- Detail

Application of pro/e and ANSYS in antenna structure design and analysis

1 introduction

antenna is the main equipment for transmitting and receiving microwave signals in satellite communication. With the development of satellite communications, the application of antennas has also been rapidly promoted. For the antenna structure, a reasonable design should ensure that the antenna accurately maintains its shape and attitude in various environments. At present, the structural design and analysis of the antenna has formed its own system, and the key part is the establishment of the design model and the stiffness and strength analysis and deformation calculation based on it. In the past, the method of combining empirical analogy design with simplified calculation of traditional material mechanics was often used, but this method largely depends on the experience of designers, and often makes the design conservative, resulting in heavy product weight and high cost. Especially in the current situation that customer requirements are becoming more and more diverse, it can no longer adapt to the rapidly changing market requirements

with the popularization and application of various advanced computer-aided design software, it is possible to use powerful CAD and CAE software to design and analyze the antenna structure, which can greatly improve the design quality and efficiency. At present, the advanced CAD software pro/engineer can directly carry out three-dimensional solid design. Its powerful feature modeling technology can quickly capture objects, generate geometric models of products, automatically divide the finite element lattice of the established solid model, and output the divided model to the finite element analysis software. ANSYS software is a large general finite element analysis software integrating structure, heat, fluid and electromagnetism. It provides excellent analysis function of finite element calculation, can obtain good calculation accuracy, and can be integrated with pro/engineer

on the basis of summarizing the experience of antenna structure design, this paper introduces the general steps of how to use the above two software to carry out solid modeling and analysis of the structure, and puts forward some methods of finite element analysis model establishment

2 basic steps of structural modeling and analysis

the analysis of antenna structure is a solid mechanics problem, which is usually calculated by finite element method. Generally speaking, the design and analysis of antenna structure is composed of the following steps

(1) establish the design model

(2) discretize the structure and divide the finite element lattice

(3) establish boundary conditions and impose constraints

(4) calculate the node load

(5) form an integral rigid matrix and solve the finite element equation

(6) sort out and analyze the calculation results

steps (1), (2), (3) and (4) in the above steps are called pre-processing of finite element analysis, and step (6) is called post-processing of finite element analysis. There have been many monographs on the finite element method of solid mechanics, which have been analyzed in detail, and will not be repeated here one by one. This paper mainly summarizes how to carry out specific operations in the pro/engineer and ANSYS software environments: first, establish a solid model in pro/engineer and input material properties, mainly including elastic modulus, Poisson's ratio and density. Note that the selection of units must be the same as that in ANSYS, otherwise the calculation results will have an order of magnitude deviation. Then in the pro/mesh module, the finite element network is divided, the coordinate system is determined, the loads and constraints are applied, and the analysis name is defined, so as to establish the analysis model. Run the analysis, select ANSYS as the solver, and generate a program named * Ans file (you can also choose to run directly in the background, etc.), so that all the pre-processing processes in the calculation can be completed in pro/engineer. The final calculation and post-processing are completed in ANSYS. After entering ANSYS, read the * Ans file. At this time, you can check whether the material properties, loads, constraints, etc. defined in pro/engineer are correct. If there is no error, you can directly calculate (solve), and use the general postprocessor to view the calculation results. Figure 1 shows the stress distribution of an antenna pedestal

Figure 1 stress nephogram of antenna pedestal

3 method of modeling with pro/engineer

for products with various spatial dimensions such as antenna structure, the solid model can be quickly established through the powerful modeling function of pro/engineer, and it is very convenient to modify. With the help of the finite element lattice division function provided by the pro/mesh module, the model can be divided into solid, shell or beam elements, and constraints and loads can be added on this basis, and finally transferred to the finite element analysis module pro/mechanical or other analysis software, such as ANSYS, for calculation

with the rapid promotion of 3D design software in recent years, it is not difficult to quickly establish a solid model. The problem is how to directly convert the model into a correct analysis model. Here are some methods often used in pro/engineer modeling

3.1 simplified model

simplified model refers to ignoring details in parts or assemblies. Because the actual structure is often complex, it is unnecessary and sometimes impossible to establish a finite element model completely according to the real object. Therefore, some detailed features of components are often compressed before finite element lattice division. Before compressing these features, you must pay attention to the following points

(1) whether the compression characteristics will change the characteristics of the analysis model. In other words, it depends on whether the feature is the basic feature necessary to ensure the structural strength or just the cosmetic feature. What we need to compress is the cosmetic feature. These features generally include round, chamfer, small groove, locating hole, etc. Never consider feature compression before performing all analyses. In addition, for modal analysis or thermal analysis, compressible features may not be applicable to structural analysis. For example, those features that can produce stress concentration can be ignored in modal analysis and do not affect stiffness, but these factors must be considered in strength analysis

(2) whether compression features will affect sensitivity and optimization. If the purpose of the analysis is to reduce the quality, the modification features mentioned above will play a key role. The radius of a fillet may be the optimization parameter. Although it is only a modification feature, it will significantly affect the optimization analysis process with high-strength and high conductivity aluminum alloy, high-strength and high elastic copper alloy, high-performance magnesium alloy, titanium alloy materials used in aerospace and other high-tech fields

(3) pay attention to the parent-child relationship between features when compressing features. If the compressed feature is the parent of other key features, the parent-child relationship must be redefined

3.2 try to use plate and beam elements

any component is three-dimensional, but when the size in one direction or two directions is much smaller than that in other directions, it can be simplified as plate or rod, which is called dimension reduction. In pro/engineer, if solid elements are used, the time taken to divide the finite element lattice is dozens of times or even more than that of using plate elements. For some complex parts with small element division, it is more likely to cause division failure or calculation overflow. Therefore, it is a scientific and economic method to use plate and beam elements as much as possible without affecting the calculation accuracy

3.3 solid model

the solid model is established by using surface, thin structures, rib and other features or sheetmetal. As mentioned earlier, it is faster and more effective to divide the finite element lattice with plate elements than with solid elements, which must be considered at the early stage of modeling. Because the pro/mesh module can automatically extract the midsurface of thin-wall, rib and other features to generate plate elements, which greatly improves the efficiency of finite element lattice division, these features should be used more in modeling, otherwise manual operation will be carried out in lattice division, resulting in a waste of time. Special attention should be paid here that in the part or assembly, whether equal thickness or variable thickness, the neutral surface of the feature or part must be connected as a whole, otherwise the unit will be interrupted. For the problem of variable thickness in parts, the neutral surface can be made as the first feature, and then use quilt both sides can be generated in two directions

3.4 shape ratio of control units

various units generally have ideal shapes, such as equilateral triangles for triangular units and squares for quadrilateral units. However, in fact, it is impossible to use ideal shape elements to discretize structures with different shapes. Therefore, only pay attention to the shape of control elements, try to make the divided lattice elements have better shape, and avoid sharp corner elements with small area or thin elements with small volume, so as to improve the calculation accuracy. In pro/engineer, you can set FEM in the configuration file nfig by_ asp_ ratio、Fem_ edge_ Angle and FEM_ Modify variables such as taper to control the quality of the unit

3.5 reasonably plan the layout of the finite element network

according to the error analysis, the error of stress is proportional to the size of the element, and the error of displacement is proportional to the square of the element. It can be seen that the smaller the unit is divided, the higher the output of refined lithium-ion battery increases by more than 40%; But on the other hand, the more units, the greater the calculation workload. Therefore, the density of the lattice must be determined according to the accuracy requirements. Generally speaking, the element should be smaller where the boundary curvature is large, and larger where the boundary curvature is relatively flat. In pro/mesh, mesh CO can be creative enough to support the birth of a start-up company, and control the density of the finite element lattice

the above method is further explained with an example below. Figure 2 shows a microwave horn. Because the antenna needs to work outdoors for a long time, the main load it bears comes from the wind. As an exposed antenna component, the horn must be able to work normally in strong winds, and the deformation cannot exceed the allowable value. First of all, it is important for many people to establish an analysis model in pro/engineer. From Figure 2, it can be seen that there are some holes and chamfers on the horn. These features are for technological considerations and do not affect the stress state of the structure. Therefore, these features can be ignored in establishing an analysis model. The simplified model is shown in Figure 3

Figure 3. When dividing the finite element lattice of the simplified model

considering that the size of the plate thickness is much smaller than that in other directions, it can be divided into plate elements. Because thin-walled features are used when creating entities, and the combination between features is controlled, plate elements can be generated directly by auto detect neutral plane. In order to understand the stress distribution of key parts (middle flange) more accurately, higher calculation accuracy can be obtained by controlling the cell size here. The model in Figure 2 is finally divided into 782 nodes and 767 quadrilateral elements, which are input into ANSYS. The completed finite element analysis model is shown in Figure 4. After constraints and loads are applied, the calculated deformation is shown in Figure 5

Figure 4 finite element model

Figure 5 deformation figure

4 Conclusion

with the development of computer technology, through the use of CAD, CAE and other advanced design means, the design cycle of products can be greatly shortened, and the design level of products can be improved on the premise of meeting the design requirements. Reasonable use of CAE technology can find problems in design in time, provide reliable analysis data for designers, and ensure the success rate of design. (end)

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