Random Vibration Process Research Articles

Dynamic Response Simulation of the Slope Triggered by Fluctuating Pressure during High Dam Flood Discharge

The problem of slope vibration induced by flood discharge of high dams cannot be ignored. In this paper, this problem is simplified to be the relationship among the fluctuating pressures, the inherent properties of the slope system, and its dynamic responses. The characteristics of fluctuating pressures in the plunge pool during flood discharge are analyzed by the hydraulic model test. And a numerical slope model consisting of the finite element domain and the PML domain is established to study the inherent characteristics and vibration responses by numerical simulation. The results show that the flow fluctuation in plunge pool is a continuous and stable random vibration process. And the fluctuating pressures on the bottom area of the plunge pool are greater than that of the sidewall, but the fluctuation phenomenon at the sidewall is more intense. In addition, the slope displacement vibration intensity caused by fluctuating pressures is small, only at the micron level. The fluctuating pressures on the bottom area of the plunge pool are the dominant factor affecting the kinetic energy density distribution of the slope. This work provides a simple and efficient method for the study of slope vibration induced by high dam flood discharge.

An approximate mathematical model for estimating the influence of vibrations on attached elements of a mobile robot video system

The problem of constructing and applying of mathematical model for assessing the influence of vibrations on the attached elements of the video system of a mobile robot is solved. This robot is considered as a mobile platform for placing of the special equipment for various purposes. The analysis of mathematical models and the results of experimental studies of vibrations of multi-support wheeled machine and its structural elements has been conducted. On the basis of this analysis, the form of a stochastic mathematical model of vibrations of the structure of a mobile robot has been substantiated. The vibration model is specified as a correlation function or spectral density of a random process for various conditions of the robot’s movement. Differential equations of the shaping filter for modeling а random vibration process with given characteristics are presented. Differential equations for the probabilistic moments of the vibration process are presented. Based on the equations for the probabilistic moments and the proposed formula, an assessment of events, which consist in exceeding the vibration amplitude of a given level was carried out. These events are named as outliers of a random process and characterize the range within the basic properties of the equipment installed on the mobile platform are preserved. An analytical study of a mathematical model to determine the intensity of emissions of a random vibration process has been carried out. The probabilistic characteristics of the vibration process and the intensity of emissions are determined. The obtained theoretical results make it possible to assess the performance of the elements of a video system installed on a mobile platform and to formulate the basic requirements for tolerances for their parameters. The results of computer modeling clearly showed the efficiency of the proposed mathematical model for assessing the influence of vibrations.

Based on the virtual experiment study of the impact of load sequence on the calculation process of random vibration fatigue damage.

At present, the linear fatigue accumulation theory proposed by Miner is used to calculate the fatigue problem of random vibration. In this process, the loading order of the loads is ignored, so that the results obtained are riskier. The nonlinear fatigue cumulative damage theory takes into account the effects of the load loading sequence, but the calculation becomes more complicated. Many scholars have shown that the fatigue calculation of alternating loads is not strictly linear, and the high and low order will affect the damage index. This phenomenon will be more obvious in the random vibration process. In this paper, the effects of loading sequence on the calculation of non-Gaussian random vibration fatigue damage are studied by virtual experiments. Through the phase selection method, 7 sets of excitations with different kurtosis were loaded onto the notched specimen. Through the calculation results of fatigue damage in the notch sensitive area, it was confirmed that the damage calculated by linear and nonlinear cumulative damage formula was improved with the increase of kurtosis. The results can make a significant difference.

Study on the Vehicle Dynamic Load Considering the Vehicle-Pavement Coupled Effect

The vibration of vehicle-pavement interaction system is sophisticated random vibration process and the vehicle-pavement coupled effect was not considered in the previous study. A new linear elastic model of the vehicle-pavement coupled system was established in the paper. The new model was verified with field measurement which could reflect the real vibration between vehicle and pavement. Using the new model, the study on the vehicle dynamic load considering the vehicle-pavement coupled effect showed that random forces (centralization) between vehicle and pavement were influenced largely by vehicle-pavement coupled effect. Numerical calculation indicated that the maximum of random forces in coupled model was 2.4 times than that in uncoupled model. Inquiring the reason, it was found that the main vibration frequency of the vehicle non-suspension system was similar with that of the vehicle suspension system in the coupled model and the resonance vibration lead to vehicle dynamic load increase significantly.

Experiments and reliability research on bonding process of micron copper wire and nanometer gold layer

Copper wire bonding process is widely used in the electronic packaging of system integration with various heterogeneous and homogeneous components due to the advantage of cost. In this paper, an achievement of parallel microgap resistance welding with 40-μm copper wire on 300-nm Au-plated quartz pendulous reed used in precision mechanical and electrical product was presented. Research on orthogonal design of experiment was carried out, and the effect of process parameters was discussed on the shape of bonding interface, tensile force, and shear force by variance analysis. It is shown that too large a heat input and electrode pressure can cause the gold layer to wrinkle or fuse and cause bonding interface mechanics performance to fall sharply. A group of optimized process parameters (0.84 N of bonding pressure, 0.45V of bonding voltage, and 17 ms of bonding time) is obtained. Reliability tests including the thermal shock, random vibration, and electric aging tests on optimized process parameters were carried out, and the mechanical properties and physical properties of the bonding interface were mainly focused. It is shown that the bonding interface resistance increases slightly and the overall bonding interface tensile strength falls slightly after 500 cycles of thermal shock test. However, there is no change during the random vibration process. When electric aging time is less than 200 h, bonding interface morphology does not change and there is no crack. When electric aging time is 360 h, bonding interface deforms and crack occurs. When electric aging time reaches 720 h, bonding interface crack area increases, and it eventually fails. It is experimentally proved that a bonding interface with better performance can be achieved by parallel microgap resistance welding with 40-μm copper wire on 300-nm Au-plated quartz pendulous reed.

Characterization of random Gaussian and non-Gaussian stress processes in terms of vibration fatigue

In the field of military land vehicles, random vibration processes generated by all-terrain wheeled vehicles in motion are not classical stochastic processes of a stationary and Gaussian nature. The non-Gaussian nature of the processes is expressed in particular by very significant flattening levels that can affect the fatigue design of mechanical structures, conventionally acquired by spectral approaches, based essentially on spectral moments of stress processes. Due to these technical considerations, techniques for the characterization of random excitation processes generated by this type of driving situation need to be developed, by proposing innovative characterization methods no longer based on deterministic spectral and/or temporal approaches but on temporal approaches of a stochastic nature. Indeed, to characterize the fatigue damage produced by non-stationary and non-Gaussian random processes, the author shows that it is now necessary to mix time-counting techniques used in the field of vibration fatigue with those of the sampling statistics used in estimation theory. This approach makes it possible to extrapolate favorably over time the level of damage to structures, from a statistical perspective, when this extrapolation phase is in practice carried out deterministically. This technique, referred to as the disjoint block method (BDM), has been tested successfully in the context of component specification techniques from the reliability standpoint since 2010, and just recently integrated AFNOR standards.

The mechanism of wheelset longitudinal vibration and its influence on periodical wheel wear

This study investigates the mechanism of wheelset longitudinal vibration and its influence on wheel periodical wear. A longitudinal wheel/rail friction model was created after analyzing the characteristics of wheel/rail longitudinal friction that fit our study. This friction model is then incorporated into a vibration analysis of a wheelset coupled with a single-wheelset longitudinal dynamical model. The response of the single-wheelset system both considers the effects of track excitation and small randomly varying velocity, and the wheelset longitudinal random vibration process is held constant. Meanwhile, from the micro perspective, wheelset longitudinal vibration will cause changes of wheel/rail contact parameters mainly in the natural frequency which will cause periodical wear. Such wear is due to the natural frequency of wheelset longitudinal vibration being the same or doubled.

Characterisation of random Gaussian and non-Gaussian stress processes in terms of extreme responses

In the field of military land vehicles, random vibration processes generated by all-terrain wheeled vehicles in motion are not classical stochastic processes with a stationary and Gaussian nature. Non-stationarity of processes induced by the variability of the vehicle speed does not form a major difficulty because the designer can have good control over the vehicle speed by characterising the histogram of instantaneous speed of the vehicle during an operational situation. Beyond this non- stationarity problem, the hard point clearly lies in the fact that the random processes are not Gaussian and are generated mainly by the non-linear behaviour of the undercarriage and the strong occurrence of shocks generated by roughness of the terrain. This non-Gaussian nature is expressed particularly by very high flattening levels that can affect the design of structures under extreme stresses conventionally acquired by spectral approaches, inherent to Gaussian processes and based essentially on spectral moments of stress processes. Due to these technical considerations, techniques for characterisation of random excitation processes generated by this type of carrier need to be changed, by proposing innovative characterisation methods based on time domain approaches as described in the body of the text rather than spectral domain approaches.

On the influence of trigger level in distribution vibration surveys

AbstractThis paper follows on from recently published research that examined the effects of recording parameters on the outcomes of distribution vibration surveys. Whereas the previous research focused on the effects of the sampling period at which sub‐records of the process are captured, this paper deals with another often‐used recording parameter, namely, the vibration level trigger. The paper describes the development of a software tool that was designed specifically to study the influence of various sampling parameters on continuously recorded vibration data. This software tool was used to undertake a thorough statistical analysis on a vibration record set consisting of continuously sampled data measured from a wide variety of vehicle types and routes. The paper shows that the outcomes of vibration surveys are very sensitive to the trigger level and can produce highly distorted results by introducing a bias that nearly always overestimates the overall vibration levels. This is reflected in estimates of common descriptors of random vibration processes such as the average power spectral density (PSD), the peak‐hold PSD and the overall root‐mean‐square values. The main outcome of this analysis is the formulation of a correction method based on relationships between the true mean and peak‐hold PSDs and estimates from sampled data. The effect and significance of the proposed correction procedure is demonstrated, especially in the context of laboratory simulation of distribution vibrations. The paper concludes by making specific recommendations for configuring high‐capacity field data recorders and applying correction strategies to ensure that vibration surveys yield statistically sound results. Copyright © 2009 John Wiley & Sons, Ltd.

On the effects of sampling parameters when surveying distribution vibrations

AbstractThis paper presents the initial outcomes of a study aimed at better understanding the effects of recording parameters on the outcomes of distribution surveys. With the advent of vibration recorders with increasing capacity, there has been a corresponding increase in the number of studies aimed at evaluating and characterizing the random vibrations generated by transport vehicles across a wide variety of distribution environments. Oftentimes, the sampling and recording parameters used in these studies are not given adequate attention, resulting in statistical estimates that are open to interpretation. The paper shows how the selection of the sampling and recording parameters can have significant effects on much used descriptors of random vibration processes such as the average power spectral density (PSD), the peak‐hold PSD and the root mean square distribution. The paper shows that the results of vibration surveys are most sensitive to the sampling period, especially when the vibrations are highly non‐stationary. The paper concludes by making specific recommendations for configuring high‐capacity vibration recorders to ensure that vibration surveys yield statistically sound results. Copyright © 2008 John Wiley & Sons, Ltd.

Analysis of the statistical error of the spectrum analysis of random vibration processes

Analysis of the statistical error of the spectrum analysis of random vibration processes

Designing simulators of wide-band random vibrations

The set of principles used in designing wide-band random-vibration simulators (WRVS) is determined by the simulated vibration-process characteristics. Analysis of vibrations and vibration-testing equipment characteristics shows the necessity for simulating wide-band random vibration processes which have very nonuniform variable energy spectra [i]. Such processes are, therefore, obtained by filtering noise-generator signals by means of complex linear systems with adjustable parameters. Requirements for the WRVS characteristics to be universal have led to the fact that the majority of known simulators are based on multichannel linear shapers whose entire working frequency range is covered by sets of narrow-band filters. The filter output signals are added in accordance with the type of the simulated vibration-process energy spectrum.