Many complex mechanical products can be considered as multibody systems; 3D computer-aided design (CAD), multibody dynamics, finite element-based strength and fatigue analyses, optimization, and other CAE tools, are often used to develop this kind of product. But design is difficult and challenging because of information inconsistence among different engineering domains, and isolated information model islands exist. Lots of research are attracted to design and analysis information integration, but attentions are mainly focused on integration of CADfinite element analysis (FEA), supporting the bottom-up design principle, while multibody dynamics analysis for analyzing global performance of a mechanical system is rarely considered, which follows the top-down design principle. In this paper, a novel multilevel system representation modeling framework for supporting both bottom-up and top-down or mixed design methods is proposed. It can integrate the product design CAD models with multibody dynamics, finite element-based strength and fatigue analyses, realizing a CAD-dynamic-FEA-fatigue analysis integration. It can also support data exchange and transfer in multidomain analyses. The framework is illustrated with a case study of a load haul dump (LHD) design using currently available software tools. Furthermore, a design case study of the working unit of the LHD is given to highlight the applicability of the modeling framework for multibody mechanical systems. It has been demonstrated that the framework can describe information exchanging and integration among CAD, FEA-based strength and fatigue analyses, and multibody dynamics analysis during a multibody mechanical product design process.

For complex mechanical systems, to overcome design inconsistencies, it is becoming more and more necessary that product design system is effectively integrated with various analysis models and tools from multiple engineering domains at different design stages. In this article, a Holistic Product Design and Analysis Model, which is well supported by TopDown design method, is conceptualized to define design and analysis integration at different levels, which will help enhance engineering design and analysis interoperability and integrate the design methods and analysis tools across multiple engineering domains. It is based on four design levels: system, subsystem, machine and component designs; at each level, design and analysis models are integrated under a Generalized Multirepresentation Architecture supporting design, analysis and optimization appropriately. For cross-level integration from top to bottom, the design models are transferred and mapped with more structural and geometric details, while analysis models obtain more detailed design constraints from the top levels. This new architecture has been developed and demonstrated with an application in a railway vehicle system design, although its optimization components have not been fully implemented. This model can be used for general mechanical product system design.

Introduction 1.1 Railway vehicle virtual prototyping In recent years, knowledge-based new product competition has become the mainstream of manufacturing competitiveness. As an important way to simulate various problems of complex mechanical systems, virtual prototyping technology is being widely used. It supports concurrent engineering and emphasizes the overall product performance, and strives to simulate the product function and behavior. Based on considering the overall product performance in three-dimensional CAD and its following function modules, virtual prototyping does the innovative design and informs a digital prototyping which do not depends on the physical prototype. Virtual Prototyping (VP) is a new product design method generated in the recent 20 years. Based on computer simulation, VP embodies not only the product's innovative design but also the product's risk-free digital test, especially suiting for high cost trial production of complex mechanical system development. The main elements of VP are: virtual prototype model-virtual test analysis-virtual prototype evaluation (qualitative and quantitative). VP embodies the global optimization process which is based on computer simulation and aims to get more realistic products. It supports "Top-to-Down" design approach. The main techniques of VP-CAX, multi-body system modeling and analysis, simulation, optimization, visualization and VR technology are used to get a digital prototype with optimized performance, thereby the development costs and the reliance on physical prototypes are reduced, product qualities are improved, and time-to-market is accelerated. Railway vehicle system which belongs to complex mechanical system areas is composed of mechanical, electrical, active control and drive systems (power distributed EMU), and its main part is mechanical systems. The quality of vehicle performances is the key problem of the vehicle product development. Based on the railway vehicle product design, especially the design results of the whole product machine, the performances include: dynamic performance, operational safety, aerodynamics, air-condition, strength and fatigue reliability. Therefore, it is inevitable to research and develop the railway vehicle virtual prototyping for advanced manufacturing technology. It is also inevitable to research the railway vehicle virtual prototyping technique for the railway transportation equipment, especially for the high-speed, heavy haul train. The past railway vehicle product development mainly takes the following forms:

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