Acta Mechanica Sinica最新文献

The extreme conditions severely constrain the dynamic characteristics of aircraft landing gear retraction mechanism (ALGRM). This paper proposes a dynamic modeling and analysis method for ALGRM considering the coupling effects of extreme conditions such as clearance joints, flexible rods, and salt spray corrosion. Firstly, the mathematical model for clearance joint and flexible rod is established and the dynamic model of ALGRM considering clearance joints and flexible rods is formulated based on Lagrangian equation. Furthermore, the salt spray corrosion model for clearance joint is developed using COMSOL simulation software. Finally, the effects of different temperatures and relative humidities on the corrosion depth of clearance joint and the dynamic characteristics of ALGRM under the coupling effects of extreme conditions are investigated. The results have found that the impact of extreme conditions on dynamics of system cannot be ignored. This study not only provides a theoretical foundation for predicting the dynamic characteristics of ALGRM under extreme conditions but also offers insights for the optimization design and corrosion protection efforts of landing gear.

The consistency of the dynamic behavior of the mechanical equivalent model of high-speed pantographs with that of actual high-speed pantographs under service conditions is crucial for the correctness and accuracy of the numerical simulation results of the pantograph-catenary interaction. Firstly, based on experimental data and the finite element method, models of a mass-point frame and reduced pan head were established, which can simulate the rolling and pitching motion characteristics of the dual-strip pan head. The correctness of the finite element numerical simulation of the pantograph-catenary system based on the model was verified through an industry standard and line tests. Then, the variation law of the standard deviation of the contact force (SDCF) in the speed range of 240–450 km/h was studied, and the mechanism of large fluctuation in SDCF was explained from the perspective of pantograph-catenary resonance. Finally, the influence of pan head degree of freedom and low-pass filtering frequency of the contact force time-domain signal on SDCF was studied, and the applicable speed level of the traditional three-mass model and 20 Hz filtering were provided.

With the increasing and refined applications of silicone rubber devices in the biomedical field, it is of great significance to accurately describe and predict the mechanical behavior of them under large deformation. This paper finds that after considering the influence of higher-order shear strain on the normal stress, the Poynting effect in ribbed silicone rubber tubes with certain cross-sectional shapes exhibits a new phenomenon—a non-monotonic trend between axial deformation and twist angle. This paper develops a nonlinear finite element program for simulating large deformations of hyperelastic materials, and studies the Poynting effect in ribbed circular tubes of twisted silicone rubber. The results show that in the ribbed circular tubes with a porosity between 12% and 40% (with the number of ribs ranging from 12 to 26), there appears a normal to reverse conversion of the Poynting effect, that is, the axial extension ratio first decreases and then increases during a monotonic loading process, indicating that the influence of higher-order shear strain on normal stress cannot be ignored when the cross-sectional shape is complex. Especially in ribbed circular tubes with about 20% porosity, a substantial change of axial normal strain from −0.035% to 0.035% can be achieved within a twist angle range of 180°. Based on this, the quantitative influence of higherorder shear strain on normal stress is studied. These research results provide a theoretical basis for accurately controlling the axial expansion and contraction of twisted parts and indicate that a normal to reverse conversion of the Poynting effect can be implemented by designing the cross-sectional shape under certain conditions.

Malignant ureteral obstruction may lead to renal function damage, renal colic, and infection. The impact of obstructive development on ureteral peristalsis was rarely studied, which requires further investigation. This study used theoretical biomechanical methods to study the motion characteristics of the ureteral wall and obtained the radial motion equation of the ureteral wall. The motion equation was solved by 4–5th order Runge Kutta method. Analyze the motion equation of the ureteral wall, derive the expression for malignant obstructive ureteral pressure, as well as the analytical expressions for radial displacement and circumferential stress of the ureteral wall. By analyzing the radial motion equation of the ureter, it can be found that peristalsis is influenced by the pressure difference between inside and outside. The analytical solutions for radial displacement and stress contained exponential terms. Under the condition of 50% obstruction, the displacement and stress of the ureter were reduced by 90.53% and 81.10%, respectively. This study established the radial motion equation of the ureter and provided analytical solutions for the radial displacement and stress of the obstructed ureter. Based on the radial motion equation of the ureter, the radial motion characteristics of the ureteral wall were explored, including peristalsis and disappearance of peristalsis. This study provided a quantitative relationship between ureteral obstruction and peristalsis. As the degree of obstruction increased, ureteral peristalsis gradually weakened or even disappeared.

This paper presents a deep learning-based topology optimization method for the joint design of material layout and fiber orientation in continuous fiber-reinforced composite structure (CFRCS). The proposed method mainly includes three steps: (1) a ResUNet-involved generative and adversarial network (ResUNet-GAN) is developed to establish the end-to-end mapping from structural design parameters to fiber-reinforced composite optimized structure, and a fiber orientation chromatogram is presented to represent continuous fiber angles; (2) to avoid the local optimum problem, the independent continuous mapping method (ICM method) considering the improved principal stress orientation interpolated continuous fiber angle optimization (PSO-CFAO) strategy is utilized to construct CFRCS topology optimization dataset; (3) the well-trained ResUNet-GAN is deployed to design the optimal structural material distribution together with the corresponding continuous fiber orientations. Numerical simulations for benchmark structure verify that the proposed method greatly improves the design efficiency of CFRCS along with high design accuracy. Furthermore, the CFRCS topology configuration designed by ResUNet-GAN is fabricated by additive manufacturing. Compression experiments of the specimens show that both the stiffness structure and peak load of the CFRCS topology configuration designed by the proposed method have significantly enhanced. The proposed deep learning-based topology optimization method will provide great flexibility in CFRCS for engineering applications.

Intracranial aneurysm (IA) is a prevalent cerebrovascular disease associated with high mortality and disability rates upon rupture. The hemodynamics of IA, which are significantly influenced by geometric parameters, directly impact its rupture. This study focuses on investigating the transient flow characteristics in saccular IA models fabricated using a water droplet-based method, specifically examining the influence of neck widths. Particle image velocimetry technique and numerical simulation were employed to investigate the dynamic evolution of flow structures within three IA models. The results reveal that neck width (W) has a substantial effect on flow characteristics in the neck region, subsequently impacting the deep flow inside the sac. Three distinct patterns were observed during flow evolution inside the sac: for W = 2 mm, two vortices occur and then disappear with relatively low average flow velocity; for W = 4 mm, enhanced effects of a high-speed jet result in periodic pulsatile flow velocity distribution while maintaining stable vortex core position; for W = 6 mm, significant changes in flow velocity occur due to size expansion and intensity increase of vortices. These findings demonstrate that neck widths play a complex role in influencing transient flow characteristics within IAs. Overall, this research contributes to further understanding transient flow behaviors in IAs.

It is commonly accepted that the formation of oil and gas reservoirs in deep-buried strata is almost impossible due to the huge compaction of in-situ crustal stresses. Nevertheless, recent hydrocarbon explorations in the Tarim Basin have discovered reservoirs at depths exceeding 8 km. The reservoirs exhibit a strong correlation to the strata’s faults and large fractures, yet the precise underlying mechanical mechanism remains obscure. To illuminate how the faults may facilitate the existence of such deep-buried reservoirs, we consider three ideal scenarios involving unconventional hole-crack interactions under remote biaxial compression. Our focus is on the stress concentration of the hole, influenced by the long main cracks. Closed-form compressive stress solutions are obtained based on our simple theoretical models, showing that long cracks significantly reduce the stress concentration of nearby holes. We quantify the reducing effect of the cracks’ angle, surface friction, and pressure on the maximum shear and von Mises stresses around a hole, combining with finite element analysis results. The stress shielding effect is qualitatively consistent with the available experimental observations that the deep-buried caves are often located near the faults and large fractures in carbonate strata. Our results will be beneficial for future exploration of superdeep petroleum reservoirs.

Recently, significant progress has been made in conceptually describing the dynamic aspects of coarse particle entrainment, which has been explored experimentally for open channel flows. The aim of this study is to extend the application of energy criterion to the low mobility aeolian transport of solids (including both natural sediment and anthropogenic debris such as plastics), ranging from incomplete (rocking) to full (rolling) entrainments. This is achieved by linking particle movements to energetic flow events, which are defined as flow structures with the ability to work on particles, setting them into motion. It is hypothesized that such events should impart sufficient energy to the particles, above a certain threshold value. The concept’s validity is demonstrated experimentally, using a wind tunnel and laser distance sensor to capture the dynamics of an individual target particle, exposed on a rough bed surface. Measurements are acquired at a high spatiotemporal resolution, and synchronously with the instantaneous air velocity at an appropriate distance upwind of the target particle, using a hot film anemometer. This enables the association of flow events with rocking and rolling entrainments. Furthermore, it is shown that rocking and rolling may have distinct energy thresholds. Estimates of the energy transfer efficiency, normalized by the drag coefficient, range over an order of magnitude (from about 0.001 to 0.0048 for rocking, up to about 0.01, for incipient rolling). The proposed event-based theoretical framework is a novel approach to characterizing the energy imparted from the wind to the soil surface and could have potential implications for modelling intermittent creep transport of coarse particles and related aeolian bedforms.

The increasing accumulation of space debris threatens the integrity and functionality of satellites and complicates orbital operations. This paper constructs an advanced rigid-flexible coupling dynamic model for tethered satellite systems, tailored to enhance space debris management. Utilizing the nodal position finite element method, the model significantly improves the precision of simulating tether dynamics and captures the complex interactions involving satellite and debris attitude dynamics. This advancement allows for detailed examination of potential tether entanglements and provides crucial data for optimizing deorbiting processes. To overcome the limitations of conventional control techniques, a robust adaptive sliding mode control strategy is developed. This approach is specifically designed to manage the unpredictable conditions of the low-Earth orbit and ensure precise satellite attitude control, critical for successful debris removal. Validated through extensive numerical simulations, our model and control strategy demonstrate substantial improvements in operational reliability and safety, significantly enhancing the success rate of deorbiting missions.

The accurate assessment of cardiac motion is crucial for diagnosing and monitoring cardiovascular diseases. In this context, digital volume correlation (DVC) has emerged as a promising technique for tracking cardiac motion from cardiac computed tomography angiographic (CTA) images. This paper presents a comprehensive performance evaluation of the DVC method, specifically focusing on tracking the motion of the left atrium using cardiac CTA data. The study employed a comparative experimental approach while simultaneously optimizing the existing DVC algorithm. Multiple sets of controlled experiments were designed to conduct quantitative analyses on the parameters “radius” and “step”. The results revealed that the optimized DVC algorithm enhanced tracking accuracy within a reasonable computational time. These findings contributed to the understanding of the efficacy and limitations of the DVC algorithm in analyzing heart deformation.