Research on Stick-Slip Vibration Suppression Method of Drill String Based on Machine Learning Optimization

During the drilling process,stick-slip vibration of the drill string is mainly caused by the nonlinear friction gen-erated by the contact between the drill bit and the rock.To eliminate the fatigue wear of downhole drilling tools caused by stick-slip vibrations,the Fractional-Order Proportional-Integral-Derivative(FOPID)controller is used to suppress stick-slip vibrations in the drill string.Although the FOPID controller can effectively suppress the drill string stick-slip vibration,its structure isflexible and parameter setting is complicated,so it needs to use the cor-responding machine learning algorithm for parameter optimization.Based on the principle of torsional vibration,a simplified model of multi-degree-of-freedom drill string is established and its block diagram is designed.The continuous nonlinear friction generated by cutting rock is described by the LuGre friction model.The adaptive learning strategy of genetic algorithm(GA),particle swarm optimization(PSO)and particle swarm optimization improved(IPSO)by arithmetic optimization(AOA)is used to optimize and adjust the controller parameters,and the drill string stick-slip vibration is suppressed to the greatest extent.The results show that:When slight drill string stick-slip vibration occurs,the FOPID controller optimized by machine learning algorithm has a good effect on suppressing drill string stick-slip vibration.However,the FOPID controller cannot get the drill string system which has fallen into serious stick-slip vibration(stuck pipe)out of trouble,and the machine learning algorithm is required to mark a large amount of data on adjacent Wells to train the model.Set a reasonable range of drilling parameters(weight on bit/drive torque)in advance to avoid severe stick-slip vibration(stuck pipe)in the drill string system.

两自由度随机干摩擦系统的Stick-slip运动

研究具有两个摩擦面的两自由度系统,引入随机摩擦模型,考虑摩擦力的随机特性,建立了系统的随机动力学模型。通过解耦,将系统分为确定性运动和随机运动的叠加。采用事件驱动法确定系统的运动状态,是全局stick状态,还是全局slip状态,或者是一个slip状态而另一个stick状态。在确定的Stick-slip运动状态下,分别求解确定性方程的解和随机方程的均值。实例分析发现,阻尼可以改变摩擦系统的运动模式跃迁的周期特性。噪声摄动改变了Stick-slip运动的运动模式,可以通过噪声摄动控制Stick-slip运动。

基于Stick-slip振动试验的Stribeck摩擦模型参数研究

开展了销-盘接触形式的Stick-slip(粘-滑)振动试验,分析试验结果的Stick-slip振动特性,辨识不同工况下Stick-slip振动中的摩擦参数,以及分析法向力和摩擦盘的转速对Stribeck摩擦模型中参数的影响。结果表明:法向力和转速会影响摩擦系统的Stick-slip振动特性;法向力会影响Stribeck模型中的动摩擦系数和衰减系数,转速则对静摩擦系数和衰减系数影响较大,对动摩擦系数影响较小。

带基础隔震器结构的Stick-slip运动模型

带基础隔振器结构的Ｓｔｉｃｋ－ｓｌｉｐ运动研究是一个很年轻的课题．有关文献指出：带可滑动基础的结构存在Ｓｔｉｃｋ－ｓｌｉｐ运动的可能，它将导致结构失稳以及由此引起疲劳破坏，因此该类结构的Ｓｔｉｃｋ－ｓｌｉｐ运动研究是有价值的．据此，调查了在地震作用下带滑动基础或基础隔振器结构，并建立其Ｓｔｉｃｋ－ｓｌｉｐ运动的离散动力学模型，指出了系统的复杂的非线性特性．

A NEW CRITERION FOR OCCURRENCE OF STICK-SLIP MOTION IN DRIVE MECHANISM

This paper,using Karnopp’s model of friction force and phase planemethod,studies the stick-slip motion of the flexible drive mechanism.It is explainedthat a sudden drop of friction force is the essential source of stick-slip motion when thesliding is impending.A new criterion for occurrence of stick-slip motion is established.The stick-slip region and the stable region in a parameter plane are separated bya critical parameter curve.Moreover,for the stick-slip motion of the flexible drivemechanism without viscous damping,a parameter expression is obtained.The resultsmay be used in design of the flexible drive mechanism.

Simulation analysis on influential factors of stick-slip

In this paper a new physical model for studying stick-slip is established. Based on the dynamics system of the model,the state equation of the system is presented. And simulation analysis on the influential factors of stick-slip is carried out. The relationship between stiffness ( horizontal and normal) ,dampness,mass, difference of static and kinetic coefficients of friction,driving velocity,and amplitude in normal direction is analyzed and parameters of stick-slip are evaluated. Results show that stick-slip can be reduced by improving horizontal stiffness,decreasing dampness,reducing mass,cutting down the difference of static and kinetic coefficients of friction,properly choosing the vertical stiffness and properly inducting the normal oscillation.

Period Doubling Bifurcation of Stress Drop for Stick-slip and Its Physical Implication

It is revealed in frictional experiments on medium-scale samples that period doubling bifurcation of stress drop for stick-slip occurs due to macroscopic heterogeneity of the sliding surface under conditions for typical stick-slip.The observed data show that the period doubling bifurcation of stress drop results from the alternate occurrence of strain release along the whole fault and along part of fault.This implies that complicated nonlinear behavior corresponds to clear physical implication in some cases.

Observer-based State Feedback Control to Suppress Stick-slip Vibrations in Oil Well Drill-string

In drilling field, stick-slip vibrations of the drill-string are the main reason for the failure of the drilling system. To suppress the undesired stick-slip vibrations, an observer-based state feedback control method is proposed. The drilling system is described by a lumped parameter model including a Karnopp friction torque model. A state observer is designed to estimate the bit velocity in bottom hole and a state feedback controller is proposed to control the top drive velocity. By simulation, the performance of the control algorithm is demonstrated. Based on the control algorithm, a stick-slip vibration control system is developed. Test results show that the control system can effectively eliminate stick-slip vibrations of the drill-string and can be applied to the drilling field.

Evolution of real contact area during stick-slip movement observed by total reflection method

We build an experiment system based on total reflection(TR) method to observe the evolution of real contact area of polymethyl methacrylate(PMMA) in the continual stick-slip movement. The bilateral friction is adopted to overcome the bending moment in the lateral friction movement. Besides some classical phenomena of stick-slip movement such as periodical slow increase of frictional force in sticking phase and a sudden drop when slipping, a special phenomenon that the contact area increases with the tangential force is observed, which was called junction growth by Tabor in 1959.Image processing methods are developed to observe the variation of the junction area. The results show that the center of the strongest contact region will keep sticking under the tangential force until the whole slipping, the strongest point undergoes three stages in one cycle, which are named as sticking stage, fretting stage, and cracking stage, respectively. The combined analysis reveals a physical process of stick-slip movement: the tangential force causes the increase of the real contact area, which reduces the pressure between the contact spots and finally leads to the slipping. Once slipping occurs,the real contact area drops to the original level resulting in the pressure increase to the original level, which makes the sticking happen again.

Study on Criterion About Overcoming Low-Speed Stick-Slip of Simulator

This paper sums up the research situation. At the influence of friction, a simulatorexists the phenomenon of low-speed stick-slip. The character of low-speed of simulator is affectedseriously. According to the phase plane method, algebra analyzing method and Lyapunov theory,the paper gives a criterion about overcoming low-speed stick-slip. Making use of the criterion, wecan conclude the relationship between system parameters and low-speed stick-slip, and determinethe condition where the parameters of PID controller should satisfy, for the purpose of overcominglow-speed stick-slip and has not the phenomenon of low-speed stick-slip. This method is simple andeasy to carry out and the experiments show that the condition is correct.

Stick-Slip Tower-Shaped Piezoelectric Actuator

Since stick-slip actuators present the advantage of allowing long displacements(several centimeters or even more)at a high speed with an ultra high resolution(<5nm),a new type of stick-slip piezoelectric actuator is proposed to attain sub-nanometer positioning accuracy.The actuator is composed of a slider and a tower-shaped stator using forced bending vibration in y-z plane to generate tangential vibration on the top of the driving foot.When excited by the sawtooth input voltage,driving foot of the stator is able to generate a tangential asymmetrical vibration on the top,and the slider is thus pushed to move.A prototype and its testing equipment are fabricated and described.Following that,the testing of vibration mode and mechanical characteristics as well as stepping characteristics are conducted.Experimental results show that under the condition that the sawtooth input voltage is400VP-Pand the pre-pressure is 6N.Velocity of the actuator reaches its maximum 1.2mm/s at the frequency of 8000 Hz and drops to its minimum 35nm/s at the frequency of 1Hz.When the excitation signal is the single-phase sawtooth stepping signal,the tower-shaped actuator can directionally move forward or backward step by step.And when excited by the sawtooth stepping signal with 1Hz and 300VP-Pduring 1cycle(200ms),the actuator has a minimum stepping distance of 22 nm.

Large Thrust Trans-scale Precision Positioning Stage Based on Inertial Stick-Slip Driving

For the smaller thrust,it is difficult to achieve 3Dtrans-scale precision positioning based on previous stick-slip driving.A large thrust trans-scale precision positioning stage is studied based on the inertial stick-slip driving.The process of the movement is divided into two steps,i.e.,the″sliding″phase and the″stickness″phase.In the whole process,the kinematics model of the inertial stick-slip driving is established,and it reveals some factors affecting the velocity of inertial stick-slip driving.Furthermore,a simulation of movement is preformed by Matlab-Simulink software,and the whole process of the inertial stick-slip driving is displayed.After one experimental prototype is designed,the back and forth velocity is tested.Finally,the simulation verifies the accuracy of the kinematics model.

Four types of acoustic emission characteristics during granular stick-slip evolution

The shear behavior of granular materials plays an important role in understanding the occurrence of geological hazards. This study introduces the use of direct shear tests and acoustic emission(AE) technology on glass beads to investigate the distributions features of AE during the stick-slip processes. Results show that the shearing behavior of granular samples was shown as a series of similar, periodic stick-slip events. Some AE features — energy and Root Mean Square(RMS) —showed significant spatial clustering. Combined with the distribution of AE in the stick-slip event, the AE signal can be divided into four types: 1. low-energy and highfrequency AE, which represent particle friction;2. highenergy and low-frequency AE, which represent structural failure, that is, the slip process;3. low-RMS and lowfrequency AE represent internal local failure;and 4.high-RMS and high-frequency AE caused by overall structure failure. The b-value representing the energy distribution of AEs is used to describe the changing of AE sources during shear process. In addition, the amount and energy of AE had a significant positive correlation with normal stress. The shear rate mainly affects the AE representing particle friction, and the faster the shear rate, the lower the incidence of these friction AEs. According to the time sequence of the occurrence of different types of AE, AE rate, b-value and local failure AE signal can be applied to the prediction or early warning of geological hazards.

Stick-slip nucleation triggering of Wenchuan earthquake

The MS8.0 Wenchuan earthquake occurred on May 12 th,2008 on the steeply reverse fault of the Longmen Shan fault zone,Western China.Catastrophic failure and rupture occurred along the listric sliding surface.Several numerical simulations have been performed to reconfigure the dynamic processes of this strong earthquake.However,few scientific studies on the stick-slip of the listric fault have been conducted.In this study,finite element method is utilized to simulate the instant stick-slip fault responses at the triggering moment.The fault surface is a non-continuous and frictional contact interface.The simulation results demonstrated that the sliding friction and sticking friction interact spatially.This interaction occurred temporarily on swarms of slip patches,rather than the entire fault slipping surface.Stick-slip causes serrated energy release,and transient aseismic slip can occur spontaneously.These tremors propagate from the epicenter upwards to the ground surface.Therefore,they may provide important details on earthquake onset rupture.

法向振动对Burridge-Knopoff模型Stick-Slip运动影响数值研究

Burridge-Knopoff模型是研究地震和其他机械系统动力学行为的实用模型。考虑到摩擦力的影响,Burridge-Knopoff模型运动呈现出动力学非线性,Stick-Slip运动是这种模型的典型运动特征。滑块法向振动对这种模型运动行为的影响规律尚未被有效研究,为此建立一种考虑了滑块法向振动影响的Burridge-Knopoff模型。Stribeck模型被用来刻画依赖于滑块与传送带之间相对速度的摩擦力。采用数值方法分析系统的典型运动规律,研究法向振动的频率和相位对系统运动模式的影响规律,考虑法向振动的Burridge-Knopoff模型存在混沌和分岔现象得到证实。

Mechanism analysis and improved model for stick-slip friction behavior considering stress distribution variation of interface

Studying the evolution of interface contact state, revealing the “black box” behavior in interface friction and establishing a more accurate friction model are of great significance to improve the prediction accuracy of mechanical system performance. Based on the principle of total reflection, a visual analysis technology of interface contact behavior is proposed. Considering the dynamic variation of stress distribution in interface contact, we analyze the nonlinear characteristics of contact parameters in different stages of stick-slip process using the above-mentioned experimental technology. Then,we find that the tangential stiffness of the interface is not a fixed value during the stick-slip process and the stress distribution variation is one of the important factors affecting the tangential stiffness of interface. Based on the previous experimental results, we present an improved stick-slip friction model, considering the change of tangential stiffness and friction coefficient caused by the stress distribution variation. This improved model can characterize the variation characteristics of contact parameters in different stages of stick-slip process, whose simulation results are in good agreement with the experimental data. This research may be valuable for improving the prediction accuracy of mechanical system performance.

Characteristics of the AE Distribution and Triggering Mechanism of a Simulated Meter-Scale Fault after Stick-Slip Events

With the more complete acoustic emission(AE)catalog improved by the multi-channel AE matched-filter technique(MFT),we study the spatiotemporal evolution of the AE activities after laboratory stick-slip events incorporate with the slip data recorded by displacement transducers on an^1.5 m granite fault.The results show that the number of the AE events identified by MFT is about 9 times larger than that of the traditional method.A logarithmic expansion of early AE events along the fault strike is observed as a function of time,whereas the fault does not slip in the same manner.Thus,we related the expansion of the early AE events along the fault to the stress transfer caused by the adjacent AE events.Moreover,there is a good correlation between the cumulative number of the later AE events and the amount of fault slip.It suggests that the stress change caused by the continuous slip of the simulated fault after the stick-slip events response for the later AE events near or on the simulated fault.

Dry Friction with Various Frictions Laws: From Wave Modulated Orbit to Stick-Slip Modulated

Choices of excitation signals are important in engineering sciences and in physical simulations;a sufficient excitation can be critical in modelling a complicated nonlinear dynamic system. The discontinuous dynamic of a non-linear, friction-induced with two idealized periodical forced oscillators is studied. The dry friction in the system follows the classical Coulomb law, and various friction characteristics of dry friction laws in engineering sciences. To capture the presence of the two driving forces, the system must be studied as a function of their frequency-modulated and its equivalent amplitude modulated waveforms. Our numerical investigation shows a rich dynamical behaviour including periodic, quasi-periodic motions, thus a variable dynamics phenomenon among others;such as modulated waves, modulated stick-slip, periodic oscillation, and periodic stick-slip. It seems that such excitation forces can be used to conveniently identify the existence of nonlinearity, dry friction effects, and strength degradation in the system. The results achieved via the Coulomb’s law are compared with those obtained via two others particular friction laws: the complete model with Stribeck effect and Coulomb viscosity.

柔性多体系统含摩擦碰撞stick-slip过程动力学仿真

基于高次刚柔耦合理论和Lagrange乘子法,研究了柔性多体含摩擦碰撞stick-slip过程的全局动力学的精确建模与自动切换仿真问题。基于变拓扑思想,根据分离、碰撞、黏滞接触和滑动接触等状态分别构造相应的约束条件和动力学方程。运用冲量/动量法求解碰撞初始条件;引入切向滑动摩擦力势能的概念描述切向滑动接触力;给出接触、分离、黏滞、正向/逆向滑动状态之间的切换准则,实现了系统全局动力学自动切换。通过算例的数值仿真,分析了滑移/黏滞(微滑动)、正/逆向滑动等复杂非光滑现象,验证了该模型和算法的有效性。

注塑中间轴Stick-slip噪音分析及改善方案

中间轴是转向系统中连接转向管柱和转向机可以传递扭矩并吸收路面激励的一种机械传动机构,车辆在启动和行驶中,转向系统由驾驶员实时操控,其噪音表现更直接被人们感知。转向注塑中间轴具有结构简单,制造工艺及成本低廉,综合性能优越。在车市竞争日趋降本争效的大环境下,越来越受到整车厂的青睐。由于是滑动副结构,两接触件相互摩擦易产生黏滑(Stick-slip)现象,注重介绍注塑中间轴结构及其在受载状态下的Stick-slip噪音分析和改善方案。