FEM/BEM analysis of diesel piston-slap induced ship hull vibration and underwater noise H. Zheng *, G.R. Liu, J.S. Tao, K.Y. Lam Institute of High Performance Computing, 89C Science Park Drive, Singapore Science Park I, Singapore 118261, Singapore Received 9 February 2000; received in revised form 10 May 2000; accepted 26 June 2000 Abstract Numerical prediction of vibration transmission from a ship diesel via a resilient mounting system to a stiened cylindrical hull is performed aiming to provide a clearer insight into the signi®cance of piston-slap in the diesel excitations to the hull vibration, and consequently, the underwater radiated noise. Finite element method (FEM) is employed to simulate the vibra- tion response of the hull due to the excitations of diesel piston-slap and vertical inertia force of reciprocating masses. Eects of the rotational stiness of resilient mounts on vibration transmission are also numerically investigated through coupled multi-DOF isolation analyses. Finite element solutions of the hull vibratory velocity are further used as boundary condition of the hull boundary element model for consequent underwater radiated noise calculation. The numerical results show that (1) piston-slap imposed rolling moment on the diesel frame may cause a higher level of ship hull vibration and underwater radiated noise than that due to the excitation of the vertical inertia force of reciprocating masses; (2) rotational stiness of elastic mounts for resilient mounting system plays an important role in the diesel vibration transmission to the hull, especially as exciting frequency increases; and (3) neglect of the excitation component of piston-slap moment can lead to overestimates of hull vibration in some cases. # 2001 Elsevier Science Ltd. All rights reserved. 1. Introduction Among the main excitation sources of radiated underwater noise that compose acoustic signature of a ship, the diesel engine is obviously one of the strongest sources in most circumstances, no matter whether it is installed as the propulsion Applied Acoustics 62 (2001) 341±358 www.elsevier.com/locate/apacoust 0003-682X/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved. PII: S0003-682X(00)00046-3 * Corresponding author. E-mail address: zhengh@ihpc.nus.edu.sg (H. Zheng).