Body-in-white NVH (Noise Vibration and Harshness) performance calculation method based on energy finite element method

Abstract

The invention relates to a body-in-white NVH (Noise Vibration and Harshness) performance calculation method based on an energy finite element method. The method comprises the following steps of: 1, constructing a simplified body-in-white finite element method model by applying universal finite element pre-processing software, and deleting small structural features; 2, generating a structural plate and an entity acoustic finite element model; thirdly, nodes between the structural plate and the entity acoustics are copied through a Pre-EFEA program, and a connection pair between the structural plate and the entity unit is generated through calculation; 4, generating an energy finite element method model; 5, generating a calculation file, and setting component and medium parameters; and 6, calculating noise level values inside and outside the body in white by applying an energy finite element method program, and calculating a difference value between the internal noise and the external noise and noise reduction. The calculation result is well matched with test data, the design and development time is effectively saved, and the development cost is saved.

Description

Technical Field

[0001] The present invention relates to a calculation method, and in particular to a calculation method for body-in-white NVH performance based on energy finite element method. Background Art

[0002] The existing NVH performance analysis method of the body in white adopts the traditional finite element method (FEA), establishes the body in white acoustic-solid coupling finite element model and acoustic boundary model, calculates the vibration of the body in white panel and the sound pressure level at the driver's ear under the specified working conditions, and on this basis, analyzes the acoustic contribution of the body in white panel, so as to find out the panel with relatively large acoustic contribution and make improvements to reduce its vibration, so as to achieve the effect of reducing the noise of the body in white. The traditional finite element method (FEA) no longer has higher computational efficiency. Because the basic solution of the differential equation solved by the FEA method changes synchronously with the space, the wavelength becomes smaller when the frequency increases, requiring too many units and huge computer resources. Summary of the invention

[0003] The present invention uses the energy finite element method (EFEA) to compile a program to calculate the internal noise level of the body-in-white (in dB), and calculates the difference between the external and internal noise levels of the body-in-white under typical working conditions (in dB). If the noise reduction level does not meet the national standard or design target, then analyze the calculation results, propose suggestions for improving the body-in-white structure, and repeatedly improve and calculate again until the calculation target is achieved, and then conduct noise tests, thereby saving development costs and design time.

[0004] The present invention is achieved by the following technical solutions:

[0005] A method for calculating NVH performance of a body-in-white based on an energy finite element method comprises the following steps:

[0006] The first step is to use general finite element pre-processing software to build a simplified body-in-white finite element method model and delete small structural features;

[0007] In the second step, the structural panels and solid acoustic finite element models are generated;

[0008] In the third step, the Pre-EFEA program is used to copy the nodes between the structural plate and the solid acoustics, and the connection pairs between the structural plate and the solid unit are calculated and generated;

[0009] Step 4: Generate the energy finite element method model;

[0010] The fifth step is to generate calculation files and set component and medium parameters, including elastic modulus, Poisson's ratio, density, and damping value;

[0011] The sixth step is to use the energy finite element method program to calculate the noise level values ​​inside and outside the body in white, and calculate the difference between the internal and external noise, as well as the noise reduction.

[0012] The present invention has the advantages that:

[0013] The application of energy finite element method (EFEA) only requires one-tenth to one-fiftieth of the number of grids of the traditional finite element method, which greatly reduces the demand for computer resources and improves computational efficiency.

[0014] The energy finite element method (EFEA) can be used to evaluate and calculate the noise level and NVH performance inside the acoustic structure with the same computational accuracy by solving a set of numerically controlled differential equations with energy density as the main variable.

[0015] The calculated results are in good agreement with the experimental data, which effectively saves design and development time and development costs. DETAILED DESCRIPTION

[0016] The present invention uses an energy finite element method (EFEA) program to calculate the internal and external noise levels (in dB) of the body-in-white.

[0017] The first step is to use general finite element pre-processing software to build a simplified body-in-white finite element model with a larger mesh size and delete small structural features, such as small chamfers, holes, ribs, etc. The number of meshes is one-tenth to one-fiftieth of that of traditional finite elements.

[0018] In the second step, the structural panels and solid acoustic finite element models are generated;

[0019] In the third step, the Pre-EFEA program is used to copy the nodes between the structural plate and the solid acoustics, and the connection pairs between the structural plate and the solid unit are calculated and generated;

[0020] Step 4: Generate the energy finite element method (EFEA) model;

[0021] The fifth step is to generate calculation files and set component and medium parameters, including elastic modulus, Poisson's ratio, density, and damping value;

[0022] The sixth step is to use the energy finite element method (EFEA) program to calculate the noise level value (in dB) inside and outside the body in white, and calculate the difference between the internal and external noise, as well as the noise reduction.

[0023] The energy finite element method (EFEA) is used to simulate and analyze the vibration and noise response of vehicles with complex structures at medium and high frequencies, while the traditional finite element method (FEA) no longer has higher computational efficiency. Because the basic solution of the differential equation solved by the FEA method changes synchronously with space, it requires an excessive number of units and huge computer resources when the wavelength becomes smaller when the frequency increases. For the EFEA method, the governing differential equation is expressed as an average energy density in space exceeding one wavelength and an average time exceeding one cycle. The basic solution corresponding to the EFEA method changes exponentially with space, so only a smaller number of units are required to obtain smooth spatial changes. This feature allows the application of fewer model units and simple features to analyze a complex system, thereby completing multiple rounds of calculation analysis in a shorter time.

[0024] The EFEA method requires the existence of a joint matrix between cells at locations where the primary variables are discontinuous. These discontinuities arise from geometric features, changes in material properties, multiple parts connected together, or different media connected to each other. Discontinuous EFEA cells are physically disconnected so that adjacent cells can replicate the nodes of the constraint pairs. In this way, the EFEA primary variables may obtain different values ​​throughout the discontinuous digital model, such as physical properties.

[0025] Representative system of unit-level equations:

[0026] [K e ]{e e}={P e )-{Q e} (1)

[0027] The superscript e indicates the number of units. e} is the nodal vector of energy density nodal values ​​at a finite element, [K e ] is the unit system matrix '{P e} is the external input power vector at the unit node location, {Q e} is the internal power flow vector across the boundary. The latter is used to integrate the global formula system of adjacent cells and to build connections between discontinuous cells and connected cells. The energy density between discrete cell boundaries is discontinuous, and the coupling of the global formula system is completed by considering the continuity of energy flow.

[0028]

[0029] Internal power loss {Q e} is expressed as the product of the connection submatrix and the energy density node value. The connection submatrix represents the energy transfer path across the discontinuity. The representative equation for sharing the connection submatrix between two node elements is as follows:

[0030] In the above formula, i and j represent the two units connecting the breakpoints, n and n+1 represent the two nodes connecting the vice at unit i, and m and m+1 represent the two nodes connecting the vice at unit j. ij ] The connection sub-matrix is ​​used to obtain the discontinuous energy transfer path between units i and j. Substituting equation (2) into equation (1) and integrating the unit matrix into the global matrix, we get:

[0031]

[0032] in, and are the matrices of cells i and j respectively, {e i} and {e j} is a vector containing all the nodal degrees of freedom of elements i and j. [JC ij ] is composed of the connection pair coefficients [J ij ] The calculation method of the unit matrix combination without discontinuity between units and the internal power flow unit vector is the same as the traditional finite element method. In this case, the energy density of the nodes between units is continuous. The final energy finite element method equation is as follows:

[0033]

[0034] Where ∑ represents all coupling matrices between discontinuities in the corresponding model [JC ij ], including all unit matrices and the external input power vector [S], {e} and {F} represent the respective system matrices, the main variable vectors and the vector of external excitations for the full system formulation. The physical characteristics of the power flow path including the main units for vehicle noise application must be applied in the energy finite element method system formulation in the appropriate format (see formula 4). This method also needs to consider the following influencing factors: structure-acoustic coupling effect, acoustic energy absorption effect, mass law effect, mass barrier effect and constrained layer damping treatment. These influencing factors are related to the acoustic simulation of the vehicle. Write a program based on the above formula to realize automatic submission of calculations.

[0035] The energy finite element method takes into account structural-acoustic effects, sound energy absorption effects, mass laws, mass barrier effects, and constrained layer damping treatments in the calculation process, and can effectively calculate the high-frequency noise levels and NVH performance inside and outside the body-in-white using fewer resources.

[0036] In this method, the number of shell elements and solid elements in the body-in-white finite element model is one tenth of the number of meshes in the traditional finite element model.

Claims

1. A method for calculating the NVH performance of a body-in-white based on an energy finite element method, characterized by: The following steps are involved: The first step is to use general finite element pre-processing software to build a simplified body-in-white finite element method model and delete small structural features; In the second step, the structural panels and solid acoustic finite element models are generated; In the third step, the Pre-EFEA program is used to copy the nodes between the structural plate and the solid acoustics, and the connection pairs between the structural plate and the solid unit are calculated and generated; Step 4: Generate the energy finite element method model; Step 5: Generate calculation files and set component and medium parameters; The sixth step is to use the energy finite element method program to calculate the noise level values ​​inside and outside the body in white, and calculate the difference between the internal and external noise, as well as the noise reduction.

2. The method for calculating the NVH performance of a body-in-white based on the energy finite element method according to claim 1 is characterized by: In the fifth step, the generated medium parameters include elastic modulus, Poisson's ratio, density, and damping value.

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