Equivalent shell element for ship structural design

This thesis presents an equivalent shell element for assessing the ship global and local static and vibration response in early design phases. The stiffened plate is considered as a three layer laminate element, where the first layer represents the plate, the second layer the stiffener web and the third the stiffener flange. The layers are described as 2D iso- and orthotropic materials, where the elasticity matrices are found by applying the Rule of Mixtures. The element includes the extension, membrane-bending coupling, bending and additionally also shear stiffness, which follows the Reissner-Mindlin plate theory for anisotropic homogenous shells. The developed shell formulation has been implemented in commercial FE software FEMAP with NX Nastran and demonstrated in three study cases: stiffened plate, passenger ship cabin area and boxlike ship. The results were validated by comparison with those obtained from 3D fine mesh analysis. All studies show that with reasonable mesh density the laminate element can be used to obtain the static and vibration response of global and local ship structure. Four 4-noded elements per vibration shape have been found to be an optimal size to evaluate eigenvalues with less than 10 % error, which fulfils the industry requirements. Compared to other available equivalent elements, the present laminate element can also predict the normal and shear stresses in stiffener web and flange