Browsing by Author "Karmakar, Debabrata."

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    Gravity Wave Damping by Stratified Porous Structures
    (National Institute of Technology Karnataka, Surathkal, 2020) Venkateswarlu; Karmakar, Debabrata.
    In the present study, wave transformation due to multiple porous structures in the presence and absence of vertical rigid wall, barrier-rock breakwaters of various configurations, multiple horizontally stratified porous absorbers, vertically stratified porous structure lying on flat seabed, elevated seabed and stepped seabed is analysed under the oblique wave incidence. The eigenfunction expansion method using the continuity of pressure and velocity along with mode-coupling relation is adopted based on linearized wave theory. The direct analytical relations are derived for finding the wave reflection and transmission coefficients due to porous breakwaters of various structural configurations. In the preliminary stage, the analytical results are validated with numerical and physical model results available in the literature. As a special case, a comparative study is performed between the vertical rigid wall, permeable wall and stepped wall away from the double horizontally stratified wave absorbers. The vertical and stepped wall shows almost similar values of wave reflection at each of the resonating crests, but minimal values of the resonating trough in wave reflection is obtained from the stepped wall. A comparative study is performed between single and multiple porous structures of fixed structural width and depth. The 42% reduction in wave transmission is achieved with double porous structures as compared with single porous structure for uniform structural width, which may be due to wave damping in the free spacing available between the two structures. The distribution of incident wave energy in the form of wave reflection and transmission is effective in the case of horizontally stratified porous structure as compared with other structures. The vertically stratified porous structures performance is partially dependent upon structural width. Higher structural width effectively reduces the wave transmission as compared with conventional porous structures. The effect of each layer porosity, friction factor, structural width, incident wavelength, number of structures, angle of incidence, free spacing and trapping chamber effect on wave reflection, transmission damping, fluid force on seaward/leeward sides of breakwater and force on vertical wall is analysed for various types of porous structures. The critical angle due to standing waves, fluid resonance in the free spacing and clapotis has an efficient role in the design of porous structures.
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    Hydroelastic Analysis of Floating and Submerged Flexible Structures
    (National Institute of Technology Karnataka, Surathkal, 2020) M, Praveen K.; Karmakar, Debabrata.
    The present work mainly deals with a class of physical problems in the broad area of wave structure interaction related to hydroelasticity. In the present study, the major emphasis is given • to analyse the hydroelastic behaviour of the very large floating structure based on the Timoshenko-Mindlin’s plate theory in both finite and shallow water depth, • to illustrate the significance of periodic array of articulation, change in bottom topography and wave attenuation due to the presence of vertical barriers in the hydroelastic analysis of floating structures which are of recent scientific interest in the field of Ocean and Coastal Engineering. In the present study, the generalized expansion formulae along with the orthogonal modecoupling relation is utilized to analyse the wave interaction with very large floating structure. The study is performed to analyse the influence of different edge support conditions on the hydroelastic behaviour of the floating elastic plate and the numerical results obtained based Timoshenko-Mindlin plate theory is compared with the EulerBernoulli plate theory. The gravity wave scattering by single and multiple articulated floating finite elastic plates are analyzed based on small amplitude linearized water wave theory. In the case of periodic array of multiple articulated floating elastic plates, the solution for the boundary value problem is analyzed by using both eigenfunction expansion method and wide-spacing approximation method. The transformation of gravity wave due to multiple variations in bottom topography in the presence of articulated floating elastic plate is studied by using orthogonal mode-coupling relation. Further, using shallow water approximation, the flexural gravity wave scattering due to (i) articulated floating elastic plates and (ii) abrupt changes in bottom topography are analyzed and the explicit relation for the wave scattering coefficients are obtained. Finally, surface gravity wave scattering due to the presence of vertical barriers along with the floating articulated elastic plate are analysed and the energy relation associated with transformations of gravity waves in the presence of vertical porous barrier is discussed. The numerical results for the reflection and transmission coefficients, plate deflection, strain along the floating elastic plate, bending moment and shear force are computed in different cases and analyzed.