Present Status and Prospect of High-Frequency Electro-hydraulic Vibration Control Technology

Electro-hydraulic vibration equipment(EHVE)is widely used in vibration environment simulation tests,such as vehicles,weapons,ships,aerospace,nuclear industries and seismic waves replication,etc.,due to its large output power,displacement and thrust,as well as good workload adaptation and multi-controllable parameters.Based on the domestic and overseas development of high-frequency EHVE,dividing them into servo-valve controlled vibration equipment and rotary-valve controlled vibration equipment.The research status and progress of high-frequency electro-hydraulic vibration control technology(EHVCT)are discussed,from the perspective of vibration waveform control and vibration controller.The problems of current electro-hydraulic vibration system bandwidth and waveform distortion control,stability control,offset control and complex vibration waveform generation in high-frequency vibration conditions are pointed out.Combining the existing rotary-valve controlled high-frequency electro-hydraulic vibration method,a new twin-valve independently controlled high-frequency electro-hydraulic vibration method is proposed to break through the limitations of current electro-hydraulic vibration technology in terms of system frequency bandwidth and waveform distortion.The new method can realize independent adjustment and control of vibration waveform frequency,amplitude and offset under high-frequency vibration conditions,and provide a new idea for accurate simulation of high-frequency vibration waveform.

Vertical vibration control using nonlinear energy sink with inertial amplifier

To reduce additional mass, this work proposes a nonlinear energy sink(NES)with an inertial amplifier(NES-IA) to control the vertical vibration of the objects under harmonic and shock excitations. Moreover, this paper constructs pure nonlinear stiffness without neglecting the gravity effect of the oscillator. Both analytical and numerical methods are used to evaluate the performance of the NES-IA. The research findings indicate that even if the actual mass is 1% of the main oscillator, the NES-IA with proper inertia angles and mass distribution ratios can still effectively attenuate the steady-state and transient responses of the main oscillator. Nonlinear stiffness and damping also have important effects. Due to strongly nonlinear factors, the coupled system may exhibit higher branch responses under harmonic excitation. In shock excitation environment, the NES-IA with a large dynamic mass can trigger energy capture of both main resonance and high-frequency resonance. Furthermore, the comparison with the traditional NES also confirms the advantages of the NES-IA in overcoming mass dependence.

Solid particle size characterization by a high-frequency collision response in pneumatic particulate flow

A novel triaxial vibration method is developed for the real-time characterization of the solid particle size distribution(PsD)in pneumatic particulate flow,which is critical for chemical industry.In this work,the particle-wall collision and friction behaviours were analysed by the time-domain statistical and timefrequency joint methods to narrow the high-frequency response range by the initial experiment of free fall for a single particle,interparticle,and multiple particles.Subsequently,verification experiments of PSD characterization in pneumatic flow were performed.First,the quantitative triaxial energy response model that considers the particle size,shape,and mass factors were established.Second,a good agreement of the particle number identification was found between the triaxial vibration energy and mean particle size of 150-550μm.Moreover,the performance with the best accuracy was focused on a range of 42-43 kHz in the x-axis and z-axis and 36.8-38.8 kHz in the y-axis.Finally,the individual particle energy was inversely analysed by the triaxial vibration response within the optimized frequency bands,and the PSD was characterized in real-time by a low error rate,that is,5.2% from the XZ-axis direction of sand(42-43 kHz)and 5.6% from the XYZ-axis of glass(30.9-33.9 kHz,46.2-47.2 kHz,38.3-41.3 kHz for each axis response).Therefore,this research complements the existing approaches for PsD characterization in particulate multiphase flow.

Effect of High-Frequency Vertical Vibration of Track on Formation and Evolution of Corrugations

The effect of high-frequency curved track vibrations in the vertical direction on the formation and development of rail corrugation was analyzed. Kalker抯 non-Hertzian rolling contact theory was modified and used to calculate the frictional work density on the contact area of the wheel and rail in rolling when a wheelset is steadily curving. The material loss unit area was assumed to be proportional to the frictional work density to determine the wear depth of the contact surface of the rail. The combined influences of the corrugation and the coupled dynamics of the railway vehicle and track were taken into consideration in the numerical simulation. For simplicity, the model considered one fourth of freight car without lateral motion, namely, a wheelset and the equivalent one fourth freight car body above it. The Euler beam was used to model the rails with the track structure under the rails replaced with equivalent springs, dumpers, and mass bodies. The numerical results show that the high-frequency track vibration causes formation of the initial corrugation on the smooth contact surface of the rail when a wheelset is steadily curving. The corrugation wave length depends on the frequencies and the rolling speed of the wheelset. The vibration frequencies also affect the depth and increase the corrugation.

Design for Vibrator Field Experiment Based-on Vibrator-earth System

Source-generated energy in seismic vibrator records high frequency harmonic behavior. Conventional vibrator-earth coupling model was set up on the linear system. Some assumptions in the application of linear theory to the vibrator problem play an insignificant role in the overall coupling structure. Obviously, non-linear behaviors can be modeled using a “hard-spring” form of the Duffing equation. Model dedicates that a qualitatively similar harmonic component is present for a broad range of possible mathematical descriptions. After some qualitative analysis about the non-linear system, some conclusion can be drawn. Firstly, The design of the vibrator weight should be abided by two points as followed: In order to avoid decoupling for the vibrator to the earth, the weight should be greater than the peak of the driving force amplitude as to keep the resultant force pointing to the earth’s core. On the other hand, for the limited energy output, the vibrator overweight may damage the system high-frequency ability.Secondly, as the driving force frequency approaching to the ground hard-spring inherent frequency, the energy transmission was found to climb its peak from the system energy absorbed curve. At last, due to the non-linear coupling model system, its load curve would come into unstable frequency range, which might limit the application of the Vibroseis conventional sweeping pattern-linear sweep. A new sweeping pattern was listed: the driving signal was the pseudo-random sequence modulated by a fixed frequency cosine signal satisfying with the exploration precision and absorbing efficiency. The synthesized signal was ready to be realized by the electromagnetic driven system. Even the side-lobes noise of its auto-correlation function was restrained well. The theory coming from the Vibrator-earth coupling model was applied to the design of the Portable High-frequency Vibrator System (PHVS), and the good result was obtained. By the analysis of the vibrator base plate signal, the model was proved to be true. The exploration research on PHVS made a first step on its following optimal design.

Whole body vibration with rest days could improve bone quality of distal femoral metaphysis by regulating trabecular arrangement

Low-magnitude, high-frequency vibration(LMHFV) with rest days(particularly seven rest days) was considerably effective in improving the morphological and mechanical properties of rat proximal femur. However, current knowledge is limited regarding the possible benefit of this mechanical regimen to other bone sites and whether the optimal rest days are the same. This study followed our previous experiment on LMHFV loading with rest days for three-month-old male Wistar rats. The experiment involved seven groups, namely, vibrational loading for X day followed with X day rest(X=1, 3, 5, 7), daily vibrational loading,tail suspension and baseline control. Micro-computed tomography(micro-CT) scanning was used to evaluate the microarchitecture of the distal femoral trabecular bone. Micro-CT image-based microfinite element analysis was performed for each distal femoral metaphysis. LMHFV with rest days substantially changed the trabecular arrangement from remarkably plate-like to rod-like. Vibrational loading with 1 day rest was substantially effective in improving the architecture and apparent-and tissuelevel mechanical properties of the rat distal femoral metaphysis. This study may provide an improved understanding of the sitespecific responses of bone tissue to LMHFV with rest days for a substantially effective therapy of a targeted bone site.

Experimental study of the wheel/rail impact caused by wheel flat within 400 km/h using full-scale roller rig

Purpose–In service,the periodic clashes of wheel flat against the rail result in large wheel/rail impact force and high-frequency vibration,leading to severe damage on the wheelset,rail and track structure.This study aims to analyze characteristics and dynamic impact law of wheel and rail caused by wheel flat of high-speed trains.Design/methodology/approach–A full-scale high-speed wheel/rail interface test rig was used for the test of the dynamic impact of wheel/rail caused by wheel flat of high-speed train.With wheel flats of different lengths,widths and depths manually set around the rolling circle of the wheel tread,and wheel/rail dynamic impact tests to the flats in the speed range of 0–400 km/h on the rig were conducted.Findings–As the speed goes up,the flat induced the maximum of the wheel/rail dynamic impact force increases rapidly before it reaches its limit at the speed of around 35 km/h.It then goes down gradually as the speed continues to grow.The impact of flat wheel on rail leads to 100–500 Hz middle-frequency vibration,and around 2,000 Hz and 6,000 Hz high-frequency vibration.In case of any wheel flat found during operation,the train speed shall be controlled according to the status of the flat and avoid the running speed of 20 km/h–80 km/h as much as possible.Originality/value–The research can provide a new method to obtain the dynamic impact of wheel/rail caused by wheel flat by a full-scale high-speed wheel/rail interface test rig.The relations among the flat size,the running speed and the dynamic impact are hopefully of reference to the building of speed limits for HSR wheel flat of different degrees.