Faculty Publications
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Item Monitoring Harmful Algal Blooms in the Indian Ocean Region Using Satellite Remote Sensing Data(Institute of Electrical and Electronics Engineers Inc., 2023) Ramesh, N.V.K.; Spandana, A.P.; Sri, N.N.; Kumar, D.R.; Ratnam, D.V.; Vani, B.V.Nowadays, fishermen and other people dependent on marine life and seafood face severe problems due to HABs (harmful algal blooms). HABs are severely affecting climate change, fishermen, and the Indian economy in many ways. Therefore, detecting harmful algal blooms in various coastal regions is necessary to increase economic growth and save aquatic animal life. The present study summarizes the algal bloom events analysis reported in India during of January 2004, September 2004, March 2008, and March 2013. The detection of algal blooms in Asian Pacific Data Research Center(APDRC) using Chlorophyll, sea surface temperature of Moderate Resolution Imaging Spectroradiometer(MODIS) satellite data is considered for the significant algal blooms events that occurred over the Indian Ocean in January 2004, September 2004, March 2008, and March 2013. In addition, the corresponding zonal total surface currents from OSCAR satellite data are analysed to investigate the HAB characteristics. It is evident from the results that various factors for such algal blooms are based on the environmental factors prevalent during the blooms period. The outcome of this work would help understand the spatial and temporal variability of Algal blooms and for developing algal bloom detection and prediction algorithm using satellite and ground-based observations. © 2023 IEEE.Item Ocean wave transmission by submerged reef-A physical model study(2007) Shirlal, K.G.; Rao, S.; Rao, M.Ocean waves can be destructive as steeper waves due to their high energy eroding the sandy beaches. During storm surge or high tide, the water level rises and if large waves occur, they will break closer to the beach, releasing enormous amount of energy resulting in strong currents. This causes heavy loss of beach material due to large-scale erosion. If these waves are made to break prematurely and away from the beach, they can be attenuated so as to reduce beach erosion. The reef, which is a homogeneous pile of armour units without a core, breaks the steeper ocean waves, dissipates a major portion of their energy and transmits attenuated waves. This paper experimentally investigates the armour stone stability of the submerged reef and the influence of its varying distance from shore and crest width on ocean wave transmission. © 2007 Elsevier Ltd. All rights reserved.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 Evaluation of tidal stream energy at major tidal inlets of Goa, India(Taylor and Francis Ltd., 2022) Mendi, V.; Seelam, J.K.; Rao, S.An attempt has been made to identify promising sites for tidal stream energy assessment along the Goa coast on central west coast of India. A two-dimensional tidal-driven validated numerical model is used to assess the tidal stream velocities. The numerical model results are further used to estimate the tidal stream energy over the simulation period which would form a resourceful input for future to optimize locations of tidal energy farms. The locations of current maxima in each of the tidal driven regions have been identified and the energy is estimated thereof. This paper describes the tidal driven currents using a numerical model and their validation with measurements; and estimation of tidal stream energy among the different selected locations to choose the most feasible location for tidal energy extraction along Goa coast. © 2019 Indian Society for Hydraulics.Item 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 ASMEItem 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 LtdItem 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.Item 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.Item Parametric study on the effect of mooring configurations on the dynamic responses of the Septon semi-submersible 5 MW floating wind turbine(Springer Science and Business Media Deutschland GmbH, 2025) Sebastian, B.; Karmakar, D.; Rao, M.Offshore floating wind turbines (FWTs) offer a promising solution for harnessing wind energy in deep waters, where fixed-bottom turbines become impractical. Over the past decade, consistent advancements in technology have significantly reduced the levelized cost of energy, making large-scale deployment of FWTs increasingly feasible. The key factors influencing both cost and performance include the design and optimization of the substructure, mooring system, and power grid. The mooring system plays a pivotal role in ensuring platform stability and minimizing excessive motions that could impact the energy production efficiency and structural integrity of the FWT. The present study investigates the effects of different mooring configurations on the dynamic response of a novel semi-submersible wind turbine platform. This study analyzes two distinct mooring arrangements, spread mooring and cross-mooring, to determine the optimal configuration. The numerical investigation takes into account multiple parametric variations, including spread angle, cross angle, mooring line diameter, and line length, assessing their effects on platform motions and mooring line tensions. Numerical simulations are performed using an aero-hydro-servo-elastic simulation, which considers the coupled interactions of wind, waves, and structural components under various irregular sea states. This study reveals that the choice of mooring configuration significantly affects both platform stability and mooring line loads. A spread mooring system with a 30–60° divergence angle is identified as the optimal configuration for minimizing platform motions while keeping mooring tensions within safe operational limits. Conversely, cross-mooring configurations tend to exhibit higher tensions, particularly at larger cross angles. The cross-moorings require a minimum of 15–35 m additional mooring length compared to spread moorings for line tension to be within safe limits. The findings from the present study offer valuable insights into the optimal design of mooring systems for floating wind turbines, contributing to enhanced performance and reliability in deep water offshore wind farms. © The Author(s), under exclusive licence to Springer Nature Switzerland AG 2025.Item 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.