In the ship hull structure, there are a lot of noise sources such as propulsion engines, diesel generators, pumps and air conditioning machinery, etc. Noise generated by these sources propagates through the decks and bulkheads in the hull structure, and becomes noise in compartments such as cabins and workrooms. It is necessary to predict the noise levels and determine appropriate noise control approaches in order to reduce the noise levels in compartments. However, in order to get accurate results for noise prediction, an effective prediction model is needed. Therefore noise transmission characteristics from various sources and source levels must be obtained properly.

This paper describes the noise transmission characteristics from the sources to the cabins when the one diesel generator is running on the Tokai University research and training ship “BOSEI MARU", and an effective and simple noise prediction model using these transmission characteristics is proposed. The noise transmission characteristics are obtained by using the distance between the diesel generator and the cabin. Then the attenuation of the noise level is expressed as coefficients of damping proportional to the number of frames and decks. The source level of the diesel generator is obtained by using these transmission characteristics and noise measurement in adjacent compartments. The noise predictions for 20 cabins are performed using both the source levels and transmission characteristics. It is shown that the accuracy of these predictions is within 5 dB in about 60 % of the cabins. It is also found that the accuracy of the predicted noise spectrum levels is typically within 5 dB using the frequency dependent damping coefficients.

船舶では船体構造内に, 推進機関, 発電機, ポンプ, 空調機器などの多くの騒音源となる機器が搭載されている.これらの機器の騒音が船体内を伝搬して客室, 船室や作業室の騒音となる.船内の騒音を低減するためには, 騒音レベルを予測して適切な騒音対策を決定することが必要である.そして, 船内騒音を精度良く予測するには, 音源機器から居住区画への騒音の伝搬特性を定量的に把握して, 適切な騒音予測法を用いることが必要となる.

本研究では, 東海大学海洋調査研修船「望星丸」のディーゼル発電機を単独で運転して, 音源機器から船内を伝搬して居住区画に伝達される騒音の伝搬特性を明らかにした.騒音計測位置とディーゼル発電機との距離の関係をフレーム数とデッキ数で表して, 騒音レベルの減衰量をフレーム数及びデッキ数に比例する減衰係数として求めた.そして, この伝搬特性を用いてディーゼル発電機の音源レベルを推定し, この音源レベルと減衰係数を用いた簡易騒音予測方法を提案した.20室について騒音予測を行った結果,約60% の船室に対して, 騒音レベルを±5dB の精度で予測できることが確認できた.また, 減衰係数の周波数特性を考慮することによって, 騒音スペクトルレベルも±5dBの精度で予測できることが確認できた.