The Low-Noise Optimization of a SWATH Ship’s Structures Based on the Three-Dimensional Sono-Elasticity of Ships

Abstract

Basic equations and numerical methods are presented for the three-dimensional sono-elasticity theory of ships in shallow sea Pekeris acoustic waveguide environment. The corresponding software three-dimensional hydroelastic analysis of floating and traveling structures-Acoustic developed based on this theory is used for low-noise optimization design of the strut structures of a 1500-ton small waterplane area twin hull (SWATH) ship. When the SWATH ship was moored in waves and laying down instruments for ocean survey, it was observed that the waves continuously beat the vertical side walls of the struts, resulting in structural vibration and acoustic radiation in the frequency band below 100 Hz. This is a new phenomenon that the hydroelastic response of a local structure disturbs ocean survey performance. This phenomenon is not good for the performance of underwater acoustic equipment because it increases the background noise in the vicinity of the SWATH ship. This problem needs a low-cost and feasible solution. The mechanism of this phenomenon is first discussed by means of a sono-elastic analysis. After a series of low-noise design calculations for the strut structures, a design of optimal acoustic performance is obtained with only a small increase in the structure weight. Some suggestions on engineering design for solving such problems are also put forward. 1. Introduction The theory of fluid-structure interaction has been widely applied in various engineering practices, including improvement of ship's seakeeping performance and structural safety, ship vibration and noise control, and enhancement of underwater acoustic stealthiness. In the late 1970s of the twentieth century, hydroelasticity of ships was established as one new branch of ship's fluid-structure coupling dynamics (Bishop & Price 1979). In the early 1980s, by combining the three-dimensional potential flow theory of ship motions with the three-dimensional structural dynamics, three-dimensional hydroelasticity was established by Wu (1984) and Bishop et al. (1986) to deal with the dynamic response of arbitrarily shaped three-dimensional deformable body under internal and external loads. Hereafter, the theory was developed continuously into two main subbranches: one is the three-dimensional hydroelasticity with respect to wave-induced dynamic responses of structures in the incompressible fluid field (Wu 1984; Bishop et al. 1986; Wu et al. 1997; Tian & Wu 2006; Kim et al. 2009; Wu & Cui 2009) and the other deals with the acoustic effect in the compressible fluid field (Zhou et al. 2010; Zou et al. 2013; Zou 2014), the latter of which is also called the three-dimensional sono-elasticity of ships.