The slat of aircraft is subjected to the combined action of thermal load and aerodynamic force during its service, which has an impact on the safety of the structure. The typical aluminum alloy structure widely used in slat structure is taken as the main research object, and the stress distribution and structural strength under the combined action of heat and force were studied by experiment and finite element method. Firstly, in order to explore the influence of temperature on material properties, the linear tensile test of 2024-T62 rectangular thin plate and the high temperature tensile failure test of perforated thin plate were carried out under four different temperature conditions. The test shows that the high temperature environment has a reduction effect on the elastic modulus of the material, and at 190 °C, the bearing strength of the test piece decreased by 15%. Therefore, considering the reduction effect of temperature on material parameters can establish a more accurate model for predicting structural strength. Secondly, aiming at the thermal stress problem of aluminum alloy parts and structures, the test and simulation of aluminum alloy sheet and simplified slat structure under the combined action of heat and force were carried out respectively. A set of modeling method and thermal stress measurement test technology under the combined action of heat and force were established. The maximum error between the simulation and test results of aluminum alloy sheet is 10%. The thermal stress simulation of the simplified slat structure has a good trend compared with the experimental results, and the maximum error is 20%. In addition, through the experiment, it is also found that the thermal stress is particularly sensitive to the setting of boundary conditions. For the model with complex constraints, it is necessary to expand the modeling range to the stable boundary conditions to simulate the actual thermal stress.

In order to study the dynamic behavior of stiffened cylindrical shells with composite material sandwiched by co-cured damping films under the clamped boundary condition, the specimens of stiffened cylindrical shell with composite material sandwiched by co-cured damping films were prepared, and the dynamic modal test platform was set up. The fundamental frequency, damping ratio and modal shapes of stiffened cylindrical shell specimens were solved, and the accuracy of finite element model was verified. The influence of geometric parameters on structural vibration characteristics was further discussed by the numerical simulation method. The results show that, the fundamental frequency, damping ratio and modal shape of the structure will change abruptly when the height of stiffeners changes, and there is a suitable height value before the abrupt change to make the whole structure consider both damping and stiffness requirements; when the thickness of composite materials is constant, the fundamental frequency of the whole structure decreases gradually and the damping ratio increases gradually with the increase of the damping thickness or damping layer number of single layer; for the stiffened cylindrical shell of single layer damping composite materials, the closer the damping layer is to the inner skin, the higher the stiffness is, and vice versa, the damping capacity is better.

In order to gain insight into the stability of the tracking frame structure of shipborne large-aperture telescopes,the stability of typical ground-level telescope tracking frames was studied. According to the external load borne by the equipment in the case of ship, the external load was parameterized and entered into the finite element software. The pretreatment software and finite element software were used to analyze the structural deformation under static wind load. Then,the natural frequency of the structure was solved, and a simple response spectrum analysis calculation was proposed instead of the tedious random response analysis to analyze the stability of the equipment under dynamic wind load and wave excitation. According to the stress and deformation values obtained from the results, it was ensured that the shipborne telescope tracking frame theoretically meets the strength requirements and design accuracy requirements under shipborne conditions. Under the static wind load, the maximum stress value of the tracking frame structure is about 14.07 MPa, which was less than the yield strength of steel 355 MPa, the maximum deformation variable was about 0.02 mm, which was less than the design accuracy error coaxiality ϕ0.1 mm, and the natural frequency 1st-6th order mode value was 40.15, 49.65, 66.86, 82.93, 91.38,115.89 Hz. Under dynamic wind load, the peak value of structural stress was 3.92 MPa and the maximum deformation variable was 0.01 mm, and under the excitation of ocean waves, the peak of structural stress was 5.88 MPa and the maximum deformation variable was 0.02 mm, which was less than the yield strength and design accuracy error coaxiality of steel. The error between the modal value obtained by the modal test and the calculated modal value is within 10%. Combining theoretical simulation and practical tests, the tracker structure can work normally under shipborne conditions.

Aiming at the noise problem of the automobile electric seat adjuster, a pair of modified worm and modified helical gear was adopted for its main transmission system to reduce the meshing impact. The mathematical model was established, and several worms and helical gears with different modifications were processed. The noise test bench was built,and the acceleration spectrum of the automobile seat adjuster under the original models and different modifications were tested. Then the whole device’s noise reduction test was conducted with the optimized combination of tooth profile modification. The analysis results show that the appropriate profile modification of the worm and helical gear can effectively reduce the acceleration spectrum peak. With 0.04 mm and 0.02 mm modification respectively for the helical gear and the worm, the acceleration peak value of seat adjuster is significantly lower than that of the original product. The difference between the 6 sets of test products maximum noise and the standard products is within 1.6 dB, and the acceleration spectrum and acceleration peak of the experimental products are significantly reduced compared to the original product, which can verify noise reduction by the tooth profile modification of worm and helical gear pair is feasible.

The noise of automotive electronic water pump (EWP) is an important indicator of the performance of EWP,and its active control is conducive to improve the sound quality of the car. In order to achieve the active control of the noise of EWP, a hybrid random carrier space vector pulse width modulation (HRCSVPWM) strategy was proposed. Firstly, the Xorshift algorithm was used to design a random sequence generator to generate random numbers with good randomness to disperse a large number of harmonics concentrated in the carrier frequency and its integer multiples. Secondly, the sawtooth wave period function was combined to increase the weakening effect on the pulse width modulation (PWM) harmonic amplitude. Then, the simulation model of the EWP was constructed to investigate the harmonic suppression effects of control strategies of space vector pulse width modulation (SVPWM), random carrier space vector pulse width modulation (RCSVPWM) and HRCSVPWM, to verify the ability of HRCSVPWM to suppress PWM harmonics. Finally, EWP noise test platform was constructed to analyses the noise of EWP under three types of control strategies.The results show that the noise suppression effect of HRCSVPWM is remarkable, which can make the noise’s sound pressure level of EWP decrease significantly, with an average decrease of about 3 dB.

The fracturing pump plunger seal pair is one of the components most prone to failure at the hydraulic end of the fracturing pump due to its long-term operation under variable load，reciprocal friction and high pressure, and acidic fracturing fluid. To study the influence of interference magnitude, medium pressure, etc. on the sealing performance of V-shaped sealing ring, the assembly process of V-shaped sealing ring was simulated by using automatic shrinkage fit, the actual fluid pressure action condition of the V-shaped sealing ring was simulated based on fluid pressure penetration, and the finite element model of V-shaped sealing ring was established. Under quasi-static and dynamic sealing, the maximum Mises stress and the variation law of contact pressure of the V-shaped sealing ring were analyzed. A two-stage differential pressure plunger seal structure was proposed, and the sealing performance analysis of the structure was carried out. The results show that the maximum contact pressure of the seals all appear in the V-shaped sealing ring near the high-pressure fluid side, and the maximum stress is mainly in the lip and shoulder of the V-shaped sealing ring in contact with the support ring and press ring,the V-shaped sealing ring is more likely to fail on the side in contact with the plunger. The use of two-stage differential pressure plunger seal can effectively reduce the Mises stress, shear stress, and friction between the V-shaped sealing ring and the plunger, which can extend the working life of the fracturing pump plunger seal and improve the reliability and economy of the fracturing operation.

In order to improve the load-bearing efficiency of the stiffened conical shell in large launch vehicle, the lightweight design of the stiffened conical shell was carried out via a data-driven multi-fidelity approximate modeling optimization method. Aiming at the problems such as low efficiency and insufficient accuracy of the single fidelity approximate modeling optimization method, a data-driven multi-fidelity approximate modeling optimization framework was built based on variable-fidelity expected improvement (VF-EI) point criterion，and accordingly the optimization design of stiffened conical shell structure was carried out. Based on the finite element models of stiffened conical shells with different mesh sizes, a Co-Kriging multi-fidelity approximate model for the collapse load of stiffened conical shells was established. In the optimization iteration, multi-fidelity sampling points were generated by using VF-EI point criterion, and the global and local approximation accuracy of Co-Kriging multi-fidelity approximation model was improved sequently. Moreover, the optimization efficiency and accuracy of the proposed method were demonstrated by comparing with radial basis function approximation model and Kriging model. Besides, 11. 5% weight reduction of the optimized stiffened conical shell structure is obtained compared with the initial design, which has certain engineering application value.

Aiming at the storage life evaluation of photodetectors, a new evaluation method for multi-parameter competitive failure storage life assessment based on Monte-Carlo method was proposed. This method comprehensively considered whether the key performance parameters of the sample have deteriorated or improved trend. Firstly, the optimal degradation model with a single parameter was selected by performance degradation modeling, so that the pseudo-life of the sample with increasing degradation trend was calculated according to the failure threshold, and the pseudo-life was regarded as the right-censored data for the sample with decreasing degradation trend. Furthermore, the optimal distribution of a single performance parameter was selected based on the pseudo-life data combined with the expectation maximization(EM)algorithm, and then the competitive failure evaluation of multi-parameters was carried out by Monte-Carlo sampling method.According to the case analysis of the photodetector storage, the feasibility of this method was verified.

Impulse current under short-circuit condition is the key factor for the structural reliability of the testing transformer. Therefore, the structural reliability analysis model of transformers was proposed based on the probability density evolution theory. Firstly, the basic principle of probability density evolution theory was introduced, and the analysis method of electromagnetic force field for windings was given considering the coupling effects of magnetic and electric fields. On the basis，the numerical analysis model of transformers structure was constructed by using the Abaqus software finite element analysis method. Taking an AGF 20 kV testing transformer as an example, the above model was validated. The longitudinal Mises stress of windings was chosen as the control variable, and the stress distribution and probability density evolution characteristics were given. Then, the structural reliability index was calculated, and the extreme mechanical response and the corresponding distribution zones of windings and iron cores were discussed. The results show that the stress of windings increases significantly under the action of short-circuit impulse current. The maximum value of windings’stress reaches 82%of the threshold, and plays the key role in structural reliability, the increase of impedance has obvious influence on the reliability of transformers.

Coatings have extensively been used to the surfaces of critical components to enhance their service life, and the research on mechanical properties of coatings is essential for advancing this technology. TiAlN/Ti and TiN/Ti multilayer coatings were prepared on aluminum matrix composite surfaces by using the vacuum ion beam sputtering technique. The microstructure, phase composition，and mechanical properties of the coatings were characterized and analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), and nanoindentor. The dimensionless function correlation between mechanical properties of material with multilayer coatings and the loading/unloading parameters of nanoindentation was derived based on dimension analysis theory, and its explicit expression was determined in conjunction with the finite element simulation method. By establishing a nanoindentation simulation model for the multilayer coating, the impact of residual compressive stress on the tensile properties of the multilayer coating was analyzed. The results indicate that residual compressive stress can enhance the yield strength of the multilayer coatings. The residual compressive stress of TiN/Ti multilayer coating is -564 MPa, increasing the yield strength by 31.25%. Similarly, the residual compressive stress of TiAlN/Ti multilayer coating is -871 MPa, resulting in a 50% increase in yield strength. An important theoretical and test basis is proposed for quantitative analysis of the factors influencing the mechanical properties of coatings.