TS-95
CASE STUDY OF SHIP NOISE ESTIMATION AT DESIGN STAGE USING SEA
Hideo IKEDA*, Nobuhiro BABA**, Minoru KAMATA***, Toru YAMAZAKI****
ABSTRACT
A various kind of studies regarding ship noise are being carried out today, Nippon Kaiji Kyokai started studies more than fifteen years ago, and published the results in the form of guidance. Moreover, to deal with rationalization of ship noise, the authors have developed a computer program (hereinafter "KNOISE") to estimation noise levels in the accommodation spaces and engine room of a ship. KNOISE has an excellent user interface offering ease of operation, reduced data input through the use of standard tables, and an interactive data input system. Accordingly) in order to examine the validly of KNOISE, the authors have carried out to make a comparison between measuring data and results of calculation.
This paper briefly outlines KNOISE and its development until now. The efficacy of "KNOISE" is inspected through a detail analysis of the measured data and numerical investigations.
Key Words: Ship Noise, Noise Estimation Program System, Statistical Energy Analysis, structure borne noise, air borne noise
1. INTRODUCTION
It is important to reduce structure borne noise on a multi-layered steel structure such as ships. It is often occurred the problem that the noise level on a location quite far from noise source exceeds the regulated level when the measure to reduce noise levels is ineffective. The knowledge of transmission path of noise in early design step provides ship designers the effective design. However, the estimation accuracy of noise is generally dependent on the know-how of designers.
In Japan, a program to predict the noise characteristics on ship was discussed in SR1 56 about twenty years ago [1]. The program is based on Statistical Energy Analysis (SEA). The authors keep improving the program. During this improvement we have the chance to measure the noise characteristics on some ships belonged to a same shipyard. These opportunities provide the technical knowledge for the ship noise estimation in early design.
In this paper, we discuss the ship noise estimation in early design step. We try the estimation of noise levels on a new ship using our improved estimation program. As the results of such arrangements, explosions in starting pipes have been reduced considerably.
However, it has been leaned from the investigations into recent accidents that explosion may take place without backfire, since latest investigation confirmed that the explosion occurred before fuel being injected.
2. OVERVIEW OF SHIP NOISE ESTIMATION
In early 1970s, Janssen [2] had started to predict ship noise characteristics in terms of his experience with many data measured in past. In his estimation, the attenuation from noise source to cabin rooms is evaluated by the number of layer and that of transverse frame and so on.
On the other hand, wave guide method and SEA are theoretical methods. The former method has proposed by Nillson [3] in 1976 and is based on the transmission of waves on and through the panels and requires the equilibrium of moments on boundary. It is verified that this method is effective using a simple ship typed structure [4].
In SEA [5], the objective structure is divided some subsystems. The power flow between or among subsystems is assumed to be parallel to the difference of the subsystems energies. The subsystem energy is an averaged value in space and frequency. The effectiveness of SEA has been verified in SR156 [1] by the application to simple structures and actual ships tested by each company in Japan. There is an individual approach in each company. One is firstly to calculate the characteristics of the parts made of steel, and next is to estimate the effect of interior materials and so on. Other is to determine the grades of rooms that are classified in advance and is to evaluate the SEA factors from measured data. Moreover, their programs keep being improved in building of luxury ship, ferry or Japan defense ministry's ship. In next chapter, the outline and the basic equation of SEA are described.
We have the SEA programs for estimation of noise on ship that was developed about 20 years ago. We keep improving the system and the graphical interface of this program and much know-how are obtained by the application of this program. In order to improve the accuracy of noise estimation by this program, we considered the optimization of parameters in this program and the measurement of transmitted path using tapping machine as artificial sources. However these measures were done only the case that the objective ship exists. The estimation of ship noise is generally required in early design before the ship is produced. This paper describes the estimation of ship noise in early design using our SEA program.
