The body of a floor model for modal analysis

1、the body of a floor model for modal analysis 1 forewordin the three major auto assembly, auto body representing the level of vehicle development, development of the car in the dominant position of possession. as the traffic process, the body structure will be in a variety of incentives vibration sou

2、rce under vibration, if these incentives frequency vibration source close to the body as a whole or in part, the natural frequency, it will happen resonance phenomenon, a violent vibration and noise, and even caused structural damage. therefore, in order to improve vehicle safety, stability and comf

3、ort, it is necessary to the body structure of the natural frequency analysis, and its structure can be designed to avoid the various vibration source of encouragement. the paper was useded to the finite element analysis methods, the body of a floor model for modal analysis, analysis of its natural f

4、requency and vibration mode, to provide reference for actual production.2 the establishment of the floor body finite element modelbody floor is a typical convex slot board structure, and its simulation modeling there are two ways, first by the true trough convex shape modeling and the other is in ac

5、cordance with the method mentioned in the literature, that is used in the slot and convex strengthen the beam to simulate the plate structure, strengthen cross-section of the beam parameters and the actual structure in line with the text of the original model using the first method.2.1modeling2.1.1

6、plane issue and thin bendingbody floor of the cad model is the creation of the catia software completed.body parts are the most pieces of sheet metal, sheet metal thickness h plane is much smaller than its size. the load plate deformation and the role of the way, when the load in parallel to the sur

7、face (the equally flat plate thickness) and the thickness along the same direction, that is the plane stress problems if the load perpendicular to the surface, it will cause the curved sheet deformation.to the plate in the face for the x-y plane, perpendicular to the surface in the shaft for the z a

8、xis. in the plane stress problem, only parallel to the x-y plane of the three stress components as:these three components along the same thickness h, which is a function of x and y, and z coordinates nothing to do, and the remaining amount is zero. plane stress of the physical equation as:plate bend

9、ing deformation, in the face by a flat surface, known as flexible surfaces. in the face of all the points in the perpendicular to the surface in the direction of the displacement w known as the deflection. when w much smaller than the thickness t, that is met, you can think of in wireless strain has

10、 no contingency kok, now known as the small deflection plate bending problems. if the deflection w t close to the thickness of the order of magnitude, you can not believe that flexible fiber surface, the length of the same, the problem will become non-linear, this situation known as the large deflec

11、tion plate bending problems. most of the works in question will be regarded as small plate of bending deflection problems, such problems can greatly simplify. plate bending small deflection of the stress and physical deformation of the equation can be expressed as: to sum up, because the floor is a

12、body of the more complicated pieces of sheet metal, in the role of the load by the time their plane stress there is the problem, there plate bending problems. so in practical engineering analysis, taking into account both the role of the two.2.1.2 unit type in the establishment of body parts finite

13、element model, taking into account both of these pieces of sheet metal to resist the direction parallel to its plane of rafah pressure, but also to resist bending and reverse the load, should be used with both types of units. the unit has a shell thickness, the full description of these characterist

14、ics, the unit used to shell modeling.2.1.3 definition of material body flooring materials commonly used sheet steel, its elastic modulus e = 2.1x105 mpa, poissons ratio for = 0.3, the density = 7.9 x103 kg/m3. in a shell unit to modeling, comes plate thickness t = 1 mm.2.2 meshingthe left side of th

15、e floor model of the mesh used finite element software hyperworks in hypermesh divided into modules, including the number of nodes for 7730, the number of quadrilateral element for 7306, the number of units to 370 triangles, triangular element of the entire unit to the percentage of the total 4.8%.

16、in order to meet these technical requirements, the need for strict control of their cell size and the warping of the unit and the quadrilateral triangle and the interior angle of perspective, the left side of the floor plans for a grid model.figure 1 left the floor grid model3 the calculation of res

17、ults and analysis3.1 modal analysismodal analysis is to study the structure of a dynamic modern way is to identify ways the system works in the field of application of vibration. modal is the mechanical structure of the inherent vibration characteristics, each with a specific mode of natural frequen

18、cy, damping ratio and the mode shape. these modal parameters can be calculated by the pilot or the analysis, such a calculation or testing of the process known as the modal analysis. if this analysis is the process by the finite element method achieved, then known as the calculation of-mind if tests

19、 will be collected through the system input and output signal parameters were identified modal parameters, known as the mode of trial. usually, modal analysis is that test mode analysis. vibration mode is the flexibility inherent in the structure of the overall characteristics. if modal analysis of

20、the structure clear in a vulnerable within the scope of the frequency bands of the main mode, it could predict the structure inherent in this band of various external or internal vibration source under the actual vibration. therefore, the modal analysis of structural dynamic design and equipment fau

21、lt diagnosis of important ways. modal analysis works in a wide range of applications, such as: on the spacecraft for modal analysis to show that its air during launch and flight environment in response to determine whether it will be damaged. on the suspension bridge for modal analysis shows it is i

22、nspired by the wind will happen resonance, calculated response can be expected after life. on the engine casing for modal analysis, the study will help generate noise vibration and noise components of proportion. of ball bearings for modal analysis, help identify failures and a vibration and noise r

23、easons. some large damping, the proportion of non-damping the complex structure (such as high-damping composite material structure), the response can not be the main mode decomposition, the points system that is different is not rp, in the form of a vibration, not node location fixed, modal vector i

24、s not real but complex. to have the characteristics of the vibration system, which can not be real modal theory and analysis methods to be used complex modal theory and analysis on the response system.3.2 floor modal analysisfigure 2 a band bending modefigure 3 a reverse-order-typefigure 4-second re

25、verse-order-typefigure 5 second bending modethe floor before the fourth-order mode shape to the image in figure 2 as shown in figure 5, the former four bands modal parameters and modes described in table 1. table 1 the first four bands modal parameters and modes describedmodal orderfirst ordersencon

26、d orderthird orderthefourth rdernatural frequency/hz8.4911.2519.0430.39modeshape descriptionfirst bendingareverse-ordersencond reverse-ordersencond bendingthrough the observation of the first four bands mode shape map, we can see that the amplitude of the largest in the region of the floor around th

27、e edges. in this fourth-order mode shape of the cloud, the maximum amplitude have超过40 mm, and even some high amplitude reached 57 mm. from figure 2, we can clearly found the hole in the side of the floor area, relatively severe vibration, the amplitude of the frequency sensitive, inward bending the

28、trend is the first order bending mode. figure 3 in the floor of the four corners of the strong vibration, to reverse the trend, this note is the first order to reverse mode. in figure 4 in the floor before the vibration even more marginalized and have to reverse deformation, that this is the second

29、reverse mode. in figure 5, because of the increased frequency from the edges of the floor intense vibration, particularly in the corners around, this is second-order bending mode.figure 6 overall first-order reverse modefigure 7 overall remove the right order to reverse an medial longitudinal beam m

30、odefigure 8 remove the whole right side of the floor of a reverse-order-typefigure 9 overall removed from the middle floor of a reverse-order-typefigure10 as a whole left side of the floor removed a reverse-order-typefigure 11 overall sleeper board removed the first order to reverse modein each mode

31、 shape cloud in the lower right corner has a modal amplitude curves. this curve is to select the former model of the edge of the 100 nodes, in the same mode of order along the z-axis direction of the amplitude of the curve. said horizontal axis for the selected node in the coordinates of the locatio

32、n of each node is the longitudinal axis corresponding to the feature vector, or vibration amplitude. from every curve of amplitude, we can clearly observed that the former model edge in the mode of amplitude changes. among them, in each curve of 0-25 mm, had a magnitude of jitter, in addition to fig

33、ure 2 shows the weak, the other three plans jitter phenomenon more strongly. as conditions, this phenomenon can not in this to make further analysis.to sum up, the floor around the edge prone to vibration deformation, and the location of other rare vibration deformation. therefore, the need to incre

34、ase the floor of the modal values, to enhance its stiffness, improve the capacity of bending twisting.3.3 floor of the assembly mode analysis as body floor assembly complex structure, and a lot of the plate structure, the assembly floor in the body of the modal calculation results in a large number

35、of local mode, that is, partial structure of the vibration mode and the overall structure caused by the bending or twisting the small vibration. the overall mode, namely, the overall framework of the vibration mode, its frequency may be just around the inherent structure of a local frequency, result

36、ing in the structure of local resonance. therefore, we adopt step-by-step approach to reduce components, compared with the overall mode of the local modal modal parameters change. figure 6 to 11 are various plans under a cloud band mode, table 2 for the first two bands modal parameters, modes and a

37、description of the natural frequency changes in the rate of contrast.table of the natural frequency rate of change in the same mode shape, changed the frequency and the frequency of change before the difference between then and change the frequency before the percentage ratio, that is (after removin

38、g components of the overall frequency - the overall components frequency) / component of the overall frequency x100%.data from the above chart the comparative analysis, can draw the following conclusions: through the same mode on the overall shape, that is the first order reversed and the first-bend

39、ing under the natural frequency of changes in the rate of comparative analysis, we can see the right of the middle floors and floor on the overall greater impact on modal parameters, the middle floor after removing the natural frequency of changes in rates were -85% and 90%, while the floor after re

40、moving the table 2 overall in the first two bands modal parameters, modesand described the natural frequency rate of changewhere f-oder reve is the first oder reverse,f-order ben is the first oder bendingright to -45% and -77% ; sleeper plate and the left side of the floor while the impact of these

41、shaoruo, the first order reversed and the first-bending under the natural frequency of changes in rates of -19%, while the left side of the floor in a band bending of the natural frequency of vibration rate of change -53%; right medial longitudinal beam is the smallest change in frequency, are less t