In order to improve the lightweight level of the automotive floor, reduce material application cost, and improve integrated process manufacturing performance through structural design and optimization, this article proposes a design method to link conceptual design and detailed design and optimize the composite floor by combining free size optimization and size optimization methods. The basic theory of composite mechanics is expounded from the stress-strain theory of single-layer plates, and the stiffness and strength theory of laminated plates, which provides theoretical support for the structural design, material design, and allowable value design of composites. The mechanical properties of CFRP were tested to obtain the basic material parameters of CFRP T300/5208. With the material parameters, the CFRP floor super layers are established in Optistruct software. The shape of the floor super layers is optimized by using the free size optimization method, with the body-in-white (BIW) lightweight coefficient as the objective and the BIW performance as the constraints. The BIW lightweight coefficient is reduced from 4.35 to 4.20 after free size optimization, and the layer blocks shape is obtained and clipped based on engineering application. With the floor mass as the objective and the BIW performance as the constraints, the size optimization of the floor layer blocks thickness is optimized. Then the number of floor layers is obtained, and the CFRP floor is established in Fibersim software. Use the simulation analysis method to compare and verify the performance of the floor before and after optimization. The results show that the failure index of the floor is far less than the failure standard, while the mass of the CFRP floor is reduced by 6.8 kg compared with the original steel floor, which an improvement rate reaching 27.5%. The design and optimization methods presented in this article provide a reference for the design and application of the CFRP floor.

In order to study the fatigue, 13° impact and 90° impact performance of wheel and propose a wheel structure design and optimization method based on these performance, taking a $16\times 6\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.\mathrm{J}$ type wheel as research objects, united topology optimization was performed based on dynamic bending and radial fatigue tests, and an assembled wheel with a magnesium alloy rim and an aluminum alloy disc was designed. Finite element models of the assembled wheel for 13° impact tests were established to analyze the effective plastic strain of the wheel under two conditions of the hammer facing the spoke and the window respectively. And established finite element models of the assembled wheel for 90° impact tests, analyzed the deformation of the inner wheel flange and the effective plastic strain of the rim and disc when the hammer impacted facing the window, and analyzed the failure range of the wheel and the effective plastic strain of the rim and disc beyond the 25% circumferential range (90°) of the impact position when the hammer impacted facing the valve window. Then studied the relationship between these performance and the wheel structure. The parametric models of the assembled wheel under four finite element conditions were established with 12 design variables defined by using the mesh morphing technology. The Optimal Latin Hypercube design and Hammersley design were used to fit the Kriging surrogate model and to validate the precision of the surrogate model in Isight software platform where the DEP-MeshWorks and LS-DYNA software were integrated. Using the established surrogate model, Non-dominated Sorting Genetic Algorithm-II (NSGA-II) was adopted to perform the multi-objective optimization of the wheel. The Pareto frontier was obtained, and a compromise solution was selected as the optimal design result. The weight of the optimized assembled wheel was 28.59% less than that of the same type cast aluminum alloy wheel. Test the optimized wheels referencing four finite element conditions, and validate the correctness of finite element models by comparing the simulation and test values of equivalent strain and maximum acceleration on measuring points. The simulation analyses were in agreement with the test results. A wheel structural design process and multi-objective optimization method based on the fatigue, 13° impact and 90° impact tests performance were realized in this article, providing the theoretical and technical basis for wheel optimization design.

With the application of new energy technology, hybrid agricultural machinery has been developed. This article designs a hybrid tractor energy management method to solve the problem of high energy consumption caused by significant load fluctuation of the tractor in field operation. This article first analyzes the characteristics of the hydrogen fuel cell, power battery, and ultracapacitor and designs a hybrid energy system for the tractor. Second, the energy management strategy (EMS) of multi-layer decoupling control based on the Haar wavelet and logic rule is designed to realize the multi-layer decoupling of high-frequency, low-frequency, and steady-state signals of load demand power. Then, the EMS redistributes the decoupled power signals to each energy source. Finally, a hardware-in-loop simulation experiment was carried out through the model. The results show that, compared with single-layer control strategies such as fuzzy control and power-following control, the multi-layer control strategy can allocate the demand power more reasonably, and the efficiency of the hydrogen fuel cell is the highest. The average efficiency of the hydrogen fuel cell was increased by 2.87% and 1.2%, respectively. Furthermore, the equivalent hydrogen consumption of the tractor was reduced by 17.06% and 5.41%, respectively, within the experimental cycle. It is shown that the multi-layer control strategy considering power fluctuation can improve the vehicle economy based on meeting the power demanded by the whole vehicle load.

In order to study the fatigue performance of wheel and enhance its lightweight design level, this article proposes the structure, design and optimization method of magnesium-aluminum alloy assembled wheel. Taking a [ ] type wheel as the research object, the optimal topology of wheel spoke is solved by constructing a topology optimization model for wheel bending and radial fatigue test conditions. A finite element model for bending and radial fatigue testing of assembled wheels was established, which simulates and analyzes the fatigue performance and its influencing factors of the wheel under two working conditions. Combined with contribution analysis method, the modified NSGA-II and entropy weight grey relation analysis (EGRA), the multi-objective optimization of assembled wheel was performed. The result demonstrated that the weight reduction of the assembled wheel after optimized design is 4.49%, while the bending fatigue life and radial fatigue safety factor are decreased by 9.95% and 25%, respectively. In order to better balance the performance of assembled wheel and achieve lightweight design, this article combines the joint topology optimization of assembled wheels with multi-objective optimization method for multiple working conditions and screens the optimal compromise solution by EGRA, which provides an approach for wheel lightweight design and multi-objective optimization.

In the past studies, the influence of wheel structure design and optimization on the aerodynamic drag of car and heat transfer performance of brake disc was less studied. To study the influence mechanism, the finite element model for wheel aerodynamic analysis was established using computational fluid dynamic method and the correctness of the model was verified by the wind tunnel test data. The influence mechanism of the flow field on aerodynamic drag of car and wheel and heat transfer performance of brake disc was studied. The influence of wheel disc structure on aerodynamic drag coefficient of the car and average convective heat transfer coefficient of the brake discs was studied. The parametric model of the wheel under the computational fluid dynamic analysis was established using mesh morphing technology. A total of 100 and 10 sample points were extracted using the Hammersley Design and Optimal Latin Hypercube Design, respectively, to fit the radial basis function surrogate model and test the accuracy of the surrogate model. Based on the established surrogate model, taking the minimum of the wheel mass, the minimum of the aerodynamic drag coefficient of the car and the maximum of the average surface convective heat transfer coefficient of brake discs as objectives and design variables of wheel as constraints to ensure the wheel structural strength, the non-dominated sorting genetic algorithm was adopted to carry out multi-objective optimization design for the wheel. Pareto frontier was obtained and a compromise solution was selected as the optimization design result. After the optimization design, the wheel mass is reduced by 8.28%, the aerodynamic drag coefficient of the car is reduced by 3.17% and the average surface convective heat transfer coefficient of brake discs is increased by 9.31%.