PSI - Issue 22

B.R. Miao et al. / Procedia Structural Integrity 22 (2019) 102–109 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction Multidisciplinary design optimization (MDO) is a methodology that combines analyses and optimizations contained within individual disciplines with the analyses and optimizations contained within the entire system of the disciplines (Sobieszczanski Sobieski J. et al., 1989). Multidisciplinary design optimization (MDO) is a field of research that studies the application of numerical optimization techniques to the design of engineering systems involving multiple disciplines or components (Hoogreef M. F. et al., 2015). As the weight of the equipment is more and more important in the entire vehicle, the design of the lightweight aluminum alloy sandwich structure also has an important negative effect on the vertical bending and torsional rigidity of the carbody. This not only greatly reduces the vertical bending frequency and torsion resistance of the carbody, but also easily causes the coupling vibration failure between the carbody and the bogie, the carbody chassis and the hanging equipment. The serious consequences of this effect will inevitably lead to damage to the suspension components of the equipment. For example, it had been found that some types of EMU ( Electric Multiple Units ) vehicles had some fatigue problems such as loose suspension under the underframe, cracks and breaks in the suspension position of the gear box in different degrees of actual operation (Miao B. et al. 2009). A multi-level and multi-functional optimization methodology is suggested for the design of a composite high speed train carbody (Wennberg, D. et al., 2014). After the analysis, it is preliminarily believed that the main cause of the fracture and looseness of the suspension joint under the vehicle is attributed to the local coupling vibration of the carbody and the hanging equipment. In addition, a high-speed EMU also has weld cracks in the equipment compartment bracket during the repair, and the specific position is the equipment cabin bracket in the skirt on the left side of the carbody. The fasteners in the transformer equipment compartment of an EMU have been found to have loose or even loosened fasteners. The C shaped slot plate of the fixed location of the EMU carbody near the end fixing bracket had occurred some break problems. Aiming at these problems, the mechanism of the coupling interaction mechanism between the structure dynamics characteristics and the failure of the vehicle structure components has been studied. And the effect of vehicle structural resonance should be performed based on the multidisciplinary fatigue optimization design method. This is because the dynamic characteristics of the vehicle system is an important factor affecting the vibration fatigue problems of the carbody structure. 2. Theory background 2.1. The coupling vibration and resonance effect of railway vehicle Vehicle safety and structural lightweight have become two important issues that high-speed trains must consider. The elastic vibration of the carbody structure affects the fatigue performance of the structure which the MDO method should been taken into account (Morteza, K. et al., 2014). It is necessary to consider the coupling vibration and resonance effect of the carbody and the under-vehicle equipment in the structural fatigue failure analysis. From the perspective of multidisciplinary design optimization, it is necessary to establish a dynamic model of rigid-flexible coupled vehicle systems. There are two main methods for establishing a dynamics model of a rigid-flexible coupled vehicle system. One method is to consider the carbody as the Euler-Bernoulli beam model using the elastic vibration theory of the beam. Combining the analyzed beam model, the kinetic numerical simulation model of the beam structure is simplified. The second method is to establish the rigid-flexible coupling dynamics model of the vehicle by using the computational multi-body dynamics theory. When the self-vibration frequency of the carbody and the under-vehicle equipment is similar, the coupled vibration and resonance phenomenon may occur between the carbody and the under-vehicle devices in both the vertical and horizontal directions. Since vehicle motion in both directions may cause weak coupled vibration problems in the vehicle, the vibration response in both directions needs to be decoupled. In general, the most influential factor in the dynamic performance of the vehicle is the vertical coupled vibration process (Hirsch, J. et al., 2011). In this paper, the influence of the under-vehicle equipment and its suspension parameters on the elastic vibration of the carbody only needs to establish a vertical dynamic model of the vehicle system. The vehicle vertical dynamics model can effectively study the effects of suspension parameters, modal frequency and longitudinal loads on the