Understanding solid- and fluid-inertia forces and their coupling with the gravity potential in complex motion scenarios is necessary for evaluating system stability and identifying root causes of system failure and accidents. Because solids and fluids have an infinite number of degrees of freedom and distributed inertia and elasticity, having meaningful qualitative and quantitative nominal measures of the kinematics and forces will contribute to a better understanding of the system dynamics. This paper proposes developing new continuum-based nominal measures for the characterization of the oscillations and forces. By using a material-point approach, these new nominal measures, which have their roots in the continuum-mechanics partial-differential equations of equilibrium and Frenet geometry, are independent of the formulation or generalized coordinates used to develop the dynamic equations of motion. The paper proposes a data-driven-science approach to define a nominal continuum space-curve geometry with nominal curvature and torsion; a nominal instantaneous motion plane (IMP), which contains the resultant of all forces including the inertia forces; and a nominal instantaneous zero-force axis (IZFA) along which the resultant of all forces vanishes. While using the material-point approach eliminates the need for introducing moment equations associated with orientation coordinates, the IMP and IZFA concepts can be used to define the instantaneous axis of significant moment components, which can lead to accidents such as in the case of vehicle rollovers.
Rapid advances in vehicle automation and communication technologies enable connected autonomous vehicles (CAVs) to cross intersections cooperatively, which could significantly improve traffic throughput and safety at intersections. Virtual platooning, designed upon car-following behavior, is one of the promising control methods to promote cooperative intersection crossing of CAVs. Nevertheless, demand variation raises safety and stability concerns when CAVs adopt a virtual platooning control approach. Along this line, this study proposes an adaptive vehicle control method to facilitate the formation of a virtual platoon and the cooperative crossing of CAVs, factoring demand variations at an isolated intersection. This study derives the stability conditions of virtual CAV platoons depending on the time-varying traffic demand. Based on the derived stability conditions, an optimization model is proposed to adaptively control CAVs dynamics by balancing approaching traffic mobility and safety to enhance the reliability of cooperative crossing at intersections. The simulation results show that, compared to the nonadaptive control, our proposed method can increase the intersection throughput by 18.2%. Also, time-to-collision results highlight the advantages of the proposed adaptive control in securing traffic safety.
The microchannel reactor is the most commonly used microreaction technology, an innovative reaction system developed in recent years. This study investigates the mass transfer behavior of a gas–liquid two-phase Taylor flow in a microchannel by coupling the volume-of-fluid model and the species transport model. The concentration distribution and the volumetric mass transfer coefficient of the gas solute are determined and discussed in detail. The simulation results reveal that the double-circulation flow influences the concentration distribution in the liquid slug. The highest value is observed at the bubble's surface and decreases rapidly along the vertical direction of the bubble. The increase of bubble velocity leads to a more apparent decreasing trend. The gas–liquid interface renewal rate of the bubble is accelerated with increasing bubble velocity, resulting in an increase in the average mass transfer rate in all regions of the bubble surface with an increase in bubble velocity. The results also indicate that the liquid film area contributes the most to the mass transfer behavior due to the most significant proportion and average mass transfer rate of the liquid film among the bubble.
The linear multibody system transfer matrix method (LMSTMM) provides a powerful tool for analyzing the vibration characteristics of a mechanical system. However, the original LMSTMM cannot resolve the eigenvalues of the systems with ideal hinges (i.e., revolute hinge, sliding hinge, spherical hinge, cylindrical hinge, etc.) or bodies under conservative forces due to the lack of the corresponding transfer matrices. This paper enables the LMSTMM to solve the eigenvalues of the planar multibody systems with ideal hinges or rigid bodies under conservative forces. For a rigid body, the transfer matrix can now consider coupling terms between forces and kinematic state perturbations. Also, conservative forces that contribute to the eigenvalues can be considered. Meanwhile, ideal hinges are introduced to LMSTMM, which enables the treatment of eigenvalues of general multibody systems using LMSTMM. Finally, the comparative analysis with ADAMS software and analytical solutions verifies the effectiveness of the proposed approach in this paper.
Magnetorheological fluids (MRFs) have been successfully used in a variety of smart control systems, but are still limited due to their relatively poor settling stability. Herein, a core/shell-structured Fe3O4/copolymer composite nanoparticle is synthesized as a new candidate material for stimulus-responsive MRFs to tackle the limitation of the long-term dispersion stability. Aniline-co-diphenylamine copolymers (PANI-co-PDPA) are loaded onto the surface of Fe3O4 nanoparticles, providing a lighter density and sufficient active interface for the dispersion of magnetic particles in the carrier medium. The features of the Fe3O4/copolymer composite nanoparticles, including morphology, compositional, and crystalline properties, are characterized. An MRF is prepared by suspending Fe3O4/copolymer composite nanoparticles in a nonmagnetic medium oil, and its rheological properties are assessed using a controlled shear rate test and dynamic oscillation tests using a rotational rheometer. Rheological models including the Bingham model and the Herschel–Bulkley model are fitted to the flow curves of the MRF. The obtained Fe3O4/copolymer composite shows soft-magnetic properties, as well as greater density adaptability and higher stability, compared to Fe3O4. Moreover, the sedimentation testing provides information about the dispersion stability characteristics of MRF and shows a good correlation with high-stability magnetorheological (MR) response. The Fe3O4/copolymer-based MRF with a tunable and instantaneous MR response is considered a promising material for smart control applications.
High-speed maglev trains are subjected to severe dynamic loads, thus posing a failure hazard. It is necessary to account for the vehicle dynamics to improve the structural strength and fatigue life assessment approach under harsh routes and super high-speed grades. As the most critical load-carrying part between the vehicle body and levitation frames, the swing bar was taken as an example to demonstrate the significance of vehicle dynamics to integrate classical structural strength and fatigue life with the service conditions. A multiphysics-coupled dynamic model of an alpha improvement scheme for an electromagnetic suspension maglev train capable of 600 km/h was established to investigate the complex dynamic loads and fatigue spectra. Using this model, the structural strength and fatigue life of the wrought swing bars were investigated. Results show only a slight effect on the structural strength and fatigue life of swing bars by the super high-speed grades. The nonaxial bending moments caused by the uncompensated relative displacement between the vehicle body and bolsters are identified as the decisive factors. The minimum safety factor of the structural strength for wrought swing bars is 1.33, while the minimum fatigue life is 34 years. Both match the design requirements but are not conservative enough. Therefore, further verification and optimization are recommended to improve the design of swing bars.
The influence of the dynamic parameters of a dual mass flywheel (DMF) on its vibration reduction performance is analyzed, and several optimization algorithms are used to carry out multiobjective DMF optimization design. First, the vehicle powertrain system is modeled according to the parameter configuration of the test vehicle. The accuracy of the model is verified by comparing the simulation data with the test results. Then, the model is used to analyze the influence of the moment of inertia ratio, torsional stiffness, and damping in reducing DMF vibration. The speed fluctuation amplitude at the transmission input shaft and the natural frequency of the vehicle are taken as the optimization objectives. The passive selection method, multiobjective particle swarm optimization, and the nondominated sorting genetic algorithm based on an elite strategy are used to carry out DMF multiobjective optimization design. The advantages and disadvantages of these algorithms are evaluated, and the best optimization algorithm is selected.
A high-fidelity multibody-system dynamic model of the looped tether transportation system (L-TTS) is proposed in this study to study its large deformation as well as large overall motion. The absolute nodal coordinate formulation (ANCF)-based gradient-deficient beam element is employed to establish the accurate model of the two flexible tethers subject to large deformations. The relative movement of climbers along tethers is described by using the sliding joint model based on ANCF. To reduce the collision risks between tethers and climbers, two libration suppression strategies, namely, the decelerated motion of climbers relative to tethers and multiple climbers per tether are investigated in this study. Several numerical simulations not only validate the effectiveness of the two strategies in reducing the collision risks between climbers and tethers, the overall librations of L-TTS, and the magnitudes of the longitudinal elastic force of tethers, but also verify the good performance of the high-fidelity model proposed in this study for dynamic simulation of the L-TTS in microgravity conditions.
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