In this paper we systematically introduce the research progress in compressible flow around a circular cylinder, which serves as a theoretical model for numerous engineering problems in aerodynamics, thermodynamics, and other fields. Studying the flow characteristics and influential factors of compressible flow around a cylinder is of practical significance for solving engineering problems and contributes to the theoretical development of compressible fluid mechanics. The paper summarizes recent research findings based on different ranges of inflow Mach numbers, including results in subsonic, transonic, and supersonic regimes. It covers aspects such as Mach number effects, shock wave structures, interactions between shock waves and vortices, as well as flow control methods. Finally, the paper provides an outlook on future research directions.

This paper presents an analytical form of equivalent stiffness lines on the surface of a conical lattice shell with spiral and ring ribs to obtain the lightest weight grid stiffened shell structure under prescribed mechanical constraints. The lightest weight structural parameters are obtained through parameterized finite element modeling and SVR (Support Vector Regression) method combined with NSGA-II (Non-dominated Sorting Genetic Algorithm-Ⅱ) algorithm. The results indicate that the surrogate model based on the SVR method has good reliability in predicting the critical buckling load of grid reinforced shell structures. The method of NSGA-II combined with parameterized finite element modeling can be used to effectively obtain the lightest mass parameters of the structure. Compared to the original geodesic structural design, the utilization of equal stiffness design can significantly improve the weight reduction of the structures.

Metal materials often show different mechanical behavior and fatigue characteristics in rolling direction and transverse direction. A series of uniaxial tensile tests and crack propagation tests with stress ratio R of 0.1, 0.3 and 0.5 were carried out for 6061 aluminum alloy by sampling parallel to the rolling direction (RD) and perpendicular to the rolling direction (VD). The results show that there is no obvious difference in tensile properties between RD and VD samples, whereas significant difference of 30 % in fatigue life, with the crack growth rate of RD sample higher than that of VD sample. Through SEM fracture analysis, it was found that the fringe width of RD sample was 25 % higher than that of VD sample under stable expansion zone R = 0.1, and 50 % higher under R = 0.5. Chain inclusions could be observed on the fracture surface during the unstable expansion stage, leading to accelerated crack growth. In addition, in this paper we combined Abaqus software and XFEM analysis technology to obtain the crack growth paths and lifetimes of the two samples, which are in good agreement with the test results.

Conducting reliability analysis of landing gear motion mechanisms plays a crucial role in ensuring normal takeoff and landing of aircraft. To improve the efficiency of reliability analysis of landing gear motion mechanisms under imprecise probability conditions, an imprecise probability directional sampling method has been developed. First, parameterization of the established multi-body dynamics simulation model of the landing gear is conducted. Consider the case where the input variables contain interval distribution parameters, a limit state function based on the actual engineering parameters is established to form the reliability analysis model. Secondly, combining the imprecise probability random simulation method with the directional sampling method, the expressions and estimation errors of each component function are derived to form the imprecise probability directional sampling method, which improves the low computational efficiency of the current method in highly nonlinear limit state surface situations. Finally, the effectiveness of the proposed method is verified through a numerical example. The developed method was used to calculate and analyze the failure probability change curve of important components of the landing gear motion mechanism, providing new thoughts and methods for improving the reliability analysis efficiency in imprecise probability situations.

Due to the nanoscale thickness of suspended two-dimensional (2D) materials, stretching instability wrinkles are prone to be introduced during the preparation process. However, the influence of wrinkles on the indentation response of two-dimensional materials is usually ignored. In this paper, the influence of wrinkles on the bending indentation response of 2D materials is investigated through theoretical analysis, and a model for the bending indentation response of 2D materials with wrinkles is proposed. It is found that under the action of central concentrated force, the bending deflection of 2D materials with wrinkles is linearly related to the load, and the relation slope is proportional to the ratio of wrinkle amplitude to wavelength A/λ. When A/λ=0.01~0.05, the slope is 1.32~3.21 times that of the case without wrinkles. This results in a significant overestimation (up to 3.21 times) of the elastic modulus of the 2D material obtained by the bending indentation test. The mechanism of overestimating the elastic modulus of 2D materials is that the wrinkles enhance the overall flexural stiffness of 2D materials, and thus increase the slope of the indentation load displacement relationship used to fit the elastic modulus.

To optimize the external piping system of an aircraft engine, a sensitivity analysis was performed on Z-pipes, a typical external component. The results indicate that both the efficiency and accuracy of the structural optimization design were significantly improved. First, the sensitivity of the natural frequency and resonant stress was analyzed based on the structural parameters of Z-pipes. Then, using the sensitivity analysis results, parameters with the highest total sensitivity index based on variance were selected for optimization. The optimal design was achieved through finite element analysis. Finally, the optimized design was validated through pipe vibration testing. This approach significantly reduced the computational effort required for optimization by eliminating less influential parameters during the sensitivity analysis. The method was proven effective in avoiding resonance and reducing resonant stress in Z-pipes, providing valuable insights for the optimization of external engine pipelines.

Polylactic acid (PLA) material is widely utilized in the field of additive manufacturing. Despite numerous studies were conducted on the mechanical properties of PLA materials, most of them employed traditional contact methods, such as strain electrical measurement, which posed challenges such as inadaptability to complex environments and cumbersome operation. In this study, a non-contact optical extensometer integrating dual-rhombic prisms and digital image correlation (DIC) is used to test the tensile mechanical properties of the 3D printed PLA specimens. Through the standard uniaxial tensile tests on PLA specimens, the strain was measured and the mechanical properties such as the elastic modulus, Poisson's ratio, strength, and elongation were obtained using the optical extensometer method. Compared with the refined strain gauge method, the non-contact technique exhibits minimal measurement errors, with deviations of merely 0.12 % and 0.34 % for elastic modulus and Poisson's ratio, respectively. The experimental results show that the non-contact optical extensometer has achieved a high level of accuracy, demonstrating its huge potential for measuring material properties in complex environments.

Traditional creep constitutive relationship is generally developed only for one of the three stages, i.e., transient, steady-state and accelerated stages. The well known power law creep relationship is only a typical creep constitutive model for steady creep stage. In high temperature allloy structures, however, the well known three stages of creep are usually mixed up in one working cycle, and the steady-state creep stage may not be dominant and even not observable. Therefore, from the perspective of engineering application, it is necessary to develop a long term creep constitutive relationship which can be applied for actual working loadings, without the limitation of traditional creep stage distinguishments. In this paper, creep tests of high temperature alloy FGH4095 are carried out at 530 ℃, 600 ℃ and 700 ℃. From the analyses of experimental results, a modified θ-projection method has been proposed, and the detailed long-term creep constitutive relationship has been developed. This model contains 5 creep state parameters, which are dependent on both temperature and stress level. For the convenience of practical application, creep tests at several different temperatures and stress levels are conducted, from which the empirical relationships of the creep state parameters depending on the temperature and stress level have been obtained.

The dynamics modeling and control of semi-passive walking of an elastic rimless wheel on an inclined plane are studied. Initially, a dynamic model of the elastic rimless wheel was constructed using the Lagrange method, based on the Spring-Loaded Inverted Pendulum (SLIP) model. Following this, a controller was devised employing the concept of feedback linearization, which, by adjusting the length of the elastic leg, reduces the walking error of the elastic rimless wheel, thereby facilitating stable periodic locomotion. Subsequently, simulation experiments based on the theoretical study were conducted to verify the effectiveness of the control strategy predicated on variable leg length under the influence of external disturbances and inherent parameter inaccuracies. The simulations also revealed that identical external perturbations exert disparate effects during the single support (ss) and double support (ds) phases, prompting an analysis of the causes behind such variations. The simulation results demonstrate that the controller designed with variable leg length is capable of ensuring the stable progression of the elastic rimless wheel along the slope. Moreover, it can effectively mitigate the external disruptions, swiftly reinstate the elastic rimless wheel to a periodic stable gait, and exhibit considerable robustness even when the elastic rimless wheel's own parameters are erroneous.

To investigate the damage and failure characteristics of rocks containing non-penetrating cracks in depth, uniaxial compression and cyclic loading experiments were conducted at different loading rates. The experimental results indicate that both cyclic disturbance and increase in loading rate can accelerate the internal degradation of the sample. Cyclic loading can cause hardening of brittle materials during the elastic stage, thus appropriate cycling of rock specimens during their elastic stage can improve their elastic moduli and stiffnesses to a certain extent. In addition, the phenomenon of spalling in rocks is often observed during the fracture process of brittle materials. In practical engineering, the stability of the rock mass on site can be evaluated based on the spalling phenomenon before rock mass failure. In specimens with non-penetrating cracks, shear failure of 'N-type'' is more likely to occur on one side, whereas intact specimens are prone to fail by splitting. These research findings hold significant scientific implications for understanding the intrinsic failure mechanisms of rocks.

In some experiments, it was found that applying external pressure to lithium-ion batteries during the charge and discharge process can improve the cycle performance. However, the mechanism of how pressure affects the fracture of active particles remains yet to be explored. The external forces applied to lithium-ion batteries usually transmit to the electrode particles in two ways. One is through the compressed gas and liquid in the sealed space of battery which uniformly transfer the force to the surface of active particles, the other is through the battery casing which transfers the force to the electrode material and then to the active particles via the binder. Based on the Finite-Discrete Element Method (FDEM), this paper presents a diffusion-induced fracture model under finite deformation to analyze the fracture behavior of ternary positive electrode polycrystalline particles under the influence of applied pressure during lithiation. The numerical results indicate that, for both types of force transmissions, even smaller uniformly distributed pressures cannot reduce the tensile stress at the center of the particles to a level that prevents cracking, resulting in the occurrence of a small number of central cracks. In comparison, larger uniformly distributed pressures change the maximum principal stress inside the active particles from tension into compression, thereby better preserving the integrity of the internal structure of the active particles. Moreover, increasing the magnitude of the applied pressure converts all tensile stresses induced by diffusion into compressive stresses, thereby avoiding cracks caused by tensile stress and suppressing the extension of cracks in the active particles during lithiation.

Cable structures have wide applications in engineering. Due to their high flexibility, geometric nonlinearity effects must be considered in structural analysis. The TL (Total Lagrangian) formulation and UL (Updated Lagrangian) formulation are two main computational formulations in the finite element method. They are based on different reference states of motion and differ in theoretical derivation and solving algorithms. Although both formulations are suitable for cable structure analysis, there is a relative lack of comparative analysis on the differences and applicable scenarios of the two in specific applications. In this paper, based on the energy variational principle, the expressions of tangent stiffness of cable elements under the two formulations are derived, and the differences in the iterative strategies of nonlinear equilibrium equations under each formulation are compared and analyzed. Finally, through specific examples, it is demonstrated that for the cable structure analysis involving only geometric nonlinearity, both formulations can yield consistent results. It indicates that compared to the UL formulation, the TL formulation has simpler concepts and more concise solving algorithms, showing significant advantages in the cable structure analysis involving only geometric nonlinearity.

The lake-at-rest steady-state problem, which finds extensive practical applications, can be represented by shallow water equations with source terms. These equations necessitate a well-balanced approach in numerical calculations. This paper presents a well-balanced, high-order entropy stable scheme based on Targeted Essentially Non-Oscillatory (TENO) reconstruction for its low numerical dissipation. The well-balanced property of this scheme is subsequently established. The TENO reconstruction with low numerical dissipation is introduced into the TeCNO framework, appending the reconstructed numerical dissipation term to the existing entropy conservation flux to obtain high-order entropy stable numerical flux. For the source term, a discrete form corresponding to the numerical flux is adopted to achieve a numerical balance between the flux function and the source term. The high resolution and well-balanced property of the algorithm are demonstrated through multiple numerical examples. The numerical results show that the high-order entropy stable scheme, based on TENO reconstruction, offers the advantages of well-balanced property, low dissipation and high resolution. Furthermore, it effectively addresses small perturbation problem in steady-state solution.

Particle contact friction coefficient and loading rate effects have significant influences on the shear strength of granular material system. For this purpose, the flexible biaxial compression tests are simulated by the discrete element method to investigate the macroscopic mechanical properties under different combinations of loading rates and friction coefficients. Based on the "rate-state shear strength theory", the influences of loading rates and friction coefficients on the "rotation-slip ratio" and shear strength of granular material system are further investigated. The results indicate that the rate-state shear strength theory can essentially reveal the macro micro relationship of particle material systems, and the macroscopic shear strength of granular material specimens can also be accurately described. The shear strength of granular material system increases with the increase of loading rate. However, there exists a critical loading rate below which the loading rate effect is negligible. The shear expansion of specimen is closely related to the sliding friction coefficient, and the irregularity of particle shape can significantly enhance the shear strength while maintaining a consistent shear expansion. The evolution of rotation-slip ratio in the shear band is affected by both the loading rates and the friction coefficients, with higher sensitivity to the sliding friction coefficient. Compared with the rotation-slip ratio, the "reference velocity" has an opposite trend, which increases significantly with the increase of loading rate and the decrease of friction coefficient. By establishing a quantitative relationship between the particle rotation slip ratio, the loading rate, and the generalized friction coefficient, theoretical guidance can be provided for further researches on the rate sensitive strength of granular materials.

This study focuses on an electroactive polymer membrane actuator, utilizing the viscoelastic Neo-Hookean model for numerical simulation research, to establish a mechanical model that evolves over time under electromechanical action. It analyzes the evolution trends of the equilibrium strain, the non-equilibrium strain, and the electric field intensity for the electroactive polymer film. The results indicated that under the coupling action of force and electricity, the performance indicators of the film gradually stabilized over time. Furthermore, when the system reaches a steady state, the effects of the external force, the voltage adjustments, and the degree of pre-stretch of the film on the strain and electric field distribution were explored. The simulation results demonstrated that by appropriately adjusting the external load and pre tension parameters, the strain response and the field strength uniformity of the film can be significantly optimized, thus improving the material efficiency and the actuator performance. These findings provide valuable reference for the design optimization of viscoelastic dielectric elastomer actuators and the improvement of their performance in practical applications.

Segments are the lining structures outside the subway shield tunnel, and are vulnerable to various degrees of cracks due to external loads and rust expansion pressure. Segments cracking can seriously reduce the stiffness and load-bearing performance of the structure. In order to determine the distribution pattern of crack morphology inside the arch waist segment of shield tunnel under the bending load and the rust expansion pressure, the CDM-XFEM (Continuum Damage Mechanics-Extended Finite Element Methods) method was used to calculate the surface crack morphology of the arch waist segment under the bending load, and the results were verified through full-scale tests. By uniformly discretizing the steel rust layer, the irregular rust layer rust expansion pressure transformation equation of the segment was derived based on the thick-walled cylinder model. Based on this, the crack morphology inside the corroded segment under different bending loads was calculated. Research has shown that under the bending loads, the outer curved surface of the segment exhibits three curved through cracks, while the internal cracks exhibit a distribution pattern of three connected ellipses. When the bending moment of the segment increases from 220 kN·m to 320 kN·m, the transverse span of the rust expansion crack at the crack section in different areas increases by 27 %, 51 %, and 37 %, respectively, indicating that the increase in bending moment has the greatest impact on the rust expansion cracking at the middle crack section of the segment. Under the same bending moment, the shape of the rust cracking angle curve of each steel bar is basically the same, indicating that the bending load has a relatively small impact on the rust cracking angle of the segment.

Understanding the geostress field in reservoirs was crucial for successful hydraulic fracturing. Current on-site stress measurement methods, limited by wellbore locations and quantities, struggled to fully capture the geostress distribution. Numerical simulation interprets the on-site stress test results and redistribute the geostress field. The variation of geostress field at the intersection of faults is complex, and the mechanism of the influence of fault interaction on geostress is still unclear. By investigating Shunbei carbonate reservoir with intersecting faults using AiFrac modeling, the geomechanical models for different types of fault intersections in reservoir areas were established, some conclusions were made. In the region far from faults, the maximum horizontal principal geostress was controlled by far-field tectonic stress. Within the faults, due to the mechanical weakening of faults, the value of maximum horizontal principal geostress was relatively low. At the ends of faults, stress concentration led to a significant increase with a symmetrical deviation. In parallel fault zones, geostress was slightly smaller near the center and slightly larger at both ends. Intersecting faults with orientations closer to parallel with the regional maximum horizontal principal geostress direction exhibited a greater reduction in internal stress, and the direction of the maximum horizontal principal geostress underwent a drastic deviation at fault boundaries. These findings supported optimizing wellbore trajectory design in reservoir reformation.

Functionally graded materials are a special kind of composite materials that can effectively relieve thermal stress at high temperature. Due to its unique structure and physical properties, the functionally graded beam will show more complicated thermodynamic behaviors under thermal shock. As an improved algorithm of the material point method (MPM), the B-spline material point method (BSMPM) has demonstrated its powerful solving ability in various kinds of complex problems. This paper proposes a discrete format of the coupled heat equations based on the framework of Fourier heat conduction theory and BSMPM, and analyzes the free vibration of SiC-Al functionally graded beams, as well as their dynamic response under temperature load. The transverse vibration frequency of SiC-Al functionally graded beams is analyzed using the Fast Fourier Transform, and compared to the results of the theoretical modeling, the finite element method, and the traditional material point method. The results show that, compared with the traditional MPM, the BSMPM effectively improves stress oscillation and energy dissipation. Under thermal shock, the temperature distribution in the functionally graded beam obtained by the BSMPM agrees well with the finite element results. The natural frequency of first-order transverse vibration can be obtained by the BSMPM. As the gradient power law index increases, the simulated frequency of the functionally graded beam decreases in the form of approximate power function, which is in good agreement with the theoretical results. This work demonstrates the effectiveness of the thermally coupled BSMPM, and broadens the engineering application of the BSMPM, providing a promising approach simulating thermodynamic responses of functionally graded materials.

During the drilling process of multiple wells in the Tahe block, severe mudstone wellbore collapse occurred in the Triassic and Carboniferous formations, leading to frequent downhole sticking and obstruction. Increasing the drilling fluid density did not resolve the issue, and switching to oil-based drilling fluid showed no significant effect. Based on geological survey test data and wellbore structure diagrams, a numerical model for wellbore stability analysis was established. Formation parameters were calculated according to logging data, and further corrected based on triaxial mechanical test results. Using FLAC3D software, the in-situ stress field of Well 1 in the Tahe block was obtained through inversion. Parameter analysis of the established numerical model indicated that: the dip angle had a small impact on the wellbore enlargement rate, with an 80° dip angle increasing the wellbore enlargement rate by 1.4 % compared to a 50° dip angle; the azimuth angle had a negligible effect on the wellbore enlargement rate; the drilling fluid density had little impact on the wellbore enlargement rate, with an increase in drilling fluid density from 1.20 g/cm³ to 1.35 g/cm³ reducing the wellbore enlargement rate by 36 %; the degree of mudstone weakening had the most significant impact on the wellbore enlargement rate and was the main controlling factor. When the residual strength of the rock mass was 30 %, the wellbore enlargement rate increased nearly threefold compared to the 44 % residual strength case.

The fracture pressure can effectively reflect the likelihood of rock fracturing during the fracturing process and is a key parameter in the design of fracturing operations. Currently, the prediction of fracture pressure mainly relies on field or laboratory testing methods, which are characterized by high costs and long durations. Moreover, the results obtained from testing in highly heterogeneous strata lack representativeness. Based on the theory of damage mechanics, in this paper we utilize the COMSOL and MATLAB software to investigate the fracturing mechanism of tight sandstone under the coupled action of fluid-solid-temperature fields, establish a method for predicting fracture pressure, and analyze the sensitivity factors of fracture pressure in tight sandstone. The numerical simulation results indicate that the prediction values of fracture pressure obtained using the simulation method established in this paper have small errors compared to those obtained through experimental testing, satisfying engineering requirements. Under the coupled action of fluid-solid-temperature fields, the stronger the heterogeneity of the reservoir, the greater the degree of rock fragmentation and the lower the fracture pressure. When the heterogeneity of the reservoir is more extreme (either very strong or nonexistent), the fracture pressure is more sensitive to the elastic modulus. Temperature difference has a significant impact on the fracture pressure. For example, when the temperature difference is 200 ℃, the obtained fracture pressure is only 52 MPa, which is 39 % of the fracture pressure obtained without considering the temperature difference. When the elastic modulus decreases by 30 GPa, the fracture pressure decreases by up to 78 %. The method proposed in this paper is characterized by the low cost and the high accuracy, demonstrating high practicality and application value.