Faculty Publications

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Author: search.filters.author.Krishna, K.R.A.

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    Wave transformation due to a submerged porous block associated with a vertical barrier
    (Springer, 2020) Krishna, K.R.A.; Venkateswarlu, V.; Karmakar, D.
    In the present study, the combination of vertical porous barrier along with the porous block is proposed for wave energy damping. Three types of vertical barriers such as (a) fully extended barrier (b) bottom-standing barrier and (c) surface piercing barrier away from the porous structure are analysed for wave trapping. The finite spacing in between vertical barrier and the porous structure is proposed for better wave trapping. The continuity of velocity and pressure at the interfaces of vertical barrier and porous structure are considered and the eigenfunction expansion method is adopted to determine the wave transformation characteristics due to the presence of submerged vertical barrier and porous block. The resistance and reactance offered by the porous structure are taken into account using the complex dispersion relation proposed by Sollitt and Cross (1972). The effect of structural porosity, width of the structure and angle of incidence on wave transformation due to the vertical barrier away from the porous structure are examined in detail. The results are compared and validated with the available literature for specific configurations as in Sollitt and Cross (1972) and Mallayachari and Sundar (1994). The study suggests that the increase in the structural porosity enhances the wave energy damping and global minima is achieved in the wave reflection coefficient due to the formation of standing waves by the breakwater system. The proposed structure can be adopted in leeward, port and harbour regions to achieve the tranquillity condition. © Springer Nature Singapore Pte Ltd. 2020.
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    Wave transformation due to stratified porous structure and vertical barrier
    (American Institute of Physics Inc., 2023) Karaseeri, A.G.; Krishna, K.R.A.; Karmakar, D.
    The present study examines hydrodynamic performance of the horizontally stratified porous structure along with fully extended vertical barrier. The combination of the submerged porous structure with barrier consists of a fully extended barrier and a fully extended stratified porous structure. The small amplitude water wave theory is adopted for the study of the wave transmission through the composite breakwater system. The Darcy's law is followed for the flow through porous media. The eigenfunction expansion method along with the mode-coupling relation is adopted to determine the hydraulic characteristics. The hydrodynamic characteristics is obtained for different geometric conditions of structure and wave parameters. The study is performed to investigate the energy dissipation in the confined regions. The porosity of the structure is varied in the numerical calculations and the optimum porosity for the structure is selected for the efficient performance of the structure. Further, the experimental study is performed to validate the numerical result and to analyse wave transmission through the combined breakwater system. To maintain the tranquil condition and to protect coastline from the severe wave attack the combination of the vertical barrier and stratified porous structure can be an effective and economical solution. The wave force over the structure is reduced by the fully extended vertical barrier, which acts as a primary structure to reduce the direct impact over the stratified structure by absorbing some part of the wave energy and also improving the durability of the structure. © 2023 Author(s).
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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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    Dissipation of Gravity Waves Due to Submerged Porous Plate Coupled With Porous Structures
    (American Society of Mechanical Engineers (ASME), 2023) Krishna, K.R.A.; Abdulla, K.; Karmakar, D.
    The present study focuses on wave trapping due to the submerged horizontal porous plate combined with the bottom-standing porous structure and surface-piercing porous structure. The submerged plate thickness is considered to be negligible as compared to the incident wavelength and water depth, and the porous structure is considered to be of finite width. The study is performed based on the eigenfunction expansion method, and the wave interaction with the combined structure is investigated using the small amplitude wave theory. The orthogonal mode-coupling relation is used to analyze the wave interaction with the combined structure. The reflection, transmission, and dissipation coefficients along with wave force on the porous structure are investigated to analyze the hydrodynamic performance of the composite porous breakwater system. Further, the effect of porosity of submerged plate and structure, submergence depth of plate and structure, angle of incidence, and the submerged plate length are investigated to analyze the effective wave dissipation by the composite breakwater. In addition, the comparative study of the numerical method is performed with the results available in the literature. The study noted that the wave damping due to the submerged porous plate backed by surface-piercing porous structure is more as compared to the submerged porous plate backed by the bottom-standing porous structure. The study performed will be helpful to scientists and engineers in the design of suitable composite breakwater systems and also assists in selecting the best structural configuration for attenuation of wave height and to protect the offshore facility from high waves in the coastal region. © 2023 American Society of Mechanical Engineers (ASME). All rights reserved.
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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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    Wave attenuation due to stratified porous structure in the presence of stepped seabed
    (Springer Nature, 2024) Varghese, A.; Krishna, K.R.A.; Karmakar, D.
    The wave transformation due to the stratified porous structures in the presence of stepped seabed at leeward side is analysed based on the small amplitude wave theory. The study is performed to analyse the effectiveness of both horizontal and vertical stratified porous structure for the wave attenuation in the nearshore regions using orthogonal mode-coupling relation and eigenfunction expansion method. The hydrodynamic coefficients such as wave reflection, transmission, dissipation, wave force acting and surface elevation are investigated for both horizontally and vertically stratified porous structures. The effect of change in the structural properties such as varying porosity, friction factor, structural width, angle of incidence and length between the porous structure and stepped seabed are examined. Thereafter, the comparative study is performed for both horizontally and vertically stratified porous structure in the presence of stepped seabed and the numerical results are validated with the results available in the literature. The present study illustrates that with the increase in step height, the wave damping efficiency is enhanced. In addition, the wave energy dissipation is observed more for horizontally stratified structure in the case of longer waves whereas vertically stratified structure is effective in dampening of shorter waves. Further, the wave reflection and transmission for vertically stratified structure is found to be more for same length between structure and stepped seabed. The stepped seabed in leeward side in combination with vertical and horizontal stratified porous structure is intended to be an effective solution for protection of coastal facility. © The Author(s), under exclusive licence to Sociedade Brasileira de Engenharia Naval 2024.