Faculty Publications
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Item Optimized design of collector topology for offshore wind farm based on ant colony optimization with multiple travelling salesman problem(Springer Heidelberg, 2018) Srikakulapu, R.; Vinatha Urundady, U.A layout of the offshore wind farm (OSWF) plays a vital role in its capital cost of installation. One of the major contributions in the installation cost is electrical collector system (ECS). ECS includes: submarine cables, number of wind turbines (WTs), offshore platforms etc. By considering the above mentioned problem having an optimized design of OSWF provides the better feasibility in terms of economic considerations. This paper explains the methodology for optimized designing of ECS. The proposed methodology is based on combined elitist ant colony optimization and multiple travelling salesman problem. The objective is to minimize the length of submarine cable connected between WTs and to minimize the wake loss in the wind farm in order to reduce the cost of cable and cable power loss. The methodology is applied on North Hoyle and Horns Rev OSWFs connected with 30 and 80 WTs respectively and the results are presented. © 2018, The Author(s).Item Design and simulation of quadrilateral relays in ac transmission lines with vsc-based hvdc systems under phase-to-ground fault condition(Politechnica University of Bucharest Splaiul Independentei 313 - Sector 6 Bucharest 77206, 2019) Muniappan, M.; Vittal, K.P.Voltage source converters (VSC)-based high voltage direct current (HVDC) transmission system can be used to integrate the offshore wind power generation with an AC grid. Due to the interconnection of VSC-HVDC system with the AC grid, an operation of distance relays might get affected. Also, fault resistance plays a significant role in the performance of ground relays. The ground faults have higher fault resistance causes the accuracy of the ground relay gets affected significantly. In this paper, the three-zone quadrilateral characteristic-based distance relay is designed to protect the AC transmission lines under phase-to-ground fault with fault resistance. Simulation studies are carried out to test the performance of the quadrilateral relay under phase-to-ground fault including various fault resistance cases in an AC transmission line with the effect of VSC-HVDC system. The impact of the dynamic conditions of the VSC-HVDC system on the performance of the quadrilateral relays under phase-to-ground fault with fault resistance cases is presented. Also, the performance comparison of the quadrilateral relay with the mho relay under such conditions is presented. © 2019, Politechnica University of Bucharest. All rights reserved.Item Performance Evaluation of Distance Relay in the Presence of Voltage Source Converters-Based HVDC Systems(Korean Institute of Electrical Engineers elecjour@kiee.or.kr, 2019) Muniappan, M.; Vittal, K.P.Voltage source converters (VSC)-based high voltage direct current (HVDC) link is an economical option for the long distance bulk power transmission, and it can be used to interconnect the offshore wind farms with an AC grid. Due to the penetration of VSC-HVDC system into the AC grid, the performance of the distance relay gets affected when a transmission line close to the point of common coupling (PCC) subjected to power system disturbances. In such condition, the PCC voltage is increased due to the VSC-HVDC control action, that causes the Zone-2 fault can be seen as a Zone-3 fault. As a result, the miscoordination of Zone-2 protection can occur in the distance relays. This paper presents both the analytical and simulation studies carried out on a VSC-HVDC system influence on the distance relay performance under fault conditions using PSCAD/EMTDC. Simulation results show that the presence of VSC-HVDC system greatly affects the performance of the Zone-2 and Zone-3 relay in an AC transmission line. Besides, the maloperation of the Zone-2 and Zone-3 relay is mitigated by varying the AC voltage reference input of the decoupled d-q controller of VSC-HVDC. Also, the effect of fault resistance on Zone-1 ground relay performance is analyzed. © 2019, The Korean Institute of Electrical Engineers.Item DC Fault Protection in Multi-terminal VSC-Based HVDC Transmission Systems with Current Limiting Reactors(Korean Institute of Electrical Engineers, 2019) Muniappan, M.; Vittal, K.P.Multi-terminal VSC-based HVDC transmission system is the recent interest for grid integration of large-scale offshore wind farms. Protection of multi-terminal voltage source converters (VSC)-based HVDC transmission systems against DC faults is challenging. This paper presents a single-ended protection scheme for DC faults in a three-terminal VSC-HVDC transmission system. The under-voltage criterion is used to distinguish the DC faults from the transient and normal conditions. The rate of change of DC voltage and current as well as the variation of transient energy is used to discriminate the internal faults from the external faults. The DC fault current has very high value within a few milliseconds during the transient phases such as the capacitor discharging and diode freewheeling stages. Therefore, current limiting reactors are introduced in series with the DC circuit breaker to maintain the DC fault current within the breaker capacity. The single-ended protection scheme is tested with the three-terminal VSC-HVDC transmission system with current limiting reactors for various DC fault conditions. The DC fault data is generated from PSCAD/EMTDC simulation and the protection scheme is tested in MATLAB environment. Test results show that the proposed protection scheme gives reliable protection for the DC faults in a three-terminal VSC-HVDC transmission system. © 2019, The Korean Institute of Electrical Engineers.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 Surface gravity wave scattering by multiple energy absorbing structures of variable horizontal porosity(Taylor and Francis Ltd., 2020) Venkateswarlu, V.; Praveen, P.; Karmakar, D.The oblique wave scattering by fully-extended two-layered, three-layered and submerged two-layered porous structures occupying finite width is reported using an analytical model based on the eigenfunction expansion method. The fully extended two-layered structure is composed of two porosities and friction factors in the surface porous layer and the bottom porous layer. In addition, the three-layered energy-absorbing structure is composed of two-porous layers along with the bottom rigid layer to replace the natural seabed variation. Further, the study is extended for multiple energy-absorbing structures to report the impact of free spacing available between the two subsequent structures on fluid resonance. The two-layered porous structure dispersion relation is derived and solved using step approach and Newton-Raphson method. The derived analytical results are validated with the published results of notable authors. The effect of the surface and bottom layers porosity, friction factor, free spacing, structural width, number of structures, and angle of contact on the wave scattering is reported. Finally, the comparative study between the single and multiple energy absorbing structures of multiple horizontal layers is discussed. Further, the significance of the critical angle of contact and fluid resonance for better wave blocking is presented precisely, which is essential for the coastal engineers to design offshore structures. © 2020 Japan Society of Civil Engineers.Item Laboratory investigation on hydraulic performance of enlarged pile head breakwater(Elsevier Ltd, 2020) Suvarna, P.S.; Hunasanahally Sathyanarayana, A.H.; Umesh, P.; Shirlal, K.G.Coastal erosion of beaches has been a common problem around the world. One of the eco-friendly control measures for coastal erosion is to dissipate the energy of waves impinging on the shores by constructing offshore breakwater. Pile breakwater is one such type of offshore breakwater that consists of a number of closely spaced piles. Construction of piles at closer spacing is highly challenging and expensive. This problem can be addressed by reducing the number of piles and modifying the pile with an enlarged head in the vicinity of the water surface, where wave energy is concentrated. In the present study, an experimental investigation on the hydraulic performance of enlarged pile head breakwater is conducted in a wave flume. The concept breakwater is subjected to monochromatic waves of varying wave heights, wave periods and water depth. The experimental results show that the least value of transmission coefficient is 0.62 and reflection coefficient is 0.123 with the highest value of dissipation coefficient of 0.77 for the structural configuration of b/D ratio of 0.2, D/Hmax of 0.6 and Y/Hmax of 1.0 at a water depth of 0.3 m. Observed results are encouraging and are in line with the similar type of pile breakwaters in a single row. The present experimental data is also validated with the available theoretical solutions. Since the results from the compared theoretical solution are not in good agreement, a hybrid theoretical model is reconstructed based on experimental results of pile head breakwater. The proposed modified version of the hybrid equation predicts encouragingly better transmission, reflection and dissipation coefficient than the existing solutions. Moreover, the results predicted by the proposed hybrid equation are in good agreement with that of other similar pile breakwater models. © 2020 Elsevier LtdItem Numerical investigation on the wave dissipating performance due to multiple porous structures(Taylor and Francis Ltd., 2021) Venkateswarlu, V.; Karmakar, D.Gravity wave interaction with porous structures is investigated under the assumption of linearized wave theory. Multiple porous blocks of finite thickness with finite spacing are investigated under the action of oblique ocean waves considering leeward unbounded region and confined region. The eigenfunction expansion method is employed to analyse the effect of multiple-confined regions in the trapping of oblique waves. The study outcomes are validated with numerical and experimental results available in the literature. The friction factor and the inertia effect of the porous medium are considered and different porosity conditions are adopted to determine the wave reflection coefficient, transmission coefficient, wave dissipation and wave force impact on the leeward wall. The functional efficiency of multiple fully extended porous structures is studied for different values of porosity, water chamber length, angle of incidence, friction factor and spacing between the porous blocks. The seabed is assumed to be uniform impermeable bottom and uneven bottom (step approximation is adopted). The study demonstrates that the better wave blocking is achieved with the increase in the series of porous structures and the confined regions can be used effectively for the trapping of oblique waves. The present study will be helpful in the design of porous structures for security of coastal facilities and coastal structures in offshore environment. © 2019 Indian Society for Hydraulics.Item 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.Item Finite element modeling and experimental validation of rectangular pin buckle arrestors for offshore pipelines(Taylor and Francis Ltd., 2022) Rao, N.R.; Kaliveeran, V.Finite element modeling was performed, and experiments were conducted on pipeline models made of stainless steel of grade SS304. Present research work focuses on the improvement in structural properties of offshore pipelines stiffened with rectangular pin buckle arrestors by varying length and placing them at different locations along the length of pipeline. The optimum length of buckle arrestors was identified from finite element analysis and pipeline models were fabricated for conducting buckling experiments. Bending experiments were conducted on the pipeline models to determine flexural capacity of the pipeline models. Finite element analysis results showed good agreement with experimental results. © 2020 Taylor & Francis Group, LLC.