Abstract: Considering the actual stress environment of urban rail trains, the transient response of the train door body was studied using the finite element method. The modal and damping characteristics of the structure were investigated in depth, and based on this, the dynamic response of the entire door structure was analyzed. The analysis shows that the dynamic stress and displacement of the structure meet the strength requirements and service conditions, providing an important basis for structural optimization design. Keywords : Urban rail; Train door; Analyze the equivalent model in numerical value; Dynamic analysis Introduction With the rapid pace of urbanization in China, the convenience and speed of urban transportation have become important indicators for measuring a city's development. Most developed cities in the world have significant advantages in convenient transportation, especially in urban rail transit, where each city attaches great importance to developing its own unique transportation system. Since the curved doors of rail vehicles are installed on rail trains and are subjected to harsh environments, in addition to fulfilling the basic function of passenger access, the doors should also maximize the vehicle's sealing performance. Therefore, from a structural perspective, the door structure must meet the following requirements: reliability, long service life, and good sealing performance. Reliability refers to the strength of the door panel, while sealing is ensured by the sealing strip; excessive door deformation can lead to strip failure. The door panel of the curved door in rail vehicles adopts a laminated plate structure, mainly composed of inner and outer panels and aluminum honeycomb. The inner and outer panels are made of special alloy aluminum plates, and the aluminum honeycomb, as the name suggests, is made of aluminum. This paper, considering the actual stress environment of urban rail trains, uses finite element analysis to study the dynamic response of the rail train door body. The modal and vibration characteristics of the structure are studied in depth, and based on this, the dynamic response of the overall door structure is analyzed. 1. Finite Element Analysis Theoretical Basis and Model Establishment 1.1 Finite Element Simplified Structural Analysis The door referred to in this paper is one of the rail vehicle door series products of a certain company. Its main structure consists of several major components, such as the door leaf body, load-bearing components, upper and lower tracks, internal and external operating devices, electrical system, and flip pedal, as shown in the left figure of Figure 1. Each component contains several smaller components or parts. It is an electromechanical product integrating mechanics, electricity, and pneumatics. The product contains a large number of parts, has complex internal constraints, and high technical content. The door panel adopts a special alloy aluminum plate and aluminum honeycomb composite structure. Its pneumatic drive mechanism adopts an advanced rodless cylinder, which is stable and reliable in movement, as shown in the middle figure of Figure 1. [align=center] Figure 1 Rail door structure and its honeycomb core layer distribution[/align] The door panel in this paper adopts a laminated plate structure. From the perspective of composite material structural mechanics, it belongs to anisotropic material with a complex failure mechanism. At the same time, the aluminum honeycomb composite structure (shown in sections a, b, and c in the right figure of Figure 1) is quite difficult to simulate numerically. Due to the complexity of the structure, boundary conditions, and loads of the analyzed object, a correct analytical model must be established, followed by numerical simulation on a finite element analysis platform. The general-purpose MSC.PATRAN/NASTRAN finite element program lacks elements for honeycomb structures, necessitating special methods for calculation, such as using three-dimensional finite element methods or laminated elements. Given the complexity of the model, this paper proposes using laminated elements for analysis, which involves the equivalent treatment of composite laminate materials. The following is a brief introduction to the theoretical methods of equivalent treatment. 1.2 Equivalent Treatment of Composite Laminate Materials For modeling composite materials, this paper adopts the sandwich panel theory. In simplification, it is assumed that the core layer can resist transverse shear deformation and has a certain in-plane stiffness, and the upper and lower skin layers obey the Kirchhoff assumption, neglecting their ability to resist transverse shear stress. Under these assumptions, the honeycomb core layer can be equivalent to a homogeneous, orthotropic layer of constant thickness. The equivalent elastic parameters of the regular hexagonal honeycomb are expressed as follows [2]: where E and G are the engineering constants of the sandwich material, l and t are the length and thickness of the honeycomb cell wall plate respectively; γ is the correction coefficient, which depends on the process, and is generally taken as 0.4 to 0.6, and the theoretical value is taken as 1.0. 2 Research on the dynamic characteristics of urban rail car door structure 2.1 Modal analysis of door structure Transient dynamic analysis First, the door should be modally analyzed to understand the natural frequency of the structure and the mode shape of the structure at each frequency. According to the calculation model, the subspace iteration method is used to solve the modal frequency and mode shape of the rail car door vibration. As shown in Figure 2. [align=center] Figure 2 First four modes of urban rail car door[/align] Table 1 Modal analysis results of door structure: 2.2 Transient impact pressure response analysis of door structure In order to detect whether the designed door body can meet the design requirements when subjected to transient pressure, that is, whether the vibration amplitude meets the requirements and whether resonance will occur, the door leaf body in the door should be subjected to transient dynamic analysis. During high-speed operation, the surrounding air undergoes significant changes in the rail vehicle door. When two trains traveling in opposite directions meet, this change intensifies at the moment of intersection, creating a transient pressure impact on the entire vehicle surface. Positive and negative pressure peaks appear successively within a few tens of milliseconds. This transient pressure shock wave can adversely affect the car body steel structure and side doors. The transient pressure load is set according to actual operating conditions, as shown in Figure 3. [align=center] Figure 3 Transient Load Variation Curve[/align] Figure 4 (left) shows the displacement response at the maximum stress point. It can be seen that the door displacement reaches its maximum at 0.1 ms, with a maximum displacement of approximately 0.3 mm, which is well within the allowable deformation range of the rail vehicle door. Figure 3 (right) shows the stress response at the maximum stress point. It can be seen that the stress reaches its maximum at 0.1 ms, approaching 4.1 MPa, thus not affecting the overall rationality of the rail vehicle door structure. [align=center]Figure 4 Transient Response Curves of Displacement and Stress of Rail Vehicle Door[/align] 3 Summary In modern transportation systems, the structural safety of vehicle doors is directly related to passenger safety. Reliability, sufficient rigidity, resistance to deformation, and noiselessness during operation are key considerations in door structure design. This paper uses finite element analysis to study the transient response of rail vehicle doors, conducting in-depth research on the modal and vibration characteristics of the structure. Based on this, the dynamic response of the overall door structure is analyzed. Whether the results obtained conform to the actual situation requires experimental verification. If a theoretical solution exists, comparing the two can determine the correctness of the analysis scheme. However, due to the complexity of the object structure, boundary conditions, and stress conditions in finite element analysis, a theoretical solution often does not exist, and only experimental methods can be used for verification. The analysis presented in this paper has certain theoretical reference value for door design. The innovation of this paper is that, as an important symbol of urbanization in China, curved doors of rail vehicles are widely used, but there is no precedent in China for conducting overall dynamic analysis of curved doors of rail vehicles with honeycomb materials. This paper combines practical experience, applies equivalent treatment of honeycomb materials and door panels with composite laminate materials, establishes an FEA model for dynamic analysis, and draws relevant conclusions. This lays the foundation for the specific application of curved doors in this type of rail vehicle and provides reference materials for my country's independent research and development of urban rail transit and participation in international competition. [References] [1] Chen Guohua. Calculation and analysis of static strength and stiffness of automobile door based on finite element method [J]. Mechanical Manufacturing and Research, 2006, 35 (6): 21-24 [2] Xu Shengjin. 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