Vibration isolation and energy harvesting integrated in a Stewart platform with high static and low dynamic stiffness

A modified Galerkin method is proposed to approximate the nonlinear normal modes in a new type of a two-stage isolator. Besides the displacement of payload and the force transmissibility of this typical nonlinear dynamic system, the nonlinear normal modes defined as invariant manifolds can provide more information about the nonlinear coupling between the system components when periodic motions corresponding to the normal modes of the system occur. The presented approach applies a combination of finite-element discretization and Fourier series expansion for the approximate invariant manifolds. A Galerkin projection of the governing equations for the approximate invariant manifolds yields a set of nonlinear algebraic equations in expansion coefficients, which can be solved numerically with a general choice of zero as initial guess for the cases in this work. The resultant approximate solutions for the invariant manifolds can accurately describe the nonlinear interactions between system components in periodic motions of the specific nonlinear normal modes. In addition, one can solve the invariant manifolds for an annular domain of interest directly by this method, without considering other domain that includes the origin of phase space.

Section: A New Type Of a Two-stage Nonlinear Isolatormentioning

confidence: 99%

Nonlinear Normal Modes in a Two‐Stage Isolator Using a Modified Finite‐Element Galerkin Method

2021

“…Vibration isolation is a common method to eliminate or weaken vibration [1,2]. For vehicle vibration, the traditional linear vibration isolator lacks the ability to isolate low-frequency vibration, and the vibration isolation effect is not obvious for 0-20 Hz low-frequency vibration, even having an amplification effect [3].…”

Section: Introductionmentioning

confidence: 99%

Design and Research of Semiactive Quasi‐Zero Stiffness Vibration Isolation System for Vehicles

Feng

Zhao

2021

The vehicle-mounted equipment is easy to be disturbed by external vibration excitations during transportation, which is harmful to the measurement accuracy and performance of the equipment. Aiming at the vibration isolation of the vehicle-mounted equipment, a semiactively controlled quasi-zero stiffness (QZS) vibration isolator with positive and negative stiffness is proposed. The vertical spring is paralleled with a magnetorheological (MR) damper, and the semiactive on-off control scheme is adopted to control the vibration. The analytical expression of the isolator’s displacement transmissibility is derived via the averaging method. Then, the vibration isolation performance under different road excitations and different driving speeds is simulated and compared with the uncontrolled passive QZS vibration isolator. In addition, the mechanical structure of the semiactive QZS isolator is designed and manufactured, and the test system is built by LabVIEW software and PXI embedded system. The isolation effect of the semiactive QZS isolator is verified through test data. It is found that the proposed semiactive QZS isolator shows excellent vibration isolation performance under various road excitations, while the passive QZS isolator is effective only under harmonic excitations. The vertical acceleration of vehicle-mounted device can be decreased over 70% after isolation, and the vibration isolation effect is remarkable. The design idea and research results of the semiactive QZS isolator may provide theoretical guidance and engineering reference for vibration isolation.

“…e research on morphing technology mainly focuses on the design of intelligence structure [19,20], but there are few studies on aerodynamic characteristics and flow mechanism of morphing airfoil. erefore, through CFD and wind tunnel tests, the influence of supercritical airfoil deformation on aerodynamic characteristics and flow structure has been discussed, and the results will be helpful for smart structure parameter choice and analysis on aerodynamic characteristics morphing airfoils.…”

Section: Introductionmentioning

confidence: 99%

Study on Flow Mechanism of a Morphing Supercritical Airfoil

Wang

Lei

et al. 2021

In order to maintain the best performance in flight, a new concept, morphing aircraft, has been proposed, which can change the real-time aerodynamic characteristics under different flight conditions. The key problem is to figure out the response of strong flow instability caused by structure changes during the morphing. To solve this problem, computational fluid dynamics (CFD) and wind tunnel tests (WTT) were employed. The results show that the deformation of thickness and camber angle of the airfoil will significantly change the distribution of pressure and result in obvious hysteresis loops of lift and drag. With the increase of deformation frequency and amplitude, the instability increases correspondingly. Moreover, the unsteady effect caused by camber deformation is much stronger than that caused by thickness deformation. In addition, the flow structures on the airfoil, such as the shock strength and boundary separation location, have a delay in response to structure changes. Therefore, there will be a hysteresis between airfoil deformation and aerodynamic characteristics, which means strong flow instability.