Faculty Publications
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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 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 Performance evaluation of submerged breakwater using Multi-Domain Boundary Element Method(Elsevier Ltd, 2021) Patil, S.B.; Karmakar, D.The gravity wave interaction with submerged breakwater of different structural configurations are investigated based on the small-amplitude wave theory. The boundary value problem is analysed in two-dimension using the linearized wave theory in water of finite depth. The submerged breakwater structural configuration such as (i) thin-walled type (impermeable), (ii) rectangular type (impermeable and permeable), (iii) triangular type (impermeable, permeable, perforated), (iv) trapezoidal type (impermeable, permeable, perforated) and (v) Tandem type (impermeable, permeable, perforated) are considered to analyse and performance of the breakwater. The numerical model is developed using the Multi-Domain Boundary Element Method (MDBEM) to analyse the hydrodynamic scattering coefficient (such as reflection, transmission and dissipation coefficient) for the change of physical parameters such as relative spacing between the breakwaters, relative water depth and structural dimensions. The convergence of the present numerical model is performed for the specific case of tandem breakwater and numerical computation is validated with the results available in the literature. The wave reflection and transmission coefficient along with wave force on the structure is analysed for different shapes, structural parameters and geometrical parameters of the breakwater to maximize the efficiency of breakwater. In the case of permeable breakwater, the submerged tandem breakwater is found to be more efficient in wave transformation as compared to rectangular, triangular and trapezoidal permeable submerged breakwaters. The comparative analysis performed on different configurations of the breakwater in the present study will be helpful in the effective design of the breakwater near the harbour regions. © 2021 Elsevier LtdItem A numerical study of forced convection in ideal and randomized reticulated porous structures and a proposal for a new correlation(Elsevier Ltd, 2022) Rambabu, S.; Parthasarathy, P.; Velamati, V.This paper presents numerical study to calculate convective heat transfer coefficients in reticulated porous media. In this study, the reticulated porous structures are modelled based on theoretical Kelvin model, representing the real porous structures. The geometry of these structures are generated with the help of in-house code and visualisation tool kit (VTK) libraries. The ideal and randomized Kelvin structures are generated for different PPI & porosities. These structures are utilized to calculate the fluid flow and heat transfer for different fluids of different Prandtl numbers (air, water & sea water). By varying the geometrical parameters, the influence of geometries on heat transfer between the flowing fluid and solid phase of open-cell foams are investigated. For this reason, the momentum and energy equations for forced convection in reticulated structures are solved using standard CFD-FVM approach. Based on the simulation outcomes, a new correlation is proposed to calculate the heat transfer coefficients in the reticulated porous structures. The proposed correlation is validated by comparing it with numerical and experimental data of real reticulated porous structures available in the literature. The effects of the Colburn j factor and performance factor are also computed to obtain the best outcome. © 2021Item Wave trapping due to composite pile-rock structure coupled with vertical barrier(SAGE Publications Ltd, 2023) Sreebhadra, M.N.; Krishna, K.R.A.; Karmakar, D.The wave transformation due to pile-rock porous structure in combination with vertical porous barrier is studied under oblique wave action. The pile-rock breakwaters consists of two rows of closely spaced piles and a rock core between them is effective in dissipating wave energy when compared with traditional rigid breakwaters due to its reduced deadweight of construction materials and additional stability. Three different cases of the vertical barrier configurations such as fully-extended barrier, bottom-standing barrier and surface-piercing barrier placed in front of the pile-rock porous structure are considered for the investigation. The numerical study is performed using the eigenfunction expansion and the associated orthogonal mode-coupling relations considering the continuity of pressure and velocity for the vertical barrier, seaward and leeward structural interfaces. The Darcy’s law is incorporated for the flow through porous media and the porosity factor of the structure is introduced using the complex porous effect parameter. The numerical results for the wave reflection, transmission and dissipation coefficient, wave force on front and rear side of porous structure along with the wave force on the barrier interface are evaluated for different hydraulic characteristics. The analysis is presented for varying structural porosity, angle of incidence, structural thickness, friction factor, length between vertical barrier and porous structure for the three different cconfigurations of vertical barrier. The numerical investigation performed in the present study will be useful for the design and analysis of the composite breakwater system to protect the offshore facility from high waves. © IMechE 2022.Item Dissipation of Gravity Waves Due to Submerged Porous Plate Coupled With Porous Structures(American Society of Mechanical Engineers (ASME), 2023) Krishna, K.R.A.; Abdulla, K.; Karmakar, D.The present study focuses on wave trapping due to the submerged horizontal porous plate combined with the bottom-standing porous structure and surface-piercing porous structure. The submerged plate thickness is considered to be negligible as compared to the incident wavelength and water depth, and the porous structure is considered to be of finite width. The study is performed based on the eigenfunction expansion method, and the wave interaction with the combined structure is investigated using the small amplitude wave theory. The orthogonal mode-coupling relation is used to analyze the wave interaction with the combined structure. The reflection, transmission, and dissipation coefficients along with wave force on the porous structure are investigated to analyze the hydrodynamic performance of the composite porous breakwater system. Further, the effect of porosity of submerged plate and structure, submergence depth of plate and structure, angle of incidence, and the submerged plate length are investigated to analyze the effective wave dissipation by the composite breakwater. In addition, the comparative study of the numerical method is performed with the results available in the literature. The study noted that the wave damping due to the submerged porous plate backed by surface-piercing porous structure is more as compared to the submerged porous plate backed by the bottom-standing porous structure. The study performed will be helpful to scientists and engineers in the design of suitable composite breakwater systems and also assists in selecting the best structural configuration for attenuation of wave height and to protect the offshore facility from high waves in the coastal region. © 2023 American Society of Mechanical Engineers (ASME). All rights reserved.Item A numerical investigation to determine longitudinal dispersion coefficient in ideal and randomized reticulated porous structures using transient direct pore level simulation(Elsevier Ltd, 2023) Rambabu, S.; Parthasarathy, P.; Velamati, V.The purpose of this numerical investigation is to characterize the longitudinal dispersion coefficients in open-cell reticulated porous structures. Open-cell foams are modelled using idealized Kelvin cell structures. Using the conventional Navier–Stokes equation, airflow has been calculated through various porous structures. Along with the flow, the dispersion of a tracer fluid is traced across the structures and analyzed in terms of the effective dispersion coefficient. Using direct pore level simulations (DPLS), a parametric study is performed to understand the influence of geometrical parameters on the dispersion in porous media. To evaluate the longitudinal dispersion coefficient (LDC), the analytic solution gradients were fitted into the simulated gradients. From the results, a new characteristic length correlation is proposed to calculate the Peclet number, and it is compared with experimental and numerical data that are available in the literature. © 2023 Elsevier LtdItem Oblique wave propagation through composite permeable porous structures(Springer Science and Business Media Deutschland GmbH, 2023) Krishna, K.R.A.; Karaseeri, A.G.; Karmakar, D.In the present study, the porous breakwater system consisting of a porous block and a permeable barrier is analysed to understand the wave dissipation due to the composite porous structure. The linearised wave theory is adopted to analyse the wave interaction with three different configurations of the composite structures including (a) porous structure and fully extended vertical barrier, (b) porous structure and bottom-standing barrier and (c) porous structure and surface-piercing barrier. The eigenfunction expansion method along with orthogonal mode-coupling relation is adopted to determine the wave reflection and transmission characteristics along with wave force on the porous structure and barrier, and surface deflection in incident and transmitted region. The experimental investigation is performed for the composite breakwater system and the results obtained are compared and validated with the numerical results. The composite breakwater system is studied for various parameters such as relative water depth, porosity of structure and barrier, structural thickness to wavelength ratio, water depth to wavelength ratio and gap between the structure and barrier. Further, the comparative study is performed with the results available in the literatures. The proposed study exhibits an informative result for the wave energy attenuation by the composite breakwater system which can be designed and implemented in coastal and harbour regions for achieving the tranquillity. © 2022, The Author(s), under exclusive licence to Sociedade Brasileira de Engenharia Naval.