系统参数对自激振动系统动力学稳定性的影响

为了研究机床进给系统的黏滑运动特性,建立了基于Stribeck摩擦模型的具有代表性的质体-弹簧-传送带摩擦自激振动模型.利用李雅普诺夫稳定性判据对自激振动系统的平衡点进行了稳定性分析,获得了系统的临界失稳速度,又经过理论公式推导出了系统的临界黏滑速度.从数值仿真得到的相图和Poincare截面图可以看出,随着系统进给速度、阻尼和传动刚度的增大,动、静摩擦差值的减小,系统的黏滞运动持续时间变短,即系统的稳定性增强;低速状态下的自激振动分为黏滑和纯滑动两个阶段,且均为准周期运动;系统进给速度是影响系统稳定性的主要参数.     

不同温度场下断层黏滑失稳过程模拟

随着国家对深部工程开发的需求增大，深部高岩温条件下断层黏滑失稳过程的演化规律和形成机制亟待研究.为此，本文借助离散元数值模拟手段，构建热力耦合数值模型，对6种不同温度场条件下的断层黏滑力学行为进行了详细研究，探究了不同温度场对断层黏滑失稳过程的影响机制.结果表明:随着温度场的不断上升，断层黏滑的破坏形态以及破坏模式均发生改变；断层黏滑次数、启滑应力以及启滑应力降整体上随温度上升，呈现不断下降的变化趋势；断层黏滑能量耗散以摩擦滑动为主；断层启滑时，总应变能与温度呈正相关，耗散能与温度呈负相关.     

基于速率-状态依赖摩擦本构关系研究不同因素对断层黏滑运动的影响

采用弹簧-滑块断层运动模型和速率-状态依赖摩擦本构关系,用数值模拟方法,模拟计算研究了构造应力加载速度、静态和动态应力扰动对断层黏滑运动的影响.结果显示,当模拟构造应力加载速度v0幅度增大时,断层的摩擦滑动由稳滑形式逐渐向黏滑运动形式转变;模拟静态应力扰动的正应力阶幅度的大小对断层黏滑出现的时间、黏滑应力降的幅度和黏滑运动周期均有较明显的影响;当断层受到方波形式的正应力扰动时,无论是应力扰动的波峰阶段还是波谷阶段,均出现了断层黏滑运动.     

二维耦合干摩擦振子黏滑运动分析

针对工程中广泛存在的二维干摩擦问题,通过引入斜弹簧建立一种可考虑x,y两个方向耦合的振子模型。定义摩擦力方位角来描述动、静摩擦力矢量分量,并考虑振子振动过程中可能出现黏滞,提出了一种分析二维耦合干摩擦振子黏滑运动的方法,给出了二维耦合干摩擦振子黏滑运动的复杂边界条件。基于指数型动态摩擦模型对二维耦合干摩擦振子的黏滑运动进行了数值仿真,给出了x方向和y方向相同激振频率相同相位角、相同激振频率不同相位角、不同激振频率不同相位角3种工况下的仿真结果及系统解随激振频率和相位角的变化规律。仿真结果表明,二维耦合摩擦振子运动中可能出现黏滑状态转换;当x方向和y方向的激励频率和相位角均不相等时,与前两种工况相比,质量块的运动轨迹、系统相图均为更加复杂的平面曲线,同时一个周期内系统可出现多次黏滑转换;两个方向激振频率相同时,改变激振频率和激励相位角,系统的解均没有出现次谐波,振子为周期运动。所提出的方法可为进一步研究二维耦合干摩擦振子的动力学特性及运动稳定性提供参考。     

非齐次泊松过程类软件可靠性增长模型

现有的基于故障覆盖率的软件可靠性增长模型多是只考虑了累计故障覆盖率 ,没有描述每个测试用例能够获得的故障覆盖率 .为了使软件可靠性增长模型能更好地刻画软件的测试过程 ,建立了两个基于故障覆盖率的非齐次泊松过程类软件可靠性增长模型 .第一个模型假设每个测试用例有相同的故障检测能力 ,能获得相同的故障覆盖率 ;第二个模型考虑了越晚检测到的故障其被检测到的概率越低的特点 ,模型假设每个测试用例的故障检测能力与其出现的次序相关 .利用一组公开发表的软件失效数据对这两个模型进行了验证 ,结果表明这两个模型在这组失效数据上均能得到较好的拟合效果 .     

Frictional ageing from interfacial bonding and the origins of rate and state friction

Earthquakes have long been recognized as being the result of stick-slip frictional instabilities. Over the past few decades, laboratory studies of rock friction have elucidated many aspects of tectonic fault zone processes and earthquake phenomena. Typically, the static friction of rocks grows logarithmically with time when they are held in stationary contact, but the mechanism responsible for this strengthening is not understood. This time-dependent increase of frictional strength, or frictional ageing, is one manifestation of the 'evolution effect' in rate and state friction theory. A prevailing view is that the time dependence of rock friction results from increases in contact area caused by creep of contacting asperities. Here we present the results of atomic force microscopy experiments that instead show that frictional ageing arises from the formation of interfacial chemical bonds, and the large magnitude of ageing at the nanometre scale is quantitatively consistent with what is required to explain observations in macroscopic rock friction experiments. The relative magnitude of the evolution effect compared with that of the 'direct effect'--the dependence of friction on instantaneous changes in slip velocity--determine whether unstable slip, leading to earthquakes, is possible. Understanding the mechanism underlying the evolution effect would enable us to formulate physically based frictional constitutive laws, rather than the current empirically based 'laws', allowing more confident extrapolation to natural faults.     

低速精密摩擦副材质与润滑介质匹配的研究

影响临界爬行速度诸多参数中,最大与最有可能影响的参数是静、劝摩擦系数差值△f。为此研制了爬行运劝试验装置,并用不同材质与不同摩擦状态的摩擦(运动)副进行研究。得出铸铁—铸铁运动副,不论润滑良否,对临界爬行速度影响不大,并且数值较小。因而铸铁是制造低速精密运动副的好材料。     

钻柱系统黏滑振动的自激振动特性研究

针对当前钻柱系统黏滑振动产生的影响不断增大的问题,研究黏滑振动的自激振动特性。通过建立钻柱系统的黏滑振动力学模型,推导了钻头于黏滞阶段与滑脱阶段的状态方程,并得到其滑脱阶段的振动响应。在得到系统黏滑振动特性的基础上,研究钻头在不同初始条件时相对转盘运动的相轨迹。结果表明,当钻头初相点存在扰动时,其运动均将趋向于稳定的黏滑振动,表现为钻头运动的相轨迹收敛于稳定的极限环。对黏滑振动产生的原因进行分析,结果表明,产生黏滑振动的钻柱系统在黏滞状态与滑脱状态转变时均存在摩擦扭矩的降落,相当于在钻头转动方向作用一个外载,即钻头临界状态转变时存在的负阻尼效应将钻柱的振动调节为自激振动。     

Fault lubrication during earthquakes

The determination of rock friction at seismic slip rates (about 1?m?s(-1)) is of paramount importance in earthquake mechanics, as fault friction controls the stress drop, the mechanical work and the frictional heat generated during slip. Given the difficulty in determining friction by seismological methods, elucidating constraints are derived from experimental studies. Here we review a large set of published and unpublished experiments (～300) performed in rotary shear apparatus at slip rates of 0.1-2.6?m?s(-1). The experiments indicate a significant decrease in friction (of up to one order of magnitude), which we term fault lubrication, both for cohesive (silicate-built, quartz-built and carbonate-built) rocks and non-cohesive rocks (clay-rich, anhydrite, gypsum and dolomite gouges) typical of crustal seismogenic sources. The available mechanical work and the associated temperature rise in the slipping zone trigger a number of physicochemical processes (gelification, decarbonation and dehydration reactions, melting and so on) whose products are responsible for fault lubrication. The similarity between (1) experimental and natural fault products and (2) mechanical work measures resulting from these laboratory experiments and seismological estimates suggests that it is reasonable to extrapolate experimental data to conditions typical of earthquake nucleation depths (7-15?km). It seems that faults are lubricated during earthquakes, irrespective of the fault rock composition and of the specific weakening mechanism involved.     

基于动力学仿真的柴油机轴系不对中故障探究

针对柴油机轴系齿式联轴器不对中故障,首先建立齿式联轴器轴向摩擦力数学模型,分析不对中产生的轴向摩擦力特点,然后构建包括齿式联轴器在内的轴系动力学仿真模型,探究齿式联轴器不对中故障下曲轴的动力学行为规律,分析曲轴推力轴承及齿轮的受力变化。仿真结果表明：不对中的齿式联轴器外齿元件会对内齿套产生轴向摩擦力,由此影响曲轴轴向窜动,进而导致曲轴止推轴承和正时齿轮轮齿接触力发生改变。通过实际故障案例验证了仿真结果的正确性。本文结论可为柴油机轴系故障的排查和诊断提供机理依据。     

Molecular dynamics simulations of atomic-scale friction in diamond-silver sliding system

Molecular dynamics simulations have been performed to explore the atomic-scale sliding friction, especially the stick-slip friction, in a system consisting of a diamond slider and a silver substrate. The mechanisms of the stick-slip behavior are investigated by considering sliding speeds between 10 m/s and 200 m/s.The analyses of the shear distance between the upmost layer and the downmost layer and displacements of a column of atoms in the slider show that shearing deformation of the slider is the main cause of the stick-slip phenomenon. Our simulations also present that a commensurate fit between the two contact surfaces is unimportant for the stick-slip friction.     

振动引起的界面切向相对运动对摩擦的影响

为了研究接触界面振动对摩擦的影响, 自主设计实验装置, 以在振动台上匀速滑动的滑块为对象, 采用理论与实验相结合的方法, 分析法向振动和切向振动引起界面切向运动减摩的机理。实验结果表明, 振动台的法向振动和切向振动经常同时存在。当界面振动, 且滑块与振动台之间的切向相对速度方向不变时, 滑块受到的平均滑动摩擦力与无振动时相同, 没有减摩作用; 当滑块与振动台之间切向相对速度的方向发生周期性变化或存在stick-slip (黏滑)时, 与无振动时相比, 滑块的平均滑动摩擦力有明显的减摩作用。根据Coulomb摩擦定律建立动力学模型进行仿真, 仿真结果与实验结果非常吻合, 说明在界面运动为已知的条件下, Coulomb摩擦模型能够反映界面间的摩擦作用。实验和仿真结果表明, 当法向振动和切向振动同时存在时, 振动引起的界面切向相对运动造成摩擦力方向的周期性变化或stick-slip是减摩的主要原因。     

冲击地压粘滑失稳的混沌特性

为探讨冲击地压发生的非线性特征,在分析断层型或构造型冲击地压粘滑失稳的原因和特点基础上,引入了模拟粘滑失稳的双滑块模型.理论分析表明,双滑块模型在对称情况下,完全相同的2个滑块可以造成空间上不相同的滑块运动,但其动力学行为只表现出周期性的特点;在非对称的情况下,滑块的粘滑失稳表现出复杂的混沌行为.通过适当考虑模型参数物理意义以及对参数值进行选取,该模型可用于解释断层型或构造型冲击地压粘滑失稳机理,描述其动力学行为复杂的非线性混沌特性.     

基于粘-滑摩擦力模型的微型压电驱动器动力学分析

提出了一种新型的靠摩擦力驱动的微型压电驱动器，采用粘一滑摩擦力模型对其进行了动力学分析．通过对比仿真结果和实验结果，得出了不同驱动信号下的驱动器动力学特性；改变驱动信号的频率和幅值，能够控制驱动器的运动方向和速度．仿真结果与试验结果吻合较好，证明该摩擦力模型能够对驱动器进行较为精确的理论分析．     

地面驱动螺杆泵负载扭矩波动机制

地面驱动螺杆泵采油技术在大庆油田深井、三元复合驱油井应用时,负载扭矩出现大幅度周期波动,出现系统杆断、脱胶等问题,免修期很短。建立螺杆泵系统黏滑物理模型,推导黏滑发生的临界速度,提出防治措施并分析现场实施效果。研究表明:螺杆泵负载扭矩波动是由于金属转子和橡胶定子静摩擦系数明显大于动摩擦系数或者在动摩擦系数随时间的变化率在某个转速下为负值时,系统在恒定驱动扭矩及转速下产生的一种黏滑现象;螺杆泵系统黏滑现象对现场设备危害大,可以通过降低黏滑发生的临界速度解决。     

汽缸摩擦力特性实验研究

研究汽缸的摩擦力特性.采用出口节流调速的方法建立汽缸摩擦力测试实验台,该实验台可进行汽缸的静动摩擦力测试.测试了汽缸在不同供气压力、不同速度和两腔压差下的动摩擦力特性,建立了汽缸的摩擦力模型,此模型将为研究汽缸的爬行现象和汽缸的伺服控制提供有意义的参考.实验结果表明:空载下汽缸的动摩擦力和速度的拟合关系为二次曲线;汽缸的动摩擦力与两腔压差及压差的方向都有关系.     

Fuzzy-Expert Diagnostics for Detecting and Locating Internal Faults in Three Phase Induction Motors

Internal faults in three phase induction motors can result in serious performance degradation and eventual system failures if not properly detected and treated in time. Artificial intelligence techniques, the core of soft-computing, have numerous advantages over conventional fault diagnostic approaches; therefore, a soft-computing system was developed to detect and diagnose electric motor faults. The fault diagnostic system for three-phase induction motors samples the fault symptoms and then uses a fuzzy-expert forward inference model to identify the fault. This paper describes how to define the membership functions and fuzzy sets based on the fault symptoms and how to construct the hierarchical fuzzy inference nets with the propagation of probabilities concerning the uncertainty of faults. The designed hierarchical fuzzy inference nets efficiently detect and diagnose the fault type and exact location in a three phase induction motor. The validity and effectiveness of this approach is clearly shown from obtained testing results.     

Effects of acoustic waves on stick-slip in granular media and implications for earthquakes

It remains unknown how the small strains induced by seismic waves can trigger earthquakes at large distances, in some cases thousands of kilometres from the triggering earthquake, with failure often occurring long after the waves have passed. Earthquake nucleation is usually observed to take place at depths of 10-20 km, and so static overburden should be large enough to inhibit triggering by seismic-wave stress perturbations. To understand the physics of dynamic triggering better, as well as the influence of dynamic stressing on earthquake recurrence, we have conducted laboratory studies of stick-slip in granular media with and without applied acoustic vibration. Glass beads were used to simulate granular fault zone material, sheared under constant normal stress, and subject to transient or continuous perturbation by acoustic waves. Here we show that small-magnitude failure events, corresponding to triggered aftershocks, occur when applied sound-wave amplitudes exceed several microstrain. These events are frequently delayed or occur as part of a cascade of small events. Vibrations also cause large slip events to be disrupted in time relative to those without wave perturbation. The effects are observed for many large-event cycles after vibrations cease, indicating a strain memory in the granular material. Dynamic stressing of tectonic faults may play a similar role in determining the complexity of earthquake recurrence.     

无刷直流电机匝间短路故障定位及定量评估方法研究

针对无刷直流电机匝间短路故障问题,提出一种结合深度迁移学习和多维特征拟合方法,以实现匝间短路故障的精确定位和定量评估.同步采集电机定子绕组的三相电流信号,将一维电流信号转化为图像信号,采用基于迁移学习的卷积神经网络实现匝间短路故障的定位,在确定故障相之后,从电流信号中提取并筛选敏感特征,采用特征拟合方法实现故障等级的定...     

南堡凹陷断层活动与油气成藏和富集的关系

基于生长断层活动性的定量评价、大量流体包裹体的光性特征和均一温度结合单井埋藏史等综合分析,对南堡凹陷断层活动与油气成藏和富集的关系进行研究。结果表明:除两条边界断层外,南堡凹陷切穿烃源岩层系且在明化镇期活动的断层总计45条;沙河街期至东营期断层活动性增强,馆陶期为相对静止期,在明化镇期断层活动性再次增强,断层停止活动时间主要为距今7～2.5Ma,平均距今4 Ma。根据明化镇早期断距的大小和断层停止活动时间,将45条断层划分为A、B、C 3类,油气主要富集在活动性相对较强、断层停止活动时间相对较晚的A、B两类断层附近的有利圈闭中。根据流体包裹体均一温度结合埋藏史得出研究区油气成藏期最晚时间主要为距今5～1 Ma,平均距今2 Ma,晚于断层停止活动时间2 Ma;断层停止活动后,当上覆地层沉积厚度为180～300 m时,其在垂向上的通道逐渐闭合。