臺灣博碩士論文加值系統

本文依據實船量測資料$,$研判何種船舶振動型式為水下噪音之主因。結
論顯示答案為螺槳所引發之流體性噪音,如螺槳空蝕,船形擾流等,而非主
機等機械振源。 此結論可由以下兩點說明: (1) 在不同之操作狀況下,位
於機艙之船側板,其振動量變化不大。 因主機基座與發電機基座有明顯之
減振功能,故主機等所引發之水中輻射值有限。 (2) 船艉板在動態時之振
動量,遠比靜態時為大。且隨轉速之增加而增加,特別是轉速到達 620rpm
以後,會有流體性振源出現。在此同時,有一明顯之寬頻訊號出現在遠場噪
音值中,顯然此寬頻訊號即為艉板所觀察到之流體振源 。在理論部分$,$
本文利用葛萊金近似法(GALERKIN METHOD)與最小誤差法(MIN. ERROR)預
測流體壓力波入射船板時,所造成之近場噪音值。此近場理論雖含有艉板
之振動模態,但從遠場訊號中,卻無法尋得,表示其只存在於近場中。

The main goal of this paper is to determine the dominant
source of the underwater noise radiated from a surface
vessel at mid-frequency range. We find that it is not the
"MACHINE-NOISE" but the "FLUID -NOISE" resulted from thep
propeller. This could be demonstrated by the following
arguement according to the experimental data : (1) The
amplitude of the plate vibration of the side wall in the
machine room of the ship and the water , did not increase
with the increasing of rotating speed of the main engine
,that is, the underwater radiational noise induced by the
main engine is NOT significant in the ship''s underwater ship
noise. (2) When the hull plate of the A.P. part of the ship is
forced by the "FLUID-NOISE" ,there is a wide-band noise
observed in the far- field pressure field . The near-field
pressure at the wet side of the hull plate of A.P part is
predicted by "GALERKIN METHOD " and " MIN. ERROR METHOD ".the
resonat mode of plate vibration is not in the far-field
measured data while it exits in the near-field theoretical
predication.