To study the effect of double circular holes on the mechanical properties of rocks and the crack extension process, a uniaxial compression model for rock specimens containing double circular holes was constructed, and the correctness and rationality of the numerical model were verified based on the comparison of the macroscopic mechanical parameters obtained from experiments and simulations. In addition, the crack extension process of specimens containing double circular holes and the evolution of the stress field around the circular holes were analyzed. The results show that the numerical simulation results are in good agreement with the experimental results；the initial tensile crack first sprouts at the upper and lower ends of the circular hole, and with the increase of axial stress, structural weak zones are usually formed at the left and right sides of the hole wall. The sprouting direction of the initial tensile crack is in the axial load-ing direction, independent of the orientation angle α, but the damage pattern of the specimen is influenced by the orientation angle α. The initial tensile crack is generated in the tensile stress concentration area；the tensile stress concentration area at the upper and lower ends of the circular hole moves and dissipates accordingly with the expansion of the initial tensile crack. The compressive stress concentration area of the stress component σ_yy is located on the left and right sides of the circular hole, while a shielding area of compressive stress is formed at the upper and lower ends of the circular hole, and the smaller the distance from the vertical center line of the circular hole, the stronger the shielding effect and the weaker the compressive stress.

The modeling of the passive dynamic walker of flexible legged rimless wheel is studied, and the influence of damping coefficient on system dynamics is analyzed. According to the geometric characteristics of the walker, the independent generalized coordinates are selected to describe the position of the system, and the second kind of Lagrange equation is used to establish the dynamic model of the passive dynamic walker of flexible legged rimless wheel. By analyzing the structure and physical properties of the flexible leg, it is concluded that the impact occurs in the tangential direction of the telescopic leg and the impact force is not transmitted between the leg and the ground in the radial direction during the impact stage, and a state jump model under the assumption of partial impact is proposed. The numerical simulation of passive dynamic walking of flexible legged rimless wheels using different damping parameters verifies the effective-ness of the proposed method. When a larger damping coefficient is selected, the double-limb support period of periodic walking accounts for 77.6% of the whole walking cycle, while the single-limb support period accounts for 22.4% of the whole walking cycle. The periodic walking can be achieved when the slope angle is in the range of 0.1-0.7 rad. The slope angle of the flexible legged rimless wheel that can passively and dynamically walk on decreases as the damping coefficient decreases.

In this paper, the effects of doping elements（Re and Ru）content on the stability and occupancy orientation of a Ni-Al binary model nickel-based single-crystal superalloy are studied by using first-principles calculations. The results show that the total energy of the system decreases gradually with the increase of the content of Re and Ru elements, which suggests that the stability of the system is improved. The system using Ru to replace Ni has the lowest stability, while the stability of system is the best by using Re to replace Al. Therefore, Re and Ru are more inclined to replace Al, which is consistent with the previous experimental results. Meanwhile, compared to other contents of Re and Ru, when Re and Ru with the content of about 1.4% are used to replace Al, the substitution formation energy is the lowest. Furthermore, two different stacking fault modes are obtained by deleting a layer of atoms in the Ni-Al binary model. Research on these two stacking fault modes indicates that replacing Al with Re and Ru can improve the stability of the systems, and systems containing Re are more stable, which have lower substitution formation energy compared to replacing Al with Ru. However, for different stacking fault modes, when replacing Al with Re and Ru, the content of Re and Ru is different for the best of a stable system and the lowest of substitution formation energy and stacking fault energy. Replacing Al with Re results in a better stability in stacking fault systems, but the content of Re in the most stable system depends on the selected stacking fault mode.

In steel-concrete composite structures, due to the existence of certain interface slip and web shear deformation, the assumption of flat section is no longer applicable. In order to scientifically study the effects of shear deformation and interface slip on the deflection and interface slip of composite beams, this paper adopts Goodman's assumption and Timoshenko beam's double generalized displacement assumption, introduces the strain relationship of composite beams and element microsegment mechanical equilibrium, and derives the elastic bending differential equation of double inverted T-shaped steel-concrete composite beams considering shear deformation and interface slip. Then based on the equivalent spring model and the equivalent rod spring model, a theoretical calculation formula for the elastic shear stiffness of the embedded web connection is derived. By using the known deformation and constraint conditions of the composite beam, we obtain the analytical solution of deflection and slip of the simply supported composite beam under concentrated load in the span and verify it through the experimental results of four double inverted T-shaped steel-concrete composite beams with different parameters. The results show that the deflection and slip values obtained from theoretical calculations are in good agreement with the measured values, and the correctness of the theoretical calculation formula for the elastic shear stiffness of the embedded web connection is verified. In the deflection deformation of double inverted T-shaped composite beams, the deflection value caused by bending accounts for about 56% of the total deflection, the deflection value caused by interface slip accounts for about 36% of the total deflection, and the deflection value caused by shear deformation accounts for about 8% of the total deflection. This article comprehensively considers the effects of shear deformation and interface slip on the deflection and slip of composite beams, and makes a significant improvement compared to the model structure that does not consider shear deformation and interface slip.

In order to determine the influence of aggregate irregularity on the mechanical properties and failure morphology of concrete, Python programs were developed to generate randomly distributed aggregate models with different sharpness in ABAQUS, and the 0-thickness cohesive element and variable-thickness solid interface transition zone（ITZ）were established respectively. First, the reliability of model was determined by changing mesh size and friction coefficient between the loading pad and concrete compared with the experiment. Then, the quality of two ITZ modeling methods was analyzed. Finally, the uniaxial compression mechanical behavior of the three-dimensional meso-concrete model was analyzed from the aspects of stress-strain curve, fracture propagation, and energy dissipation. The simulation results show that the 0 thickness cohesive ITZ and the solid thickness ITZ model can predict the compressive strength of concrete, and the stress-strain curve and failure morphology of the ITZ model with solid thickness are more consistent with the experiment. The fracture propagation of concrete is obviously affected by the shape parameters of aggregate. The interior and surface of the spherical aggregate model are penetrating cracks. The strain energy of polyhedral aggregate model is larger, and there are many micro-cracks in the concrete, the possibility being compressed and destroyed into more fragments is higher. With the increase of aggregate irregularity, the compressive strength of concrete increases slightly, but the peak strain is not affected.

In order to characterize the distribution law of active earth pressure with depth for a circular platform foundation pit under transient infiltrations, this study derived the slip line equation for the active earth pressure of circular platform foundation pits. The derivation was based on the strength equation of generalized effective stress for unsaturated soils and matric suction under transient infiltration conditions. Subsequently, the differential iterative method was adopted to obtain the slip line solution of active earth pressure for circular platform foundation pits under transient infiltrations. Last, the accuracy of the obtained slip line solution was verified, and an influencing factor analysis was conducted. The results indicate that the obtained slip line solution, compared with the existing solutions, can reasonably account for comprehen-sive influences of transient infiltration（time, infiltration ratio, nonlinear profiles of suction stress）, soil types（sand, silt, clay）, foundation pit model parameters（wall dip angle, wall-soil friction angle）, and the circumferential stress coefficient on the active earth pressure of foundation pits. The accuracy of the obtained slip line solution of active earth pressure under specific reduced conditions is demonstrated by comparing it with the slip line solution of circular platform foundation pits in saturated soils（when suction stress is zero）, and the limit equilibrium solution of plane retaining walls under transient infiltrations（when the radius of foundation pit tends to infinity）reported in the literature. The influence of time and infiltration ratio on the value and distribution of active earth pressure is most pronounced for foundation pits in clay, followed by foundation pits in silt. However, it is negligible for foundation pits in sand, which is caused by nonlinear profiles of suction stress for different soils. The active earth pressure of foundation pits decreases significantly with the increase of wall dip angle, wall-soil friction angle and circumferential stress coefficient, while its distribution and change with depth are closely related to soil types.

In the past decade, approximately one-third of civil aviation safety incidents have been related to landing, with hard landings comprising one-fifth of these landing-related incidents. Hard landings not only damage aircraft structures but also can lead to aircraft destruction or loss of life in severe cases. However, statistical data on hard landings remain limited. This paper systematically analyzes hard landing criteria through a review of quantitative standards, simulation analysis, and machine learning techniques. It also conducts a statistical examination of 53 typical hard landing incidents of mainstream aircraft such as Boeing-737 and Airbus-A320 over the past decade, offering a detailed exploration of common structural damage patterns associated with hard landings. Results show that heavy landing incidents often cause damage of different degrees to the aircraft's landing gear, fuselage, wings, and other key components. Moreover, the extent of damage differs significantly among various types of heavy landing incidents.

Hypersonic aircraft face extremely high aerodynamic resistance and heating during flight, posing a threat to flight safety and stability. Taguchi-gray correlation method is utilized to study the impact of size on the resistance and heat reduction performance of hypersonic aircraft. An orthogonal test is conducted, wherein design factors such as spike length-diameter ratio, airway diameter ratio, pneumatic disk diameter ratio, and lateral jet angle are considered. The response targets comprise total flight resistance, peak pressure coefficient, and Stanton number. Test results are obtained through numerical simulation. The findings indicate that the flight resistance is most significantly affected by the length-diameter ratio of the spike，while the lateral jet angle has the least effect. In regard to the peak pressure coefficient and Stanton number，the size factors exhibit a similar rank of influence. Among these factors，the length-diameter ratio of the pneumatic disk exerts the most significant impact. Increasing the length-diameter ratio of the spike and the diameter ratio of the pneumatic disk can effectively improve overall resistance and heat reduction performance. However，it should be noted that as the size increases，the lifting efficiency gradually diminishes. In comparison to the optimal group of orthogonal design，the optimized configuration demonstrates an overall performance improvement of 4.6%，thus indicating a favorable optimization effect.