The noise level in engine rooms of general merchant ships is relatively higher than in other facilities for transportation. In the engine room, the noise from a main engine, mainly of low speed diesel types, greatly influences noise levels. Actually at some positions on large bore engines with big turbochargers, it is not rare for the noise level to reach close to the IMO requirement of 110 dB(A). Under such situations, various efforts have been done to reduce the noise level aiming towards the improvement of livability and also work environment of the crew in engine room. In this paper, firstly, we report a noise characteristic of low speed diesel engine and also the present status of the noise level in the engine room. Secondly, we report some samples of the countermeasures for noise reduction including the application of Helmholtz resonators and absorption materials. Finally, we report on the newly introduced spherical beamforming technique with its principle and effectiveness in noise measurement. Contents 1. Present noise measurement methods and IMO noise requirements for engine room 2. Noise characteristics of low speed diesel engine Usually, noise level is measured higher at the scavenging area, that is, around the turbocharger, air cooler, scavenging pipe and its connection part. The dominating sound source are the turbochargers, especially the compression noise. It's caused by the recurring compression shocks and emitted as air born sound through the air intake silencers on the one hand but also trough to high-pressure-side (compressor outlet) over the connected pipes (like expansion bellow, air cooler, scavenging air pipe). The frequency spectrum is dominated by the compressor wheels blade passing frequency and (in some cases) his first harmonic. It corresponds with the number of main blades multiplied by the turbocharger rotor speed (and twice that frequency). 3. Countermeasures of low speed diesel engine noise The countermeasures are mainly applied in the turbocharger and the scavenging area. We report the present countermeasures and their effects in noise reduction such as introducing low noise turbochargers and additional insulation of diffuser pipes between the turbocharger compressor outlets and air coolers and scavenging air pipes. Further, we report new countermeasures and confirmation test results as follows. Example 1 Silencers of Helmholtz resonators and absorption materials M/E MITSUI-MAN B&W 11K98MC (62920kW x 94rpm), T/C 3 x ABB TPL85B for 6350TEU container vessel: The countermeasures consisted of resonance type silencers (called CoRes) designed by ABB in the expansion bellow between the turbocharger compressor outlet and diffuser pipe and inside noise absorption in the area above the air cooler elements (called CABS). Example 2 New Silencers of Helmholtz resonators M/E MITSUI-MAN B&W 12K98MC(68640kW x 94rpm), T/C 3 x MAN TCA88 for 8250TEU container vessel: The new resonance type silencers designed by MAN Diesel were located at diffuser pipes. Test results will be reported. 5. New noise measurement by using spherical beamforming technique The noise measurement technique using spherical beamforming has been developed for identifying and visualizing the noise sources as well as analyzing their characteristics (frequencies and levels) within a very short time. This technique has been recently used for investigations of noise sources for automobiles, etc.


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    Title :

    Noise reductions for low speed diesel engines and application of noise measurement using spherical beamforming technique


    Contributors:


    Publication date :

    2010


    Size :

    13 Seiten, 31 Bilder, 16 Quellen


    Type of media :

    Conference paper


    Type of material :

    Storage medium


    Language :

    English




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