We start from the idea of establishing an interactive CAD design environment, MxCAD online control has been introduced by dozens of domestic units, and has been widely used in many railroad lines, achieving good economic and social benefits. Now combined with the development of bridge CAD targeted at the application of CAD in railroad design.
parametric
variable modeling technology using parametric, variable modeling technology, to complete the engineering object entity modeling, is the basis of engineering CAD design. Parametric, variable modeling techniques are constraint-based entity modeling techniques. Based on features: some representative planar geometric shapes are defined as features, and all their dimensions are stored as adjustable parameters to form entities. Full-size constraints: Shape and size are considered together, and geometric control is achieved through size constraints. Dimension-driven design modification: geometry changes are driven by editing dimension values; full data correlation: modification of dimensional parameters leads to changes in related dimensions in other related modules to maintain design consistency. Variationalization is a design idea based on parameterization and further improved. In addition to the consideration of geometric constraints, variational design can also be used as a constraint on the engineering relationship directly with the geometric equations, without the need to build a separate model to deal with. The modeling process is similar to that of an engineer thinking of a design solution in his head, where the geometry that meets the design requirements comes first, and the dimensional details are refined later. The design process is relatively free and loose, the designer can have more time and energy to consider the design program, which is in line with the creative thinking of engineers. Therefore, the variable technology is the basis of engineering CAD.
Dynamic data exchange
Dynamic data exchange Its overall design program can be directly operated by the designers of the screen for intuitive comparison. The most fundamental in interactive design is to maintain the consistency of graphics and data at any time, to achieve two-way communication between data and graphics. Data can be modified to achieve the purpose of modifying the corresponding graphics, but also through the modification of graphics, to achieve the purpose of modifying the corresponding data. Designers can choose different methods according to the actual situation. In bridge design, when the designer modifies the center mileage, hole-span arrangement or pier height, foundation depth and other control parameters, the application program will analyze and calculate the structure at the same time, parameterize the graphic design, and update the corresponding data in the database to ensure the real-time data. Designers can be phased, layered graphics or data for multiple modifications, process control. This is an iterative human-computer interactive two-way communication process, which can give full play to the designer's subjective initiative.
Dynamic Link Library (DLL)
Dynamic Link Library (DLL) is one of the important components of CAD. With a dynamic link library in several applications can share a copy of the function code, saving memory, improve efficiency. Through dynamic link libraries, applications can share code and resources. Dynamic libraries are most advantageous in large applications. In the auxiliary design of simply supported girder bridges, there are design modules for curves, geology, girders, piers, abutments, foundations, seismic calculations, and so on. Many of these applications use the same structural checking routines. If these common processes are put into a regular target library and added to each program module when using LINK static linking, this approach is inefficient because each program in the software contains the same code as the common routines, and if one of the routines in the library is modified, it is necessary to re-link all the programs that use this routine. However, if these public routines are put into a dynamic link library (DLL), these two problems can be solved, and the library module can be modified without re-linking the individual programs.
