Low Frequency Torsional Vibration Research Articles

Low-frequency band gaps in quasi-zero stiffness locally resonant metamaterial shaft

The suppression of low-frequency torsional vibration has always been a difficult problem in the field of vibration control. Recently, metamaterials have attracted considerable attention due to their superior vibration insulation properties, at least in some targeted and tunable band gaps ranges. In particular, the position of the local resonance band gaps is related to the resonance frequency of the local resonator (LR). In this paper, a novel quasi-zero-stiffness torsional LR is proposed and a metamaterial shaft is devised by periodically attaching this LR onto a uniform shaft. The statics analysis for the torsional LR is conducted, and the propagation characteristics of the torsional vibration in the metamaterial shaft is studied with the transfer matrix theory and the Galerkin method. The analytical dispersion relation and the band gap structure indicate the existence of low frequency band gaps. And the location of the band gaps and the attenuation ability of torsional vibration can be effectively controlled by tuning the structural parameters of LR and the material of shaft, which provide a theoretical basis and guidance for addressing the challenge of low-frequency torsional vibration suppression.

Superconducting Precursors in Bi/Pb Multiphase Cuprates Fabricated by the Solar Technology and their Comparative Study by Torque Magnetometry Methods

A special method has been applied to synthesize HTSC samples of Bi1.7Pb0.3Sr2Ca(n-1)CunOy with increased local inhomogeneities, using solar energy for the melting and following superfast quenching of the melt (SFAQ-T technology). This study carried out a comparative analysis using low-frequency torsional vibration and resonant vibrating reed spectroscopy methods. The results showed a possibility for the existence of high-temperature superconducting precursors with Tc = 107-138 K and the potential advantages of the application of the resonant vibrating reed method.

Study on low-frequency torsional vibration suppression of integrated electric drive system considering nonlinear factors

The integrated electric drive system (IEDS) is widely used in battery electric vehicles due to its advantages of high power density, small size, and low cost. However, on account of the electromechanical coupling between its subsystems, the problem of high torsional vibration is brought about. Therefore, based on the establishment of the electromechanical coupling model of IEDS and the analysis of the influence of time-varying mesh stiffness and backlash on the system characteristics, this paper proposes a double-layer optimization control strategy of IEDS torsional vibration basis of the torque command optimization and the principle of minimum error of instantaneous current tracking. By adjusting the motor torque command in real-time and reducing the error between the actual current and the target current, the oscillation amplitude of IEDS under Tip in/out condition is reduced by 63.7%, and the time required to achieve stability is shortened by 79.04% and 76.90% respectively. The simulation results show that the proposed control strategy greatly reduces the torsional vibration of IEDS and improves the comfort of the vehicle.

Circular Halbach negative stiffness isolating from torsional vibration: Design, modeling and experiments

Excessive torsional vibration is detrimental to the operation performance of key mechanical equipment. To attenuate low-frequency torsional vibration in high payload occasions, the negative stiffness isolator has been widely employed. However, due to the space constraints of compact rotating machinery, it is difficult to promote negative stiffness for counteracting high positive stiffness. Therefore, a circular Halbach torsion negative stiffness isolator is proposed to provide high torsional magnetic negative stiffness for low-frequency isolation. The semi-analytical expressions of tangential-tangential coupling and tangential-radial coupling for tile magnets are derived to calculate the magnetic torque and the torsional stiffness of circular magnetic arrays, and then the influences of structural parameters on magnetic negative stiffness are investigated. The simulation results show that the circular Halbach array has the much higher magnetic stiffness than the circular traditional array. The dynamic responses of the proposed torsional isolator are analyzed based on harmonic balance method. Moreover, experimental results show that the onset isolation frequencies of circular Halbach isolator and circular traditional isolator can be decreased by 32.57% and 17.90% respectively compared with the linear isolator. Therefore, it is demonstrated that the proposed circular Halbach isolator has a preferable performance for low frequency torsional isolation.

Wearable bistable triboelectric nanogenerator for harvesting torsional vibration energy from human motion

It is ubiquitous for torsional vibration of joint in human motion. However, it is difficult to harvest low-frequency torsional vibration energy from human motion using conventional triboelectric nanogenerators (TENGs). Herein, we propose a wearable bistable triboelectric nanogenerator (WBTENG) with a bistable stiffness feature, which enables high-efficiency torsional vibration energy harvesting from human motion. The prototype of the WBTENG is fabricated to test the electrical performance of the WBTENG. The dependencies of the electrical performance of the WBTENG on dynamic behaviors are investigated. Subsequently, the experiments are carried out to investigate the output voltages under different excitation frequencies, the output power varying with the load resistances and the durability of the WBTENG. In addition, the effect of the excitation amplitude on the electrical output performance of the WBTENG is investigated in detail. The bistable mechanism of the WBTENG is proved to switch the motion pattern between interwell and intrawell oscillations. The peak power is found to reach the highest value of 3.39 mW at 3 Hz with the resistance of 90 MΩ when the WBTENG exhibits interwell oscillation. Moreover, the WBTENG can power a light-emitting diode (LED) array and drive a temperature sensor under human motions. Therefore, the WBTENG can harvest torsional vibration energy efficiently from human motion.

Compliant quasi-zero-stiffness isolator for low-frequency torsional vibration isolation

The structures of traditional torsional quasi-zero-stiffness (QZS) vibration isolators are too complicated to achieve the desired vibration isolation performance as theoretically predicted. To resolve this issue, this study proposes a compliant quasi-zero-stiffness (CQZS) isolator to isolate low-frequency torsional vibrations in the shaft system. First, the configuration of the CQZS isolator is devised using a compliant mechanism, and the stiffness characteristics of the CQZS isolator are deduced analytically based on the energy method and verified using the finite element method. Subsequently, a dynamic model of the shaft system integrated with the CQZS isolator is established. The equation of motion for the shaft system is solved theoretically using the harmonic balance method. Finally, a prototype is fabricated using 3D printing technology with polylactic acid material, and static and dynamic experiments are conducted to verify the theoretical prediction. The results indicate that the CQZS isolator can achieve ideal torsional QZS characteristics and fulfil low-frequency torsional vibration isolation. The proposed CQZS isolator is much more compact, lightweight, and easier to manufacture than conventional QZS isolators.

Design and theoretical investigation of a torsional bistable triboelectric nanogenerator

Triboelectric nanogenerator (TENG) has been proven to be a high-efficiency device for converting vibration energy into electrical energy. However, the conventional TENG is unable to harvest energy from torsional vibration. To solve this issue, a torsional bistable triboelectric nanogenerator (TBTENG) is proposed. The essential part of the TBTENG is the S-shaped compliant beam, which enables bistability during torsional vibration. Firstly, the stiffness expression of the S-shaped beams is derived using the energy method, and verified by the finite element analysis (FEA). Then, the mechanical and electrical responses of the TBTENG are obtained by solving the equation of motion, and the unidirectional coupled electromechanical equation, respectively. The numerical simulations of the circuit model are also carried out using MATLAB/SIMULINK to validate the theoretical predictions. The effects of system parameters of the TBTENG on both the dynamic responses and electrical outputs are investigated. Finally, the experiment on the prototype of the TBTENG is conducted to verify the design concept. The results show that the novel bistable structure can drive the system to oscillate with large amplitude, which enables the TBTENG to effectively harvest energy from low-frequency torsional vibration. The peak power reaches the maximum value of 0.7 mW at 4 Hz. Moreover, the bandwidth of harvesting energy from low-frequency torsional vibration can be effectively broadened by enhancing the bistability.

Dual-objective torque control of electric vehicles drivetrain with robust global finite-time stability guarantee

The low-frequency torsional vibration caused by a sudden input torque change seriously affects electric vehicles' comfort and dynamic performance (EVs). This paper proposes a novel torque controller with robust global finite-time stability based on terminal sliding mode control to achieve the dual objectives of anti-jerk control and traction torque control. For this purpose, a general second-order system of EVs drivetrain with a disturbance term is established, and a new finite-time terminal sliding surface is designed. The proposed finite time torque controller (FT-TC) includes a finite-time sliding mode disturbance observer for real-time disturbance estimation and a finite-time sliding mode motor controller for calculating motor torque control law. In addition, the elimination of inherent chattering of the controller is considered in this paper. Finally, the proposed FT-TC is verified and compared with parallel double-loop PID controller and sliding mode controller on the Matlab/Simulink platform and an electric SUV platform under the condition of suddenly pressing/releasing the accelerator pedal during starting. The results indicate that the proposed FT-TC is effective and has a better synthetic evaluation performance in achieving the dual objectives.

An electromagnetic torsion active vibration absorber based on the FxLMS algorithm

Dynamics vibration absorbers are an effective solution to the problem of vibration. However, there are relatively few applications in low-frequency torsional vibration control. Therefore, for low-frequency torsional vibration, this paper proposes an electromagnetic torsional active vibration absorber, and establishes an active control system based on the filter-x least mean square (FxLMS) algorithm. First of all, the electromagnetic torsion actuator structure is designed with an electromagnetic-permanent magnetic hybrid structure, and the theoretical model of electromagnetic torque is established. Moreover, the influence of structural parameters on the linear stable interval of electromagnetic torque is analyzed, and the effective stroke range of electromagnetic torsion actuator is determined. Then, based on the FxLMS algorithm, the control system of the electromagnetic torsion active vibration absorber is established, and the theoretical model of the secondary channel transfer function is obtained. Furthermore, it is verified by simulation analysis, the results show that the electromagnetic torsional active vibration absorber can achieve good low-frequency torsional vibration absorption performance and is significantly better than without control under the excitation of harmonic torque and white noise torque. Finally, an experimental investigation is carried out on the electromagnetic torsion active vibration absorber based on the FxLMS algorithm to verify the feasibility and effectiveness of the electromagnetic torsion active vibration absorber.

Semi-analytical torque modeling of Ti-6Al-4V-alloy internal trapezoidal thread extrusion forming with an emphasis on low-frequency torsional vibration

Abstract Conventional cold extrusion is generally considered to be less practical for trapezoidal threads, requiring a relatively large form tapping torque. The machining of it is always based on cutting, but the actual demands of high strength and long life have brought this process to its limits. These requirements drove the present work, which proposes a new process for the fabrication of a Ti-6Al-4V-alloy trapezoidal thread using low-frequency torsional vibration extrusion (LTVE) through a forming tap. A semi-analytical model of torsional vibration extrusion with friction was established by solving the problem of mechanical friction and slip-line field. The influence of low-frequency torsional vibration on the form tapping torque was studied, and the total amounts were determined quantitatively. The conclusion shows that the total tapping torque was composed of the positive pressure load and the friction load on the forming tap. The friction load was generated by the tool/workpiece friction, which is the largest component, accounting for more than 90 %. The introduction of vibration can reduce the friction in the thread form tapping so as to obtain high rheological properties, which is applicable for the low-frequency stage. Finally, a mechanical LTVE tapping excitation device was proposed based on this process method, and an experimental prototype that can meet the requirements of titanium alloy trapezoidal thread machining was developed. Experimental verification indicated that the LTVE forming process had reduced the total form tapping torque. It also proved the method’s overall reliability and effectiveness and the underlying insights needed to guide the thread manufacturing.

Modern Diagnostics of Aircraft Gas Turbine Engines

The article deals with the assessment of the technical condition of gas turbine engines. The analysis of the application of traditional approaches to the assessment of the technical condition of gas turbine engines. The technique of obtaining parameters of low-frequency torsional vibrations of the shaft on the basis of precision chronometric measurements is presented.

Effect of Repeated Cutting on Low-frequency Torsional Vibration Tapping Torque

Low-frequency torsional vibration tapping can significantly reduce the tapping torque, which is an effective method to solve the problem of precision machining of small and deep threaded holes on difficult-to-cut materials. In this paper, the mechanism of repeated cutting of low-frequency torsional vibration tapping is studied by comparing continuous tapping with low-frequency torsional vibration tapping on titanium alloy, and the influence law and mechanism of the process parameters such as repeated cutting times and net cutting angle on the tapping torque are studied through the vibration tapping experiments on different materials. The research results show that under the premise of ensuring the processing efficiency, smaller net cutting angle and larger repeated cutting times should be selected to obtain a good process effect.

Mechanism analysis and suppression strategy research on permanent magnet synchronous generator wind turbine torsional vibration

Torsional vibration of flexible drive chain is a historical issue. With the maximization development and the rotating machinery high-speed operation, the drive chain systems of large-scaled units become more and more complex, which makes the torsional vibration problems becoming increasingly prominent in recent years. This article deeply analyzed the small signal stability of large-scaled WECS based on CMT, elaborated the torsional vibration mechanism and reasons for the first time and pointed out torsional vibration is caused by the disturbance wind and the DPC strategy. The disturbance wind is an external stimulus and can produce a low-frequency torsional vibration at the same frequency as wind speed. The DPC could weaken the drive chain damping. If the total damping of drive chain is negative, the unstable torsion vibration will occur. And if the drive chain is still a under-damped dynamic, the high-frequency torsional vibration at natural frequency will be generated. Therefore, large-scaled WECS must have damping control. This study found that appropriate enhancing drive chain stiffness could reduce low-frequency torsional vibration caused by wind speed. Therefore, a damping and stiffness compensation control method was proposed to suppress the torsional vibration. Compared with the conventional damping control, the new method not only can suppress the high-frequency torsional vibration but also has a good restraining effect on the low-frequency torsional vibration. Furthermore, the detailed design procedures including the calculation of injection damping and stiffness were given in this paper. Finally, the correctness and effectiveness of our analysis were further verified by the simulation experiments

Experimental analysis of driveline shuffle with focus on the interaction between traction and torsional vibrations

Abstract Recent research showed by theoretical analysis a significant role of the interaction between traction and low-frequency torsional vibrations (known as driveline shuffle) on anti-jerk controller design in passenger cars. This paper addresses the experimental validation of these findings in a wide range of operating points. Various experiments have been performed with a plug-in hybrid electric vehicle. Several excitation amplitudes have been applied at different vehicle speeds and driving conditions. As a result, the dependency of the driveline shuffle characteristics is quantified in this study. These results are the first step towards a guideline for control engineers during the model selection process for either anti-jerk controller concept design, parametrization or validation. Based on these results a linear parameter varying model (LPV) is proposed.

Анализ возможности подавления крутильных колебаний антенны космического аппарата с помощью динамического гасителя

The paper deals with dynamics of truss antenna systems with a dynamic absorber in the region of low-frequency natural torsional vibrations. The use of a dynamic absorber is due to the weak dissipative properties of the antenna system. Owing to the internal resonance, energy is transferred from the elastically fixed antenna system to the dynamic absorber, whose vibrations are damped quite simply. A theoretical study of the dynamic characteristics of the absorber was carried out on a simple linear model of a two-degree-of-freedom vibrating system. The equations of motion are integrated numerically. Findings of research show that the mass of the dynamic absorber is about 5% of the mass of the reflector, the absorber should be as far as possible relative to the axis of rotation of the system, and it can be used instead of balancing weights. The ranges of design parameters of the dynamic absorber and the levels of loads at which it operates efficiently are determined

Double-Target Switching Control of Vehicle Longitudinal Low-Frequency Vibration Based on Fuzzy Logic

Rapid increase of vehicle longitudinal acceleration is required in an engine torque increasing phase, whereas little overshoot and oscillating acceleration are required in a torque holding phase. These two features give satisfying results with respect to both drivability and comfortability. However, when subjected to a sudden torque change in the tip-in condition, the driveline undergoes strong low-frequency torsional vibration which has an adverse impact on vehicle comfortability. Normally, a linear quadratic (LQ) controller has a good comfort performance in reducing the vibration but with negative impact on the dynamic response of the vehicle which weakens the drivability. The two different performance demands in the two phases cannot be achieved simultaneously by only adjusting the weighting coefficients of the LQ controller. Therefore, a new control strategy decoupling the two phases is necessary and proposed in this paper. A linear quadratic regulator (LQR) is used in the torque increasing phase for dynamic response demand while a linear quadratic tracking (LQT) controller is applied in the torque holding phase for comfortability demand. The two controllers are switched smoothly via a fusion weighting factor based on the proposed fuzzy logic switching strategy. A quantitative evaluation method is used to evaluate the performances of the proposed control strategy. The results show that the double-targets switching control keeps better performances in both drivability and comfortability. The comfortability index of the proposed strategy is improved by 79.74% compared with that of the LQT whereas the dynamic response index is improved by 21.88% compared with that of the LQR.

A novel vibration measurement and active control method for a hinged flexible two-connected piezoelectric plate

Abstract A novel non-contact vibration measurement method using binocular vision sensors is proposed for piezoelectric flexible hinged plate. Decoupling methods of the bending and torsional low frequency vibration on measurement and driving control are investigated, using binocular vision sensors and piezoelectric actuators. A radial basis function neural network controller (RBFNNC) is designed to suppress both the larger and the smaller amplitude vibrations. To verify the non-contact measurement method and the designed controller, an experimental setup of the flexible hinged plate with binocular vision is constructed. Experiments on vibration measurement and control are conducted by using binocular vision sensors and the designed RBFNNC controllers, compared with the classical proportional and derivative (PD) control algorithm. The experimental measurement results demonstrate that the binocular vision sensors can detect the low-frequency bending and torsional vibration effectively. Furthermore, the designed RBF can suppress the bending vibration more quickly than the designed PD controller owing to the adjustment of the RBF control, especially for the small amplitude residual vibrations.

The He2-OCS complex: Comparison between theory and experiment

OCS is an ideal probe for quantum solvation effects in cold helium clusters. He2-OCS is the “second step” in going from a single OCS molecule to a large doped superfluid helium cluster. Here assignment of the spectrum of He2-OCS is significantly extended to higher values of J, K, and vt (the low frequency torsional vibration). The observation of a new infrared band, OCS ν1 + ν3, taken together with the known ν1 band, enables assignments to be verified by comparing ground state combination differences. Relatively straightforward scaling of previously calculated theoretical energy levels gives a remarkably good fit to experiment.

Study on Vibration Tapping for SiCp/Al Particle-reinforced Metal Matrix Composite

Aiming at answering the question that low tap service life of ordinary tapping and bad thread quality on particle-reinforced metal matrix composite SiCp/Al, the reason of question and the mechanism of low-frequency torsional vibration tapping are analyzed. The experiments were carried out to compare the tap service life and the thread quality of vibration tapping with ordinary tapping without cutting fluid. It indicates that vibration tapping could make tapping torque reduce greatly, the tap service life could be prolonged twice comparing with continuous tapping without cutting fluid, and could ensure the good thread quality. Moreover, it promotes metal matrix composite’s further application.

Investigation of electromechanical coupling vibration characteristics of an electric drive multistage gear system

In order to investigate the electromechanical interaction mechanism, a dynamic model of an electric drive multistage gear system is established, wherein the electromagnetic characteristics of the induction machine and the translational-rotational vibration of the gearbox are considered. The influence of the electromagnetic effect on the natural vibration characteristics of the gearbox is studied. An integrated method using Campbell diagram, modal energy and speed sweep analysis is presented to identify the resonances of the electromechanical system. The spectrum characteristics of the mechanical signals and the electrical signals are also compared. The results demonstrate that the magnetic field introduces a new vibration mode to the gearbox and changes the low-frequency torsional vibration characteristics of each component. The system investigated in this study exhibits resonance risk when the rotor speed approaches 989 r/min, and it requires special attention during actual operation. When mechanical resonance occurs, recognizable shape features appear in the spectrum of the current and electromagnetic torque. This study supplies some guidance to the design, speed adjustment, and monitoring of electric drive gear systems.