Nonlinear Dynamic Analysis of Coupled Gear-Rotor-Bearing System with the Effect of Internal and External Excitations

Extensive studies on nonlinear dynamics of gear systems with internal excitation or external excitation respectively have been carried out. However, the nonlinear characteristics of gear systems under combined internal and external excitations are scarcely investigated. An eight-degree-of-freedom(8-DOF) nonlinear spur gear-rotor-bearing model, which contains backlash, transmission error, eccentricity, gravity and input/output torque, is established, and the coupled lateral-torsional vibration characteristics are studied. Based on the equations of motion, the coupled spur gear-rotor-bearing system(SGRBS) is investigated using the Runge-Kutta numerical method, and the effects of rotational speed, error fluctuation and load fluctuation on the dynamic responses are explored. The results show that a diverse range of nonlinear dynamic characteristics such as periodic motion, quasi-periodic motion, chaotic behaviors and impacts exhibited in the system are strongly attributed to the interaction between internal and external excitations. Significantly, the changing rotational speed could effectively control the vibration of the system. Vibration level increases with the increasing error fluctuation. Whereas the load fluctuation has an influence on the nonlinear dynamic characteristics and the increasing excitation force amplitude makes the vibration amplitude increase, the chaotic motion may be restricted. The proposed model and numerical results can be used for diagnosis of faults and vibration control of practical SGRBS.

Financial frictions and the cash flow – external financing sensitivity: evidence from a panel of Pakistani firms

This paper uses a large panel of Pakistani non-financial firms over the period 2000-2013 to examine the role of financial constraints in establishing the relationship between cash flow and external financing.The results reveal that there exists a negative and significant relationship between external financing and cash flow.The finding of the substitutionary relation between internal funds availability and external financing has been viewed as evidence supporting the pecking order theory of capital structure.Yet,we show that this negative relationship is weak in case of financially constrained firms.We also analyze how credit multiplier affects external financing decisions of financially constrained and unconstrained firms.The results show that for financially unconstrained firms,the negative sensitively of external financing increases with asset tangibility.However,for financially constrained firms,the negative sensitivity of external financing to cash flow either decreases or turns positive as the tangibility of assets increases.This finding implies that financially constrained firms benefit more from investing in tangible assets because such assets not only help relax financial constraints but also having a potential to be a direct source of funds in periods of negative cash flow shocks.

Cerebral blood flow volume measurements of the carotid artery and ipsilateral branches using two-dimensional phase-contrast magnetic resonance angiography

The optimal velocity encoding of phase-contrast magnetic resonance angiography (PC MRA) in measuring cerebral blood flow volume (BFV) ranges from 60 to 80 cm/s.To verify the accuracy of two-dimensional (2D) PC MRA,the present study localized the region of interest at blood vessels of the neck using PC MRA based on three-dimensional time-of-flight sequences,and the velocity en-coding was set to 80 cm/s.Results of the measurements showed that the error rate was 7.0 ± 6.0% in the estimation of BFV in the internal carotid artery,the external carotid artery and the ipsilateral common carotid artery.There was no significant difference,and a significant correlation in BFV between internal carotid artery + external carotid artery and ipsilateral common carotid artery.In addition,the BFV of the common carotid artery was correlated with that of the ipsilateral internal carotid artery.The main error was attributed to the external carotid artery and its branches.Therefore,after selecting the appropriate scanning parameters and protocols,2D PC MRA is more ac-curate in the determination of BFV in the carotid arteries.

Middle or low water pressure direct spiral double helix converging nozzle structure optimization and flow field analysis

In order to solve the problem of using middle or low water pressure to form fine water mist,a new nozzle is proposed in fire rescue robot.Existing water mist nozzles are basically used for high pressure and in large size,complex structure and poor low pressure atomization effect in comparison with requirement of snake-like fire rescue robots.On the basis of comprehensive typical spray nozzles,a direct spiral double helix converging nozzle(DSDHCN) is proposed,which has the advantages of small volume,light weight,simple structure,and convenient installation.To make the spray nozzle have good performance,and meet the requirements of more efficient fire extinguishing,a numerical study is carried out to analyze the internal and external full flow field of nozzle.A gas-liquid two-phase flow is applied to simulate the external full flow field of nozzle with VOF model in fluent software.The simulation results show the real situation of water flow out of the atomization nozzle and the water jet trajectory.Some simulations about middle or low water pressure direct spiral double helix converging optimized nozzle have been done in 30 bar pressure.The simulation results show that the optimized nozzle structure not only makes the spray droplets have a good cone angle,but also have a sufficient axial velocity,which proves the structure rationality of the proposed optimized nozzle.

抽水蓄能机组水轮机工况启动过程内部流场分析

本文采用CFD数值模拟的方法,模拟计算了抽水蓄能机组在水轮机工况启动过程内部流场特征。得到了在活动导叶开启过程中的速度、压力随时间的瞬态分布规律,讨论了蓄能机组开启过程中外特性的变化曲线。结果表明:活动导叶的开启规律可以大体分为五个阶段。活动导叶的开启规律是先缓慢开启,然后以较快的速度关闭,最后再保持到空载的开度,从第四阶段,导叶再逐渐打开直到额定开度。转轮扭矩和机组流量呈现出先增大后减小的趋势,当导叶逐渐打开时,转轮扭矩和机组流量再逐渐上升。本文为研究蓄能机组水轮机工况下启动过程的内部流动变化提供了参考依据,同时对提高水轮机工况的启动稳定性具有重要意义。

基于CFD的果园喷雾风筒装置流体分析与试验

针对传统果园风送式喷雾机存在风能利用率低、风场较为分散等问题,开发一种与独立风机直接装配的小型喷雾风筒装置。运用CFD软件对该风筒装置内外流场进行模拟仿真,分析内流场风场云图及距外流场出风口不同距离平面中心区域的风速。结果表明:风筒内流场风速线分布均匀,能很好地产生旋流风,风能损失小;在外流场中,各平面风速分散性较小,出口风速达到17.15 m/s,满足果园喷雾机的风筒出口速度要求。并通过试验平台验证在距离出风口0.6 m处,实际风速为10.48 m/s,与仿真分析结果相比,相对误差为2.58%,且竖直高度上喷幅可达0.650 m,覆盖宽度可达0.669 m,证明所设计的风筒装置在该喷雾距离下能对果树冠层有较好的覆盖性,为进一步设计机架及风筒装置布置方案提供理论支撑。

直通调节阀内流场流道分析

随着油田的大量开发,油气井的工作情况更加复杂,一些出砂井常用螺杆泵,为了满足不同井深和产液量的需求,需要对压力调节阀进行检测。此次设计一种直通调节阀,在进出口压力一定的情况下,模拟仿真所设计的调节阀是否具有一定的稳定调节性能。调节阀又称控制阀,基于SOLIDWORKS三维模型,利用Fluent软件对其进行数值模拟,通过不同开度下的阀芯进行对比,通过分析压力云图、速度云图和流线图分析其流动规律。结果表明:(1)随着阀门开度的增大,阀芯阀座间流通面积变大,流速随着阀门开度的增加而减小。(2)随着阀门开度的不断增大,内流场压力会出现明显的变化。(3)随着阀门开度的增加,调节阀内流场会出现明显的漩涡。利用ANASYS软件进行流-固耦合,联合使用流场模块、静力场模块和温度场模块对调节阀内流场进行应力形变,当流体进入时,调节阀内流场发生应力形变比较稳定。以上所有模拟结果均符合实际情况,具有良好的稳定调节性能。

内外液流通道筒式磁流变制动器制动性能分析

针对传统磁流变制动器磁场利用率不高的问题,提出了一种具有内外液通道的筒式磁流变制动器;通过在缸筒和旋转套筒中增设非磁性器件,使得磁力线蜿蜒通过内外轴向液流通道的6段有效阻尼间隙,从而使该制动器在外形尺寸不变的前提下能产生较好的转矩性能;阐述了内外液流通道筒式磁流变制动器的结构和工作原理,并对有效阻尼间隙在磁场作用下的磁路进行分析;同时推导建立了制动转矩和温度场数学模型;基于COMSOL软件对磁流变制动器电磁场和温度场进行了仿真分析。由电磁场仿真可知,在外加电流为2.0 A、转速400 r/min时,制动转矩可达101.96 N·m,转矩动态可调范围由1.00增加至29.69;由温度场仿真可知,在多次紧急制动下最高温度为42.88℃,符合磁流变液正常工作范围。

旋涡泵定常流动特征及外特性分析

旋涡泵具有高扬程、扬程曲线陡降等典型的外特性以及易于加工的结构特征,因而被广泛用于化工、医药等行业。为了探究旋涡泵内部复杂流动特性以及对其外特性分析,采用标准k-ε两方程模型对旋涡泵全流道全流量工况进行了数值模拟分析。结果表明:该旋涡泵最高效率约为35%,且外特性曲线中扬程具有陡降特征;内流场分析发现,压力分布均匀并呈现一定的压力梯度,叶轮流道内有明显的环流运动,存在明显的纵向、径向旋涡;大流量工况下,当环流区域长度约为叶轮周向2/3长度时,为旋涡泵工作的最优工况。

计及进排气效应翼身融合布局机体—动力装置气动干扰研究

高气动效率是翼身融合布局获得竞争优势的关键因素。为有效抑制动力装置对该布局气动效率的不利干扰,需对适用于翼身融合布局的动力装置布置形式进行深入研究。本文采用计算流体力学(CFD)技术和可计及进排气影响的动力短舱模型,对某翼身融合—背撑发动机构型进行了精细内、外流耦合数值模拟,研究了巡航点附近动力装置和翼身融合机体之间的气动干扰特征。研究结果表明,相对于孤立翼身融合体构型,全机构型的翼身融合体部件升力系数大幅降低,阻力显著增大,短舱溢流在机身上形成的高压区是升力系数降低的主要原因;转速增大,发动机对机身边界层抽吸效应增强,翼身融合体部件升力系数降低量明显减小;在低转速状态,短舱无发动机喷流部件的唇口吸力效应较强,转速增大至接近全转速时,吸力效应被抵消,该部件产生阻力。

Development and Study on Nitrogen Removal Controller in A/O Process

In this paper three controllers for A/O process are developed, including a DO cascade controller, an external carbon flow rate controller and an internal recycling flow rate controller. The objective of the different controllers is to control the nitrate and ammonia concentration. Simulation study demonstrated that these controllers could efficiently control nitrogen removal and meet stricter effluent quality standards at a minimum cost.

Optimisation analysis of nanocomposite pipes with internal fluid flow under external excitation

The harmony search algorithm is applied to optimum designs of a functionally graded (FG)-carbon nanotubes (CNTs)-reinforced pipes conveying fluid subjected to moving load. The structure is modelled by Reddy cylindrical shell theory and the final equations are obtained by principal of Hamilton. Based on differential quadrature method (DQM), the dynamic displacement of system is derived.

基于非接触耦合式潮流控制器的不停电融冰装置拓扑及控制方法研究

现有分裂子导线的交流融冰技术大多将改变负荷电流,影响正常电力输送,或者影响电力线路正常开断,增加线路停电风险。利用分布式潮流控制器的调控原理,将单匝耦合变压器分布式地卡合在分裂子导线上,将被融冰段内的间隔棒进行绝缘改造,使融冰电流只在融冰段内的子导线间进行轮换;在耦合变压器的控制侧采用旁路开关将融冰装置退出,在并联联接电容与电感元件中采用可控开关实现耦合变压器等效阻抗的柔性调控,与单匝耦合变压器共同形成非接触耦合式交流融冰拓扑;为了不改变负荷电流的大小,基于融冰电流与负荷电流的分流比,推导了被融冰段对外等效阻抗不变的各子导线与融冰子单元等效阻抗的数学关系式,提出不影响正常电力传输的、各子导线依次融冰的各融冰子单元协调控制策略。基于某500kV输电线路实例,从理论计算和数字仿真2个方面验证了所提方法的有效性。

考虑外部博弈和内部协同的耦合系统时序随机生产模拟

火电与可再生能源在同一并网点集成为耦合系统能够有效促进可再生能源消纳。传统随机生产模拟方法难以充分考虑外部市场竞争以及内部机组协同对耦合系统运行的影响。为此,提出一种考虑外部博弈和内部协同的耦合系统时序随机生产模拟方法。首先,基于主从博弈,刻画耦合系统与其他发电商及电网之间的电量-电价竞争关系,基于合作博弈,建立了反映耦合系统内火电与可再生能源机组合作竞争关系的内部协同模型;然后,建立考虑外部博弈和内部协同嵌套的耦合系统时序随机生产模拟方法,提出耦合系统的可靠性评估指标以及内部机组经济收益分配方法;最后,采用中国东北某区域电网的实测数据,验证了所提方法的有效性和正确性。仿真结果表明,通过外部博弈和内部协同,耦合系统的经济性和可靠性大幅提升。

并联型TBCC推进系统变维度一体化数值模拟方法研究

为了缩短组合动力系统内外流一体化数值仿真时间,加快高超声速飞行器的研制进度,基于商业软件发展了一种飞行器进/排气系统多维仿真与发动机等效一维模型相结合的TBCC推进系统变维度一体化数值仿真方法,其中进/排气系统采用多维数值仿真,涡轮发动机采用部件特性的数学模型,冲压发动机采用准一维数学模型,结合商业软件通过边界条件调用,实现变维度一体化数值仿真。数值仿真对比分析表明:TBCC推进系统等效一维模型模拟结果与GasTurb 10和风洞试验结果变化规律一致吻合较好,误差不大于3.0%;采用变维度数值模拟方法对某TBCC推进系统沿飞行轨迹加速爬升过程的分析表明,进气道总收缩比从2.0增大到5.5,喷管面积比从1.2增大到7.8。涡轮模态时,TBCC喷管出现明显过膨胀现象;冲压模态时,喷管的落压比随马赫数增大从8.3逐渐增大至20.4,过膨胀现象减弱,从而验证了多维与一维耦合数值仿真方法的可行性。

中国经济国内国际“双循环”协调发展水平统计测度

选取2007—2021年省级面板数据,利用耦合协调模型测度中国经济国内国际“双循环”协调发展水平。研究表明:中国经济国内国际“双循环”协调发展水平呈现上升趋势,但总体处于较低水平阶段,仍有较大提升空间;中国经济国内国际“双循环”协调发展水平表现出明显空间集聚特征,较高省份主要聚集在东部地区,呈现“东部>中部>西部”的布局。进一步分析发现,技术创新、经济发展水平、贸易开放度、产业结构均可促进中国经济国内国际“双循环”协调发展水平提升。鉴于此,应设计区域经济协同发展方案,建立国内外价值链协同联动新格局,实施特色化资源配置策略,综合推进中国经济国内国际“双循环”协调发展水平提升。

基于电机拖拽系统的垂直管柱振动响应特性试验研究

为研究钻采机械作业时,垂直管柱在内、外流作用下的振动响应特性,以南海某深水钻井管柱为研究对象,基于相似理论,采用重力相似准则,通过电机拖拽支架产生相对流速,搭建含内流的单、双管柱振动响应试验测试平台,对内、外流作用下的垂直管柱进行了试验研究。结果表明:内流的存在使管柱自振频率降低,随着内流速度的增大,自振频率减小;外流是引起水下管柱振动的主要因素,外流速度越大,参与振动的响应模态越多;串联排列的双管柱在间距比小于4时,能明显减小管柱振动响应。

内外流作用下的U型管流致振动分析

为了探究U型管在内、外流体共同作用下的流致振动特性,基于ANSYS Workbench平台采用单向流固耦合方法,对外流为空气及内流为水联合作用下的单根U型管的振动特性进行了研究。结果表明,系统主要激励来自外流,外流会影响系统稳态响应的振动幅值及频率;内流对平均位移及固有频率影响则更为显著,内流对U型管各阶固有频率的降低幅度约为11.9%;由于内、外流体力的作用方向存在差异,每一个外流流速都存在一个最佳减振内流流速,某些流速组合(例如vout=10 m/s,vin=6 m/s时)可以使U型管的平均位移降低90%以上。

海洋温差能发电冷水管涡激振动性能

以海洋温差能发电(Ocean Thermal Energy Conversion,OTEC)平台的冷水管为研究对象,根据结构方程和尾流振子方程建立冷水管流固耦合模型,采用有限元方法和Newmark-β法对冷水管涡激振动(Vortex-Induced Vibration,VIV)进行时域分析,并在MATLAB软件中开发相应的求解程序。针对冷水管所面临的复杂工况,分别研究外部流场、内部流场、长径比和压载质量等因素对VIV产生的影响。结果表明:随着外流流速和长径比的增大,冷水管横流向VIV模态和振动幅值也发生相应改变,振动强度呈现波动上升;在不发生动态失稳的情况下,内流流速的增加可有效减小冷水管横流向振动幅值,压载质量可大幅减小冷水管自由端的振动位移。

综掘工作面内外双旋流风幕发生装置设计与控尘效果研究

针对煤矿综掘工作面粉尘浓度超限的问题,设计了一种新型内外双旋流风幕发生装置,通过数值模拟和相似试验分析了装置应用前后综掘工作面的风流流场特性和粉尘扩散规律。结果表明:司机位置粉尘质量浓度随风幕发生装置射流出口风速的增大呈先降低后增大的变化趋势,有效控尘临界风速为35 m/s;风幕发生装置可以形成阻挡粉尘向外扩散的漏斗状旋流风幕,并将综掘工作面分成粉尘控制区和工作区2部分;旋流风幕将粉尘颗粒的扩散速度降低了84%,且对5μm以下呼吸性粉尘控尘效率更优;新型风幕发生装置应用后司机位置处的粉尘质量浓度由337 mg/m^(3)降到38 mg/m^(3),控尘效率为88.7%。