钛合金冷坩埚连续熔铸与定向凝固电磁场研究

利用ANSYS软件建立冷坩埚连续熔铸过程的数学模型,计算在近矩形冷坩埚连续熔铸过程中冷坩埚内的磁感应强度,分析负载和电流强度变化对钛合金连续熔铸与定向凝固过程冷坩埚内磁感应强度的影响。结果表明:钛合金物料的加入并没有影响轴向磁感应强度的空间分布趋势;轴向磁感应强度在感应线圈与坩埚所包围的区域内聚集分布,且在感应线圈内壁中点处其强度达到最大值,并随着与内壁距离的增加逐渐衰减;磁感应强度随着输入电流的增加线性增大。     

燃油电磁阀电磁铁的环境温度影响特性仿真

为研究环境温度对燃油电磁阀电磁铁驱动性能的影响,基于电磁阀工作原理和执行机构作动特性等关系,建立了热环境下电磁阀的数学模型,通过温度与磁场特性分析确定了对温度最敏感的关键功能部件为电磁线圈。利用有限元软件Ansoft Maxwell对由线圈和衔铁构成的电-机械转换器进行了数值模拟,得到了不同环境温度下电磁铁磁感应强度分布及系统关键响应指标,研究了阀启闭过程的静态和动态特性。分析了在额定工作状态下环境温度对电磁铁磁场分布和响应特性的影响,获得了不同环境温度下的线圈电流、电磁力、衔铁速度及位移的变化和响应规律。结果表明：环境温度升高引起线圈材料电阻变大,进而导致线圈电流和电磁力减小,最终缩短了电磁阀启闭时间,也易导致在同样驱动电压下电磁阀无法开启。     

一种基于超导的重力梯度敏感结构分析

 为了构建小型化全张量重力梯度测量系统,提出一种轴向分量与交叉分量同时敏感的基于超导的重力梯度敏感结构。基于螺旋理论分析两分量敏感结构的自由度,利用自由空间的运动螺旋系与互逆原理得到约束螺旋系,进一步得到具有冗余约束的对称约束构型,并选择柔性元件构建并联机构形式的两分量敏感结构,利用柔性虎克铰的横向与竖向柔性铰链实现等效球铰的功能。然后分析转臂质量沿轴移动与绕轴转动时柔性元件的变形,根据几何关系与功能定理得出两分量敏感结构的沿轴移动刚度与绕轴转动刚度。通过实际参数的计算,明确了各参数对结构刚度的影响,仿真结果验证了分析过程的准确性。     

脉冲感应式电推进中平面型线圈激励等离子体的流动特征分析

感应等离子体推力器是一种具有较好应用前景的空间推进方式,受到复杂瞬态电磁场的影响,流场中热力学和动力学参数的时变特性难以实验测量。采用单流体磁流体力学理论,结合高温气体的热力学和输运模型,数值计算初始静止且无预电离的情况下,等离子体参数的二维分布,着重分析等离子体在前半周期内的流动特征。对内径ri为0.05m,外径ro为0.15m的线圈计算表明,其等离子体-线圈耦合距离约为0.032m,以Ar为工质情况下,有效冲量产生时,高价离子(Ar3+,Ar4+)与低价离子(Ar+,Ar2+)由于受电磁力影响不同,产生了局部分离电场,推动了电流片运动,且在电流片内部,前缘主要为低价离子,后缘主要为高价离子。单脉冲能量210.7J、峰值径向磁感应强度为0.5T、有效作用时间约12μs条件下,5μs时刻的Ar2+,Ar3+的最大数密度大于6×1021m-3,且大于Ar+,Ar4+的数密度。电流片运动大于耦合距离后,受径向运动以及激励电流反转的影响,线圈表面等离子体磁场非线性特征显著,而前缘磁场维持规则分布。对外径为0.15m,0.3m和0.5m的线圈计算发现,ro为0.5m时,电流片径向均匀长度达到0.3m,表明较大线圈尺寸除增加耦合距离外,可提高径向电流密度的均匀性。     

基于Helmholtz的低感抗电子束偏转扫描线圈仿真

为了提高电子束偏转扫描频率和磁场均匀性,采用Helmholtz空心线圈结构设计了一种低感抗电子枪偏转扫描线圈。采用ANSYS有限元分析软件对偏转扫描线圈的电磁场分布进行仿真,并采用高斯计对线圈内部的电磁场进行了测量,仿真结果与实际测量值基本吻合,线圈内部的磁感应强度大小和电磁场分布的均匀性可以满足电子束高频偏转扫描的要求。实际扫描试验表明,该线圈实现了两点电子束高频偏转扫描,扫描频率可达30 k Hz。     

红外成像系统无热化设计

讨论了红外成像系统在工作温度变化时产生的温度效应及其对成像的影响,包括光学元件的热变形、光学窗口的热应力及窗口的热辐射噪声,将结构件材料的线胀系数作为优化变量,提出了光学机械综合被动补偿无热化设计方法.采用热瞳判定与高密度光线计算法分析了光学窗口的热辐射,提出了基于表面辐射分析的无热化优化方法.计算表明,无热化设计使系统对温度的均匀变化和轴向温度梯度不敏感,对热应力不敏感,但径向温度梯度对像质影响较大.基于表面辐射分析的优化设计可以减少窗口辐射在探测器上的功率密度.     

带阻尼线圈的无轴承永磁同步电机控制研究

分析了无轴承永磁同步电机(BPMSM)的悬浮原理,在转子中加入了一组阻尼线圈,建立了带有阻尼线圈BPMSM径向悬浮力的精确数学模型。通过对加入阻尼线圈前后的数学模型进行计算、对比、分析,证明了阻尼线圈对转子稳定性的增强。采用转子磁场定向控制策略设计并构建了BPMSM的控制系统,对转子的位移等参数进行仿真。结果表明加入阻尼线圈后,有效提高了电机的稳定悬浮性能及系统的鲁棒性。     

重力异常特征提取方法研究

将主元分析和独立分量分析相结合应用于重力异常信号的特征提取.采用主元分析对测量数据进行去相关和降维预处理,再利用独立分量分析算法提取重力信号的特征系数.结合重力异常变化与特征系数的关系,提出了应用特征量化参数表征重力异常信号变化程度的方法.基于实测的重力异常信号进行了仿真试验,试验结果表明,本文提出的特征量化参数能有效的反映重力异常的幅值变化程度.     

基于响应曲面法的高速内冷铣削AISI304不锈钢铣削力

针对硬质合金刀具高速内冷铣削AISI304不锈钢时,切削力大、切削温度高及加工表面质量低的问题。基于响应曲面中心复合设计方法进行高速内冷铣削实验,建立了铣削力分量二阶回归预测模型,并进行了实验验证。对比了干式与内冷铣削后的加工表面质量,分析了铣削参数对铣削力分量的影响规律,以铣削力分量最小为目标优化了铣削参数。结果表明:进给力和径向力的预测值与实验值的误差分别为4. 77%和6. 16%;内冷铣削的Ra为0. 193～0. 327μm;对铣削力分量的影响是铣削深度转速进给量,随着铣削深度和转速的增加,进给力先升高后降低,径向力逐步增加,铣削深度与转速的交互作用对进给力和径向力的影响显著;转速11 643. 63 r/min、铣削深度1 mm、进给量0. 08 mm/r为最优铣削参数组合。     

轴流压气机动态失速过程三维计算

基于三维非定常欧拉方程和三维激盘模型发展了一种用于研究轴流压气机动态失速过程的三维计算方法.利用该计算方法研究了某型高压压气机第一级的动态失速过程,并就转子总静压升特性的三种不同径向分布对失速过程的影响进行了分析.计算结果表明该方法能够反映出压气机的三维动态失速过程、失速团的三维空间结构,并能有效地表现出转子沿径向的特性变化对压气机气动稳定性的影响,而且还能够用于判断压气机的危险截面.      

基于等效磁路法的轴向磁场磁通切换型永磁电机静态特性分析

轴向磁场磁通切换型永磁(AFFSPM)电机是一种轴向长度短、转矩密度高的新型永磁电机。该电机磁场呈三维分布,与径向磁场电机不同,需要对该电机进行三维有限元分析,从而增加了电机分析和优化时的计算时间和成本。基于等效磁路法分析了AFFSPM电机的静态特性,建立了AFFSPM电机的非线性等效磁路模型,采用该模型计算、分析了气隙磁密、空载永磁磁链、反电动势和电感等特性,并与采用三维有限元方法的计算结果进行比较,验证了AFFSPM电机等效磁路模型的准确性,表明等效磁路模型适用于AFFSPM电机初始设计和分析。     

Investigation into the transient flow characteristics of noble gas propellants using the pulsed inductive discharge in electric propulsion

The Pulsed Inductive Thruster (PIT) has the advantages of repeatable startup, no corruption and in-situ propellant feed. To study the flow expansion and circuit characteristics of PITs, the circuit-fluid model is developed, and the high temperature thermodynamic and transport models are combined with the circuit-fluid model to predict the critical plasma parameters. The flow fields of initial mass of 2–8 mg and charge voltages of 10–14 kV are simulated. Comparison of the flow fields of argon and helium propellants suggests that, the flow field structures are similar. Slight differences exist on the magnitude of the density and magnetic field, caused by larger velocity in lighter atom case and difference on the ionization gap between adjacent ionization levels. Analysis of the circuit characteristics by the two-dimensional results indicates that the ratio of coil inductance to circuit inductance affects both the rise rate and phase of the plasma current, the larger the ratio, the greater the rise rate and the better the following characteristic. The calculations show that the magnetic energy obtained within the decoupling distance determines the overall performance the thruster can be obtained; self-induced field maintained by the thermal motion after the main pulse leads to the long attenuation process and difference on the total impulse when the angle of conical pylon is varied under constant coil dimension.     

A fault-tolerant triple-redundant voice coil motor for direct drive valves: Design, optimization, and experiment

A direct drive actuator (DDA) with direct drive valves (DDVs) as the control device is an ideal solution for a flight actuation system. This paper presents a novel triple-redundant voice coil motor (TRVCM) used for redundant DDVs. The TRVCM features electrical/mechanical hybrid triple-redundancy by securing three stators along with three moving coils in the same frame. A permanent magnet (PM) Halbach array is employed in each redundant VCM to simplify the system structure. A back-to-back design between neighborly redundancies is adopted to decouple the magnetic flux linkage. The particle swarm optimization (PSO) method is implemented to optimize design parameters based on the analytical magnetic circuit model. The optimization objective function is defined as the acceleration capacity of the motor to achieve high dynamic performance. The optimal geometric parameters are verified with 3D magnetic field finite element analysis (FEA). A research prototype has been developed for experimental purpose. The experimental results of magnetic field density and force output show that the proposed TRVCM has great potential of applications in DDA systems.     

Coronal Holes and Open Magnetic Flux

Coronal holes are low-density regions of the corona which appear dark in X-rays and which contain “open” magnetic flux, along which plasma escapes into the heliosphere. Like the rest of the Sun’s large-scale field, the open flux originates in active regions but is subsequently redistributed over the solar surface by transport processes, eventually forming the polar coronal holes. The total open flux and radial interplanetary field component vary roughly as the Sun’s total dipole strength, which tends to peak a few years after sunspot maximum. An inverse correlation exists between the rate of flux-tube expansion in coronal holes and the solar wind speed at 1 AU. In the rapidly diverging fields present at the polar hole boundaries and near active regions, the bulk of the heating occurs at low heights, leading to an increase in the mass flux density at the Sun and a decrease in the asymptotic wind speed. The quasi-rigid rotation of coronal holes is maintained by continual footpoint exchanges between open and closed field lines, with the reconnection taking place at the streamer cusps. At much lower heights within the hole interiors, “interchange reconnection” between small bipoles and the overlying open flux also gives rise to coronal jets and polar plumes.     

超磁致伸缩电静液作动器磁场分析与优化

提出一种超磁致伸缩电静液作动器（GMEHA）结构,采用永磁体与控制线圈组合提供驱动磁场.首先建立了该组合磁路数学模型,并给出了超磁致伸缩棒内磁感应强度计算解析式;其次,对以上结构进行了有限元分析（FEA）,得出了磁路主要结构参数与磁场分布均匀性之间映射规律;最后进行了作动器磁场试验研究并与有限元分析结果进行了对比,验证了理论与有限元模型的可预测性,给出了该电静液作动器结构设计方法.结果表明:该电静液作动器的最佳驱动频率为250Hz,最大无负载体积流量为0.85L/min,最大阻断力达到了120N.      

具有高精度的永磁容错电机非线性电感分析及其解析式求取

 以六相十极永磁容错电机（FTPMM）为例,通过对电机中磁力线分布的分析,得出FTPMM绕组自感的各个主要组成部分,即激磁感、谐波漏感、槽口漏感和槽内漏感,并分析出FTPMM的大电感是通过增加槽口漏感和谐波漏感来实现的。为提高电机优化设计的正确性,提出了新的磁路模型,并引入槽口磁压降参数和槽口计算厚度参数,得出了具有高精度的非线性绕组自感及其组成部分的解析式。最后通过有限元法(FEM)及实验验证,该解析式的精度在13%以内,并且电机具有很强的容错能力,对永磁容错电机的优化设计和性能分析有理论指导意义。     

高精度加速度计力矩器磁路的设计与仿真分析

力矩器磁路性能决定了加速度计标度因数的性能,为此利用有限元方法对力矩器磁路的磁通密度进行分析,在此基础上提出了两种结构优化设计方案,并对其进行仿真计算。仿真结果表明,改变导磁帽的形状可以提高气隙磁场的磁通密度的稳定性和均匀性,但导磁帽易出现饱和现象;通过降低磁钢的高度,同时增加导磁帽的高度,既能大幅度的提高磁场的稳定性和均匀性,导磁帽也不会出现饱和现象,但气隙磁场的磁通密度均值会降低37.25%,非线性误差为1.83%,优化后气隙磁场存在着磁通密度稳定（径向均值为0.42868T）和均匀的区域。     

磁阻型电磁发射系统的发射体形态优化研究

根据磁阻型电磁发射原理及驱动线圈内部磁场分布情况,推导了基于线性化电感的发射体运动模型,给出了一个用于计算发射体在线圈中的受力和加速情况的简化方法,并归纳了部分影响因素。使用ANSYS Maxwell仿真软件对不同形状发射体在线圈中的受力变化进行仿真分析。研究结果为实际磁阻型电磁发射中应用的发射体形状设计提供了参考。     

The Expansion of Coronal Plumes in the Fast Solar Wind

Coronal plumes are believed to be essentially magnetic features: they are rooted in magnetic flux concentrations at the photosphere and are observed to extend nearly radially above coronal holes out to at least 15 solar radii, probably tracing the open field lines. The formation of plumes itself seems to be due to the presence of reconnecting magnetic field lines and this is probably the cause of the observed extremely low values of the Ne/Mg abundance ratio. In the inner corona, where the magnetic force is dominant, steady MHD models of coronal plumes deal essentially with quasi-potential magnetic fields but further out, where the gas pressure starts to be important, total pressure balance across the boundary of these dense structures must be considered. In this paper, the expansion of plumes into the fast polar wind is studied by using a thin flux tube model with two interacting components, plume and interplume. Preliminary results are compared with both remote sensing and solar wind in situ observations and the possible connection between coronal plumes with pressure-balance structures (PBS) and microstreams is discussed. This revised version was published online in June 2006 with corrections to the Cover Date.