Switching Frequency Improvement of a High Speed on/off Valve Based on Pre-excitation Control Algorithm

The high-speed on/off valve(HSV)serves as the fundamental component responsible for generating discrete fluids within digital hydraulic systems.As the switching frequency of the HSV increases,the properties of the generated discrete fluid approach those of continuous fluids.Therefore,a higher frequency response characteristic of HSV is the key to ensure the control accuracy of digital hydraulic systems.However,the current research mainly focuses on its dynamic performance,but neglect its FRC.This paper presents a theoretical analysis demonstrating that the FRC of the HSV can be enhanced by minimizing its switching time.The maximum switching frequency(MSF)is mainly determined by opening dynamic performance when HSV operates with low switching duty ratio(SDR),whereas the closing dynamic performance limits the MSF when HSV operates with high SDR.Building upon these findings,the pre-excitation control algorithm(PECA)is proposed to reduce the switching time of the HSV,and consequently enhance its FRC.Experimental results demonstrate that PECA shortens the opening delay time of HSV by 1.12 ms,the closing delay time by 2.54 ms,and the closing moving time by 0.47 ms in comparison to the existing advanced control algorithms.As a result,a larger MSF of 417 Hz and a wider controllable SDR range from 20%to 70%were achieved at a switching frequency of 250 Hz.Thus,the proposed PFCA in this paper has been verified as an effective and promising approach for enhancing the control performance of digital hydraulic systems.

EXPERIMENT STUDY ON SPEED RATIO CONTROL OF METAL V-BELT TYPE CVT

Based on the control scheme of force and position, the controlling andtesting system of metal V-belt type CVT is developed. Having taken account of the complex nonlinearcharacteristics of the CVT shift dynamics and the saturation and nonlinear characteristics of thespeed ratio control valve, the speed ratio fuzzy controller based on the speed ratio feedback isdesigned. The experiment results show that the developed speed ratio control system is practical andfeasible.

Optimal Split Ratio in Small High Speed PM Machines Considering Both Stator and Rotor Loss Limitations

The split ratio which is defined as the ratio between rotor and stator outer diameters is critical for permanent magnet(PM)machines.In this paper,the split ratio in small high speed PM machines is optimized analytically by considering both stator and rotor loss limitations.By this way,the thermal constrains in both stator and rotor parts can be taken into account.It shows that both losses can significantly affect the optimal split ratio and the machine performance.By considering the influence of rotor losses,especially the rotor eddy current loss,the optimal split ratio is increased significantly in certain scenarios.The output torque is calculated analytically and the influences of several key design parameters on the optimal split ratio,i.e.slot/pole combinations and magnet materials,are also investigated in details.Finally,finite element(FE)analyses are carried out for validating of the analytical model.

Relationships between the sound speed ratio and physical properties of surface sediments in the South Yellow Sea

Building empirical equations is an effective way to link the acoustic and physical properties of sediments.These equations play an important role in the prediction of sediments sound speeds required in underwater acoustics.Although many empirical equations coupling acoustic and physical properties have been developed over the past few decades,further confirmation of their applicability by obtaining large amounts of data,especially for equations based on in situ acoustic measurement techniques,is required.A sediment acoustic survey in the South Yellow Sea from 2009 to 2010 revealed statistical relationships between the in situ sound speed and sediment physical properties.To improve the comparability of these relationships with existing empirical equations,the present study calculated the ratio of the in situ sediment sound speed to the bottom seawater sound speed,and established the relationships between the sound speed ratio and the mean grain size,density and porosity of the sediment.The sound speed of seawater at in situ measurement stations was calculated using a perennially averaged seawater sound speed map by an interpolation method.Moreover,empirical relations between the index of impedance and the sound speed and the physical properties were established.The results confirmed that the existing empirical equations between the in situ sound speed ratio and the density and porosity have general suitability for application.This study also considered that a multiple-parameter equation coupling the sound speed ratio to both the porosity and the mean grain size may be more useful for predicting the sound speed than an equation coupling the sound speed ratio to the mean grain size.

Influence of Rotating Speed Ratio on the Annular Turbulent Flow between Two Rotating Cylinders

Rotating flows represent a very interesting area for researchers and industry for their extensive use in industrial and domestic machinery and especially for their great energy potential, annular flows are an example that draws the attention of researchers in recent years. The best design and optimization of these devices require knowledge of thermal, mechanical and hydrodynamic characteristics of flows circulating in these devices. An example of hydrodynamic parameters is the speed of rotation of the moving walls. This work is to study numerically the influence of the rotating speed ratio Γ of the two moving cylinders on the mean and especially on the turbulent quantities of the turbulent flow in the annular space. The numerical simulation is based on one-point statistical modeling using a low Reynolds number second-order full stress transport closure (RSM model), simulation code is not a black box but a completely transparent code where we can intervene at any step of the calculation. We have varied Γ from -1.0 to 1.0 while maintaining always the external cylinder with same speed Ω. The results show that the turbulence structure, profiles of mean velocities and the nature of the boundary layers of the mobile walls depend enormously on the ratio of speeds. The level of turbulence measured by the kinetic energy of turbulence and the Reynolds stresses shows well that the ratio Γ is an interesting parameter to exploit turbulence in this kind of annular flows.

Investigation of Optimal Split Ratio of 6-Slot/2-pole High Speed Permanent Magnet Motor with Toroidal Winding

Split ratio,i.e.the ratio of stator inner diameter to outer diameter,has a closed relationship with electromagnetic performance of permanent magnet(PM)motors.In this paper,the toroidal windings with short end-winding axial length are employed in the 6-slot/2-pole(6s/2p)PM motor for high speed applications.The split ratio is optimized together with the ratio of inner slot to outer slot area,i.e.slot ratio,considering stator total loss(stator iron loss and copper loss).In addition,the influence of maximum stator iron flux density and tooth-tip on the optimal split ratio,slot ratio,and average torque is investigated.The analytical predictions show that when the slot ratio is 0.5,the maximum torque can be achieved,and the optimal split ratio increases with the decrease of slot ratio,as confirmed by the finite element(FE)analyses.Finally,some of predicted results are verified by the measured results of 6s/2p prototype motor with 0.5 slot ratio.

电动汽车用新型模块化聚磁转子永磁电机设计及其对比分析

将轮辐型内置式转子和Halbach永磁阵列结合,并取消转子铁心加强筋,减小漏磁达到高聚磁同时兼顾凸极比,实现高转矩/功率密度和宽调速范围。在保证永磁体用量相同的情况下,建立新型高凸极比聚磁转子和V型转子两种电机模型,针对两者的分段转子拓扑,开展电磁性能对比分析,包括气隙磁密、凸极比、功率以及弱磁扩速能力等。同时,考虑到无转子铁心加强筋会导致转子分段存在结构强度问题,仿真验证新型高凸极比聚磁转子结构在最高转速6000 r/min时给予碳纤维护套保护下转子结构强度的可靠性;分析温度限制下新型高凸极比转子电机的功率输出。另外,对比两种不同电机结构的振动噪声情况。最后,研制一台16极/72槽新型高凸极比转子永磁电机样机,实验验证有限元分析结果的准确性。进一步说明了新型高凸极比转子永磁电机在转矩/功率密度和宽调速运行等方面的性能优势。

基于波噪比的高速铁路钢轨波磨快速检测方法

为实现高速铁路钢轨波磨里程覆盖式、高频次、快速测量,提出基于波噪比的钢轨波磨快速检测方法。采用便携式添乘仪检测高速列车车体振动和车内噪声数据,提出基于车体纵向加速度进行数值积分来计算列车速度和里程,采用曲线地段车体摇头角速度里程与台账里程的偏差值修正速度积分误差。利用提取的里程修正后车厢噪声数据与钢轨波磨对应的400~700 Hz频带成分,计算频带能量占噪声总能量的比值,并获取波噪比超限时的钢轨波磨波长和里程。结合高速列车实测数据分析,研究结果表明:速度修正后列车定位里程最大误差为87 m,对波磨比大于0.3的线路区段进行钢轨波磨波形测量和轴箱加速度振动能量比分析,钢轨波磨波长范围为53~57 mm,实测波长为53 mm,验证了该方法的正确性,为高速铁路钢轨波磨的快速测量提供技术支撑。

IGSA-PID算法的双带式全电调节CVT速比优化控制

双带式全电调节无级变速器(Double-Belt Electro-Mechanical Continuously Variable Transmission,简称DEMCVT)具有两组带传动装置,能够有效提升CVT的承载能力;DEM-CVT具有单带与双带两种工作模式,通过设计基于效率最优的模式切换策略,能够有效提高燃油经济性;采用直流电机调节主从动轮工作半径从而实现速比变化调节,针对DEM-CVT速比控制,设计了针对不同工况的速比控制策略,以PID算法为基础,提出了一种改进算法IGSA对PID算法进行参数优化,并通过建模仿真得到仿真结果,验证了提出的速比控制策略和控制方法的有效性。

沙土比对混凝土试件空蚀影响的试验研究

在小型循环式水洞中试验研究了沙土比对混凝土试件空蚀影响的机理。首先,在循环式水洞内筒中配制11种沙土比(0%,10%,20%,30%,40%,50%,60%,70%,80%,90%,100%)试样,用红外测沙仪测定相同沙土比的3种不同含沙量(2,12,30 kg/m 3)的挟沙水样,用压力传感器和压力数据采集系统实时采集水洞文丘里工作段空化区和空蚀区的压力;然后,制作了水灰比为0.4、灰砂比为1.5,7 d龄期强度f cu,k=17.8 MPa的混凝土试件,将其安放在水洞文丘里工作段混凝土试件盒中进行4 h的空蚀试验。试验结果表明:沙土比的增大对空化和空蚀破坏均具有促进作用;消失空化数随沙土比的增加而增加,对空化发生具有抑制作用;相同沙土比时,混凝土试件的空蚀量随着含沙量的增加而增加。

高速低载频比传感信号下的逆变器有源阻尼自适应控制

逆变器工作在高频运行和控制载波比低的情况下,存在谐振尖峰抑制,提出了高速低载频比传感信号下的逆变器有源阻尼自适应控制技术。在高速低载频比传感信号下,构建逆变器数学模型。输出电流到电容电压与定子电流之间的传递函数,将逆变器的有源阻尼等效成一个控制电压环。调整有源阻尼自适应控制回路的参数,制定逆变器有源阻尼自适应控制策略。实验结果表明:文中技术的稳定裕度由2.46 dB下降至1.18 dB,可以保证逆变器的稳定运行;在不同采样频率下,可以控制逆变器输出与电网电压相同相位和频率的并网电流,其中在采样频率为5.9f时,输出并网电流和电压均表现为正弦状态,波动范围分别为[35 A,58 A]和[185 V,225 V],具有较好的控制效果。

基于相对船速比的避让行动效果分析

基于相对船速比(来船的相对速度与本船速度之比),当来船保向保速且存在碰撞危险时,本船采取转向结合变速避让行动和两船相互采取转向避让行动而产生的避让效果进行定量分析,并提出了基于相对船速比的来船真运动要素计算方法。

台风条件下航站楼风环境数值模拟研究

以杭州萧山机场T4航站楼为对象,采用Realizable k-ε湍流模型进行了周边风环境数值模拟。首先通过与刚性模型测压风洞试验结果的对比,验证了该数值模拟方法及参数的有效性;然后,研究了不同风向角下行人高度(2 m)处加速比的变化规律,以及台风登陆情况下距离地面10 m高度处的风速分布情况。结果表明:航站楼两侧的角点位置处和西侧建筑群迎风面道路间易受角隅效应和峡谷效应的影响,存在明显的风加速现象,在台风登陆条件下,航站楼周边大部分区域风速达到六级(强风)以上,而陆侧交通中心区域由于四周建筑的遮挡,所受影响相对较小。

多RIS辅助车载通信信号优化及部署规划

针对匀变速运动的汽车产生的多普勒扩展和时延扩展以及接收信噪比的问题,提出了一种多智能超表面(RIS)辅助匀变速移动物体通信的方案。与传统信道估计不同的是,使用了信道增益的方法和优化RIS相位以及多目标优化来让移动物体能达到最大接收瞬时信噪比的同时,获得小的多普勒扩展和时延扩展。通过优化后的RIS相位来研究RIS的位置对接收信号的影响,分别研究了RIS之间的距离以及RIS之间距离一定时,RIS摆放在什么位置使得接收信号的信噪比以及时延扩展保持较低的范围,对于这个问题提出了相对运动的理论,且各自提出一种算法解决这两个问题。仿真表明,多RIS辅助的通信系统对车载通信接收信号的功率提升了约10 dB。RIS的部署位置应该让第一个RIS靠近基站并且RIS之间的距离在现实允许的情况下尽可能靠近。由此多RIS的通信方案可以广泛应用于车载通信中。

清梳效果的评估与改进

为合理控制纺纱半制品质量、提高成纱品质,详细介绍清梳效果评估的目的、方法及标准,结合实际生产经验及乌斯特公报数据,重点从半制品棉结、杂质、短绒及纤维伸直度等方面对清梳效果进行评估,分析问题及成因,并对梳棉、清梳等重点工序及部位提出改进方法。指出:清梳效果的评估与改进应依据半制品结杂、短绒、伸直度变化规律,分析判断清梳联各工序的清梳效果,结合落棉率的分配及落物对具体问题进行分析,及时调整不达标工序和部位,充分发挥器材专件作用。

无量纲最小二乘有限元法GPU实现及其在变压器绕组流场仿真中的应用研究

为了提高变压器流体场的计算效率,利用统一计算设备架构(compute unified device architecture,CUDA)实现流场的并行计算。首先基于C语言实现无量纲最小二乘有限元法的串行计算方法。然后在Visual Studio 2019+CUDA 10.2的环境下实现并行运算,对于串行程序中最耗时的线性方程组求解部分调用了CUDA自带的函数库进行优化;在大规模模型的数值计算中使用了十字链表格式存储整体刚度阵形成时的非零元素,以解决满阵存储时的内存不足问题。为验证所提方法的有效性,针对方腔模型,分析了不同剖分网格数量下的加速比,分析结果表明,数据规模越大并行效果越好,验证了无量纲最小二乘有限元并行程序的准确性和高效性。最后将该方法应用到大型变压器绕组的流体场分析中,取得了18.3倍的加速效果,为产品级变压器的流体场仿真奠定了基础。

掺氢天然气管网数值仿真轻量化算法

目前针对管网数值仿真算法的优化主要集中在代数方程组的求解上。针对管网流动数值仿真算法提升计算效率方案中缺少针对封闭关系与状态方程的优化,分析了目前优化方案各模块的耗时情况,发现了仿真程序中耗时模块为封闭关系与状态方程求解。最后,结合计算机库函数的缺点以及现代CPU中SIMD (Single Instruction Multiple Data)模型的特点,提出了针对封闭关系与状态方程的轻量化算法,并验证了算法的高效性。研究结果表明:(1)封闭关系与状态方程模型中的耗时原因为直接调用库函数的次幂运算、指数运算、对数运算以及除法运算;(2)由于次幂运算效率远低于其他运算,通过变换消除了模型中几乎所有的次幂运算;(3)利用SIMD指令来计算指数运算与对数运算,实现了在单核CPU上同时计算多个数据的指数与对数,最后通过数学变换将所有除法转换为乘法;(4)轻量化算法加速效果显著,其整体加速比为18,而在状态方程求解模块的加速比更是高达70以上。结论认为,该轻量化算法在不影响计算精度的条件下提高了计算速度,对于提高掺氢天然气管网在线仿真与智能管网的建设具有重要的理论价值和技术支撑。

基于RBF神经网络和模型在线更新的风速估计方法

基于NREL5MW风力发电机原模型和简化模型,进行流固耦合和计算流体力学仿真,研究结果表明风力发电机桨距角和叶尖速比影响风轮上游来流风速演化。结合来流风速演化和推力系数理论模型表明,通过推力更新诱导系数,进而在线更新风速演化模型,能提高风速估计精度。考虑推力时变性和非定常性,提出以桨距角和叶尖速比为输入,基于RBF神经网络的推力逼近方法,进而提出基于模型在线更新的风轮平面有效风速估计方法。最后通过激光雷达现场测风数据进行验证,结果表明,基于RBF神经网络和模型在线更新的风速估计方法较基于时间信息提取算法和来流风速演化模型的风速估计方法精度提高15.5%。

适于新疆单膜收获的大豆割台设计及拨禾过程分析

针对新疆大豆覆膜滴灌栽培技术,设计一款带有地形起伏检测装置的大豆割台。通过田间生长特性测量,确定适于新疆单膜大豆收获的拨禾轮主轴长度为2 000 mm、直径为650 mm。依此设计一种前置轮式地形检测装置,该装置安装于大豆割台两侧,确定检测装置角度转动量与割刀离地高度之间的关系式为:H=80-Δh=80-320(sinθ-sinθ′)。对所设计的大豆割台进行地面起伏检测试验,试验中实际距离与检测距离之间的相对误差均值为0.037~0.039。对拨禾轮工作原理进行分析,研究其产生拨禾作用时的拨禾速比范围。将拨禾轮三维模型导入Adams软件中,分析不同拨禾速比下弹齿的运动轨迹,发现当拨禾速比λ≤1.0时拨禾轮无拨禾作用,当λ>1.0时拨禾轮具有拨禾作用,但拨禾速比过大后,相邻弹齿间会产生作用重叠区域。设计的割台利于新疆大豆单膜收获,地形检测装置可为割台高度的实时调节提供依据。

某V型发动机凸轮轴扭振突变原因分析与改进

针对某V型发动机在油泵速比4:3情况下运行过程中传动链条断裂的问题,开展发动机转速波动与扭振测试,发现右侧凸轮轴在发动机全负荷加速进程中存在转速突增和4阶扭振突变现象,怀疑传动链条断裂与右侧凸轮轴扭振突增有关。为解决右侧凸轮轴扭振突增的问题,更改油泵速比为10:9,再次开展测试进行对比分析,结果表明:油泵驱动齿轮与右侧排气凸轮轴转速波动与扭振具有一定相似性,油泵速比改变后,转速波动与扭振均未发生突变现象,右侧排气凸轮轴转速波动率由52.6%降至20.7%,凸轮轴扭振在3.3阶处达到最大值,最大扭振角由1.57度降至0.506度,转速波动与扭振得到明显改善,提供了一种右侧凸轮轴转速波动与扭振突增问题的解决方案。