Figure 6 The energy flow transmitted upward via the points

　

For example, Figure 6 shows the energy flow transmitted upward via the points referred as from A1 to A4 or from B1 to B4 in Figure 4. It can be seen from these data that the results of the calculation is as same as the measurement.

One of the problems at the comparison is the reliability of the data of the measurement. The measurement of the structure borne sound is usually carried out at only once at the center of the plate considered as the reference point. This is because of the lack of time for the measurement. But it is not clear in such case that the energy measured at such reference point is equal to the average of the energy of the plate to be measured. To investigate this problem, the measurements at more than one point of one plate. Figure 7 shows the differences (1 kHz Octave band) between each measuring point and the reference point which is indicated as the "R" in Figure 7. It can be seen from this measurement that the measured value at each point is not same each other. It may be thought as the reason of this that the opposite side of the steel plate is installed with the material for the absorption in some case. As regards the floor, if the some equipment is installed, the measured data may not be the average of that floor. It can be thought from these observation that the global flow of the noise energy calculated may be almost acceptable if there are only part of the elements at which the difference between the calculation and the measurement is not small.

　

Figure 7 The differences between each measuring point and the reference point

　

6. CONCLUSIONS

　

The authors reported the feature of the KNOISE and the case study of the noise prediction at the design stage of the ship in this paper. Conclusions are as follows.

・The procedure for the prediction described in this paper is that the calculation of the noise prediction for the ship concerned was carried out after the calculation and the measurement with the similar ship was carried out. The parameters necessary for calculation of the noise prediction for the ship concerned is obtained from the matching work with the similar ship. It can be said that the result obtained through this procedure is acceptable.

・Two kinds of the coupling loss factors were used when the model for the calculation was made. One is for the accommodation space above the upper deck, and the other is for the machinery space below the upper deck. The accuracy of the prediction could be improved by this convenient means because the modification of these factors could be carried out with each spaces respectively. However, the validity of this means is not investigated at present.

・The sound power was used as the sound source in the calculation instead of the sound pressure. This contributes to the sufficient result.

・The information necessary for the design or the construction with the ship noise would be one which is helpful to judge whether the measure to decrease the sound must be done or not. If so, it is important to estimate the global flow of the sound energy, though it is also important to predict the sound pressure level. According to the case study described in this paper, it can be said that the estimation with the proper accuracy can be achieved by estimating the main flow of the sound energy.

There are only a few cases in which KNOISE is applied. The authors will investigate problems brought through the study until now and make the better system to be able to calculate with high accuracy.

　

ACKNOWLEDGMENTS

　

Before concluding this paper, the authors also wish to help and advice in developing the computer program to Systems Dynax Co., Ltd., by Dr. Y. Nagai. The author would like to thank their gratitude to the personnel of Research institute of Nippon Kaiji Kyokai, by Mr. Kidoguchi, Mr. Sasaki, and Ms. Sugawara, Mr. Omata for their assistance with the full scale measurement.

　

REFERENCES

　

[1] The Shipbuild., Research Associate Japan, Investigations onShip-Board Noise, Research Report, No.252 (1976), No.270 (1977), No.286-1, 2 (1978). (in Japanese)

[2] J. H. Janssen, J.Buiten, On Acoustical Designing in Naval Architecture, Proceedings of inter-noise73, p349, (1973).

[3] A.C, Nilsson, Wave Propagation in Simple Full-Frame Structures of Ships, Journal of Sound and Vibration, Vol.44, p393, (1976).

[4] A.C.Nilsson, Attenuation of Structure-Borne Sound in Superstructures on Ships, Journal of Sound and Vibration, Vol.55, p71, (1977).

[5] R.H.Lyon, Statistical Energy Analysis of Dynamic Systems:

Theory and Applications, MIT Press, (1975).

[6] Shinkichi Tashiro et.al, Noise Prediction Program on Board Ship -Application of Statistical Energy Analysis-, Journal of the society of naval architects of Japan, Vol.150, p564, (1981) (in Japanese)

[7] G.Maidanik: Response of Ribbed Panels to Reverberant Acoustic Fields, J.A.S.A. Vol.34, No.6, 1962.

[8] L.Cemer: Structure-borne Sound. Springer Verlag 1973.

[9] Tastuki Yoshikai, Kazuo Hattori, Toshio Sato, Prediction of Noise Level on Board Ship Using Statistical Energy Analysis, Proceedings of inter-noise81, p1049, (1981).

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