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Optimization design of pipe support under pro/mechanica environment

with the development of electronic computer, modern mechanical design methods also show diversity. It has become a trend to use advanced cad/cae tools to carry out research on mechanical systems. Pro/engineer is a large-scale design software integrating cad/cam/cae. The common modules of CAE include mechanism design extension (mdx) and pro/mechanica. The function of geometric modeling of most professional analysis software is relatively weak, and data exchange must be carried out through IGES format or step format, which often leads to data loss and requires a lot of time and energy to repair the geometric model. Pro/mechanica can overcome this weakness. It can directly use the geometric model of pro/engineer for finite element analysis. Due to the powerful parameterization function of pro/engineer, pro/mechanica makes use of the advantages of parameterization tools to carry out sensitivity analysis and optimization design of geometric models, which is the most significant feature that pro/mechanica distinguishes from other finite element software

I. optimization design in pro/mechnica environment

o/mechnica structure module introduction

like other professional finite element analysis software, pro/mechnica structure module can complete finite element analysis and model optimization design. Its design research types mainly include three kinds: standard analysis, sensitivity analysis and optimization design analysis. Figure 1 shows the main menu of pro/mechanica structure module

Figure 1 main menu of pro/mechanicastructure module

generally speaking, the analysis tasks of pro/mechanicastructure module are divided into two categories. The first category is design verification or design verification, such as carrying out stress-strain inspection of design model. Like other finite element analysis software, it is necessary to create geometric model, simplify model, set unit and material properties, define constraints, define loads, define analysis tasks, run analysis Display the workflow of evaluation calculation results; The second type is the design optimization of the model, which is the most significant feature that pro/mechanica distinguishes from other finite element software. Its workflow is shown in Figure 2. Taking the pipe support as an example, this paper briefly describes the unique optimization design function of pro/mechanica

Figure 2 pro/mechanica optimization design workflow chart

2 Optimization design of pipe support

pipe support is a kind of supporting parts widely used in construction, electric power and other industries. Finite element analysis and optimization design of it have important guiding significance for actual production

(1) establishment of geometric model

Figure 3 is the three-dimensional modeling diagram of a pipe support under pro/e, which is mainly composed of intermediate plate, edge plate, intermediate notch and left end fixed plate, and its left Jinan assay plastic bending detector end face is fixed. It can be seen from the mechanics of materials that the connection surface of the left end fixed plate of the support with the intermediate plate and the edge plate is a dangerous section, and the point at the upper and lower positions of the section bears the maximum stress, which is a dangerous point. Therefore, measurement points pnt0 and PNT1 are established respectively to monitor the stress value at the dangerous point

Figure 3 three dimensional rendering of pipe support

(2) set the material properties of the model

the selected material of the model is 45 steel, and its density is ρ= 7.8x103kg/m3, elastic modulus e=200gpa, Poisson's ratio μ= 2.7。 According to the material properties, we choose the material model in the material library in the pro/mechanica structure module, which is also planned to be put into production steel in May this year, and then sort it out. Figure 4 shows the defined material properties table

Figure 4 definition box of material properties of pipe support

(3) definition of constraints and loads

since the left end surface of the pipe support is fixed, the 6 degrees of freedom of the end surface are completely fixed when defining constraints; The upper end face of the support bears the pipe weight of 1000N, so the load distribution form is selected as uniform total load, and the component of Y axis is -1000n, which is applied at 50 × 100, as shown in Figure 5

Fig. 5 constraints and loads of pipe supports

(4) sensitivity analysis

in the process of building the model, the designer has defined many design parameters, such as target design parameters, physical parameters, etc. when these design parameters change, it will inevitably affect the performance of the model. If these design parameters are used for optimal design, it will inevitably increase the amount of calculation. Considering that different design parameters have different degrees of influence on the performance of the model, if we can quantitatively express this degree of influence, we can determine which are important design parameters and exclude those with small degrees of influence, so as to improve the efficiency of optimal design, which should be emphatically considered in optimal design. The sensitivity analysis of pro/m just provides such quantitative analysis function, which ensures the high efficiency of optimal design

1) local sensitivity analysis

local sensitivity analysis is to quantitatively analyze the impact of each design parameter on the performance of the model, so as to determine which parameters have the greatest impact on the performance of the model, that is, important design parameters, which should be considered in design optimization

in the above pipe supports, the design parameters mainly include mid_length, mid_width, mid_thickness, edge_width, edge_thickness, cut_length and cut_width of the middle notch, etc. Therefore, the local sensitivity analysis of these parameters is carried out respectively, and finally the important parameters that have the deepest impact on the maximum stress of the model are determined. After running the local sensitivity analysis, figures 6 to 12 show the curves of the influence of seven parameters on the stress of the model, including the length, width and thickness of the intermediate plate, the width and thickness of the edge plate, and the length and width of the intermediate notch. It can be seen from the curve that the stress of the pipe support model is the most sensitive to the changes of the design parameters mid_width and mid_thickness, that is, the changes of the mid plate width and thickness have the greatest impact on the model stress, so this is the key parameter to be considered in the optimization design; The changes of other design parameters have little effect on the maximum stress of the model

Fig. 6 influence curve of intermediate plate length on model stress

Fig. 7 influence curve of intermediate plate width on model stress

Fig. 8 influence curve of intermediate plate thickness on model stress

Fig. 9 influence curve of edge plate width on model stress

Fig. 10 influence curve of edge plate thickness on model stress

Fig. 11 influence curve of intermediate notch length on model stress

Fig. 12 influence curve of intermediate notch width on model stress Curve

2) global sensitivity analysis

global sensitivity analysis is to determine the variation range for optimal design for these important design parameters based on the parameters that have a great impact on the performance of the model through local sensitivity analysis, that is to say, global sensitivity analysis can accurately describe the sensitivity of the performance of the model to the important design parameters used for optimal design and determine its reasonable variation range of parameters, So as to seek the best design in the variation range of these parameters

since the results of the local sensitivity analysis of the pipe support show that the width and thickness of the intermediate plate have the greatest impact on the model stress, the global sensitivity analysis tasks are established respectively (define the parameters mid_width and mid_thickness, so the tensile testing machine for testing high molecular polymers has a certain difference from the general tensile testing machine for material tensile properties, and the variation ranges are 160 ~ 240mm and 15 ~ 25mm respectively), After the analysis and calculation, the sensitivity of the stress of the pipe support model to the changes in the width and thickness of the intermediate plate is accurately determined, as shown in figures 13 and 14

Figure 13 global sensitivity analysis curve of intermediate plate width

Figure 14 global sensitivity analysis curve of intermediate plate thickness parameters

(5) optimization design

the main content of optimization design research is to achieve the target conditions of light weight, small volume, reasonable shape, minimum cost and mechanical aspects to minimize the stress concentration in the transition zone on the premise of ensuring the constraints of the model. Its mathematical model can generally be written in the following format:

where D is the value range of the design variable x in the European Space RN, which is called the feasible region; "S.T." is the constraint. That is, the mathematical model of optimal design includes three factors: design variable x, objective function f (x) and constraint conditions

in the example of pipe support in this paper, three elements are determined as follows:

objective function: minimize the quality of support

design parameters: mid_width and mid_thickness. According to the sensitivity analysis, the maximum stress of the pipe support model is most sensitive to the change of the width and thickness of the intermediate plate, and insensitive to the change of other parameters. It will be felt after the production capacity is released to the market after the resumption of production. Therefore, the width and thickness of the intermediate plate are the parameters to be studied emphatically. Original size mid_ Width=200mm，Mid_ Thickness=20mm。

constraint condition: strength condition =40mpa, the previously established measurement points pnt0 and PNT1 can reflect the stress situation at the dangerous section. On the premise of meeting the material strength, the maximum stress value at the dangerous section must be controlled to slow down the stress phenomenon, that is,

according to the above mathematical model, the optimization design task is established and run, and a group of optimization results that make the weight of the pipe support the lightest are obtained. Now make a comparison between the original value and the optimal value, as shown in Table 1

it can be seen from the above table: after optimization; The weight of the support was reduced by 0.00526 (tonne), and the weight reduction rate was 12.6%; The maximum stress and displacement are slightly higher than the original

value, but the premise is that all constraints are met, which has little impact on the model. Figure 15 shows the historical result curve of the optimization process, and Figure 16 shows the finally determined optimized pipe support model

Figure 15 optimization history result curve

Figure 16 how many dimensions of the optimized pipe support geometric model

II. Conclusion

using the advantages of the powerful parameterization function of pro/engineer, pro/mechanica can carry out sensitivity analysis and optimization design of the model, which is the most significant feature that pro/mechanica is different from other finite element software. Through the optimal design of the pipe support, the determination of the size of the pipe support is more reasonable and scientific. Under the condition of meeting the strength of the support, the weight of the support is reduced, and the weight reduction effect is obvious. At the same time, it is more important to obtain important design parameters through sensitivity analysis, which improves the efficiency of the optimal design. Therefore, using pro/mechanica environment to optimize design is a very effective design method, which has a very important guiding significance for actual production

author unit: School of mechanical and electrical engineering, Kunming University of technology

Original: cad/cam and manufacturing informatization (end)

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