JP2008234589A - Structural design support system and structural design support program of vehicle body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve efficiency in developing a vehicle, by enhancing efficiency in a structure and sound analysis using a model, by determining an optimal structure capable of reducing noise by optimization of an index of evaluating a structure-sound coupling characteristic, without solving a structure-sound coupling equation. <P>SOLUTION: A calculation model of a structure of a vehicle body being a design object is generated by a calculation model generation means 2, and a proper value analysis of a structural system and a proper value analysis of a sound system are respectively performed to this calculation model by a structure system analyzing means 3 and a sound system analyzing means 4. A sound level at an evaluation point in the calculation model is calculated by a sound evaluating means 5, and when this sound level is a desired value or more, a structure-sound coupling characteristic evaluating index calculating means 7 calculates the index of evaluating the structure-sound coupling characteristic. Sensitivity to the index of evaluating this structure-sound coupling characteristic is calculated by a sensitivity calculation means 7, and a structure optimizing means 8 changes the structure of the vehicle body being the design object based on its sensitivity. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a structural design support system and a structural design support program that support structural design of a vehicle body of an automobile by obtaining an optimal structure capable of reducing noise by analyzing a structure and sound using a model.

  2. Description of the Related Art Conventionally, as a technique for supporting the design of a structure such as an automobile body, a technique for obtaining an optimal structure by analyzing and optimizing a design model created by a computer is known. For example, Patent Document 1 divides a design area of a structure at a plurality of predetermined nodes, creates a design model in which adjacent nodes and non-adjacent nodes are connected by beam elements, and optimizes the design model. Thus, there is disclosed a method for designing a structure in which an optimum structure is obtained.

  Since the design method disclosed in Patent Document 1 is configured by using a plurality of beam elements to form a design model, it is possible to obtain a reasonable shape that matches the boundary conditions. It is considered effective as a method for obtaining a structure optimized for a portion. However, the design method disclosed in Patent Document 1 does not consider the noise generated by the vibration of the structural portion and the sound of the space that becomes the sound field. For example, the noise inside the cabin of an automobile is reduced. From the viewpoint of doing, there is a problem that an optimal structure cannot always be obtained.

Regarding the problem of noise in which the structural system and the acoustic system are coupled, such as the noise in the cabin of an automobile, in Non-Patent Document 1, the condition for the sound pressure at the evaluation point to be zero, that is, the optimum condition Introducing an optimality phase diagram that can be used to represent changes in the characteristics of structures from the viewpoint of optimality, and to understand the effects of structural changes on the evaluation point sound pressure. Based on the obtained knowledge It has been reported that an optimization structure can be searched for by an optimization method.
Japanese Patent No. 3551910 Kohei Furuya, Takuya Yoshimura, Akira Sudo, Seiya Narukuni, “Optimum Condition of Vibro-Acoustic Coupled Problem for Minimizing Sound Pressure and Structural Optimization Based on it”, Preprint of Academic Lecture at the Spring Meeting of 2006 No. 5-06, Japan Automobile Engineers Association, P1-6

  However, as reported in Non-Patent Document 1, in order to calculate the condition for the sound pressure at the evaluation point to be zero, that is, the optimality condition, in addition to structural eigenvalue analysis and acoustic eigenvalue analysis, In addition, there is a problem that it takes time to calculate because the coupled equation of structure and sound is solved. In addition, even if the sound level changes, there is a problem that it is difficult to understand the mechanism by which the sound level changes. In addition to the non-patent document 1, many documents that deal with the optimization of noise in which structure and sound are coupled are disclosed. However, the contents disclosed in any document are the coupled equations of structure and sound. It is assumed that it will be solved, and the problem that calculation takes time is common.

  The present invention was devised in view of the conventional situation as described above, and noise can be reduced by optimizing the index for evaluating the structural acoustic coupling characteristics without solving the structural and acoustic coupling equations. To provide a structural design support system and a structural design support program that can improve the efficiency of vehicle development by improving the efficiency of structural and acoustic analysis using models. It is aimed.

  The present invention does not directly optimize the sound pressure at the evaluation point in the model, but considers a combination of selecting one eigenvalue of each of the structural system and the acoustic system, and sets an index for evaluating the structural acoustic coupling characteristics. The basic idea is to obtain an optimum structure capable of reducing noise with a small amount of calculation by a technique of optimizing this index.

  The structural design support system according to the present invention is a system that supports the structural design of the vehicle body of the automobile by reflecting the basic idea of the present invention as described above, and is a calculation that generates a calculation model of the structure of the vehicle body to be designed. Model generation means, structural system analysis means for performing eigenvalue analysis of the structural system using the calculation model, acoustic system analysis means for executing eigenvalue analysis of the acoustic system using the calculation model, and in the calculation model Sound evaluation means for calculating the sound level at the evaluation point for excitation at the input point, and an index for evaluating the structural acoustic coupling characteristics when the sound level at the evaluation point is higher than a desired value Based on the sensitivity to the structural acoustic coupling characteristic evaluation index calculation means, the sensitivity calculation means to calculate the sensitivity to the index to evaluate the structural acoustic coupling characteristics, the sensitivity to the index to evaluate the structural acoustic coupling characteristics, And structural optimization means for changing the vehicle body structure comprising a total object and is characterized in that it comprises.

  The structural design support program according to the present invention is a program that supports the structural design of the vehicle body of the automobile by reflecting the basic idea of the present invention described above, and a computer is provided with a calculation model of the structure of the vehicle body to be designed. A function to generate eigenvalue analysis of a structural system using the calculation model, a function to perform eigenvalue analysis of an acoustic system using the calculation model, and excitation at an input point in the calculation model A function for calculating a sound level at an evaluation point for the sound, a function for calculating an index for evaluating a structural acoustic coupling characteristic when the sound level at the evaluation point is equal to or higher than a desired value, and the structural acoustic coupling. A function for calculating the sensitivity to the index for evaluating the synthesis characteristics and a function for changing the structure of the vehicle body to be designed based on the sensitivity to the index for evaluating the structural acoustic coupling characteristics And it is characterized in and.

  According to the present invention, an optimum structure capable of reducing noise without solving the structure-acoustic formulation equation is required. Therefore, the structure and acoustic analysis using the model can be improved, and vehicle development can be achieved. Efficiency improvement can be realized.

  Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings.

  The structural design support system of the present invention is a system that supports structural design of a vehicle body at the development stage of an automobile. In the development of automobiles, a method of obtaining a vehicle body with a structure that can keep the noise level below a target level for a given input by repeating a series of steps of design, prototyping, analysis, and experiment is used. It has been. However, at present, it takes a lot of time to experiment and calculate the body of an automobile, and it takes a lot of time to complete a vehicle body having a structure that is finally marketed by repeatedly executing these processes. Yes. For this reason, there is a strong demand for timely provision of vehicles that improve development efficiency and respond to market needs and environmental changes. The structural design support system of the present invention responds to such a demand, and improves efficiency of vehicle development by improving the efficiency of the analysis part.

  A schematic configuration of a structural design support system to which the present invention is applied is shown in FIG. The structural design support system 1 includes a calculation model generation unit 2, a structural system analysis unit 3, an acoustic system analysis unit 4, a sound evaluation unit 5, a structural acoustic coupling characteristic evaluation index calculation unit 6, a sensitivity calculation unit 7, and a structural optimization. Means 8 are provided.

  The calculation model generation means 2 is a means for generating a calculation model of the structure of the vehicle body to be designed, and the structural system analysis means 3 and the acoustic system analysis means 4 correspond to the calculation model generated by the calculation model generation means 2. And eigenvalue analysis of the structural system and eigenvalue analysis of the acoustic system. The sound evaluation means 5 is a means for calculating the sound level at the evaluation point with respect to the excitation at the input point in the calculation model generated by the calculation model generation means 2, and the structural acoustic coupling characteristic evaluation index calculation The means 6 is a means for calculating an index for evaluating the structural acoustic coupling characteristics when the sound level at the evaluation point calculated by the sound evaluation means 5 is not less than a desired value. The calculation of the index for evaluating the structural acoustic characteristic is for an arbitrary combination of one eigenvalue for each of the structural system and the acoustic system, and the result of the eigenvalue analysis by the structural system analysis means 3 and the acoustic system analysis means 4 is used. . The sensitivity calculation means 7 is a means for calculating the sensitivity to the index for evaluating the structural acoustic characteristics, and the structure optimization means 8 is the vehicle body to be designed based on the sensitivity to the index for evaluating the structural acoustic characteristics. It is a means to change the structure.

  Each means constituting the structural design support system 1 to which the present invention is applied as described above, for example, installs a predetermined processing program in a computer such as a personal computer or a workstation and executes the processing program on the computer. Can be realized as a function of a computer. Specifically, for example, the calculation model generation means 2 can be realized by a general-purpose finite element model creation pre-post program, and the structural system analysis means 3, the acoustic system analysis means 4, and the sound evaluation means 5 are general-purpose such as “NASTRAN”. It can be realized by the structure analysis program. The structural acoustic characteristic evaluation index calculation means 6 can be realized by a program for calculating an index for evaluating the structural acoustic coupling characteristics from eigenvalues, eigenmodes, etc. calculated by the structural analysis program. The sensitivity calculation means 7 is a structural analysis program. This can be realized by a program that calculates the sensitivity to the index for evaluating the structural acoustic coupling characteristics from the sensitivity of the eigenvalue, eigenmode, etc. calculated in (1). The structure optimizing means 8 can be realized by an optimization program in which linear programming, sequential linear programming, exploratory optimization methods and the like are collected.

  FIG. 2 is a flowchart schematically showing a flow of a series of processes by the structural design support system 1 to which the present invention is applied.

  In the structural design support system 1 to which the present invention is applied, first, a calculation model of the structure of the vehicle body to be designed is generated by the calculation model generation means 2 in step S1. Next, in step S2, the structural system analysis means 3 performs eigenvalue analysis of the structural system on the calculation model generated by the calculation model generation means 2, and in step S3, the acoustic system analysis means 4 performs the calculation model. An eigenvalue analysis of the acoustic system is performed on the calculation model generated by the generation unit 2. In step S4, the sound evaluation means 5 calculates the sound level at the evaluation point for the excitation at the input point in the calculation model generated by the calculation model generation means 2, and in step S5 It is determined whether the sound level is equal to or higher than a desired value.

  Here, if the sound level at the evaluation point is less than a desired value, the vehicle body structure with a reduced noise level is obtained, and the process is terminated. On the other hand, if the sound level at the evaluation point is equal to or higher than a desired value, the vehicle body structure needs to be changed, and the process proceeds to step S6. In step S6, the structural acoustic coupling characteristic evaluation index calculation means 6 calculates an index for evaluating the structural acoustic coupling characteristic. In addition, the specific example of the parameter | index which evaluates this structural acoustic coupling characteristic is mentioned later for details.

  Next, in step S7, the sensitivity calculation means 7 calculates the sensitivity for the index calculated by the structural acoustic coupling property evaluation index calculation means 6. In step S8, the structure optimization unit 8 changes the structure of the vehicle body to be designed based on the sensitivity to the index for evaluating the structural acoustic coupling characteristics calculated by the sensitivity calculation unit 7, and the process returns to step S1. And subsequent processing is repeated. The calculation of the sensitivity for the index for evaluating the structural acoustic coupling characteristics in step S7 is performed by, for example, calculating the sensitivity of the natural frequency of the structural system and the acoustic system and the sensitivity of the mode shape by using a structural analysis program. The sensitivity of the coupling coefficient can be calculated from the sensitivity of the natural frequency of the acoustic system and the sensitivity of the mode type.

  In the structural design support system 1 to which the present invention is applied, an optimal vehicle body structure in which the noise level is finally suppressed can be obtained by executing the series of processes described above. The processing by the structural design support system 1 is an index for evaluating the structural acoustic coupling characteristics instead of directly optimizing the sound pressure when the sound level of the evaluation point in the calculation model is not less than a desired value. And adopting a method of optimizing this index. Therefore, the optimal vehicle body that suppresses the noise level without performing a process that requires a huge amount of calculation such as solving the coupled equation of structure and sound, as in the case of directly optimizing the sound pressure at the evaluation point. The structure can be obtained and the efficiency of vehicle development can be improved.

  In the following, the features of the present invention will be described in more detail with reference to an example of sound optimization analysis inside a model using the simple model shown in FIG. The model 10 shown in FIG. 3 is composed of a sound field 11, a plate 12 set on the upper surface of the sound field 11, a beam 13 having a square cross section set on the plate 12, and an input point 14 for applying vibration and an evaluation for evaluating sound pressure. Point 15 is set. The design variable when optimizing the sound is the length H of the side of the cross section of each beam 13 when the total mass of the beams 13 is constant.

The sound level is determined by the coupled mode of structure and sound, and can be calculated using the uncoupled structure and sound eigenmodes. The sound pressure generated at the evaluation point 15 with respect to the input point 14 to the structure can be obtained by solving the equation (1) below.

In Equation (1), ξ _s is the mode amplitude of the structural system, m _s is the mode mass of the structural system, b _s is the damping of the structural system, k _s is the mode rigidity of the structural system, and Q _s is the modal force of the structural system. Ξ _f is the acoustic system mode amplitude, m _f is the acoustic system mode mass, b _f is the acoustic system attenuation, and k _f is the acoustic system mode stiffness. C is a matrix of coupled terms of the structural system and the acoustic system. As described above, in sound optimization, since the equation (1) is calculated for a large number of frequencies, it takes time to calculate.

In the present invention, instead of directly optimizing the sound pressure at the evaluation point 15, an index for evaluating the structural acoustic coupling characteristics in consideration of a combination made by selecting one eigenvalue of each of the structural system and the acoustic system. And take a method to optimize this indicator. Considering a system in which the structural system and the acoustic system are each in one mode and there is no attenuation and no acoustic load, the sound at the evaluation point 15 can be calculated by the following equation (2).

Solving equation (2) for ξ _f yields equation (3) below.

Here, ω _s ² = k _s / m _s , ω _f ² = k _f / m _f , m _s = 1, and m _f = 1. Assuming that the load applied to the structural system is f, the value of the mode shape at the input point 14 is φ _s0 , and the value of the mode shape at the evaluation point 15 is φ _f0 , the sound pressure p _{0 at the} evaluation point 15 is expressed by the following equation (4). become.

From this equation (4), it can be seen that p ₀ / f has the maximum amplitude at two coupled natural frequencies where the denominator is zero.

Next, when calculating the sound pressure in the vicinity of the coupled natural frequencies Ω _s and Ω _f by Δ, p ₀ / f is expressed by the following equations (5) and (6).

Roughly speaking, ω = Ω _s is the resonance of the structural system, and ω = Ω _f is the natural frequency whose sound level is increased by the resonance of the acoustic system.

  In an actual structure, since there is attenuation, the sound amplitude does not become infinite. However, if an expression obtained by adding attenuation to Expression (4) is used as an index, it is possible to perform strict sound optimization. However, since equation (4) is a function of frequency and a value is calculated for each frequency, the change in sound caused by optimization, the eigenvalue representing the essential characteristics of structure and sound, the change in eigenmode shape, The correlation cannot be grasped. Moreover, since a certain frequency range is set, calculation time is also required.

  The present invention is characterized in that sound is optimized using a combination of terms constituting the expressions (5) and (6) as an index for evaluating the structural acoustic coupling characteristics. Since these equations do not have a frequency term, it is possible to grasp the sound level as a combination of only the natural frequency of the structural system and the acoustic system, the natural mode shape, and the coupling coefficient.

More specifically, in the present invention, the mode shape value (φ _s0 ) of the input point 14 and the mode shape value (φ _f0 ), coupling coefficient (c), difference between squares of coupled natural frequencies of structural system and acoustic system (−Ω _s ² + Ω _f ² , −Ω _f ² + Ω _s ² ), structural system and acoustic At least one of the differences between the squares of the uncoupled natural frequencies of each system is set as an index for evaluating the structural acoustic coupling characteristics, and the index for evaluating the structural acoustic coupling characteristics is set. Sensitivity is calculated to obtain an optimized body structure. Strictly speaking, the denominator of equations (5) and (6) is the difference between the squares of the coupled natural frequencies, but in an actual car, the difference between the squares of the uncoupled natural frequencies. Substituting with does not produce a large difference, so instead of the square difference of the coupled natural frequency, the square difference of the uncoupled natural frequency is used as an index for evaluating the structural acoustic coupling characteristics. It can be used as one.

For an arbitrary combination of one eigenvalue for each of the structural system and the acoustic system, the mode shape value (φ _s0 ) of the input point 14, the mode shape value (φ _f0 ) of the evaluation point 15, and the coupling coefficient (c ), And at least one of them as a numerator, the difference between the squares of the coupled natural frequencies of the structural system and the acoustic system (−Ω _s ² + Ω _f ² , −Ω _f ² + Ω _s ² ), Or, if the difference between the squares of the uncoupled natural frequencies of the structural system and the acoustic system is used as an index for evaluating the structural acoustic coupling characteristics, more rigorous optimization can be achieved. It can be carried out.

Further, when performing more rigorous optimization, the mode shape value (φ _s0 ) of the input point 14 and the mode shape of the evaluation point 15 are obtained for an arbitrary combination of one eigenvalue for each of the structural system and the acoustic system. The product of the value of (φ _f0 ) and the coupling coefficient (c) is the numerator, and the difference between the squares of the coupled natural frequencies of the structural system and the acoustic system (−Ω _s ² + Ω _f ² , −Ω _f ² + Ω _s ² ), or the difference between the squares of the uncoupled natural frequencies of the structural system and the acoustic system as the denominator is effective to set as an index for evaluating the structural acoustic coupling characteristics. is there.

However, when priority is given to shortening the calculation time, it is desirable to use an index composed of as few terms as possible. Here, since the mode of the acoustic system is determined by the shape of the air that becomes the sound field, there is almost no possibility of change in the development of the automobile. Therefore, the term of the mode value (φ _f0 ) of the evaluation point is less important in the development of an automobile. For example, φ _s0 · c / −Ω _s ² + Ω _f ² is an index for evaluating the structural acoustic coupling characteristics. As a result, it is possible to perform sufficiently accurate optimization in a short time.

In the model 10 shown in FIG. 3, the results of optimization using the method of the present invention are shown with the length H of the side of the cross section of each beam 13 when the total mass of the beams 13 is constant as a design variable. 4 shows. Here, φ _s0 · c / −Ω _s ² + Ω _f ² is used as an index for evaluating the structural acoustic coupling characteristics, and the two sound peaks in the figure are simultaneously optimized. As a comparative example, FIG. 5 shows the result of optimization while strictly calculating the sound level using the above equation (1). As can be seen from FIGS. 4 and 5, by performing the optimization by the method of the present invention, it is possible to reduce the noise as in the case of performing the strict optimization. In addition, since the method of the present invention can reduce noise without directly calculating the sound level, the calculation time can be greatly shortened and the efficiency of analysis can be improved, and the efficiency of vehicle development can be improved. it can.

  As described above in detail with specific examples, according to the structural design support system to which the present invention is applied, the noise level is optimized by performing the optimization using the index for evaluating the structural acoustic coupling characteristics. Thus, an optimum vehicle body structure with reduced squeeze can be obtained in a very short time, and vehicle development efficiency can be improved. The above is an example of the embodiment of the present invention, and the technical scope of the present invention is not limited to the contents disclosed in the description of the above embodiment, and is easily derived from these disclosures. Of course, the various alternative techniques that can be obtained are also included.

It is a block diagram which shows schematic structure of the structural design support system to which this invention is applied. It is a flowchart which shows roughly the flow of a series of processes by the structural design support system to which this invention is applied. It is a figure which shows the simple model comprised from the sound field, the board of a sound field upper surface, and the beam of the square cross section set to the board. It is a figure which shows the result of having optimized by the method of this invention by making the length of the side of the cross section of a beam into a design variable in the model shown in FIG. It is a figure which shows as a comparative example the result at the time of optimizing by the conventional general method by making the length of the side of the cross section of a beam into a design variable in the model shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Structural design support system 2 Calculation model production | generation means 3 Structural system analysis means 4 Acoustic system analysis means 5 Sound evaluation means 6 Structural acoustic coupling property evaluation index calculation means 7 Sensitivity calculation means 8 Structure optimization means

Claims (5)

A structural design support system that supports structural design of a car body of an automobile by seeking an optimal structure capable of reducing noise by analyzing the structure and sound using a model,
A calculation model generation means for generating a calculation model of the structure of the vehicle body to be designed;
Structural system analysis means for performing eigenvalue analysis of the structural system using the calculation model;
Acoustic system analysis means for performing eigenvalue analysis of the acoustic system using the calculation model;
Sound evaluation means for calculating a sound level at an evaluation point with respect to excitation at an input point in the calculation model;
A structural acoustic coupling property evaluation index calculating means for calculating an index for evaluating the structural acoustic coupling characteristics when the sound level at the evaluation point is equal to or higher than a desired value;
Sensitivity calculating means for calculating sensitivity to an index for evaluating the structural acoustic coupling characteristics;
A structural design support system comprising: structure optimization means for changing a structure of a vehicle body to be designed based on sensitivity to an index for evaluating the structural acoustic coupling characteristics.   The structural acoustic coupling property evaluation index calculation means is configured to calculate a mode-shaped value of the input point, a mode-shaped value of the evaluation point, a coupling coefficient for an arbitrary combination of eigenvalues for each of the structural system and the acoustic system. , At least one of the difference between the squares of the coupled natural frequencies of the structural system and the acoustic system, and the difference of the squares of the uncoupled natural frequencies of the structural system and the acoustic system, The structural design support system according to claim 1, wherein the structural design support system is calculated as an index for evaluating the structural acoustic coupling characteristics.   The structural acoustic coupling property evaluation index calculation means is configured to calculate a mode-shaped value of the input point, a mode-shaped value of the evaluation point, a coupling coefficient for an arbitrary combination of eigenvalues for each of the structural system and the acoustic system. The difference between the squares of the coupled natural frequencies of the structural system and the acoustic system, or the square of the uncoupled natural frequencies of the structural system and the acoustic system. The structural design support system according to claim 2, wherein the value is used as an index for evaluating the structural acoustic coupling characteristics.   The structural acoustic coupled property evaluation index calculation means calculates a mode shape value of the input point, a mode shape value of the evaluation point, and a continuous value for an arbitrary combination of eigenvalues for each of the structural system and the acoustic system. The product of the coefficient of synthesis is the numerator, and the difference between the squares of the coupled natural frequencies of the structural system and the acoustic system or the square of the uncoupled natural frequencies of the structural system and the acoustic system is denominator. The structural design support system according to claim 3, wherein the structural design is calculated as an index for evaluating the structural acoustic coupling characteristics. A structural design support program that supports the structural design of a car body of an automobile by seeking an optimal structure capable of reducing noise by analyzing the structure and sound using a model,
On the computer,
A function to generate a calculation model of the structure of the body to be designed;
A function of performing eigenvalue analysis of a structural system using the calculation model;
A function of performing eigenvalue analysis of an acoustic system using the calculation model;
A function of calculating a sound level at an evaluation point with respect to excitation at an input point in the calculation model;
A function for calculating an index for evaluating the structural acoustic coupling characteristics when the sound level at the evaluation point is equal to or higher than a desired value;
A function of calculating sensitivity to an index for evaluating the structural acoustic coupling characteristics;
A structural design support program that realizes a function of changing a structure of a vehicle body to be designed based on sensitivity to an index for evaluating the structural acoustic coupling characteristics.

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