Analysis and Numerical Modeling of a 20W Microwave Electrothermal Thruster

The microwave electrothermal thruster (MET) is an electric propulsion device that uses an electromagnetic resonant cavity within which free-floating plasma is ignited and sustained in a propellant gas. The thrust is generated when the heated propellant gas is exhausted out of a gas-dynamic nozzle. For an empty cavity without any perturbing regions—e.g., dielectric regions or antenna regions—it is fairly straightforward to accurately calculate the cavitys resonant frequency and describe the electric field intensity distribution within the cavity. However, actual METs do contain perturbing regions, which means that analytical solutions are no longer possible to fully characterize the device. Hence, the numerical methods to simulate the electric field intensity and distribution within the resonant cavity were employed. The simulation results are that with the cap height increasing, the resonant frequency and electric field strength decrease, also increasing the permittivity of dielectric material causes decreasing the resonant frequency and electric field strength. A decrease in resonant frequency and maximum electric field strength, and an increase in resonant bandwidth, were observed with increasing antenna depth. Rounding an antenna of a given depth equals decreasing the depth.     

Sealing of Ejection Hole at the Bottom of Projectile for Wired Transmission System of Penetration Data

It is difficult to find the projectile when people want to get the penetration data in a hard recovery method, so a recovery system of penetration data is designed based on an ejection mode from the projectile base and a method of wired transmission, at the same time, the system was sealed with a designed sealing device, the working principle of which was introduced. Using Fluent as the simulation platform, the transient pressure of seal cavity was simulated based on the change of chamber pressure, and steady-state pressure of seal clearance and seal cavity were simulated based on the maximum chamber pressure. The sealing performance was tested by a pressure test system. The results of simulation and experiment show that the maximum pressure of seal cavity is 139.4.kPa when the maximum chamber pressure is 242.9.MPa and the maximum temperature of gunpowder explosive gas is 2.166.5.K, so the sealing performance can be assured. The sealing device can be taken as a reference in sealing research on gunpowder gas at the bottom of projection.     

Geophysical criterion of pre-outburst coal outsqueezing from the face space into the working

The initial process of coal and gas sudden outburst is studied in the article when under the influence of rock and gas pressure the part of a coal seam layer(a coal section) is squeezed out from the mouth of the future outburst cavity in a jump-like manner into the working. Geo-mechanical criterion for a part of a coal seam layer outsqueezing in the form of the relation of active(squeezing out) and passive(preventing the outsqueezing) forces is defined in the article. Based on it, the geophysical criterion is defined by expressing basic physical parameters through geo-physical ones: the current stress is defined by spectral-acoustic method through the ratio of high frequency and low-frequency components of an acoustic signal, which is generated into a face working space by the mining equipment operating in the face; in-situ gas pressure is defined by gas analytical method by the concentration of methane in the atmosphere of the working; the strength of the most broken coal layer is defined by a strength measuring device(a device for measuring the depth of a steal cone punched into the coal by a spring mechanism). This paper studies the influence of acoustic, strength and filtrating and collecting properties of a face working space on the limit value of an obtained geophysical criterion of pre-outburst squeezing of a coal ‘‘plug" out of the mouth of the future outburst cavity into the working.     

Numerical investigation of radial inflow in the impeller rear cavity with and without baffle

In typical small engines, the cooling air for high pressure turbine(HPT) in a gas turbine engine is commonly bled off from the main flow at the tip of the centrifugal impeller. The pressurized air flow is drawn radially inwards through the impeller rear cavity. The centripetal air flow creates a strong vortex because of high inlet tangential velocity, which results in significant pressure losses. This not only restricts the mass flow rate, but also reduces the cooling air pressure for down-stream hot components. The present study is devoted to the numerical modeling of flow in an impeller rear cavity. The simulations are carried out with axisymmetric and 3-D sector models for various inlet swirl ratio β_0(0–0.6), turbulent flow parameter lT(0.028–0.280) with and without baffle. The baffle is a thin plate attached to the stationary wall of the cavity, and is proved to be useful in reducing the pressure loss of centripetal flow in the impeller rear cavity in the current paper. Further flow details in impeller rear cavity with and without baffle are displayed using CFD techniques. The CFD results show that for any specified geometry, the outlet pressure coefficient of impeller rear cavity with or without baffle depends only on the inlet swirl ratio and turbulent flow parameter. Meanwhile, the outlet pressure coefficient of the cavity with baffle is indeed smaller than that of cavity without baffle, especially for the cases with high inlet swirl ratio. The suppression of the effect of centrifugal pumping and the mixing beween the main air which is downstream of the baffle and the recirculating flow of the vortex in the stationary cavity, which are caused by the use of baffle, are the underlying reasons that lead to the reduction of outlet pressure loss.     

Pressure-controlled elliptical cavity expansion under anisotropic initial stress: Elastic solution and its application

This paper presents an elastic solution to the pressure-controlled elliptical cavity expansion problem under the anisotropic stress conditions. The problem is formulated by the assumption that an initial elliptical cavity is expanded under a uniform pressure and subjected to an in-plane initial horizontal pressure Kσ_0 and vertical pressure σ_0 at infinity. A conformal mapping technique is used to map the outer region of the initial elliptical cavity in the physical plane onto the inner region of a unit circle in the phase plane. Using the complex variable theory, the stress functions are derived; hence, the stress and displacement distributions around the elliptical cavity wall can be obtained. Furthermore, a closed-form solution to the pressure-expansion relationship is presented based on the elastic solution to the stress and displacement. Next, the proposed analytical solutions are validated by comparing with the Kirsch's solution and the finite element method(FEM). The solution to the presented pressure-controlled elliptical cavity expansion can be applied to two cases in practice. One is to employ the solution to the interpretation of the shear modulus of the soil or rocks and the in-situ stress in the pre-bored pressuremeter test under the lateral anisotropic initial stress condition. The other is the interpretation of the membrane expansion of a flat dilatometer test using the pressure-controlled elliptical cavity expansion solution. The two cases in practice confirm the usefulness of the present analytical solution.     

On ferroelectric domain polarization switching mechanism subject to an external electric field by simulations with the phase-field method

The ferroelectric domain formation(FDF) and polarization switching(FDPS) subjected to an external electric field are simulated using the phase-field(PF) method,and the FDPS mechanism under different external electric fields is discussed.The results show that the FDF is a process of nucleation and growth in ferroelectric without applying any external stress.Four kinds of parallelogram shaped ferroelectric domains are formed at the steady state,in which the 180° anti-phase domains regularly align along the 45° direction and the 90° anti-phase domains regularly distribute like a stepladder.Steady electric fields can rotate domain polarization by 90° and 180°,and force the orientation-favorite domains and the average polarization to grow into larger ones.The greater the steady electric field,the larger the average polarization at the steady state.In ferroelectrics subject to an alternating electric field,domain polarization switches to cause a hysteresis loop and an associated butterfly loop with the alternating electric field.The coercive field and remnant field are enhanced with the increase of the electric field frequency or strength,or with the decrease of temperature.     

SOC distribution-based modeling for lithium-ion battery for electric vehicles using numerical optimization

In order to simulate electrical characteristics of a lithium-ion battery used in electric vehicles in a good manner,a three-layer battery model is established.The charge of the lithium-ion battery is assumed to distribute among the three layers and their interaction is used to depict hysteresis and relaxation effect observed in the lithium-ion battery.The model parameters are calibrated and optimized through a numerically nonlinear least squares algorithm in Simulink Parameter Estimation Toolbox for an experimental data set sampled in a hybrid pulse test of the battery.Evaluation results showed that the established model is able to provide an acceptable accuracy in estimating the State of Charge of the lithium-ion battery in an open-loop fashion for a sufficiently long time and to describe the battery voltage behavior more accurately than a commonly used battery model.The battery modeling accuracy can thereby satisfy the requirement for practical electric vehicle applications.     

Description of the Cover Picture

正The cover picture is taken from the article "The Dynamical FSI Simulation for Bellows Inflating to Disperse Bomblets",which shows the distribution of gas temperature and velocity vector at the first FSI stage,namely the stage of inflating with constant volume.The purpose of this FSI model is to analyze the interaction between the metal bellows(1 mm thick)and the propellant gas with high     

A learning method for energy optimization of the plug-in hybrid electric bus

The optimal energy management for a plug-in hybrid electric bus(PHEB)running along the fixed city bus route is an important technique to improve the vehicles’fuel economy and reduce the bus emission.Considering the inherently high regularities of the fixed bus routes,the continuous state Markov decision process(MDP)is adopted to describe a cost function as total gas and electric consumption fee.Then a learning algorithm is proposed to construct such a MDP model without knowing the all parameters of the MDP.Next,fitted value iteration algorithm is given to approximate the cost function,and linear regression is used in this fitted value iteration.Simulation results show that this approach is feasible in searching for the control strategy of PHEB.Simultaneously this method has its own advantage comparing with the CDCS mode.Furthermore,a test based on a real PHEB was carried out to verify the applicable of the proposed method.     

A growth manner of butterfly martensite

The growth of butterfly martensite in an Fe-Ni-V-C alloy was investigated using an optical microscope and transmission electron microscope through observing its morphology. The present butterfly martensite is dislocation-type, with a few fine twins. One wing of a butterfly martensite is layered more heavily than the other and the concave part is layered more obviously than other regions. Most butterfly martensites have a lath plate outside of and next to one wing. The outside martensite plates grow first, and then two wings of butterfly martensite. The smooth parts of a butterfly martensite grow earlier than the layered regions. A wing of a butterfly martensite grows like a group of lath martensites.     

矩形压缩谐振腔内基底对电场影响的仿真模拟

针对微波等离子体化学气相沉积金刚石过程中,矩形谐振腔中激发的等离子体稳定性和均匀性差的问题,提出通过用Ansoft软件对矩形压缩谐振腔进行模拟计算来优化设计谐振腔的方法．模拟中,假设除了微波输入端口以外,所有的边界都定义为理想电导体;微波能以平面波的形式,通过矩形波导被耦合到微波谐振腔内;再用高频结构仿真器联合求解满足模型条件的麦克斯韦方程组,得出谐振腔中的电场分布结果．分别模拟了基底深入谐振腔内高度为1．5、2、2．5、3、4mm和基底半径为11、13、15、17mm时,腔体内的电场分布．数值模拟结果表明,压缩谐振腔内的最大电场强度为817V／m左右,较压缩之前的电场强度增高了近一倍,且基底深入谐振腔高度为2mm,基底半径为13mm左右时,装置内电场强度较集中．     

MPCVD装置圆柱谐振腔的仿真设计

根据电磁场理论设计了用于微波等离子体化学气相沉积系统的TE11模圆柱谐振腔,推导了该谐振腔的电场分布,计算了圆柱腔的几何尺寸.利用电磁场仿真软件CST对圆柱腔内的电场分布进行仿真,比较分析了不同天线耦合深度以及不同石英窗厚度对电场分布的影响.仿真优化结果表明天线耦合深度为5mm、石英窗厚度为5mm时腔内微波耦合良好,能...     

微波等离子推力器圆柱谐振腔等离子体流的数值研究

为了获得微波等离子推力器(MPT)圆柱形谐振腔小型化的设计参数，采用时域有限差分法(FDTD)求解Maxwell方程、有限体积法求解N-S方程、单温度局域热平衡模型求解等离子体数密度、温度等参数的全数值方法，对MPT圆柱形谐振腔在不同微波频率、相同谐振模式情况下的微波等离子体耦合流场进行了数值模拟计算。计算结果表明，提高微波频率可缩小圆柱形谐振腔尺寸。圆柱形谐振腔小型化后，在腔内压强一定的情况下，相应地工质气体的流量减小、消耗的微波功率减小，喷管喉径也减小、从而MPT的推力也减小，且不同微波频率、相同谐振模式情况下，腔内等离子体区温度、压强、电子数密度的变化规律相同。这些结论为今后MPT的小型化设计提供了理论依据。     

单负材料平面微腔结构的共振模研究

利用传输矩阵法研究了由单负材料构成的平面微腔结构的共振模特性。研究表明,腔模频率主要由腔中介质的物质参数和结构参数来决定。单负材料层的厚度影响共振模的线宽,随厚度增加而谱线变窄。单负材料损耗的存在,影响共振模的透射率,使腔内局域电场减小。选择合适的单负材料层厚度,可使腔中局域电场达到最大。还研究了斜入射时腔模的偏振特性,在一定条件下可实现TM腔模的全向透射,用以设计全向滤波器。     

关于具有空气隙的矩形微带天线的谐振频率探讨

对微带天线的腔模理论进行修改,利用电磁场理论推导了具有空气隙的矩形微带天线的谐振频率的计算公式,同时考虑了边缘效应,引入了有效介电常数,对谐振频率的计算公式进行了修正。最后将其用于实例的计算结果与文献[3,4]实测结果相比较。结果表明,理论计算结果与实测值有良好的吻合。     

非均匀电介质边缘效应的研究

论述了非均匀电介质中电极边缘电场强度的理论和计算方法,表明如果材料介电常数随着接近电极边缘而增大,非均匀电介质电场强度增益系数会大大低于均匀电介质电场强度的增益系数.非均匀电介质材料影响空间测量特性和电场对称性,以致在非均匀电介质中采用平面电极设计得到电场强度的分布规律类似于均匀电介质非对称装置中电场强度的分布.     

基于电磁模型的大气压表面波等离子体数值模拟

针对表面波等离子体模拟复杂程度高和计算工作量大的问题,提出基于电磁模型来开展大气压等离子体的数值模拟.根据表面波等离子体的放电特性,合理建立和简化电磁模型.通过对比实验诊断与数值计算结果,验证了模型的可靠性及其参数适用范围,拟合得到的电子有效碰撞频率((1.5±0.25)×1011 s?1)与实验测量值吻合.在此基础上...     

新型三角形微带天线及其分析

内场结构研究表明，方形微带天线含对角线的两个空腔横截面分别属于理想电壁和理想磁壁，提出了两种新型三角形微带天线，在谐振频率不变的情况下，将天线贴片面积缩减了一半，给出了用于分析三角形微带天线的一种新方法，理论计算和基于矩量法解的Ensembe软件模拟结果一致性很好。     

基于RFID的微带天线应变传感器的仿真分析

为了研究应变传感器的无线检测技术,提出一种基于无线射频识别(radio frequency identification,RFID)微带天线应变传感器的无线检测方法,将超高频RFID技术与微带天线技术相结合,以微带天线作为标签天线,接收RFID阅读器发射的能量,激活RFID的标签芯片,芯片再通过信号调制技术,消除环境中的噪声干扰,并将天线谐振频率随应变变化信息返回阅读器,实现无源无线的应变检测.分别设计了插入馈电式和边缘馈电式2种RFID微带天线传感器,利用HFSS电磁仿真软件对二者进行了结构和参数优化设计;利用COMSOL仿真软件,通过固体力学和电磁学相耦合的仿真分析,明确了不同应变状态下,2种传感器谐振频率的偏移量与应变均呈线性关系,其仿真结果与理论值相吻合,满足结构应变测量的要求,为实验研究奠定了理论基础.     

中波电台电磁环境影响分析

为了分析广播通信系统中波天线产生的电磁环境影响规律,在麦克斯维电磁场理论的基础上,建立了中波天线场强值的计算模型,并模拟了中波单塔工作模式和双频共塔工作模式的电场分布规律.同时,对北京市郊区某中波电台的电场分布进行了实际测量.结果表明,中波天线电场强度随着水平距离的增加而迅速衰减,电场强度理论值和实测值远小于国家标准,二者的分布规律吻合较好.对中波发射台的环境影响评价工作具有重要的参考价值.