国际机械系统动力学学报(英文)最新文献

This paper aims to analyse the free vibrations of doubly curved imperfect shear deformable functionally graded material microshells using a five-parameter shear deformable model. Porosity is modeled via the modified power-law rule by a logarithmic-uneven variation along the thickness. Coupled axial, transverse, and rotational motion equations for general doubly curved microsystems are obtained by a virtual work/energy of Hamilton's principle using a modified first-order shear deformable theory including small size dependence. The modal decomposition method is then used to obtain a solution for different geometries of microshells: spherical, elliptical, hyperbolic, and cylindrical. A detailed study on the influence of material gradation and porosity, small-length scale coefficient, and geometrical parameters on the frequency characteristics of the microsystem is conducted for different shell geometries.

This study investigates the application of the inverse finite element method (iFEM) in fracture mechanics by developing a novel two-dimensional six-node triangular inverse crack-tip element. With its simplified formulation, the proposed inverse element is computationally efficient and ensures strain singularity at the crack tip by repositioning midside nodes. Its displacement-based stress intensity factor (SIF) computation methodology integrates seamlessly with the existing iFEM framework, making it highly suitable for real-time health assessment of structures with pre-existing cracks. The inverse element has been rigorously validated for shape-sensing and mixed-mode SIF calculations by considering various crack geometries and mixed-mode loading conditions. The triangular inverse element demonstrates superior flexibility in handling structured and unstructured discretizations in mapping regular and complex geometries, particularly high-stress gradient areas like crack tips. The study also explores the variational least squares method for optimal sensor placement within the inverse element domain, ensuring accurate shape-sensing and SIF computations with fewer onboard strain sensors. The proposed inverse formulation, with its accurate shape-sensing capabilities and precise reconstruction of fracture parameters, represents a significant advancement in the real-time Structural Health Monitoring of engineering structures with pre-existing cracks.

The BallBot, a versatile robot system, finds applications in various domains of life. It comprises a frame moved by three wheels mounted on a ball. The robot performance is significantly influenced by its parametric configuration, including body mass, chassis size, and ball diameter. This study examines the impact of these configuration parameters on the control of the BallBot. The mathematical model of the BallBot is discussed, considering the assumptions and coordinate systems. To control the robot, a Linear Quadratic Regulator controller is designed. Subsequently, the simulation model is used to assess the effects of changing the initial parametric configuration. It is observed that altering the robot mass has a notable impact on the BallBot response, while changes in the ball diameter have a relatively insignificant effect.

Analytic expressions of the dynamic coefficient (DC) factor and vibrational behavior of a uniformly elastic isotropic beam with a simple boundary condition caused by accelerating masses with varying velocities are analyzed. The motion of this problem is described by a fourth-order partial differential equation, which governs its behavior. The weighted residual method converts the governing equation into a sequence of linked second-order differential equations to facilitate the analysis. A rewritten version of Struble's asymptotic method further simplifies the transformed governing equation. This modification aids reduction in the complexity of the equation. The closed-form response is contrasted across three force motions: acceleration, deceleration, and uniform motion. The study thoroughly examines how different velocities and frequencies of the moving force affect the dynamic behavior of the beam. The study also examines the influence of load velocity on the DC of the beam subjected to pinned–pinned boundary conditions.

With the removal of indoor pollutants and the assurance of air quality emerging as critical research topics, the optimization of the internal environment in offices, where people stay for extended periods, is essential for controlling the spread of infectious respiratory particles. Frequent movements of personnel and the operation of doors and windows within offices significantly impact the mechanisms of droplet transmission, warranting further investigation. This study employs computational fluid dynamics simulations to explore the droplet dispersion characteristics and pollutant removal efficiency of the simplified model of perforated plate ventilation system (PPVS) (the diameter of the air supply openings has been reasonably simplified and uniformly set to 0.02 m) in office settings, as well as the impact of dynamic door operation scenarios on droplet spread and concentrations in breathing zones. To optimize the ventilation system's pollutant removal efficiency, airflow velocities (2.86, 3.18, and 5.00 m/s) are varied, with simulations conducted at the optimal velocity of 3.18 m/s. The effects of continuous door operations, door-opening directions (towards the office and towards the isolation room), and opening speeds (π/4, π/6, π/8, and π/10 rad/s) are also examined, revealing significant impacts on droplet spread. Results indicate that PPVS effectively reduces indoor pollutant concentrations at all tested airflow velocities, with the optimal speed identified as 3.18 m/s. Additionally, door-opening direction and speed can significantly influence droplet spread. Opening doors towards isolation rooms at smaller angles (less than 30°) effectively reduces droplet concentrations in personnel breathing zones, thereby mitigating the risk of droplet transmission. Faster door-opening speeds also contribute to lower droplet concentrations in these zones. This innovative study explores the impacts of PPVS and dynamic door operation dynamics on droplet transmission during respiratory disease outbreaks, providing valuable theoretical insights and technical support for disease prevention and indoor air quality improvement.

To address the difficulty in extracting early fault feature signals of rolling bearings, this paper proposes a novel weak fault diagnosis method for rolling bearings. This method combines the Improved Complementary Ensemble Empirical Mode Decomposition with Adaptive Noise (ICEEMDAN) and the Improved Maximum Correlated Kurtosis Deconvolution (IMCKD). Utilizing the kurtosis criterion, the intrinsic mode functions obtained through ICEEMDAN are reconstructed and denoised using IMCKD, which significantly reduces noise in the measured signal. This approach maximizes the energy amplitude at the fault characteristic frequency, facilitating fault feature identification. Experimental studies on two test benches demonstrate that this method effectively reduces noise interference and highlights the fault frequency components. Compared with traditional methods, it significantly improves the signal-to-noise ratio and more accurately identifies fault features, meeting the requirements for discriminating rolling bearing faults. The method proposed in this study was applied to the measured vibration signals of the gearbox bearings in the new high-speed wire department of a Long Products Mill. It successfully extracted weak characteristic information of early bearing faults, achieving the expected diagnostic results. This further validates the effectiveness of the ICEEMDAN–IMCKD method in practical engineering applications, demonstrating significant engineering value for detecting and extracting weak impact characteristics in rolling bearings.

Electrically assisted turbochargers (EAT) improve intake efficiency by motor-assisted compressor impeller rotation, enhancing the system's transient response. However, the addition of motor rotor components has increased the number of unbalanced positions in the shaft system, leading to problems such as excessive compressor end vibration and complex changes in oil film stability. To evaluate the effects of unbalance in the motor rotor, along with the parameters of floating ring bearings (FRB), on the dynamic response of EAT, a finite element model of an EAT rotor supported by nonlinear FRB is developed, and the vibration response of the compressor end bearing is obtained by numerical integration. The results indicate: (1) In contrast to the effect of compressor and turbine unbalance, proper motor rotor unbalance is more effective in suppressing oil whirl instability in the high-speed operating range. However, a new inner oil film whirl “instability interval” is also induced in the low-speed operating range, leading to an increase in the Y₁ compressor-end amplitude at low and medium speeds, and this “instability interval” increases with the amount of unbalance. (2) When an oil whirl occurs in the oil film, the maximum eccentricity of the bearing surges and is greater than 0.3, which can be used as an effective threshold for determining whether the oil film is unstable in engineering applications. (3) A suitable outer oil-film clearance range should be $$, otherwise, a wide range of outer oil-film whirl instability occurs. Controlling the amount of unbalance and oil-film clearance to suppress the sub-synchronous vibration of the EAT, provides a theoretical basis for the design of the dynamics of the nonlinear rotor bearing system and improves the stability of the turbocharger's operation.

Having accurate values of the dynamic parameters is necessary to characterize the dynamic behaviors of mechanical systems and for the prediction of their responses. To accurately describe the dynamic characteristics of industrial robots (IRs), a new method for dynamic parameter identification is proposed in this study with the goal of developing a real IR dynamics model that combines the multibody system transfer matrix method (MSTMM) and the nondominated sorting genetic algorithm-II (NSGA-II). First, the multibody dynamics model of an IR is developed using the MSTMM, by which its frequency response function (FRF) is calculated numerically. Then, the experimental modal analysis is conducted to measure the IR's actual FRF. Finally, the objective function of the minimum errors between the calculated and measured eigenfrequencies and FRFs are constructed to identify the dynamic parameters of the IR by the NSGA-II algorithm. The simulated and experimental results illustrate the effectiveness of the methodology presented in this paper, which provides an alternative to the identification of IR dynamic parameters.

Cover Caption: An innovative negative-stiffness device (NSD) that modifies the apparent stiffness of the supported structure for seismic isolation is presented. The NSD comprises a lower base on the bottom and a cap on the top, together with a connecting rod, vertical movable wall, and compressed elastic spring, as well as circumferentially arranged, pretensioned external ropes, and inclined shape memory wires. This configuration can deliver negative stiffness and energy dissipation in any direction within the horizontal plane. A numerical model of the device is developed through a two-step semirecursive method to obtain the force–displacement characteristic relationship. Such a model is first validated through comparison with the results obtained via the commercial software ADAMS. Finally, a large parametric study is performed to assess the role and the influence of each design variable on the overall response of the proposed device. Useful guidelines are drawn from this analysis to guide the system design and optimization.

In response to the limitations of the single-chamber water jet thruster used in underwater vehicles mimicked by natural cephalopods, a novel approach involving a double-chamber water jet thruster has been proposed. This thruster utilizes electromagnetic force to manipulate the diaphragm, thereby altering the volume of the upper and lower chambers to achieve water jet propulsion. Experimental investigations were conducted to determine the tensile length-force characteristics of the diaphragm made of Agileus30. Subsequently, key parameters of essential propulsion components, such as solenoid coils, electromagnets, and currents, were established based on the tensile length-force curve, and the propulsion capabilities of the system were evaluated through theoretical analysis. Theoretical assessments indicate that the system does not produce reverse thrust regardless of whether the coil moves up or down. Further experimental results demonstrate that the maximum peak propulsion force generated by the dual-chamber water jet thruster within a 3-s cycle is 0.253 N.