Development of ship noise prediction system using vibration and acoustic data base for shipbuilders engineers

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1 Development of ship noise prediction system using vibration and acoustic data base for shipbuilders engineers Hideyuki SHURI 1 1 Tokai University, Japan ABSTRACT Shipbuilders engineers need to predict the noise levels in cabins during early design phase in order to satisfy the noise level limits of IMO Noise Code, which became mandatory in July 1st, 14 for ships of a gross tonnage of 1, and over. If the predicted noise levels exceed the noise level regulations, proper noise control measures to reduce noise levels must be implemented. This paper presents a newly developed noise prediction program for shipbuilders engineers. The noise prediction program is constructed using statistical energy analysis (SA) method, an empirical method and measured data base of vibration and acoustic. The noise levels of 37 cabins of a bulk carrier (37, DWT) are predicted in order to evaluate the practical applicability and the prediction accuracy of the program. The hull shape model, noise and vibration source data, mechanical and acoustic characteristics data are prepared. So prediction results are obtained in a few days. The difference between the predicted result and measured result of the noise level is within ±3dB in 84% of all sound receiving rooms, and ±5dB in 97% of all sound receiving rooms. This indicates that the noise prediction program can be used to predict the noise levels in cabins during early design phase. Keywords: Ship Noise, Prediction, SA I-INC Classification of Subjects Number(s): INTRODUCTION In 1, the amendments of Code on noise levels onboard ships (IMO Noise Cord) and SOLAS convention were adopted by the 91st meeting of the International Maritime Organization Maritime Safety Committee (IMO/MSC91) and the noise level regulation value became a regulation for construction contract of ships of 1,GT and over since July 1st, 14 (1)The new noise level regulation value for accommodation spaces is 5dB lower than the previous regulation value for ships of,gt and over and the same for ships of 1,GT and up to,gt. In order to satisfy the IMO ship noise level regulation value, the noise level of accommodation spaces must be estimated during the design phase in order to determine the necessity of noise control measures. It is also important to perform simulations for estimating the effect of noise control measures in order to select the appropriate measure. So a noise prediction program with high accuracy is required during the design phase. Research for ship noise prediction method has been conducted in urope since the late 19 s. J.H. Janssen and others () proposed a practical noise prediction method (hereinafter referred to as the Janssen method ) to Inter-Noise 73 by organizing noise and audio frequency band vibration ( vibration ) data of actual ships. The Statistical nergy Analysis method ( SA method ) proposed by R.H. Lyon and others (3) that handles the vibration energy propagation of random vibrations was also applied for ship noise prediction by J.O. Jensen and others (4). On the other hand, large scale experiments and analyses were performed for applying the Janssen method and SA method to ship noise prediction during the Research and study for ship noise (5) by the Japan Ship Technology Research Association from 1974 to 1978, and ship noise prediction programs using the Janssen method or SA method were developed. Recently, a ship noise prediction program using the Janssen method for small and medium-sized ships (6), and a ship noise prediction system including a general purpose acoustic analysis program VA One using the SA method (7) have been developed. However, since the Janssen method obtains the vibration transmission loss in the hull structure using an empirical formula organizing the number of frames and decks between the sound source and sound receiving room, it can only be applied to ships similar to the ships used to obtain the data in 1 h_shuri@scc.u-tokai.ac.jp 56

2 order to assure sufficient prediction accuracy. Furthermore, the effect of the positions of steel walls and pillars in the engine room and accommodation space cannot be considered. On the other hand, the SA method requires several weeks and millions of yen in order to create a detailed geometry model of the hull and accommodation space structures. Also, in order to assure sufficient prediction accuracy, the user must have sufficient experience for creating analysis models of the sound source, structure near the sound source and interior structure of the sound receiving room. Furthermore, although the sound source data and material property/acoustic property data of interior members of rooms and hull structure members are necessary for calculation, such information is not disclosed to the general public. In order to solve these problems, this paper reports the development of a ship noise prediction program combining the Janssen method, SA method and vibration/acoustic data obtained by actual ship tests/model tests as well as application results for noise prediction of actual ships and verification results of the prediction accuracy.. SHIP NOIS PRDICTION PROGRAM.1 Program Overview Five types of noise can be calculated by the ship noise prediction program (8). The structure borne sound and air borne sound propagated from the sound source in the ship to the sound receiving room as well as the external blower sound and funnel exhaust sound propagated from the exposed area to the sound receiving room can be calculated. The air conditioning sound in the sound receiving room can also be calculated. Fig.1 shows the calculation flow of the ship noise prediction program. After creating the hull shape data using a general purpose CAD program AutoCAD and the hull structure information and noise calculation input data in MS xcel format, the data is entered in the analysis part included in the general purpose pre/post program TSV-Pre/Post. In the analysis part, the analysis model is created, prediction calculation is performed and the result is displayed as geometry data on the PC screen. The calculated results are also exported in MS xcel format. In this paper, the prediction methods of the air borne sound and structure borne sound are introduced. Fig. shows the noise prediction model of the air borne sound and structure borne sound of the ship noise prediction program. Figure 1 Calculation flow of ship noise prediction program 57

3 Figure Models for predicting air borne sound and structure borne sound. Predicting Air Borne Sounds Air borne sounds are predicted by first calculating the sound pressure levels of the sound receiving room adjacent to the room where the sound source is placed for each frequency of the 1/3 octave band using Formulas (1) and () and then obtaining the noise level by combining the sound pressure levels of the entire frequency range. L 4 Lp LW log db A (1) S pa S Lp TL log db A () db L Sound power level of sound source W A Sound absorption area of sound source room m S S A S Average sound absorption coefficient of sound source room S Total surface area of sound source room S m L Sound pressure level of sound receiving room pa db L Sound pressure level of sound source room p db S Area of walls or deck between sound receiving room and sound source room m A Sound absorption area of sound receiving room m A S Average sound absorption coefficient of sound receiving room S Total surface area of sound receiving room m TL Transmission loss of partition walls or deck db The sound power and sound pressure level of the sound source in Formulas (1) and () are obtained from shop tests of the sound equipment, and the average sound absorption coefficient of the sound source room and sound receiving room are obtained from actual ship tests. The transmission loss between the sound source room and sound receiving room is obtained from full-size model/actual ship tests. These data are organized as an MS xcel format database and referenced from the noise prediction program..3 Predicting Structure Borne Sounds Structure borne sounds are calculated by combining the Janssen method and SA method. The vibration velocity level propagating from the sound equipment to the deck of the sound receiving room is obtained using the SA method. Based on the vibration velocity level of the deck, the sound pressure level emitted in the sound receiving room is obtained using the Janssen method by Formulas (3) to (5).The noise level is obtained by calculating the sound pressure level for each frequency of the 1/3 octave band and then combining them for the entire frequency range. S S S 58

4 L psf 4S f Lv ILn log log n A db (3) L 4S i psi Lv Lvwi log log n A db (4) log 5 Lpsf Lpsi Lps db i1 (5) L Sound pressure level of sound receiving room ps db L Sound pressure level emitted from floor psf db L Sound pressure level emitted from i th member psi db L Vibration velocity level of sound receiving room deck v db L vwi Transmission loss from floor to i th member db S Area of floor f m S Area of i th member m i A Sound absorption area of sound receiving room m Average acoustic radiation efficiency of members of sound receiving room ( n ) n IL Vibration insertion loss of deck structure of sound receiving room ( n ) db n.3.1 Calculation of Vibration Transmission The vibration velocity level propagating from the sound source to the sound receiving room is calculated using the SA method. In order to drastically reduce the time required for creating the analysis model of the SA method, the cross section geometry CAD data of the hull structure is used to create the hull shape model for the SA method. All decks, hull plates, steel walls and pillars in the vibration propagation path from the sound source to the sound receiving room is included in the hull shape model. However, members such as girders or stiffeners are not included. Also, only the vibration energy transmission of bending waves is included in the SA method. The effect of reduced members and simplified SA method on the vibration energy transmission is considered by adjusting internal loss factor and coupling loss factor of the analysis model. Fig.3 shows the geometry model of the engine room and accommodation space of a bulk carrier (37, DWT). Fig.4 shows cross section geometry models of Fr.16- and Fr.1-4 between web frames. This hull shape model can be created in several days including the CAD data creation. The analysis model is created by entering thickness and material property data in MS xcel format. 59

5 Figure 3 Hull shape model of engine room and accommodation space of a bulk carrier Figure 4 Cross section hull shape models between web frame sections.3. Calculating the Sound Pressure Level of the Sound Receiving Room The sound pressure level of the sound receiving room is calculated based on the vibration velocity level of the deck using the Janssen method. In the Janssen method, the vibration transmission loss from the deck and acoustic radiation efficiency are required for all interior members (floor, wall, and ceiling) of the sound receiving room. However, these data are difficult to obtain by actual ship/full-size model tests. Therefore, the combinations of interior members (floor, wall, ceiling) of a cabin in an actual ship are divided into 3 types of interior specifications, after which the average acoustic radiation efficiency of the 3 types of interior specifications and the vibration transmission loss from the floor is obtained from data which could be measured by the actual ship test, namely the sound pressure level and vibration velocity level of interior members in order to create the vibration/acoustic database. Then, interior specifications of the sound receiving room are selected from the database and the sound pressure level emitted from each member is calculated using Formulas (3) and (4). The insertion loss of the deck structure is obtained and used by organizing the results of an actual ship test or full-size model test as a vibration/acoustic database. Fig.5 shows the positions for measuring the sound pressure level and the vibration velocity level of the interior members of a cabin and the deck at an actual ship test.

6 Sound pressure level Vibration velocity level Figure 5 Positions for measuring sound pressure and vibration velocity levels of the interior members 3. NOIS PRDICTION RSULTS AND PRDICTION ACCURACY 3.1 Analysis Model Fig.6 shows the hull shape model of the engine room and accommodation space of a 37, DWT bulk carrier as well as the positions of the main engine and diesel generator. The engine room, 5 decks of accommodation space, engine casing and funnel are modeled using,357 plate elements. The position of the sound receiving room in the hull shape model is defined using deck names and frame numbers/longi numbers surrounding the sound receiving room. Also the positions of the main engine and diesel generator are defined using deck name and frame numbers/longi numbers. So the vibration velocity level at the corresponding element is entered as the vibration source level. Pillars in the engine room are also defined using elements connecting other elements at the position of the pillars. The hull plate elements in contact with sea water are specified based on the user-defined draft position in order to consider the radiation damping into the sea water and the effect of additional water mass. Diesel generator Main engine lements contacting seawater Figure 6 Model for predicting noise levels in cabins of a 37, DWT bulk carrier 3. Noise Level Prediction Results Fig.7 shows the predicted noise level results of 37 cabins during sea trial by displaying a color contour on the floor surface of the sound receiving room of the hull shape model. Fig.8 compares the predicted results and measured results of the noise level of all sound receiving rooms from the Upp. Dk. to the Nav. Dk. The predicted noise level of the sound receiving room includes the calculated result of the structure borne sound from the main engine/diesel generator and the measured data of the air conditioning sound. The vibration velocity level measured near the main engine during sea trial is used as the vibration source data of the main engine, and the vibration velocity level measured near the 61

7 diesel generator during individual operation is used as the vibration source data of the diesel generator. The sound pressure level measured in the sound receiving room during individual operation of the air conditioner is used as the sound source data of the air conditioning sound. Fig.9 shows the distribution of the difference between the predicted result and measured result of the noise level during sea trial. Fig.7 shows that the predicted noise level becomes smaller from the Upp. Dk. towards the Nav. Dk. in the upper floors. Fig.8 shows that the predicted result and measured result of the noise level match well in most sound receiving rooms, except for some of the sound receiving rooms in the Upp. Dk., A Dk. and Nav. Dk. Fig.9 shows that the difference between the predicted result and measured result of the noise level is within ±3dB in 31 sound receiving rooms (84% of all sound receiving rooms) and ±5dB in 36 sound receiving rooms (97% of all sound receiving rooms). The predicted result has cleared a target of the noise level prediction accuracy, which is "the level differences are within ±3dB in 8% of all sound receiving rooms". The difference between the predicted result and measured result in the sound receiving rooms of the Nav. Dk. is over 8dB. Since the measured result of the noise level is larger in the sound receiving rooms of the Nav. Dk. than those of the C Dk., it can be assumed that there are sound sources other than the structure borne sounds of the main engine and diesel generator and the air conditioning sound. Figure 7 Calculated noise levels in cabins of a bulk carrier Sea rial Calculated noise level Noise LeveldB] Nav. C - DK B - DK A - DK Upper WHLHOUS PILOT C/NG'S DAY RM C/NG'S BD RM /NG. /OFF. CAP'S BD RM CAP'S DAY RM 3/OFF. OFF'S SPAR(A) OFF'S SPAR(B) 3/NG. 1/NG'S DAY RM 1/NG'S BD RM NO.1 OILR BOATSWAIN C/OFF'S BD RM C/OFF'S DAY RM AB.S.M.(A) AB.S.M.(B) AB.S.M.(C) Cabins OILR(C) OILR(B) OILR(A) WIPR CRW'S SPAR C/STW COOK BOY ORD.SM. OFF'S MSS RM OFF'S LOUNG CRW'S MSS RM CRW'S LOUNG GYMNASIUM SHIP'S OFFIC HOSPITAL Figure 8 Comparison between predicted and measured noise levels in cabins at sea trial 6

8 Number of Cabins < > Noise Level Difference [db] Figure 9 Distribution of difference between predicted and measured noise levels in cabins Fig. shows the predicted results of the noise level, in which Calculated noise level includes the structure borne sounds of the main engine and diesel generator and the air conditioning sound, and Structure borne sound includes the structure borne sounds of the main engine and diesel generator. The structure borne sounds of the main engine and diesel generator are stronger from the Upp. Dk. to parts of the B Dk., and the air conditioning sound is stronger from the B Dk. to the Nav. Dk. The results show that the air conditioning sound must be included in the sound source for noise prediction. Structure borne sound Calculated noise level Noise LeveldB] Nav. C - DK B - DK A - DK Upper WHLHOUS PILOT C/NG'S DAY RM C/NG'S BD RM /NG. /OFF. CAP'S BD RM CAP'S DAY RM 3/OFF. OFF'S SPAR(A) OFF'S SPAR(B) 3/NG. 1/NG'S DAY RM 1/NG'S BD RM NO.1 OILR BOATSWAIN C/OFF'S BD RM C/OFF'S DAY RM AB.S.M.(A) AB.S.M.(B) AB.S.M.(C) Cabins OILR(C) OILR(B) OILR(A) WIPR CRW'S SPAR C/STW COOK BOY ORD.SM. OFF'S MSS RM OFF'S LOUNG CRW'S MSS RM CRW'S LOUNG GYMNASIUM SHIP'S OFFIC HOSPITAL Figure Calculated structure borne sounds and noise levels including air conditioning sound 3.3 Frequency Characteristic of the Noise Level Fig.11 compares the predicted result and measured result of the frequency characteristics of the noise level in a cabins of the B Dk. during sea trial. Fig.11 shows that the predicted result and measured result of the noise level match well in the range between 1/3 octave band center frequency 1Hz to khz. However, in the frequency range lower than 15Hz the predicted result is 5dB to db smaller than the measured result. Since the over-all noise level in a sound receiving room is mostly determined by sound pressure levels between frequencies 1Hz to 4kHz, the level differences are within ±3dB in 84% of the sound receiving rooms, as shown in Fig.9. Fig.1 and Fig.13 compares the predicted result and measured result of the noise levels at 1/3 octave band center frequency Hz and 1kHz for all sound receiving rooms from the Upp. Dk. to the Nav. Dk.. Fig.1 shows that the predicted result is smaller than the measured result at frequency Hz for almost all sound receiving rooms from the Upp. Dk. to the Nav. Dk.. And Fig.13 shows that the predicted result and measured result match well at frequency 1kHz. As for other frequencies, the predicted result and measured result of the noise level match well in the 1/3 octave band center frequency range between 1Hz to khz. On the other hand, the predicted result is 5dB to db smaller than the measured result in the frequency range lower than 15Hz. Therefore, it can be assumed that there are sound sources other than the structure borne sounds of the main engine and diesel generator and the air conditioning sound in the frequency range lower than 15Hz. 63

9 Cabin at B-Dk. Sea rial Calculated noise level k 1.5k 1.6k k.5k 3.15k 4k 5k 6.3k 8k k 1.5k 16k k Noise Level db] 1/3 Octave Band Center FrequencyHz Figure 11 Comparison between predicted and measured noise levels of 1/3 octave band in a cabin at B Dk. f=hz Sea rial Calculated noise level Noise LeveldB] Nav. C - DK B - DK A - DK Upper WHLHOUS PILOT C/NG'S DAY RM C/NG'S BD RM /NG. /OFF. CAP'S BD RM CAP'S DAY RM 3/OFF. OFF'S SPAR(A) OFF'S SPAR(B) 3/NG. 1/NG'S DAY RM 1/NG'S BD RM NO.1 OILR BOATSWAIN C/OFF'S BD RM C/OFF'S DAY RM AB.S.M.(A) AB.S.M.(B) AB.S.M.(C) Cabins OILR(C) OILR(B) OILR(A) WIPR CRW'S SPAR C/STW COOK BOY ORD.SM. OFF'S MSS RM OFF'S LOUNG CRW'S MSS RM CRW'S LOUNG GYMNASIUM SHIP'S OFFIC HOSPITAL Figure 1 Comparison between predicted and measured noise levels at Hz f=1khz Sea rial Calculated noise level Noise LeveldB] Nav. C - DK B - DK A - DK Upper WHLHOUS PILOT C/NG'S DAY RM C/NG'S BD RM /NG. /OFF. CAP'S BD RM CAP'S DAY RM 3/OFF. OFF'S SPAR(A) OFF'S SPAR(B) 3/NG. 1/NG'S DAY RM 1/NG'S BD RM NO.1 OILR BOATSWAIN C/OFF'S BD RM C/OFF'S DAY RM AB.S.M.(A) AB.S.M.(B) AB.S.M.(C) Cabins OILR(C) OILR(B) OILR(A) WIPR CRW'S SPAR C/STW COOK BOY ORD.SM. OFF'S MSS RM OFF'S LOUNG CRW'S MSS RM CRW'S LOUNG GYMNASIUM SHIP'S OFFIC HOSPITAL Figure 13 Comparison between predicted and measured noise levels at 1kHz 64

10 3.4 Predicted Result of Vibration Acceleration Level Fig.14 (a) shows the predicted result of the vibration acceleration levels on a hull shape model at 1/3 octave band center frequency Hz. Fig.14 (b) shows the predicted result of the vibration acceleration levels at frequency 1kHz. Fig.14 (a) shows that the vibration acceleration level of the main engine propagates through web frames of the 3rd. Dk. and nd. Dk. of the engine room to the accommodation space. It also shows that the vibration acceleration level of the main engine is larger than that of the diesel generator at frequency Hz. Fig.14 (b) shows that the vibration acceleration level of the diesel generator propagates through the nd. Dk., steel walls and aft walls of the engine room to the accommodation space. It also shows that the vibration acceleration level of the diesel generator is larger than that of the main engine at frequency 1kHz. These results indicate that the propagation path of the vibration acceleration level from the sound source can be estimated by displaying a contour of the predicted results of the vibration acceleration level on the hull shape model. Fr.1-4 Fr.1-4 (a) Frequency Hz (b) Frequency 1kHz Figure 14 Predicted vibration acceleration levels on hull shape model at Hz and 1kHz Fig.15 and Fig.16 compares the predicted result of the vibration acceleration level on the port side of the cross section (Fr.1-4) where the main engine is positioned and the measured result during sea trial. Fig.15 shows results at frequency Hz. Fig.16 shows results at frequency 1kHz. Fig.17 compares the predicted result and measured result of frequency characteristic of vibration acceleration levels at the A Dk. However, the predicted result is the average vibration acceleration level of the elementthe measured result is the vibration acceleration level of a specific position within the element. Fig.15 shows that the predicted result of the vibration acceleration level is over db smaller than the measured result at frequency Hz for decks and steel walls from the Upp. Dk. to the Nav. Dk., except for the Lower Dk. and 3rd. Dk. where the main engine and diesel generator are positioned. On the other hand, Fig.16 shows that the predicted result and measured result from the Upp. Dk. to the Nav. Dk. match well at frequency 1kHz. As for other frequencies, the predicted result and measured result of the vibration acceleration level match well in the frequency range over 315Hz. On the other hand, the predicted result is smaller than the measured result in the frequency range lower than Hz. Fig.17 shows that the difference between the predicted result and measured result is approximately ±5dB in the frequency range over Hz. On the other hand, the predicted result is 5dB to db smaller than the measured result in the frequency range lower than 315Hz. The relationship between the predicted result and measured result of the vibration acceleration level is the same as the predicted noise level result of the sound receiving room described in Section 3.3. Therefore, the noise level of the sound receiving rooms in the frequency range over 1Hz is considered to be the structure borne sound of the main engine and diesel generator. On the other hand, the cause of the predicted noise level result being smaller than the measured result in the frequency range lower than 15Hz is considered to be the structure borne sound of sound sources other than the main engine and diesel generator not being included in the prediction calculation. The structure borne sound caused by fluctuating pressure of the propeller is assumed to be a major sound source and needs consideration in the future. 65

11 f=hz Fr.1-4 section Calculated vibration acceleration level Sea trial Vibration Acceleration Level [db] 9 8 Navi. Dk. C Dk. B Dk. A Dk. Upp. Dk. nd Dk. 3rd. Dk. Lower Dk lement number Figure 15 Comparison between predicted and measured vibration acceleration levels at Hz f=1khz Fr.1-4 section Calculated vibration acceleration level Sea trial Vibration Acceleration Level [db] 9 8 Navi. Dk. C Dk. B Dk. A Dk. Upp. Dk. nd Dk. 3rd. Dk. Lower Dk lement number Figure 16 Comparison between predicted and measured vibration acceleration levels at 1kHz Deck at A Dk. Calculated vibration acceleration level Sea trial Vibration Acceleration Level [db] k 1.5k 1.6k k.5k 3.15k 4k 5k 6.3k 8k k 1.5k 16k k 1/3 Octave Band Ceter FrequencyHz Figure 17 Comparison between predicted and measured vibration acceleration levels at A Dk. 4. SUMMARY In order to satisfy the new IMO ship noise level regulation value, a highly accurate noise prediction program that can be used during the design phase has been developed. By combining the SA method, the Janssen method and vibration/acoustic databases obtained from actual ship tests and model tests, both the analysis model creation time and analysis time have been drastically reduced while maintaining prediction accuracy. A noise prediction is performed on a bulk carrier (37, DWT) in order to verify the application on actual ships and the prediction accuracy. It is confirmed that the noise prediction on a bulk carrier can be performed in one week, including the hull shape model creation from CAD data, analysis model creation, analysis execution, output of prediction result and result confirmation. However, the time required for creating vibration/acoustic databases is not included. 66

12 The difference between the predicted result and measured result of the noise level is within ±3dB in 84% of all sound receiving rooms, and ±5dB in 97% of all sound receiving rooms. The predicted result has cleared a target of the noise level prediction accuracy, which is "the level differences are within ±3dB in 8% of all sound receiving rooms". Regarding the noise level of sound receiving rooms and vibration acceleration level of the decks of the hull structure and steel walls, the predicted result and measured result match well in the frequency range between 1Hz or 315Hz up to khz, which indicates that the structure borne sounds of the main engine and diesel generator and the air conditioning sound can be estimated. However, the predicted result is 5dB to db smaller than the measured result in the frequency range lower than 1Hz. It can be assumed that sound sources other than the main engine and diesel generator exist, for example the structure borne sound caused by fluctuating pressure of the propeller. This phenomenon needs to be explored in the future in order to improve the prediction accuracy of the program. Finally, the vibration/acoustic database requires continuous updating and additional data in order to assure and improve the prediction accuracy of the program. However, it takes several days to several months in order to perform actual ship tests for measuring vibration acceleration levels and noise levels of sound equipment or collecting sound data such as sound absorption coefficient or sound transmission loss and to perform full-size model tests for collecting vibration/acoustic characteristic data of interior members to create a vibration/acoustic database. The costs are also needed. So shipbuilding companies, material manufacturers and equipment manufacturers are recommended to work together in order to continuously update and add data to the vibration/acoustic database. ACKNOWLDGMNTS This ship noise prediction program is jointly developed by ClassNK, shipbuilding companies in Japan and Tokai University based on the ClassNK Joint R&D for Industries scheme. RFRNCS 1. IMO/MSC 91//Add.1 Annex 1, Resolution MSC.337(91). Janssen J.H., Buiten J. On acoustical designing in naval architecture. Proc INTR-NOIS 73; -4 August: Lyngby, Denmark 1973, p Lyon R.H., R.G. DeJong R.G. Theory and application of statistical energy analysis, B.H., Jensen J.O. Calculation of structure borne noise transmission in ships using the Statistical nergy Analysis approach. International Symposium on Shipboard Acoustics 1976, LSVIR, 1977, p Research and study for ship noise, Report of SR156 working group of the Japan Ship Research Association, xperimental studies for noise control for small and medium-sized ships. Report of the Cooperative Association of Japan Shipbuilders, Kimura K., Inoue., Okoshi S., Sato K., Nakahara R., Suzuki H., Kinoshita T. Development of prediction system for ship noise and underwater radiated sound. Technical Report of Mitsui ngineering & Shipbuilding, 15, Vol.14, P Shuri H. Development of noise prediction programs for acoustic ship designs, ClassNK Technical Bulletin, 13, Vol.31, p