CN111157096B - Closed space panel acoustic contribution degree identification method based on local measurement - Google Patents
Closed space panel acoustic contribution degree identification method based on local measurement Download PDFInfo
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Abstract
The invention discloses a closed space panel acoustic contribution degree identification method based on local measurement, which comprises the following steps: two semi-closed holographic measuring surfaces are arranged in the closed space, and the sound pressure value on the holographic measuring surfaces is measured; based on the acoustic equivalent source principle, establishing an external sound field virtual source surface and an inward sound field virtual source surface in a closed space, establishing a transfer relation between a holographic measuring surface and the sound field virtual source surface, and calculating a source intensity column vector on the inward sound field virtual source surface; calculating a scattered sound field generated by the fact that the virtual source surface of the inward sound field is incident to the surface of the vibrating panel to be tested by utilizing the admittance boundary condition of the surface of the vibrating panel to be tested and the source strength column vector on the virtual source surface of the inward sound field, and reducing the sound pressure and the normal vibration velocity on the vibrating panel to be tested under the condition of a free field; dividing the vibration panel to be tested into a plurality of discrete units, and calculating the acoustic contribution degree of the vibration panel to be tested to the closed sound field. The method can flexibly and quickly identify the local acoustic contribution degree of the panel of the closed space structure.
Description
Technical Field
The invention relates to the technical field of noise source identification, in particular to a closed space panel acoustic contribution degree identification method based on local measurement.
Background
The space sound field formed by the vibration of the complex elastic closed cavity structure under the external excitation is the most representative sound field in engineering practice, such as the sound field in the cabin of automobiles, ships and airplanes, and the noise problem in the closed space structure is increasingly emphasized by people along with the continuous improvement of the comfort requirement of people on the living and working environments. After external excitation energy is transmitted to the closed cavity structure, each panel vibrates to radiate structural noise into the sound cavity, and the main factors finally influencing the sound field characteristics in the closed space are the vibration and acoustic characteristics of all plates forming the sound cavity. The analysis of acoustic contribution degree of each panel forming the closed structure is carried out, and the panel with larger influence on the internal sound field is selected and preferentially controlled in a targeted manner, which is the key of noise reduction and acoustic optimization.
The existing panel acoustic contribution degree identification method is mostly carried out on certain specific points in a sound field, and the selected specific points cannot completely represent the characteristics of the whole sound field and can only represent the sound pressure contribution degree of the panel to the specific points in the sound field. The method mainly comprises two types: (1) based on finite element/boundary element method modeling method. In 1995, Zhang proposed a method for calculating the contribution of a panel around a closed cavity to the noise response of a certain field point in the cavity based on an acoustic boundary element model. In 2000, Mohanty calculated the panel acoustic contribution of the spatial sound field using a numerical method of finite elements and boundary elements. Ding in 2002 proposes an acoustic contribution algorithm of local panel vibration of an elastic closed thin plate acoustic cavity to an internal sound field based on a finite element numerical method and combined with an acoustic reciprocity measurement principle. Wolff in 2007 proposed a closed space sound field panel acoustic contribution algorithm based on Kirchhoff integral formula. In 2009 Han introduced the concepts of "sum of acoustic contributions", "ratio of acoustic contributions", and "total contribution of sound field", and proposed a panel acoustic contribution analysis method suitable for multi-feature field points and multi-response peaks. The panel acoustic contribution identification method which obtains the structural vibration response through an acoustic finite element method and uses the structural vibration response as the boundary condition of an acoustic boundary element model is proposed in the 2010 Zhao Jing. Lisuho in 2016 performed panel acoustic contribution analysis based on a body structure-sound field finite element coupling model using commercial software, virtual. The calculation accuracy of the method depends on the fineness of the divided units of the model and the simplification degree of the boundary conditions to a great extent, and meanwhile, the method has the problems of large calculation amount and low calculation efficiency. (2) Based on near-field acoustic holography. In 2006, the method provides a panel acoustic contribution degree identification method based on statistical optimal near-field acoustic holographic measurement, and the method measures near-field acoustic information of each vibration panel in a sound field in a closed space by using a double-sided array, and then obtains a transfer function by carrying out reciprocity measurement through a volume velocity sound source, so that the acoustic contribution degree of any vibration panel in a closed space structure is identified. The method can obtain the acoustic contribution of the part to the sound field only by carrying out local near-field acoustic holographic measurement on the interested panel once, does not need to carry out full-field measurement, has better flexibility, but has the problem of huge workload because the reciprocity measurement of a transfer function is still carried out. Wu in 2013 provides a near-field acoustic holography panel acoustic contribution identification method based on a Helmholtz least square method. The method utilizes a near-field acoustic holography measurement technology, obtains the surface acoustic intensity of the vibration panel by reconstructing the vibration acoustic response of the surface of the complex vibration structure, and establishes the relation between the acoustic power flow of each panel and the acoustic pressure level of a designated field point. However, the panel acoustic contribution degree defined by the algorithm has no positive and negative properties, so that the panel acoustic contribution degree has certain limitation in practical application. In 2015, showy based on an internal near-field acoustic holography technology of an equivalent source method, a method for calculating panel acoustic contribution of a sound field in a complex-shaped closed cavity structure can be identified. The method reconstructs the whole sound field information by a group of holographic sound pressure measurements, solves the acoustic contribution degree of each vibration panel of the closed structure to any position in the cavity by utilizing the sound field equivalent principle, has the characteristic of definite parameter significance, but needs to complete the whole acoustic measurement of the whole closed space, and for a larger sound source structure, the requirement can cause the problems of increased measurement time and cost, and the calculation efficiency is reduced.
Disclosure of Invention
The invention aims to provide a method for identifying the acoustic contribution degree of a panel of a closed space based on local measurement, which is used for solving the problems in the prior art and can flexibly and quickly identify the acoustic contribution degree of the panel of the closed space structure.
In order to achieve the purpose, the invention provides the following scheme: the invention provides a closed space panel acoustic contribution degree identification method based on local measurement, which comprises the following steps of:
two semi-closed holographic measuring surfaces are arranged in a closed space, and the sound pressure values on the two holographic measuring surfaces are measured; the holographic measuring surface is parallel to the vibration panel to be measured; the holographic measuring surface is spaced from the inner surface of the vibration panel to be measured;
based on an acoustic equivalent source principle, establishing an equivalent virtual source of a sound source in the closed space, wherein the equivalent virtual source consists of an outward sound field virtual source surface and an inward sound field virtual source surface, establishing a transfer relationship between the two holographic measuring surfaces and the outward sound field virtual source surface and the inward sound field virtual source surface, and calculating a source strong column vector on the inward sound field virtual source surface based on sound pressure values on the two holographic measuring surfaces;
calculating a scattering sound field generated when the virtual source surface of the inward sound field is incident to the surface of the vibration panel to be tested by utilizing the admittance boundary condition of the surface of the vibration panel to be tested and the source intensity column vector on the virtual source surface of the inward sound field; based on the relation between the scattering sound field on the holographic measuring surface and the radiation sound field under the free field condition, reducing the sound pressure and normal vibration speed on the vibration panel to be measured under the free field condition;
dividing the vibration panel to be tested into a plurality of discrete units, calculating the radiation sound power generated by the vibration of each discrete unit through the boosting and normal vibration speed of the surface of each discrete unit, and summing to obtain the radiation sound power of the vibration panel to be tested, namely the acoustic contribution degree of the vibration panel to be tested to a closed sound field.
Preferably, the two holographic measuring surfaces are respectively a holographic measuring surface Sh1And a holographic measuring surface Sh2The holographic measuring surface Sh1And a holographic measuring surface Sh2The semi-closed surfaces are conformal with the vibration panel to be tested; the holographic measuring surface Sh2Is enclosed on the holographic measuring surface Sh1Of the outer part of (1).
Preferably, the holographic measuring surface Sh1The distance between the vibration panel to be measured and the holographic measurement surface S is not more than 0.25 lambdah2With the holographic measuring surface Sh1Is not more than 0.25 lambda; the holographic measuring surface Sh1The size in the transverse direction and the longitudinal direction is not smaller than that of the vibration panel to be tested; the holographic measuring surfaceSh2The dimensions in the transverse and longitudinal directions are not less than the holographic measuring surface Sh1The size of (d); where λ is the wavelength corresponding to the highest frequency of the test band.
Preferably, the holographic measuring surface Sh1And a holographic measuring surface Sh2A plurality of sound pressure sensors are arranged on the holographic measuring surface Sh1And a holographic measuring surface Sh2The sound pressure value of (3); the sound pressure sensors are distributed in a grid mode, and the distance between adjacent grid points is smaller than 0.25 lambda.
Preferably, the virtual source surface of the outward sound field is arranged on the holographic measuring surface Sh1The virtual source surface of the inward sound field is arranged on the holographic measuring surface Sh2Inside of (2).
Preferably, the specific calculation method of the sound pressure and the normal vibration speed on the vibration panel to be measured under the free field condition includes:
calculating the relation between an inward sound field generated by an inward sound field virtual source surface and a scattering sound field generated by the inward sound field incident to the surface of the vibration panel to be tested by utilizing the admittance boundary condition of the surface of the vibration panel to be tested; constructing a virtual source surface of a scattering sound field, and calculating a source intensity column vector on the virtual source surface of the scattering sound field based on the source intensity column vector on the virtual source surface of the inward sound field, so as to obtain the sound pressure of the scattering sound field on the holographic measurement surface; based on the relation between the scattering sound field on the holographic measuring surface and the radiation sound field under the free field condition, obtaining the sound pressure of the radiation sound field on the holographic measuring surface under the free field condition; constructing a virtual source surface of a radiation sound field under the free field condition, thereby obtaining a source intensity column vector on the virtual source surface of the radiation sound field under the free field condition; and obtaining the sound pressure and normal vibration speed on the vibration panel to be detected under the free field condition based on the source intensity column vector on the virtual source surface of the radiation sound field under the free field condition.
Preferably, the virtual source surface of the scattering sound field is arranged outside the closed space; the virtual source surface of the scattering sound field is conformal with the vibration panel to be measured, and the distance between the virtual source surface of the scattering sound field and the vibration panel to be measured is 1.5 times of the average measurement distance of sound pressure on the holographic measurement surface.
Preferably, the position of the virtual source surface of the radiation sound field under the free field condition is the same as the position of the virtual source surface of the scattering sound field.
The invention discloses the following technical effects:
(1) according to the method, the acoustic information of the vibration panel is reconstructed through near-field holographic measurement, so that the calculation of the acoustic radiation and the coupling effect of a complex acoustic vibration system is avoided, and the calculation process is simplified;
(2) the invention arranges two semi-closed holographic measuring surfaces above a vibrating panel to be measured, establishes a transmission relation between the sound pressure of the measuring surfaces and the source intensity of an equivalent virtual source based on the principle of an acoustic equivalent source, separates an inward sound field and an outward sound field of the measuring surfaces, further removes a scattered sound field of the inward sound field on the surface by utilizing the admittance boundary condition of the surface of the vibrating panel to be measured, restores a radiation sound field under a free field condition, reconstructs the surface sound pressure and the normal vibration velocity of the vibrating panel to be measured according to the restored radiation sound field under the free field condition, calculates the radiation sound power of each unit of the surface of the vibrating panel to be measured to the sound field in a cavity, further obtains the acoustic contribution degree of the plate to the sound field of the whole closed cavity, thereby being capable of adapting to the closed sound field of any shape and being capable of locally investigating the interested panel according to actual needs, the whole vibration structure does not need to be modeled and measured, the calculation efficiency is high, the implementation method is flexible and quick, and the method is easy to implement and apply in engineering practice;
(3) the invention defines the panel acoustic contribution degree by the radiation sound power of the vibration panel from the energy angle, obtains the acoustic contribution of the panel to the whole internal sound field as a whole, can provide the positive and negative attributes of the acoustic contribution, has better superiority and can provide more targeted basis for the structure acoustic optimization design and treatment.
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In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.
FIG. 1 is a schematic diagram of a method for identifying acoustic contribution of a panel of an enclosed space based on local measurement according to the present invention;
FIG. 2 is a schematic diagram of a closed space structure model according to an embodiment of the present invention;
FIG. 3 is a geometric diagram of a virtual source plane and a holographic measurement plane according to an embodiment of the present invention;
FIG. 4 is a comparison of the calculation results of the normal vibration velocity distribution of the vibration panel to be measured in the closed space at the frequency of 150Hz in the embodiment of the present invention; wherein fig. 4(a) is a calculation result using the free field theory; fig. 4(b) is a calculation result of a method of measuring sound pressure using a hologram; FIG. 4(c) is a calculation result using the method of the present invention;
FIG. 5 is a comparison of the calculation results of the normal vibration velocity distribution of the vibration panel to be measured in the closed space at the frequency of 250Hz according to the embodiment of the present invention; wherein fig. 5(a) is a calculation result using the free field theory; fig. 5(b) is a calculation result of a method of measuring sound pressure using a hologram; FIG. 5(c) is a calculation result using the method of the present invention;
FIG. 6 is a comparison of the normal vibration velocity distribution calculation results of the vibration panel to be measured in the closed space at the frequency of 300Hz in the embodiment of the present invention; wherein fig. 6(a) is a calculation result using the free field theory; fig. 6(b) is a calculation result of the sound pressure measurement method using the hologram; FIG. 6(c) is a calculation result using the method of the present invention;
FIG. 7 is a comparison between the surface normal vibration velocities of two observation points of the vibrating panel to be measured and a theoretical value according to the embodiment of the present invention; FIG. 7(a) is a comparison of the surface normal vibration velocity at the observation point (0.150m,0.103m,0) with the theoretical value; FIG. 7(b) is a comparison of the surface normal vibration velocity at the observation point (-0.159m, -0.132m,0) with the theoretical value;
FIG. 8 is a comparison of the surface sound pressure distribution calculation results of the vibration panel to be measured at the frequency of 150Hz in the embodiment of the present invention; wherein fig. 8(a) is a calculation result using the free field theory; fig. 8(b) is a calculation result of the sound pressure measurement method using the hologram; FIG. 8(c) is a calculation result using the method of the present invention;
FIG. 9 is a comparison of the surface sound pressure distribution calculation results of the vibration panel to be measured at a frequency of 250Hz in accordance with the embodiment of the present invention; wherein fig. 9(a) is a calculation result using the free field theory; fig. 9(b) is a calculation result of the sound pressure measurement method using the hologram; FIG. 9(c) is a calculation result using the method of the present invention;
FIG. 10 is a comparison of the surface sound pressure distribution calculation results of the vibration panel to be measured at 300Hz frequency according to the embodiment of the present invention; wherein fig. 10(a) is a calculation result using the free field theory; fig. 10(b) is a calculation result of the sound pressure measurement method using the hologram; FIG. 10(c) is a calculation result using the method of the present invention;
FIG. 11 is a graph showing radiated acoustic power of a vibrating panel to be measured in an enclosed space at frequencies of 150,250 and 300Hz in accordance with an embodiment of the present invention; wherein FIG. 11(a) is the radiated acoustic power at 150 Hz; FIG. 11(b) is radiated acoustic power at 250 Hz; FIG. 11(c) is radiated acoustic power at 300 Hz;
FIG. 12 panel acoustic contributions at the center frequency of the 1/3 octaves in the 20-400Hz frequency band for embodiments of the present invention;
wherein, in fig. 2, 1, a front side plate; 2. a rear side plate; 3. a left side plate; 4. a right side plate; 5. a top plate; 6. a base plate; 7. an upper sloping plate.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.
Referring to fig. 1 to 12, the present embodiment provides a method for identifying acoustic contribution of a panel of an enclosed space based on local measurement, including the following steps:
s1, two semi-closed holographic measuring surfaces S are arranged in the closed spaceh1And Sh2The holographic measuring surface Sh1And Sh2And the vibration panel S to be testedpParallel connection; the holographic measuring surface Sh2Is enclosed on the holographic measuring surface Sh1Of the holographic measuring surface Sh1And the vibration panel S to be testedpThe inner surface of (a) is spaced;
setting the wavelength corresponding to the highest frequency of the test frequency band as lambda, and setting the holographic measurement surface S for engineering treatmenth1And Sh2Set up as with vibrating panel S to be testedpA conformal semi-closed face; the holographic measuring surface Sh1And the vibration panel S to be testedpIs not more than 0.25 lambda, the holographic measuring surface Sh2With the holographic measuring surface Sh1Is not more than 0.25 lambda; the holographic measuring surface Sh1The size in the transverse direction and the longitudinal direction is not less than that of the vibration panel S to be testedpThe size of (d); the holographic measuring surface Sh2The dimensions in the transverse and longitudinal directions are not less than the holographic measuring surface Sh1The size of (c).
The holographic measuring surface Sh1And Sh2Are provided with a plurality of sound pressure sensors for measuring the holographic measuring surface Sh1And Sh2The sound pressure value of (3); the sound pressure sensors are distributed in a grid mode, and the distance between adjacent grid points, namely the measurement distance of the sound pressure sensors, is smaller than 0.25 lambda.
Due to the holographic measuring surface Sh1And Sh2Has sound sources on both sides, and measures the holography of the surface Sh1And Sh2The sound pressure of the upper part is divided into two parts of the sound pressure of an inward sound field and the sound pressure of an outward sound field, wherein the inward sound field and the outward sound field are both relative to a holographic measuring surface Sh1And Sh2In other words, close to the vibrating panel S to be measuredpIs an outer side, has an outward sound field and is far away from the vibration panel S to be detectedpIs the inner side, there is an inward sound field. Holographic measuring surface Sh1And Sh2The sound pressure of (2) is shown as formula (1) and formula (2), respectively:
wherein, Ph1And Ph2Respectively representing holographic measuring surfaces Sh1And Sh2The sound pressure of the sound source is higher,
and
respectively representing holographic measuring surfaces Sh1And Sh2The sound pressure of the upward-outward sound field,
and
respectively representing holographic measuring surfaces Sh1And Sh2Up to the sound pressure of the inward sound field.
S2, based on the basic principle of the equivalent source method, the radiation sound field of the actual sound source is regarded as the superposition of the sound fields generated by a plurality of simple sound sources placed outside the sound field; establishing an equivalent virtual source of a sound source in the closed space, wherein the equivalent virtual source consists of an outward sound field virtual source surface Sq1And an inward sound field virtual source surface Sq2Composition of said virtual source surface S of outward sound fieldq1Is located on the holographic measuring surface Sh1Said virtual source plane S of the inward sound fieldq2Is located on the holographic measuring surface Sh2Is arranged to establish a holographic measuring surface Sh1And Sh2Upper sound pressure and outward sound field virtual source surface Sq1And an inward sound field virtual source surface Sq2The transfer relationship between the source strengths of (1):
wherein,
and
respectively an outward sound field virtual source surface Sq1To the holographic measuring surface Sh1And Sh2The sound pressure transfer matrix of (a) is,
and
respectively an inward sound field virtual source surface Sq2To the holographic measuring surface Sh1And Sh2Of the sound pressure transmission matrix, QoutAnd QinRespectively an outward sound field virtual source surface Sq1And an inward sound field virtual source surface Sq2A source strong column vector of; gp(m,n)＝iρckg(rhm,rqn)，
Is a free field Green's function, rhmIndicating the position of the m-th measuring point on the holographic measuring surface, rqnIs the position of the nth equivalent virtual source on the virtual source surface, ρ is the density of the medium, c is the sound propagation speed in the medium, k ═ ω/c is the wave number of the sound wave, ω is the angular frequency,
is a virtual unit.
Substituting expressions (3) to (6) for expressions (1) and (2), and measuring the hologram area Sh1And Sh2The sound pressures of (1) and (8) are respectively shown as formula (7):
combining the formulas (7) and (8) to obtain an outward sound field virtual source surface Sq1And an inward sound field virtual source surface Sq2Upper source strong column vector QoutAnd QinAs shown in formulas (9) and (10):
where the superscript "+" represents the generalized inverse of the matrix.
S3 holographic measurement surface Sh1Sound pressure of upward and outward sound field
As shown in formula (11):
wherein,
for vibrating panel S to be testedpThe sound field radiated under the condition of free field is on the holographic measuring surface Sh1The sound pressure generated is generated by the sound source,
for virtual source surface S of inward sound fieldq2The generated inward sound field is incident to the vibration panel S to be measuredpThe scattered sound field generated by the surface is on the holographic measuring surface Sh1The resulting sound pressure.
On the vibrating panel S to be measuredpUpper, inward sound field virtual source surface Sq2The generated inward sound field and the inward sound field are incident to the vibration panel S to be measuredpThe relationship of the scattered sound field generated by the surface is shown in formula (12):
Vs in+Vs scat＝As(Ps in+Ps scat)………………………………(12)
wherein A issFor vibrating panel S to be testedpAdmittance matrix of the surface, Ps inAnd Vs inRespectively an inward sound field virtual source surface Sq2Generated inward sound field on vibration panel S to be measuredpUpper generated sound pressure and normal vibration velocity, Ps scatAnd Vs scatRespectively an inward sound field virtual source surface Sq2The generated inward sound field is incident to the vibration panel S to be measuredpVibration panel S to be measured with scattered sound field generated on surfacepThe generated sound pressure and normal vibration speed.
Arranging a vibration panel S to be tested outside the closed spacepConformal scattering sound field virtual source surface Sq0Scattering sound field virtual source surface Sq0And the vibration panel S to be testedpParallel and to-be-tested vibration panel SpAnd a virtual source surface S of a scattered sound fieldq0Has a distance of holographic measuring surface Sh1The average measurement distance of the upper sound pressure sensor is 1.5 times, and by using an equivalent source method, the following results are obtained:
wherein,
and
respectively an inward sound field virtual source surface Sq2To the vibrating panel S to be testedpThe sound pressure and the normal vibration velocity of mass points of the matrix,
and
respectively a virtual source surface S of a scattered sound fieldq0To the vibrating panel S to be testedpThe sound pressure and the normal vibration velocity of mass point of (Q)scatFor scattering the virtual source surface S of the sound fieldq0The upper source strong column vector.
Combining the formulas (12), (15) and (16) to obtain a virtual source surface S of a scattering sound fieldq0Upper source strong column vector Qscat：
Using virtual source surface S of scattered sound fieldq0Upper source strong column vector QscatCalculating scattering sound field on holographic measuring surface Sh1Generated sound pressure
As shown in equation (18):
wherein,
for scattering the virtual source surface S of the sound fieldq0To the holographic measuring surface Sh1The sound pressure transfer matrix of (a).
Combining the formulas (3), (11) and (18) to obtain the vibration panel S to be testedpRadiation sound field under free field condition on holographic measuring surface Sh1Generated sound pressure:
using the basic principle of equivalent source to make the scattering sound field virtual source surface Sq0Setting a virtual source surface S of a radiation sound field under the condition of a free field at the same positionqfObtaining the vibration panel S to be measuredpRadiation sound field in free field condition on measuring surface Sh1Generated sound pressure:
wherein,
for radiating a virtual source surface S of a sound field under the condition of a free fieldqfTo the holographic measuring surface Sh1Of the sound pressure transmission matrix, QfFor radiating a virtual source surface S of a sound field under the condition of a free fieldqfThe upper source strong column vector.
From the formula (20), a virtual source surface S of a radiation sound field under the condition of a free field can be obtainedqfUpper source strong column vector:
under the condition of a free field, the magnetic field,vibration panel S to be testedpSound pressure of
And normal vibration velocity
Respectively expressed as:
wherein,
and
respectively a virtual source surface S of a free radiation sound fieldq0To the vibrating panel S to be testedpThe sound pressure and particle normal vibration velocity transmission matrix;
rpjfor vibrating panel S to be testedpPosition of the upper jth node, rqiFor radiating a virtual source surface S of a sound field under the condition of a free fieldqfThe position of the ith equivalent sound source, n is the vibration panel S to be measuredpThe outer normal at the position of the upper jth node.
S4, vibrating panel S to be testedpIs dispersed as SkObtaining the normal sound intensity I generated by the vibration of the first discrete unit according to the step S3nlAs shown in formula (24):
wherein,
and
respectively a vibration panel S to be measuredpThe surface acoustic pressure and normal vibration velocity of the first discrete element above, the superscript "indicating the complex conjugate.
Radiated sound power W generated by vibration of the first discrete unitlAs shown in equation (25):
Wl＝Inl·ΔSl……………………………………(25)
wherein, Delta SlIs the area of the ith discrete cell.
Calculating the vibration panel S to be measuredpRadiated acoustic power WkAs shown in formula (26):
vibration panel S to be testedpAcoustic contribution D to sound field in enclosed spacekAs shown in equation (27):
Dk＝Wk………………………………………(27)。
in order to verify the closed space panel acoustic contribution degree identification method based on local measurement, the sound field inside the irregular closed space with a similar car structure is selected as an analysis object in the embodiment, as shown in fig. 2. The correctness of the closed space panel acoustic contribution degree identification method based on local measurement is verified by comparing the calculation results of the acoustic information of the surface of the vibration panel of the closed space.
The closed space structure of the embodiment is composed of a front side plate 1, a rear side plate 2, a left side plate 3, a right side plate 4, a top plate 5, a bottom plate 6 and an upper inclined plate 7. Each panel of the closed space structure has a thickness of 2mm, is made of thin steel plate and has a material density of 7.8 multiplied by 103kg/m3The elastic modulus is 210GPa, the Poisson ratio is 0.3, and the system damping ratio is 0.01.
The origin of coordinates of the closed space structure is set at the center point of the bottom plate 6.
The whole structure is excited from the bottom surface, the amplitude of the excited vibration is 0.2N, the frequency bandwidth is 20-400Hz, and the coordinates of the excitation point are (0.038m, -0.015m, 0).
Selecting a vibration panel to be measured with the size of 0.7(x) x 0.5(y) m on the bottom plate 62。
The holographic measuring surface is composed of two semi-closed rectangular surfaces above the vibrating panel to be measured, wherein the measuring surface Sh1Has a size of 0.7(x) x 0.5(y) x 0.04(z) m3Measuring surface Sh2Has a size of 0.8(x) x 0.8(y) x 0.09(z) m3Holographic measuring surface Sh1And Sh2The spacing therebetween was 0.05 m. The measurement distances in the x and y directions are 0.05m for both holographic measurement surfaces, while in the z direction the holographic measurement surface Sh1Upper measuring space of 0.02m, holographic measuring surface Sh2The measurement pitch of (3) is 0.025 m.
As shown in fig. 3, the virtual source surface S of the inward sound fieldq2Arranged to contact the holographic measuring surface Sh2Conformal semi-closed rectangular surface, inward sound field virtual source surface Sq2And holographic measuring surface Sh2Has a distance of holographic measuring surface Sh2The upper sound pressure sensor measures 1.5 times of the interval on average. Due to the holographic measuring surface Sh1The space between the bottom plate and the sound field is small, so that the virtual source surface S of an outward sound fieldq1Arranged as a plane, an outward sound field virtual source surface Sq1And holographic measuring surface Sh1The distance between them is the measuring plane Sh1The upper sound pressure sensor measures 1.5 times of the interval on average. Scattering sound field virtual source surface Sq0And virtual source surface S of radiation sound field under free field conditionqfAlso set as a plane with coincident positions, scattering the virtual source surface S of the sound fieldq0And virtual source surface S of radiation sound field under free field conditionqfAnd the vibration panel S to be testedpThe distance between them is the measuring plane Sh1The upper sound pressure sensor measures 1.5 times of the interval on average.
Because the shape of the closed space structure is irregular and cannot be described by an analytic expression, acoustic field calculation is carried out by using an acoustic software LMS virtual. Lab and a coupled acoustic finite element method, the obtained sound pressure value of each measuring point on the holographic measuring surface is used as 'input quantity' for carrying out internal holographic reconstruction, and random noise with the signal-to-noise ratio of 30dB is added to be closer to the actual situation. The simulation sound pressure on the holographic surface in the cavity is used as 'measurement' data, the surface sound pressure and the normal vibration speed of the vibration structure panel to be inspected are calculated by using the method, and the calculation result is compared with the result obtained by using a coupled acoustic finite element method.
The normal vibration velocity distributions of the vibration panel under test at frequencies of 150,250 and 300Hz are shown in fig. 4-6, respectively. Wherein, (a) is the surface normal vibration velocity distribution of the free field theory, (b) is the surface normal vibration velocity distribution calculated by directly adopting the holographic measurement sound pressure, and (c) is the surface normal vibration velocity distribution calculated by adopting the method of the invention. Obviously, the surface normal vibration velocity calculated by the method has very high consistency with the theoretical value.
The comparison between the surface normal vibration velocity calculated by the method of the present invention and the theoretical value at the two node positions (0.150m,0.103m,0) and (-0.159m, -0.132m,0) on the vibration panel to be measured is shown in fig. 7. Obviously, the surface normal vibration speed is well matched with the theoretical value in the whole analysis frequency band of 20-400Hz, and the accuracy of the method for calculating the surface normal vibration speed is verified.
The surface sound pressure distributions of the vibration panel to be measured at frequencies of 150,250 and 300Hz are shown in fig. 8-10, respectively. Wherein (a) is the surface sound pressure distribution of the free field theory, (b) is the surface sound pressure distribution calculated by directly adopting the holographic measurement sound pressure, and (c) is the surface sound pressure distribution calculated by adopting the method of the invention. Obviously, the surface sound pressure distribution obtained by the calculation of the method has very high consistency with a theoretical value.
The radiated sound power generated by the vibration of the vibration panel to be measured at different frequencies is shown in fig. 11, in which (a) is 150Hz, (b) is 250Hz, and (c) is 300 Hz. Obviously, the method can calculate the acoustic contribution degree of each unit on the vibration panel at different frequencies to the sound field. And the contribution degree of each unit on the surface of the vibration panel to be tested at each frequency to the sound field can be calculated by the method, and the contribution degree has positive and negative attributes which respectively represent the sound power entering and exiting the unit. If the contribution of a certain cell is positive, the acoustic radiation of that cell will increase the acoustic energy of the whole internal sound field; conversely, if the contribution of a cell is negative, the acoustic radiation of that cell will reduce the acoustic energy of the internal acoustic field.
The acoustic contribution of the vibrating panel under test at the center frequency of the 1/3 octaves in the frequency band of 20-400Hz is shown in fig. 12. And summing the acoustic contribution degrees of all the units on the vibration panel to be tested at each characteristic frequency to obtain the overall acoustic contribution degree of the whole vibration panel to be tested to the sound field of the internal space. Therefore, the method of the invention not only can define the whole vibration panel to be tested as an area, but also can determine the contribution degree of different parts on the surface of the panel to the sound field according to the requirement, so that the panel vibration acoustic contribution analysis of the closed sound field is more detailed, and the pertinence of the low-noise design improvement is stronger.
In the description of the present invention, it is to be understood that the terms "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like, indicate orientations or positional relationships based on those shown in the drawings, are merely for convenience of description of the present invention, and do not indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and thus, are not to be construed as limiting the present invention.
The above-described embodiments are merely illustrative of the preferred embodiments of the present invention, and do not limit the scope of the present invention, and various modifications and improvements of the technical solutions of the present invention can be made by those skilled in the art without departing from the spirit of the present invention, and the technical solutions of the present invention are within the scope of the present invention defined by the claims.
Claims (5)
1. A closed space panel acoustic contribution degree identification method based on local measurement is characterized by comprising the following steps:
two semi-closed holographic measuring surfaces are arranged in a closed space, and the sound pressure values on the two holographic measuring surfaces are measured; the holographic measuring surface is parallel to the vibration panel to be measured; the holographic measuring surface is spaced from the inner surface of the vibration panel to be measured;
based on an acoustic equivalent source principle, establishing an equivalent virtual source of a sound source in the closed space, wherein the equivalent virtual source consists of an outward sound field virtual source surface and an inward sound field virtual source surface, establishing a transfer relationship between the two holographic measuring surfaces and the outward sound field virtual source surface and the inward sound field virtual source surface, and calculating a source strong column vector on the inward sound field virtual source surface based on sound pressure values on the two holographic measuring surfaces;
calculating a scattering sound field generated when the virtual source surface of the inward sound field is incident to the surface of the vibration panel to be tested by utilizing the admittance boundary condition of the surface of the vibration panel to be tested and the source intensity column vector on the virtual source surface of the inward sound field; based on the relation between the scattering sound field on the holographic measuring surface and the radiation sound field under the free field condition, reducing the sound pressure and normal vibration speed on the vibration panel to be measured under the free field condition;
dividing the vibration panel to be tested into a plurality of discrete units, calculating the radiation sound power generated by the vibration of each discrete unit through the boosting and normal vibration speed of the surface of each discrete unit, and summing to obtain the radiation sound power of the vibration panel to be tested, namely the acoustic contribution degree of the vibration panel to be tested to a closed sound field;
the two holographic measuring surfaces are respectively holographic measuring surfaces Sh1And the holographic measuring surface Sh2The holographic measuring surface Sh1And the holographic measuring surface Sh2The semi-closed surfaces are conformal with the vibration panel to be tested; the holographic measuring surface Sh2Is enclosed on the holographic measuring surface Sh1(ii) an outer portion;
the holographic measuring surface Sh1The distance between the holographic measuring surface Sh and the vibration panel to be measured is not more than 0.25 lambda2The distance between the holographic measuring surface Sh1 and the holographic measuring surface is not more than 0.25 lambda; the holographic measuring surface Sh1The size in the transverse direction and the longitudinal direction is not smaller than that of the vibration panel to be tested; the holographic measurementFace Sh2The size in the transverse direction and the longitudinal direction is not less than the holographic measuring face Sh1The size of (d); wherein λ is the wavelength corresponding to the highest frequency of the test band;
the holographic measuring surface Sh1And the holographic measuring surface Sh2Are provided with a plurality of sound pressure sensors which are used for measuring the holographic measuring surface Sh1And the holographic measuring surface Sh2The sound pressure value of (3); the sound pressure sensors are distributed in a grid mode, and the distance between adjacent grid points is smaller than 0.25 lambda.
2. The method as claimed in claim 1, wherein the virtual source surface of the outward sound field is set on the Sh holographic measuring surface1The virtual source surface of the inward sound field is arranged on the holographic measuring surface Sh2Inside of (2).
3. The method for identifying the acoustic contribution of the panel of the enclosed space based on the local measurement according to claim 1, wherein the specific calculation method of the sound pressure and the normal vibration velocity on the vibrating panel to be measured under the condition of the free field comprises:
calculating the relation between an inward sound field generated by an inward sound field virtual source surface and a scattering sound field generated by the inward sound field incident to the surface of the vibration panel to be tested by utilizing the admittance boundary condition of the surface of the vibration panel to be tested; constructing a virtual source surface of a scattering sound field, and calculating a source intensity column vector on the virtual source surface of the scattering sound field based on the source intensity column vector on the virtual source surface of the inward sound field, so as to obtain the sound pressure of the scattering sound field on the holographic measurement surface; based on the relation between the scattering sound field on the holographic measuring surface and the radiation sound field under the free field condition, obtaining the sound pressure of the radiation sound field on the holographic measuring surface under the free field condition; constructing a virtual source surface of a radiation sound field under the free field condition, thereby obtaining a source intensity column vector on the virtual source surface of the radiation sound field under the free field condition; and obtaining the sound pressure and normal vibration speed on the vibration panel to be detected under the free field condition based on the source intensity column vector on the virtual source surface of the radiation sound field under the free field condition.
4. The method for identifying acoustic contribution of panel in enclosed space based on local measurement as claimed in claim 3, wherein the virtual source surface of the scattered sound field is located outside the enclosed space; the virtual source surface of the scattering sound field is conformal with the vibration panel to be measured, and the distance between the virtual source surface of the scattering sound field and the vibration panel to be measured is 1.5 times of the average measurement distance of sound pressure on the holographic measurement surface.
5. The method for identifying the acoustic contribution of the panel in the enclosed space based on the local measurement as claimed in claim 4, wherein the position of the virtual source surface of the radiated sound field under the free field condition is the same as the position of the virtual source surface of the scattered sound field.
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| CN113432703B (en) * | 2021-06-04 | 2023-01-17 | 大连海事大学 | Method for restoring free radiation sound field of steady-state sound source with any shape |
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