Fast finite element modeling technology of the hot

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Abstract: in the process of concurrent design, facing the technical requirements of digitization and paperless, how to realize the rapid finite element modeling of complex thin-walled composite structures is one of the most important technical issues that engineering designers are most concerned about. Based on the open platform of MSC, this paper summarizes the characteristics and complexity of FEA modeling in 3D solid design of thin-walled composite structures, and explores the technical ways and methods to realize cad/cae integration and secondary development, FEA structural model simplification and rapid modeling. The application test shows that it can effectively shorten the finite element modeling cycle of thin-walled composite structures, and make the finite element model more accurate in simplification than the CAD digital model

1 characteristics and complexity of FEA modeling of thin-walled composite structures

aircraft and ships are complex thin-walled composite structures, which are the traditional engineering application fields of msc/nastran system. How to quickly and effectively establish finite element analysis (FEA) model for msc/nastran system is often the daily work of engineering technicians in these industries. Today, through e-commerce, we can easily purchase the basic platforms of modern digital technology, such as cad/cae/cam/pdm and other commercial software, including ibm/catia, msc/nastran and other products. In this respect, compared with similar foreign companies, we are almost the same; However, in the application of these basic platforms to solve the analysis of complex thin-walled composite structures, we do have a big gap with our foreign counterparts. For example, some military and civilian enterprises need more than 20 people to prepare for the finite element analysis model of the whole machine for more than one year, while the foreign counterparts need much less manpower and time to solve the same problem; It will take several weeks abroad to realize the finite element analysis model of the whole machine in the scheme design stage, but it will take several months for us to work overtime. The same software and hardware technology environment, but there are so different results, the reason is that we lack practical development technology and personalized technical support based on the general digital platform

the overall solution recommended by CAD software providers to us, that is, the automatic conversion of 3D CAD solid models into 3D finite element analysis models, may be used at the part solid level (for example, the FEA function of CATIA), but at the component level or machine level of complex thin-walled composite structures, this solution often leads to FEA models with hundreds of thousands to millions of nodes, and the final results cannot convince experts of its correctness. In this solution, the thin-walled composite structure is regarded as a three-dimensional continuous solid structure, and the cad/3d model is directly converted into fea/3d model. "Combination" becomes "fusion", and "thin-walled" becomes "voxel", which distorts the force transmission and mechanical properties of the structure

because of this, FEA modeling of complex thin-walled composite structures should have its inherent mechanical methods and approaches. The basic practice of simplifying the structural model of aircraft by using the thin-walled composite structure (plate bar beam) theory by Chinese engineers and technicians has been greatly popularized in the aerospace field. Since the ninth five year plan, according to the traditional model simplification method of thin-walled composite structures, we have explored the development platform based on msc/patran, and used the digital model provided by CAD system and the FEA feature design of thin-walled composite structures to quickly establish the related technology of FEA model. Some examples show that it can effectively shorten the FEA modeling cycle, not only reflect the computational mechanics theory of thin-walled composite structures, but also make FEA models more accurate in geometry than CAD models

2 simplification and FEA feature design of thin-walled composite structures

in thin-walled composite structures, three types of structures are very typical: box section, frame section and stiffened wall panel. These typical structures have a specific combination mode and can be described by a set of parameters, which are called characteristic structures. Generally speaking, the characteristic structure is composed of external geometric features, internal structural layout features (partition coefficient, or the location of ribs, frames, and trusses), material and physical characteristics, boundary coordination features, etc. The airframe structure of aircraft and ships can be described by this kind of characteristic structure; Different feature structures will have different pattern expressions. In this way, FEA modeling of thin-walled composite structures turns into structural layout according to characteristics, and structural combination turns into finite element configuration of structures according to mechanical functions

The geometric characteristics of the box segment feature structure are determined by the boundary determined by the region definition (the surface pieces of the wall panel and the upper and lower outer surfaces). The internal structural layout characteristics are determined by the location of the truss and rib, the cross-sectional area of the truss and rib flange and the support, the wall plate in the direction of the rib and span, and the thickness of the outer surface surface surface skin. Material and physical property parameters are required by a set of element definitions. The boundary coordination feature will determine the elements on the boundary, the characteristics of nodes, and the connection mode with other feature structures. Different types of regions (quadrilateral and triangle) determine different box segment characteristics. The wing rib structure of aircraft and the double-layer structure of ship mostly belong to this kind

The geometric feature of the frame segment feature structure is a structure determined by a shape surface piece (it may be a simple isosurface or ruled surface, or an extremely complex surface) and the position parameters of its beam frame and truss, and its boundary is determined by the area definition and surrounded by the intersection line obtained from the area evaluation of the fuselage shape surface. The internal structural layout is determined by the location of the truss and frame beam, the sectional area of the truss, the type of beam profile, the thickness of the skin and other parameters. For frame segment features with openings, there are corresponding requirements for element combination characteristics. The fuselage structure of aircraft and the single-layer hull structure of ships belong to this category

the characteristic structure of stiffened wallboard is the simplest type of feature, including the overall partition frame of the body structure, the bulkhead of the hull structure and the single deck

Figure 1 wing characteristic structure icon figure 2 fuselage characteristic structure icon

figures 1 and 2 are characteristic structure icons of aircraft fuselage structure, and figures 3 and 4 are characteristic structure icons of ship hull structure. According to the combination method, stress characteristics and inherent regularity of these characteristic structures, it is easy to establish parametric FEA models and automatically generate their FEA models (see [1], [2]). For example, for double bottom structure, double side structure, double deck structure, etc., the simplified method is similar to the aircraft wing structure, and cqud4, ctria3, cbeam, crod, cshear elements can be used for discretization. The main structural features include: rectangular features, trapezoidal features, rhombic features, bottom side compartment features, top side compartment features and double side features. For single-layer bottom structure, single-layer side structure and single-layer deck structure, the simplified method is similar to the aircraft fuselage structure, and cquad4, ctria3, cbeam and crod units can be used for discretization. The main types of structural features are: plate, rod, beam combination features; The combination features of plates, rods and rib plates, the features of single-layer bottom, the features of single-layer rectangular deck, etc

Figure 3, double-layer structure feature icon figure 4, single-layer structure feature icon

3 FEA rapid modeling technology based on structural features

3.1 FEA model library of feature structure

according to different types of feature structures, different FEA model libraries need to be developed. Each library is composed of several FEA model programs; Each program realizes the automatic generation of FEA model of specific area shape. As shown in the structural feature icon in the figure, the development of steel and aluminum models with various feature structures is the most important basic work. Through basic practice, the main links are:

· define a group of structural features according to the engineering application objectives

· for each structural feature, define the characteristic parameters and establish the topological description data (including: define the geometric position and the evaluation method of surface patches, define the element type of structural combination and the characteristic parameters of materials and profiles, and define the boundary connection characteristics)

· input interface of design characteristic parameters and output interface of FEA model

· use msc/pcl language to develop msc/pcl class programs generated by FEA model of structural features

3.2 material properties and physical profile properties library

we have established a common material library through cooperation with MSC. For physical properties, the physical property Library of standard profiles (as shown in Figure 5) and the parameterized physical property model of non-standard profiles are established for users to call

Figure 5 call of standard physical profile library

3.3 extraction and evaluation of geometric features

based on msc/patran open platform, realize the close integration of cad/cae, and the key is to extract and evaluate geometric features. Establishing FEA model of thin-walled composite structure requires CAD surface/curve model, while modern CAD system provides 3D solid CAD model. Therefore, we want to:

· extract the shape surface of the 3D solid CAD model or the shape curve of the control section, which needs to be prepared in the CAD system according to the specifications as a subset of the CAD model

· establish effective geometric evaluation methods. In principle, different CAD systems have different geometric evaluation methods; Msc/patran establishes the geometric evaluation function that PCL can call, which can calculate the intersection line of the surface and the coordinates of the projection point

· for a structural feature, it is necessary to develop a geometric evaluation subroutine to evaluate the CAD surface of the boundary and the coordinates of the structural lattice in the region

· it is necessary to develop a subroutine automatically generated by FEA combined element family, which can generate nodes and connection parameters, physical and material properties and other parameters for each element family

3.4 FEA fast modeling operation process

based on MSC/patran development platform, we have established an automatic FEA modeling process for aircraft structural characteristics. It can not only support FEA modeling of aircraft conceptual design, but also support FEA modeling of aircraft detailed design

Figure 6 shows these two basic processes. In the scheme design stage, the aircraft shape is completed by the general CATIA system. In order to optimize the layout and design of the structure, it is often required to carry out structural analysis and comparison of various design schemes under a given shape. 11. Experimental reports: (according to the needs of customers) to achieve structural optimization design. This requires that after the user gives the structural layout and the initial parameters of the elements, F should be given quickly. Under the condition of fixed power, it is inversely proportional to the engine speed EA. The ideal size and physical characteristic parameters of the structural elements will be comprehensively given by the structural optimization program. Establish the automatic generation process of FEA quick mode, use the parameter model file of characteristic structure, and automatically call the relevant parameter model design program of characteristic structure to form the FEA model of scheme design

Figure 6 Operational process design of aircraft FEA rapid modeling

in the detailed design stage, the shape and layout of the structure, the material and physical characteristic parameters of the elements have been completely determined, and engineers need to carry out component analysis and overall analysis of this kind of love wear structure to provide strength check reports for production and experiments. Establish the parametric process of Graphic Interaction definition to generate FEA model, accurately define and modify the parametric model of feature structure, and call the parametric model design program to get the accurately defined FEA model

obviously, it is a common part of the process to establish the CAD shape of the aircraft, evaluate the characteristic structure area, and call the characteristic structure parameter model design program to generate FEA model. Establishing FEA model has different processes for aircraft conceptual design and detailed design. about

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