Impact of Varying Excitation Frequency on the Behaviour of 2-DoF Mechanical System with Stick-Slip Vibrations

2016 ◽  
pp. 187-199
Author(s):  
Wojciech Kunikowski ◽  
Paweł Olejnik ◽  
Jan Awrejcewicz
Keyword(s):  
Mechanical System ◽  
Excitation Frequency ◽  
Stick Slip

Mechanisms and Mitigation of 3D Coupled Vibrations in Drilling with PDC Bits

2021 ◽  
Author(s):  
Shilin Chen ◽  
Chris Propes ◽  
Curtis Lanning ◽  
Brad Dunbar
Keyword(s):  
Torsional Oscillation ◽  
Excitation Frequency ◽  
Low Frequency ◽  
Coupled Vibration ◽  
Stick Slip ◽  
Rock Interaction ◽  
Bottom Hole ◽  
New Type ◽  
Design Characteristics ◽  
Axial Resonance

Abstract In this paper we present a new type of vibration related to PDC bits in drilling and its mitigation: a vibration coupled in axial, lateral and torsional directions at a high common frequency (3D coupled vibration). The coupled frequency is as high as 400Hz. 3D coupled vibration is a new dysfunction in drilling operation. This type of vibration occurred more often than stick-slip vibration. Evidences reveal that the coupled frequency is an excitation frequency coming from the bottom hole pattern formed in bit/rock interaction. This excitation frequency and its higher order harmonics may excite axial resonance and/or torsional resonance of a BHA. The nature of 3D coupled vibration is more harmful than low frequency stick-slip vibration and high frequency torsional oscillation (HFTO). The correlation between the occurrence of 3D coupled vibration and bit design characteristics is studied. Being different from prior publications, we found the excitation frequency is dependent on bit design and the occurrence of 3D coupled vibration is correlated with bit design characteristics. New design guidlines have been proposed to reduce or to mitigate 3D coupled vibration.

scholarly journals Study of the Complex Stiffness of a Vibratory Mechanical System with Shape Memory Alloy Coil Spring Actuator

2014 ◽  
Vol 2014 ◽  
pp. 1-11 ◽  
Author(s):  
Samuell A. Holanda ◽  
Antonio A. Silva ◽  
Carlos J. de Araújo ◽  
Alberdan S. de Aquino
Keyword(s):  
Shape Memory ◽  
Mechanical System ◽  
Smart Materials ◽  
Excitation Frequency ◽  
Structural Response ◽  
Scientific Development ◽  
Temperature Control System ◽  
Coil Spring ◽  
Sensors And Actuators ◽  
Context Shape

The vibration control is an important area in the dynamic of structures that seeks to reduce the amplitude of structural responses in certain critical frequency ranges. Currently, the scientific development leads to the application of some actuators and sensors technologically superior comparing to the same features available on the market. For developing these advanced sensors and actuators, smart materials that can change their mechanical properties when subjected to certain thermomechanical loads can be employed. In this context, Shape memory alloys (SMAs) may be used for developing dynamic vibration dampers which are capable of acting on the system providing proper tuning of the excitation frequency and the natural frequency. This paper aims to analyze the behavior of the stiffness and damping of a SMA helical coil spring actuator coupled to a mechanical system of one degree of freedom (1 DOF) subjected to an unbalanced excitement force and a temperature control system. By analyzing the effect of these parameters on the structural response and considering the concept of complex stiffness, it can be possible to predict the system's behavior within certain acceptable ranges of vibration, already in the design phase.

An Experimental and Analytical Investigation Into Friction-Induced Vibrations and Parameters Affecting Its Occurrence

2010 ◽  
Author(s):  
A. Bahzad ◽  
M. O. A. Mokhtar ◽  
A. M. A. El-Butch ◽  
A. F. Fahim
Keyword(s):  
Damping Ratio ◽  
Excitation Frequency ◽  
Analytical Investigation ◽  
Load Factor ◽  
Stick Slip ◽  
Single Degree Of Freedom ◽  
Ratio Speed ◽  
Friction Models ◽  
Stick Slip Motion ◽  
Slip Motion

The condition for the occurrence of friction-induced vibrations is examined numerically and experimentally based on a single degree of freedom system with different friction models that relates the friction force with the relative interface speed. In this study the dimensionless parameters which control the occurrence of stick-slip motion are investigated, it is found that some of these parameters results in the occurrence of stick-slip motion while others are acting to avoid it. The equations governing the occurrence of friction-induced vibrations are derived in dimensionless form and solved numerically in order to have both high accuracy and reducing the number of the system parameters. The attained numerical results are validated by the comparison with the experimental results. Results also showed that damping ratio, speed, load factor, the used friction models and excitation frequency greatly affecting the occurrence of stick-slip motion.

Structural Stiffness, Dry-Friction Coefficient and Equivalent Viscous Damping in a Bump-Type Foil Gas Bearing

2005 ◽  
Author(s):  
Dario Rubio ◽  
Luis San Andre´s
Keyword(s):  
Friction Coefficient ◽  
Dry Friction ◽  
Structural Parameters ◽  
Excitation Frequency ◽  
Single Frequency ◽  
Viscous Damping ◽  
Periodic Load ◽  
Stick Slip ◽  
Equivalent Viscous Damping ◽  
Frequency Domain Methods

High performance oil-free turbomachinery implements gas foil bearings (FBs) to improve mechanical efficiency in compact units. FB design, however, is still largely empirical due to their mechanical complexity. The paper provides test results for the structural parameters in a bump-type foil bearing. The stiffness and damping (Coulomb or viscous type) coefficients characterize the bearing compliant structure. The test bearing, 38.1 mm in diameter and length, consists of a thin top foil supported on bump-foil strips. A prior investigation identified the stiffness due to static loads. Presently, the test FB is mounted on a non-rotating stiff shaft and a shaker exerts single frequency loads on the bearing. The dynamic tests are conducted at shaft surface temperatures from 25 °C to 75°C. Time and frequency domain methods are implemented to determine the FB parameters from the recorded periodic load and bearing motions. Both methods deliver identical parameters. The dry friction coefficient ranges from 0.05 to 0.20, increasing as the amplitude of load increases. The recorded motions evidence a resonance at the system natural frequency, i.e. null damping. The test derived equivalent viscous damping is inversely proportional to the motion amplitude and excitation frequency. The characteristic stick-slip of dry friction is dominant at small amplitude dynamic loads leading to a hardening effect (stiffening) of the FB structure. The operating temperature produces shaft growth generating a bearing preload. However, the temperature does not affect significantly the identified FB parameters, albeit the experimental range was too small considering the bearings intended use in industry.

Influence of Tensioner Dry Friction on the Vibration of Belt Drives With Belt Bending Stiffness

2007 ◽  
Vol 130 (1) ◽  
Author(s):  
Farong Zhu ◽  
Robert G. Parker
Keyword(s):  
Dry Friction ◽  
Harmonic Balance ◽  
Excitation Frequency ◽  
Harmonic Balance Method ◽  
Friction Torque ◽  
Stick Slip ◽  
Pulley System ◽  
Coulomb Damping ◽  
Belt Drives ◽  
Linear Subsystem

A model of dry friction tensioner in a belt-pulley system considering transverse belt vibration is developed, and the influence of the dry friction on the system dynamics is examined. The discretized formulation is divided into a linear subsystem including linear coordinates and a nonlinear subsystem addressing tensioner arm vibration, which reduces the dimension of the iteration matrices when employing the harmonic balance method. The Coulomb damping at the tensioner arm pivot mitigates the tensioner arm vibration but not necessarily the vibrations of other system components. The extent of the mitigation varies for different excitation frequency ranges. The critical amplitude of the dry friction torque beyond which the system operates with a locked arm is determined analytically. Superharmonic resonances are observed in the responses of the generalized span coordinates, but their amplitudes are small. The energy dissipation at the tensioner arm hub is discussed, and the stick-slip phenomena of the arm are reflected in the velocity reversals near the arm extreme location. Dependence of the span tension fluctuations on Coulomb torque is explored.

scholarly journals Cluster synchronization of dry friction oscillators

2018 ◽  
Vol 148 ◽  
pp. 10004
Author(s):  
Michał Marszal ◽  
Andrzej Stefański
Keyword(s):  
Dry Friction ◽  
Numerical Study ◽  
Excitation Frequency ◽  
Friction Model ◽  
Cluster Synchronization ◽  
Stick Slip ◽  
Closed Ring ◽  
Mass Spring ◽  
Friction Oscillators ◽  
Two Parameter

Synchronization is a well known phenomenon in non-linear dynamics and is treated as correlation in time of at least two different processes. In scope of this article, we focus on complete and cluster synchronization in the systems of coupled dry friction oscillators, coupled by linear springs. The building block of the system is the classic stick-slip oscillator, which consists of mass, spring and belt-mass friction interface. The Stribeck friction itself is modelled using Stribeck friction model with exponential non-linearity. The oscillators in the systems are connected in nearest neighbour fashion, both in open and closed ring topology. We perform a numerical study of the properties of the dynamics of the systems in question, in two-parameter space (coupling coefficient vs. angular excitation frequency) and explore the possible configurations of cluster synchronization.

Influence of Tensioner Dry Friction on the Vibration of Belt Drives With Belt Bending Stiffness

2007 ◽  
Author(s):  
Farong Zhu ◽  
Robert G. Parker
Keyword(s):  
Dry Friction ◽  
Harmonic Balance ◽  
Excitation Frequency ◽  
Harmonic Balance Method ◽  
Friction Torque ◽  
Stick Slip ◽  
Pulley System ◽  
Coulomb Damping ◽  
Belt Drives ◽  
Linear Subsystem

A model of dry friction tensioner in a belt-pulley system considering transverse belt vibration is developed, and the influence of the dry friction on the system dynamics is examined. The discretized formulation is divided into a linear subsystem including linear coordinates and a nonlinear subsystem addressing tensioner arm vibration, which reduces the dimension of the iteration matrices when employing the harmonic balance method. The Coulomb damping at the tensioner arm pivot mitigates the tensioner arm vibration but not necessarily the vibrations of other system components. The extent of the mitigation varies for different excitation frequency ranges. The critical amplitude of the dry friction torque beyond which the system operates with a locked arm is determined analytically. Superharmonic resonances are observed in the responses of the generalized span coordinates but their amplitudes are small. The energy dissipation at the tensioner arm hub is discussed, and the stick-slip phenomena of the arm are reflected in the velocity reversals near the arm extreme location. Dependence of the span tension fluctuations on Coulomb torque is explored.

Modeling Mechanical Stick-Slip Friction Using Electrical Circuit Analysis

1988 ◽  
Vol 110 (4) ◽  
pp. 440-443 ◽  
Author(s):  
Paul J. Kolston
Keyword(s):  
Mechanical System ◽  
Mechanical Systems ◽  
Electrical Circuit ◽  
Circuit Analysis ◽  
New Technique ◽  
Analysis Program ◽  
Stick Slip ◽  
A New Technique ◽  
Vast Range

A new technique for modeling stick-slip friction in mechanical systems is proposed. The technique uses an electrical circuit analysis program to analyze the electrical circuit equivalent of the mechanical system. The stick-slip characteristic can be altered to take almost any form. The method is easy to apply to a vast range of systems, and two examples are given to illustrate its validity.

Maximum Response of a Slow-Variant Mechanical System During Transition Through a Resonance

1999 ◽  
Author(s):  
Dmitri Balashov ◽  
Horst Irretier
Keyword(s):  
Mechanical System ◽  
Transient Response ◽  
Natural Frequencies ◽  
Excitation Frequency ◽  
Maximum Response ◽  
Asymptotic Formulas ◽  
Viscous Damping ◽  
New Approach ◽  
Bogoliubov Approximation ◽  
Run Up

Abstract A new approach to the estimation of the maximum transient response of a mechanical system with slow-variant natural frequencies and linear viscous damping is worked out. Based on the modal decomposition, the vibration response of a system is modeled using a set of simple vibrators with slow-variant natural frequencies. The passage through a resonance which is induced by a sweep of the excitation frequency during run-up or run-down is studied. Exact asymptotic formulas for the maximum transient response and the corresponding excitation frequency are derived analytically, starting from the first Krylov-Bogoliubov approximation. The obtained formulas are tested numerically and compared to known approximations.

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