Browsing by Author "Vijay, K.G."

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Experimental study on liquid sloshing with dual vertical porous baffles in a sway excited tank
(Techno-Press, 2021) Sahaj, K.V.; Nasar, T.; Vijay, K.G.
Sloshing behavior of liquid within containers represents one of the most fundamental fluid-structure interactions. Liquid in partially filled tanks tends to slosh when subjected to external disturbances. Sloshing is a vicious resonant fluid motion in a moving tank. To understand the effect of baffle positioned at L/3 and 2L/3 location, a shake table experiments was conducted for different fill volumes of aspect ratio 0.163, 0.325 and 0.488. For a fixed amplitude of 7.5 mm, the excitation frequencies are varied between 0.457 Hz to 1.976 Hz. Wave probes have been located at both tank ends to capture the surface elevation. The experimental parameters such as sloshing oscillation and energy dissipation are discussed here. Comparison is done for with baffles and without baffles conditions. For both conditions, the results showed that aspect ratio of 0.163 gives better surface elevation and energy dissipation than obtained for aspect ratio 0.325 and 0.488. Good agreement is observed when numerical analysis is compared with the experiments results. © 2021 Techno-Press, Ltd
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.
Oblique wave interaction with a two-layer pile-rock breakwater placed on elevated bottom
(Taylor and Francis Ltd., 2022) Venkateswarlu, V.; Praveen, K.M.; Vijay, K.G.; Anil, K.; Karmakar, D.
The two-layer pile-rock porous breakwater consisting of the upper porous layer, middle porous layer placed over the bottom rigid layer (elevated bottom) is proposed as an active wave absorber for significant wave damping and wave trapping. The two-layer rock core is placed between the two thin porous barriers (piles), and the thin barriers/ piles are useful to reduce the wave force experienced by active two-layered breakwater. The eigenfunction expansion method is used to analyse the physical problem on considering the continuity in fluid velocity and pressure along with mode-coupling relation based on classical linearised potential flow theory. The developed analytical model is validated with the available results and then various hydrodynamic characteristics such as wave reflection, transmission, damping, wave forces on seaward, leeward barriers and wave force experienced by the vertical cliff are presented. The porosity of surface layer shows an effective role in reducing the harmonic oscillatory pattern in the hydrodynamic quantities, and the study suggests the higher surface layer porosity (Formula presented.) as compared with bottom layer porosity for optimal wave damping. © 2021 Informa UK Limited, trading as Taylor & Francis Group.
Performance of barge-type floaters for floating wind turbine
(2016) Vijay, K.G.; Karmakar, D.; Uzunoglu, E.; Guedes, Soares, C.
The hydrodynamic performance of barge-type floaters for floating wind turbine is analysed with and without moonpool. In the case of barge-type floaters with moonpool, the effect of moonpool sizes and its effects on the coupled dynamics of floater motions with waves and winds are studied and presented. The moonpool can be used as floating oscillating water column. The piston mode and sloshing mode are studied for the floaters with moonpool. The analysis is carried out for the floater�s motion responses in both regular and irregular waves. The wind turbine is positioned at the centre of the floater in all of the case studies. The numerical study on the coupled dynamic response of the barge-type floaters with the wind turbine support structure is conducted using aero-servo-hydroelastic simulation. The platform motion responses along with the power spectral density of the motion characteristics are analysed. � 2016 Taylor & Francis Group, London.
Performance of barge-type floaters for floating wind turbine
(CRC Press/Balkema http://Pub.NL@taylorandfrancis.com, 2016) Vijay, K.G.; Karmakar, D.; Uzunoglu, E.; Guedes Soares, C.
The hydrodynamic performance of barge-type floaters for floating wind turbine is analysed with and without moonpool. In the case of barge-type floaters with moonpool, the effect of moonpool sizes and its effects on the coupled dynamics of floater motions with waves and winds are studied and presented. The moonpool can be used as floating oscillating water column. The piston mode and sloshing mode are studied for the floaters with moonpool. The analysis is carried out for the floaterâ€™s motion responses in both regular and irregular waves. The wind turbine is positioned at the centre of the floater in all of the case studies. The numerical study on the coupled dynamic response of the barge-type floaters with the wind turbine support structure is conducted using aero-servo-hydroelastic simulation. The platform motion responses along with the power spectral density of the motion characteristics are analysed. Â© 2016 Taylor & Francis Group, London.
Scattering of Gravity Waves by Multiple Submerged Rubble-Mound Breakwaters
(Springer Science and Business Media Deutschland GmbH info@springer-sbm.com, 2020) Vijay, K.G.; Venkateswarlu, V.; Karmakar, D.
A numerical model based on multi-domain is developed to investigate the scattering of surface gravity waves by an array of submerged rubble-mound breakwaters. The boundary value problem is analysed in two dimensions under the assumption of small-amplitude wave theory in the water of finite depth. Analytical solution based on the eigenfunction expansion method is independently developed to validate the numerical model in addition to available results in the literature. Various configurations such as trapezoidal, triangular, and circular shapes are investigated parametrically. The performance characteristics are discussed by analysing the scattering coefficients (such as reflection, transmission, and damping coefficient) for different physical parameters like relative water depth, relative structural dimensions, relative spacing, and the number of submerged breakwaters. In the case of trapezoidal breakwaters, the crest width plays a major role in dampening the wave energy by a whopping 90%. Moreover, the wave damping performance of triangular breakwaters is very poor. The Bragg resonant reflection is observed to be a trivariate function, which depends on structural porosity, structural thickness, and the number of submerged breakwaters. The free spacing is evident in adjusting the position of Bragg resonant reflection by multiple equi-spaced structures of several shapes. The present study will be useful in the effective design of Bragg breakwaters for establishing a calm wave environment near the harbour regions. © 2020, King Fahd University of Petroleum & Minerals.
Wave attenuation by multiple slotted barriers with a zig-zag arrangement -A physical and numerical approach
(Elsevier B.V., 2022) Kumaran, V.; Neelamani, S.; Vijay, K.G.; Al-Anjari, N.; Al-Ragum, A.
In the present study, scattering of surface gravity waves by multiple slotted vertical barriers arranged in a zig-zag manner is analyzed by employing Computational Fluid Dynamics (CFD) and validated with physical model tests. The porosity of the vertical slotted barrier is varied from 10% to 40%, and the number of slotted barriers varied from 1 to 6. The results from CFD correlate well with the laboratory measurements on the scattering coefficients for a wide range of input conditions giving a high level of confidence. For relatively short waves (h/λ > 0.3, h- water depth and λ- wave length), slotted barriers up to 3 numbers and porosity from 20% to 30% are required to achieve wave transmission coefficient in the range of 0.2 to 0.3. For relatively long waves (h/λ < 0.3), slotted barriers of 5 to 6 numbers and porosity in the range of 10% to 20% are needed to obtain wave transmission of 0.2 to 0.3. The results presented in this study can be used for a wide range of wave damping applications in the field of coastal engineering. © 2022 International Association for Hydro-environment Engineering and Research, Asia Pacific Division
Wave trapping efficiency of a flexible membrane near a partially reflecting seawall
(American Society of Mechanical Engineers (ASME), 2021) Venkateswarlu, V.; Vijay, K.G.; Pandi, R.R.; Nishad, C.S.
The gravity wave interaction with a flexible membrane placed at a finite distance from the partially reflecting seawall is analyzed under the framework of linear water wave theory using the multi-domain boundary element method (BEM). The flow through a flexible membrane is assumed to follow Darcy's law in addition to membrane displacements. As a viable alternative to the existing wave dampers, the flexible membrane is examined for the effective dampening of incident waves. The correctness of the numerical results is affirmed with the known results available in the literature. The effect of membrane tension, submergence depth, membrane width, porosity, angle of inclination, and confined chamber spacing on hydrodynamic coefficients is discussed as a function of dimensionless wavenumber. The partially reflecting harbor wall diminishes the wave reflection coefficient in the long-wave regime. The increase in the flexible membrane width does not necessarily ensure the ideal wave capturing performance. A shift in the peak of the maximum deflection is observed with the increase of membrane width while there is a shift in peak outward for the increase in the submergence depth. Moreover, the maximum deflection is found to decrease with the increase in porosity, and it is 62% reduction for membrane porosity b = 1 due to the significant wave damping. The wave run-up and the wall force coefficients are found to be minimum when the relative plate width is B/h = 1. The present study is expected to be useful for the design of cost-effective wave attenuating systems. © © 2021 by ASME.