To achieve rapid prediction of aerodynamic noise in the rearview mirror area of vehicles, an stochastic noise generation and propagation (SNGR) method is adopted. Unlike general aerodynamic noise simulation methods, this method is based on the reynolds-averaged navier-stokes (RANS) equation to solve the steady flow field, reconstructing the sound source term through a velocity random model, and finally using the finite interpolation method to solve the acoustic analogy equation, greatly reducing the computational period of aerodynamic noise simulation. Based on actual vehicle data, a wind tunnel model is established, with a speed of 120 km/h as the simulation condition. Under the same conditions, the SNGR method and the general unsteady method using large eddy simulation as the flow field calculation model are respectively used for simulation. The results show that the calculation time of the SNGR method is greatly reduced, and the calculation results are consistent in the frequency range of 500-5 000 Hz, proving the efficiency of this method. On this basis, the flow field results in the rearview mirror area are analyzed, and the design of the car rearview mirror is optimized based on the principle of aerodynamic noise generation. Install the rearview mirrors before and after optimization on the entire vehicle for wind tunnel experiments, and verify the accuracy of the SNGR method calculation results by comparing the sound pressure level reduction before and after rearview mirror optimization. The simulation and experimental error of this method is between 4%-5%, proving that this method can be used in the optimization stage of aerodynamic noise performance of vehicle rearview mirrors.

In order to solve the problems of incomplete balance equation, inaccurate balance equation and large error of cam contour caused by the influence of piston deflection on cam dynamic moment in existing cam construction of pedal brake unit, the structure of pedal brake cam and output force stability were studied. Firstly, the concept of optimum compensation angle is introduced, and the rotating moment of the thrust caused by piston deflection in two directions to the cam articulation point is included in the new balance equation, which makes the balance equation more complete, accurate and has less error. Based on this, a new cam mechanism is designed and constructed. Then, on the pedal brake unit routine tester, a comparative experiment is carried out on the stability of output force value between the original cam mechanism and the newly constructed cam mechanism with optimized compensation angle. Finally, the above data and the curves of action travel and output force are comprehensively compared and analyzed. The results show that the output force value stability of cam with compensation angle is better than that of cam without compensation angle. In actual operating stroke, the maximum difference of output force between two times is (-0.8, +0.6) kN with compensation angle cam error, and (-1.2, +1.2) kN without compensation angle cam error. The error with compensation angle cam is also less than that without compensation angle cam error.

In order to explore the effects of maintenance difficulty degree of component on the maintenance cost and availability of the model. Taking a mechanical component of electric multiple unit (EMU) as the research object, and a component reliability threshold as the decision variable, the two-parameter Weibull distribution is adopted to describe the evolution law of component failure rate, combined with the existing fixed period multi-level imperfect maintenance rule of EMU in China, a preventive maintenance strategy for single component of EMU with bi-objective optimization is established. Bi-level imperfect maintenance is implemented in the maintenance mode and the concept of efficiency-cost ratio is introduced to discriminate the selection of each maintenance method of the component. Considering four factors, the difficulty of detecting parts, the location of parts, the difficulty of disassembling parts and the complexity of parts. Analytic hierarchy process (AHP) is adopted to quantify the maintenance difficulty degree and to study impact on the cost and availability of maintenance. The analysis shows that the maintenance model considering the maintenance difficulty can effectively reduce the maintenance cost and improve the availability, which provides a theoretical reference for the development of the maintenance strategy of EMU.

In order to solve the problems of insufficient monitoring strength, poor interaction and low digitization degree during the operation of mobile crane, the construction method of digital twin system for real-time monitoring of crane operation status was proposed. A five-dimensional digital twin model is introduced to establish a digital twin framework for virtual and real control of cranes. Build a physical space from the service scene and physical entity; Establish virtual space from virtual model and visual scene and action control. Based on MySQL database, the twin database is constructed by using inherent, collected and virtual information. Virtual and real interaction, dynamic monitoring and visualization are realized in combination with communication protocols. Taking YDC20/30 light and small mobile crane as an example, the feasibility of this method is verified, and a new scheme is provided for comprehensively controlling the service process of the crane.

In order to explore the factors influencing the slip rate between tracked combine harvester and paddy soil, a coupled simulation model of tracked combine harvester and paddy soil is established by the RecurDyn software. Selecting the mass, driving speed, steering angular speed of the tracked combine harvester and the moisture content, positive slope, and oblique slope of the paddy soil as test factors, simulations under different conditions are implemented. Through a six-factor two-level PB (Plackett-Burman) test was conducted to screen out the slip rate significant factors that is soil moisture content, positive slope, and steering angle velocity. Then, a three-factor three-level BB (Box-Behnken) test was conducted on the three selected factors. The results show that soil moisture content, positive slope, and steering angle velocity have a very significant impact on slip rate, and the order of significance is steering angle velocity>soil moisture content>positive slope. As the positive slope and steering angle velocity increase, the slip rate increases significantly, while as the soil moisture content increases, the slip rate slowly decreases. The soil moisture content has a certain interaction with the positive slope and steering angular velocity. However, there is basically no interaction between positive slope and steering angular velocity. This study has important reference value and scientific significance for improving the path tracking accuracy and stability of tracked combine harvester for autonomous harvesting operation in paddy soil.