JP6991942B2 - Structural design support system - Google Patents

Description

The present invention relates to a vehicle body structural design support system.

In the design support system for the body structure of an automobile, there is known that the body structure is optimized by using a model in order to reduce noise at a predetermined evaluation point in the vehicle interior. In such a vehicle body structure design system, the vehicle body design area is divided into a plurality of nodes, and a physical model of the vehicle body structure (structural system) in which the nodes are connected by beam elements, flat plate elements, polyhedral elements, etc. is generated. Next, the design system similarly divides the passenger compartment at a plurality of nodes to generate a physical model of the passenger compartment air (acoustic system). Furthermore, the design system derives a coupled equation that couples the structural system and the acoustic system, and calculates the sound pressure generated at the evaluation point when a predetermined vibration is input to the vehicle body based on the coupled equation. .. Then, the acoustic sensitivity indicating the relationship between the vibration input to the vehicle body and the sound pressure is calculated, and the vehicle body structure is optimized to minimize the acoustic sensitivity.

In such a design system, in order to interconnect the structural system and the acoustic system, it is necessary to set a sufficient number of nodes on the wet surface where the vehicle body and the passenger compartment air are in contact with each other. Therefore, when solving the coupled equation, for example, a large calculation resource is required in the memory capacity, and there is a problem that the calculation takes time. Therefore, in the vehicle body structure design support system, the natural frequency of the structural system and the natural frequency of the acoustic system are selected one by one, and the sound pressure generated by the coupling of the two selected natural modes is used for acoustics. Those that evaluate the sensitivity and optimize the vehicle body structure are known (for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2008-234589

However, in the actual vehicle interior, the vibration of the vehicle body causes sounds of different frequencies to be generated in a plurality of places. The generated sounds reach the evaluation points and interfere with each other in a complicated manner. Since the design support system of Patent Document 1 considers only the sound of one natural frequency, it is difficult to accurately evaluate the effect of interference on the acoustic sensitivity.

In order to consider the effect of interference caused by sounds of a plurality of natural frequencies, it is conceivable to formulate an approximate equation for sounds of natural frequencies below a predetermined cutoff frequency to calculate acoustic sensitivity. However, as the number of unique modes to consider increases, so does the amount of data to be stored and the amount of computation required.

In view of the above background, the present invention reduces the resources required for calculation in the vehicle body structural design support system, and optimizes the vehicle body structure based on the acoustic sensitivity in consideration of interference between specific modes. The task is to do.

In order to solve the above problems, one aspect of the present invention is a structural design support system (1) for designing a vehicle body structure capable of reducing acoustic sensitivity from the vehicle body to an occupant, wherein the physical model of the vehicle body structure. Using the physical model generation means (6) that generates the physical model of the cabin air and the structural acoustic coupling equation in the physical coordinates, and the physical model of the vehicle body structure, the natural frequency and the natural mode of the vehicle body structure are calculated. Structural analysis means (7), acoustic analysis means (8) for calculating the natural frequency and natural mode of the vehicle interior air using the physical model of the vehicle interior air, the natural mode of the vehicle body structure, and the vehicle. After performing coordinate conversion based on the intrinsic mode of the room air and deriving the structural acoustic coupled equation in modal coordinates, the intrinsic mode of the vehicle body structure having a structural cutoff frequency or less and the vehicle having an acoustic cutoff frequency or less. A coupled equation derivation means (9) for deriving an approximate structural acoustic coupled equation with respect to the eigenmode of room air, an acoustic sensitivity calculating means (10) for calculating the acoustic sensitivity based on the approximate structural acoustic coupled equation, and the like. Based on the acoustic sensitivity, there is a changing means (11) for changing at least one selected from the natural frequencies of the vehicle body structure having the structural cutoff frequency of the approximate structure acoustic coupling equation or less. The acoustic sensitivity is minimized by repeating the calculation by the coupled equation deriving means and the acoustic sensitivity calculating means based on the approximate structural acoustic coupled equation changed by the changing means. ..

According to this aspect, the acoustic sensitivity is calculated based on the approximate structural acoustic coupled equation for the intrinsic mode of the vehicle body structure having a structural cutoff frequency or less and the intrinsic mode of the cabin air having an acoustic cutoff frequency or less. As a result, the resources required for the calculation can be reduced, and the acoustic sensitivity can be calculated based on the unique modes of the plurality of vehicle body structures and the plurality of unique modes of the vehicle interior air, which greatly contribute to practical use. Further, since the unique modes of the air in the plurality of vehicle interiors are taken into consideration, the acoustic sensitivity can be calculated in consideration of the interference of the sounds in the plurality of vehicle interiors.

In addition, optimization is performed by changing the natural frequency of the vehicle body structure. Therefore, when optimizing, it is only necessary to change the part that depends only on the natural frequency of the approximate structure coupled equation, and the approximate structure when optimizing is executed compared to the case where the vehicle body structure is changed. It is possible to reduce the change part of the coupled equation. As a result, the resources required for the calculation can be reduced, and the calculation speed can be increased. Further, since the optimization is performed by changing the natural frequency of the vehicle body structure, it is easy to obtain a change guideline for optimizing the acoustic sensitivity.

In the above embodiment, the structural cut-off frequency and the acoustic cut-off frequency are preferably 100 Hz or more and 1000 Hz or less, respectively.

According to this aspect, for example, the cutoff frequency can be set higher than the primary resonance frequency of the windshield, so that the natural vibration mode of the tire, suspension, windshield, etc. can be considered.

According to the above configuration, in the structural design support system of the vehicle body, the resources required for calculation are reduced, and the vehicle body structure is optimized based on the acoustic sensitivity in consideration of the interference between the unique modes. Can be done.

Block diagram of the structural design support system according to the present invention Flow chart of the structural design support system according to the present invention

Hereinafter, specific embodiments of the structural design support system according to the present invention will be described. In the following explanation, it is assumed that the structural design support system is used to design the structure of an automobile.

The structural design support system is a system for designing a vehicle body structure that can reduce the noise in the vehicle interior generated by the vibration of the vehicle body. The vibration generated by driving the engine and the vibration generated by the road surface reaction force when the vehicle is running are transmitted to the vehicle body. Due to such vibration, a plurality of vibrations in a specific mode are generated in the vehicle body. The air in the passenger compartment (air in the passenger compartment) is in contact with the vehicle body structure, for example, a frame as a skeleton or a panel for partitioning the passenger compartment space. Therefore, the vibration generated in the vehicle body is transmitted to the air in the vehicle interior, and a plurality of vibrations in the specific mode according to the shape of the vehicle interior space are generated in the vehicle interior air. Due to the vibration of the passenger compartment air, sound pressure is generated at the occupant's ear (evaluation point), and the sound pressure is transmitted to the occupant as noise.

In order to reduce noise, it is effective to reduce the vibration of the vehicle body and design the structure of the vehicle body so that the vibration of the vehicle body is less likely to be transmitted to the air around the occupant's ears. The ease with which such vibrations are transmitted can be evaluated using the acoustic sensitivity, which is the sound pressure level at the evaluation point with respect to the unit input to the vehicle body. Therefore, the structural design support system 1 calculates the acoustic sensitivity based on the given vehicle body structure. Further, the structural design support system 1 executes an optimization process for optimizing the vehicle body structure in order to minimize the acoustic sensitivity.

The structural design support system 1 according to the embodiment is composed of a computer such as a personal computer or a workstation, and as shown in FIG. 1, a central processing unit (CPU), an arithmetic processing unit 2 including a memory, and a storage medium such as a hard disk. 3. An input unit 4 such as a keyboard and an output unit 5 such as a monitor are provided.

The storage medium 3 holds vehicle body data such as the shape of the vehicle body including the frame and panel of the target automobile, the rigidity of each part of the vehicle body, and the material. The vehicle body data may be stored in the storage medium 3 in advance before the optimization process is executed.

The arithmetic processing unit 2 generates a physical model of the vehicle body structure and the vehicle interior air, and derives the equation of motion (structural acoustic coupled equation) of the vehicle body structure and the vehicle interior air in the physical coordinates from the physical model generation means 6 and the physical model. Physical coordinates using the structural analysis means 7 that calculates the intrinsic mode of the vibration of the vehicle body structure, the acoustic analysis means 8 that calculates the intrinsic mode of the vibration of the vehicle interior air from the physical model, and the intrinsic mode of the vehicle body structure and the vehicle interior air. Coordination equation derivation means 9 for deriving the approximate structural acoustic coupled equation by performing coordinate conversion from to modal coordinates and performing approximation processing on the structural acoustic coupled equations in the modal coordinates, and the derived approximate structural acoustics. It is provided with an acoustic sensitivity calculating means 10 for solving an coupled equation to calculate an acoustic sensitivity, and a changing means 11 for changing the vehicle body structure in order to optimize the acoustic sensitivity based on the acoustic sensitivity calculated by the acoustic sensitivity calculating means 10. There is. In the present embodiment, the physical model generation means 6, the structural analysis means 7, the acoustic analysis means 8, the coupled equation derivation means 9, the acoustic sensitivity calculation means 10, and the change means 11 are each configured by software in the arithmetic processing unit 2. Has been done.

式（１）において、｛ｕ｝は車体構造の各節点における変位を示す変位ベクトル、［Ｍ_ｓ］は車体構造の質量マトリクス、［Ｂ_ｓ］は車体構造の減衰マトリクス、［Ｋ_ｓ］は車体構造の剛性マトリクス、｛Ｆ｝は車体に加わる荷重ベクトルである。｛ｕ｝はＮ_ｓ次元のベクトルであり、［Ｍ_ｓ］、［Ｂ_ｓ］、［Ｋ_ｓ］はそれぞれＮ_ｓ×Ｎ_ｓの行列である。｛ｕ｝の文字上の１つのドットは変位ベクトルの１階の時間微分を示し、２つのドットは変位ベクトルの２階の時間微分を示す。但し、｛｝はベクトルを示す記号であり、［］は行列を示す記号とする。また、｛０｝は零ベクトルを示し、［０］は全ての要素が０である行列を示す。 The physical model generation means 6 generates a physical model of the vehicle body structure based on the vehicle body data stored in the storage medium 3. The physical model is a model in which the vehicle body is divided by _Ns degrees of freedom and the nodes are connected by beam elements or the like, and is expressed by the equation of motion of the equation (1).

In equation (1), {u} is a displacement vector indicating the displacement at each node of the vehicle body structure, [M _s ] is the mass matrix of the vehicle body structure, [B _s ] is the damping matrix of the vehicle body structure, and [K _s ] is the vehicle body. The rigidity matrix of the structure, {F}, is a load vector applied to the vehicle body. {U} is an N _s -dimensional vector, and [M _s ], [B _s ], and [K _s ] are N _s × N _s matrices, respectively. One dot on the character {u} indicates the first derivative of the displacement vector, and two dots indicate the second derivative of the displacement vector. However, {} is a symbol indicating a vector, and [] is a symbol indicating a matrix. Further, {0} indicates a zero vector, and [0] indicates a matrix in which all the elements are 0.

式（２）において、｛ｐ｝は車室空気の各節点における圧力の大気圧からの変動分（以下、音圧）を示す音圧ベクトル、［Ｍ_ｆ］は車室空気の質量マトリクス、［Ｂ_ｆ］は車室空気の減衰マトリクス、［Ｋ_ｓ］は車室空気の剛性マトリクスである。｛ｐ｝はＮ_ｆ次元のベクトルであり、［Ｍ_ｆ］、［Ｂ_ｆ］、［Ｋ_ｆ］はそれぞれＮ_ｆ×Ｎ_ｆの行列である。｛ｐ｝の文字上の１つのドットは音圧ベクトルの１階の時間微分を示し、｛ｐ｝の文字上の２つのドットは音圧ベクトルの２階の時間微分を示す。 The physical model generating means 6 further generates a physical model of the vehicle interior air based on the vehicle body data stored in the storage medium 3. The physical model is a model in which the passenger compartment is divided by N _f degrees of freedom and the nodes are connected by polyhedral elements or the like, and is expressed by the equation of motion of the equation (2).

In the equation (2), {p} is a sound pressure vector indicating the fluctuation amount (hereinafter referred to as sound pressure) of the pressure at each node of the passenger compartment air from the atmospheric pressure, [M _f ] is the mass matrix of the passenger compartment air, [ B _f ] is a damping matrix of the passenger compartment air, and [K _s ] is a rigidity matrix of the passenger compartment air. {P} is an N _f -dimensional vector, and [M _f ], [B _f ], and [K _f ] are N _f × N _f matrices, respectively. One dot on the character of {p} indicates the first derivative of the sound pressure vector, and two dots on the character of {p} indicate the second derivative of the sound pressure vector.

Next, the physical model generating means 6 derives the structural acoustic coupled equation (3) in physical coordinates in consideration of the exchange of internal force on the surface (wet surface) where the vehicle body structure and the vehicle interior air are in contact with each other. After the derivation, the physical model generation means 6 outputs the structural acoustic coupled equations in the physical coordinates to the structural analysis means 7, the acoustic analysis means 8, and the coupled equation derivation means 9.

In the formula (3), [A] is a structural acoustic coupled matrix of N _f × N _s . [A] ^T represents the transposed matrix of [A].

The structural analysis means 7 calculates the natural frequency λ _si of the vehicle body structure and the natural mode {φ _si } (i = 1 to N _s ) based on the physical model (1) of the vehicle body structure. At this time, the structural analysis means 7 may numerically solve the equation (4) shown below. Each eigenmode {φ _si } is an N _s dimension vector. Further, the natural frequency λ _si is arranged so that the smaller i is, the smaller it is.

The acoustic analysis means 8 calculates the natural frequency λ _fi of the sound pressure and the natural mode {φ _fi } (i = 1 to N _f ) based on the physical model (2) of the vehicle interior air. At this time, the acoustic analysis means 8 may numerically solve the equation (5) shown below. Each eigenmode {φ _fi } is an N _f -dimensional vector. Further, the natural frequency λ _fi is arranged so that the smaller i is, the smaller it is.

The coupled equation derivation means 9 in the physical coordinates derived by the physical model generation means 6 by converting the physical coordinates into modal coordinates based on the eigenmode derived by the structural analysis means 7 and the acoustic analysis means 8. Convert the structural acoustic coupling equation to the structural acoustic coupling equation in modal coordinates. The following equation (6) represents the conversion from the physical coordinates to the modal coordinates, and the equation (7) represents the structural acoustic coupled equation in the modal coordinates.

{Η _s } in Eqs. (6) and (7) is an N _s -dimensional vector, and {η _f } is an N _f -dimensional vector. In equation (7), [φ _s ] and [φ _f ] are the matrices shown in equation (8), respectively. However, [φ _s ] is a matrix of N _s × N _s , and [φ _f ] is a matrix of N _f × N _f .

Next, the coupled equation derivation means 9 derives the approximate structural acoustic coupled equation (9) by performing an approximation process ignoring the higher-order eigenmode in order to reduce the size of the matrix of the equation (7). .. More specifically, the coupled equation derivation means 9 extracts the eigenmode of the vehicle body structure having a structural cutoff frequency of λ _sc or less. Further, the coupled equation derivation means 9 extracts a specific mode of sound pressure having an acoustic cutoff frequency of λ _fc or less. After that, the coupled equation derivation means 9 uses the extracted vehicle body structure eigenmode {φ _si } (i = 1 to n _s ) and the extracted sound pressure eigenmode {φ _fi } (i = 1 to n). The approximate structural acoustic coupled equation (9) for _f ) is derived.

In the equation (9), {ξ _s } is a modal displacement vector of the vehicle body structure, and is a vector obtained by extracting the first line to the n _s line of η _s . {Ξ _f } is a modal displacement vector of the passenger compartment air, and is a vector obtained by extracting the first line to the n _f line of {η _f }. The modal mass matrix [ _ms ] of the vehicle body structure, the modal damping matrix [bs] of the vehicle body structure, and the modal stiffness matrix [ _{ks] of the vehicle body structure are [φ s ]} ^T [M _s ] [φ _s ] and [, _respectively . In the matrix of φ _s ] ^T [B _s ] [φ _s ] and [φ _s ] ^T [K _s ] [φ _s ], the range of the 1st row to the n _s row and the 1st column to the n _s column is set. It is a matrix of n _s × n _s calculated by extracting each. The modal mass matrix [m _f ] of the passenger compartment air, the modal decay matrix [b _f ] of the passenger compartment air, and the modal stiffness matrix [k _f ] of the passenger compartment air are [φ _f ] ^T [M _f ] [φ _f , respectively. ], [φ _f ] ^T [B _f ] [φ _f ], [ _{φ f} ] ^T [K _f ] [ _{φ f} ] It is a matrix of n _f × n _f calculated by extracting.

The modal structure acoustic coupled matrix [a _HH ] was calculated by extracting the range of the 1st to _nf rows and the 1st to _ns columns of [φ _s ] ^T [A] [φ _f ]. It is a matrix, and the modal load vector {f} is a vector calculated by extracting the first row to the n _s row of [φ _s ] ^T {F}.

Next, the coupled equation derivation means 9 outputs the derived approximate structural acoustic coupled equation to the acoustic sensitivity calculation means 10.

The acoustic sensitivity calculation means 10 solves the approximate structure acoustic coupled equation input from the coupled equation derivation means 9 to calculate {ξ _f }. However, when the changing means 11 inputs the changed approximate structure acoustic coupling equation, the acoustic sensitivity calculating means 10 solves the changed approximate structure acoustic coupling equation to calculate {ξ _f }.

但し、｛ξ_F｝はＮ_ｆ次元のベクトルであり、｛ξ_F｝の１～ｎ_ｆ行目までの要素は、｛ξ_ｆ｝の要素と等しく、ｎ_ｆ＋１行目～Ｎ_ｆ行目までの要素は０である。 Next, the acoustic sensitivity calculation means 10 substitutes the calculated solution {ξ _f } into the equation (10) to calculate an approximate sound pressure vector {p _eff }.

However, {ξ _F } is an N _f -dimensional vector, and the elements from the 1st to _nf lines of {ξ _F } are equal to the elements of {ξ _f }, and the elements from the n _f +1 line to the N _f line are equal to each other. The elements up to are 0.

The acoustic sensitivity calculation means 10 calculates the sound pressure p _a at the occupant's ear based on the sound pressure vector {p _eff }, divides the p _a by the magnitude (norm) of the input load vector {F}, and divides the p a by the magnitude (norm) of the input load vector {F}. The acoustic sensitivity H is calculated. The acoustic sensitivity calculation means 10 extracts the element corresponding to the sound pressure at the node corresponding to the position of the occupant's ear from the sound pressure vector {p _eff }, thereby extracting the sound pressure _pa at the occupant's ear (evaluation point). Should be calculated.

When the calculation of the acoustic sensitivity H is completed, the acoustic sensitivity calculating means 10 outputs the approximate structure acoustic coupled equation used in the calculation and the calculated acoustic sensitivity H to the changing means 11.

When the changing means 11 receives the input of the unique mode number r of the vehicle body structure from the input unit 4 and the input of the approximate structure acoustic coupled equation and the acoustic sensitivity H from the acoustic sensitivity calculating means 10, the optimization process is performed. The number of times these inputs have been received (hereinafter referred to as the number of changes) has been calculated since the start of. When the number of changes is a specified number (for example, 1000 times) or more, the input approximate structure acoustic coupled equation and acoustic sensitivity H are displayed on the output unit 5 of the design support system. In the present embodiment, the changing means 11 calculates and inputs the natural frequency λ _r of the natural mode {φ _sr } of the vehicle body structure corresponding to the number r based on the input approximate structural acoustic coupling equation. The calculated natural frequency λ _r is displayed on the output unit 5 of the design support system together with the approximate structure acoustic coupled equation and the acoustic sensitivity H.

When the number of changes is less than the specified number of times, the changing means 11 performs a changing process in order to minimize the acoustic sensitivity. In the change process, the change means 11 calculates the change amount _δλ of the natural frequency λr corresponding to the natural mode {φ _sr } of the vehicle body structure of the number r based on a predetermined optimization algorithm. The optimization algorithm executed by the changing means 11 may be a known algorithm.

Next, the changing means 11 changes the natural frequency from λ _r to λ _r without changing the natural mode {φ s _r } of the vehicle body structure of the number r in the approximate structure acoustic coupling equation input from the acoustic sensitivity calculating means 10. The modified process of changing to + δλ is performed to generate the modified approximate structural acoustic coupled equation.

但し、式（１１）において、［δΛ］は、ｒ行ｒ列目の要素がδλであり、他の要素が０であるｎ_ｓ×ｎ_ｓの行列を表している。 Next, the changing means 11 changes the modal stiffness matrix [ _ks ] of the vehicle body structure of the equation (9) as shown in the equation (11) in the approximate structural acoustic coupled equation input from the acoustic sensitivity calculating means 10. It is advisable to generate an approximate structural acoustic coupled equation.

However, in the equation (11), [δΛ] represents a matrix of n _s × n _s in which the element in the r-th row and the r-th column is δλ and the other elements are 0.

Next, the changing means 11 outputs the changed approximate structural acoustic coupling equation to the acoustic sensitivity calculating means 10 to complete the changing process.

Next, the optimization process executed by the structural design support system 1 will be described with reference to the flowchart shown in FIG. In step ST1, the structural design support system 1 receives inputs of the structural cutoff frequency λ _sc and the acoustic cutoff frequency λ _fc in the input unit 4. When the input is completed, the structural design support system 1 executes step ST2.

The structural cutoff frequency λ _sc and the acoustic cutoff frequency λ _fc are both preferably 100 Hz or more and 1000 Hz or less. Since the primary natural frequency of the tire is about 40 Hz, the primary natural frequency of the suspension is about 10 Hz, and the primary natural frequency of the windshield is about 30 Hz, it should be set in this way. Allows consideration of primary natural mode vibrations of tires, suspensions and windshields. In the present embodiment, the structural cutoff frequency λ _sc is set to an arbitrary value of 300 Hz to 600 Hz, and the acoustic cutoff frequency λ _fc is set to an arbitrary value of 400 Hz to 800 Hz.

In step ST2, the physical model generating means 6 reads the vehicle body data from the storage medium 3 and generates a physical model of the vehicle body structure and a physical model of the vehicle interior air. Next, the physical model generating means 6 calculates the structural acoustic coupling matrix A and derives the structural acoustic coupling equation in the physical coordinates. After completion, the structural design support system 1 executes step ST3.

In step ST3, the structural analysis means 7 calculates the natural frequency and the natural mode of the vehicle body structure based on the structural acoustic coupled equations in the physical coordinates derived by the physical model generation means 6. Further, the acoustic analysis means 8 calculates the natural frequency and the natural mode of the sound pressure based on the structural acoustic coupled equation in the physical coordinates derived by the physical model generation means 6. After completion, the structural design support system 1 executes step ST4.

In step ST4, the coupled equation derivation means 9 has the natural frequency of the vehicle body structure calculated by the structural analysis means 7 and the acoustic analysis means 8, the natural mode of the vehicle body structure, the natural frequency of the sound pressure, and the natural frequency of the sound pressure. Based on the mode, we derive the structural acoustic coupled equations in modal coordinates. When the derivation is completed, the structural design support system 1 executes step ST5.

In step ST5, the coupled equation derivation means 9 derives an approximate structural acoustic coupled equation based on the structural cutoff frequency λ _sc and the acoustic cutoff frequency λ _fc input in step ST1. When the derivation is completed, the structural design support system 1 executes step ST6.

In step ST6, the structural design support system 1 receives the input of the number r of the unique mode of the vehicle body structure to be changed in the input unit 4. When the user selects and inputs the unique mode number r, the structural design support system 1 executes step ST7.

In step ST7, the acoustic sensitivity calculation means 10 solves the approximate structure acoustic coupled equation input from the coupled equation derivation means 9 to calculate the acoustic sensitivity H. When the modified approximate structure acoustic coupling equation is input from the modification means 11, the acoustic sensitivity calculation means 10 solves the modified approximate structure acoustic coupling equation to calculate the acoustic sensitivity H. When the calculation of the acoustic sensitivity H is completed, the structural design support system 1 executes step ST8.

In step ST8, the changing means 11 determines whether the number of changes has reached the specified number of times or more. When the number of times exceeds the specified number, step ST9 is executed. When the number of changes has not reached the specified number of times, the structural design support system 1 executes step ST10.

In step ST9, the changing means 11 has the input approximate structure acoustic coupling equation, acoustic sensitivity H, and the natural frequency λ of the natural mode φ _sr of the vehicle body structure corresponding to the number r in the input approximate structure acoustic coupling equation. _{The r} is output to the output unit 5. When the output is completed, the structural design support system 1 ends the optimization process.

In step ST10, the changing means 11 changes the natural frequency λ _sr of the natural mode {φ _sr } of the natural mode based on the number r of the natural mode input from the input unit 4 in step ST6, and has an approximate structure. Performs a change process to change the acoustic coupled equation. The changing means 11 outputs the changed approximate structural acoustic coupling equation to the acoustic sensitivity calculating means 10. After the output, the structural design support system 1 returns to step ST7.

The effect of the structural design support system 1 configured as described above will be described. The structural acoustic coupled equation in the physical coordinates shown in the equation (3) consists of a matrix of (N _s + N _f ) × (N _s + N _f ). In particular, in order to consider that the vibration of the vehicle body structure is transmitted to the vehicle interior air, many points are required on the contact surface (wet surface) between the vehicle body structure and the vehicle interior air, and the formula (3) has about 10 million degrees of freedom. It becomes a degree. On the other hand, the approximate structural acoustic coupled equation shown in Eq. (9) consists of a matrix of ( _{ns + n f) × (ns + n f), and is derived from a matrix of (N s + N f) × (N s + N f ) .} Also becomes smaller. Generally, when the structural cutoff frequency λ _sc and the acoustic cutoff frequency λ _fc are set to about 600 Hz, n _s + n _f becomes about 1000, and the size of the matrix constituting the equation solved by the structural design support system 1 becomes small. In this way, since the size of the matrix is reduced, the resources required for the calculation can be reduced and the calculation speed can be increased. Further, in the structural design support system 1, the acoustic sensitivity H is calculated based on the unique modes of a plurality of sound pressures. Therefore, it is possible to consider the effect of interference caused by the overlapping of a plurality of sound pressures in the intrinsic mode.

Generally, when the parameters related to the vehicle body structure (for example, the plate thickness of the frame constituting the vehicle body) are changed, the unique mode {φ _si } (i = 1 to n _s ) of the vehicle body structure changes, so that the modal structure acoustic coupled matrix [ a _HH ] needs to be changed. On the other hand, in step ST10, the changing means 11 changes the natural frequency for the natural mode {φ _sr } of the vehicle body structure of the number r from λ _r to λ _r + δλ without changing the natural mode of the vehicle body structure, and approximates it. The structural acoustic coupling equation is derived. At this time, since the unique mode of the vehicle body structure is not changed, the changing means 11 can change the approximate structure acoustic coupling equation in the change process without newly calculating the modal structure acoustic coupling matrix [a _HH ]. can. Therefore, the calculation resource can be reduced and the calculation speed can be increased as compared with the case where the modal structure acoustic coupled matrix [a _HH ] is changed in the change process. In particular, in the present embodiment, the size of the modal structural acoustic coupled matrix [a _HH ] can be stored in the memory by appropriately setting the structural cutoff frequency λ _sc and the acoustic cutoff frequency λ _fc . Can be made smaller. As a result, the size of the modal structure acoustic coupled matrix [a _HH ] is large, and the access speed to the data can be increased as compared with the case where the modal structure acoustic coupled matrix [a _HH ] is stored in the hard disk. The calculation speed can be further increased. Further, in the modification process, the modal mass matrix [ _{m f} ] of the vehicle interior air, the modal rigidity matrix [k _f ] of the vehicle interior air, the modal damping matrix [bs] of the vehicle body structure, and the modal damping matrix [b] of the vehicle interior air. _f ] can be changed without calculating the approximate structural acoustic coupling equation. As a result, the calculation resource can be reduced and the calculation speed can be increased as compared with the case where the matrix [m _f ], [k _f ], [b _s ] and [b _f ] are changed. Further, in the present embodiment, in the change process, only the modal stiffness matrix [ _ks ] is changed based on the equation (11), and the modal mass matrix [ms] is not changed, so that [ _{ks ]} and [ _ms ] are changed. ] Is changed, the calculation speed is higher. Further, compared to the case where the specific mode of the vehicle body structure is changed by changing the parameters of the vehicle body structure, the structural design support system 1 makes it easier to follow the specific mode of the vehicle body structure, and it is possible to understand the noise reduction mechanism. It's easy.

Further, in step ST9, the element of the modal structure acoustic coupled matrix [a _HH ] may be output. This makes it easier to understand the noise reduction mechanism because information indicating which structural mode is coupled to which acoustic mode is output.

In addition, when diagonalization is executed again in the change process, the order of the natural modes after diagonalization may be changed compared to the order before diagonalization based on the value of the natural frequency. .. At this time, it is preferable to replace the elements of the modal structure acoustic coupled matrix [ _aHH ] based on the correspondence between the order before the change and the order after the change of the eigenmode. As a result, it is not necessary to recalculate the elements of the modal structure acoustic coupled matrix [a _HH ], so that the amount of calculation required for the optimization process can be reduced.

Although the description of the specific embodiment is completed above, the present invention is not limited to the above embodiment. The changing means 11 was configured to change one of the natural modes of the vehicle body structure, but the changing means 11 was configured to change the natural frequency of two or more vehicle body structures in the natural mode. You may.

1: Structural design support system 2: Arithmetic processing unit 3: Storage medium 4: Input unit 5: Output unit 6: Physical model generation means 7: Structural analysis means 8: Acoustic analysis means 9: Coupled equation derivation means 10: Acoustic sensitivity Calculation means 11: Change means

Claims (2)

It is a structural design support system for designing a vehicle body structure that can reduce the acoustic sensitivity from the vehicle body to the occupants.
A physical model generating means for generating a physical model of the vehicle body structure, a physical model of the cabin air, and a structural acoustic coupled equation in physical coordinates, respectively.
A structural analysis means for calculating the natural frequency and the natural mode of the vehicle body structure using the physical model of the vehicle body structure.
An acoustic analysis means for calculating the natural frequency and the natural mode of the vehicle interior air using the physical model of the vehicle interior air,
After performing coordinate conversion based on the eigenmode of the vehicle body structure and the eigenmode of the cabin air to derive the structural acoustic coupled equation in modal coordinates, the eigenmode of the vehicle body structure having a structural cutoff frequency or less, and Approximate structure for the eigenmode of the vehicle interior air below the acoustic cutoff frequency.
An acoustic sensitivity calculation means for calculating the acoustic sensitivity based on the approximate structural acoustic coupling equation, and an acoustic sensitivity calculation means.
It has a changing means for changing at least one selected from the natural frequencies of the vehicle body structure which are equal to or less than the structural cutoff frequency of the approximate structural acoustic coupling equation based on the acoustic sensitivity.
A structural design support system characterized in that the acoustic sensitivity calculating means minimizes the acoustic sensitivity by repeating an operation based on the approximate structural acoustic coupled equation changed by the changing means. The structural design support system according to claim 1, wherein the structural cut-off frequency and the acoustic cut-off frequency are 100 Hz or more and 1000 Hz or less, respectively.

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