CA2008274C - Areal sound intensity receiver - Google Patents
Areal sound intensity receiverInfo
- Publication number
- CA2008274C CA2008274C CA 2008274 CA2008274A CA2008274C CA 2008274 C CA2008274 C CA 2008274C CA 2008274 CA2008274 CA 2008274 CA 2008274 A CA2008274 A CA 2008274A CA 2008274 C CA2008274 C CA 2008274C
- Authority
- CA
- Canada
- Prior art keywords
- points
- microphone arrays
- microphones
- sound
- sound intensity
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
- 238000003491 array Methods 0.000 claims abstract description 32
- 239000013598 vector Substances 0.000 claims description 23
- 238000000034 method Methods 0.000 claims description 12
- 230000033001 locomotion Effects 0.000 claims description 8
- 238000012544 monitoring process Methods 0.000 claims description 5
- 238000005259 measurement Methods 0.000 abstract description 11
- 239000002245 particle Substances 0.000 description 8
- 238000005336 cracking Methods 0.000 description 5
- 238000013480 data collection Methods 0.000 description 4
- 239000004677 Nylon Substances 0.000 description 2
- 230000001133 acceleration Effects 0.000 description 2
- 230000007797 corrosion Effects 0.000 description 2
- 238000005260 corrosion Methods 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 239000012636 effector Substances 0.000 description 2
- 239000012530 fluid Substances 0.000 description 2
- 238000007689 inspection Methods 0.000 description 2
- 229920001778 nylon Polymers 0.000 description 2
- 230000001902 propagating effect Effects 0.000 description 2
- 238000012935 Averaging Methods 0.000 description 1
- 241000283153 Cetacea Species 0.000 description 1
- 229910000831 Steel Inorganic materials 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 230000003213 activating effect Effects 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 238000009530 blood pressure measurement Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000009795 derivation Methods 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000018109 developmental process Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000006870 function Effects 0.000 description 1
- 230000014509 gene expression Effects 0.000 description 1
- 230000005484 gravity Effects 0.000 description 1
- 239000006249 magnetic particle Substances 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000013507 mapping Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000005457 optimization Methods 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 238000005070 sampling Methods 0.000 description 1
- 238000001228 spectrum Methods 0.000 description 1
- 239000010959 steel Substances 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
- 238000003466 welding Methods 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
- G01H3/00—Measuring characteristics of vibrations by using a detector in a fluid
- G01H3/10—Amplitude; Power
- G01H3/12—Amplitude; Power by electric means
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Measurement Of Mechanical Vibrations Or Ultrasonic Waves (AREA)
- Transducers For Ultrasonic Waves (AREA)
- Measurement Of Velocity Or Position Using Acoustic Or Ultrasonic Waves (AREA)
Abstract
A system of three or more hydrophone arrays are utilised to measure underwater areal sound intensity. The hydrophone arrays bound at least one plane through which an areal sound intensity measurement is desired. Each hydrophone array comprises three orthogonal pairs of hydrophones with coincident acoustic centers.
The output of each hydrophone in the system is simultaneously sampled and the outputs processed to obtain a vectorial sound intensity representation at each of the hydrophone arrays from which a representation of the areal sound intensity across the noted plane may be derived.
The output of each hydrophone in the system is simultaneously sampled and the outputs processed to obtain a vectorial sound intensity representation at each of the hydrophone arrays from which a representation of the areal sound intensity across the noted plane may be derived.
Description
2~82~
AREAL SOUND INTENSITY RFCEIVER
Back~round of the Invention Many oEfshore oil field developments utilize floating production systems consisting of semi-submersible units, shuttle tanker fleets and sub-sea wells/flo~lines, because the oil and gas reserve sizes are not significantly high to favour the use of a massive gravity structure. The majori-ty of these structures are entirely constructed of steel plates, beams and tubulars joined together by welding; they may have to operate in an environment frequented by drifting first year or multi-year ice, mobile bergybits/growlers and extreme hostile waves. Consequently~ they are subjected to considerable deterioration and damage due to corrosion fatigue cracking at the welded joints and impact wi-th the drifting ice field or mobile lce masses. Furthermore, the commercial transport oE oil and gas across ice-bound nortilern regions requires ice-transiting ships capable of breaking through 4-5m thick ice and larger ice ridges; such ships are therefore subjec-ted to impact stresses.
The recent disasters of Alexander Kielland, Ocean Ranger and Pier Alpha have heightened the need for accurate monitoring of the saEety of these offshore structures. Known inspection procedures and techniques to detect and quantify cracks and defects at welded joints of oEfshore s-tructures include diver assisted Magnetic Particle Inspec-tion (MPI), Alternating Current Field Measurement (ACFM), E~dy Current (EC) and Ultrasonic Techniques.
Current acoustical approaches for monitoring fatigue cracks are based on -the measurement of sound pressure levels~ These are 2 ~ 7 ~
scalar quantities and hence no directional infor~ation can be revealed. Further, all of the known techniques have been -found to be limited in à pplication because they must operate in the close vicinity of welded joints and become useless iE positioned a short distance away from the zone of damage.
Accordingly there is a need for an improved technique ~or detecting corrosion fatigue and impact Eatigue in structures.
Summary of the invention The subject invention recognises that intensity - which is a vector quantity indicative of the magnitude and direction oE
acoustic energy flow - would be an inherently better descriptor of ac-tive sound Eields. This is for the following reasons. A sound field will have both active and reactive components. Ambient noise is predominantly reactive and tends to have low particle velocities~ Vibrational energy radiated from structures forms active fields with high particle velocities. Consequently, signal~
to-noise ratios have the po-tential for a gain of up to 20 dB
through intensity mapping ins-tead of pressure measurements because of the high particle velocities and direc-tional nature of an active field over the reac-tiveness of noise environments.
Accordingly, the present invention ~rovides a device for measuring the intensity of sound from an acoustic source in a medium comprisingo at least three microphone arrays spaced from each other, each of said microphone arrays comprising six microphones configured as three orthogonal pairs of microphones;
means Eor simultaneously sensing the output from each of said microphones in order to determine a real-time sound intensity vector at each of said microphone arrays; and means ~or providing ,; ;, , "
. ., . :. : ~ ~:,,. ....... . . ::
:,-7 ~
an indication of the areal intensity of sound through a notional plane bounded by at least three of said at least three microphone arrays.
In another aspect there is provided a method of deriving a sound intensity vector field over an area in a medium comprising the steps of: simultaneously sensing sound pressure in the medium at a plurality of points comprising at least three clusters of points, each cluster of poin-ts configured as three orthogonal pairs of points wherein the mid-points of the three orthogonal pairs of points of a cluster are coincident; determining the sound intensity '~
vector at the center of each of said clusters of points; and determin,ing an indicating of the sound intensity vector field over an area bounded by at least three of said at least three clusters of points. ~, In the figures which represent example embodiments of the invention:
: figure 1 is a perspective diagram of an array of hydrophones made in accordance with this invention;
figure 2 is a perspective view of an apparatus for use : as an areal sound intensity receiver incorporating four of the arrays of figure l;
figures 3 is a block diagram of a system for the operation of the apparatus of figure 2; and figure ~ is a perspective schematic of an alternate apparatus for use as an areal sound intensity receiver, shown surrounding an object.
... .. . .. . .. .
2 ~ ~
:~etailed Description The classic definition for sound intensity is a vector quantity that describes the net amount and direction of flow of acoustic power at ~ given point in sp~ce (where intensity is in W/m2 and the intensity level is in d3 re lpW/m~). It is well established and stated in physics that if the intensity vector I
(the energy flow vector) is the net rate of flow of energy per unit area at the given position, then the acoustic power, w, passing through a surface, S is:
W = I I. dS (1) W = r In- dS (2) where In is the vector component normal to the surface. I~ a mediu~ without flow or bulk movement, the intensity vector I is equal to the ti~e averaged product of the instantaneous pressure p(t) and the corresponding particle velocity V(t) at the same point. This is expressed mathematically as:
+T/2 .~ lim I = T-~ - p(t) .v(t)dt (3) T
Hence the intensity veotor co~ponent in a given direction Ic is:
+T/2 lim I = T~ T p(t) .vr(~)dt (4) From Eulers equatio~ we know that, ~or a sound field propagating in a fluid, the particle acceleration A is given by the ratio of the pressure gradient to the fluid density p :
~ _ ~Q~27~
A ~ ( Eulers equation~ (5) p ar The particle velocity can thus be ohtained by integrating the particle acceleration:
J (6) P ar The pressure gradient is a continuous function which ~or two closely spaced microphones can be approximated u~ing a finite difference method:
ap = Pb - Pa (7) ar ~r where P~ and Pb are the pres~ures measured at the two microphones, and ~r is the receiver spacing.
Thi~ gives an approximation for the pressure gradient at the centre of the microphone pair. The pressure at this point is derived from the average pres~ure of the two microphones:
( 8 ) Sub~tituting expressions (6), (7) and (8) into (4) we find that inten~ity c~n in practice be computed from:
Pa + Pb ( b a) t ( ) There ar~ inherent limitations in measuring intensity using tWG clo~ely spaced microphones and a finite pressure difference approximation for the derivation of the particle velocity 20~827~
The use of this technique in the measurement of sound intensit~ introduces a number oE errors which limit the useful frequency range of the system. These errors can be synthesized into the following categories:
i) a finite difference approximation error at high frequencies, ii) an error due to the phase mismatch when the phase difference between the two element positions is small, and iii) a random error.
Errors can be minimized by optimizing the receiver array and i-ts configuration, and by having high transducer performance in accordance with IEC, ISO and ANSI standards (e.g. ANSI Sl.12 1967 type X~, M). Signal averaging, as dictated by the ambient background conditions, will substantially reduce the random error.
For the detection of fakigue cracks, the application of a continuous calibration and a collective learning feedback diminishes the eEfect of errors and meets operational specifications and standards. Continuous optimization of the measurement system yields a high level of precision.
Equation (9) suggests the ability to obtain directional information. That is, lf a source emits an acoustic intensity, I, in a direction which makes an angle, B, with a notional line passing -through the centers of the microphone pair then the intensity in the direction of the notional line, I~, is related to I as follows:
Ir = I cos ~ (10) ~ . ; -~a~827~
Accordingly, an array oE three orthogonal pairs of microphones, with the acoustic centers of -the three orthogonal pairs coincident, is able to identify the direction and magnitude of an intensity vector impinging on the array.
The device 20 of figure 1 provides such an array adapted for underwater measurement. More particularly, a cluster of six hydrophones 22a, 22b, 22c, 22d, 22e, and 22f is arranged as three orthogonal pairs. That is, three pairs may be found such that a notional line through the center of the two hydrophones of each pair form three orthogonal lines. In figure 1, hydrophones 22a and 22c form one such pair, hydrophones 22b and 22d form a second such pair, and hydrophones 22e and 22f form the third such pair.
The distance, d, between the centers of the hydrophones of each orthogonal pair of hydrophones is equivalent and the acoustic centers of the three orthogonal pairs of hydrophones in the array are coincident.
Each of the six hydrophones is spherical in shape. Each hydrophone is supported at one end of a hollow tube 24a, 24b, 24c, 24d~ 24e, and 24f. The tubes are received by resilient C-shaped sections 28a through 28f of bracket 26 ~28c and 28e are hidden in figure 1). Nylon pads 30a through 30f line the inside surface of the C-shaped sections (30c and 30e are hidden in figure 1). The connecting wires to the hydrophones pass through the centers of the hollow tubes 24a through 24f.
Reflections at the measuring device are a problem in underwater acoustic measurement. The device of figure 1 minimizes these as follows. Tubes 24a through 24f are made small to minimize reflections from the tubes. Energy that is absorbed by the tuhes .;
. . . :
~82~
propagates -toward the bracket 26 which acts as a sink; nylon pads 30a through 30f provide a mismatched impedance at the termination of the tubes which prevents reflection of the absorbed energy back toward the hydrophones 22a through 22f.
In figure 2~ four figure 1 arrays 120, 220~ 320, and 420 are supported at the four corners of the square platform 140.
Rotatable end-effector 144 of articulated robot arm 142 ls affixed to the central beam 146 of the platform. The robot arm is articulated at joint 145. An attitude and motion sensor 148 is supported by flared end 149 of central beam 145.
The control system for the apparatus of figure 2 is shown in figure 3. The four figure 2 hydrophone arrays are illustrated schematically a~ 120', 220', 320'l and 420'. A data collection circuit 150 is connected to the output of each hydrophone 122 of the system. The six data collection circuits associa-ted with one array of hydrophones feed a controller. Thus there are four controllers 152, 252, 352, and 452, associated with the four arrays 120' r 220', 320' and 420', respectively. The four controllers are connected to bus 154.
The attitude and motion sensor 148' is operatlvely connected to a computer controller 156 which is in turn connected to the bus 154. The actuating motors 158 of end-effector 144 and joint 145 (shown in figure 2), are connected to robot arm controller 160 which is in turn connected to bus 1540 Bus 154 feeds multiplexer 162 and the muleiplexer feeds computer 164. The computer 164 is connected to a mass storage device 166, a keyboard 168, and a display 170.
As energy propagates -through a medium it can be redistributed as reflections, back-scatter and attenuation. The flexing o~ an object in the medium is displayed by the Eirst two redistribution modes while fatigue cracking at nodes oE the object is revealed by the absorption tha-t occurs. Thus, an object in the medium can be considered an acoustic source. The areal sound intensity receiver of figures 2 and 3 may be used to scan an underwater acoustic source, as follows.
Platform 140 is moved into a position proximate an object to be analy~ed by selectively activating motors 158 associated with the robot arm 142 by way of control signals passed to robot arm controller 160 by the system computer via multiplexer 162 and bus 154.
Pressure waves propagating under~ater impinge upon the hydrophones 122 and result in a signal indicative of the pressure pasaing to the data collection circui-t 150 associated with each hydrophone~ Under control of controllers 152, 252, 352, and 452, the data collection circuits simul-taneously sample an analog signal from their respective hydrophones and convert it to a digital signal which is passed to the controllers. At the same time, signals are sampled by the attitude and motion sensors and passed to its computer controller 156. The attitude and motion sensors provide an indication of the degree of vibrational motion or varying attitude of the platform itself. These sarnplinys may be repeated in order to obtain average readings. The timing of the sampling is controlled by the sys-tem computer 164. The samples are converted to intensity vectors at each controller 152, 252~
352, and 452. Because the acoustic centers of the hydrophones of ., :; - ' - ,' ~, 2 ~ ~
each hydrophone array are coincident, the signals from the six hydrophones of each array may be converted into a vector measured at this acoustic center of the array. These vectors, along with attitude and motion information, are then passed to the system computer 16~ through bus 154 and multip]exer 162. An indication of the intensi-ty vector field within the square formed by the four hydrophone arrays is obtained by assuming a linear change between the four measured intensi-ty vectors. As will be well understood to those skilled in the art, the power passing through the square formed by the four hydrophone arrays may be calculated from this intensity field As will be obvious to those skilled in the art, a greater number of figure 1 hydrophone arrays may be placed about the square platform to improve the accuracy of the apparatus of figures 2 and 3.
As mentioned hereinbefore, intensity measurements screen out background noise. Thus, the intensity vectors will relate to pressure waves originating at the proximate object which is to be analyzed. This object may be, for example, the below water portion of a shipls hull, in which case, as the hull is scanned, any areal intensity measurement which shows a reduced intensity lndicates fatigue cracking. The attitude and mction sensors provide an indication of the magnitude of the error in the readings.
The areal sound intensi-ty receiver of figures 2 and 3 may also be used as a passive sonar device in a reac-tive sound environment, as follows. Consider the underwater arctic environment where shifting ice contributes significant sound levels to the background noise. Conventional systems require a high : ' , , , ! ~'., ' , ': ' :
', , ''' '': ' ': ''' '' ' '~:
,' ' ~ ' ' 2~ 7~ 04121-31 RDF
degree of sen~sitivity to passively detect the sound emissions Erom a moving submersible object at a distance. However, sensitive detectors are susceptible to the constant noise bursts from the shifting ice. The dynamic range of a receiving system needs to be large to detect the low level sound emissions from a distant source in the presence oE nearby ice cracking noiseO
Now consider one of the three dimensional sound intensity arrays. Each element of the array is highly sensitive but as an array the output is the sound intensity vector at the centre oE
the array. The vector sum of the sound intensity at that field point will be zero over a carefully chosen (site speciEic) time interval, despite the high level of -the pressure field as long as the noise emissions are random in origin~ In other words, the high level background noise would read zero sound intensity. Any source in the area originating from a speciEic direction would add constructively and therefore be de-tectable even if it were weak.
The standard signal processing techniques can still be applied to the data. For example, the intensity spectrum oE the source can be analyzed to look for characteristic Erequencies to distinguish different types oE source emissions (whales, submarines, etc.) With the Eour arrays of -the apparatus of Eigure 2, any known automatic focussing and range Einding techniques (such as triangulation) can be employed by appropriate software control in the system computer 164 (of figure 3) utilizing the vectoral informa-tion oE each array.
Figure 4 illustrates another apparatus 500 incorporating a number of the arrays 20 oE figure 1. More particularly, arrays 520, 720, 920~ and 1120 are supported at -the corners of a :::
2~2~
tetrahedronal structure 502. Arrays 620, 820, 1020, 1220, 1320, and 1420 ~hidden) are supported at the midpoints of the sides of the tetrahedronal structure. The tetrahedronal structure surrounds a submersed object 504. The control system for the device is ident;cal to that depicted ln figure 3 save that there are eight arrays of hydrophones with elght controllers associated therewith and blocks 158 and 160 are unnecessary since the apparatus 500 is stationary. With the areal sound intensity receiver of figure 3 ~with the noted modifications) and figure 4, the total energy emi-tted from the object 504 may be monitored and changes in energy, which could be indicative of fatigue cracking, noted. This receiver is particularly suited to, for example, monitoring the energy flow from the base of an oil platform. ~ecause of the directional nature of the information obtained by the receiver, the tetrahedronal s-tructure need not be in close proximity to damaged welded joints in order to detect damage at such joints because triangulation may be employed to pinpoint the location of such join-ts.
The number of arrays along each side of the tetrahedronal structure is shown as three, however, an increased number along each side is possible and would have the effect oE increasing the accuracy of the measurements.
While the areal sound intensity receivers of the example embodiments are adapted Eor measurement in waterr it will be apparent to those skilled in the art that the receivers could be adapted for use in other media, such as air~
- :,: :,~, ::
-..: ~ :
.. : :
-.: -
AREAL SOUND INTENSITY RFCEIVER
Back~round of the Invention Many oEfshore oil field developments utilize floating production systems consisting of semi-submersible units, shuttle tanker fleets and sub-sea wells/flo~lines, because the oil and gas reserve sizes are not significantly high to favour the use of a massive gravity structure. The majori-ty of these structures are entirely constructed of steel plates, beams and tubulars joined together by welding; they may have to operate in an environment frequented by drifting first year or multi-year ice, mobile bergybits/growlers and extreme hostile waves. Consequently~ they are subjected to considerable deterioration and damage due to corrosion fatigue cracking at the welded joints and impact wi-th the drifting ice field or mobile lce masses. Furthermore, the commercial transport oE oil and gas across ice-bound nortilern regions requires ice-transiting ships capable of breaking through 4-5m thick ice and larger ice ridges; such ships are therefore subjec-ted to impact stresses.
The recent disasters of Alexander Kielland, Ocean Ranger and Pier Alpha have heightened the need for accurate monitoring of the saEety of these offshore structures. Known inspection procedures and techniques to detect and quantify cracks and defects at welded joints of oEfshore s-tructures include diver assisted Magnetic Particle Inspec-tion (MPI), Alternating Current Field Measurement (ACFM), E~dy Current (EC) and Ultrasonic Techniques.
Current acoustical approaches for monitoring fatigue cracks are based on -the measurement of sound pressure levels~ These are 2 ~ 7 ~
scalar quantities and hence no directional infor~ation can be revealed. Further, all of the known techniques have been -found to be limited in à pplication because they must operate in the close vicinity of welded joints and become useless iE positioned a short distance away from the zone of damage.
Accordingly there is a need for an improved technique ~or detecting corrosion fatigue and impact Eatigue in structures.
Summary of the invention The subject invention recognises that intensity - which is a vector quantity indicative of the magnitude and direction oE
acoustic energy flow - would be an inherently better descriptor of ac-tive sound Eields. This is for the following reasons. A sound field will have both active and reactive components. Ambient noise is predominantly reactive and tends to have low particle velocities~ Vibrational energy radiated from structures forms active fields with high particle velocities. Consequently, signal~
to-noise ratios have the po-tential for a gain of up to 20 dB
through intensity mapping ins-tead of pressure measurements because of the high particle velocities and direc-tional nature of an active field over the reac-tiveness of noise environments.
Accordingly, the present invention ~rovides a device for measuring the intensity of sound from an acoustic source in a medium comprisingo at least three microphone arrays spaced from each other, each of said microphone arrays comprising six microphones configured as three orthogonal pairs of microphones;
means Eor simultaneously sensing the output from each of said microphones in order to determine a real-time sound intensity vector at each of said microphone arrays; and means ~or providing ,; ;, , "
. ., . :. : ~ ~:,,. ....... . . ::
:,-7 ~
an indication of the areal intensity of sound through a notional plane bounded by at least three of said at least three microphone arrays.
In another aspect there is provided a method of deriving a sound intensity vector field over an area in a medium comprising the steps of: simultaneously sensing sound pressure in the medium at a plurality of points comprising at least three clusters of points, each cluster of poin-ts configured as three orthogonal pairs of points wherein the mid-points of the three orthogonal pairs of points of a cluster are coincident; determining the sound intensity '~
vector at the center of each of said clusters of points; and determin,ing an indicating of the sound intensity vector field over an area bounded by at least three of said at least three clusters of points. ~, In the figures which represent example embodiments of the invention:
: figure 1 is a perspective diagram of an array of hydrophones made in accordance with this invention;
figure 2 is a perspective view of an apparatus for use : as an areal sound intensity receiver incorporating four of the arrays of figure l;
figures 3 is a block diagram of a system for the operation of the apparatus of figure 2; and figure ~ is a perspective schematic of an alternate apparatus for use as an areal sound intensity receiver, shown surrounding an object.
... .. . .. . .. .
2 ~ ~
:~etailed Description The classic definition for sound intensity is a vector quantity that describes the net amount and direction of flow of acoustic power at ~ given point in sp~ce (where intensity is in W/m2 and the intensity level is in d3 re lpW/m~). It is well established and stated in physics that if the intensity vector I
(the energy flow vector) is the net rate of flow of energy per unit area at the given position, then the acoustic power, w, passing through a surface, S is:
W = I I. dS (1) W = r In- dS (2) where In is the vector component normal to the surface. I~ a mediu~ without flow or bulk movement, the intensity vector I is equal to the ti~e averaged product of the instantaneous pressure p(t) and the corresponding particle velocity V(t) at the same point. This is expressed mathematically as:
+T/2 .~ lim I = T-~ - p(t) .v(t)dt (3) T
Hence the intensity veotor co~ponent in a given direction Ic is:
+T/2 lim I = T~ T p(t) .vr(~)dt (4) From Eulers equatio~ we know that, ~or a sound field propagating in a fluid, the particle acceleration A is given by the ratio of the pressure gradient to the fluid density p :
~ _ ~Q~27~
A ~ ( Eulers equation~ (5) p ar The particle velocity can thus be ohtained by integrating the particle acceleration:
J (6) P ar The pressure gradient is a continuous function which ~or two closely spaced microphones can be approximated u~ing a finite difference method:
ap = Pb - Pa (7) ar ~r where P~ and Pb are the pres~ures measured at the two microphones, and ~r is the receiver spacing.
Thi~ gives an approximation for the pressure gradient at the centre of the microphone pair. The pressure at this point is derived from the average pres~ure of the two microphones:
( 8 ) Sub~tituting expressions (6), (7) and (8) into (4) we find that inten~ity c~n in practice be computed from:
Pa + Pb ( b a) t ( ) There ar~ inherent limitations in measuring intensity using tWG clo~ely spaced microphones and a finite pressure difference approximation for the derivation of the particle velocity 20~827~
The use of this technique in the measurement of sound intensit~ introduces a number oE errors which limit the useful frequency range of the system. These errors can be synthesized into the following categories:
i) a finite difference approximation error at high frequencies, ii) an error due to the phase mismatch when the phase difference between the two element positions is small, and iii) a random error.
Errors can be minimized by optimizing the receiver array and i-ts configuration, and by having high transducer performance in accordance with IEC, ISO and ANSI standards (e.g. ANSI Sl.12 1967 type X~, M). Signal averaging, as dictated by the ambient background conditions, will substantially reduce the random error.
For the detection of fakigue cracks, the application of a continuous calibration and a collective learning feedback diminishes the eEfect of errors and meets operational specifications and standards. Continuous optimization of the measurement system yields a high level of precision.
Equation (9) suggests the ability to obtain directional information. That is, lf a source emits an acoustic intensity, I, in a direction which makes an angle, B, with a notional line passing -through the centers of the microphone pair then the intensity in the direction of the notional line, I~, is related to I as follows:
Ir = I cos ~ (10) ~ . ; -~a~827~
Accordingly, an array oE three orthogonal pairs of microphones, with the acoustic centers of -the three orthogonal pairs coincident, is able to identify the direction and magnitude of an intensity vector impinging on the array.
The device 20 of figure 1 provides such an array adapted for underwater measurement. More particularly, a cluster of six hydrophones 22a, 22b, 22c, 22d, 22e, and 22f is arranged as three orthogonal pairs. That is, three pairs may be found such that a notional line through the center of the two hydrophones of each pair form three orthogonal lines. In figure 1, hydrophones 22a and 22c form one such pair, hydrophones 22b and 22d form a second such pair, and hydrophones 22e and 22f form the third such pair.
The distance, d, between the centers of the hydrophones of each orthogonal pair of hydrophones is equivalent and the acoustic centers of the three orthogonal pairs of hydrophones in the array are coincident.
Each of the six hydrophones is spherical in shape. Each hydrophone is supported at one end of a hollow tube 24a, 24b, 24c, 24d~ 24e, and 24f. The tubes are received by resilient C-shaped sections 28a through 28f of bracket 26 ~28c and 28e are hidden in figure 1). Nylon pads 30a through 30f line the inside surface of the C-shaped sections (30c and 30e are hidden in figure 1). The connecting wires to the hydrophones pass through the centers of the hollow tubes 24a through 24f.
Reflections at the measuring device are a problem in underwater acoustic measurement. The device of figure 1 minimizes these as follows. Tubes 24a through 24f are made small to minimize reflections from the tubes. Energy that is absorbed by the tuhes .;
. . . :
~82~
propagates -toward the bracket 26 which acts as a sink; nylon pads 30a through 30f provide a mismatched impedance at the termination of the tubes which prevents reflection of the absorbed energy back toward the hydrophones 22a through 22f.
In figure 2~ four figure 1 arrays 120, 220~ 320, and 420 are supported at the four corners of the square platform 140.
Rotatable end-effector 144 of articulated robot arm 142 ls affixed to the central beam 146 of the platform. The robot arm is articulated at joint 145. An attitude and motion sensor 148 is supported by flared end 149 of central beam 145.
The control system for the apparatus of figure 2 is shown in figure 3. The four figure 2 hydrophone arrays are illustrated schematically a~ 120', 220', 320'l and 420'. A data collection circuit 150 is connected to the output of each hydrophone 122 of the system. The six data collection circuits associa-ted with one array of hydrophones feed a controller. Thus there are four controllers 152, 252, 352, and 452, associated with the four arrays 120' r 220', 320' and 420', respectively. The four controllers are connected to bus 154.
The attitude and motion sensor 148' is operatlvely connected to a computer controller 156 which is in turn connected to the bus 154. The actuating motors 158 of end-effector 144 and joint 145 (shown in figure 2), are connected to robot arm controller 160 which is in turn connected to bus 1540 Bus 154 feeds multiplexer 162 and the muleiplexer feeds computer 164. The computer 164 is connected to a mass storage device 166, a keyboard 168, and a display 170.
As energy propagates -through a medium it can be redistributed as reflections, back-scatter and attenuation. The flexing o~ an object in the medium is displayed by the Eirst two redistribution modes while fatigue cracking at nodes oE the object is revealed by the absorption tha-t occurs. Thus, an object in the medium can be considered an acoustic source. The areal sound intensity receiver of figures 2 and 3 may be used to scan an underwater acoustic source, as follows.
Platform 140 is moved into a position proximate an object to be analy~ed by selectively activating motors 158 associated with the robot arm 142 by way of control signals passed to robot arm controller 160 by the system computer via multiplexer 162 and bus 154.
Pressure waves propagating under~ater impinge upon the hydrophones 122 and result in a signal indicative of the pressure pasaing to the data collection circui-t 150 associated with each hydrophone~ Under control of controllers 152, 252, 352, and 452, the data collection circuits simul-taneously sample an analog signal from their respective hydrophones and convert it to a digital signal which is passed to the controllers. At the same time, signals are sampled by the attitude and motion sensors and passed to its computer controller 156. The attitude and motion sensors provide an indication of the degree of vibrational motion or varying attitude of the platform itself. These sarnplinys may be repeated in order to obtain average readings. The timing of the sampling is controlled by the sys-tem computer 164. The samples are converted to intensity vectors at each controller 152, 252~
352, and 452. Because the acoustic centers of the hydrophones of ., :; - ' - ,' ~, 2 ~ ~
each hydrophone array are coincident, the signals from the six hydrophones of each array may be converted into a vector measured at this acoustic center of the array. These vectors, along with attitude and motion information, are then passed to the system computer 16~ through bus 154 and multip]exer 162. An indication of the intensi-ty vector field within the square formed by the four hydrophone arrays is obtained by assuming a linear change between the four measured intensi-ty vectors. As will be well understood to those skilled in the art, the power passing through the square formed by the four hydrophone arrays may be calculated from this intensity field As will be obvious to those skilled in the art, a greater number of figure 1 hydrophone arrays may be placed about the square platform to improve the accuracy of the apparatus of figures 2 and 3.
As mentioned hereinbefore, intensity measurements screen out background noise. Thus, the intensity vectors will relate to pressure waves originating at the proximate object which is to be analyzed. This object may be, for example, the below water portion of a shipls hull, in which case, as the hull is scanned, any areal intensity measurement which shows a reduced intensity lndicates fatigue cracking. The attitude and mction sensors provide an indication of the magnitude of the error in the readings.
The areal sound intensi-ty receiver of figures 2 and 3 may also be used as a passive sonar device in a reac-tive sound environment, as follows. Consider the underwater arctic environment where shifting ice contributes significant sound levels to the background noise. Conventional systems require a high : ' , , , ! ~'., ' , ': ' :
', , ''' '': ' ': ''' '' ' '~:
,' ' ~ ' ' 2~ 7~ 04121-31 RDF
degree of sen~sitivity to passively detect the sound emissions Erom a moving submersible object at a distance. However, sensitive detectors are susceptible to the constant noise bursts from the shifting ice. The dynamic range of a receiving system needs to be large to detect the low level sound emissions from a distant source in the presence oE nearby ice cracking noiseO
Now consider one of the three dimensional sound intensity arrays. Each element of the array is highly sensitive but as an array the output is the sound intensity vector at the centre oE
the array. The vector sum of the sound intensity at that field point will be zero over a carefully chosen (site speciEic) time interval, despite the high level of -the pressure field as long as the noise emissions are random in origin~ In other words, the high level background noise would read zero sound intensity. Any source in the area originating from a speciEic direction would add constructively and therefore be de-tectable even if it were weak.
The standard signal processing techniques can still be applied to the data. For example, the intensity spectrum oE the source can be analyzed to look for characteristic Erequencies to distinguish different types oE source emissions (whales, submarines, etc.) With the Eour arrays of -the apparatus of Eigure 2, any known automatic focussing and range Einding techniques (such as triangulation) can be employed by appropriate software control in the system computer 164 (of figure 3) utilizing the vectoral informa-tion oE each array.
Figure 4 illustrates another apparatus 500 incorporating a number of the arrays 20 oE figure 1. More particularly, arrays 520, 720, 920~ and 1120 are supported at -the corners of a :::
2~2~
tetrahedronal structure 502. Arrays 620, 820, 1020, 1220, 1320, and 1420 ~hidden) are supported at the midpoints of the sides of the tetrahedronal structure. The tetrahedronal structure surrounds a submersed object 504. The control system for the device is ident;cal to that depicted ln figure 3 save that there are eight arrays of hydrophones with elght controllers associated therewith and blocks 158 and 160 are unnecessary since the apparatus 500 is stationary. With the areal sound intensity receiver of figure 3 ~with the noted modifications) and figure 4, the total energy emi-tted from the object 504 may be monitored and changes in energy, which could be indicative of fatigue cracking, noted. This receiver is particularly suited to, for example, monitoring the energy flow from the base of an oil platform. ~ecause of the directional nature of the information obtained by the receiver, the tetrahedronal s-tructure need not be in close proximity to damaged welded joints in order to detect damage at such joints because triangulation may be employed to pinpoint the location of such join-ts.
The number of arrays along each side of the tetrahedronal structure is shown as three, however, an increased number along each side is possible and would have the effect oE increasing the accuracy of the measurements.
While the areal sound intensity receivers of the example embodiments are adapted Eor measurement in waterr it will be apparent to those skilled in the art that the receivers could be adapted for use in other media, such as air~
- :,: :,~, ::
-..: ~ :
.. : :
-.: -
Claims (9)
1. A device for measuring the intensity of sound from an acoustic source in a medium comprising:
(a) at least three microphone arrays spaced from each other, each of said microphone arrays comprising six microphones configured as three orthogonal pairs of microphones;
(b) means for simultaneously sensing the output from each of said microphones in order to determine a real-time sound intensity vector at each of said microphone arrays; and (c) means for providing an indication of the areal intensity of sound through a notional plane bounded by at least three of said at least three microphone arrays.
(a) at least three microphone arrays spaced from each other, each of said microphone arrays comprising six microphones configured as three orthogonal pairs of microphones;
(b) means for simultaneously sensing the output from each of said microphones in order to determine a real-time sound intensity vector at each of said microphone arrays; and (c) means for providing an indication of the areal intensity of sound through a notional plane bounded by at least three of said at least three microphone arrays.
2. The device of claim 1 wherein said microphones are spherical hydrophones.
3. The device of claim 2 including attitude and motion sensors for monitoring vibrational behaviour of said at least three microphone arrays.
4. The device of claim 3 wherein the distance between the microphones of each orthogonal pair of microphones in a microphone array is equivalent and wherein the acoustic centers of the three orthogonal pairs of microphones in a microphone array are coincident.
5. The device of claim 4 wherein said at least three microphone arrays comprise at least four microphone arrays and wherein the coincident acoustic centers of the at least four microphone arrays bound a notional square.
6. The device of claim 4 wherein said at least three microphone arrays comprise at least four microphone arrays and wherein the coincident acoustic centers of the at least four microphone arrays bound a notional tetrahedron.
7. The device of claim 1 including means for determining the range of, and direction to, an acoustic source.
8. A method of deriving a sound intensity vector field over an area in a medium comprising the steps of:
(a) simultaneously sensing sound pressure in the medium at a plurality of points comprising at least three clusters of points, each cluster of points configured as three orthogonal pairs of points wherein the mid-points of the three orthogonal pairs of points of a cluster are coincident;
(b) determining the sound intensity vector at the center of each of said clusters of points; and (c) determining an indication of the sound intensity vector field over an area bounded by at least three of said at least three clusters of points.
(a) simultaneously sensing sound pressure in the medium at a plurality of points comprising at least three clusters of points, each cluster of points configured as three orthogonal pairs of points wherein the mid-points of the three orthogonal pairs of points of a cluster are coincident;
(b) determining the sound intensity vector at the center of each of said clusters of points; and (c) determining an indication of the sound intensity vector field over an area bounded by at least three of said at least three clusters of points.
9. The method of claim 8 wherein step (c) includes monitoring the relative positions of said points.
Priority Applications (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2008274 CA2008274C (en) | 1990-01-22 | 1990-01-22 | Areal sound intensity receiver |
| PCT/CA1991/000014 WO1991010905A1 (en) | 1990-01-22 | 1991-01-21 | Areal sound intensity receiver |
| AU70604/91A AU7060491A (en) | 1990-01-22 | 1991-01-21 | Areal sound intensity receiver |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2008274 CA2008274C (en) | 1990-01-22 | 1990-01-22 | Areal sound intensity receiver |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2008274A1 CA2008274A1 (en) | 1991-07-22 |
| CA2008274C true CA2008274C (en) | 1998-04-28 |
Family
ID=4144094
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2008274 Expired - Lifetime CA2008274C (en) | 1990-01-22 | 1990-01-22 | Areal sound intensity receiver |
Country Status (3)
| Country | Link |
|---|---|
| AU (1) | AU7060491A (en) |
| CA (1) | CA2008274C (en) |
| WO (1) | WO1991010905A1 (en) |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2262303A1 (en) * | 1974-02-22 | 1975-09-19 | Commissariat Energie Atomique | Position detector for source of strain waves - employs piezoelectric transducer network with counter and computer |
| DE3641027A1 (en) * | 1986-12-01 | 1988-06-09 | Fraunhofer Ges Forschung | Method for locating sound emission sources and device for carrying out the method |
-
1990
- 1990-01-22 CA CA 2008274 patent/CA2008274C/en not_active Expired - Lifetime
-
1991
- 1991-01-21 AU AU70604/91A patent/AU7060491A/en not_active Abandoned
- 1991-01-21 WO PCT/CA1991/000014 patent/WO1991010905A1/en not_active Ceased
Also Published As
| Publication number | Publication date |
|---|---|
| WO1991010905A1 (en) | 1991-07-25 |
| AU7060491A (en) | 1991-08-05 |
| CA2008274A1 (en) | 1991-07-22 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| Schock et al. | Buried object scanning sonar | |
| US6161434A (en) | Method and device for detecting and locating a reflecting sound source | |
| US8125850B2 (en) | Method for identifying gas leaks using a stationary seabed placed steered beamformed acoustic antenna with active narrow beam transmitter interrogation capability | |
| CN111854704A (en) | Marine geophysical comprehensive survey system | |
| WO2009038456A1 (en) | Inspection device and method for inspection | |
| CN114909610B (en) | A method and control system for leak detection and positioning of underwater oil and gas pipelines | |
| US12566447B2 (en) | Method for steering an autonomous underwater vehicle along a buried object in the seabed | |
| KR860001348A (en) | Ultrasonic Scanning Methods and Devices | |
| US20040073373A1 (en) | Inertial augmentation of seismic streamer positioning | |
| CN112857699A (en) | Method for detecting and positioning leakage of long-distance oil and gas pipeline of acoustic vector sensor | |
| US4481818A (en) | Method of detecting cracks in constructions | |
| US3992923A (en) | Underwater pipelines | |
| CN116520248A (en) | A vector sonar water environment monitoring system capable of stable installation and deployment | |
| EP0516662A1 (en) | Electrooptical sensor system for marine seismic data acquisition. | |
| CN117930206A (en) | Submarine topography measurement system for unmanned surface vehicle and measurement data correction method | |
| US4955001A (en) | Areal sound intensity receiver | |
| GB2521681A (en) | Underwater leak detection apparatus, underwater leak detection system and method of detecting an underwater leak of a fluid | |
| CA2008274C (en) | Areal sound intensity receiver | |
| US9100317B1 (en) | Self surveying portable sensor nodes | |
| CN111579645B (en) | Underwater near-source wave field nondestructive testing device and method | |
| CN114923136A (en) | Multi-array pipeline leakage positioning method and device | |
| KR101809666B1 (en) | Method for predicting defect location by triangulation sensors | |
| CN112946085B (en) | Ultrasonic positioning method for plate-like structure damaged sound source | |
| JPH02115782A (en) | Estimated stranding distance instrument | |
| EP1089092A1 (en) | Method and apparatus for measuring physical parameters from the phase and amplitude histories of an acoustic signal |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKEX | Expiry |