Stick-slip Vibration Research Articles

Nonstick and Stick-Slip Motion of a Coulomb-Damped Belt Drive System Subjected to Multifrequency Excitations

In this paper, the rotational vibration of a belt drive system with a dry friction tensioner subjected to multiple harmonic excitations is studied. The work is focused on the impact of the dry friction torque combined with the multiexcitation frequencies on dynamic characteristics of the system. An analytical solution procedure is developed for the first time to predict two kinds of periodic responses of the system, i.e., nonstop and one-stop motion characterized by the nonstick and stick-slip vibration of the tensioner arm in the system, respectively. Utilizing this method, parametric studies are carried out to obtain the frequency response of a prototypical belt drive system subjected to harmonic excitations from both the driving and driven pulleys. It is found that the tensioner Coulomb friction torque has a significant impact on the amplitude response of the system—it reduces the vibration amplitude of the tensioner arm, but for other components in the belt system it can either decrease or increase the amplitudes under different situations. Furthermore, if the excitation frequency from the driving pulley is larger than or equal to that from the driven pulley, the system vibration amplitudes are much larger than those under the opposite condition.

Frictional Phenomena in Dynamical Systemwith Two-Frequency Excitation

The paper deals with investigation of a self-excited vibrating system with dry friction. The system is composed of a mass connected by viscoelastic element with the referring frame and interacting with a moving belt by means of dry friction. An experimentally identified, multi-parametric dry friction model for the pair composed of soft and hard elements like steel–polyester pair, describing both the case of stick-slip and quasi-harmonic vibration, has been applied. Additionally, the system is influenced by external, two-frequency kinematic excitation. The results of computer simulation for different excitation conditions are submitted in the present paper.

PW-02 DEVELOPMENT OF MINIATURE FAILURE DIAGNOSIS MODULE WITH VIBRATION SENSOR, DIGITAL SIGNAL PROCESSOR AND WIRELESS TRANSMITTER

A method to diagnose wear of lathe cutting tools for precision parts of watch was studied. Theoretical analysis of cutting tool's vibration was made using dummy tools. It was demonstrated that stick-slip vibration occurred and level of first resonance frequency increased remarkably when a cutting tool wore. From this result, the types of prototype modules, analog and digital, were fabricated. The digital type can transmit information periodically with a transmitter, and the remote surveillance of a cutting state will be attained. This module is called "Nature Interfacer for failure diagnosis."

Analytical approximations for stick–slip vibration amplitudes

The classical “mass-on-moving-belt” model for describing friction-induced vibrations is considered, with a friction law describing friction forces that first decreases and then increases smoothly with relative interface speed. Approximate analytical expressions are derived for the conditions, the amplitudes, and the base frequencies of friction-induced stick–slip and pure-slip oscillations. For stick–slip oscillations, this is accomplished by using perturbation analysis for the finite time interval of the stick phase, which is linked to the subsequent slip phase through conditions of continuity and periodicity. The results are illustrated and tested by time-series, phase plots and amplitude response diagrams, which compare very favorably with results obtained by numerical simulation of the equation of motion, as long as the difference in static and kinetic friction is not too large.

Formation mechanism and countermeasures of rail corrugation on curved track

From full-scale stand tests, commercial line experiments and numerical simulation, we found that corrugation of rail in curve section of track is formatted by stick–slip vibration between wheel and rail, which is caused by the large creepage and vertical force fluctuation on wheel/rail contact surface. On the basis of this theory, we analyzed the growing process of corrugation by numerical simulation.

Stick-slip Whirl Interaction in Drillstring Dynamics

Abstract This paper attempts to explain the complicated behavior of oilwell drillstring motion when both torsional stick-slip and lateral whirl vibration are involved. It is demonstrated that the observed phenomena in experimental drillstring data could be due to the fluid forces of the drilling mud. A Stick-slip Whirl Model is presented which consists of a submodel for the whirling motion and a submodel for the stick-slip motion, both as simple as possible. The Stick-slip Whirl Model is a simplification of a drillstring confined in a borehole wall with drilling mud. The model is as simple as possible to expose only the basic phenomena but is discontinuous. Bifurcation diagrams of this discontinuous model for varying rotation speeds reveal discontinuous bifurcations. The disappearance of stick-slip vibration when whirl vibration appears is explained by bifurcation theory. The numerical results are compared with the experimental data from a full-scale drilling rig.

Field Investigation of the Effects of Stick-Slip, Lateral, and Whirl Vibrations on Roller-Cone Bit Performance

SummaryThe effects of downhole vibrations on the performance of poly-crystalline diamond compact (PDC) bits have been well discussed in recent years. However, most studies on the downhole dynamics of roller-cone bits have focused on axial vibration and its effects. The questions that remain to be answered are what kinds of vibrations a roller-cone bit experiences and what the effects of these vibrations are on roller-cone bit performance.To investigate these questions, a series of laboratory and field tests was conducted. Downhole vibration data were recorded by an advanced instrumented sub. Soft-to medium-hard formations were drilled with four 8½-in. roller-cone bits (IADC 517). Three kinds of harmful vibrations were observed, and their effects on bit performance in terms of rate of penetration, insert breakage, and bearing/seal life are discussed.

Dynamics of transient events at the head/disk interface

Slider/disk contacts of nano and pico sliders are investigated using an acoustic emission sensor and a high bandwidth laser Doppler vibrometer (LDV). The following cases are studied: (a) influence of scratch impact on the airbearing stiffness; (b) influence of lubricant thickness on slider dynamics for single bump impacts; (c) influence of lubricant thickness on slider vertical stick–slip vibrations; (d) dynamics of take-off and landing. Linear time frequency analysis is applied to study simultaneously the impact response of the airbearing and the slider torsional and bending modes. The contact dynamics of single bump impacts is examined as a function of disk velocity and lubricant thickness. Increased slider vibrations are found for thick lubricant films both for sliding contacts as well as for single bump impacts. During the transition from sliding to flying a change of the bending mode frequency is observed.

The tribology of rosin

Rosin is well known for its ability to excite stick–slip vibration on a violin string but the precise characteristics of the material which enable it to exhibit this behaviour have not been studied in any detail. A method is described in which the coefficient of friction of rosin is measured during individual cycles of a stick–slip vibration. Friction versus sliding velocity characteristics deduced in this way exhibit hysteresis, similar to that found in other investigations using different materials. No part of the hysteresis loops follow the friction/velocity curve found from steady-sliding experiments. Possible constitutive laws are examined to describe this frictional behaviour. It is suggested by a variety of evidence that contact temperature plays an important role. Friction laws are developed by considering that the friction arises primarily from the shear of a softened or molten layer of rosin, with a temperature-dependent viscosity or shear strength. The temperature of the rosin layer is calculated by modelling the heat flow around the sliding contact. The temperature-based models are shown to reproduce some features of the measurements which are not captured in the traditional model, in which friction depends only on sliding speed. A model based on viscous behaviour of a thin melted layer of rosin gives predictions at variance with observations. However, a model based on plastic yielding at the surface of the rosin gives good agreement with these observations.

An approximate analysis of dry-friction-induced stick-slip vibratons by a smoothing procedure

This paper deals with a systematic procedure to find both stable and unstable periodic stick-slip vibrations of autonomous dynamic systems with dry friction. In this procedure, the discontinuous friction forces are approximated by smooth functions. Using the simple shooting method with a stiff-ODE solver, in combination with a path following algorithm, branches of periodic solutions are computed for a changing design variable. For testing purposes, both 1 and 2-DOF autonomous block-on-belt models and a 1-DOF autonomous drill string model from literature are investigated. Comparison of the results shows that the smoothing procedure accurately describes the behavior of the discontinuous systems. The proposed procedure can also easily be applied to more complex MDOF models, as well as to nonautonomous dynamic systems.

An Investigation into Stick-Slip Vibrations on Vehicle/Track Systems

SUMMARY A model for the numerical simulation of vehicle/track interaction and stick-slip vibration is presented. A finite element model is developed to calculate vertical contact forces. These forces are then coupled through the contact patch into a non-linear time-domain model by which the stick-slip vibration behaviour of a wheel-rail system is analysed. The investigation suggests that stick-slip vibration may occur if a vehicle which has a maligned or an initial ‘wind-up’ wheeiset meets a vertical irregularity or contaminants on the track.

COUPLED TORSIONAL AND BENDING VIBRATIONS OF DRILLSTRINGS SUBJECT TO IMPACT WITH FRICTION

A dynamic model for coupled torsional and bending vibrations of drillstrings is presented. The bit/formation interactions are assumed to be related to the bit motion, leading to a set of highly non-linear equations with a potential for self-excited behaviour. Impacts with the borehole wall are accounted for by a consistent contact model which is capable of capturing rolling both with and without slip of the drill collars along the borehole wall. Simulation results show that the non-linear coupling significantly affects the response. Due to the combined parametric and forcing excitations and the effect of strong non-linearities, the response is not simple or easily predictable. At certain frequencies, there is significant energy transfer between the two modes of vibrations. The simulation results agree well with laboratory and field observations when the so called stick–slip vibrations occur. This study suggests a new mechanism for this behaviour which was shown to be due to static friction or speed dependent torque on bit.

Suppression of Micro Stick-Slip Vibrations in Hydraulic Servo-System

This paper deals with suppression of two kinds of micro stick-slip vibrations occurring in a typical computer-controlled hydraulic servo-system. The relevant system consists of a single-rod hydraulic cylinder, an electrohydraulic servo-valve and a personal computer. The discontinuous control signal from a D/A converter causes a stick-slip vibration of micron order of magnitude over a wide range of the feedback gain. Increasing the feedback gain results in the other stick-slip vibration of nearly ten times larger amplitude due to the nonlinear pressure-flow characteristic of the servo-valve. The numerical simulation revealed the latter micro stick-slip vibration could be efficiently suppressed with the feedback linearization technique to compensate the nonlinearity of the servo-valve, while the former one reduced by improving the resolution of the D/A converter. Validities of both the methods were also confirmed with experiment. [S0022-0434(00)00102-7]

Nonlinear Control of Micro Stick-Slip Vibration in Hydraulic Servo Systems.

This paper treats nonlinear control of a hydraulic servo system to suppress micro stick-slip vibrations. The system consists of a hydraulic cylinder, a servo-valve and a personal computer. Self-excited vibrations of two different types occur in the conventional feedback control system. Discontinuous control signal generated through a D/A converter causes a stick-slip vibration of micron order over the wide range of the feedback gain. Increasing the feedback gain results in the other type of stick-slip vibration of nearly ten times larger amplitude due to the locally increased flow gain in the underlap region of the servo-valve. The feedback linearization technique is applied to compensate the nonlinearity of the valve. Numerical simulation and experiment were performed for both the present nonlinear control system and the ordinary linear control system to confirm the validity of the former one in suppressing the micro stick-slip vibration. The other type of micro stick-slip vibration due to the D/A converter was effectively suppressed by improving the resolution of the input signal.

Stick-slip vibrations induced by alternate friction models

In the present paper a simple and efficient alternate friction model is presented to simulate stick-slip vibrations. The alternate friction model consists of a set of ordinary non-stiff differential equations and has the advantage that the system can be integrated with any standard ODE-solver. Comparison with a smoothing method reveals that the alternate friction model is more efficient from a computational point of view. A shooting method for calculating limit cycles, based on the alternate friction model, is presented. Time-dependent static friction is studied as well as application in a system with 2-DOF.

Micro Stick-Slip Vibration in Hydraulic Servo Systems.

This report treats micro stick-slip vibrations occurring in a typical computer-controlled hydraulic servo system. The relevant system consists of a hydraulic cylinder, a servo valve and a personal computer. First, an experiment was performed for a conventional feedback control system to confirm the occurrence of two different types of stick-slip vibration of small amplitude. Detailed numerical analysis was then performed to identify the main factors contributing to the vibrations. The control signal generated by the D/A converter causes micro stick-slip vibration of small amplitude over a wide range of control feedback gain. Increasing the feedback gain results in another type of micro stick-slip vibration of large amplitude due to the locally increased flow gain within the underlap of the servo valve. Computational results agree well with the experimental ones.

Some considerations of slideway friction characteristics by observing stick-slip vibration

It is important to clarify the frictional characteristics of a slideway and to prevent unstable vibration, such as stick-slip vibration, for the improvement of kinematic performance and for precise positioning. In this research, the relations among the dynamic friction characteristics, the pitching motion or the floating up of the slider, the surface roughness of a slideway, and the lubricant property are investigated experimentally. As a result, some points necessary for the kinematic performance improvement of the slider are clarified.

Bifurcation and stability analysis for a non-smooth friction oscillator

Friction-induced self-sustained oscillations, also known as stick-slip vibrations, occur in mechanical systems as well as in everyday life. On the basis of a one-dimensional map, the bifurcation behaviour including unstable branches is investigated for a friction oscillator with simultaneous self-and external excitation. The chosen way of mapping also allows a simple determination of Lyapunov exponents.

Complementarity Problems of Stick-Slip Vibrations

Multibody systems with many friction contacts not being decoupled by some force laws afford a special treatment with respect to the uniqueness of the solution after a contact event. This problem can be solved by an optimization technique including unequality constraints which corresponds exactly to the physical properties of stick-slip vibrations. The theoretical background to this complementarity problem is presented and illustrated by examples from machine dynamics.

Formation Mechanism of Rail Corrugation on Curved Track. 1st Report. Longitudinal Stick-Slip Vibration Model Considering Contact Stiffness.

By using the corrugation formatting and developing model we successfully fixed the formatting and developing mechanism of rail corrugation on curved track. The frequency of corrugation is governed by the vertical dynamic system of the wheelset including the contact stiffness between rail and wheel, but not by the torsional dynamic system of the wheelset. From the simulation results we find that, (1) reducing the wheelset mass and static wheel load, (2) increasing the radius difference between inside/outside wheels in curving, the damping of axle suspension and axle torsional stiffness, are useful means to reduce corrugation. However, reducing axle suspension stiffness has almost no influence on the reduction of corrugation, because the contact stiffness between rail and wheel is much greater than the suspension stiffness.