Faculty Publications
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Item Numerical investigation of semi-submersible floating wind turbine combined with flap-type WECs(Springer, 2019) Kumawat, A.K.; Karmakar, D.; Guedes Soares, C.G.Offshore renewable energy has great potential to meet the increasing energy demands. Ammon different energy source, the offshore wave and wind energy are considered the best possible option as renewable source. To increase renewable energy yield per unit square kilometre of ocean space, there is an increasing interest in investigating the technological and the economic feasibility of combining offshore wind turbines with wave energy converters. In the past two decades, combined concepts of utilizing different floating support platforms and wave energy converters have been studied. In the present study, the hydrodynamic coefficients and response amplitude operators (RAOs) of semi-submersible floater combined with flap-type wave energy converter is analysed. The semi-submersible floater with flap-type wave energy converter is a combined concept of wave and wind energy converters which consists of three elliptical cylinder flap-type wave energy converters (WECs) and a 5 MW floating wind turbine installed on semi-submersible platform. The hydrodynamic coefficients are calculated in frequency domain and the power take off (PTO) system is modelled as a linear damper and spring. A parametric study is made to compute hydrodynamic coefficients of flap and three column semi-submersible platform combined wave and wind energy system. Further, RAO analysis is performed for three column semi-submersible platform relative to combined wave and wind energy platform with incident wave heading angles. © Springer Nature Singapore Pte Ltd. 2019.Item Wave interaction with multiple submerged porous structures(Springer, 2019) Venkateswarlu, V.; Karmakar, D.In the present study, two submerged porous structures under the action of ocean waves are analysed to understand the wave control performance due to porosity parameter. The studies in the first case consider the submerged porous structure kept at finite depth backed by rigid wall at a distance L. The second case explains the two submerged porous structures with sea wall. The numerical study is performed considering the velocity potentials in (i) open water region (seaside), (ii) porous region (primary porous structure), (iii) open water region (in between the porous structures), (iv) porous region (second porous structure) and (v) open water region (lee side). The linearized wave theory is used to analyse the wave interaction with submerged porous structures. The matching conditions are adopted based on continuity of mass and velocity, and the orthogonality condition is used to formulate the boundary value problem, and the eigenfunction expansion method is adopted for the determination of reflection, transmission coefficients, energy loss and wave forces on submerged porous structures. Numerical computation is performed for predicting the wave reflection and transmission from the submerged porous structures for different structure width and angle of incidence conditions. The existence of the porosity and friction causes energy loss and minimum friction; maximum porosity results in high wave transmission and less wave reflection. The significant difference is observed when submerged porous structure is divided into two submerged porous structures with rigid wall. In all the cases, the width of the porous structure is considered similar and is observed to play a predominant role in wave reflection, transmission and stability of the structure. The study will help in the novel economic design of the submerged porous structures for the protection of coastal facilities. © Springer Nature Singapore Pte Ltd. 2019.Item Wave transformation due to floating elastic thick plate over changing bottom topography(Springer, 2019) Praveen, K.M.; Karmakar, D.In the present study, the wave interaction with floating thick elastic plate is studied over changing bottom topography. The effect of flexible floating plates is studied based on Timoshenko–Mindlin’s theory in finite water depth and shallow water approximations. The hydroelastic analysis is performed at varying water depths and plate sizes to get the behaviour of elastic plate under the action of ocean wave. Different bottom topography cases are considered in the analysis of wave interaction with floating thick elastic plate. A mathematical model considering the mode-coupling relation along with the orthogonality condition is formulated to analyse the wave scattering due to floating thick elastic plate with varying bottom topography. The numerical results for the hydroelastic behaviour are obtained for wave interaction with floating plate with free-edge condition in varying bottom topography. The present analysis helps to understand the significance of rotary inertia and transverse shear deformation for the floating elastic plates. The study provides an insight into the effect of seabed profile over the wave interaction with floating thick elastic plate in finite water depth. © Springer Nature Singapore Pte Ltd. 2019.Item Wave energy conversion by multiple bottom-hinged surging WEC(Springer, 2019) Kumawat, A.K.; Karmakar, D.; Guedes Soares, C.G.The power capture and performance of arbitrary array of submerged bottom-hinged deflectors of finite width is analysed for two different configurations. The bottom-hinged deflectors are modelled as non-zero thickness and rotated at small angle in the vertical plane about an axis located in the seabed orthogonal to the direction of the wave propagation. The numerical study is performed on the hydrodynamic performance of the flapping deflector type oscillating wave surge converter (OWSC). Three-dimensional boundary element method is used to calculate hydrodynamic coefficients in frequency domain. A parametric study was made by comparing two geometrically different deflectors, i.e., rectangular and wedge cross-section for power capture assessment. Further, the analysis is performed for arbitrary array configurations of OWSC with oblique incident wave heading angles and the power take off (PTO) system is modelled as a linear damper and spring. The study for multiple arrays of the flap-type wave energy converters is essential for economical design of project in order to exploit more renewable energy from the ocean waves. © Springer Nature Singapore Pte Ltd. 2019.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 Extreme response analysis for TLP-type floating wind turbine using Environmental Contour Method(CRC Press, 2022) Sreebhadra, M.N.; Rony, J.S.; Karmakar, D.; Guedes Soares, C.G.The reliability of structures against extreme loading conditions is a significant factor to be accounted for the design of marine structures. In Environmental Contour Method, using inverse reliability technique the most significant contributing environmental factors associated with the structure at the particular site can approximately give the long-term extreme response. In the present study, the extreme responses on five different configurations of TLP-type floating offshore wind turbine are analysed using the environmental contour method. The various responses including the maximum and minimum tower base bending moment loads at the blade root, tower base shear force is studied. The simulations are performed for the different wind speed and wave and a comparative study is made for the different TLP-type platforms. The estimation of extreme responses is obtained using the Environmental Contour Method and the present study will be helpful for the long-term load estimation of offshore structures. © 2022 the Author(s).Item Dynamic response analysis of a combined wave and wind energy platform under different mooring configuration(CRC Press, 2022) Rony, J.S.; Karmakar, D.; Guedes Soares, C.G.In the present study, a novel concept of combining a submerged tension leg platform (STLP) with six heaving type point absorbers WEC in circular pattern is presented for different mooring configur-ations. The tensioned tendons are used to fix the floating combined wave and wind energy system in position. The safety, stability and power production of the combined floating platform depends significantly on the integrity of the tendons. The combined wind and wave platform supported by four, five, eight and nine tendons are analysed for the operating conditions of the 5MW wind turbine under regular waves. Time domain numerical simulation tool FAST developed by NREL is used to perform the aero-servo-hydro-elastic simulation. The spectra of surge, sway, roll, pitch and yaw motion of the combined system under each mooring configuration is presented to analyze the behavior of the combined wave and wind energy system. Statistical results on the tension developed on each tendon for different mooring configurations is also presented to study the import-ance of mooring and the influence of mooring system on the dynamic responses of the combined floater. The study performed will be helpful in the design and analysis of possible configurations of mooring lines support-ing the floating platform and improving the structural integrity of the combined floating concept. © 2022 the Author(s).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.