Browsing by Author "KARMAKAR, DEBABRATA"

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Dynamic Analysis of Offshore Floating Wind Turbine Combined with Wave Energy Converter
(National Institute of Technology Karnataka, Surathkal, 2024) J. S, RONY; KARMAKAR, DEBABRATA
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) and Frustum Tension-Leg Platform (FTLP) 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. The study analyses the responses of the combined system to understand the influence of the WECs on the STLP and FTLP platforms for various operating conditions of the wind turbine under regular and irregular waves. The platform responses are analysed for the North Atlantic wave region. A positive synergy is observed between the platform and the WECs, and the study 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. Further, the hydrodynamic performance of circular and concentric arrangements of cone-cylinder-type heaving WECs around STLP and FTLP is analysed. The influence of the hydrodynamic coefficients is analysed by determining the ratio of the hydrodynamic coefficients for a single WEC system to those for a hybrid system. The study analyses the instantaneous wave power absorbed and the wave power under the influence of PTO for the WECs arranged around the TLP floaters. The rigid body analysis observed reduced motion response for the STLP+6WECs and FTLP+8WECs configurations. The dynamic responses of the hybrid platforms for different mooring layouts are studied for different met ocean 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 different mooring configurations. Further, the most probable values of the motion amplitudes are calculated using long-term response analysis for the hybrid wave and wind energy system. The long-term distribution is performed using the short-term responses based on Rayleigh distribution and North Atlantic wave data. The transfer function for the long-term analysis of the floater is obtained using the numerical simulation tool FAST. The analysis is performed for zero-degree wave heading angle and different operational conditions of the wind turbine. Thereafter, the reliability of hybrid floating wind turbine platforms against extreme loads is established using the Inverse First Order Reliability Method (IFORM) which includes the randomness in the gross wind environment and the extreme response given wind conditions. The maximum values of the responses for both 1-D and 2-D models are studied and compared. The probability of the exceedance of the responses (Surge, sway, and yaw) for the platforms is studied for different return periods. The study suggests 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 combined wave and wind energy device for wave power absorption.
Hydrodynamic Performance of Submerged Tandem Breakwaters and Integrated Hybrid Floating Structures
(National Institute of Technology Karnataka, Surathkal, 2024) PATIL, SHIVAKUMAR B.; KARMAKAR, DEBABRATA
In the present study, the gravity wave interaction with submerged tandem breakwater of different structural configurations and integrated hybrid Floating structures are investigated based on the small-amplitude wave theory. The boundary value problem is analysed in two- dimension using Multi-Domain Boundary Element Method (MDBEM) considering the linearized wave theory in finite water depth. The wave transformation characteristics, wave forces and wave energy dissipation are analysed with and without the presence as reef structure in front of the primary submerged breakwater. The comparative study is performed for the submerged tandem breakwaters 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 induced force, wave reflection, transmission and energy dissipation characteristics are derived for the suggested submerged breakwater and tandem breakwater models. In case of floating structures, the hydrodynamic characteristics of Fixed Floating Structure (FFS) of various configurations such as Rectangular Fixed Floating Structures (RFFS) and Trapezoidal Fixed Floating Structures (TFFS) coupled with submerged breakwaters of two different shapes namely, rectangular breakwater (RBW) and trapezoidal breakwater (TBW) are investigated for the variation in physical parameters such as a change in structural parameters of the submerged breakwater (shape, relative submergence depth, relative crest width, and structural porosity), structural parameters of FFS (shape and structural width), wave parameter (angle of incidence) and relative spacing between the FFS and submerged breakwater. Furthermore, three typical Submerged Floating Tunnel (SFT) cross-sections (rectangular, trapezoidal, and circular) of equal area and structural height in the presence of submerged rubble mound breakwater (SRMB) under similar operating conditions are investigated as comparative study to investigate the influence of SFT shape on hydrodynamic performance. Further, in the case of Wave Energy Converter (WEC) integrated into a Pile-Restrained rectangular Floating Breakwater (PRFB) in presence of a partially reflecting vertical seawall is analysed for scattering and radiation problems under a framework of small amplitude linear wave theory using the Boundary Element Method (BEM). The linear power take-off (PTO) damping is employed to calculate the absorbed power, while the rectangular floating breakwater is designed to heave with pile restrained in position. In addition, on assuming only iv a small amount of sloshing within the tank of the hybrid floating breakwater (within the application scope of linear potential wave theory), the WEC capabilities and the hydrodynamic coefficients (wave reflection and transmission coefficients) were estimated for a certain range of excitation frequencies with the help of numerical and experimental investigations. The study on the submerged tandem breakwater structure and floating structures illustrates that the presence of the reef like structure decreases aids in lowering the wave stresses inflicted on the primary breakwaters and aids in optimum wave transformations. On the other hand, studies on WEC integrated with structures can assist the designer to determine the appropriate degrees of efficiency of the WEC device without sacrificing the hydrodynamic performance by fine- tuning the system's geometrical parameters.