civil Engineers.Item Wave motion over stratified porous absorber combined with seaward vertical barrier(SAGE Publications Ltd info@sagepub.co.uk, 2020) Venkateswarlu, V.; Karmakar, D.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. © IMechE 2020.Item Gravity wave trapping by series of horizontally stratified wave absorbers away from seawall(American Society of Mechanical Engineers (ASME), 2020) Venkateswarlu, V.; Karmakar, D.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. © © 2020 by ASMEItem Numerical investigation on the wave dissipating performance due to multiple porous structures(Taylor and Francis Ltd., 2021) Venkateswarlu, V.; Karmakar, D.Gravity wave interaction with porous structures is investigated under the assumption of linearized wave theory. Multiple porous blocks of finite thickness with finite spacing are investigated under the action of oblique ocean waves considering leeward unbounded region and confined region. The eigenfunction expansion method is employed to analyse the effect of multiple-confined regions in the trapping of oblique waves. The study outcomes are validated with numerical and experimental results available in the literature. The friction factor and the inertia effect of the porous medium are considered and different porosity conditions are adopted to determine the wave reflection coefficient, transmission coefficient, wave dissipation and wave force impact on the leeward wall. The functional efficiency of multiple fully extended porous structures is studied for different values of porosity, water chamber length, angle of incidence, friction factor and spacing between the porous blocks. The seabed is assumed to be uniform impermeable bottom and uneven bottom (step approximation is adopted). The study demonstrates that the better wave blocking is achieved with the increase in the series of porous structures and the confined regions can be used effectively for the trapping of oblique waves. The present study will be helpful in the design of porous structures for security of coastal facilities and coastal structures in offshore environment. © 2019 Indian Society for Hydraulics.Item Wave trapping efficiency of a flexible membrane near a partially reflecting seawall(American Society of Mechanical Engineers (ASME), 2021) Venkateswarlu, V.; Vijay, K.G.; Pandi, R.R.; Nishad, C.S.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. © © 2021 by ASME.Item Oblique wave interaction with a two-layer pile-rock breakwater placed on elevated bottom(Taylor and Francis Ltd., 2022) Venkateswarlu, V.; Praveen, K.M.; Vijay, K.G.; Anil, K.; Karmakar, D.The two-layer pile-rock porous breakwater consisting of the upper porous layer, middle porous layer placed over the bottom rigid layer (elevated bottom) is proposed as an active wave absorber for significant wave damping and wave trapping. The two-layer rock core is placed between the two thin porous barriers (piles), and the thin barriers/ piles are useful to reduce the wave force experienced by active two-layered breakwater. The eigenfunction expansion method is used to analyse the physical problem on considering the continuity in fluid velocity and pressure along with mode-coupling relation based on classical linearised potential flow theory. The developed analytical model is validated with the available results and then various hydrodynamic characteristics such as wave reflection, transmission, damping, wave forces on seaward, leeward barriers and wave force experienced by the vertical cliff are presented. The porosity of surface layer shows an effective role in reducing the harmonic oscillatory pattern in the hydrodynamic quantities, and the study suggests the higher surface layer porosity (Formula presented.) as compared with bottom layer porosity for optimal wave damping. © 2021 Informa UK Limited, trading as Taylor & Francis Group.