According to the requirements of rain ingestion of airworthiness regulations, the rain ingestion calculation was carried out for the no booster fan part. The movement trajectory of water droplets with different water speeds was studied based on Lagrangian particle tracking, and the separation amount of water droplets ingested to inner duct was obtained. Further more, the requirements for water spray speed from the rain ingestion test rig in the certification for turbofan engine was discussed,which can support the design and verification of rain ingestion airworthiness of turbofan engine. The results show that with the decrease of water speed, the amount of rain impacting on the fan blade and other walls increases, and no water droplets can pass through the fan blade and enter the inner duct. The water entering the engine inner duct at 250 m/s is 15.3 percent of the total amount of water, about 19.1 times of that at 10 m/s. Under the same water velocity, as the distance between the splitter and the fan blade decreases, the increase in water ingested to inner duct increases. At different fan rotational speeds, the change trend of the water ratio ingested to inner duct with initial water velocity is consistent, basically increasing with the increase in water drop velocity, and then remaining or slightly decreasing.

Understanding the failure mechanism of cracked rock mass under the general stress state is essential for underground engineering construction safety. A series of true triaxial fracture tests on the sandstone with single pre-existing flaw were conducted. The failure modes of the cracked sandstone were analysed, and the multi-scale fracture characteristics and mechanisms of the basic types of crack were identified. Moreover, the influences of the stress state and the pre-existing flaw on the rock failure mechanism were summarized. The results indicate that the rock failure mode is controlled by the true triaxial stress and the pre-existing crack. Based on the multi-scale fracture characteristics, the fracture mechanism of the crack. The rise of minimum principal stress σ₃ can significantly reduce the percentage of the shear crack, while the rise of intermediate principal stress σ₂ conduces to the increase of the percentage of the tensile crack. The pre-existing flaw has a certain promoting effect on the initiation of the tensile crack, however, the true triaxial stress is the decisive factor controlling the rock failure mechanism.

In order to analyze the influence of evolution of the dominant order of wheel polygonal wear on the vibration response of the train-bridge coupling system, the key influencing factors and evolution patterns of the dominant order of polygon wear were summarized first. Meanwhile, the coupled dynamic model of the train-bridge system was established by utilizing a combined simulation approach with ANSYS and SIMPACK. Subsequently, the impact of evolution of the dominant order of wheel polygonal wear on the vibration response of the train-bridge coupled system under different operational mileages, train operating speeds, vertical stiffness of fasteners, and variations in wheel diameter, was explored. The research results indicate that the evolution of the dominant order of wheel polygonal wear significantly affects the dynamic response of the train-bridge coupled system. In general, when the wheels experience high-order polygonal wear, the lateral and vertical accelerations at the mid-span of the bridge increase significantly. Moreover, the wheel-rail force and derailment coefficient also increase significantly, with the train wheels experiencing momentary bouncing. This has an impact on both the quality of high-speed train operation on the bridge and the safe operation of the bridge structure, necessitating timely wheel re-profiling.

In order to investigate the durability of fiber gypsum-based cementation material, a composite material was prepared by incorporating polypropylene and ramie fibers into high-strength gypsum, fly ash, and slag in a ratio of 44∶34∶22.Sodium methylsilicate was utilized for waterproofing the fiber gypsum-based cementitious material, and the effects of freeze-thaw cycles on its softening property, water absorption, and mass loss were studied after 5, 15, 25, 45, and 90 days under the combined action of H₂SO₄ or NaOH corrosion and freeze-thaw. Freeze-thaw strain testing, flexural and compressive strength testing, as well as industrial computed tomography(CT) scanning were conducted. The results indicate that fibers can mitigate both elastic and plastic deformation of the gypsum-based cementitious material during freeze-thaw cycles. Furthermore, under the combined effect of acid-base corrosion and freeze-thaw cycles, NaOH causes greater damage than H₂SO₄ does. After undergoing 90 days of freeze-thaw cycling with sodium methylsilicate treatment applied to it,the flexural and compressive softening coefficients increase by 0.28 and 0.13 respectively compared to specimens without waterproofing; meanwhile water absorption rates decrease by 1.56% while mass loss rates decreased by 9.52%. As freezing-and thawing times increase,pore development in specimens is still dominated by small holes,and crack diameters are mainly between 0.1~2 mm.

Based on the reservoir conditions of tight conglomerate reservoirs in the Mahu area of the Junggar Basin, an experiment was conducted to study the interaction between tight conglomerates, CO₂, and water. The results indicate that after CO₂ dissolves in water to form carbonic acid, it primarily reacts chemically with feldspar and calcite in the cement between the conglomerate grains. This leads to significant around-grain dissolution, with dissolution being the main process and precipitation being secondary. Ultimately, this increases the porosity and permeability of the rock, enhancing the reservoir fluid seepage capacity. The maximum increases in porosity and permeability are 3.65% and 87.36%, respectively. Additionally, the surface roughness of the rock increases after the interaction, with hydrophilic mineral quartz exposed on the surface. The water-phase wetting contact angle of the rock decreases by 7.4°, enhancing hydrophilicity. The CO₂ huff and puff process has a positive effect on improving oil recovery, with the main oil-increasing mechanisms being the enlargement of pore space to enhance fluid seepage capacity and the improvement of rock water-phase wettability, which increases reservoir water-phase imbibition capacity and crude oil mobility, thereby improving oil recovery.

In order to improve the output performance of permanent magnet assisted synchronous reluctance motor (PMa-SynRM), a multi-objective optimization design method for external rotor PMa-SynRM based on kernel extreme learning machine (KELM) and fast non-dominated sorting genetic algorithm (NSGA-II) was proposed. Firstly, the preliminary design of the PMa-SynRM rotor magnetic barrier was carried out and the working principle of the PMa-SynRM was analyzed. Secondly, the influence of each design variable on the optimization goal was evaluated through comprehensive sensitivity analysis, and the main optimization parameters were selected. Thirdly, with high output torque, high efficiency and low torque ripple as the optimization goals, a surrogate model based on KELM was established. Finally, NSGA-II was used for global optimization, and the optimal solution was selected from the Pareto frontier generated by NSGA-II, which was verified by finite element analysis. The simulation results show that the average torque of the optimized motor is increased by 15.83%, the torque ripple is reduced by 60.27%, and the efficiency of the optimized motor is also improved compared with the initial motor, which verifies the effectiveness of the optimized design method proposed in this paper.

In order to improve the control performance of a doubly-fed wind turbine grid-side converter under unbalanced and harmonic grid voltages, a direct power control algorithm with an improved super-helix fast terminal sliding mode was proposed. First, the mathematical model of the grid-side converter under unbalanced and harmonic grid voltages with power as the state variable was analyzed in a two-phase stationary coordinate system. Then, the power inner-loop design was carried out with a nonlinear expansion state observer for the negative sequence in the mathematical model as well as the disturbances due to each harmonic component. Secondly, to ensure that the system can reach the steady state in a shorter time, the non-singular fast terminal sliding mode surface was constructed and the sliding mode control law for the power inner loop was designed by combining with the improved super-helical sliding mode convergence law. Similarly the terminal sliding mode control rate was also designed for the voltage outer loop. The stability of the non-singular fast terminal sliding mode surface, the improved super-helix control algorithm and the nonlinear expanding state observer was also proved by using the Lyapunov function. Finally, the method was verified to have faster convergence and stronger robustness by comparing it with three different control schemes to perform simulations.

Under the background that the accuracy of voltage amplitude detection is increasing year by year, a voltage amplitude detection method based on improved second-order generalized integrator was proposed to solve the problem that the existing voltage amplitude detection methods were susceptible to the interference of harmonic and DC components, which leaded to insufficient detection accuracy. First, the composition change of voltage after fault was analyzed, and the existence of harmonic component and DC component in fault voltage was proved. Then, the principle and performance of voltage amplitude detection by sine-cosine component method and traditional second-order generalized integral method were analyzed. Then, the output of traditional second-order generalized integrator without DC component was taken as the input of the improved second-order generalized integrator’s second module. In this way, the effective filtering of the DC component was realized, and the Bode diagram, zero pole and step response of the improved second-order generalized integrator under different gain coefficients were analyzed. The optimal gain coefficient was selected considering the influence of filtering effect, stability and response speed. Finally, the simulation results show that the method proposed in this chapter has stronger filtering ability and higher precision than the other two methods.

Macro-encapsulated phase change material (PCM) capsules are the core components that form the heat storage tank of the packed bed. In order to enhance the heat storage rate of the packed bed tank, it is necessary to optimize the heat storage and discharge rate of individual PCM capsules. Four different encapsulated shapes of PCM capsules were established while ensuring the uniform volume of individual PCM capsules. The capsules were placed in a flow field with an obstruction rate of 0.5, and the melting and solidification processes of PCM under different encapsulation shapes were analyzed with full consideration of gravity direction and heat transfer fluid flow direction in practical applications. The results show that the natural convection of liquid PCM inside the capsule can accelerate the melting and solidification process of PCM and increase the rate of charging and discharging; compared with the spherical encapsulation capsule, the heat transfer area per unit volume of cylindrical encapsulation capsule is increased by 14.47% and the melting time of PCM is shortened by 42.50%. Therefore, the cylindrical encapsulated capsule has the best thermal performance, and the cylindrical capsule can be applied to the packed-bed storage tank in future research to optimize its thermal storage performance.

Transformer calibrators are a kind of equipment used to test the transformer error in the power system. With the development of technology, the transformer calibrator is also constantly innovating, from manual, and automatic to intelligent development, which has become a research hot spot. Two types of calibrators according to the usage method, namely the difference measurement method and the direct comparison method were introduced and the advantages and disadvantages of each method and related products were analyzed. Currently, digital calibrators had became a research hotspot because of their high degree of automation and multiple functions. The digital calibrator could be used for both conventional and non-conventional transformers, with a wide range of applications. Three key technologies that affect the accuracy of the digital calibrator are focused on by the paper. And a new technology based on small-signal on-site calibration were introduced, which had significant advantages over the current commonly used on-site calibration methods, with strong compatibility and high security, making the transformer calibration device smaller and more portable, and suitable for a wide range of occasions. Finally, it was pointed out that the transformer calibrator should continuously develop towards digitalization, intelligence, portability, accuracy improvement, and comprehensive performance improvement.