To enhance the computational efficiency of structural lightweight design for complex structures, a structural lightweight design method based on the Kriging surrogate model is proposed. The proposed method incorporates a hybrid addition strategy and a sample deletion strategy considering a distance threshold，aiming to rapidly improve the fitting accuracy of the Kriging surrogate model. This model was then applied to a multi-objective lightweight design model of the truck frame, with the optimization objectives of minimizing frame mass and maximum stress. Subsequently, the multi-objective lightweight model was solved using the non-dominated sorting genetic algorithm-II (NSGA-II). The results demonstrate that the proposed hybrid addition strategy and sample deletion strategy considering the distance threshold effectively enhance the update process of the Kriging surrogate model. The structural lightweight design method based on the Kriging surrogate model exhibits significant advantages in both computational efficiency and lightweight performance.

In view of the problem that the formulary design load based on the design standard can't truly reflect the actual service conditions of the welded frames of subway vehicles, and a large number of online measured data information has not been fully explored in the structural design of the frame, an anti-fatigue design spectrum compilation method based on the stress-time history sample information measured at the weak position of the subway vehicle frame was proposed.The small stress threshold value was determined by clustering ordered samples using the rain-flow counting method to compile measured stress spectrum reflecting structural damage, determining the stress-frequency-damage relation based on the fatigue damage theory, and using the methods of Bayesian parameter estimation and kernel density estimation to obtain stress extrapolation results. Considering the stress concentration caused by structural geometry changes in the cross-section of the welding site, the hot spot stress method and stress linearization method were used to obtain the stress concentration coefficient, and the measured stress spectrum was corrected to achieve the compilation of the design load spectrum. The research results show that the small stress threshold value is 3.18 MPa determined by extrapolation of stress extremes and the relation analysis between normalized stress-frequency-damage, which is 8.19% higher than the stress threshold value determined by traditional methods, the effect of discarding the number of small stress cycles is significant. Considering the load dispersion and stress concentration factor at the weld seam, while ensuring that the structure meets the current service conditions, the relation between the design mileage and equivalent stress is determined, the necessity of compiling the design spectrum is emphasized further. The above research builds the construction method of load spectrum compilation and the equal strength design of structures.

The gap between the rotor and the ball bearing in a wide temperature range increases with the increase in temperature. At the same time, the internal clearance of the bearing changes with the temperature. The inner ring of the bearing is subject to increased friction torque, which reduces its speed. This results in the deviation of the characteristic frequency of the outer ring defect, which is not conducive to the fault diagnosis of the ball bearing and the stable operation of the equipment. Considering the temperature-variable gap between the rotor and the bearing, a dynamic model of the bearing with an outer ring defect in a wide temperature range was established. The time-domain waveform and frequency of the model were analyzed. The simulation and test results show that the bearing vibration increases with the temperature, and the characteristic frequency of the outer ring defect decreases with the increasing temperature. Properly increasing the interference between the rotor and the bearing according to process requirements is beneficial for reducing the bearing system vibration in a wide temperature range and improving the accuracy of bearing defect frequency identification. The results provide reference for the use and health monitoring of ball bearings in a wide temperature range.

To address the issue of damage caused by low-speed impacts on composite material laminates coated with polyurethane coating, a numerical analysis method based on three-dimensional progressive cumulative damage in composite laminates and a yield damage criterion for polyurethane coatings was proposed. Firstly, a damage numerical model of polyurethane coating-carbon fiber reinforced composite laminates under erosion was established, and a Vumat subroutine was written. Subsequently, referring to the ASTM D7136 test standard, impact tests with various energy levels were conducted on samples coated with 1 mm and 2 mm polyurethane coatings and uncoated samples. Simultaneously, the proposed damage model was employed to study the formation reasons and propagation patterns of primary damages such as fiber damage, matrix damage, and delamination, thereby revealing the mechanism of polyurethane coating in absorbing impact energy. The results indicated that the mechanical response results calculated by the proposed damage model showed a high degree of agreement with the test results, validating the correctness of the proposed model. Additionally, comparative tests demonstrated the enhancement effect of polyurethane coating on the impact damage resistance of carbon fiber composite laminates. The findings of this study can provide a reference for the design of protective coatings for aircraft.

Rolling bearing looseness faults are likely to induce transmission system fault. Considering the factors such as nonlinear contact force of rolling bearings, rub-impact force, damping force between outer ring and housing, a six-degree-of-freedom nonlinear dynamics model was established under the fault of rolling bearing outer ring looseness, and the vibration characteristics of rolling bearing outer ring looseness were analyzed. The simulation results show that the characteristic frequency of the outer ring looseness fault is presented as the rotational frequency of the rotating shaft and its multiple components, and the actual tested wind power bearing ring fault data verifies the accuracy of the model. The results of this paper show that the rolling bearing outer ring looseness is caused by loosing between the outer ring and the housing, and the cyclic impact and friction between the outer ring and housing are formed under the unbalance force with the rotational speed of the shaft and its harmonics. The research results provide a theoretical basis for realizing the mechanism analysis of rolling bearing outer ring looseness and fault diagnosis of the rolling bearing.

Aiming at the problem of the low fault diagnosis accuracy caused by the lack of fault samples for the rolling bearings of doubly fed wind turbines under normal conditions for a long time, an improved generative adversarial network fault diagnosis method based on expanding high-quality fault samples and using dual feature extraction was proposed. Firstly,a finite number of rolling bearing fault samples were expanded through a Wasserstein type generative adversarial network with maximum mean discrepancy and penalty constraints. Secondly, based on the dual feature extraction model, the time-frequency converted temporal features and local features were extracted separately. Finally, the fault diagnosis of the rolling bearing balance data was completed through a classifier. The standard dataset and test results show that the proposed method improves the fault diagnosis performance while lacking fault samples.

To enhance the energy absorption efficiency of conventional sandwich panels, a biomimetic tree-like fractal core (BTLFC) inspired by the dendritic fractal structure of the royal lotus leaf vein was designed. Firstly, quasi-static compression tests revealed that the 2-order BTLFC exhibited a specific energy absorption 5.69% higher and an average load 4.46% greater than traditional honeycomb cores. Secondly, a finite element numerical model of the BTLFC was established;combined with quasi-static compression test data, the finite element model error was within 2.2%, demonstrating high accuracy of the model. Finally, Latin hypercube test design, Kriging surrogate model, and the non-dominated sorting genetic algorithm-II (NSGA-II) were employed to perform multi-objective optimization on the structural parameter combinations of the BTLFC (size ratio r, bifurcation angle θ, fractal order D). The optimized BTLFC structure exhibited superior comprehensive performance, with specific energy absorption increased by 10.19%, peak crushing force reduced by 12.27%,and mass decreased by 11.79% compared to traditional honeycomb cores. The findings provide novel biomimetic design insights for developing high-performance energy absorption structures.

To compensate for the intermittency of renewable energy generation, coal-fired power units are required to operate under low-load conditions over a long time, which causes the last stage blades of steam turbine low-pressure cylinders under small flow conditions persistently, leading to increased dynamic stresses and fatigue damage in the blades. To evaluate the safety of these last-stage blades, the fluid-structure interaction analysis of the last two-stage flow path and last stage rotating blades were conducted for a 660 MW air-cooled steam turbine under typical operating conditions. The results demonstrate that as the load decreases, both the maximum equivalent stress and deformation of the last stage rotating blades gradually diminish first, then slightly increasing. The maximum equivalent stress of the last stage rotating blades remains consistently below the material’s yield strength, indicating that the blades are in the stage of elastic deformation and no plastic deformation has occurred. Using the Goodman curve analysis method for the high-cycle fatigue life assessment of the last stage rotating blades, the dynamic stress levels of the last stage rotating blades fall within the safe zone of the Goodman curve,indicating that there is no risk of fatigue damage to the blades.

To investigate the influence of structural parameters on the yield strength and deformation behavior of truss lattice structures, face-centered cubic (FCC) porous lattices were fabricated and the mechanical responses were systematically studied. A finite element model was developed to evaluate the yield strength and failure modes of structures with varying geometric parameters. The analysis revealed a correlation between the member slenderness ratio and the transition from progressive collapse to global yielding under different loading orientations. Structures with lower slenderness ratios tend to exhibit global yielding, while those with higher slenderness ratios are prone to layer-by-layer compression failure.Furthermore, lattices supported along the face diagonals demonstrate more uniform global deformation, whereas those supported along the body diagonals are characterized by localized deformation.

To enhance the assembly connection performance of adhesive structures in heavy machinery and aerospace equipment, a numerical analysis model based on the cohesive force element was developed to investigate the failure behavior of adhesive joints. The evolution of shear stress distribution in the adhesive layer during the tensile-shear failure process under different loading stages was analyzed. The variations in ultimate failure load and structural stiffness with different adhesive joint parameters were systematically studied, and tensile-shear failure tests were conducted. The results indicate that the shear stress distribution in the adhesive layer transitions from an initial U-shaped profile to an M-shaped and finally evolves into an approximately inverted U-shaped pattern as the load increases. Increasing the length or width of the adhesive layer significantly improves both the ultimate failure load and overall structural stiffness. However, increasing the adhesive layer thickness or substrate thickness exhibits a minor effect on the ultimate failure load. Notably, the structural stiffness decreases with increasing adhesive thickness but increases with higher substrate thickness.