Zastosowanie metody sztywnych elementów skończonych do obliczeń częstości drgań własnych ustrojów okrętowych

The method of calculation consists in replacing the actual system by a system of rigid finite elements interconnected and attached to the foundation by elastic elements with linear characteristics. The matrix of the equations of motion is constructed directly without their explicit derivation. The accuracy of the computerized method depending upon the number of finite elements (see fig. 5) is shown on the example of a simply supported prismatic beam. The method described is widely applied in shipbuilding industry, especially for calculations of ship hull vibrations, bending vibrations of the shafting fitted on many elastic supports, bending vibrations of elastic Grim-type propeller shafts, vibrations of the ''raft'' with flexibly fitted equipment and torsional vibrations of branch propulsion systems. The method of rigid finite
elements is most useful in calculation of natural vibration frequencies of the frames and grillages with varying cross-sections. The influence of shearing and inertia forces are taken into account.