In order to ensure the safe and stable operation of gas turbine units, and grasp the heat transfer mechanism of the ventilation system of the mainframe housing, a study on the ventilation and heat dissipation of the main engine box of gas turbine units was carried out. Based on the principle of field synergy, the internal flow field, temperature field and heat dissipation performance of key equipments in the mainframe cabinet were analysed, and an optimized scheme for adding a flow-guiding device was proposed. The results show that the volume of the high-temperature area inside the mainframe housing is 7.6%, mainly concentrated near the gas turbine shaft component, which is the main heat source inside the mainframe housing, with an average external surface temperature of 86.94 ℃. After the installation of a 50° flow-guiding device, the volume of the high-temperature area inside the mainframe housing is reduced to 5.1%, and the average external surface temperature of the gas turbine shaft is reduced to 81.98 ℃. The heat dissipation effect is significantly improved.

The mechanical response of external rotor direct drive generator under time-varying loads is analyzed theoretically, calculated by simulation and verified by test. Firstly, the source of magnetic pull of the rotor core of the external rotor generator and its variation with load were analyzed. The expression of magnetic pull of the rotor and the characteristics of time and space order were determined. The basic vibration model of the external rotor core was analyzed, and the basic vibration equation of the external rotor core was determined. Then the simulation model of the external rotor generator was established, and the spatiotemporal order characteristics of the magnetic pull and the typical daily variation rule with time were obtained. The magnetic pull density obtained from the electromagnetic field was used as the input load to guide the structure field. The magnetic-solid coupling simulation was carried out, and the deformation and stress distribution and noise response of the external rotor core were calculated and analyzed. Finally, a simulation example of a 13 kW external rotor direct-drive generator proved the correctness of the analysis and simulation. The results of the study determined the time-varying load on the outer rotor core and its mechanical response distribution. It is found that the time and position of the rotor core should be tested emphatically when the generator is running. Noise characteristics under time-varying loads are also analyzed. The analysis provides reference for the maintenance and design of the generator.

The bearing section of the work roll neck often suffers burnout failure due to bearing seizure, and additive manufacturing is usually used in the field to repair it. Life prediction of the repaired roll neck is the key to predict the safe service of the work roll in the field production and carry out overhaul，but there is a lack of research on the related issues. In view of the above problems, the stress analysis and multi-axis life prediction of the working roll neck bearing section of the four-high mill were carried out. Based on the SIMS model and the influence function method, the rolling force and the stress between the rolls were calculated. The moment balance equation of the roll neck end was established in the bearing section,and the bending stress model of the roll neck bearing section was established. The deformation resistance was regarded as the plastic deformation energy per unit volume to calculate the rolling torque in the deformation zone, and the torsional shear stress model of the roll neck bearing section was established. Using the first strength theory, the equivalent stress was obtained by combining the bending stress and the torsional shear stress. On the basis of proving the calculation accuracy of the model,the multi-axis fatigue model was used to predict the fatigue life of the roll neck bearing section, and compared with the service life of the actual roll in the production line. The results show that the stress calculation model of the working roll neck bearing section of the four-high mill is in line with the actual stress state of the roll neck. The error between the expected service life predicted by the theoretical model and the actual service life is less than 20%, which meets the actual engineering error requirements.

In order to investigate the compression damage evolution of carbon fiber laminates with wrinkles and accurately predict the mechanical behavior of damage initiation and propagation, a progressive damage finite element model was proposed based on three-dimensional elastic theory by employing a spatial decomposition of damage variables method to establish the damage constitutive relation. Firstly, the maximum stress and Puck failure criteria were used to predict the intralaminar damage initiation, and the damage variables were calculated in combination with the mixed-mode damage evolution law. Secondly, based on the physical meaning of the damage variables, a spatial decomposition was carried out in the fracture plane coordinate system, and the damage constitutive relation was derived by substituting the damage stiffness matrix.Then in order to predict the interlaminar stress state and damage behavior of laminates, a cohesive zone model with a bilinear traction-separation law was adopted. Finally the corresponding Vumat subroutine was developed and implemented in Abaqus software for the numerical simulation analysis of quasi-static compression loading at 0.25 mm/min.The stress-displacement curves and damage distribution of laminates predicted by the finite element model are in good agreement with test results. The proposed calculation method is simple and direct for determining true stress, making it convenient for analyzing and identifying the damage location and damage evolution of composite laminates with wrinkles.

The gearbox of wind turbine is in the complex environment such as random wind load for a long time, and the gear contact fatigue becomes a key factor limiting the stability and reliability of wind turbine equipment. The research on the gear contact damage evolution mechanism is faced with difficulties such as complex stress states, damage anisotropy and failure modeling. Material configurational force theory can describe the effect of defect configurational change on the free energy of materials and can be used to predict the damage and failure behavior of materials. A wind turbine gear contact damage model was constructed based on this theory. The gear contact interface stress field simulation analysis was carried out for the key bearing area of gear contact, and the gear contact damage evolution process under contact load was simulated. The results show that the configurational force theory damage model can effectively simulate the contact damage phenomenon of gear and explain the pitting and spalling of gear surfaces. It has significance to predict contact fatigue life of gears accurately.

In view of the difficulty of obtaining durability test specifications for axle components, a method of constructing driving load of the front axle dynamic model was proposed to provide the input for system-level bench test and life verification of front axle components. The life of front axle was obtained based on the whole vehicle dynamics model and the measured road load, and the useful information and life prediction results in the above process were employed to guide the construction of driving load applied on front axle. Firstly, the frequency band of the measured six-component forces at the wheel center was adjusted. Then, with the goal of minimizing the difference between the damage/life of the front axle and the reference value under each working condition, the adjustment coefficient of the amplitude of the three-way forces at the wheel center was optimized by combining the response surface method and genetic algorithm. The optimized three-way forces at the wheel center and the other three-way torques constituted the driving signal of the front axle model. The results show that the constructed wheel center drive signal is used to simulate the dynamic load of the front axle model. The life of the front axle,the failure sequence of risk points and the damage contribution ratio of various road conditions to dangerous points are obtained and in good agreement with the reference results, which verified the effectiveness of the proposed method and provided reference for the drive signal construction and component life evaluation of system-level bench durability test.Finally, the damage distribution of the front axle can be consistent with the reference results by modifying the main damage load of the shaft tube.

In order to simulate the crack propagation by corrosion fatigue, a coupled peridynamics corrosion-fatigue fracture model was proposed and applied to the simulation and analysis of crack propagation in A7N01P-T4 aluminum alloy.In this model, the interaction of hydrogen and stress was used to reflect the synergy between the two mechanisms of anodic dissolution and hydrogen cracking in corrosion, and the corrosion solution step and the mechanical solution step were coupled when quantifying the fracture behavior of the material due to corrosion. Since hydrogen reduces the plasticity of the material and brittle fracture occurs, a bonded peridynamics theory suitable for simulating isotropic brittle damage was used, and the relation between near-field force and elongation was described using an intrinsic force function for quasi-brittle materials that incorporates both linear and nonlinear mechanical behavior. The feasibility of the model is verified by comparing the simulation results with the test results of A7N01P-T4 aluminum alloy in 3.5% NaCl solution, and it is found that the results are in good agreement between them.

At present, the research on supersonic civil aircraft wings mainly focuses on the low sonic boom design and supersonic drag reduction technologies. There are relatively few studies on the wing structural design. Therefore, a multi-level optimization method for the wing structural design in the preliminary design stage of supersonic civil aircrafts was proposed. It included the parametric modeling of the wing structural layout, the automatic generation of the finite element model for the structural size optimization, construction and training of a surrogate model for the deep neural network. And the optimization was solved based on the deep neural network. The analysis results show that the proposed optimization strategy could quickly design the wing structure of the supersonic civil aircraft. The deep neural network model has higher prediction accuracy than the traditional surrogate model. Thus, the proposed approach can improve the efficiency of the preliminary design for wing structure.

The relative curvature of the spur gear mesh point is one of the key geometric parameters of the tooth profile,which has a significant impact on the stress distribution and mesh stiffness of the gear. Starting from the relevant research on constant relative curvature (CRC) gears, three types of non-involute spur gear tooth profiles were constructed based on the relative curvature control strategy considering the time-varying mesh characteristics of gears, and the mesh simulation of gear pairs was implemented. The influence of relative curvature control on the maximum contact stress, maximum bending stress,and mesh stiffness of gears was analyzed. The effectiveness of the control strategy was verified. This work provides some reference for the design of spur gears based on the relative curvature control.

Sandwich structures composed of PET foam core and aluminium alloy panel were taken as reserch object. In the process of fabricating sandwich structures, four types of core materials were employed. Firstly, untreated PET foam core and PET foam cores subjected to subtractive process treatment (unidirectional slotting, bidirectional slotting，and punching).Secondly, the peel resistance performance between the aluminium alloy panel and PET foam core was tested through the drum peel test, while the influence of material subtractive process on shear performance of the sandwich structures was evaluated through the pure shear test. Finally, the peel and shear failure modes, load-displacement responses, and peel and shear strengths of the structures were analysed. The results show that the peel strength between the panel and PET foam core is improved by 48.31%, 32.29%, and 16.67% respectively, compared with the untreated structure, by using bidirectional slotting, unidirectional slotting and punching processes. Although the three processing techniques cause damage to the PET foam core, they actually increase respectively the shear yield strength of the sandwich structures by 3.12%, 3.90%, and 2.92%, compared to the untreated structure.