Dynamic analysis of a rigid body mounting system with flexible foundation subject to fluid loading

This paper presents an investigation of the force transmission from a rigid body mounting system to a flexible foundation with light and heavy fluid l oading under the force and moment excitation. The analytical expression has been derived in which the flexible foundation effects are incorporated int o a revised system stiffness matrix that is derived from the receptance mat rix at mounting points. A typical case with a thin infinite plate as the fo undation has been studied with the point and transfer receptances theoretic ally and numerically analysed in the case of light and heavy fluid loading. The results show that, compared with the rigid foundation, the force trans mission is reduced and system natural frequencies are shifted. The detailed analysis demonstrates that the force reduction and frequency shifting are more obvious at low frequencies where the receptance value is significant. The study is also carried out to compare the transfer receptances from diff erent waves in plate as it couples with water with the objective to simplif y the calculation of receptance. It is found that, in the low frequency and after a short distance from driving point, the transfer receptance calcula tion for the heavy fluid loading can be simplified by only accounting the c ontribution from free wave which may easily be evaluated from the point rec eptance in air. It implies the plate response under heavy fluid loading cou ld be directly derived from that with light fluid loading.