This paper presents a semi analytic time domain method for the analysis of the symmetric hydroelastic response of a container ship subject to slamming and green water loads. An Impulse Response Function (IRF) is adopted for the calculation of radiation, diffraction and wave excitation forces. Local hydrodynamic forces associated with green water on decks and slamming loads are respectively modelled by the Buchner’s Dam Break Model and a Generalised Wagner Model. The structural responses are captured by Euler-Bernoulli beam theory and solved by the modal superposition method. The Duhamel Integral technique is used to evaluate the dynamic response. A parametric study demonstrates how external forces may affect the global wave induced vertical bending moments and shear forces. Numerical simulations are compared against a hybrid method that combines computational fluid dynamics, boundary element and finite element methods for low to medium frequency induced dynamic response. It is concluded that the proposed semi analytic methodology is fast and accurate and may be useful at concept ship design stage.
A semi analytic three-dimensional time domain method is developed to predict the hydroelastic effect due to wave induced loads on a floating body. The methodology being a semi analytic approach is able to capture real life scenario of bending of a ship like structure on sea taking both flexural and torsional vibrations. A prismatic beam equation with analytically defined modeshapes is taken into consideration to represent the structural response. The elastic deformation is solved using modal superposition technique. The radiation forces for elastic modes are obtained through impulse response function in time domain where frequency domain added mass, damping coefficients and wave exciting forces for the flexible modes are derived from a frequency domain panel method code. The Duhamel integral is employed in order to get the flexural and torsional deflection, velocity. A rectangular barge with zero forward speed is chosen for the analysis. Structural responses, torque, bending moments are calculated to assess the wave induced loads on the floating elastic body. The proposed technique, developed in Fortran, appears to be robust, efficient and computationally less expensive and can be used to predict the wave induced loads on a flexible structure as a first approximation in the initial design stage.
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