国际机械系统动力学学报(英文)最新文献

To address the dual challenges of routine driving vibration and impact loads in vehicle seat suspensions, a novel variable-gap magnetorheological damper (VGMRD) is proposed. By combining a tapered piston with a conformal variable-diameter cylinder, stroke-dependent, dual-mode damping characteristics are achieved without the need for complex control valves. A theoretical model incorporating the stroke-dependent gap flow dynamics is established, and a finite element analysis of the internal magnetic field distribution is conducted. Numerical results indicate that the magnetic flux lines are concentrated by the converging geometry of the buffer zone, increasing the magnetic flux density by 17.4% without additional power input. Experimental validations utilizing a servo-hydraulic testing system are performed, and the experimental results show good agreement with the theoretical predictions. Specifically, the damping force remains stable within the damping zone. As the piston enters the buffer zone, the damping force increases significantly with displacement. Through the passive self-reinforcement mechanism, the peak damping force is effectively elevated from 2240 N in the damping zone to a maximum of 4296 N. These findings demonstrate the reliability of the proposed VGMRD in preventing mechanical “bottoming-out” while maintaining routine ride comfort.

This cover highlights a multistage control framework for solar-powered wheeled mobile robots, enabling accurate bidirectional trajectory tracking under varying operating conditions. The proposed strategy integrates input–output linearization with differential flatness–based control of the actuator-driver and power-stage subsystems, including an H-bridge and a Buck converter. By explicitly modeling and controlling the actuator-driver dynamics for the first time in this context, the approach achieves robust real-time performance despite parameter uncertainties and voltage disturbances. The experimental validation on a real differential-drive robot prototype, when an emulated photovoltaic source is used, confirms the effectiveness of the integrated control architecture.

This study explores the nonlinear dynamics associated with a passive dynamic walker (PDW), focusing on the bifurcation and stability insights derived from spring and damper mechanics. PDWs, which rely on gravity for stable locomotion without active control, exhibit a rich spectrum of behaviors, from periodic to chaotic motion. The study examines the effects of key system parameters, such as the hip mass ratio, the leg center of mass (CoM) location, spring stiffness, and damper coefficient, on the stability and gait performance of the walker. Through a combination of theoretical analysis and numerical simulations, the paper identifies bifurcation points where periodic orbits transition into chaotic dynamics, shedding light on the critical conditions for stable walking. The results reveal that increased hip mass, spring stiffness, and leg CoM location ratio contribute to faster walking speeds. All of these physical parameters show a non-monotonic effect on stability. Stability first improves and then deteriorates as the parameter values increase. In contrast, the influence of damping on passive walking is relatively minor, and increasing damping does not significantly improve stability, even sometimes leading to the inability to find a stable solution. Moreover, the results also suggest that the addition of the spring can mitigate the bifurcations of the system. This research provides a deeper understanding of the stability transitions in PDWs, with implications for the design of more efficient and robust legged robots.

Understanding the dynamic behavior of structural components is crucial for optimizing performance and ensuring structural integrity. This study presents a new method that combines a systematic experimental investigation of four distinct hole geometries (circular, square, compact rectangular, and long rectangular) with varying hole counts, all designed to maintain equal material removal, and the application of Gaussian Process Regression to model and predict natural frequencies from experimental modal analysis. Experimental modal testing was conducted on 36 beam specimens to evaluate changes in vibrational properties. The results demonstrate a clear relationship between hole geometry and the attenuation of natural frequencies: circular holes resulted in minimal reductions due to uniform stress distribution, whereas square and rectangular holes caused greater stiffness loss, with the most substantial attenuation observed in beams with long rectangular holes where the first natural frequency decreased by up to 44%. The proposed Gaussian Process Regression model achieved high predictive accuracy on the test set, with coefficients of determination (R²) of approximately 0.98 for the first natural frequency, 0.93 for the second, and 0.92 for the third. Sensitivity analysis identified the number of holes as the most influential parameter, contributing 67.8% to variations in the first natural frequency. These findings provide practical guidelines for structural design by identifying optimal hole geometries and counts to achieve weight reduction while maintaining stiffness, and demonstrate the utility of Gaussian Process Regression for reliable modeling of vibrational behavior in perforated beams.

Despite the great potential of diamagnetic levitation accelerometers in detecting low-frequency and weak motion, there is still a demand to further enhance their sensitivity for geophysical and microgravity applications. In this study, a straightforward structural modulating approach is presented to enhance the sensitivity of diamagnetic levitation accelerometer from both theoretical and experimental aspects. It is demonstrated that by regulating the structural parameters of sensing element and permanent magnets, one can refine the magnetic field, diamagnetic forces, and eddy current effect, making it feasible to improve the sensitivity. With the optimized structural parameters, a remarkable sensitivity of 7.32 mm/g, accompanied by ultra-low frequency detection capability (0–1.8 Hz), fine resolution (32 μg), and low noise (6.256 μg/Hz^1/2), can be achieved, highlighting the viability of structural design in developing a high-sensitivity accelerometer.

In-wheel motor drive is the developing direction of automobile electrification and intelligence. However, the increased unsprung mass in in-wheel motor-driven electric vehicles (IWMEVs) leads to higher dynamic tire loads, thereby intensifying vehicle–road coupling interactions. To address this problem, an 11-degree-of-freedom nonlinear dynamic model of a vehicle–motor–road coupled system is developed, incorporating nonlinear suspension, tire stiffness, and road foundation. Using the Galerkin method and trigonometric product formulas, an analytical expression for the sandwich plate road model on a nonlinear viscoelastic foundation is obtained. The vehicle–motor–road coupled model is solved with a validated fixed-step Runge–Kuta method to investigate the coupled effects of electromagnetic excitation, road irregularity, and road vibration. Results reveal that the amplitude–frequency characteristics of electromagnetic excitation are closely related to vehicle–road coupled vibrations. Multiple excitations adversely affect the IWMEV ride comfort. Furthermore, comparative analysis of linear and nonlinear models demonstrates the importance of the developed nonlinear vehicle–motor–road coupling model.

In the present era, powering sensors using green energy is a significant challenge. One promising solution for the power supply of small sensors relies on piezoelectric energy harvesters excited by vortex-induced vibrations (VIVs) generated by wind. In these devices, the harvester typically features a cylindrical bluff body that generates the vortex shedding and also tunes the natural frequency of the cantilever according to the frequency of the excitation. However, in many practical applications, the harvester is not mounted on a perfectly rigid base. The compliance of the base can significantly influence the behavior of the system. Furthermore, harvesters are often installed on moving structures or machines, where base vibrations introduce additional complexities. Therefore, understanding the impact of both harmonic and random base excitations on VIV is essential for harvester design. This paper investigates these phenomena in a comprehensive way. It presents a multiphysics mathematical model of a piezoelectric energy harvester mounted on a moving base, numerical results, and a wide series of experimental tests. The model reliably predicts the harvester behavior under various conditions and enables to extend the experimental investigation. Experimental and numerical results show that base vibrations and VIV can generate voltage in a synergistic way. Nevertheless, for large base vibrations, nonlinear effects take place that affect the maximum amplitude of the generated voltage in the lock-in region. The study shows that these phenomena happen with both harmonic and random base excitation.

This study investigates the hydrodynamic influence of forward transom tapering on a displacement catamaran hull using computational fluid dynamics (CFD) simulations. Five taper configurations ranging from a vertical transom base design to a fully tapered stern (1.00B) were evaluated over a wide Froude number range (Fr = .3 to 1.0). The simulations were performed using a RANS-based solver coupled with the volume of fluid (VOF) method to accurately capture free-surface effects. Turbulence was modeled using the SST k–ω approach to account for boundary layer evolution and wake separation. The analysis focused on resistance components, free-surface wave elevation mapping, transom pressure distribution, and wake streamline to assess hydrodynamic performance. Results indicate that forward tapering significantly affects pressure resistance while frictional resistance is slightly altered. The 0.75B taper configuration consistently demonstrated optimal performance, reducing the total resistance coefficient (C_T) by up to 6.39% and enhancing stern pressure recovery without introducing flow instabilities at higher speeds. Wave elevation analysis revealed a marked reduction in stern hollows and improved surface coherence with longer tapers. Transom pressure mapping showed attenuation of suction zones, while streamline visualizations illustrated wake narrowing and recirculation suppression in tapered configurations. The novelty of this study lies in its focus on geometric forward transom tapering. These findings not only advance the understanding of transom hydrodynamics but also establish the 0.75B forward taper configuration as a practical and efficient design recommendation for resistance reduction in high-speed displacement catamarans.

The derivation of linearized equations and subsequent eigenvalue analysis is the basis for tasks such as frequency-domain response analysis, control design, and stability assessment for mechanical systems. However, for general multibody systems with redundant or nonholonomic constraints, practical challenges persist in achieving numerically stable linearization and reliable eigenvalue analysis. This study provides numerically reliable linearization and eigenvalue analysis algorithms of Lagrange's equations of the first kind for general multibody systems, and forms a systematic computational framework. First, a robust linearization methodology is developed to automatically generate linearized state-space equations. Coordinate partitioning is employed not only to eliminate redundant constraints and dependent coordinates, but also to significantly simplify the calculations. Second, a direct eigenvalue analysis on Redundant Coordinate Set Jacobians is performed instead of decomposing the state matrix, for its better numerical conditioning and sparsity. The equivalence of the eigenvalue problems is strictly proven theoretically. The methodology is validated by various benchmark problems and practical cases. The proposed approach has been implemented and released with a general-purpose rigid-flexible coupled multibody dynamics software INTESIM-FMBD (v7.0), and provides a reliable numerical tool for linearizing general mechanical systems.