A flexible two degrees of freedom (2-DOF) steering model of multi-axlevehicle (MAV) is presented with considering the effect of frame flexibility based on the classic2-DOF model. A method to calculate the frame flexib...A flexible two degrees of freedom (2-DOF) steering model of multi-axlevehicle (MAV) is presented with considering the effect of frame flexibility based on the classic2-DOF model. A method to calculate the frame flexibility is derived by using three moments equation.The steering stability of MAV is analyzed. The steering performance of MAV is also researched infrequency domain. Simulation results show that the dynamic effects of flexible model are more severethan rigid model and the flexible effect of frame will weaken the steering stability of MAV.Different disposals of steering axles lead to different steering characteristics of MAV. Thein-phase steering mode improves the steering characteristics and stability at high speed. Theanti-phase steering mode increases the steering mobility at low vehicle speed.展开更多
Till now, there have been lots of researches on numerical simulation of vortex-induced vibration. Acceptable results have been obtained for fixed cylinders with low Reynolds number. However, for responses of 2-DOF vor...Till now, there have been lots of researches on numerical simulation of vortex-induced vibration. Acceptable results have been obtained for fixed cylinders with low Reynolds number. However, for responses of 2-DOF vortex-induced vibration with low mass ratio, the accuracy is not satisfactory, especially for the maximum amplitudes. In Jauvtis and Williamson＇s work, the maximum amplitude of the cylinder with low mass ratio m＊=2.6 can reach as large as 1.5D to be called as the ＂super-upper branch＂, but from current literatures, few simulation results can achieve such value, even fail to capture the upper branch. Besides, it is found that the amplitude decays too fast in the lower branch with the RANS-based turbulence model. The reason is likely to be the defects of the turbulence model itself in the prediction of unsteady separated flows as well as the unreasonable setting of the numerical simulation parameters. Aiming at above issues, a modified turbulence model is proposed in this paper, and the effect of the acceleration of flow field on the response of vortex-induced vibration is studied based on OpenFOAM. By analyzing the responses of amplitude, phase and trajectory, frequency and vortex mode, it is proved that the vortex-induced vibration can be predicted accurately with the modified turbulence model under appropriate flow field acceleration.展开更多
The sense of touch as a man-machine communication channel can be as acute as the sense of sight and sound. In some scenarios such as those seen in aerobatics, stunt flying, and combat flights, tactile sensors can even...The sense of touch as a man-machine communication channel can be as acute as the sense of sight and sound. In some scenarios such as those seen in aerobatics, stunt flying, and combat flights, tactile sensors can even outperform the conventional non-contact sensors in terms of situation awareness. Fusion of tactile sensory information with those obtained via sight and sound can avoid diverting the user’s attention away from the operational task at hand as well. In this study, the performance of an operator, to servo control the motion of a 2-dof model helicopter with pitch/yaw maneuverability, subjected to an intuitive body-referenced arrangement of a cluster of vibro-tactile sensors is investigated. A blindfolded operator will then control the helicopter to a safe attraction zone via a joystick based on this tactile sensory information. A fine-tuned local controller would take over for the end-of-motion precise homing. This study can pave the way towards a systematic integration and characterization of tactile sensors in high performance weapon platforms with improved situation awareness in visually awkward maneuvers such as those seen in aerial combat scenarios.展开更多
文摘A flexible two degrees of freedom (2-DOF) steering model of multi-axlevehicle (MAV) is presented with considering the effect of frame flexibility based on the classic2-DOF model. A method to calculate the frame flexibility is derived by using three moments equation.The steering stability of MAV is analyzed. The steering performance of MAV is also researched infrequency domain. Simulation results show that the dynamic effects of flexible model are more severethan rigid model and the flexible effect of frame will weaken the steering stability of MAV.Different disposals of steering axles lead to different steering characteristics of MAV. Thein-phase steering mode improves the steering characteristics and stability at high speed. Theanti-phase steering mode increases the steering mobility at low vehicle speed.
基金financially supported by the National Natural Science Foundation of China(Grant No.51509045)
文摘Till now, there have been lots of researches on numerical simulation of vortex-induced vibration. Acceptable results have been obtained for fixed cylinders with low Reynolds number. However, for responses of 2-DOF vortex-induced vibration with low mass ratio, the accuracy is not satisfactory, especially for the maximum amplitudes. In Jauvtis and Williamson＇s work, the maximum amplitude of the cylinder with low mass ratio m＊=2.6 can reach as large as 1.5D to be called as the ＂super-upper branch＂, but from current literatures, few simulation results can achieve such value, even fail to capture the upper branch. Besides, it is found that the amplitude decays too fast in the lower branch with the RANS-based turbulence model. The reason is likely to be the defects of the turbulence model itself in the prediction of unsteady separated flows as well as the unreasonable setting of the numerical simulation parameters. Aiming at above issues, a modified turbulence model is proposed in this paper, and the effect of the acceleration of flow field on the response of vortex-induced vibration is studied based on OpenFOAM. By analyzing the responses of amplitude, phase and trajectory, frequency and vortex mode, it is proved that the vortex-induced vibration can be predicted accurately with the modified turbulence model under appropriate flow field acceleration.
文摘The sense of touch as a man-machine communication channel can be as acute as the sense of sight and sound. In some scenarios such as those seen in aerobatics, stunt flying, and combat flights, tactile sensors can even outperform the conventional non-contact sensors in terms of situation awareness. Fusion of tactile sensory information with those obtained via sight and sound can avoid diverting the user’s attention away from the operational task at hand as well. In this study, the performance of an operator, to servo control the motion of a 2-dof model helicopter with pitch/yaw maneuverability, subjected to an intuitive body-referenced arrangement of a cluster of vibro-tactile sensors is investigated. A blindfolded operator will then control the helicopter to a safe attraction zone via a joystick based on this tactile sensory information. A fine-tuned local controller would take over for the end-of-motion precise homing. This study can pave the way towards a systematic integration and characterization of tactile sensors in high performance weapon platforms with improved situation awareness in visually awkward maneuvers such as those seen in aerial combat scenarios.
