Faculty Publications

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Author: search.filters.author.Karmakar, D.Subject: search.filters.subject.Wave energy conversion

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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
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    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.
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    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.
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    Performance of a hybrid TLP floating wind turbine combined with arrays of heaving point absorbers
    (Elsevier Ltd, 2023) Rony, J.S.; Karmakar, D.
    In the present study, the hydrodynamic performance of circular and concentric arrangements of cone-cylinder-type heaving point absorbers around a Submerged Tension-Leg Platform (STLP) is analysed using the numerical model in the frequency domain based on the potential flow theory. The presence of the Wave Energy Converters (WECs) around the STLP floating wind turbine platform affects the hydrodynamic performance of the hybrid floating platform. So to illustrate the effects of WECs on the platform, the ratio of hydrodynamic coefficients for a single WEC system to that for a hybrid system is analysed. An array of heaving point absorbers is placed in circular and concentric patterns to understand the performance of heaving point absorbers in the absorption of wave energy. The cone-cylinder type heaving point absorber is selected for the present study as they yield more power as compared to other shaped point absorbers. The study compares the wave power absorption of each point absorber around the platform for irregular wave conditions of the North Sea. The effect of incoming waves is illustrated by analysing four different wave heading angles. To quantify the performance of the WECs in an array, the q-factor and coefficient of variation are studied for each array at different sea states. The study suggested the best possible arrangement pattern for wave power absorption and power uniformity among the floaters in the array. The study performed will be helpful in the design and analysis of the possible arrangement of point absorbers around the floating wind turbine platform for wave power absorption. © 2023 Elsevier Ltd
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    Numerical investigation of Edinburgh Duck wave energy converter integrated with floating breakwaters
    (Springer Nature, 2023) Vidyabhushan, R.R.; Karmakar, D.
    Hydrodynamic performance of hybrid floating structures consisting of Edinburgh Duck Wave Energy Converter (ED-WEC) integrated to different shapes of Floating Breakwaters (FBW) namely (i) box-type FBW, (ii) trapezoidal-type FBW, (iii) π -type FBW, (iv) parabolic-type FBW and (v) semi-circular-type FBW are investigated based on small amplitude wave theory. The study is performed on the harvesting of wave energy and increasing the wave power absorption from the scattered and the reflected waves due to the presence of oceanic structures integrated with WEC. The hydrodynamic analysis for the hybrid floating breakwater-WEC system is analysed using Ansys AQWA. The associated diffractions and motions of the hybrid floating breakwater-WEC system are examined. The motion responses and resulting wave forces for the heave motion of ED-WEC with different parameters such as width of ED, draft of ED, distance between ED-WEC and floating breakwater and angle of incident are investigated. Further, the study is carried out for isolated ED-WEC and isolated breakwaters. The study performed will help in developing an efficient and reliable form of device for harnessing maximum wave energy into electricity along with the breakwater having practical application of ED-WEC at the initial stages of design. The study will provide a potential solution of generating power from the wave energy and as a coastal defence structure with the presence of floating breakwaters. © 2023, The Author(s), under exclusive licence to Sociedade Brasileira de Engenharia Naval.
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    Numerical investigation of offshore wind turbine combined with wave energy converter
    (Springer Nature, 2023) Rony, J.S.; Sai, K.C.; Karmakar, D.
    The coupled dynamic analysis is performed for three different types of offshore floating platforms combined with a wave energy converter (WEC) mounting a 5-MW NREL (National Renewable Energy Laboratory) wind turbine. The Response Amplitude Operators (RAOs) are analysed for the three concepts of combined wind and wave energy platforms for different wind and wave conditions. The hydrodynamic performance for the three different platforms is conducted considering different load cases. The time domain aero-servo-hydro-elastic tool is used to study the motion responses of the combined system under real operational conditions. The platform’s responses are observed to increase with the increase in the wind speed. In the case of floating hybrid platform, surge responses are minimal for the hybrid spar-tours combination for any load case condition. Minimum surge and sway ensure higher wind power absorption. The study further focuses on the tower base forces and moments to study the impact of wind and waves on the combined floater. Fore-aft shear forces and fore-aft bending moments are higher for the platforms indicating the importance of wind-wave loading. The time domain responses are further used as the transfer function to predict the most probable maximum values of motion amplitude expected to occur during the life-time of the structure which can be used for designing a floating wind turbine (FWT) against overturning in high waves. The long-term models are constructed using various short-term situations expected to occur during the structure’s life-time and weighing them appropriately. The long-term distribution uses North Atlantic wave data, and short-term responses are calculated considering Rayleigh distribution. A brief comparative study of the three combined offshore floaters is performed to understand the structural integrity, power performance and dynamic motions of the floating wind energy platform combined with WECs. © 2023, The Author(s), under exclusive licence to Sociedade Brasileira de Engenharia Naval.
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    Hydrodynamic performance of wave energy converter integrated with pile restrained floating structure near a partially reflecting seawall
    (Elsevier Ltd, 2023) Patil, S.B.; Karmakar, D.
    The integration of a Wave Energy Converter (WEC) with a Pile-Restrained Rectangular Floating Breakwater (PRFB) in the presence of a partially reflecting vertical seawall is analysed to enhance the hydrodynamic performance and WEC efficiency of the integrated breakwater-WEC device based on small amplitude wave theory using the Boundary Element Method (BEM). The rectangular floating breakwater is designed to have heave motion with a pile-restrained floating structure placed in a position to attenuate the incoming wave in the transmitted region and the linear power take-off (PTO) damping is employed to calculate the absorbed power. The study is performed to understand the effectiveness of wave energy conversion and its hydrodynamic performance due to changes in the seawall's porosity, relative structural width, relative structural draft, wave energy conversion power take-off damping coefficients, and the relative gap of the WEC integrated with PRFB from the seawall. The study demonstrated that in the presence of a fully reflecting seawall, the wave energy extraction is enhanced for the integrated WEC system without compromising the defined threshold wave reflection coefficient but at the expense of a constrained range of wavenumbers that correspond near the system's fundamental natural frequency. Moreover, the capture width ratio is noted to be higher for relatively smaller structural drafts, while the wave reflection coefficient shows precisely the reverse trend. However, under such circumstances, the integrated WEC system operates as a motion-trapping structure, especially when the reflection coefficient of the seawall, CR≥0.75. Thus, the present study will assist the designer in determining the appropriate degrees of efficiency of the WEC device without sacrificing hydrodynamic performance by fine-tuning the hybrid floating breakwater system's geometrical parameters. © 2023 Elsevier Ltd
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    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.
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    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.
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    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.