CN110532584B - Non-bearing type body-in-white light weight method based on relative sensitivity - Google Patents
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Abstract
The invention discloses a light weight method of a non-bearing type body-in-white based on relative sensitivity, which is mainly used for reducing the over-rigidity phenomenon and carrying out weight calculation on various direct sensitivities to obtain the relative sensitivities for size optimization by adopting a Beam unit to simulate the position of a wheel center point when the non-bearing type body-in-white is restrained; the method solves the problems of over-rigidity constraint during the calculation of the rigidity of the non-bearing type body-in-white and the screening of light-weight parts caused by the weight difference of the design variables of the sensitivity of a plurality of responses.
Description
The technical field is as follows:
the invention belongs to the field of optimization design of automobile body structures, and particularly relates to a non-bearing type body-in-white light-weight method based on relative sensitivity.
The background art comprises the following steps:
the light weight of the automobile body becomes the development direction of the automobile body design industry at present. According to statistics, when the total weight of the automobile is reduced by 10%, the fuel consumption is reduced by 6% -8%, and the emission is reduced by 5% -6%. The lightening of automobiles is not simply increasing or decreasing the thickness of the parts, or increasing or decreasing the parts. But an optimal solution is found on the premise of ensuring the performances of the original vehicle body such as rigidity, modal and the like. The automobile structure is improved from the aspects of multiple disciplines such as size optimization, shape optimization, appearance optimization and the like.
An unsupported body-in-white is a body structure that is mounted to a vehicle frame. For non-self-supporting body-in-white, most of the prior art analysis techniques analyze the body-in-white together with the frame structure, thereby increasing the time cost of the analysis process.
Meanwhile, the non-bearing type body-in-white only bears part of the whole vehicle rigidity and vibration absorption, and the problem of contribution degree of the frame and the vehicle body to the whole vehicle rigidity and the mode can be ignored when load is applied to a common research object of the body-in-white and the frame. How to accurately and independently research the performance of the non-bearing type body-in-white becomes a key technology.
The information disclosed in this background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.
The invention content is as follows:
the invention aims to provide a non-bearing type body-in-white light-weight method based on relative sensitivity, so as to overcome the defects in the prior art.
In order to achieve the aim, the invention provides a non-bearing type body-in-white light-weight method based on relative sensitivity, which comprises the following steps:
step 1, establishing a finite element analysis model according to a CATIA three-dimensional model;
step 2, performing non-bearing type white car body bending rigidity and torsional rigidity and modal analysis;
step 3, respectively establishing a rigidity and modal sensitivity response analysis model;
step 4, performing relative sensitivity analysis on the basis of sensitivity analysis and selecting light-weight components;
step 5, performing multi-target size optimization on the screened components;
and 6, performing performance verification on the lightened non-bearing type body-in-white.
The invention further defines the technical scheme as follows:
preferably, in the above technical solution, step 1 specifically includes:
1.1, establishing a finite element model according to the CATIA three-dimensional model, wherein the grid quality needs to meet the following requirements: warpage or warp <15 °; skewness <60 °; jacobian ≧ 0.6; ratio of length to width ≦ 5; minimum internal angle of CQUAD4=45 °; maxmum internal angle of CQUAD4=135 °; minimum internal angle of CTRIA3=15 °; maxmum internal angle of CTRIA3=105 °;
1.2 the welding spot unit at the connection part of the thin plate adopts the ace (general) type; the joint of the bolts adopts an RBE3 unit; the frame body connection part and the suspension mounting point adopt RIGID units;
1.3 double-layer washber units are adopted around the bolt holes, and the grid density of the welding edge part of the thin plate is double-layer;
1.4 assign different material properties to the assembly according to the part library table.
Preferably, in the above technical solution, step 2 specifically is:
2.1, carrying out free mode analysis on the non-bearing type body-in-white, namely, not adding boundary conditions and loads; the mathematical model is as follows:
k, C and M are respectively a stiffness matrix, a damping matrix and a mass matrix of the system; x and F
Respectively, the displacement vector and the excitation force vector of the system, respectively expressed as:
X＝[x 1 x 2 ......x r ......x N ] Γ ，
F＝[f 1 f 2 ......f r ......f N ] Γ ；
decoupling the two vectors, wherein certain conversion is required in the decoupling process; the physical coordinates are replaced by modal coordinates, and finally decoupling of an equation set is realized to obtain the modes and the vibration modes under various frequencies;
2.2, carrying out bending rigidity analysis on the non-bearing type body-in-white, and firstly setting boundary conditions; the restraint positions are two simulation wheel points on the left and right of the white body and the front part of the frame and two simulation wheel mounting points of the rear frame body; the constraint mode is as follows: the left front connection part restrains the degree of freedom of the Z-direction translation; the right front connection part restrains the freedom degrees of the translation in the Y direction and the Z direction; the left back connection part restrains X and Z translational freedom degrees; the right rear connection part restrains the freedom degrees of the translation in the Y direction and the Z direction; the load is set as follows: loading left and right at a middle rail of a non-bearing type body-in-white by adopting a rigid unit concentrated loading mode;
2.3, carrying out torsional rigidity analysis on the non-bearing type body-in-white, and firstly setting boundary conditions; the restraint positions are the middle position of the connection position of the front frame body and the last frame body; the constraint mode is as follows: constraining the Z-direction flatness degree of freedom in the middle of the mounting point of the front vehicle body frame; restraining all degrees of freedom of the mounting point of the rear vehicle body frame in six directions; the load is set as follows: a pair of moments with the same magnitude and opposite directions are loaded at the left and right positions of a mounting point of a front vehicle body frame.
Preferably, in the above technical solution, in step 3, sensitivity analysis is performed with the plate thickness d as a design variable; the basic format of the sensitivity assay is:
wherein X is a vector formed by design parameters of the vehicle body structure at a reference point; x is the change of the design parameters of the vehicle body structure, and the default value is 1 percent of the difference between the upper limit and the lower limit; e is a vector of the same dimension as X; u is a vehicle body structure performance parameter; the mathematical model of stiffness sensitivity is represented by the stiffness calculation formula:
[K] n*n {u} n*l ＝{F} n*l ，
wherein [ K ]] n*n Is the global stiffness of the subject; { u } n*l A displacement vector of the analytical model; { F } n*l Is the external load vector of the analytical model. The above formula can be obtained by deviatoric derivation of the design variable d, i.e. the thickness:
[K, d ] n*n {μ} n*l +[K] n*n {u, d } n*l ＝{F, d } n*l ＝{0} n*l ，
{μ， d }＝-[K] n*n -1 [K, d ] n*n {μ} n*l ，
wherein, the ratio of [ K, d ] n*n -1 the total rigidity matrix of the overall rigidity inverse matrix structure model is analyzed and formed by superposing corresponding order expansion matrixes of all units;
in the calculation of the stiffness sensitivity, the displacement of the measuring point can be used as a substitute for the stiffness response; under the condition that the load is not set, the change of the displacement is the change of the rigidity;
modal sensitivity is determined by material properties and thickness, targeting minimum body-in-white mass; and the first-order bending mode is larger than the original value as constraint, and the mass and the mode frequency are used as response for analysis.
Preferably, in the above technical solution, step 4 specifically includes:
calculating the sensitivities of bending rigidity, torsional rigidity, first-order torsional mode and mass according to the step 3, and defining a formula according to the relative sensitivities:
wherein S w For direct sensitivity of mass, S b is a Direct bending stiffness sensitivity, S t For direct torsional stiffness sensitivity, S f Is a direct modal sensitivity.
Preferably, in the above technical solution, step 5 specifically includes: selecting a part which can improve the rigidity and modal performance of the vehicle body and does not greatly increase the mass of the vehicle body according to the relative sensitivity result obtained in the step 4; performing experimental design on the performance of each design variable in the step 2 by using an optimal Latin hypercube method; establishing a first-order response surface model after obtaining sample points for the test:
in the formula, a is a polynomial coefficient; x is the number of j Is a design variable; q is the number of design variables;
then using the complex correlation coefficient R 2 To verify the accuracy of the response surface fit. It is defined as:
R 2 ＝1-Q C /Q Z ，
in the formula, Q C Is the sum of the squares of the residual deviations; q Z Is the sum of squares of the deviations;
finally, the minimum mass of the vehicle body is taken as a target, and a first-order torsional mode, bending rigidity and torsional rigidity are taken as constraints; and performing multi-objective optimization by adopting a particle swarm algorithm. Wherein the particle swarm algorithm is generally of the form:
v id ＝w×v id +c 1 ×rand()×(p id -x id )+c 2 ×Rand()×(p gd -x id )
x id ＝x id +v id ，
wherein w is the inertial weight, c 1 And c 2 For the acceleration constant, rand () and Rand () are two at [0, 1%]Random values that vary over a range; the first formula is an inertia term, so that the particles have the tendency of expanding a search space; the second item is a cognitive item, which represents the thought of the particle itself for improving the direction; the third item is a "social" item, representing the sharing of optimal information among the particles.
Preferably, in the above technical solution, step 6 specifically includes: and (3) after the components subjected to size optimization are endowed with attributes again, performing static rigidity and modal analysis again according to the method in the step 2, and comparing whether the performance of the body-in-white after size optimization is reduced or not.
Compared with the prior art, the invention has the following beneficial effects:
according to the invention, through establishing the non-bearing type white body rigidity constraint model, the basic performances of bending rigidity, torsional rigidity, mode and the like of the part above the non-bearing type white body frame are calculated more accurately. And establishing a body-in-white sensitivity analysis model, and performing multi-objective size optimization by a response surface model-based method. The development process is shortened, and the light-weight reliability of the non-bearing type body-in-white is improved.
Description of the drawings:
fig. 1 is a schematic flow chart of a relative sensitivity-based non-bearing body-in-white weight reduction method of the present invention.
FIG. 2 is a schematic view of a non-load bearing body in white construction according to the present invention.
FIG. 3 is a schematic flow chart of the sensitivity analysis of the present invention.
The specific implementation mode is as follows:
the following detailed description of specific embodiments of the invention is provided, but it should be understood that the scope of the invention is not limited to the specific embodiments.
Throughout the specification and claims, unless explicitly stated otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element or component but not the exclusion of any other element or component.
A non-bearing type body-in-white light weight method based on relative sensitivity comprises the following specific steps:
the method comprises the following steps: a) Establishing a finite element model according to the CATIA three-dimensional model, wherein the grid quality needs to meet the following requirements: warpage or warp <15 °; skewness <60 °; jacobian ≧ 0.6; ratio of length to width ≦ 5; minimum internal angle of CQUAD4=45 °; maxmum internal angle of CQUAD4=135 °; minimum internal angle of CTRIA3=15 °; maxmum internal angle of CTRIA3=105 °.
b) Welding spot units at the joints of the thin plates adopt ace (general) types; the joint of the bolt adopts an RBE3 unit; the frame body connection part and the suspension mounting point adopt RIGID units.
c) Double-layer washbler units are adopted around the bolt holes, and the grid density of the welding edge part of the thin plate is double.
d) Assigning different material properties to components according to component library tables
a) Step two: and (4) carrying out free mode analysis on the non-load-bearing type body-in-white, namely, not adding boundary conditions and loads. The mathematical model is as follows:
wherein K, C and M are respectively a rigidity matrix, a damping matrix and a mass matrix of the system. X and F
Respectively, the displacement vector and the excitation force vector of the system, respectively expressed as:
X＝[x 1 x 2 ......x r ......x N ] Γ
F＝[f 1 f 2 ......f r ......f N ] Γ ，
the two vectors are decoupled, and certain conversion is needed in the decoupling process. The physical coordinates are replaced by modal coordinates, decoupling of an equation set is finally achieved, and modes and vibration modes under various frequencies are obtained.
Step two: the bending stiffness analysis is performed on the non-bearing type body-in-white, and boundary conditions are set firstly. The restraint positions are a white vehicle body, a left wheel simulation point and a right wheel simulation point at the front part of the vehicle frame and a rear vehicle frame vehicle body simulation point. The constraint mode is as follows: the left front connection part restrains the degree of freedom of the Z-direction translation; the right front connection part restrains the freedom degrees of the translation in the Y direction and the Z direction; the left back connection part restrains X and Z translational freedom degrees; the right rear connection constrains the degrees of freedom of the Y and Z translational motion. The load is set as follows: and loading left and right by adopting a rigid unit concentrated loading mode at the middle rail of the non-bearing type body-in-white.
The torsional rigidity analysis is carried out on the non-bearing type body-in-white, and boundary conditions are set firstly. The restraint positions are the middle position of the frame joint of the front vehicle body and two mounting points of the vehicle body of the last vehicle body. The constraint mode is as follows: and the Z-direction flatness freedom degree in the middle of the mounting point of the front vehicle body frame is restrained. And the whole degrees of freedom of the mounting point of the rear vehicle body frame in six directions are restrained. The load is set as follows: a pair of moments with the same magnitude and opposite directions are loaded at the left and right positions of the mounting point of the front vehicle body frame.
Step three: sensitivity analysis was performed with the plate thickness d as a design variable. The basic format of the sensitivity assay is:
wherein X is a vector formed by design parameters of the vehicle body structure at a reference point; x is the change of the design parameters of the vehicle body structure, and the default value is 1% of the difference between the upper limit and the lower limit; e is a vector of the same dimension as X; and u is a vehicle body structure performance parameter. The mathematical model of stiffness sensitivity is represented by the stiffness calculation formula:
[K] n*n {u} n*l ＝{F} n*l ，
wherein [ K ]] n*n Is the global stiffness of the subject; { u } n*l A displacement vector for the analytical model; { F } n*l Is the external load vector of the analytical model. The above formula can be obtained by deviatoric derivation of the design variable d, i.e. the thickness:
[K, d ] n*n {μ} n*l +[K] n*n {u, d } n*l ＝{F, d } n*l ＝{0} n*l
{μ， d }＝-[K] n*n -1 [K, d ] n*n {μ} n*l ，
wherein, the ratio of [ K, d ] n*n -1 the total rigidity matrix of the overall rigidity inverse matrix structure model is analyzed
The corresponding order expansion matrixes of the units are superposed.
In the stiffness sensitivity calculation, the displacement of the measurement point may be used as an alternative to the stiffness response. The change in displacement can be used as a constraint on stiffness sensitivity with no change in load setting.
Modal sensitivity is determined by material properties and thickness, with a goal of minimum body-in-white mass. The first-order bending mode is larger than the original value as the constraint, and the quality and the mode frequency are used as the response for analysis.
Step four: the sensitivity of bending rigidity, torsional rigidity, first-order torsional mode and mass is calculated respectively in the step 3, and then a formula is defined according to the relative sensitivity:
wherein S w For direct sensitivity of mass, S b is a Direct bending stiffness sensitivity, S t For direct torsional stiffness sensitivity, S f Is a direct modal sensitivity.
Step five: and (4) selecting a part which can improve the rigidity and modal performance of the vehicle body and does not greatly increase the mass of the vehicle body according to the relative sensitivity result obtained in the step (4). And (3) selecting an optimal Latin hypercube method to carry out experimental design on the performance of each design variable in the step (2). Establishing a first-order response surface model after obtaining sample points for the test:
in the formula, a is a polynomial coefficient; x is the number of j Is a design variable; q is the number of design variables.
Then using the complex correlation coefficient R 2 To verify the accuracy of the response surface fit. It is defined as:
R 2 ＝1-Q C /Q Z
in the formula, Q C Is the sum of the squares of the residual deviations; q Z Is the sum of the squares of the deviations.
And finally, aiming at the minimum mass of the vehicle body, and using a first-order torsional mode, bending rigidity and torsional rigidity as constraints. And performing multi-objective optimization by adopting a particle swarm algorithm. Wherein the particle swarm algorithm is generally of the form:
v id ＝w×v id +c 1 ×rand()×(p id -x id )+c 2 ×Rand()×(p gd -x id )
x id ＝x id +v id ，
wherein w is the inertial weight, c 1 And c 2 For the acceleration constant, rand () and Rand () are two at [0,1 ]]Random values that vary within the range. The first formula is an inertia term, so that the particles have the tendency of expanding a search space; the second item is a cognitive item, which represents the thought of the particle itself for improving the direction; the third item is a "social" item, representing the sharing of optimal information among the particles.
Step six: and (4) after the components subjected to size optimization are endowed with attributes again, performing static rigidity and modal analysis again according to the method of the step 2. And (4) comparing whether the performance of the white body after size optimization is reduced or not.
The following embodiments of the present invention are described in detail, and the embodiments of the present invention are implemented on the premise of the technical solution of the present invention, and detailed embodiments and specific operation procedures are given, but the scope of the present invention is not limited to the following embodiments.
Examples
As shown in fig. 1, a method for lightening a non-bearing body-in-white based on relative sensitivity specifically comprises the following steps:
the method comprises the following steps: establishing a non-bearing white body finite element model, wherein the grid quality needs to meet the following requirements: warpage or warp <15 °; skewness <60 °; jacobian ≧ 0.6; ratio of length to width ≦ 5; minimum internal angle of CQUAD4=45 °; maxmum internal angle of CQUAD4=135 °; minimum internal angle of CTRIA3=15 °; maxmum internal angle of CTRIA3=105 °.
b) Welding spot units at the joints of the thin plates adopt ace (general) types; the joint of the bolt adopts an RBE3 unit; the frame body connection part and the suspension mounting point adopt RIGID units.
c) Double-layer washbler units are adopted around the bolt holes, and the grid density of the welding edge part of the thin plate is double.
d) Assigning different material properties to components according to component library tables
Step two: free mode analysis was first performed. The results of the first six-order modal analysis obtained by the model are shown in the following table.
| Order of the scale | Frequency of | Vibration mode |
| 1 | 16.2Hz | Vehicle body integral torsion |
| 2 | 19.8Hz | Torsion of front frame section and rear cab section |
| 3 | 23.2Hz | Integral front side bending of vehicle body |
| 4 | 25.2Hz | One-step bending of whole body of vehicle |
| 5 | 27.7Hz | Surging of the front roof of the cab |
| 6 | 31.5Hz | Surge of vehicle in the middle of cab |
Secondly, the bending rigidity of the non-bearing type body-in-white is analyzed, and boundary conditions are set firstly. The restraint positions are two mounting points of a white automobile body, the left mounting point and the right mounting point of the front part of the frame and the two mounting points of the automobile body of the final frame. The constraint mode is as follows: the left front connection part restrains the degree of freedom of the Z-direction translation; the right front connection part restrains the freedom degrees of the translation in the Y direction and the Z direction; the left rear connection part restrains X-direction and Z-direction translational freedom degrees; the right rear connection constrains the degrees of freedom of the Y and Z translational motion. The load is set as follows: and loading 1000N left and right at the middle rail of the non-bearing type body-in-white by adopting a rigid unit concentrated loading mode. According to the calculation formula of bending rigidity
The maximum Z displacement was found to be 0.572mm. The bending stiffness was 3500N/mm.
And finally, carrying out torsional rigidity analysis on the non-bearing type body-in-white. Boundary conditions are first set. The restraint positions are the middle position of the frame joint of the front vehicle body and two mounting points of the vehicle body of the last vehicle body. The constraint mode is as follows: and the Z-direction flatness freedom degree in the middle of the mounting point of the front vehicle body frame is restrained. And all degrees of freedom in six directions of a mounting point of the rear vehicle body frame are restrained. The load is set as follows: a pair of forces with the same magnitude and opposite directions are loaded at the left and right positions of the mounting point of the front vehicle body frame, and the magnitude of the pair of forces is 1000N. According to the calculation formula of torsional rigidity
Wherein GJ is the torsional rigidity of the vehicle body; t is the torsional force applied to the vehicle body; l is the wheelbase of the vehicle body; and theta is the torsion angle between the vehicle body shafts. The calculation formula is as follows:
U 1 、U 2 the Z-direction deflection of the left side longitudinal beam and the right side longitudinal beam is respectively. The following table shows the part stringer deformation data.
| Serial number | ID number | Z-direction coordinate | ID number | Z-direction displacement |
| 1 | 1532987 | -1.45E-01 | 1532987 | -1.45E-01 |
| 2 | 1533030 | -1.93E-01 | 1533030 | -1.94E-01 |
| 3 | 1531784 | -2.48E-01 | 1531784 | -2.50E-01 |
| 4 | 1532485 | -3.20E-01 | 1532485 | -3.23E-01 |
| 5 | 1532569 | -4.33E-01 | 1532569 | -4.37E-01 |
| 6 | 1532643 | -5.56E-01 | 1532643 | -5.62E-01 |
| 7 | 1561353 | -6.50E-01 | 1561353 | -6.58E-01 |
| 8 | 153758 | -1.03E+00 | 153758 | -1.04E+00 |
| 9 | 3246599 | -1.38E+00 | 3246599 | -1.40E+00 |
| 10 | 1470930 | -2.03E+00 | 1470930 | -2.06E+00 |
And measuring the Z-direction deformation of the position of the left force loading point to be 4.945mm below zero and the Z-direction deformation of the position of the right force loading point to be 4.808mm. And the distance between the two loading points is 1001.673mm. The calculated twist angle was 0.557 °. K =13157Nm/deg is calculated from the torsional rigidity.
Step three: and (5) carrying out flexural rigidity, torsional rigidity and first-order sensitivity analysis. The minimum total mass of the body-in-white is taken as a target, and the position displacement of the load loading point of the bending rigidity and the torsional rigidity is taken as a constraint. And responding by using the displacement of the measuring point of the vehicle frame and the total mass of the vehicle body. And (5) calculating the rigidity sensitivity of the non-bearing type body-in-white. And secondly, performing first-order torsional modal sensitivity and mass sensitivity calculation. Again with the goal of overall mass minimization. Responding with modality and overall mass. Sensitivity calculation is performed with the first order torsional mode as a constraint. The following table shows the results of the sensitivity section calculations.
Step four: and D, calculating the direct sensitivity calculated in the step three according to a relative sensitivity calculation formula:
the relative sensitivity is calculated. Finally 8 groups of components with the highest sensitivity relative to the first-order torsional mode are selected. The following table shows the selected part numbers and locations.
| Serial number | ID number | Location of a body part |
| 1 | I05801990190_0P8MM_HC220Y | Front bumper water tank frame part |
| 2 | I05801996552_0P8MM_DC04 | Front windshield lower edge inner plate crossbeam |
| 3 | I05801990248_0P8MM_HC180Y | Front bumper anti-collision beam |
| 4 | I05801994671_1P2MM_DC04 | Firewall frame |
| 5 | I05801994690_0P8MM_DC04 | Front firewall |
| 6 | I05801994754_0P8MM_DC04 | Left and right side coaming outer plate |
| 7 | I05801994617_1P2MM_DC03 | Top large plate beam |
| 8 | I05801994614_1P0MM_DC04 | Tail door frame outer plate |
Step five: and performing multi-objective optimization based on the response surface model on the selected parts, wherein the optimization result is shown in the following table.
| Serial number | ID number | Initial thickness | After optimization |
| 1 | I05801990190_0P8MM_HC220Y | 0.8mm | 0.7mm |
| 2 | I05801996552_0P8MM_DC04 | 0.8mm | 0.7mm |
| 3 | I05801990248_0P8MM_HC180Y | 0.8mm | 0.8mm |
| 4 | I05801994671_1P2MM_DC04 | 1.2mm | 1.0mm |
| 5 | I05801994690_0P8MM_DC04 | 0.8mm | 0.7mm |
| 6 | I05801994754_0P8MM_DC04 | 0.8mm | 0.8mm |
| 7 | I05801994617_1P2MM_DC03 | 1.2mm | 1.1mm |
| 8 | I05801994614_1P0MM_DC04 | 1.0mm | 0.8mm |
Step six: and (4) after the components subjected to size optimization are endowed with attributes again, performing static rigidity and modal analysis again according to the method of the step 2. The optimized bending rigidity is slightly improved at 3720N/mm, and the torsional rigidity is basically kept equal to k =13200Nm/deg according to a calculation formula. Therefore, the light weight scheme is feasible.
The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. It is not intended to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above teaching. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and its practical application to enable one skilled in the art to make and use various exemplary embodiments of the invention and various alternatives and modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims and their equivalents.
Claims (5)
1. A non-bearing type body-in-white light weight method based on relative sensitivity is characterized in that: the method comprises the following steps:
step 1, establishing a finite element analysis model according to a CATIA three-dimensional model;
step 2, performing non-bearing type white car body bending rigidity and torsional rigidity and modal analysis;
step 3, respectively establishing a rigidity and modal sensitivity response analysis model;
step 4, carrying out relative sensitivity analysis on the basis of sensitivity analysis and selecting a lightweight component;
step 5, performing multi-target size optimization on the screened components;
step 6, carrying out performance verification on the lightened non-bearing type body-in-white vehicle;
in step 3, the plate thickness d is taken as a design variable to carry out sensitivity analysis; the basic format of the sensitivity assay is:
wherein X is a vector formed by design parameters of the vehicle body structure at a reference point; x is the change of the design parameters of the vehicle body structure, and the default value is 1% of the difference between the upper limit and the lower limit; e is a vector of the same dimension as X; u is a vehicle body structure performance parameter; the mathematical model of stiffness sensitivity is represented by the stiffness calculation formula:
[K] n*n {u} n*l ＝{F} n*l ，
wherein [ K ]] n*n Is the global stiffness of the subject; { u } n*l A displacement vector for the analytical model; { F } n*l An external load vector of the analysis model;the above formula can be obtained by deviatoric derivation of the design variable d, i.e. the thickness:
[K, d ] n*n {μ} n*l +[K] n*n {u, d } n*l ＝{F, d } n*l ＝{0} n*l ，
{μ， d }＝-[K] n*n -1 [K, d ] n*n {μ} n*l ，
wherein, the content of [ K, d ] n*n -1 the total rigidity matrix of the overall rigidity inverse matrix structure model is analyzed and formed by superposing corresponding order expansion matrixes of all units;
in the stiffness sensitivity calculation, the displacement of the measurement point can be used as an alternative to the stiffness response; under the condition that the load is not set, the change of the displacement is the change of the rigidity;
modal sensitivity is determined by material properties and thickness, targeting minimum body-in-white mass; the first-order bending mode is larger than the original value, and the first-order bending mode is used as constraint and is analyzed by using the mass and the mode frequency as response;
the step 4 specifically comprises the following steps:
calculating the sensitivities of bending rigidity, torsional rigidity, first-order torsional mode and mass according to the step 3, and defining a formula according to the relative sensitivities:
wherein S w For direct sensitivity of mass, S b is a Direct bending stiffness sensitivity, S t For direct torsional stiffness sensitivity, S f Is a direct modal sensitivity.
2. The relative sensitivity-based non-supported body-in-white weight reduction method according to claim 1, wherein the step 1 is specifically:
1.1 establishing a finite element model according to the CATIA three-dimensional model, wherein the grid quality needs to meet the following requirements: warpage or warp <15 °; skewness <60 °; jacobian ≧ 0.6; ratio of length to width ≦ 5; minimuminternal angle of CQUAD4=45 °; maxmominal angle of CQUAD4=135 °; minimuminternal angle of CTRIA3=15 °; maxmominal angle of CTRIA3=105 °;
1.2 the welding spot unit at the connection part of the thin plate adopts the ace (general) type; the joint of the bolts adopts an RBE3 unit; the frame body connection part and the suspension mounting point adopt RIGID units;
1.3 double-layer washber units are adopted around the bolt holes, and the grid density of the welding edge part of the thin plate is double-layer;
1.4 assign different material properties to the component according to the component library table.
3. The relative sensitivity-based non-self-supporting body-in-white weight reduction method according to claim 2, wherein the step 2 is specifically:
2.1, carrying out free mode analysis on the non-bearing type body-in-white, namely, not adding boundary conditions and loads; the mathematical model is as follows:
k, C and M are respectively a stiffness matrix, a damping matrix and a mass matrix of the system; x and F
Respectively, the displacement vector and the excitation force vector of the system, respectively expressed as:
X＝[x 1 x 2 ......x r ......x N ] Γ
F＝[f 1 f 2 ......f r ......f N ] Γ ；
decoupling the two vectors, wherein certain conversion is needed in the decoupling process; the physical coordinates are replaced by modal coordinates, and finally decoupling of an equation set is realized to obtain the modes and the vibration modes under various frequencies;
2.2, carrying out bending rigidity analysis on the non-bearing type body-in-white, and firstly setting boundary conditions; the restraint positions are two simulated wheel points on the left and right of the white body and the front part of the frame and two simulated wheel mounting points of the rear frame body; the constraint mode is as follows: the left front connection part restrains the degree of freedom of the Z-direction translation; the right front joint restrains the freedom degrees of the Y-direction translation and the Z-direction translation; the left back connection part restrains X and Z translational freedom degrees; the right rear connection part restrains the freedom degrees of the translation in the Y direction and the Z direction; the load is set as follows: loading left and right at a middle rail of a non-bearing type body-in-white by adopting a rigid unit concentrated loading mode;
2.3, carrying out torsional rigidity analysis on the non-bearing type body-in-white, and firstly setting boundary conditions; the restraint positions are the middle position of the connection position of the front frame body and the last frame body; the constraint mode is as follows: constraining the Z-direction flatness degree of freedom in the middle of the mounting point of the front vehicle body frame; restraining all degrees of freedom of the mounting point of the rear vehicle body frame in six directions; the load is set as follows: a pair of moments with the same magnitude and opposite directions are loaded at the left and right positions of a mounting point of a front vehicle body frame.
4. The relative sensitivity-based non-supported body-in-white weight reduction method according to claim 1, wherein the step 5 is specifically: selecting a part which can improve the rigidity and modal performance of the vehicle body and does not greatly increase the mass of the vehicle body according to the relative sensitivity result obtained in the step 4; performing experimental design on the performance of each design variable in the step 2 by using an optimal Latin hypercube method; after obtaining sample points for testing, establishing a first-order response surface model:
in the formula, a is a polynomial coefficient; x is the number of j Is a design variable; q is the number of design variables;
then using the complex correlation coefficient R 2 Verifying the accuracy of the response surface fitting; it is defined as:
R 2 ＝1-Q C /Q Z ，
in the formula, Q C Is the sum of the squares of the residual deviations; q Z Is the sum of squares of the deviations;
finally, the minimum mass of the vehicle body is taken as a target, and a first-order torsional mode, bending rigidity and torsional rigidity are taken as constraints; performing multi-objective optimization by adopting a particle swarm algorithm, wherein the general form of the particle swarm algorithm is as follows:
v id ＝w×v id +c 1 ×rand()×(p id -x id )+c 2 ×Rand()×(p gd -x id )
x id ＝x id +v id ，
wherein w is the inertial weight, c 1 And c 2 For the acceleration constant, rand () and Rand () are two at [0,1 ]]Random values that vary over a range; the first formula in the first formula is an inertia term, so that the particles have the trend of expanding a search space; the second item is a cognitive item, which represents the thought of the particle itself for improving the direction; the third item is a "social" item, representing the sharing of optimal information among the particles.
5. The relative sensitivity-based non-self-supporting body-in-white weight reduction method according to claim 1, characterized in that: the step 6 specifically comprises the following steps: and (3) after the components subjected to size optimization are endowed with attributes again, performing static rigidity and modal analysis again according to the method in the step 2, and comparing whether the performance of the body-in-white after size optimization is reduced or not.
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