Browsing by Author "Karmakar, D."

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Coupled Dynamic Analysis of Hybrid Offshore Wind Turbine and Wave Energy Converter
(American Society of Mechanical Engineers (ASME), 2022) Rony, J.S.; Karmakar, D.
The combined offshore wind and wave energy on an integrated platform is an economical solution for the offshore energy industry as they share the infrastructure and ocean space. The study presents the dynamic analysis of the Submerged Tension-Leg Platform (STLP) combined with a heaving-type point absorber wave energy converter (WEC). The feasibility study of the hybrid concept is performed using the aero-servo-hydro-elastic simulation tool FAST. The study analyzes the responses of the combined system to understand the influence of the WECs on the STLP platform for various operating conditions of the wind turbine under regular and irregular waves. Positive synergy is observed between the platform and the WECs, and the study also focuses on the forces and moments developed at the interface of the tower and platform to understand the effect of wind energy on the turbine tower and the importance of motion amplitudes on the performance of the combined platform system. The mean and standard deviation for the translation and rotational motions of combined wind and wave energy converters are determined for different sea states under both regular and irregular waves to analyze the change in responses of the structure. The study observed a reduction in motion amplitudes of the hybrid floating system with the addition of the wave energy converters around the STLP floater to improve the energy efficiency of the hybrid system. The study helps in understanding the best possible arrangement of point absorber-type wave energy converters at the conceptual stage of the design process. © © 2021 by ASME
Coupled dynamic analysis of hybrid STLP-WEC offshore floating wind turbine with different mooring configurations
(Springer Science and Business Media Deutschland GmbH, 2023) Rony, J.S.; Karmakar, D.
The novel concept of six cone-cylinder-shaped point absorbers around the submerged tension leg platform (STLP) in a circular pattern is studied considering the STLP fixed in position using tensioned mooring cables. The hybrid floating platform consisting of offshore wind turbine platform with a wave energy converter (WEC) reduces the overall logistic cost and eases the transportation process. The stability and safety of the hybrid floating concept depend significantly on the integrity of the tensioned tendons. The present study proposes four different mooring configurations (four, five, eight and nine) to stabilize the hybrid STLP-WEC floater. The numerical simulation in the time domain is performed using the aero-servo-hydro-elastic simulation. The time histories and the motion response spectrums of the surge, sway, heave, roll, pitch and yaw motion of the hybrid system for each mooring configuration are analyzed to study the behaviour of the hybrid system under irregular wave conditions. The time history and spectrum of the generator power are analysed to observe the effect of second-order wave load and turbulent wind loads on the power production of the hybrid floater under each mooring configuration. Further, the study is performed to determine the forces and moments developed at the base of the floating wind turbine to analyze the impact of wind load on the responses of the hybrid floater. The study also analyses the tension developed on each tendon for different mooring configurations and reports the importance of mooring and the influence of the mooring system on the dynamic responses of the combined floater. © 2023, The Author(s), under exclusive licence to Springer Nature Switzerland AG.
Coupled dynamic analysis of semi-submersible floating wind turbine integrated with oscillating water column WEC
(Springer Science and Business Media Deutschland GmbH, 2024) Sebastian, B.; Karmakar, D.; Rao, M.
The present study envisages to investigate the coupled dynamic behaviour of three configurations of a hybrid wind-wave energy system integrating Oscillating Water Column (OWC) wave energy converters to DeepCwind semi-submersible supporting an NREL (National Renewable Energy Laboratory) 5 MW wind turbine. DeepCwind semi-submersible is a platform designed specifically for the purpose of supporting floating offshore wind turbines and the stability of the platform has been well confirmed by scaled-down experiments and numerical studies. The numerical simulation for the present study is performed using the aero-hydro-servo-elastic tool OpenFAST. The dynamic responses of the hybrid platforms are determined for different operational and parked wind speed conditions of the wind turbine in irregular waves. The motion responses, tower base forces and moments, mooring tensions and power absorption of the hybrid configurations have been characterized. Furthermore, the effect of coupling between the semi-submersible platform and the OWCs is studied by comparing the results of the combined platforms with that of the uncoupled wind energy platform. The coupled dynamic analysis in the time domain shows that increasing the number of OWC helps to reduce the motion responses in heave and pitch. The capture width ratio of the system is observed to be highest for hybrid configuration with a single OWC device. The present study will be helpful in the design and analysis of hybrid floating wave-wind energy platform. © The Author(s), under exclusive licence to Springer Nature Switzerland AG 2024.
Coupled dynamic analysis of spar-type floating wind turbine under different wind and wave loading
(Springer Science and Business Media Deutschland GmbH, 2021) Rony, J.S.; Karmakar, D.; Guedes Soares, C.G.
In the present study, the coupled dynamic modelling of three different configurations of spar platform is performed using time-domain aero-servo-hydro-elastic simulation. The spar platforms are coupled with 5 MW NREL floating wind turbine and mooring sub-models. The coupled aero-servo-hydro-elastic simulation is performed using the simulation tool FAST with WAMIT as the sub module to obtain frequency domain hydrodynamic characteristics. The major emphasis is given to analyse the Response Amplitude Operators (RAOs) to understand the stability of the structures. The responses are calculated for surge, sway, heave, roll, pitch and yaw motions. The study determines the performance of the structure under the wind load developed for the turbine support structure on analysing the tower base forces and moments. The analysis for three different configurations of spar platform is performed for various environmental conditions of North Sea. The studies observed that the responses of the platforms tend to increase with increase in wind speed and wave height. Further, it is observed that surge and pitch motion is dominant for all the three configurations of spar platform. The present study provides an insight into the power performance, structural integrity and dynamic motions of the floating wind turbine under various operational and survival conditions which help the designers to develop better design standards. © 2021, Sociedade Brasileira de Engenharia Naval.
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.
Dynamic analysis of a semi-submersible offshore floating wind turbine combined with wave energy converters
(Taylor and Francis Ltd., 2025) Sebastian, B.; Karmakar, D.; Rao, M.
Hybrid wind–wave energy systems harness both offshore wind and wave energy resources using a shared floating platform, reducing capital and operational costs through common infrastructure. The present study numerically investigates the dynamic performance and power absorption of three hybrid concepts combining the DeepCwind Semi-submersible Platform (SSP) with (i) Oscillating Water Columns (OWC), (ii) Torus Wave Energy Converter (WEC), and (iii) Flap-type WEC. Frequency-domain analyses using WAMIT and time-domain simulations using OpenFAST are performed to assess platform motions, tower base moments, mooring tensions, and WEC power output for different sea states. The integration of WECs significantly improves the hydrodynamic behaviour of the DeepCwind SSP. Flap-type WECs demonstrate the best dynamic performance, reducing heave and pitch by up to 68% and 58%, and mooring tension by 54%. The OWC system achieves the highest power absorption and a 55% capture width ratio, but increases surge and pitch motions by 6% and 27%, respectively, on introducing additional loads on the system. © 2025 Informa UK Limited, trading as Taylor & Francis Group.
Dynamic analysis of a TLP-type floating wind turbine combined with OWC wave energy converter
(Springer Nature, 2025) Sebastian, B.; Joju, A.; Karmakar, D.
The present study examines the dynamic effects of integrating oscillating water column wave energy converters on the offset columns of a tension leg floating wind turbine platform in an asymmetric and symmetric configuration. Two configurations are considered, featuring two and four oscillating water columns combined with the tension leg platform supporting a 5 MW wind turbine. The hydrodynamic analysis of the combined wind-wave energy system uses a linear diffraction-radiation tool to compute hydrodynamic coefficients and wave excitation forces in the frequency domain. The coupled dynamic responses of the hybrid platforms are evaluated in the time domain under various irregular sea states, using an aero-hydro-servo-elastic simulation tool. The performance of the hybrid systems is compared with a baseline floating wind turbine platform to quantify changes in dynamic responses. Power absorption of the oscillating water columns is computed using a linear power take-off system. The findings indicate that adding oscillating water columns leads to a slight increase in the heave and pitch motions of the platform. The system with a diagonally placed two-oscillating water column configuration demonstrates higher efficiency, achieving a maximum capture width ratio of 57%. This study provides valuable insights into the feasibility of hybrid offshore renewable energy concepts. It supports the design and implementation of integrated wind-wave systems to deliver clean and sustainable energy. © The Author(s), under exclusive licence to Sociedade Brasileira de Engenharia Naval 2025.
Dynamic analysis of different configurations of offshore floating wind turbine
(2018) Daranikota, A.; Karmakar, D.
The dynamic response of different types of spar and semi-submersible type floating offshore wind turbines are investigated subjected to wave and wind loads in operational conditions. The study is performed for the NREL 5MW wind turbine supported on spar and semi-submersible platforms. The study includes the analysis on the wave interaction with supporting structure and determination of the time-domain dynamic response of offshore floating wind turbine. The hydrodynamic coefficients added mass, damping, excitation forces and Response Amplitude Operators (RAOs) of the different motions of the floating platform are analyzed for different wave heading angles. The coupled dynamic analysis is performed for both regular and irregular waves and the coupled response of platform motions, tower base forces and moments for different wave and wind load conditions is analysed. The present study focuses on the overall performance of the different types of spar and semi-submersible type offshore floating wind turbines. � 2018 World Scientific Publishing Co. Pte. Ltd.
Dynamic analysis of different configurations of offshore floating wind turbine
(World Scientific, 2018) Daranikota, A.; Karmakar, D.
The dynamic response of different types of spar and semi-submersible type floating offshore wind turbines are investigated subjected to wave and wind loads in operational conditions. The study is performed for the NREL 5MW wind turbine supported on spar and semi-submersible platforms. The study includes the analysis on the wave interaction with supporting structure and determination of the time-domain dynamic response of offshore floating wind turbine. The hydrodynamic coefficients added mass, damping, excitation forces and Response Amplitude Operators (RAOs) of the different motions of the floating platform are analyzed for different wave heading angles. The coupled dynamic analysis is performed for both regular and irregular waves and the coupled response of platform motions, tower base forces and moments for different wave and wind load conditions is analysed. The present study focuses on the overall performance of the different types of spar and semi-submersible type offshore floating wind turbines. Â© 2018 World Scientific Publishing Co. Pte. Ltd.
Dynamic analysis of frustum TLP-type wind turbine multi-purpose floating platform
(Taylor and Francis Ltd., 2024) Rony, J.S.; Karmakar, D.
The coupled dynamic analysis of a hexagon-shaped Frustum Tension-leg platform (FTLP) combined with wave energy converters (WECs) supporting a 5-MW wind turbine is performed to analyse the dynamic responses of the hybrid system. The responses of the FTLP are investigated using the time-domain numerical simulation for the operational sea-states of the wind turbine. The FTLP is integrated with an array of point absorber-type WECs in a circular pattern to analyse the influence of the WECs on the dynamic responses of the floating platform. The aero-servo-hydro-elastic simulation tool FAST and hydrodynamic simulation tool WAMIT is used to study the rigid body motions of the system. The study observes higher rigid body motions in the surge, sway and yaw directions for the hybrid system. Further, the investigation is performed for the forces and moments developed at the base of the wind turbine and the tension developed on mooring cables to understand the integrity and stability of the hybrid platform. © 2023 Informa UK Limited, trading as Taylor & Francis Group.
Dynamic analysis of submerged tension leg platform combined with wave energy converters for different mooring configuration
(American Institute of Physics Inc., 2023) Rony, J.S.; Karmakar, D.
In the present study floating wind turbine combined with a wave energy converter is analysed deriving both wind and wave energy, and thus ensuring continuous supply of energy. The study combines a submerged tension leg platform (STLP) with heaving type point absorber wave energy converter (WEC). Submerged tension leg platform is stable in both transportation phase and operational phase. The point absorber WEC has a floater system having diameter smaller than the incident wave length. The floater tends to oscillate in one or more degrees of freedom (DOF) and absorbs energy by damping the floater motion and converting it into electrical energy. The study combines STLP floater with six wave energy converters in circular pattern. The time domain simulation is performed for the combined platform configuration using fully coupled aero-hydro-servo-elastic simulation tool FAST developed by NREL for different mooring line configuration. The analysis is performed to study the responses (surge, sway, heave, roll, pitch, yaw) for the combined configuration for wind and wave load conditions corresponding to North Atlantic Ocean. The tower base bending moment, shear force and the tension developed on the mooring lines of the combined platform is analysed along with the responses of the floating combined energy platform. The study performed is expected to provide an insight into the dynamic motions and structural integrity of the floating wind and wave concept under different survival conditions helping the designers to develop better design standards. Â© 2023 Author(s).
Dynamic analysis of submerged TLP wind turbine combined with heaving wave energy converter
(CRC Press/Balkema, 2021) Rony, J.S.; Karmakar, D.; Guedes Soares, C.G.
A submerged tension-leg-platform for offshore wind turbine combined with a heaving type point absorber wave energy converter is analysed considering different configurations of array of wave energy converters. A time domain simulation is performed for the combined platform using fully coupled aero-hydro-servo-elastic simulation. The analysis is performed to study the effect of different combinations of wave energy converters on the responses of the proposed system. The responses considered for the study include the six degrees of motion along with tower base bending moment and shear force of the combined wind and wave energy platform. The study will provide an insight into the dynamic motions of the floating wind and wave concept under operating condition, which will help the designers to develop better design standards. Â© 2021 the Author(s).
Dynamic behaviour and power performance of a Septon semisubmersible floating wind turbine integrated with wave energy converters
(Nature Research, 2025) Sebastian, B.; Karmakar, D.; Rao, M.
The development of renewable energy sources is inevitable to create a sustainable society for the future. Hybrid wind and wave energy systems are highly regarded as a solution to reduce the cost of energy from offshore wind and waves. The manuscript presents a novel semi-submersible floating wind platform referred to as Septon which is designed with the intention of hosting a multitude of wave energy devices in addition to a wind turbine. Three different wave energy converters (WEC) namely oscillating water column, Torus and point absorber along with their combinations with the Septon platform are considered in the study to understand the dynamic behaviour and power absorption of standalone and integrated configuration. Seven different configurations of the hybrid system are considered for the analysis. Coupled dynamic analysis is performed using an aero-hydro-servo-elastic tool based on boundary element method to analyze the responses of the hybrid platforms under realistic sea states. The motion responses, tower base moments, mooring tensions and power absorption of the hybrid systems are analyzed and compared with the Septon floating wind platform to quantify the effect of various combination of WECs around the wind turbine platform. The numerical results shows that different combinations have a significant impact on the dynamic responses of the platform. The study identifies the hybrid system combining OWC and Torus with the proposed Septon platform as the concept with maximum efficiency in power absorption. © The Author(s) 2025.
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.
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).
Effect of seabed condition on the hydrodynamic performance of a pile-restrained H-shaped floating breakwater
(Taylor and Francis Ltd., 2025) Panda, A.; Karmakar, D.; Rao, M.
The present study investigates the hydrodynamic analysis of pile-restrained H-shaped porous breakwater for various seabed conditions using the small amplitude wave theory. The Multi-Domain Boundary Element Method (MDBEM) is employed to investigate the influence of parametric variations on the hydrodynamic coefficients and horizontal wave force under normal and oblique incident waves. The numerical accuracy is ensured by comparing it with the available literature. The numerical investigation on the hydrodynamic performance of the H-shaped breakwater is performed for various seabed configurations considering different angles of slope, the width of slope/step/obstacle, step height, number of steps, soil permeability, angle of wave incidence, the width of flange and submergence draft of the web of the H-shaped structure. The findings indicate that the seabed undulation has a higher wave impact on the breakwater than the horizontal seabed. In addition, the study suggests that the sloped seabed is preferable in deeper water depths to reflect waves efficiently and the seabed permeability can affect the hydrodynamic coefficients in shallow and intermediate water depths. The study performed on the H-shaped breakwater for varying seabed topography will be helpful in the design and construction of a suitable H-shaped breakwater for an effective wave absorber in coastal regions. © 2025 Informa UK Limited, trading as Taylor & Francis Group.
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
Exploring the Potential of Kite-Based Wind Power Generation: An Emulation-Based Approach
(Multidisciplinary Digital Publishing Institute (MDPI), 2023) Castelino, R.V.; Kumar, P.; Kashyap, Y.; Karthikeyan, A.; Sharma K, M.; Karmakar, D.; Kosmopoulos, P.
A Kite-based Airborne Wind Energy Conversion System (KAWECS) works by harnessing the kinetic energy from the wind and converting it into electric power. The study of the dynamics of KAWECS is fundamental in researching and developing a commercial-scale KAWECS. Testing an actual KAWECS in a location with suitable wind conditions is only sometimes a trusted method for conducting research. A KAWECS emulator was developed based on a Permanent Magnet Synchronous Machine (PMSM) drive coupled with a generator to mimic the kite’s behaviour in wind conditions. Using MATLAB-SIMULINK, three different power ratings of 1 kW, 10 kW, and 100 kW systems were designed with a kite surface area of 2.5 m (Formula presented.), 14 m (Formula presented.), and 60 m (Formula presented.), respectively. The reel-out speed of the tether, tether force, traction power, drum speed, and drum torque were analysed for a wind speed range of 2 m/s to 12.25 m/s. The satellite wind speed data at 10 m and 50 m above ground with field data of the kite’s figure-of-eight trajectories were used to emulate the kite’s characteristics. The results of this study will promote the use of KAWECS, which can provide reliable and seamless energy flow, enriching wind energy exploitation under various installation environments. © 2023 by the authors.
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).
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 ASME