Taking a 1.5 MW wind turbine tower with different initial crack lengths as the research object, vertical and horizontal earthquake loads with four earthquake intensities and three actual earthquakes were applied, respectively. The influence of vertical and horizontal earthquake loads on the strain field at the crack tip of the wind turbine tower was studied and compared. The results indicate that both under vertical and horizontal earthquake loads, the equivalen plastic strain area at the crack tip increases with the increase of earthquake intensity, but under horizontal earthquake loads, the equivalent plastic strain area at the crack tip increases more rapidly. Under earthquake intensities of Ⅵ and Ⅶ, the impact of vertical earthquake loads is greater than that of horizontal earthquake loads. As the earthquake intensity increases, the impact of horizontal earthquake loads increases sharply under earthquake intensities of Ⅷ and Ⅸ, and far exceeding the impact of vertical earthquake loads. The impact of vertical actual earthquake load on the crack tip equivalent plastic strain area is related to the magnitude and earthquake acceleration time-history curve, while the impact of horizontal actual earthquake load on the crack tip equivalent plastic strain area is related to the earthquake acceleration time-history curve.

The traditional Paris formula ignores the influence of various uncertain factors in the crack growth process,which leads to a big difference between the predicted crack growth process and the real crack growth process. In order to improve the prediction accuracy of fatigue crack growth, a fatigue crack growth prediction method based on the improved particle swarm optimization particle filtering (IPSO-PF) algorithm was proposed. Firstly, based on the framework of the particle filtering (PF) algorithm, the particle swarm optimization (PSO) algorithm was used to optimize some particles based on the updated observation information，keeping the state of particles with large weights unchanged, and particles with small weights tend to high likelihood region, and IPSO-PF algorithm was designed. Then，combining IPSO-PF algorithm with Paris formula, a fatigue crack growth prediction model based on Paris formula and IPSO-PF algorithm was constructed. Finally, the validity of the model was verified by using the open 2024-T351 aluminum alloy data set. The results show that compared with the traditional PF algorithm, IPSO-PF algorithm can improve the diversity of particles. The prediction error of the crack growth prediction model based on IPSO-PF algorithm is 2.6%, which is better than 9.2% based on PF algorithm.

Due to the similarity between the internal structure of wind turbine blades and plant leaves, a new type of bionic leaf vein structural distribution was proposed, along with an entire composite blade layup program based on the bionic method of applying the mid-axis morphology of plant blades to 5 MW wind turbine blades. The modal analysis and static analysis of the new bionic vein blade were performed using the fluid-solid coupling method. The results show that the first six-order of the nature frequency of the bionic blade are improved in comparison to the traditional layup blade and are difficult to resonate, as well as its torsion resistance. Under the extreme wind load of 50 m/s, the displacement of the bionic blade’s tip is significantly smaller than that of the traditional blade, and the distribution of the strain and the distribution of the shear stress are more uniform than those of the traditional layup blade, but the maximum value of shear stress rises.

To address the creep issue that arises during the long-term vertical storage of solid rocket motor (SRM), a method was proposed that involved embedding a specially shaped functional combustible core model (reinforcement structure) into the propellant grain matrix without altering the basic structure of the grain. Initially, the distribution patterns of creep in the propellant grain under the coupled effect of solidification cooling and vertical self-weight were analyzed by using three-dimensional numerical simulation methods. Subsequently, the reinforcement structure was designed by using the solid isotropic material with penalization (SIMP) method for topology optimization, determining the geometric configuration of the embedded reinforcement structure. Finally, the final optimized design results were determined through comparative analysis of the anti-creep effect of the topology-optimized reinforcement structure. The research results demonstrate that the deformation stress and strain of the solid rocket motor propellant grain with the reinforcement structure are significantly reduced compared to those without the reinforcement structure, effectively suppressing the creep of the grain.

Metal structures are widely used in industry. Metal structures in service are prone to crack defects under tensile and compressive fatigue load.In order to realize quantitative detection of metal structures’ crack defects, a quantitative analysis method of metal structures’ weak magnetic detection based on back propagation (BP) neural network was studied. In view of the poor effect and low efficiency of BP neural network in parameter adjustment, the improved whale optimization algorithm (IWOA) based on Sine chaotic mapping was adopted to optimize the BP neural network parameter adjustment mode,giving consideration to global optimization while improving the local optimization ability, and then the optimal parameters searched by IWOA were assigned to BP neural network, improving the quality of initial network parameters.The length, width and depth of the artificial rectangular slot were quantified by inversion. The results show that the average prediction accuracy of IWOA-BP neural network is above 80%, and the prediction accuracy of depth, length and width is improved respectively by 106.72%, 9.68% and 6.86%.

High-speed machining technology by improving the cutting speed and feed rate to improve the material cutting rate, machining accuracy and machining quality, is one of the main ways of modern processing. Therefore, to ensure the stability of high-speed machining is the basis of application of high-speed machining. Firstly, based on the traditional stability analysis, the influence of feed rate on the static cutting thickness was further considered, the stability model related to feed rate and radial cutting depth ratio of tool was established, and the stability of high-speed milling was analyzed by combining stability variance ratio. Secondly, based on the single factor variable feed rate test, a filter was designed to filter the frequency component of the spindle speed. The variance ratio between the filtered signal sequence and the original signal sequence was used to analyze the milling stability changes of the continuous variable axial depth test, and the validity of the analysis method considering the feed rate to affect the stability of high-speed milling was verified. The results show that the proposed method can determine milling stability more accurately for high-speed machining with small radial cutting depth. And the axial cutting depth of unstable cutting limit changes slightly with the increase of feed rate, and the feed rate will aggravate the instability of milling system.

To solve the problems of high-power downstream belt conveyors in large inclination angles, high belt speed conditions which are very prone to flying cars and belt breakage, a kind of disk-type adjustable permanent magnet damping roller device was put forward by adjusting the size of the area of engagement between the permanent magnet and the coil to realize the braking adjustment. The Maxwell software was used to study the transient magnetic density distribution law of the disk-type permanent magnet damping device under stable conditions and the changing law of damping torque by different air gap thicknesses, and the test bench was built for test verification. The results show that with the increase of the air gap thickness, the magnetic density gradually increases, up to 2.1 T. The damping moment increase when air gap thickness is from 1 mm to 2 mm, the damping moment decrease when from 2 mm to 3.5 mm. The research can provide data support for improving and optimizing high-power downstream belt conveyors.

In order to construct a bone scaffold structure with good biological properties, P-type, FRD-type homogeneous multi-porous scaffolds and P&FRD gradient multi-porous scaffolds with different porosities and unit cell scales were designed based on the triply periodic minimal surface（TPMS）.The effects of unit cell types, porosities and unit cell scales on the mechanical and biological properties of TPMS multi-porous scaffolds were investigated by tests and finite element simulation.The results show that the internal pores of homogeneous and gradient multi-porous scaffolds based on TPMS have good connectivity.The mechanical properties of multi-porous scaffolds decrease with the increase of porosity, but the permeability increases with the increase of porosity.Increasing the unit cell scale can significantly improve the permeability of multi-porous scaffolds.The permeability of the gradient multi-porous scaffold is also affected by the seepage direction.The gradient multi-porous scaffolds can synthesize the performance characteristics of each homogeneous unit cell structure, and show different mechanical and biological properties in different regions of the scaffold, which is closer to the structure and biological properties of human bone.

A single-degree-of-freedom mechanical collision vibration system model with nonlinear terms and unilateral new nonlinear constraints was studied.The dynamics characteristics of the p/1 periodic motion of the system under low-frequency excitation were analyzed by using the variable-step fourth-order Runge-Kutta numerical algorithm and multi-parameter co-simulation.And the frequency hysteresis characteristics of the grazing bifurcation and saddle-node bifurcation in the p/1 periodic motion were analyzed.It was found that two different motions will exist at the same time，revealing the irreversibility of the transition between adjacent periodic motions.Finally, the influence of the change of the gap on the multi-state coexistence region of the system was studied.As the gap increases, the coexistence region of partial periodic motion decreases and transits to the low-frequency region.

As the key equipment for collecting signals, the coupling performance of oil and gas exploration geophone and earth vibration affects the quality of collected signals and determines the exploration accuracy. In order to improve the exploration ability of the geophone, the structure of the tail vertebra of the geophone was taken as the research object. Based on the single-degree-of-freedom coupling vibration theory, a vibration model for the coupling of the tail vertebra of the geophone and the earth surface under the sweep frequency signal was proposed. The acceleration,velocity and displacement response of the received signal of the tail vertebra of the geophone under the sweep frequency were extracted and analyzed.The coupling degree evaluation index of the mean value of vibration displacement and the standard deviation of vibration acceleration was established, and the coupling degree response of the tail vertebra of the geophone and the earth was mastered.Through the geophone receiving test, the maximum error between the acceleration signal received by the geophone tail vertebra and the acceleration signal received by the test was less than 15%, which verified the correctness of the model and method. Finally, based on the response surface method, the key parameters of the length and radius of the tail vertebra under different shapes were optimized. The results show that the coupling degree of the tail vertebra under the triangular pyramid shape is the best. The coupling mean value of the displacement of the optimized ground-geophone tail vertebra is reduced by 7.94%, and the standard deviation of the acceleration is reduced by 6.42%, which effectively improve the ability of the geophone tail vertebra to receive signals.