engleski

Finite element formulation of different restoring stiffness issues and their influence on response

Two different restoring stiffness formulations for ship hydroelastic analysis are considered, i.e. consistent one, as an extension of the ordinary restoring stiffness in ship rigid body motion in waves, and another structurally oriented one which comprises geometric stiffness with ship stress distribution in calm sea. In order to increase the accuracy of the stiffness coefficients in modal analysis the finite element technique is employed. Triangular and rectangular finite elements are worked out for panels of wetted surface and structural members, i.e. plates and beams. The geometric stiffness matrix consists of three parts, one related to plate deflection, well-known in buckling analysis, and two additional for membrane displacements, which complete expression for ship stability. For all three parts the same shape functions of membrane displacements are used due to reason of simplicity. A special software for generation of restoring stiffness is developed and incorporated in package for ship hydroelastic analysis. The hydroelastic response of a thin-walled barge is determined by employing the consistent restoring stiffness in two variants, i.e. with distributed structural mass and lumped masses, and the complete restoring stiffness. The response includes the transfer functions of rigid body and elastic modes, and those for vertical, horizontal and torsional sectional forces. Moderate differences of three sets of calculations are noticed in a narrow region of the lower frequency range. Some valuable conclusions based on that numerical test are drawn.

hydroelasticity; restoring stiffness; finite element method; barge response

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