Faculty Publications
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Item Prediction of Hydrodynamic Coefficients of Stratified Porous Structure Using Artificial Neural Network (ANN)(Springer Science and Business Media Deutschland GmbH, 2023) Gupta, A.; Shilna, K.; Karmakar, D.The breakwater is designed to offer tranquility in the harbor to protect the offshore facilities and also to prevent coastal erosion. The use of soft computing approaches in coastal engineering helps to solve the nonlinear problems and predicts the hydrodynamic performance of the device. In the present study, the artificial neural networks (ANNs) with different topologies are considered to predict the hydrodynamic coefficients for the wave interaction with the stratified porous breakwater. The experimental study is performed to determine the reflection and transmission coefficient for the horizontally stratified porous structure with three layers of different porosity and width of the structure. The hydrodynamic performance is analyzed by considering the feed-forward back-propagation neural network, and the results are compared for different numbers of hidden nodes. Further, the root mean square error (RMSE) and coefficient of correlation (CC) are considered to assess the ability of ANN topologies to predict the transmission coefficient. The numerical results obtained using ANN are noted to fall within the range that represents the network’s ability to predict accurate results. The study performed will provide an insight in the design and analysis of the stratified porous breakwater in the nearshore regions. © 2023, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.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 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.Item Hydrodynamic analysis of floating tunnel with submerged rubble mound breakwater(Elsevier Ltd, 2022) Patil, S.B.; Karmakar, D.The wave interaction with a Submerged Floating Tunnel (SFT) of two different shapes (rectangular and circular) in the presence of a submerged rubble mound breakwater (SRMB) is analyzed using Multi-Domain Boundary Element Method (MDBEM). Furthermore, three typical SFT cross-sections (rectangular, trapezoidal, and circular) of equal area and structural height in the presence of SRMB under similar operating conditions are investigated as comparative study to analyse the influence of SFT shape on hydrodynamic performance. The performance of the tunnel configurations is analyzed as a (a) measurement in terms of hydrodynamic efficiency and (b) criterion for tunnel structure safety. In both shallow and intermediate water depth regions, the critical wave number and the critical angle of incidence followed by resonant wave reflection are identified, and suitable structural parameters of SRMB such as structural porosity in the armour layer, relative crest width, relative gap width between the SFT and the SRMB, structural width and position (relative draft of tunnel structure measured from the free water surface) of SFT are investigated. The present parametric investigation of SFT with SRMB reveals an improved wave transformation properties for a specific range of water depth. The coupling of SRMB has resulted not only in a reduction of wave-induced force acting on SFTs, but also in improved performance in wave transformation characteristics as a coastal protection structure, which is substantially determined by SRMB structural properties. Due to the presence of SRMB, the SFT's safety is improved, which may also add stability to the SFT. A comparative study of different distinct cross-sections of SFTs indicates that, due to its shape, the circular SFT has a reduced reflection capability and lower wave-induced force with nearly the same wave transmission as the rectangular and trapezoidal SFT. The study performed on the coupled SFT and rubble mound breakwater may be useful in determining the suitability of breakwaters not only for maintaining shore dynamics but also for protecting important floating structures for underwater transit. © 2022 Elsevier LtdItem Hydrodynamic performance of submerged breakwater in tandem with thin-walled as submerged reef structure(SAGE Publications Ltd, 2023) Patil, S.B.; Karmakar, D.The interaction of gravity waves with submerged tandem breakwater of different structural configurations is analysed in finite water depth using the Multi-Domain Boundary Element Method (MDBEM). The wave transformation characteristics, wave forces and wave energy dissipation are analysed considering the presence of impermeable type thin-walled as reef structure in front of the primary submerged breakwater. The comparative study is performed for the submerged structures of various shapes (trapezoidal, triangular, rectangular and thin-walled) and types (rubble mound, permeable, impermeable) that are designed to function together as a tandem breakwater. The effect of varying angle of incidence, relative submergence depth, and relative gap between the reef structure and primary breakwater on wave reflection and transmission are derived for the suggested tandem breakwater models. Among all the impermeable-type models, the thin-walled as reef structure designed at a distance in front of thin-walled as a primary submerged breakwater as a tandem is observed to perform efficiently in terms of energy dissipation and also offers an optimum wave transmission for both short and long wave conditions. Further, the permeable and rubble mound type trapezoidal tandem breakwater offers higher energy dissipation in comparison with all other breakwaters. In view of the design considerations and structural stability of submerged breakwaters, the addition of a reef structure acts as a defence system for the primary breakwater and also creates an energy dissipation zone that allows the shore dynamics to be preserved, making tandem models more effective in the harbour region. © IMechE 2022.Item Wave Energy Damping due to Coupled Porous Structure and Submerged Porous Plate(Editorial Board of Journal of Harbin Engineering, 2023) Athul Krishna, K.R.; Abdulla, K.; Karmakar, D.The present study investigates the wave-damping characteristics due to the combination of bottom-standing porous structure, submerged porous plate, and fully-extended porous structure of finite width using the small amplitude wave theory. The hydrodynamic characteristics such as reflection, transmission, and dissipation coefficients are determined to analyse the wave energy dissipation by the composite breakwater using the matched eigenfunction expansion method and orthogonal mode-coupling relation. Darcy’s law is incorporated to the flow through porous media. The composite breakwater system is investigated experimentally to validate and compare the numerical results with the physical model study. The complex porous effect parameter for the submerged plate is incorporated in the numerical analysis, which represents the reactance and resistance of the porous structure. The wave forces on the submerged plate and porous structure for the composite breakwater are investigated by considering the effects of changing parameters such as structural porosity, plate submergence, angle of incidence, width of the submerged porous structure and distance between the structures. The study illustrates that the increasing width of the fully-extended porous structure improves the performance of the breakwater system. The proposed study on the composite breakwater yields an useful information for wave energy attenuation, which can be designed and implemented in coastal and harbour areas to achieve wave tranquillity. © 2023, Harbin Engineering University and Springer-Verlag GmbH Germany, part of Springer Nature.Item Hydrodynamic performance of hybrid floating breakwater integrated with oscillating water column(SAGE Publications Ltd, 2025) Vishwakarma, R.D.; Karmakar, D.The present study investigates the hydrodynamic performance of different types of hybrid floating breakwaters (HFB) integrated with an oscillating water column (OWC). The study is performed for five different cross-sectional shapes of HFB, such as rectangular, box, H, ?, and trapezoidal, with the inclusion of OWC of the same dimension in all of the hybrid floating breakwaters. The performance of the HFBs is examined for its motion response, wave transmission coefficient, and power capture under the action of the regular waves, considering the incident wave normal to the structure. The motion response and wave transmission characteristics assessment are based on potential flow theory, and the power capture due to the HFB is assessed using the volume of fluid (VOF) flow computation method. The HFB model performing better in terms of transmission coefficient and power capture considering wider bandwidth for the considered surface gravity wave frequencies is selected to investigate the effect of changes in HFB’s parameters, such as length, width, draft, and wave incident angle on the hydrodynamic performance. Additionally, the streamline contours for the air flow velocity variation through the OWC chamber in different types of hybrid floating structures are analysed for better understanding of flow through visualisation. The aforementioned streamline contour is determined for the wave frequency where the maximum wave energy capture in the HFB models is observed. The study will facilitate the researchers to comprehensively investigate the stability of hybrid floating breakwater under the influence of regular waves with the help of the findings of the present investigation. © IMechE 2025