Search Results (202)

The physicochemical processes that occur during selective transfer in the contact area of a bronze/steel friction pair lubricated with glycerin are experimentally studied by the polarization method to observe how they influence the tribological properties (friction and wear) of the pair. The proposed method allows for the study of tribochemical transformations of glycerin and the friction pair materials during the work process with selective transfer. The analysis of the experimental results allows for the establishment of the conditions for a stable and stationary selective transfer during the operation of the bronze/steel pair, by friction, at which the friction coefficient (COF) values and wear are low. This was achieved by implementing continuous lubrication with fresh glycerin in the contact area, choosing the optimal flow rate, and maintaining an optimal ratio between glycerin and the chemical transformation products, within well-established limits, to avoid undesirable consequences. Acrolein, as a product of chemical transformation (resulting from the catalytic dehydration of glycerin), is the most important for the initiation and stability of the selective transfer, and as the main reaction product, also represents a pathway of regeneration. Thus, it was found that the friction relative moments and the acrolein concentration presented conclusive/specific results at loads of 4–15 MPa and a sliding speed of 0.3 m/s. The optimum lubricant entry speed is 15–30 mg/min, for a minimum COF and reduced wear (about 0.028–0.03 at relatively high operating temperatures (45 and 60 °C)), and at low temperatures (30 °C) the minimum COF is about 0.038, but the lubricant inlet entry speed increases considerably, by around 1000 mg/min. Therefore, this paper aims to demonstrate the possibility of moving to another stage of practical use of a friction pair (with greatly improved tribological properties) that operates with selective transfer, much different from the ones still present, using a lubricant with special properties (glycerin). The research method used (polarization) highlights the physicochemical properties, tribochemical transformations of the lubricant, and the friction pair materials present in the contact area, for the understanding, maintenance, and stability of selective transfer, based on experiments, as a novelty compared to other studies. Full article

Field foundation pile loading tests were conducted in the context of an actual bridge pile foundation project. The test data were analyzed to determine the reasons for the variation in the complex geological conditions of the seashore. Moreover, finite element analysis was conducted to evaluate the influence of pile length and diameter on the settlement of coastal friction foundation piles. Increasing the pile length from 65 m to 75 m reduced the settlement by 25.7%, while increasing the diameter from 1.5 m to 2.0 m led to a 35.9% reduction. Increasing the pile spacing reduced the amount of structural settlement. Group pile foundation pile spacings should be 2.5–3.0 D. Pile group superposition reduced the most obvious effects and the settlement reduction rate was the fastest. Under seismic conditions, the pile group foundation exhibited 5.60 times greater horizontal displacement, 3.57 times higher bending moment, and 5.30 times increased shear force relative to static loading. The formula for predicting the settlement of oversized friction pile group foundations was modified based on settlement values calculated using finite elements. The revised formula is suitable for calculating the settlement of friction pile group foundations in coastal areas. Full article

This study, in response to the optimization needs of fall risks for the elderly in the context of cultural and tourism integration in Hebei Province, China, established a quantitative correlation system between ten gait parameters and ten types of spatial risk factors. By collecting gait data (Qualisys infrared motion capture system, sampling rate 200 Hz) and spatial parameters from 30 elderly subjects (with mild, moderate, and severe functional impairments), a multi-level regression model was established. This study revealed that step frequency, step width, and step length were nonlinearly associated with corridor length, door opening width, and step depth (R² = 0.53–0.68). Step speed, ankle dorsiflexion, and foot pressure were key predictive factors (OR = 0.04–8.58, p < 0.001), driving the optimization of core spatial factors such as threshold height, handrail density, and friction coefficient. Step length, cycle, knee angle, and lumbar moment, respectively, affected bed height (45–60 cm), switch height (1.2–1.4 m), stair riser height (≤35 mm), and sink height adjustment range (0.7–0.9 m). The prediction accuracy of the ten optimized values reached 86.7% (95% CI: 82.1–90.3%), with Hosmer–Lemeshow goodness-of-fit x² = 7.32 (p = 0.412) and ROC curve AUC = 0.912. Empirical evidence shows that the graded optimization scheme reduced the fall risk by 42–85%, and the estimated fall incidence rate decreased by 67% after the renovation. The study of the “abnormal gait—spatial threshold—graded optimization” quantitative residential layout optimization provides a systematic solution for the data-quantified model of elderly-friendly residential renovations. Full article

Traditional three-row roller YRT turntable bearings exhibit high friction torque during operation, which limits their performance in high-precision and high-response applications. To address this issue, a novel ball–roller composite turntable bearing is proposed that effectively reduces friction torque while maintaining a high load capacity. A mechanical model based on statics is established, and the Newton–Raphson method is employed to calculate the contact load. The formation mechanism of friction torque is analyzed, and a corresponding computational model is developed and validated using experimental data. The effects of axial load, eccentricity, overturning moment, rotational speed, and axial clearance on friction torque are systematically studied. Results indicate that friction torque increases with these parameters. Axial clearance has a significant influence, and an optimal clearance value between the balls and rollers is determined. Additionally, a reasonable range for the raceway curvature radius coefficient is proposed. When the numerical ratio of balls to rollers is 1, the bearing exhibits optimal friction performance. Among various roller crowning strategies, logarithmic crowning yields the best results. This study provides a theoretical basis and technical support for the optimized design of ball–roller composite turntable bearings. Full article

This study presents an adaptive integrated chassis control strategy for enhancing vehicle stability under different road conditions, specifically through the real-time estimation of tire cornering stiffness. A hierarchical control architecture is developed, combining active front steering (AFS) and direct yaw moment control (DYC). A recursive regularized weighted least squares algorithm is designed to estimate tire cornering stiffness from measurable vehicle states, eliminating the need for additional tire sensors. Leveraging this estimation, an adaptive sliding mode controller (ASMC) is proposed in the upper layer, where a novel self-tuning mechanism adjusts control parameters based on tire saturation levels and cornering stiffness variation trends. The lower-layer controller employs a weighted least squares allocation method to distribute control efforts while respecting physical and friction constraints. Co-simulations using MATLAB 2018a/Simulink and CarSim validate the effectiveness of the proposed framework under both high- and low-friction scenarios. Compared with conventional ASMC and DYC strategies, the proposed controller exhibits improved robustness, reduced sideslip, and enhanced trajectory tracking performance. The results demonstrate the significance of the real-time integration of tire dynamics into chassis control in improving vehicle handling and stability. Full article

Coordinating vehicle handling stability and energy consumption remains a key challenge for distributed driving electric vehicles (DDEVs). In this paper, a hierarchical torque vectoring control strategy is proposed to address this issue. First, a tire road friction coefficient (TRFC) estimator based on the fusion of vision and dynamic is developed to accurately and promptly obtain the TRFC in the upper layer. Second, a direct yaw moment control (DYC) strategy based on the adaptive model predictive control (MPC) is designed to ensure vehicle stability in the middle layer, where tire cornering stiffness is updated dynamically based on the estimated TRFC. Then, the lower layer develops the torque vectoring allocation controller, which comprehensively considers handling stability and energy consumption and distributes the driving torques among the wheels. The weight between stability and economy is coordinated according to the stability boundaries derived from an extended phase-plane correlated with the TRFC. Finally, Hardware-in-the-Loop (HIL) simulations are conducted to validate the effectiveness of the proposed strategy. The results demonstrate that compared with the conventional stability torque distribution strategy, the proposed control strategy not only reduces the RMSE of sideslip angle by 44.88% but also decreases the motor power consumption by 24.45% under DLC conditions, which indicates that the proposed method can significantly enhance vehicle handling stability while reducing energy consumption. Full article

To address the stability of high embankment slopes and investigate the influence of spatial variability of gravel soil on slope stability, this study proposes a simplified reliability analysis method of slope stability. Based on FLAC^3D, a numerical model was developed to simulate slope behavior, and a linear regression-based empirical model was formulated to quantify the relationship between soil pressure and spatial variability indicators (e.g., coefficient of variation and correlation length). By mapping the spatial variability of soil parameters to soil pressure fluctuations, the slope reliability was evaluated through the first-order second-moment method (FOSM). The results demonstrate that the mean value of internal friction angle has a significant effect on the stability of gravel soil embankment slope, whereas the coefficient of variation in this parameter is limited. Furthermore, the correlation length of soil spatial variability shows marginal influence on stability outcomes. The computational model was validated against case study data, demonstrating its applicability for practical slope stability assessments. Full article

In the modern corporation, understanding sustainable cost management practices is essential for promoting economic resilience and resource efficiency. This study investigates how ownership structures influence the behavior of selling, and general and administrative (SG&A) costs during periods of sales fluctuations in South Korean firms, with particular attention to Chaebols. Drawing upon agency theory and corporate governance perspectives, we examine whether proxies for agency costs, namely, free cash flow, asset utilization ratios, and operating expense ratios, explain variations in SG&A cost responses to changes in revenue. Utilizing a panel dataset of 4279 firm-year observations from KOSPI-listed companies over the period 2011–2021, we employ Pooled Ordinary Least Squares (OLS), Fixed Effects, Random Effects, and Generalized Method of Moments (GMM) estimations to model SG&A cost behavior. The analysis incorporates regression-based interaction terms that capture asymmetric cost adjustments during sales declines, commonly referred to as cost stickiness. Our findings indicate that firms with concentrated ownership, such as Chaebols, exhibit significantly lower SG&A cost stickiness, reflecting stronger financial discipline and more efficient resource allocation. In contrast, firms with dispersed ownership demonstrate more pronounced cost stickiness, consistent with governance frictions and managerial discretion. These results emphasize the moderating role of ownership structure in cost behavior and highlight its implications for sustainable corporate governance. Our study contributes to the literature on cost management and financial sustainability by offering empirical insights from a distinctive institutional setting. Policy recommendations include enhancing internal controls, promoting transparent cost practices, and encouraging shareholder oversight to reinforce long-term efficiency. Full article

In many applications, it is necessary to optimise the performance of hydrodynamic (HD) bearings. Many studies have proposed different strategies, but there remains a lack of conclusive research on the suitability of various optimisation methods. This study evaluates the most commonly used algorithms, including the genetic (GA), particle swarm (PSWM), pattern search (PSCH) and surrogate (SURG) algorithms. The effectiveness of each algorithm in finding the global minimum is analysed, with attention to the parameter settings of each algorithm. The algorithms are assessed on HD journal and thrust bearings, using analytical and numerical solutions for friction moment, bearing load-carrying capacity and outlet lubricant flow rate under multiple operating conditions. The results indicate that the PSCH algorithm was the most efficient in all cases, excelling in both finding the global minimum and speed. While the PSWM algorithm also reliably found the global minimum, it exhibited lower speed in the defined problems. In contrast, genetic algorithms and the surrogate algorithm demonstrated significantly lower efficiency in the tested problems. Although the PSCH algorithm proved to be the most efficient, the PSWM algorithm is recommended as the best default choice due to its ease of use and minimal sensitivity to parameter settings. Full article

Induced seismicity resulting from mining activities is one of the major challenges faced by the mining industry. Although such events have been documented for over a century in countries with extensive mining traditions, such as Canada, Australia, and Chile, their impact has intensified over time. This increase is primarily attributed to the greater extraction depths, where elevated stress levels and environmental conditions heighten the likelihood of rockburst occurrences. Seismic events within mines lead to significant human casualties and substantial infrastructure damage, necessitating the implementation of various safety protocols. Among these, seismic indicators are employed to identify periods when high-magnitude seismic events are most likely to occur through the analysis of parameters such as magnitude, energy, time, and decay rate. In this context, the present study aims to utilize the accumulated frictional energy generated by microearthquakes within the Bobrek mine, Poland, as a seismic indicator (variation of frictional energy in time), establishing its correlation with the occurrence of high-magnitude seismic events exceeding the background activity. Thousands of combinations of seismic parameters were tested to maximize the performance of this frictional energy-based indicator, parameters such as moment magnitude, frictional energy, and rock properties. The optimal set of parameters was determined using the Piece Skill Score (PSS) and subsequently applied to the Accumulated Frictional Heat (AFH) methodology. According to the results, the seismic indicator forecasts 86.6% of events with magnitudes M_w ≥ 2.3, with an average forecasting time of 9.76 h, indicating that, on average, these events can be anticipated approximately 10 h before their occurrence. Full article

The startup dynamics of wind turbines have a direct impact on their cut-in speed and thus their capacity factor, considering highly transient winds in urban environments. Due to the complex nature of the startup dynamics, the published research on it is severely lacking. Unless the startup dynamics and cut-in speed of a wind turbine are known, it is difficult to evaluate its capacity factor and levelized cost of energy (LCoE) for commercial viability. In this study, a Savonius vertical-axis wind turbine (VAWT) has been considered and its startup dynamics evaluated using numerical techniques. Moreover, the effects of turbine inertia, arising from bearing frictional losses, generator load, etc., on the startup dynamics have been studied. Advanced computational fluid dynamics (CFD)-based solvers have been utilized for this purpose. The flow-induced rotation of the turbine blades has been modeled using a six degree of freedom (6DoF) approach. Turbine inertia has been modeled using the mass moment of inertia of the turbine rotor and systematically increased to mimic the additional inertia and losses due to bearings and the generator. The results indicate that inertia has a significant impact on the startup dynamics of the VAWT. It was observed that as the turbine inertia increased, it took longer for the turbine to reach its steady or peak operational speed. Increasing the inertia by 10%, 20% and 30% increased the time taken by the turbine to reach its peak rotational speed by 13.3%, 16.7% and 23.2%, respectively. An interesting observation from the results obtained is that an increase in turbine inertia does not change the peak rotational speed. For the Savonius rotor considered, the peak rotational speed remained 122 rpm, and its tip speed ratio (TSR) remained 0.6 while increasing the turbine inertia. Full article

Active patient participation in the rehabilitation process after stroke has been shown to accelerate neural remodeling. The control framework of rehabilitation robots should provide appropriate assistive forces to users. An assist-as-needed (AAN) control method is proposed to help users to move upper limbs in the workspace freely, and to control the exoskeleton to provide assistance. The method is based on zero moment control (ZMC), helping the user achieve robotic traction with minimal interaction force. Based on the posture of the upper arm and forearm, an AAN controller can modify assistive forces at two human–robot-interaction (HRI) points along the direction opposite to gravity. A shoulder motion prediction model is proposed to enable the exoskeleton to mimic the user’s upper limb natural movements. In order to improve the transparency during rehabilitation training, a nonlinear numerical friction model based on the Stribeck friction model is developed. A healthy adult male was recruited to perform various activities of daily living (ADL) tests to assess the effectiveness of the controllers. The experimental results show that the proposed ZMC controller has high HRI transparency and can control the exoskeleton to complete a wide range of upper limb movements, and the maximum interaction force and torque can be captured within −7.76 N and 4.58 Nm, respectively. The AAN controller can provide appropriate assistance in the desired direction, and the exoskeleton maintains kinematic synchronization with the user’s shoulder during shoulder girdle movement. Full article

The spacecraft microgravity simulation air-bearing platform is a crucial component of the spacecraft ground testing system. Special disturbances, such as the flatness and roughness of the contact surface between the air bearings and the granite platform, increasingly affect the control accuracy of the simulation experiment as the number of air bearings increases. To address this issue, this paper develops a novel compensation control system based on Active Disturbance Rejection Control (ADRC), which estimates and compensates for the disturbing forces and moments caused by the roughness and levelness of the contact surface, thereby improving the control precision of the spacecraft ground simulation system. A dynamic model of the multi-air-bearing platform under disturbance is established. A cascade ADRC algorithm based on the Linear Extended State Observer (LESO) is designed. The Gauss–Newton iteration method is used to identify the parameters of the sliding friction coefficient and the tilt angle of the air-bearing platform. A full-physics simulation experimental platform for spacecraft with rotor-based propulsion is constructed, and the proposed algorithm is validated. The experimental results show that on a marble surface with a flatness of grade 00, an overall tilt angle of 0–1 degrees, and a surface friction coefficient of 0–0.01, the position control accuracy for the simulated spacecraft can reach 1.5 cm, and the attitude control accuracy can reach 1°. Under ideal conditions, the identification accuracy for the contact surface friction coefficient is 2 × 10⁻⁴, and the recognition accuracy for the overall levelness of the marble surface can reach 1 × 10⁻³, laying the foundation for high-precision ground simulation experiments of spacecraft in multi-air-bearing scenarios. Full article

This paper presents a novel strut-free earth retaining wall system for excavation, referred to as the asymmetric double-row pile wall (ARPW) retaining system. This system comprises three key elements: front-row reinforced concrete piles, back-row walls, and connecting crossbeams at the top of the piles. This paper aims to analyze the deformation characteristics and mechanical behavior of the ARPW retaining system, double-row pile wall (DRPW) retaining system, and single-row pile wall (SPW) retaining system using both physical model tests and numerical simulations. The study reveals that, with reasonable row spacing, double-row structures exhibit substantially lower earth pressure and bending moments compared to SPW. Additionally, all double-row structures display reverse bending points. The optimal row spacing for DRPW and ARPW is within the ranges of 2D to 6D and 4D to 8D, respectively. ARPW outperforms DRPW by efficiently utilizing active zone friction force and soil weight force (G_s) to resist overturning moments, thereby resulting in improved anti-overturning capabilities, reduced deformations, lower internal forces, and enhanced stability. The study also presents a case study from the Jinzhonghe Avenue South Side Plot in Tianjin, demonstrating the practical application and effectiveness of the ARPW system in meeting stringent deformation requirements for deep foundation pits. These research findings provide valuable insights for practical engineering applications. Full article

In addition to the vertical external load and soil settlement load, the pile foundation in reinforced high-fill areas is also affected by the horizontal load caused by the rear stacking load, and pile stress is affected by the soil-arching effect in reinforced areas that have typical passive pile characteristics. In order to study the symmetry of the soil-arching effect of pile foundations in a reinforced-fill area, indoor model tests were designed and the relevant data for the pile foundation and reinforced soil under surcharge were obtained. Through the analysis, the following conclusions were drawn: the peak bending moment of the pile body is basically consistent with the position of the potential sliding surface of reinforced soil; the maximum shear force of the pile body appears about 150 mm below the embedding point; with an increase in depth, the soil-arching effect becomes obvious. There are two different forms of friction, soil-arching and direct soil-arching between piles and behind piles, and the soil between single-row piles has a symmetrical distribution. In addition to the vertical external load and soil settlement load, the pile foundation in reinforced high-fill areas will also be affected by the horizontal load caused by the rear stacking load, and pile stress will be affected by the soil-arching effect in reinforced areas, which has typical passive pile characteristics. In order to study the symmetry of the soil-arching effect of pile foundations in a reinforced-fill area, indoor model tests were designed, and the relevant data for pile foundation and reinforced soil under surcharge were obtained. Through analysis, the following conclusions were drawn: (1) the peak bending moment of the pile body is basically consistent with the position of the potential sliding surface of reinforced soil; the maximum shear force of the pile body appears about 150 mm below the embedding point; with an increase in depth, the soil-arching effect becomes obvious. There are two different forms of friction, soil-arching and direct soil-arching between piles and behind piles, and the soil between single-row piles has a symmetrical distribution. Full article