Characterization of a novel fluidic friction-reduction tool used in extended-reach well considering periodic particle-laden jet

Fluidic oscillators(FOs)can be used as an efficient fluidic vibration tool to solve high friction problems in extended-reach wells.However,the complex mechanism of FOs makes the design challenging,and the dynamic erosion behavior inside FOs is still unclear.In this paper,new FOs are proposed and the working characteristics under the influence of periodic particle-laden jets are investigated.Firstly,the results reveal the working mechanism of new FOs,showing that the generation of pressure pulses is closely connected with periodic jet switching and the development of vortices.Secondly,the important performance parameters,i.e.,pressure pulse and oscillation frequency,are extensively studied through numerical simulation and experimental verification.It is found that the performance can be optimized by adjusting the tool structure according to different engineering requirements.Finally,the oscillating solid-liquid two-phase flow inside FO is studied.It is demonstrated that the accumulation of particles leads to a significant reduction in performance.The results also reveal five locations that are susceptible to erosion and the erosion behavior of these locations are studied.It has been shown that the periodic jet causes fluctuations in the amount of erosion at the outlet and splitter.This research can provide valuable references for the design and optimization of vibration friction-reduction tools.

In-situ formation of nitrogen doped microporous carbon nanospheres derived from polystyrene as lubricant additives for anti-wear and friction reduction

This study presents a nitrogen-doped microporous carbon nanospheres(N@MCNs)prepared by a facile polymerization–carbonization process using low-cost styrene.The N element in situ introduces polystyrene(PS)nanospheres via emulsion polymerization of styrene with cyanuric chloride as crosslinking agent,and then carbonization obtains N@MCNs.The as-prepared carbon nanospheres possess the complete spherical structure and adjustable nitrogen amount by controlling the relative proportion of tetrachloromethane and cyanuric chloride.The friction performance of N@MCNs as lubricating oil additives was surveyed utilizing the friction experiment of ball-disc structure.The results showed that N@MCNs exhibit superb reduction performance of friction and wear.When the addition of N@MCNs was 0.06 wt%,the friction coefficient of PAO-10 decreased from 0.188 to 0.105,and the wear volume reduced by 94.4%.The width and depth of wear marks of N@MCNs decreased by 49.2% and 94.5%,respectively.The carrying capacity of load was rocketed from 100 to 400 N concurrently.Through the analysis of the lubrication mechanism,the result manifested that the prepared N@MCNs enter clearance of the friction pair,transform the sliding friction into the mixed friction of sliding and rolling,and repair the contact surface through the repair effect.Furthermore,the tribochemical reaction between nanoparticles and friction pairs forms a protective film containing nitride and metal oxides,which can avert direct contact with the matrix and improve the tribological properties.This experiment showed that nitrogen-doped polystyrene-based carbon nanospheres prepared by in-situ doping are the promising materials for wear resistance and reducing friction.This preparing method can be ulteriorly expanded to multi-element co-permeable materials.Nitrogen and boron co-doped carbon nanospheres(B,N@MCNs)were prepared by mixed carbonization of N-enriched PS and boric acid,and exhibited high load carrying capacity and good tribological properties.

Oil-soluble polymer brushes-functionalized nanoMOFs for highly efficient friction and wear reduction

Nanomaterials as lubricating oil additives have attracted significant attention because of their designable composition and structure,suitable mechanical property,and tunable surface functionalities.However,the poor compatibility between nanomaterials and base oil limits their further applications.In this work,we demonstrated oil-soluble poly(lauryl methacrylate)(PLMA)brushes-grafted metal-organic frameworks nanoparticles(nanoMOFs)as lubricating oil additives that can achieve efficient friction reduction and anti-wear performance.Macroinitiators were synthesized by free-radical polymerization,which was coordinatively grafted onto the surface of the UiO-67 nanoparticles.Then,PLMA brushes were grown on the macroinitiator-modified UiO-67 by surface-initiated atom transfer radical polymerization,which greatly improved the lipophilic property of the UiO-67 nanoparticles and significantly enhanced the colloidal stability and long-term dispersity in both non-polar solvent and base oil.By adding UiO-67@PLMA nanoparticles into the 500 SN base oil,coefficient of friction and wear volume reductions of 45.3%and 75.5%were achieved due to their excellent mechanical properties and oil dispersibility.Moreover,the load-carrying capacity of 500 SN was greatly increased from 100 to 500 N by the UiO-67@PLMA additives,and their excellent tribological performance was demonstrated even at a high friction frequency of 65 Hz and high temperature of 120℃.Our work highlights oil-soluble polymer brushes-functionalized nanoMOFs for highly efficient lubricating additives.

Mechanical behavior of drillstring with drag reduction oscillators and its effects on sliding drilling limits

Practice has proved that drag reduction oscillators can decrease the axial friction and increase wellbore extension effectively in sliding drilling operations.However,the complicated mechanical behavior of drillstring with drag reduction oscillators has not been revealed sufficiently.In this paper,the mechanical model of drillstring with drag reduction oscillators is established by considering the friction nonlinearity.Further introducing the initial conditions,boundary conditions and continuity conditions,the finite differential equation of drillstring vibration is obtained and solved.The new model has been applied to a case study,in which the drag reduction effects of drillstring with and without oscillators are compared and the effects of relevant factors on drag reduction are analyzed.The results show that the hook loads increase obviously by reducing downhole average friction coefficient for drillstring with oscillators.Increasing vibration amplitude of the drag reduction oscillator can decrease axial friction,but the vibration frequency is nearly irrelevant to drag reduction.Increasing number of drag reduction oscillators can decrease axial friction,but may lead to large hydraulic power loss and high risk of drillstring fatigue.Therefore,there is an optimal number of drag reduction oscillators.The re search re sults are of significant guiding significance for optimal design and safety control in sliding drilling operations.

Turbulent drag reduction by spanwise slot blowing pulsed plasma actuation

This work studies the turbulent drag reduction(TDR)effect of a flat plate model using a spanwise slot blowing pulsed plasma actuator(SBP-PA).Wind tunnel experiments are carried out under a Reynolds number of 1.445×10^(4).Using a hot-wire anemometer and an electrical data acquisition system,the influences of millisecond pulsed plasma actuation with different burst frequencies and duty cycles on the microscale coherent structures near the wall of the turbulent boundary layer(TBL)are studied.The experimental results show that the SBP-PA can effectively reduce the frictional drag of the TBL.When the duty cycle exceeds 30%,the TDR rate is greater than 11%,and the optimal drag reduction rate of 13.69%is obtained at a duty cycle of 50%.Furthermore,optimizing the electrical parameters reveals that increasing the burst frequency significantly reduces the velocity distribution in the logarithmic region of the TBL.When the normalized burst frequency reaches f+=2πf_(p)d/U_(∞)=7.196,the optimal TDR effectiveness is 16.97%,indicating a resonance phenomenon between the pulsed plasma actuation and the microscale coherent structures near the wall.Therefore,reasonably selecting the electrical parameters of the plasma actuator is expected to significantly improve the TDR effect.

Study on Friction Reducing and Anti-wear of CaCO_(3) Nanoparticles as Additives in Lubricating Oils

This paper has insepected the size and the structure of the calcium carbonate (CaCO3) particles by adopting X-ray diffraction and transmission electron microscope (TEM). The suitable surfactants have been selected and put into lubricating oil with nanometer CaCO3 particles. By testing some parameters, such as the maximum non-seizure load, the shape and diameter of wear scar, the friction factor, the nanometer CaCO3 particles’ properties of extreme pressure, anti-wear and friction reduction have been tested and analyzed. The properties of the nanometer CaCO3 particles’ tribology chemistry have been analyzed through X-ray photoelectron spectrum (XPS) test. Also the nanometer CaCO3 particles’ mechanism of anti-wear and friction reduction has been studied systematically. The research results show that, the lubricating oil with nanometer CaCO3 particles have good tribological properties.

水下高速外流减摩擦阻力功效测试方案设计与验证

为了支撑高速水下航行器减摩擦阻力(摩阻)方案的选型和优化,本文提出较好的减摩阻试验研究技术方案和特征参量表达方法以提高测量精度的技术途径,并以聚氧化乙烯(PEO)减摩阻实际试验演示上述方案和途径的可行性。相关结果可为高速水下航行器减摩阻方案的选型和优化提供支撑。

钛合金摩擦磨损性能及减磨方法研究进展

钛合金具有比强度高、抗腐蚀性强、耐高温以及生物相容性好等优点,在汽车制造、生物医疗等众多领域具有重要应用。但钛合金的摩擦磨损性能较差,会影响机械系统的使用寿命和可靠性。首先论述了摩擦磨损过程中摩擦层的形成过程以及摩擦层对钛合金磨损机理的作用,分析了润滑条件、环境温度、滑动速度、载荷等工况条件对钛合金摩擦磨损性能的影响规律。其次,对比总结了钛合金减磨的常见工艺方法及优缺点,指出了当前钛合金磨损机理研究和性能改善方面存在的问题。最后,对今后的研究工作进行了展望:将实验与仿真相结合,阐明钛合金摩擦层和磨损机理的动态变化规律;考虑各种环境因素对钛合金磨损机理的影响,完善钛合金磨损机制图;通过对多种技术协同配合时的工艺参数进行优化,促进钛合金表面强化复合技术的发展,从而提升钛合金的耐磨减摩性能。

主动磁悬浮轴承系统保护轴承热特性研究及减摩设计

针对主动磁悬浮轴承系统(AMBs)转子跌落过程中转子与保护轴承碰摩产生巨大冲击、振动和大量摩擦热,易使保护轴承失效的问题,对立式转子跌落到保护轴承过程中的热特性进行了研究,分析了转子跌落对保护轴承造成破坏的主要影响因素,进而提出了一种采用磁控溅射技术在保护轴承关键表面沉积固体润滑薄膜(类石墨碳基薄膜,GLC)的减摩方法,并对镀膜、未镀膜的保护轴承进行了转子跌落试验。研究结果表明:跌落转速为20000 r/min时,保护轴承的最高温度为210.60℃,出现在转子与轴承内圈端面高速碰摩阶段,该温度超过了轴承钢160℃的回火温度,导致轴承烧伤而失效。在跌落试验中,镀有GLC薄膜的自润滑保护轴承试验后的沟道和端面外观明显优于未镀膜保护轴承,由碰摩发热导致的内圈端面硬度下降也较轻,质心轨迹和轴向位移更加平稳,温升更低,GLC薄膜起到了关键的自润滑和减摩功能,提高了保护轴承的使用寿命和服役可靠性,为解决主动磁悬浮轴承系统中保护轴承易失效而发生重大事故的问题提供了一种思路和方法。

超浅层大位移水平井“三低”钻井液技术

针对东部超浅层水平井水平段钻井中降摩阻扭矩大、托压严重等问题,分析了该区块的储层特征,构建了“低摩阻、强携砂、防水锁”的思路,优选了低成本的关键处理剂,形成了低摩阻、低成本和低伤害的水基钻井液体系,评价了其主要性能,并进行了现场试验。研究结果及试验表明,羧甲基纤维素(CMC)增黏提切效果好,最优加量为0.3%~0.5%,聚丙烯酸钾(KPAM)降失水明显,最优加量为1.0%~1.5%,复合润滑剂中固体润滑剂(SH-2)和液体润滑剂(RY-838)最佳复配比例为3∶7,防水剂为0.5%F-113。该钻井液体系渗透率恢复平均值为85.38%,中压失水小于5 mL,泥饼粘滞系数为0.0524~0.0612,动塑比为0.52~0.55。现场应用1口井,未出现严重托压,较邻井钻速提高13.5%,钻井液成本降低5.3%,有效解决了超浅层水平井钻井难题。

密封端面声发射信号降噪处理技术研究

针对利用声发射技术监测密封端面摩擦状态,受到轴承、电机等部件摩擦产生背景噪声对密封端面摩擦信号的干扰,导致获取密封端面声发射信号信噪比不高的问题,文章提出的基于经验小波变换和相对熵(EWT-KLD)的滤波降噪方法,对采集到的原始信号进行滤波降噪处理,以提高密封端面摩擦产生声发射信号的信噪比。通过试验验证,该方法可适用于不同工况、不同介质、不同摩擦状态的声发射信号进行降噪,提高50 kHz以上声发射信号的信噪比,尤其是密封端面微弱摩擦产生信号的信噪比,有效地提高了密封端面摩擦声发射检测的精度和灵敏度,对于早期密封端面摩擦监测的作用尤为明显,使得密封端面摩擦状态累积变化过程的监测更准确。

双水相聚合物乳液的制备及减阻性能

以丙烯酰胺(AM)、2-丙烯酰胺-2-甲基丙磺酸(AMPS)为原料,采用水分散聚合法,制备双水相聚合物(NPAM)。相对分子量为380万,粒子分布集中,且粒径小,平均粒径为182.7 nm。室内评价聚合物的减阻效果,其在清水中减阻率达到80%,在10%的盐水中减阻率达到77%。黏弹性能分析,NPAM的抗应变能力较强。双水相聚合物可用作减阻剂,为油气田压裂作业提供优秀的减阻性能。

织构化刀具表面摩擦磨损特性与减摩降磨机制研究

在刀具表面设计并加工出一定结构的微织构,可大幅改善刀具-切屑表面的摩擦状态。为了探究不同形态的织构刀具在干摩擦状态下的摩擦磨损特征,通过有限元仿真分析软件ABAQUS对不同织构类型的刀具进行分析,结合刀具的应力状态分布情况分析各类织构对减摩抗磨作用的影响。同时,利用飞秒激光器在刀具表面加工不同类型的织构并与钛合金磨球进行摩擦磨损实验,测定其摩擦因数,分析不同类型织构刀具表面的磨损情况和形貌。仿真及试验结果表明:刀具T1应力集中区分布广泛,应力集中严重;相对于T1,刀具T2、T3、T4、T5的等效应力值出现大幅降低,且应力分布较为均匀,其中刀具T4的表面等效应力值最低,且降温效果最优。上述结果表明:带有不同类型织构的刀具较无织构刀具的摩擦因数均有不同程度降低,一定程度上缓解了刀具表面的黏结磨损,其中T4摩擦因数降低最为显著,减摩效果最为突出。

半周负刚度摩擦阻尼装置振动台试验研究

对具有负刚度特征的半周负刚度摩擦阻尼装置进行了振动台试验,以某四层钢结构框架为减震研究对象,分别在钢结构框架的一层和二层布置半周负刚度摩擦阻尼装置,研究了在不同地震动工况下结构的地震响应。结果表明,半周负刚度摩擦阻尼装置可实现结构的位移与加速度响应双重控制,安装在结构变形较大位置会获得更好的振动控制效果。

仿生表面织构在农林机械中的研究现状

近年来,仿生学研究发现,生物在漫长的生存进化过程中,体表进化出许多具有优异摩擦学性能的表面织构,为机械材料摩擦学行为研究提供了大量的参考蓝本,仿生表面织构也成为了减摩减阻及摩擦学性能的重要手段。为此,基于国内外对仿生表面织构的研究,笔者概述了仿生表面织构的类型、发展、减摩减阻机理及应用,介绍了仿生表面技术在农林机械中的发展运用,总结了当前研究的不足并提出展望。

巷道通风摩擦阻力系数遗传投影寻踪回归预测

为满足智能通风准确获得巷道摩擦风阻的需求,基于遗传算法的投影寻踪回归预测方法预测矿井通风摩擦阻力系数。研究空气密度变化和巷道有无支护两种类型时模型预测的准确性。利用通风摩擦阻力系数影响因素进行训练,对不同支护类型巷道采集学习样本建立模型,使用部分样本进行验证。将模型预测结果与主成分分析预测和BP神经网络预测结果进行比较。对不同支护类型巷道进行了预测,最大误差为1.76%,平均误差为1.07%;仅对圆木支护进行了分析,最大误差为1.73%,平均误差为0.79%;对不同密度无支护巷道预测表明,平均误差为-0.99%,最大误差为-1.01%,风流密度对模型预测结果的准确性基本没有影响。无论是风流密度还是支护形式,该方法预测精度均优于主成分分析和BP神经网络。

水下平板通气减阻特性研究

为了研究通气射流对水下平板阻力特性的影响,本文采用Mixture多相流模型和Realizable k-ε湍流模型研究了三维水下平板通气射流的流动结构特征,得到了水下平板表面气液流场结构和减阻特性。数值结果表明:气体注入后,受来流影响而紧贴壁面向下游发展。当气体稳定覆盖在平板壁面后,平板阻力系数较不通气情况降低了16.73%。另外,因气体注入壁面边界层后,提升了壁面上的速度梯度,降低了壁面流体粘性系数;在气膜覆盖区(α_(l)>80%),因流体粘性系数的下降量远大于速度梯度的上升量,使流体粘性系数对气膜核心区内的减阻率起决定性作用;对于远离气膜核心区外的壁面,切向速度梯度对摩擦阻力系数的贡献增强。

低温高雷诺数下摩擦阻力测量及多孔介质减阻研究

为研究低温高雷诺数条件下多孔介质湍流减阻规律及雷诺数效应,在0.3 m低温连续式风洞开展了壁面摩擦阻力测量及多孔介质减阻试验。分别在光滑平板和多孔介质区域下游布置低温脉动压力传感器和油流,对脉动压力功率谱及下游全局摩擦阻力进行测量。结果表明:摩擦阻力系数随雷诺数的增大而减小;多孔介质减阻率随雷诺数的增大(增大马赫数或降低来流总温),呈无固定规律下降趋势,且多孔介质的引入,使下游脉动压力的低频信号强度增加,高频信号强度减弱;在马赫数Ma=0.300、雷诺数Re=7.51×10^(6)、来流总温T_(0)=140 K这一典型工况下,多孔介质仍具有11.4%的减阻率,初步验证了在低温高雷诺数条件下使用多孔介质减阻控制策略的可行性。

低速船舶微气泡减阻数值研究

为了研究船舶微气泡减阻规律,本文基于OpenFOAM中两相欧拉数值模型,对低速散货船进行微气泡减阻数值研究。对气液两相分别建立控制方程,考虑五种相间作用力及气泡聚合和破碎,采用考虑气泡影响的改进k-ε湍流模型,忽略自由面影响,采用叠模模型研究喷气量、气泡直径、航速及吃水等因素对船舶微气泡减阻的影响,分析气体体积分数、湍流粘度和气泡直径分布等。结果表明:微气泡可以同时减少船舶摩擦阻力、粘压阻力和总阻力;喷气量直接影响减阻率,喷气量越大,减阻率越高;较小气泡的平均气体体积分数较大且气体分布更均匀,同时湍流运动粘度较小,可以更有效减阻;气泡沿着流向会聚并,气泡越小聚并越剧烈;较高航速和小吃水更有利于减阻。

分体式凸轮轴球轴承座优化设计及研究

为最大限度提升凸轮轴球轴承的减摩收益,重点优化了分体式轴承座结构设计,采用CAE和工艺试验手段验证了球轴承变形量、轴承座上下盖的贴合间隙以及凸轮轴盘动扭矩。结果表明,轴承座与球轴承外圈过盈量、轴承座固定螺栓的位置、轴承座的刚度对球轴承的减摩有显著影响,优化后的分体式轴承座结构能显著降低球轴承的外圈变形,降低轴承座上下盖的贴合间隙,从而降低球轴承内部的卡滞效应,提升滚动摩擦减摩收益。