Research on modeling and self-excited vibration mechanism in magnetic levitation-collision interface coupling system

The modeling and self-excited vibration mechanism in the magnetic levitation-collision interface coupling system are investigated.The effects of the control and interface parameters on the system's stability are analyzed.The frequency range of self-excited vibrations is investigated from the energy point of view.The phenomenon of self-excited vibrations is elaborated with the phase trajectory.The corresponding control strategies are briefly analyzed with respect to the vibration mechanism.The results show that when the levitation objects collide with the mechanical interface,the system's vibration frequency becomes larger with the decrease in the collision gap;when the vibration frequency exceeds the critical frequency,the electromagnetic system continues to provide energy to the system,and the collision interface continuously dissipates energy so that the system enters the self-excited vibration state.

Dynamic Response of Foundations during Startup of High-Frequency Tunnel Equipment

The specialized equipment utilized in long-line tunnel engineering is evolving towards large-scale,multifunctional,and complex orientations.The vibration caused by the high-frequency units during regular operation is supported by the foundation of the units,and the magnitude of vibration and the operating frequency fluctuate in different engineering contexts,leading to variations in the dynamic response of the foundation.The high-frequency units yield significantly diverse outcomes under different startup conditions and times,resulting in failure to meet operational requirements,influencing the normal function of the tunnel,and causing harm to the foundation structure,personnel,and property in severe cases.This article formulates a finite element numerical computation model for solid elements using three-dimensional elastic body theory and integrates field measurements to substantiate and ascertain the crucial parameter configurations of the finite element model.By proposing a comprehensive startup timing function for high-frequency dynamic machines under different startup conditions,simulating the frequency andmagnitude variations during the startup process,and suggesting functions for changes in frequency and magnitude,a simulated startup schedule function for high-frequency machines is created through coupling.Taking into account the selection of the transient dynamic analysis step length,the dynamic response results for the lower dynamic foundation during its fundamental frequency crossing process are obtained.The validation checks if the structural magnitude surpasses the safety threshold during the critical phase of unit startup traversing the structural resonance region.The design recommendations for high-frequency units’dynamic foundations are provided,taking into account the startup process of the machine and ensuring the safe operation of the tunnel.

Experimental and Numerical Evaluation of the Cavitation Performances of Self-Excited Oscillating Jets

Self-excited oscillating jets(SOJ)are used in several practical applications.Their performances are significantly affected by structural parameters and the target distance.In this study,a geometric model of the SOJ nozzle accounting for multiple structural parameters is introduced,then the related cavitation performances and the optimal target distance are investigated using a Large-Eddy Simulation(LES)approach.Results are also provided about an experiment,which was conducted to validate the simulation results.By analyzing the evolution of the vapor volume fraction at the nozzle outlet,a discussion is presented about the effect of the aforementioned structural parameters on the cavitation performances and the target distance.It is shown that the distribution of cavitation clouds at the outlet of the SOJ nozzle displays a non-monotonic trend(first increasing,then decreasing).Under working conditions with an inlet pressure of 4 MPa,a SOJ nozzle outlet/inlet diameter ratio(D_(1)/D_(2))of 1.2,and a chamber diameter ratio(D/L)close to 1.8,the nozzle outlet cavitation performance attains a maximum.The optimal structural parameters correspond to the optimal target distance,which is near 50 mm.The experiments have revealed that the SOJ nozzle with the above parameters displays a good cavitation erosion effect at the target distance of 50 mm,in satisfactory agreement with the numerical simulation results.

Performance Study of a Self-Excitation Dual Stator Winding Induction Generator for Renewable Distributed Generation Systems

Renewable power generation is a suitable technology used to deliver energy locally to customers especially in remote regions. Wind energy based on induction generator situates in a foreground position in the total energy produced using renewable sources. In the last few decades, a new self- excitation generator was based on multi-stator induction strongly emerges. This article presents a systematic modelling, a detailed analysis and the performance analysis of self-excitation dual stator winding induction generator (SE-DSWIG). The modelling of the SE-DSWIG was done with taking in account the common mutual leakage inductance between stators and the magnetizing inductance, which played a principal role in the stabilization of the output voltage in the steady state. The generator feeds the end user emulated by an inductive-resistive load. In order to simulate the weather conditions’ variation, a step change of the prime mover speed was applied on the SE-DSWIG. A passive series and shunt compensator was used to mitigate the voltage sag and swell appeared in the power system due to wind variation and the lack of reactive power consumed by the inductive load.

Dynamical analysis and anti-synchronization of a new 6D model with self-excited attractors

A novel 6D dissipative model with an unstable equilibrium point is introduced herein.Some of the dynamic characteristics of the proposed model were explored via analyses and numerical simulations including critical points,stability,Lyapunov exponents,time phase portraits,and circuit implementation.Also,anti-synchronization phenomena were implemented on the new system.Firstly,the error dynamics is found.Then,four different controllers are adopted to stabilize this error relying on the nonlinear control technique with two main ways:linearization and Lyapunov stability theory.In comparison with previous works,the present controllers realize anti-synchronization based on another method/linearization method.Finally,a comparison between the two ways was made.The simulation results show the effectiveness and accuracy of the first analytical strategy.

Impact frequency variation of self-excited oscillation pulsed supercritical carbon dioxide jets

In order to obtain the impact frequency of resonant coal breaking by self-excited oscillation pulsed supercritical carbon dioxide(SC-CO_(2))jet,large eddy simulation was used to analyze the formation and development process of self-excited oscillation pulsed SC-CO_(2)jet,the variation of jet impact frequency in the nozzle and the free flow field,and the variation of jet impact frequency at different positions in the jet axis and under different cavity lengths.The test device of jet impact frequency was developed,and experiments were performed to verify the conclusions of the numerical simulations.The results show that the frequency of the self-excited oscillation pulsed SC-CO_(2)jet is different in the nozzle and the free flow field.In the nozzle,the frequency generated by the fluid disturbance is the same,and the jet frequency at the exit of the nozzle is consistent with that inside the nozzle.In the free flow field,due to the compressibility of CO_(2),the pressure,velocity and other parameters of SC-CO_(2)jets have obvious fluctuation patterns.This feature causes the impact frequency of the self-excited oscillation pulsed SC-CO_(2)jet to decrease gradually in the axis.Changing the cavity length allows the adjustment of the jet impact frequency in the free flow field by affecting the disturbance frequency of the self-excited oscillation pulsed SC-CO_(2)jet inside the nozzle.

企业—用户互动、敏捷开发与数字产品创新绩效

数字技术的可重新编程性、开放性等特征增强了市场需求的不确定性,企业通过与用户互动进行敏捷开发以提升数字产品创新绩效,成为获取竞争优势的关键。基于精益创业理论和利益相关者理论,深入分析企业—用户互动、敏捷开发与数字产品创新绩效间的作用机理。结果表明:企业—用户互动通过敏捷开发积极影响数字产品创新绩效,且组织创新氛围将增强三者间的作用关系。研究有助于丰富对于数字情境下企业—用户互动创新的理解,推动敏捷开发研究的发展,为解释数字产品创新绩效差异化提供有价值的研究思路,也为数字产品创新绩效的提升提供重要的管理启示。

我国政府债务的跨周期平衡治理——兼论政府债务短期逆周期调控与长期可持续性研究

文章构建了政府债务对经济增长作用机制的理论框架,以经济波动为内生条件变量构建Self-Exciting IVAR模型,实证检验了政府债务在经济周期不同阶段下对经济增长的非对称效应。研究发现,经济衰退期政府债务对经济增长的冲击效应在短期内大于经济扩张期,中长期政府债务的经济增长效应在经济扩张期强于衰退期,经济衰退期可以适度扩大政府债务规模,提高其短期逆周期调控效应,经济扩张期应稳定政府债务杠杆保持其长期可持续性;进一步分析发现政府债务能够有效刺激投资、消费,进而拉动经济增长。文章为抵御经济下行压力,有效实施政府债务逆周期调控并保持其长期可持续性,实现逆周期与跨周期调控有效组合提供理论参考与经验证据。

B-Spline曲线聚风装置直线翼垂直轴风力机启动性能数值模拟

为了提升直线翼垂直轴风力机的启动性能,基于B-Spline曲线生成方法,提出一种具有流线型轮廓的聚风装置,将其分别安装在风轮顶端和底端,用以提升风轮附近的来流风速,使风轮汲取更多风能,达到更易启动的特点.选取聚风装置的5个结构参数进行设计:聚风装置与风轮间隙距离ΔL、底圆半径R_(1)、顶圆半径R_(2)、入口角度α_(1)和出口角度α_(2).设计方法采用二次旋转正交组合筛选最优模型,通过三维数值模拟研究聚风装置参数对直线翼垂直轴风力机启动性能的影响,获得了最佳外形参数组合.此外,对有无加装聚风装置的直线翼垂直轴风力机进行了静态三维数值模拟.结果表明,通过添加具有外凸流线型轮廓的聚风装置,直线翼垂直轴风力机的启动性能有显著提升.在风速较低的情况下,性能改善更加明显.聚风装置可使直线翼垂直轴风力机的平均启动力矩系数最大增加38.8%,峰值平均启动力矩系数最大可增加31.2%.

一种基于相位误差校正技术的快速启动晶体振荡器

随着超低功耗(Ultra-Low Power,ULP)物联网(Internet of Things,IoT)系统的发展,采用能量注入技术的快速启动晶体振荡器因对IoT系统功耗影响巨大而逐渐成为研究热点.能量注入技术可以显著降低晶体振荡器的启动时间和启动能量,但是对注入源的精度要求苛刻.为了扩大注入频偏容限以及实现高注入效率,本文提出了一种基于延迟锁定环的相位误差校正技术.该技术将注入频偏容限扩大到2%,启动过程的非注入持续时间仅为4个周期,实现了高效注入.本文所述晶体振荡器采用40 nm CMOS工艺设计并流片.在1.0 V电源电压下采用24 MHz晶体进行测试,当注入频偏高达2%时,实现了7.2μs的启动时间,启动能量为5.1 nJ.相比同频偏下的传统注入方案,启动时间缩短了99.66%.

价值重构视角下科技型新创企业商业模式创新的驱动因素研究

随着新兴信息技术的蓬勃发展,商业模式创新成为科技型新创企业寻求新竞争优势的重要途径。据此,从价值重构角度出发构建科技型新创企业商业模式创新的驱动因素模型,并基于336份调查问卷运用结构方程方法对该模型进行实证分析。研究结果表明:创业网络强度、用户需求响应程度、管理认知能力对科技型新创企业商业模式创新的推动作用最为明显,创业初期强联结的资源网络结构、消费者的多性化需求、管理者的认知水平往往是一个企业商业模式创新的原生动力;创业学习、企业家精神、企业战略导向、行业竞争强度的正向激励作用虽次之,但企业通过对标学习、破坏性创新、科学布局、多方竞争仍能有效促使自身进行商业模式创新。因此科技型新创企业在推动商业模式创新中应培育高质量、多层次创业网络,精准对接用户需求,深化战略机制,开展协同创新,以此促进企业发展。

某660MW机组汽轮机热态启动最佳温升率的确定

为进一步缩短火电机组热态启动时间,满足机组快速启动参与电网调峰的要求,以某660MW汽轮机组热态启动为例,编制程序确定不同启动阶段转子表面的蒸汽参数及换热系数,之后采用ANSYS软件对汽轮机热态启动下的转子温度场及应力场进行了数值模拟计算,分析了汽轮机转子重点监测部位热应力随温升率变化规律。并从不同温升率启动对汽轮机转子低周疲劳寿命的损耗进行分析,得到了机组热态启动的最佳温升率。研究结果可使汽轮机组热态启动下相比设计条件下缩短启动时间18%。所做工作对大型火电机组深度调峰具有一定参考价值。

基于积分分析方法对聚变堆启动氚量与所需氚增殖比的评估

托卡马克聚变堆的主要发展方式包括混合堆、纯聚变堆。关于托卡马克聚变堆氚自持的研究,国内外主要采用平均滞留时间方法进行研究,并且针对聚变功率较低的混合堆的氚自持研究较少。本工作采用更符合实际的积分分析方法分析了混合堆、纯聚变堆氚自持的启动氚量、氚增殖比(TBR)要求。研究结果表明:启动氚量、备用氚量与聚变功率具有线性关系,所需TBR与聚变功率呈反比例关系;混合堆聚变功率较低,所需TBR较高,工程实现所需TBR挑战较大,需要通过限制长期氚滞留量以降低所需TBR要求;纯聚变堆聚变功率高,所需TBR较低,工程实现所需TBR挑战较小,但备用氚需求达数十千克,应考虑氚系统的冗余设计或提高氚系统的可靠性、可维护性,以降低备用氚的使用规模;运行因子是聚变堆的一个重要设计指标,在此着重分析了运行因子对所需TBR的影响,并重新定义了一个聚变堆氚自持的关系式,以突出运行因子对氚自持的重要影响。

燃煤发电机组灵活调峰下机炉安全状态监测与调控研究综述

“双碳”背景下新能源大量接入电网,燃煤发电机组承担调峰任务,长期处于瞬态运行过程,其灵活运行水平需进一步提升,但深度调峰与快速变负荷使机组运行可靠性下降,机组灵活调峰能力面临设备安全性制约。该文对燃煤发电机组在灵活调峰下安全稳定运行的研究现状进行评述。首先,综述调峰工况下锅炉换热面、汽轮机转子等部件存在的安全技术问题,明确灵活运行对机组设备安全性的影响。其次,对比分析监测温度、应力等关键运行状态参数的不同方法优缺点与适用性;针对存在的安全技术问题介绍现有的机组运行参数优化与设备结构优化方法。未来将可靠性评估与诊断、停机保温预热及智能先进控制等技术应用于燃煤发电机组的调峰运行将对其安全性提升具有重要意义。最后,对目前燃煤发电机组灵活安全运行的研究现状及面临问题进行总结。

泵入口参数对全流量补燃循环发动机动态特性影响研究

全流量补燃循环发动机性能高,并具备便于重复使用的优势,是未来重复使用运载器的最佳选择之一。在液体火箭发动机启动过程中,泵入口推进剂的压力和温度变化会对全流量补燃循环发动机动力系统的启动特性造成一定的影响。为分析其影响规律,建立了涡轮泵、预燃室、推力室、两相流和混合气体组件等动力学模型并进行求解。结果表明,随着燃料泵入口压力升高或氧化剂泵入口压力降低,涡轮泵系统参数的波动将会逐渐增大,甲烷温度和液氧温度所产生的影响要强于甲烷压力和液氧压力,而液氧的影响则强于甲烷。为动力系统中泵入口推进剂状态参数控制提供了一定的指导。

BOG再液化工艺动态模拟教学

液化天然气(LNG)的运输储存方式主要是通过LNG运输船,由于LNG温度低,易挥发,在LNG船的液货舱中LNG与环境存在热交换,蒸发产生的闪蒸气(BOG)会使液货舱压力升高造成安全隐患。安全、环保处理BOG的方法是将其再液化为LNG重新输送回液货舱。基于此,介绍一种利用软件模拟动态的BOG液化工艺,使用再液化方法为过冷LNG喷射制冷再液化。借用软件模拟再液化工艺的流程,对工艺流程的开、停车过程进行模拟,形成了一套BOG再液化工艺的动态模拟。通过案例教学可加强学生及员工利用软件进行工艺动态模拟的能力,提高对虚拟仿真技术的掌握。

基于货车启动延误的交叉口信号优化模型

为研究货车停车启动行为对信号控制交叉口车辆延误的影响,根据货车的行驶特性给出了货车启动延误定义。基于概率统计原理及道路交通流特征,推导了欠饱和、过饱和两种状态下货车启动延误的计算方法。进一步以最小车均延误为目标,建立了基于货车启动延误的交叉口最小延误信号周期计算模型。通过实例仿真,对实测数据、理论数据和仿真数据进行对比分析。结果显示,与现有延误计算模型相比,该文延误计算模型理论值与仿真值的平均误差降低了40.9%。且设计配时方案与Webster最佳信号周期方案相比,车均延误降低了10.7%;与传统最小延误方案相比,车均延误降低了5.6%,有效验证了模型的适用性。

深水气田长距离混输模式下水相运动规律研究

陵水25-1深水气田混输管道距离长、管道爬坡段坡度大,初始投产阶段混输流体水相到达平台的时间长且预测困难,给管道安全运行带来风险。基于多相流计算模型,运用LedaFlow软件,对陵水25-1深水气田初始投产阶段的水相运动规律进行研究,并深入分析含水率、油量、气量、油水相间摩擦系数等因素对水相运行的影响。结果表明:初始投产阶段水相在爬坡段分离和积聚,形成长时间的停滞,管道坡度越大,水相波动越剧烈;含水率越高的物流,水相在爬坡段聚集时间越短;气量增大则会降低水相滞液程度,提高水相运行速度,有助于水相爬坡;油量变化对水相运行速度的影响较小,油水相间摩擦系数对爬坡段水相运动有直接影响,油水相间摩擦系数修正拟合,对实际管道运行有重要指导意义。研究结果可为深水气田开发研究提供借鉴。

数字平台信息生产与新创企业股权融资研究——基于多源数据方法

以2014—2020年在京东众筹平台发起预售众筹的新创企业为样本,考察预售众筹融资表现是否对融资企业后续获得风险资本产生影响。实证发现,较好的融资表现可以彰显企业家才能和揭示市场需求,从而产生信号效应,提高新创企业后续获得风险资本的可能性,这一效应主要受最近一次众筹经历影响,且不受众筹之前早期风险资本的介入影响。进一步研究发现,预售众筹的信号效应弱于股权众筹的信号效应,但两者可以形成互补。新创企业应重视预售众筹的信息生产作用,利用良好的融资表现发送高质量信号。

造纸技术中一种小型电机的启动测试

电机受研发和生产等各种因素影响,其性能参数与指标会发生变化。造纸技术中小型电机的启动测试是非常重要的一步。启动测试能在电机运行的初始阶段将电机的各种性能参数进行检测,避免在电气设备运行过程产生安全问题。基于此,介绍电机测试技术及发展趋势,以微型直流电机为研究对象,重点介绍小型电机的启动测试。该测试系统包括硬件设计、软件设计、仿真模拟及调试分析,采用PLC-1200控制器实现的小型电机的启动测试系统全过程自动化有助于提高生产效率并减少安全隐患。