NO20210013A1

NO20210013A1 - Apparatus and method for measuring underwater radiated noise of vessel in particular dockyard

Info

Publication number: NO20210013A1
Application number: NO20210013A
Authority: NO
Inventors: Dajing Shang; Qi Li; Rui Tang; Jundong Sun; Hongzhe Xu
Original assignee: Univ Harbin Eng
Priority date: 2020-01-09
Filing date: 2021-01-06
Publication date: 2021-07-12
Also published as: KR20210090553A; FI20215006A1; CN111189526A

Description

APPARATUS AND METHOD FOR MEASURING UNDERWATER RADIATED NOISE

OF VESSEL IN PARTICULAR DOCKYARD

TECHNICAL FIELD

The present disclosure relates to an underwater acoustical measuring apparatus, further to a measuring method based on the underwater acoustical measuring apparatus, and more particularly, to a system and method for measuring underwater radiated noise of a vessel in a particular dockyard.

BACKGROUND

The measurement of underwater radiated noise of vessels is a crucial step in vibration and noise reduction of vessels. At present, standard measurement of underwater radiated noise of vessels is required to be carried out in the deep sea, and the testing method thereof is carried out based on the spherical wave propagation rule of acoustical waves in free field. Such a testing method is difficult to achieve because the surrounding sea areas of China are shallow continental shelves, which are affected by the shallow sea waveguide effect, and there is great marine environmental noise influence in marine testing environment, resulting in large measurement errors.

Up to now, Up to now, the standards or specifications for the measurement of underwater radiated noise of vessels that have been promulgated at home and abroad include: "ANSI S-12.64" issued by the American Standards Institute, "RULES FOR CLASSIFICATION OF DET NORSKEVERITAS AS Ships PART 6 CHAPTER 24" issued by the Det Norske Veritas, "ISO/PAS 17208-1" issued by the International Organization for Standardization, and "NR 614 DT R01E" issued by the Bureau Veritas. At present, standard GJB273A-96: "Testing Guidelines for Underwater Radiated Noise of Vessels 2018" issued by the China Classification Society is mainly used for the measurement of underwater radiated noise of vessels in China. The methods mentioned in the above standard and specification documents are all free-field measurement methods of vessel radiated noise, which are fundamentally different from the reverberation-field measurement method of the present disclosure in terms of measuring acoustical environment and acoustical principles.

Dockyard is a building for shipbuilding and ship repair. It is a good way to measure underwater noise of vessels in a dockyard with good acoustical test conditions. From the perspective of acoustics, the dockyard is an enclosed sound space where acoustical waves are constantly reflected between dock walls, dock floor and the water surface, forming an enclosed spatial sound field. From the perspective of hydrodynamics, with the outer circulation system of the dockyard, a vessel can have a wake field close to that in open water and sound radiation close to that under normal cruising conditions of the vessel. Since the sound absorption capacity of the existing underwater materials is far from meeting the design performance of free-field environment, it is difficult to construct free-field conditions in a dockyard. Therefore, the construction of a non-anechoic water tank sound field that conforms to hydrodynamic tests in the dockyard is the best choice for vessel radiated noise testing.

In a non-anechoic water tank, the measurement problem of the radiated sound power of underwater complex sound sources that do not meet diffusion field conditions can be solved based on a space averaging technique. This method can be extended to dockyard water tanks, but vessel anchoring, diversion and space averaging need to be specially designed according to the characteristics of the dockyard water tanks. Reference document 1 similar to the method of the present disclosure: "METHOD FOR MEASURING LOW-FREQUENCY RADIATED SOUND POWER OF UNDERWATER SOUND SOURCES IN RECTANGULAR REVERBERATION WATER TANK PLACED IN AIR” (CN104501938A). The present disclosure and the reference document 1 both relate to a measuring method for use in underwater enclosed space, and differ in that a small water tank is used in reference document 1 to measure the radiated sound power of a small underwater sound source in a low frequency band below the cut-off frequency, with a spatial scanning averaging approach being used. The reference document 1 does not mention the measurement of radiated noise of large-scale structured sound sources such as vessels under the conditions of mechanical noise and hydrodynamic noise. Reference document 2 similar to the method of the present disclosure: "METHOD FOR RECIPROCITY CALIBRATION OF UNDERWATER ACOUSTICAL TRANSDUCER USING REVERBERATION WATER TANK" (CN106501795A), which is also a testing method based on reverberation water tank theory. The difference is that the space averaging technique in the reference document 2 is a scanning approach with a transducer and a hydrophone to complete the calibration of a small-scale underwater acoustical transducer. However, this method cannot perform "spatial disordered scanning movement" on large equipment such as vessels. Moreover, the reference document 2 involves electric parameter measurement, while the present disclosure involves acoustical parameter measurement. The present disclosure also involves fixed anti-flow anti-flow design of the hydrophones to reduce the hydrodynamic noise of the hydrophones and improve the testing accuracy.

SUMMARY

An objective of the present disclosure is to provide an apparatus for measuring underwater radiated noise of a vessel in a particular dockyard that can realize full-band narrow-band measurement of vessel radiated noise. Another objective of the present disclosure is to provide a measuring method based on an apparatus for measuring underwater radiated noise of a vessel in a particular dockyard, which is convenient for measurement and suitable for technical tests on vibration and noise reduction during vessel design and for measurement and evaluation of underwater radiated noise of a vessel.

The objectives of the present disclosure are achieved as follows:

The apparatus for measuring underwater radiated noise of a vessel in a particular dockyard disclosed in the present disclosure includes a dockyard. Hydrophone arrays are arranged in the dockyard. The hydrophone arrays are vertical arrays, which are deployed in the dockyard in the form of fixed arrays. The hydrophone arrays are distributed on two sides of a measured vessel with a shortest distance away from the vessel being not less than half of a minimum test frequency wavelength.

The apparatus for measuring underwater radiated noise of a vessel in a particular dockyard disclosed in the present disclosure may further include:

1. An interval between array elements in each hydrophone array may be a minimum of 1/4 of the maximum wavelength corresponding to a testing frequency band and 1 m; a horizontal interval between arrays may be not less than 1/4 of the maximum wavelength corresponding to the testing frequency band; and the total number of hydrophones may be not less than 250.

2. The hydrophone array may be wrapped with an anti-flow acoustic transmission material. The measuring method based on the apparatus for measuring underwater radiated noise of a vessel in a particular dockyard disclosed in the present disclosure includes:

step 1: allowing the vessel to enter the dockyard and fixing the vessel by mooring, wherein a tail propeller of the vessel faces a dock gate of the dockyard; a part, located under a waterline, of the vessel has a length of not more than 2/3 of a length of the dockyard and a breadth of not more than 2/3 of a breadth of the dockyard; and a draft of the vessel is not more than 1/2 of a depth of water in the dockyard;

step 2: deploying hydrophone arrays, which are vertical arrays, in the dockyard in the form of fixed arrays, distributing the hydrophone arrays on two sides of the vessel with the shortest distance away from the vessel being not less than half of a minimum test frequency wavelength, and adjusting the posture of the hydrophone arrays to keep vertical and stable;

step 3: calibrating a sound field in the dockyard;

step 4: enabling vessel equipment to normally start or operate according to testing conditions; step 5: starting to record, by data acquisition equipment, acoustical wave signals measured by the hydrophones after the vessel equipment normally starts or operates;

step 6: averaging a power spectrum of the acoustical wave signal measured by each hydrophone, then averaging all the averaged power spectra of the hydrophones, and converting the averaged sound power into a sound pressure, thereby obtaining a spatial average sound pressure level of the sound field.

The measuring method disclosed in the present disclosure may further include:

2. The calibrating a sound field in the dockyard may include calibrating sound field characteristic variations after the vessel enters the dockyard; sound field parameters may be calibrated by means of reverberation time measurement in the dockyard; in the reverberation time measurement, sound sources may be arranged in at least 8 positions around the vessel; and a correction of the sound field may be calculated based on the reverberation time according to an attenuation curve of the average sound pressure of the sound field measured by the hydrophone arrays.

3. The correction of the sound field may be a difference 10l g(4/R) between the spatial average sound pressure level <SPL> of the sound field and an average sound power level SWL of free field, expressed as:

where R is a room constant, which has a value only related to the physical characteristics of the dockyard and is expressed as a function of a volume V of water in the dockyard, a total area S of parts, located under the waterline of the vessel, of a hull and a dockyard wall, and a sound velocity c0 in water:

4. In step 5, a testing signal may have a signal-to-noise ratio of not less than 5 dB; and for stable operation, the data acquisition equipment may record the acoustical wave signals for not less than 1 minute after the equipment operates stably.

The first proposed method for measuring underwater radiated noise of a vessel in a particular dockyard disclosed in the present disclosure has the following beneficial effects: the present disclosure relates to a method for measuring underwater radiated noise of a vessel in a large particular dockyard; the large particular dockyard specified in the method of the present disclosure refers to a dockyard for testing radiated noise of a large vessel. The dockyard is equipped with measuring hydrophone arrays and an outer circulation system for wake flow during the operation of the vessel's propeller. The fixed anti-flow treatment on the hydrophones in the method of the present disclosure can reduce the flow noise influence and improve the measurement accuracy. The testing accuracy of 250 hydrophones mentioned in the present disclosure can reach the range of ±1dB. When the number of the hydrophones is insufficient, the method of the present disclosure is still applicable, but the test accuracy will be slightly reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is flowchart of a method for measuring underwater radiated noise of a vessel in a particular dockyard according to an embodiment of the present disclosure.

FIG. 2 is flowchart of a method for calculating radiated sound power of a vessel according to an embodiment of the present disclosure.

FIG. 3 is a schematic diagram of mooring of a vessel and deployment of hydrophones according to an embodiment of the present disclosure.

FIG. 4 is a schematic diagram of an apparatus for measuring underwater radiated noise of a vessel in a particular dockyard according to an embodiment of the present disclosure.

FIG. 5 is a top view of FIG.4.

DETAILED DESCRIPTION

The present disclosure provides an apparatus for measuring underwater radiated noise of a vessel in a particular dockyard and a measuring method based on the apparatus. The measuring method includes the following steps:

Step 1: the vessel enters the dockyard 1 via a dock gate and is fixed by mooring. A tail propeller of the vessel faces the dock gate 2 of the dockyard. A part, located under a waterline, of the vessel has a length of not more than 2/3 of a length of the dockyard and a breadth of not more than 2/3 of a breadth of the dockyard. A draft of the vessel is not more than 1/2 of a depth of water in the dockyard.

Step 2: hydrophone arrays for spatial average measurement are vertical arrays, which are deployed in the dockyard in the form of fixed arrays. The hydrophone arrays are distributed on two sides of the vessel with the shortest distance away from the vessel being not less than half of a minimum test frequency wavelength, and the posture of the hydrophone arrays is adjusted to keep vertical and stable.

In the step 2, the hydrophone arrays 3 are deployed in the form of vertical arrays. An interval between every two array elements may be a minimum of 1/4 of the maximum wavelength corresponding to a testing frequency band and 1 m. A horizontal interval between arrays is not less than 1/4 of the maximum wavelength corresponding to the testing frequency band. The total number of hydrophones is not less than 250.

In the step 2, the hydrophone array is wrapped with an anti-flow acoustic transmission material which is capable of resisting weak water flow impact and has acoustic transmission capability. The material is subjected to anti-flow treatment.

Step 3: a sound field in the dockyard is calibrated. The calibration of the sound field in the dockyard mainly includes calibrating sound field characteristic variations after the vessel enters the dockyard. Sound field parameters are calibrated by means of reverberation time measurement in the dockyard. In the reverberation time measurement, sound sources are required to be arranged in at least 8 positions around the vessel. A correction of the sound field is calculated based on the reverberation time according to an attenuation curve of the average sound pressure of the sound field measured by the hydrophone arrays.

In the step 3, the correction of the sound field is a difference 10l g(4/R) between the spatial average sound pressure level <SPL> of the sound field and an average sound power level SWL of a free field, expressed as:

Step 4: vessel equipment is enabled to normally start or operate according to testing conditions. In the step 4, the types of the testing conditions in the method of the present disclosure may include: vessel’s mechanical noise, propeller noise and hydrodynamic noise.

In the step 4, the equipment mode of operation under the testing conditions in the method of the present disclosure may include: unit operation within the vessel, combined operation of multiple sets of equipment, and whole operation. For example, a main machine operates independently; main and auxiliary machines operate simultaneously; and a whole vessel system including a propelling system, a power system, etc. operates.

In the step 4, normal operation of vessel equipment refers to, for equipment capable of operating stably, for example, the auxiliary machine capable of operating normally and stably, such equipment being required to operate stably for more than one minute.

Step 5: data acquisition equipment starts to record acoustical wave signals measured by the hydrophones after the vessel equipment normally starts or operates.

In the step 5, a testing signal should have a signal-to-noise ratio of not less than 5 dB.

In the step 5, for stable operation, the data acquisition equipment records the acoustical wave signals for not less than 1 minute after the equipment operates stably.

Step 6: long time averaging is carried out for a power spectrum of the acoustical wave signal measured by each hydrophone, and then all the averaged power spectra of the hydrophones are averaged. The averaged sound power is converted into a sound pressure, thereby obtaining a spatial average sound pressure level of the sound field.

Further, in the step 6, the average sound power level of free field of the vessel’s underwater radiated noise may be obtained according to the spatial average sound pressure level of the sound field and the correction of the sound field.

The disclosure will be described by way of example in more detail below.

Embodiment 1: Measurement of Underwater Radiated Mechanical Noise of Vessel in Particular Dockyard

The testing method of this embodiment includes steps as shown in FIG. 1 and FIG. 2, and the type of the dockyard used is as shown in FIG.3.

Water is injected into the dockyard, and the vessel enters the dockyard. A space equal to 1/3 of the length of the vessel is reserved for the prow. The vessel is parked in the lateral central position of the dockyard with the stern facing the inlet of an outer circulating pipe of the dockyard. The vessel is moored. The dock gate is closed, and water is injected into the dockyard so that the water level is twice the draft of the vessel.

The hydrophone array is a 32-element vertical array, where the distance between the hydrophone at the top of the array and the water surface is 1/4 of the lowest frequency wavelength of testing, and the distance between the hydrophone at the bottom of the array and the dock floor is 1/4 of the lowest frequency wavelength of testing. The hydrophone arrays are deployed near the prow with a distance away from the prow being 1/2 of the lowest frequency wavelength of testing. The positions of the hydrophones in the middle of the array are halved. In total, 8 hydrophone arrays and 256 hydrophones are used. Every 4 arrays form an area array at intervals of 1/4 of the lowest frequency wavelength of testing. Two area arrays are deployed along the inner walls of the dockyard, respectively, with a distance away from the inner wall of the dockyard being 1/4 of the lowest frequency wavelength of testing.

The hydrophone array is wrapped with fiber nylon cloth, or other anti-flow acoustic transmission materials.

Standard sound sources are used around at 45-degree equal intervals in the dockyard. According to the measurement principle of an interrupted sound source method, the hydrophone arrays are used to measure the attenuation curve of the spatial average sound pressure of the sound field, thereby obtaining the reverberation time of the sound field. The correction of the sound field is obtained based on the reverberation time.

Vessel equipment normally starts or operates according to the testing conditions. In this embodiment, the auxiliary machine starts, while other equipment such as the main machine is in off state.

After the auxiliary machine stably operates for a period of time, the data acquisition equipment starts to record time-domain signals of sound pressure of the sound field for 1 minute.

Then, the data acquisition equipment stops recording, and the auxiliary machine stops operating. Power spectrum calculation is performed on each of the acoustical signals measured by 256 hydrophones, and the power spectra during the testing duration are averaged. The time-averaged power spectrum signals of 256 hydrophones are averaged to obtain the spatial average sound power level for measurement of all the array elements. Then, the spatial average sound power level is converted into the spatial average sound pressure level of the sound field based on the square relationship between the sound power and the sound pressure amplitude.

In combination with the formula (1), the average sound power level of free field of the vessel’s underwater radiated noise is calculated from the average sound pressure level of the sound field and the correction of the sound field of the dockyard water tank.

Further, the main machine of the vessel is turned on, while the auxiliary machine and other equipment are turned off. The step of measuring the time-domain signals of the vessel radiated noise and the following steps are repeated, thereby obtaining the average sound power level of free field of the vessel’s underwater radiated noise under the condition that the main machine is turned on.

Still further, different vessel equipment is turned on to operate independently or different sets of vessel equipment are turned on to operate in combination with each other, to measure the underwater radiated noise of the vessel.

This embodiment is a case of measuring the mechanical noise of the vessel.

This embodiment is directed not only to measuring and evaluating the radiated noises of the vessel under different operating conditions and identifying the characteristics of the radiated noise, but also to realizing identification and diagnosis of noise sources by comparison between different operating conditions.

Embodiment 2: Measurement of Vessel Propeller Noise in Particular Dockyard

In combination with the disclosure, steps 1, 2, 3 and 4 are the same with embodiment 1 in implementation.

The wake flow formed by operating vessel propeller enters an outer circulating pipe system via the inlet of the outer circulating pipe; after the velocity of the operating vessel propeller reaches a set revolving velocity or navigational velocity, the vessel propeller keeps stable operation for a period of time. After the water circulation is stable, the hydrophones start measuring.

The steps 5 and 6 are continued.

This embodiment is a case of measuring vessel propeller noise and is also suited for the measurement of vessel’s hydrodynamic noise.

The method for measuring underwater radiated noise of a vessel in a particular dockyard disclosed in the present disclosure is directed to measuring vessel’s hydrodynamic noise such as mechanical noise and propeller noise in a large dockyard, and realizing measurement and evaluation of vessel radiated noise and identification and diagnosis of noise sources in vibration and noise reduction techniques.

The method of the present disclosure realizes measurement of underwater radiated noise of a large vessel in a dockyard, and is high in testing efficiency and high in measurement accuracy.

Claims

What is claimed is: 1. An apparatus for measuring underwater radiated noise of a vessel in a particular dockyard, comprising a dockyard, wherein hydrophone arrays are arranged in the dockyard; the hydrophone arrays are vertical arrays, which are deployed in the dockyard in the form of fixed arrays; and the hydrophone arrays are distributed on two sides of a measured vessel with a shortest distance away from the vessel being not less than half of a minimum test frequency wavelength.
2. The apparatus for measuring underwater radiated noise of a vessel in a particular dockyard according to claim 1, wherein an interval between array elements in each hydrophone array is a minimum of 1/4 of the maximum wavelength corresponding to a testing frequency band and 1 m; a horizontal interval between arrays is not less than 1/4 of the maximum wavelength corresponding to the testing frequency band; and the total number of hydrophones is not less than 250.
3. The apparatus for measuring underwater radiated noise of a vessel in a particular dockyard according to claim 1 or 2, wherein the hydrophone array is wrapped with an anti-flow acoustic transmission material.
4. A measuring method based on an apparatus for measuring underwater radiated noise of a vessel in a particular dockyard, comprising: step 1: allowing the vessel to enter the dockyard and fixing the vessel by mooring, wherein a tail propeller of the vessel faces a dock gate of the dockyard; a part, located under a waterline, of the vessel has a length of not more than 2/3 of a length of the dockyard and a breadth of not more than 2/3 of a breadth of the dockyard; and a draft of the vessel is not more than 1/2 of a depth of water in the dockyard; step 2: deploying hydrophone arrays, which are vertical arrays, in the dockyard in the form of fixed arrays, distributing the hydrophone arrays on two sides of the vessel with a shortest distance away from the vessel being not less than half of a minimum test frequency wavelength, and adjusting the posture of the hydrophone arrays to keep vertical and stable; step 3: calibrating a sound field in the dockyard; step 4: enabling vessel equipment to normally start or operate according to testing conditions; step 5: starting to record, by data acquisition equipment, acoustical wave signals measured by the hydrophones after the vessel equipment normally starts or operates; step 6: averaging a power spectrum of the acoustical wave signal measured by each hydrophone, then averaging all the averaged power spectra of the hydrophones, and converting the averaged sound power into a sound pressure, thereby obtaining a spatial average sound pressure level of the sound field.
5. The measuring method based on an apparatus for measuring underwater radiated noise of a vessel in a particular dockyard according to claim 4, wherein an interval between array elements in each hydrophone array is a minimum of 1/4 of the maximum wavelength corresponding to a testing frequency band and 1 m; a horizontal interval between arrays is not less than 1/4 of the maximum wavelength corresponding to the testing frequency band; and the total number of hydrophones is not less than 250.
6. The measuring method based on an apparatus for measuring underwater radiated noise of a vessel in a particular dockyard according to claim 5, wherein the calibrating a sound field in the dockyard comprises calibrating sound field characteristic variations after the vessel enters the dockyard; sound field parameters are calibrated by means of reverberation time measurement in the dockyard; in the reverberation time measurement, sound sources are arranged in at least 8 positions around the vessel; and a correction of the sound field is calculated based on the reverberation time according to an attenuation curve of the average sound pressure of the sound field measured by the hydrophone arrays.
7. The measuring method based on an apparatus for measuring underwater radiated noise of a vessel in a particular dockyard according to claim 6, wherein the correction of the sound field is a difference 10l g(4/R) between the spatial average sound pressure level <SPL> of the sound field and an average sound power level SWL of free field, expressed as:

wherein R is a room constant, which has a value only related to the physical characteristics of the dockyard and is expressed as a function of a volume V of water in the dockyard, a total area S of parts, located under the waterline of the vessel, of a hull and a dockyard wall, and a sound velocity c0 in water:
8. The measuring method based on an apparatus for measuring underwater radiated noise of a vessel in a particular dockyard according to claim 4, wherein in step 5, a testing signal has a signalto-noise ratio of not less than 5 dB; and for stable operation, the data acquisition equipment records the acoustical wave signals for not less than 1 minute after the equipment operates stably.