Nonlinear Dynamics of Viscoelastic Pipe Conveying Pulsating Fluid Subjected to Base Excitation

Based on the Euler-Bernoulli beam theory and Kelvin-Voigt model,a nonlinear model for the transverse vibration of a pipe under the combined action of base motion and pulsating internal flow is established.The governing partial differential equation is transformed into a nonlinear system of fourth-order ordinary differential equations by using the generalized integral transform technique(GITT).The effects of the combined excitation of base motion and pulsating internal flow on the nonlinear dynamic behavior of the pipe are investigated using a bifurcation diagram,phase trajectory diagram,power spectrum diagram,time-domain diagram,and Poincare map.The results show that the base excitation amplitude and frequency significantly affect the dynamic behavior of the pipe system.Some new resonance phenomena can be observed,such as the period-1 motion under the base excitation or the pulsating internal flow alone becomes the multi-periodic motion,quasi-periodic motion or even chaotic motion due to the combined excitation action.

Experimental study on vibration suppression in a rotor system under base excitation using an integral squeeze film damper

Base excitation is one of common excitations in rotor system.In order to study the dynamic characteristics of rotor systems under base excitation and the effect of integral squeeze film dampers(ISFDs)on their dynamic characteristics,a single-disk rotor test rig,where mass imbalance and base excitation could be applied,is developed.Experimental research on the rotor system response under sinusoidal base excitation conditions with different frequencies and excitation forces is performed and the effect of ISFD on the dynamic characteristics of the rotor is investigated.The experimental results demonstrate that when the sinusoidal base excitation frequency approaches the first critical speed of the rotor system or the natural frequency of the rotor system base,strong vibration occurs in the rotor,indicating that the base excitation of the two frequencies has a greater impact on rotor system response.In addition,with the increase of the base excitation force,the vibration of the rotor will be increased.ISFDs can significantly inhibit the vibration due to unbalanced forces and sinusoidal base excitation in rotor systems.To a certain extent,ISFDs can improve the effect of sinusoidal base excitation with most frequencies on rotor system response,and they have a good vibration reduction effect for sinusoidal base excitation with different excitation forces.

Experimental Analysis of Dynamic Stiffness Coefficient of the New Mn-Cu Alloy Annular Parts

Based on excitation-resonance mass testing principle, a proper experiment testing system is designed for annular parts. The dynamics characters of the axis sleeve, which is made of a new Mn-Cu alloy and used as a vibration reductor in high acceleration rotary testing machine for fusee, is investigated. The relationship between stiffness coefficient and utilizing frequency is obtained, and the simplified dynamics model of crystal is established From the viewpoint of crystal microstructure of the Mn-Cu alloy, the experiment result is analyzed by the viscoelastic theory, and the characters of stress and strain in the condition of high frequency are discussed. The results indicate that the Mn-Cu alloy annular parts are fit to be used on the high accleration rotary testing machine for fusee.

Vibration transmissibility characteristics of smart spring vibration isolation system

The objective of this work was to study the vibration transmissibility characteristics of the undamped and damped smart spring systems. The frequency response characteristics of them were analyzed by using the equivalent linearization technique, and the possible types of the system motion were distinguished by using the starting and ending frequencies. The influences of system parameters on the vibration transmissibility characteristics were discussed. The following conclusions may be drawn from the analysis results. The undamped smart spring system may simultaneously have one starting frequency and one ending frequency or only have one starting frequency, and the damped system may simultaneously have two starting frequencies and one ending frequency. There is an optimal control parameter to make the peak value of the vibration transmissibility curve of the system be minimum. When the mass ratio is far away from the stiffness ratio, the vibration transmissibility is small. The effect of the damping ratio on the system vibration transmissibility is significant while the control parameter is less than its optimal value. But the influence of the relative damping ratio on the vibration transmissibility is small.

Detection of long bones based on Barker code excited ultrasonic guided waves

Single pulse excited ultrasonic guided wave surfers high attenuation during the propagation in long bones.This results in small amplitude and low signal-to-noise ratio（SNR）of measured signals.Thus,the Barker code excitation is introduced into long bone detection to improve the quality of received signals,due to its efficiency in increasing amplitude and SNR.Both simulation and in vitro experiment were performed,and the results were decoded by the weighted match filter（WMF） and the finite impulse response- least squares inverse filter（FIRLSIF）,respectively.The comparison between the results of Barker code excitation and sine pulse excitation was presented.For 13-bit Barker code excitation,WMF produced 13 times larger amplitude than sine pulse excitation,while FIR-LSIF achieved higher peak-sidelobe-level（PSL） of -63.59 dB and better performance in noise suppression.The results show that the Barker code excited guided waves have the potential to be applied to the long bone detection.

A speech coding algorithm based on harmonic-stochastic excitation

A very low bit rate algorithm for encoding speech signals at 825 bps based on a mixed harmonic and stochastic modeling of the excitation signal is presented. The algorithm is more robust in the V/UV decision, reliable pitch estimation, and excitation signals synthesis. The bit allocation schedules in every case and the analysis-by-synthesis processes of the parameters are also described. The Diagnostic Rhyme Test (DRT) results show that the performance of the proposed algorithm is comparable to that of the MELP algorithm at 2.4 kbps, and the speech distinctness is 90.25%.

Pitch perception of harmonic complex tones based on excitation patterns

Fundamental frequency difference limens were measured to study whether pitch perception of medium-rank harmonic complex tones depends on the resolvability of the compo- nents and to study the effect of masker tone on discrimination performance. Target tone was presented alone, or mixed with the masker, which were filtered into the same bandpass frequency region （low, medium, or high） to obtain different resolvability. There were five kinds of funda- mental frequency difference and four kinds of phase combination between target and masker. Five young subjects participated in experiments, all of whom had normal hearing （thresholds ≤ 15 dB HL）. Results found fundamental frequency difference limens were increased with up-shift frequency region of the harmonics. The fundamental frequency difference between target and masker had a significant impact on the performance, while phase effects were small. Analysis suggested that resolvability of harmonics had a significant impact on the fundamental frequency difference limens, but pitch perception of medium-rank harmonics was not based on the resolv- ability. Analysis also suggested that most results of pitch perception of target-masker mixture were closely correlated with peaks on the excitation patterns.

Vibration test condition for spacecraft lift-off environment

The purpose of the vibration test of spacecrafts is to assess their adaptability to low-frequency vibration environment during lift-off.This paper gives the simulation of the satellite ground vibration test(GVT) and the state of the satellite along with rocket during lift-off.The simulation results of these two states are compared on condition that the lateral vibration of satellite/launching vehicle(S/LV) interface is the same.It is shown that the dynamic responses of satellite vertex are totally different.This is because there is angular motion of S/LV interface during lift-off,but in the GVT,the angular motion is restrained.By means of numerical simulation of the lift-off state,the angular motion related to the translation motion of S/LV interface can be determined.Then,using this angular motion as supplementary condition to simulate the vibration test,the calculated dynamic responses of satellite vertex are identical with the lift-off state.It demonstrates that supplementing angular motion condition is an effective method to improve spacecraft ground vibration test more identically with the real lift-off environment.Furthermore,it is useful for the application of the multi-degree-of-freedom shaking table,and provides the basis for test condition requirement.

Nonlinear Forced Vibration of Cantilevered Pipes Conveying Fluid

The nonlinear forced vibrations of a cantilevered pipe conveying fluid under base excitations are explored by means of the full nonlinear equation of motion, and the fourth- order Runge-Kutta integration algorithm is used as a numerical tool to solve the discretized equations. The self-excited vibration is briefly discussed first, focusing on the effect of flow velocity on the stability and post-flutter dynamical behavior of the pipe system with parameters close to those in previous experiments. Then, the nonlinear forced vibrations are examined using several concrete examples by means of frequency response diagrams and phase-plane plots. It shows that, at low flow velocity, the resonant amplitude near the first-mode natural frequency is larger than its counterpart near the second-mode natural frequency. The second-mode frequency response curve clearly displays a softening-type behavior with hysteresis phenomenon, while the first-mode frequency response curve almost maintains its neutrality. At moderate flow velocity, interestingly, the first-mode resonance response diminishes and the hysteresis phenomenon of the second-mode response disappears. At high flow velocity beyond the flutter threshold, the frequency response curve would exhibit a quenching-like behavior. When the excitation frequency is increased through the quenching point, the response of the pipe may shift from quasiperiodic to periodic. The results obtained in the present work highlight the dramatic influence of internal fluid flow on the nonlinear forced vibrations of slender Pipes.