JP4893516B2 - Vibration calculation system - Google Patents

Description

  The present invention relates to a vibration calculation system that performs vibration calculation of a structure, and more particularly to a technique for performing vibration calculation of a structure in which a soundproofing material is provided between the structure and a sound field.

  In vehicle development, vehicle interior sound field analysis using FEM (finite element method) or the like is performed. In vehicle interior sound field analysis, it is known that accurate analysis cannot be performed particularly in a high-frequency region of 100 kHz or more unless a soundproofing material interposed between the body and the vehicle interior (sound field) is taken into consideration (patent) Reference 1).

  The soundproofing material is composed of an intermediate layer part made of a porous material such as felt and urethane, and a skin part corresponding to a so-called carpet. Its main functions are a vibration damping function that attenuates body vibration, a vehicle interior There is a sound absorption function that absorbs the sound of the vehicle, and a sound insulation function that blocks sound from outside the passenger compartment. As a method for modeling the soundproof material, for example, the BIOT theory is known (see Non-Patent Document 1). In this method, the characteristics of the porous material are modeled by solid phase characteristics, air phase characteristics, and their coupled characteristics.

  However, applying the FEM model of a soundproof material to vibration calculation of a relatively large sound field such as a vehicle interior space has the following problems.

  The dynamic stiffness matrix of the body and sound field reaches millions of degrees of freedom. Therefore, in vehicle development, direct frequency response calculation, which requires a long calculation time, is rarely used, and modal frequency response calculation (mode analysis) is usually used. In the modal frequency response calculation, the body and sound field eigenvalues are calculated first, and the body and sound field eigenvalues and eigenmodes obtained therefrom are used. As a result, the degree of freedom of the matrix is reduced to the order of several thousand, and calculation in a short time becomes possible. However, since the soundproofing material has high frequency-dependent attenuation characteristics, even if the soundproofing material matrix is directly added to the body or sound field matrix and the modal frequency response calculation is applied, the accuracy is poor. However, if a frequency response calculation is directly performed using a vehicle model incorporating a soundproof material model, the calculation takes about one month, which is not realistic.

Patent Document 1 proposes a method in which a soundproof material is modeled by a spring / mass / damper model and applied to a modal frequency response calculation. However, this model is appropriate for the sound absorbing function and sound insulating function of the soundproof material, but further improvement is desired in that the vibration damping function is not taken into consideration. Patent Document 2 discloses an optimized CAE method for determining an optimal vibration suppression layout in a vehicle structure from the viewpoint of acoustic performance. Patent Document 3 proposes a method for predicting vehicle interior noise of an indirect sound component in the vehicle interior in which the tire axle force predicted by the finite element method is transmitted through the vehicle body. Patent Document 4 proposes a method for calculating the degree of contribution that the transmission force exerts on the acoustic level of the evaluation point for the vibration transmitted from the excitation point of the structure.
JP 2006-65466 A JP 2007-509383 A JP 2004-85235 A JP 2006-185193 A JFAllard, "PROPAGATION OF SOUND IN POROUS MEDIA-Modeling Sound Absorbing Materials-", Elsevier Applied Science (1993)

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a technique capable of executing vibration calculation in consideration of the characteristics of the soundproof material with high speed and high accuracy.

  In order to achieve the above object, the present invention employs the following means and processing.

  The vibration calculation system according to the present invention is a vibration calculation system for performing a modal frequency response calculation of a structure in which a soundproofing material is provided between a structure and a sound field, and generating means for generating a matrix of the soundproofing material And means for converting the matrix of the soundproofing material into an intermediate matrix composed of the structure and the modal degree of freedom of the sound field, and synthesizing the intermediate matrix into the structure and the modal matrix of the sound field. And a vibration calculation means for performing a modal frequency response calculation using the combined modal matrix.

  According to this configuration, since the characteristics of the soundproofing material can be incorporated into the modal matrix of the structure or the sound field, it is possible to calculate the modal frequency response with high accuracy in consideration of the characteristics of the soundproofing material.

  Specifically, the conversion means generates a degenerate matrix by degenerating a degree of freedom that is not shared with either the structure or the sound field among the degrees of freedom of the matrix of the soundproof material, and generates the degenerate matrix. Is preferably converted into the intermediate matrix.

  The generating means generates a matrix of the soundproofing material for a plurality of representative frequencies, and the converting means converts each of the plurality of representative frequency matrices into an intermediate matrix and interpolates the plurality of intermediate matrices. An intermediate matrix corresponding to frequencies between the representative frequencies may be generated by

  The generating means generates a matrix of the soundproofing material based on a soundproofing material model modeled by a solid phase having a degree of freedom shared with the structure and an air phase having a degree of freedom shared with the sound field. It is preferable to produce.

  The present invention can be understood as a vibration calculation system having at least a part of the above means. The present invention can also be understood as a vibration calculation method including at least a part of the above processing, or a program for realizing the method. Each of the above means and processes can be combined with each other as much as possible to constitute the present invention.

  According to the present invention, vibration calculation in consideration of the characteristics of the soundproof material can be executed at high speed and with high accuracy.

  Exemplary embodiments of the present invention will be described in detail below with reference to the drawings.

  FIG. 1 is a block diagram showing a configuration of a vibration calculation system according to an embodiment of the present invention. This vibration calculation system 1 is a device that performs modal frequency response calculation (mode analysis) using FEM, and is used for, for example, vehicle interior sound field analysis in vehicle development CAE. However, the present invention is preferably applicable not only to a vehicle but also to an analysis (vibration calculation) of a structure having a soundproof material. Note that the basic concept of FEM and modal frequency response calculation itself is known to those skilled in the art, and a detailed description thereof will be omitted.

  As shown in FIG. 1, the vibration calculation system 1 includes, as main functions, a sampling frequency determination unit 10, a storage unit 11, a soundproof material matrix generation unit 12, an eigenvalue analysis unit 13, a degeneration unit 14, a conversion unit 15, and an interpolation unit. 16, a synthesis unit 17, and a vibration calculation unit 18. This system can be configured by a general-purpose computer system including a CPU (Central Processing Unit), a storage device, a display device, an input device, etc. in terms of hardware. Each function described above is stored in the storage device. The program is executed by the CPU.

  Now, the function of the vibration calculation system 1 will be described in detail along the flow of the vibration calculation process.

(1) Eigenvalue Analysis of Body and Cabin Sound Field The eigenvalue analysis unit 13 executes actual eigenvalue calculation analysis using the FEM models 21 and 22 of the body and the cabin sound field stored in the storage unit 11 in advance. The modal degrees of freedom and the modal matrix of the body and the sound field of the passenger compartment are calculated. These analysis results are stored in the storage unit 11 as eigenvalue data 23.

(2) Determination of sampling frequency Next, the sampling frequency determination unit 10 determines a plurality of frequencies (referred to as sampling frequencies, sampling points, or representative frequencies) at which the soundproof material matrix degeneracy calculation is performed. The number of sampling points is set to a number smaller than the number of frequencies at which modal frequency response calculation is performed (referred to as response calculation frequency). For example, in this embodiment, the response calculation frequency is set to 2 Hz steps and the sampling frequency is set to 25 Hz steps.

  The reason why the number of sampling points is reduced in this way is to reduce the number of times of degeneracy calculation of the soundproofing material matrix, which takes a long calculation time, and to improve the processing efficiency. However, if the interval between the sampling points is too wide, the accuracy may be lowered. Therefore, it is important to set the sampling points within a range that does not affect the accuracy. For example, instead of setting the sampling points at regular intervals as in a 25 Hz step, the number of sampling points, the interval, the density, and the like may be adaptively changed based on the vibration characteristics of the soundproof material. For example, as shown in FIG. 2, if the vibration response of the soundproof material is known in advance, setting the sampling point to cover the sudden change part of the vibration response can ensure both accuracy and shorten the calculation time. It becomes.

  The following processes (3) to (5) are repeated for each of the sampling frequencies set here.

(3) Generation of Dynamic Stiffness Matrix of Soundproofing Material The soundproofing material matrix generating unit 12 performs FEM analysis using the FEM model 20 of the soundproofing material stored in the storage unit 11, and generates a dynamic stiffness matrix of the soundproofing material. .

  FIG. 3 schematically shows the FEM model of the soundproofing material. The soundproofing material is made of a porous material, and is provided between the body (structure) and the vehicle compartment sound field for vibration suppression, sound absorption and sound insulation. In the present embodiment, a soundproof material is modeled by using a porous material model based on the BIOT theory, and a solid phase having a degree of freedom shared with the body and an air phase having a degree of freedom shared with the passenger compartment sound field. . The solid phase portion has three translational degrees of freedom of x, y, and z per node, and the air phase portion has sound pressure freedom per node.

  By oscillating the FEM model at a given sampling frequency, a dynamic stiffness matrix of the soundproof material can be obtained. As schematically shown in FIG. 4, the dynamic stiffness matrix [Z] of the soundproofing material is composed of the degree of freedom of the solid phase, the degree of freedom of the air phase, and their coupled terms, and a part of the degree of freedom of the solid phase is body. And a part of the degree of freedom of the air phase is shared with the passenger compartment sound field (hatched portion in FIG. 4).

(4) Degeneration of the dynamic stiffness matrix Subsequently, the degeneration unit 14 degenerates the dynamic stiffness matrix [Z] of the soundproof material obtained in (3) and is configured only by the degree of freedom of sharing with the body or sound field. Generate a matrix.

As a specific process, the degeneration unit 14 first classifies each degree of freedom of the dynamic stiffness matrix [Z] according to whether it is a degree of freedom shared with the body or the passenger compartment sound field, and replaces rows and columns. The dynamic stiffness matrix [Z] is deformed as follows. Here, the submatrix [Ztaa] summarizes the degree of freedom of sharing with the body and the degree of freedom of sharing with the vehicle compartment sound field (the degree of freedom of the hatched portion in FIG. 4). The other parts of the submatrix [Ztoo], [Ztoa], and [Ztao] are degrees of freedom that are not shared with either the body or the vehicle interior sound field.

Then, the degeneration unit 14 obtains a degeneration matrix [Ztaa ′] by the following equation. This calculation reduces the degree of freedom that is not shared with either the body or the cabin sound field. Depending on how the FEM model is made, the dynamic stiffness matrix [Z] of the soundproofing material has hundreds of thousands to several million degrees of freedom, whereas the degenerate matrix [Ztaa '] shrinks to thousands to tens of thousands of degrees of freedom. Is done.

(5) Conversion to Body / Sound Field Eigen Modes Next, the conversion unit 15 converts the degenerate matrix [Ztaa ′] obtained in (4) into a matrix composed of modal degrees of freedom of the body and the cabin sound field ( Converted to [Zthh]. The eigenvalue data 23 stored in the storage unit 11 is referred to for the modal degrees of freedom of the body and the cabin sound field.

  Here, [φ] is a matrix for conversion, [φs] is an eigenmode matrix of body degrees of freedom shared with the soundproof material, and [φf] is an eigenmode matrix of sound field degrees of freedom shared with the soundproof material. is there.

(6) Interpolation of Intermediate Matrix An intermediate matrix [Zthh] of each sampling frequency is obtained by repeating the processes (3) to (5). The interpolation unit 16 generates an intermediate matrix of all response calculation frequencies by interpolating those intermediate matrices. Any method may be used for the interpolation method. For example, in the example of FIG. 5, three points of the sampling frequency intermediate matrix (●) are selected, and a value (◯) at the response calculation frequency between the sampling frequencies is calculated using Lagrange's quadratic interpolation method. ing.

(7) Matrix Synthesis The synthesizer 17 synthesizes (adds) the intermediate matrix [Zthh] of each frequency obtained in (6) with a modal matrix of the body and the sound field to obtain a dynamic stiffness matrix for the entire system.

(8) Modal frequency response calculation The vibration calculation unit 18 executes a modal frequency response calculation of each frequency using the dynamic stiffness matrix obtained in (7). The result is output to a display device or the like and used for evaluation of vibration and noise in the passenger compartment.

  As described above, this system calculates the dynamic stiffness matrix of the soundproofing material for multiple frequencies, incorporates the soundproofing material freedom at each frequency into the modal freedom of the body / sound field, and uses it for modal frequency response calculation. Since it is used, it is possible to perform accurate vibration calculation in consideration of the frequency dependence characteristics of the soundproofing material. In addition, since the number of times of degeneracy calculation of the soundproof material matrix is reduced by using the interpolation processing, the calculation time can be further shortened. Note that the calculation that took about one month in the direct frequency response calculation was shortened to about two days in the method of this embodiment.

  The above embodiment is merely an example of the present invention. The scope of the present invention is not limited to the above embodiment, and various modifications can be made within the scope of the technical idea. For example, the matrix degeneracy calculation may be executed for all response calculation frequencies without performing the interpolation process. Although it takes more calculation time than the above embodiment, it is possible to perform vibration calculation with higher accuracy than in the past, and to significantly reduce the time compared to direct frequency response calculation.

FIG. 1 is a block diagram showing a configuration of a vibration calculation system according to an embodiment of the present invention. FIG. 2 is a diagram for explaining sampling frequency determination processing. FIG. 3 is a diagram schematically showing an FEM model of a soundproof material. FIG. 4 is a schematic diagram of a dynamic stiffness matrix of a soundproof material. FIG. 5 is a diagram for explaining the interpolation processing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Vibration calculation system 10 Sampling frequency determination part 11 Memory | storage part 12 Soundproof material matrix production | generation part 13 Eigenvalue analysis part 14 Degeneration part 15 Conversion part 16 Interpolation part 17 Synthesis | combination part 18 Vibration calculation part 20 FEM model of soundproof material 21 FEM model of body 21 FEM model of passenger compartment sound field 23 Eigenvalue data

Claims (4)

A vibration calculation system for calculating a modal frequency response of a structure provided with a soundproof material between the structure and the sound field,
Generating means for generating a matrix of the soundproofing material;
Converting means for converting the matrix of the soundproof material into an intermediate matrix composed of modal degrees of freedom of the structure and the sound field;
Synthesizing means for synthesizing the intermediate matrix into the structure and the modal matrix of the sound field;
Vibration calculation means for performing a modal frequency response calculation using the synthesized modal matrix;
A vibration calculation system comprising: The converting means includes
Among the degrees of freedom of the matrix of the soundproof material, by degenerating a degree of freedom that is not shared with either the structure or the sound field, a degenerate matrix is generated,
The vibration calculation system according to claim 1, wherein the degenerate matrix is converted into the intermediate matrix. The generating means generates a matrix of the soundproofing material for a plurality of representative frequencies,
The conversion means converts each of the plurality of representative frequency matrices into an intermediate matrix, and generates an intermediate matrix corresponding to a frequency between the representative frequencies by interpolating the plurality of intermediate matrices. Or the vibration calculation system of 2. The generating means generates a matrix of the soundproofing material based on a soundproofing material model modeled by a solid phase having a degree of freedom shared with the structure and an air phase having a degree of freedom shared with the sound field. The vibration calculation system according to claim 1, wherein the vibration calculation system is generated.

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