Faculty Publications
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Publications by NITK Faculty
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Item Influence of damping on an oscillating water column WEC integrated with a breakwater(CRC Press, 2019) Rajan, S.N.; Karmakar, D.; Guedes Soares, C.In the present study, the oscillating water column under consideration is integrated with caisson type breakwater. The air column under pressure due to the damping from the PTO device drives the turbine placed at the orifice of OWC. The relationship between the hydrodynamic efficiency of the OWC and the PTO damping is analyzed which would give more precision about efficient wave energy extraction using an OWC. The PTO damping on the chamber is characterized using a linear pressure drop law with the permeability coefficient derived from Darcy’s equation for flow through porous media. An open Computational Fluid Dynamics tool, REFF3D, is used for the simulations to analyze the reaction of the OWC under different different damping conditions due to the PTO device. Flat bottom and slope bottom configurations are studied and the results are obtained for zero damping, low damping, moderate damping and high damping. The hydrodynamic efficiency for the flat and slope bottom configurations with breakwater are compared to analyze the performance of OWC integrated with breakwater due to the change in the bottom configuration inside the OWC chamber. © 2019 Taylor & Francis Group, London,.Item Performance analysis of freely heaving U-OWC integrated with Π-shaped breakwater using Boundary Element Method(CRC Press, 2024) Muduli, R.; Karmakar, D.; Guedes Soares, C.In the present study, a free heave-only U-shaped OWC device integrated with a Π-shaped breakwater is analysed considering three different OWC chamber bottom profiles. The hydrodynamic performance is assessed on analysing the theoretical maximum efficiency, radiation susceptance and conductance coefficients. The influence of the draft of U-OWC and width of internal chamber on the hydrodynamic performance is analysed using Boundary Element Method (BEM). The peak efficiency is observed when resonance occurs as observed in the case with traditional OWC devices. Moreover, the radiation susceptance coefficient (indicative of energy left unutilised) is noted to be zero at peak efficiency and the radiation conductance coefficient (indicative of energy transferred into the system) is noted to have peak values. The study found that, irrespective of the chamber bottom profile, on increasing the width of the “U” channel, the energy conversion efficiency of the U-OWC gets diminished but increasing the width of the internal chamber enhances the efficiency of the device. A larger draft resulted in better efficiency of the device, which is intuitively expected, however a draft 0.75h is preferable than a draft of 0.9h as both configurations have almost similar performance. © 2024 selection and editorial matter, Carlos Guedes Soares and Tiago A. Santos; individual chapters, the contributors.Item Dynamic performance of Torus wave energy converter combined with offshore wind turbine semi-submersible platform(CRC Press, 2024) Sebastian, B.; Karmakar, D.; Guedes Soares, C.This article investigates the effect of incorporating a heaving wave energy converter (WEC), namely Torus on DeepCwind Semi-submersible platform (SSP) supporting a 5MW wind turbine. The hydrodynamic performance of the hybrid torus-SSP is studied using linear diffraction/radiation code WAMIT. The coupled dynamic analysis of the platform is carried out in the OpenFAST tool which takes the hydrodynamic parameters from WAMIT as input. The motion responses of the hybrid system are obtained in time domain for different irregular sea states. Statistics of motion of hybrid system is computed and compared with the initial platform to quantify the variation. The power absorption of the WEC is computed using a stand-alone MATLAB code. The maximum power is found to be absorbed at the resonance period of the semi-submersible platform. The results indicate that incorporating Torus does not cause a considerable change in the platform dynamics while rendering higher power output to the overall system. © 2024 selection and editorial matter, Carlos Guedes Soares and Tiago A. Santos; individual chapters, the contributors.Item Performance of oscillating water column wave energy converters integrated in breakwaters(CRC Press/Balkema http://Pub.NL@taylorandfrancis.com, 2016) Anvesh, V.; Karmakar, D.; Guedes Soares, C.Two-dimensional CFD simulations are used to study the response of Oscillating Water Columns (OWC) integrated in breakwaters for different bottom configurations of the OWC chamber. The integration of the OWC in breakwater reduces the costs of investments and generates more energy by using multiple chambers all along the breakwater length in the predominant wave direction. The work is performed to analyse the influence of bottom sloping configurations of OWC on the chamber pressure, free surface motion, free surface velocity and power output of integrated OWC in breakwaters. The optimum wave energy captured and the performance of the OWC device in breakwater is analysed for two different wavelengths in the case of zero damping. The numerical results are computed for the output power for different bottom sloping configurations at resonant condition of the device. © 2016 Taylor & Francis Group, London.Item Performance of barge-type floaters for floating wind turbine(CRC Press/Balkema http://Pub.NL@taylorandfrancis.com, 2016) Vijay, K.G.; Karmakar, D.; Uzunoglu, E.; Guedes Soares, C.The hydrodynamic performance of barge-type floaters for floating wind turbine is analysed with and without moonpool. In the case of barge-type floaters with moonpool, the effect of moonpool sizes and its effects on the coupled dynamics of floater motions with waves and winds are studied and presented. The moonpool can be used as floating oscillating water column. The piston mode and sloshing mode are studied for the floaters with moonpool. The analysis is carried out for the floater’s motion responses in both regular and irregular waves. The wind turbine is positioned at the centre of the floater in all of the case studies. The numerical study on the coupled dynamic response of the barge-type floaters with the wind turbine support structure is conducted using aero-servo-hydroelastic simulation. The platform motion responses along with the power spectral density of the motion characteristics are analysed. © 2016 Taylor & Francis Group, London.Item Wave Interaction With Floating Elastic Plate Based on the Timoshenko-Mindlin Plate Theory(American Society of Mechanical Engineers (ASME) infocentral@asme.org, 2019) Praveen, K.M.; Karmakar, D.; Guedes Soares, C.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. © 2019 by ASME.Item Long term response analysis of TLP-type offshore wind turbine(Taylor and Francis Ltd. michael.wagreich@univie.ac.at, 2020) Vijay, K.G.; Karmakar, D.; Guedes Soares, C.The performance of offshore wind turbine supported with different configurations of Tension-leg-platform (TLP) are studied for vertical plane motion responses (surge, heave, and pitch) along with the side-to-side, fore–aft, and yaw tower base bending moments. The long-term distribution is carried out using the short-term floating wind turbine responses based on Rayleigh distributions and North Atlantic wave data. The long-term response analysis is performed for the 5 MW TLP-type offshore wind turbine. The study aims at predicting the most probable maximum values of motion amplitudes that can be used for design purposes. The transfer functions for surge, heave and pitch motions of the floater are obtained using the FAST code. The performance of floating structure in the long-term analysis not only depends on the transfer functions but also on the careful selection of design wave spectrum model. Among different theoretical design wave spectrum models, three models are chosen that closely represents the sea states and the response spectrums are computed for these models. As the nature of the response spectrum of the floating structure is analogous with the input wave spectrum model, it can be assumed to have the same probabilistic properties and modeled as a stationary stochastic process. The long-term probability distributions for TLP-type floater configuration for surge, heave and pitch motion amplitudes along with the tower base bending moments are used for design purposes, so as to guarantee the safety of the floating wind turbines against overturning/capsizing in high waves and wind speed. The calculation of the long-term distribution using FAST will help in the preliminary analysis of the performance of floaters in the study of wave-induced response of floaters. © 2018, © 2018 Indian Society for Hydraulics.Item Hydroelastic analysis of periodic arrays of multiple articulated floating elastic plate(Taylor and Francis Ltd. michael.wagreich@univie.ac.at, 2020) Praveen, K.M.; Karmakar, D.; Guedes Soares, C.The periodic array of multiple articulated floating elastic plate acted upon by ocean waves is analysed considering Timoshenko-Mindlin plate theory. The floating elastic plate is placed periodically and is interconnected with vertical linear and flexural rotational springs which acts as an articulated joint. The hydroelastic behaviour of multiple articulated floating elastic plate is analysed based on eigenfunction expansion method along with the orthogonal mode-coupling relation in finite water depth and the continuity of energy and mass flux are used in the hydroelastic analysis of floating plate at shallow water depth. Further, the application of the wide-spacing approximation (WSA) method is employed to analyse the hydroelastic characteristics of the multiple articulated floating elastic plate. The results obtained using the eigenfunction expansion method is compared with the results based on WSA at finite water depth and validated with the results available in the literature. © 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group.Item Effect of the wind turbine floater geometry on the uncertainty associated with the hydrodynamic loading(Elsevier Ltd, 2025) Raed, K.; Karmakar, D.; Guedes Soares, C.The study aims to contribute to the establishment of the reliability-based design for floating offshore wind turbines by quantifying the uncertainty in Morison's wave force in the extreme conditions for two floating wind turbine platforms, namely, the Spar and the OC4 DeepCwind semi-submersible. Numerical models are developed to estimate the wave forces on cylindrical members with different configurations and then to quantify the uncertainty in the output using the propagation law of uncertainty. Morison's coefficients are extracted from Sarpkaya's data as a function of relative roughness, Keulegan-Carpenter number, Reynolds number and the member inclination angle. The combined uncertainty for each input is investigated based on the gathered data from different sources of uncertainties. The First-Order Second-Moment method is then adopted to quantify the output uncertainty based on the uncertainty in the input variables. Furthermore, the contribution of each random variable to the total uncertainty is analysed. The study reveals that wave height is the most significant contributing random variable to the total uncertainty. © 2025