# Finite Element Analysis and Optimization of Hydrogen Fuel Cell City Bus Body Frame Structure
## 1 Introduction  
The bus provides a convenient mode of transportation, solves traffic congestion, reduces transportation costs, minimizes environmental pollution, and promotes interconnection between urban and rural areas. It is an indispensable public transportation vehicle in daily life. Under the background of advocating for low-carbon alternatives and environmental protection in the world, the hydrogen fuel cell bus has been actively promoted by society with its characteristics of energy saving and emission reduction [1; 2; 3]. Due to its environmental friendliness, sustainability, long-range, rapid charging, and powerful performance, the hydrogen fuel cell bus has gained favor from numerous countries and automotive companies [4; 5; 6; 7]. However, compared to traditional fuel-powered bus, the hydrogen fuel cell city bus is equipped with additional systems, such as hydrogen storage, power batteries, and fuel cell systems, causing significant changes in the load distribution of the bus body frame [8; 9; 10]. Therefore, it is essential to conduct safety analyses of the static and dynamic characteristics of the bus body frame under typical operating conditions [11; 12]. Safety analysis of the automobile body is commonly conducted using the finite element method, which enables the shortening of the vehicle's development time during the early stages of automotive product research. Additionally, it facilitates subsequent improvements and adjustments, significantly reducing the development costs of vehicles [13; 14; 15; 16]. [PERSON] et al. established a finite element model of the bus body and conducted a dynamic modal analysis to obtain its eigenvalues and mode shapes [17]. [PERSON] et al. conducted a modal analysis to verify the dynamic performance of the body frame [18]. [PERSON] et al. conducted a static analysis to investigate the strength and modal characteristics of the busbody frame [19]. [PERSON] et al., conducted a safety analysis of the strength and stiffness of the bus body frame by performing static finite element simulations based on the established bus model [20]. Performing static finite element analysis on the bus body frame allows us to obtain its maximum stress values, stress concentration locations, and maximum displacement values, which reflect the static structural mechanical performance of the bus body frame, including its strength and stiffness characteristics [21; 22; 23]. Performing dynamic modal analysis on the bus body frame allows us to obtain its natural frequencies and mode shapes, which reflect its dynamic performance, evaluate the body's connection conditions, and identify the possibility of body resonance [24; 25]. Therefore, an increasing number of researchers have adopted static and modal analysis methods to verify the safety of bus body frame structures. In this paper, the strength and stiffness performance of the hydrogen fuel cell city bus body frame are examined through static finite element simulations. Additionally, the dynamic characteristics of the body frame are analyzed for safety through modal simulation tests. When the vehicle body does not meet safety requirements or requires lightweighting due to excessive safety margins, it is common to achieve the desired objectives by either optimizing the body structure or replacing it with high-strength lightweight materials [24; 25; 26; 27]. [PERSON] et al., conducted a topology optimization of the bus body frame based on its stress characteristics, thereby enhancing the strength and stiffness of the body frame [28]. [PERSON] et al., conducted a lightweight design of electric buses by optimizing the dimensions of the electric bus structure, thus improving the electric bus's driving range [29]. [PERSON] et al. conducted a strength analysis of automobile beams using the finite element method and subsequently achieved the goal of improving their strength and reducing weight by applying high-strength materials [30].