JOURNAL OF SOUND AND VIBRATION Journal of Sound and Vibration 285 (2005) 391–406 On active vibration isolation of floating raft system Junchuan Niu a,Ã , Kongjie Song a , C.W. Lim b a School of Mechanical Engineering, Shandong University, No. 73 Jingshi Road, Jinan 250061, People’s Republic of China b Department of Building and Construction, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong Received 18 August 2003; received in revised form 13 April 2004; accepted 26 August 2004 Available online 16 December 2004 Abstract A novel analytical active–passive model of floating rafts, a type of special isolation structures which present high-level vibration isolation and are widely used in large ships and submarines particularly, is developed for the first time. Then the mobility matrices of the subsystems are derived, thereby a general mathematical description of this combined active–passive model is realized. Based on the model, the concepts and relationships of machine control, raft control and full control are extensively discussed. The solution of the power flow transmitted into the foundation is obtained, and power transmission characteristics of the system are investigated under different control types when minimization of total power flow strategy is applied. Through numerical simulations, the control efficiencies of the different control types (machine control, raft control and full control) are compared, illustrating the efficiency of the presented model, obtaining some valuable results, and presenting some general design principles of the active floating raft isolation systems. r 2004 Elsevier Ltd. All rights reserved. 1. Introduction With the development of the vibration control techniques and increasing strict requirements for the vibration isolation in industry and everyday life, classical one-stage isolation systems exhibit poor performances [1–4]. To achieve more efficient vibration cancellation, some two-stage even multi-stage isolation systems have received increasingly research attention in recent years [5–8], ARTICLE IN PRESS www.elsevier.com/locate/jsvi 0022-460X/$-see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.jsv.2004.08.013 Ã Corresponding author. Fax: +865312602351. E-mail address: niujc@sdu.edu.cn (J. Niu).