螺旋慢波电路高频特性的三维计算模拟

 使用MAFIA软件对螺旋慢波线高频特性进行计算模拟，避免解析理论中的假设处理，提高了计算精度，与实验测试值相比色散特性的平均模拟误差为1%左右，耦合阻抗的平均误差为0.2%左右；并对不同建模方法下的不同模拟方法在计算时间和精度上作了比较，证明了准周期边界条件的模拟方法是一种在实际工程应用上同时满足精度与效率要求的模拟方法。     

强流直线感应加速腔微波特性

 介绍了确定不同加速间隙形状和设计结构的强流直线感应加速腔微波特性的方法,即确定频域中加速腔横向阻抗值的方法,包括数值模拟和实验测试。 横向阻抗测试实验中采用了两种测试方法:一种为同轴线束流模拟法,另一种为对加速腔形状因子的测试。实验中测试了3种不同的腔型,并和数值模拟结果进行了比较。两种横向阻抗的测试方法所得结果都与计算结果基本符合,从测试过程的繁简程度和多次实验结果的重复性来看,对于强流直线感应加速腔来说,形状因子值测试方法优于双芯同轴线束流模拟法。实验测试和数值模拟结果显示,确定直线感应加速腔横向阻抗值,测试实验和数值模拟是相辅相成的,缺一不可。     

微波腔内波混沌散射的初步研究

 通过建立的微波腔模拟产生大量腔体散射矩阵和辐射散射矩阵,并转化得到归一化散射矩阵和阻抗矩阵。利用戴桑环系综对归一化散射矩阵的本征值和本征相位进行了统计分析,其本征值的模和本征相位具有统计独立性,且本征相位近似均一分布,验证了腔体中波混沌散射的存在。对数值模拟和随机矩阵理论预测得到的归一化阻抗的统计特性进行了比较,其结果基本一致,说明随机矩阵理论对归一化阻抗具有一定的预测功能。     

典型自由面流动问题的SPH-ALE数值模拟

应用基于黎曼解的SPH-ALE方法对两种典型自由面流动问题进行数值模拟,并提出一种一阶核函数修正压力计算方法,通过对临近边界的水粒子压力进行核积分,近似估算固壁边界压力.给出不同时刻的流场压力分布及自由液面演化过程,将计算结果与相关的试验值及数值解进行对比,分析结果表明：SPH-ALE方法较传统SPH方法在流场压力计算精度上有较大的改进,在处理强非线性自由面流动问题时能够达到较高的精度.     

相对论行波管高频系统的数值模拟及实验验证

 分别采用有限元算法软件（HFSS）和有限积分法软件（MAFIA）对相对论行波管盘荷波导慢波结构进行建模，求出了相应的色散曲线。在此基础上设计了可用于相对论行波管的一种宽带和一种窄带的盘荷波导结构。加工了它们的冷测模型，测试曲线和模拟曲线吻合很好，从而验证了这两种软件尽管计算方法不同，但都可以对行波管慢波结构本征值问题进行求解。     

速调管输入腔开放腔的高频特性分析与实验研究

 建立了带输入波导结构的S波段速调管放大器输入腔开放腔模型,利用3维软件对其高频特性进行了数值计算研究,并对输入腔结构进行了优化设计。利用已加工的输入腔进行了高频参数的冷测实验研究,实验中的输入腔结构尺寸与高频分析中的完全相同,实验结果与高频分析结果一致。用3维PIC程序对电子束经过该输入腔后的束流调制以及注入微波的吸收情况进行了模拟。模拟结果表明：该输入腔与微波注入波导匹配很好,注入微波能被电子束和谐振腔全部吸收,在输入腔间隙后37 cm处得到了13%的基波电流调制深度。     

求解不可压Navier-Stokes方程的一种新方法

以方腔自然对流问题为例阐述了数值求解不可压Navier-Stokes方程的新方法．该方法将四阶紧致差分格式(FCDS)和具有并行性的交替组显(AGE)迭代方法相结合；兼顾了稳定性，计算精度及并行性能．针对不同的Raleigh数和Prandtl数，对方腔内稳态自然对流进行了数值模拟，并将数值结果同前人结果进行了比较．     

耦合腔慢波特性及其注-波互作用的三维软件模拟

 利用MAFIA软件分别对休斯型耦合腔慢波结构进行了由冷腔到热腔的计算机模拟，并将冷腔模拟结果分别与理论计算结果和实验测试结果进行比较，发现模拟结果更加接近实验值，色散特性的平均误差在0.02%左右，耦合阻抗的平均误差在5%左右，基本满足设计要求；由冷腔模拟结果导入MAFIA三维粒子模拟模块中进行注 波互作用模拟，对其工作机理进行了定性分析。     

基于SIMPLE求解对流-扩散方程的一种新方法

针对SIMPLE系列算法,通过分别求解控制容积界面和节点两个位置的对流-扩散方程来提高数值计算精度,提出了一种流动与传热数值模拟的新方法。采用新的数值方法对顶盖驱动流与正方腔自然对流进行了数值模拟。数值模拟结果表明,在相同网格划分时,新的数值方法相对迎风格式、乘方格式、QUICK格式SIMLE算法的计算精度高;而在计算精度基本相同时,新方法有较高的计算效率。     

Ka波段带状注相对论速调管模拟研究

利用三维电磁场与粒子模拟软件对Ka波段带状注相对论速调管放大器进行了分析设计和模拟计算。通过对谐振腔本征模的计算确定了腔体的冷腔高频特性,采用三维粒子模拟软件(PIC)模拟分析速调管各腔及整管的束波互作用过程。模拟结果表明:在带状电子注电压500kV、束流1kA、宽高比40∶1,注入微波功率1.94kW和均匀聚焦磁场0.8T的条件下,获得的输出微波功率达到142MW,频率40GHz,效率28.4%,增益约48.6dB。     

142.8MHz次谐波聚束腔的结构优化设计

 使用二维有限差分法分析软件Superfish和三维有限积分法分析软件MAFIA，对142.8MHz次谐波聚束腔的结构进行了模拟和优化研究，给出了聚束腔结构优化设计的步骤和方法，确定了优化后聚束腔的基本结构。分析比较了Superfish和MAFIA两个软件的模拟优化结果，得出了基本一致的结论。还探讨了Superfish和MAFIA在聚束腔设计中的应用方法。     

Three Dimension Simulation of Millimeter Wave Double Staggered Coupled Cavity Structure

After analyzed the cavity field mean method theory resolution, the software simulation method to obtain the resonance frequency, Q value and RF dispersion by MAFIA and ANSYS software is discussed for the double staggered coupled cavity Millitron structure in the millimeter-wave TWT. The resonance frequency and Q value of the single cavity is obtained and is consistent with two kind of the simulation software. Their average error is about 0.6%. The two kind of the simulation result is consistent to the design precise. The simulation method saves on the cost and time in the experiment, improve the data precise and work efficiency. The trend of the dispersion simulation result is consistent with the cavity field mean method theory result. The high end of the theory result is great contrast to that of MAFIA result. It shows that the theory adopt some hypothetical conditions, But the theory result has some instructional signification in initialization design of the novel slow wave structure.     

含空腔的功能梯度声学覆盖层水下吸声特性

针对传统的声学覆盖层吸声频带窄的问题,基于功能梯度材料的特点提出了一种含空腔结构的水下功能梯度声学覆盖层结构,引入梯度有限元法建立了功能梯度型声学覆盖层的水下声学计算模型,研究了功能梯度声学覆盖层结构的水下吸声特性。与传统的功能梯度结构声学建模方法相比,在保证计算精度和计算效率的基础上,文中所建立的功能梯度结构声学计算模型可适用于更复杂的功能梯度声学结构声学性能评估。研究结果表明,功能梯度声学覆盖层能够有效改善中高频段的吸声性能,获得较好的宽频吸声效果。此外,空腔形状采用锥型空腔结构或者组合型空腔结构可以有效地拓宽功能梯度声学覆盖层的吸声频带。      

微波元件与加速结构的有限元分析

研究了有限元方法在二维均匀结构和轴对称加速结构中的应用,采用了带宽优化技术和子空间求解特征值方法,并给出了部分例子,结果表明该方法精度高、速度快.这些方法可直接用于三维程序、并行计算.     

Correlating the breakdown strength with electric field analysis for polyethylene/silica nanocomposites

The experimental findings on the DC and AC breakdown strength of polyethylene/silica nanocomposites are reported and correlated with simulation results on the electric field distribution of possible nanocomposite models. Specifically, the effects of interphase permittivity and interparticle distances on the electric field intensity and the breakdown strength are discussed with the aid of the Finite Element Method Magnetics (FEMM) 4.2 software. The results showed that the presence of the interphase, when assigned a unique interphase permittivity value, led to variations in electric field distributions. The electric field also changed as adjacent nanoparticles separated from each other with different interparticle distances.     

方腔驱动流的数值模拟研究

利用CFD软件对方腔的温度场和速度场进行了数值模拟计算。采用有限元法对模型的连续性方程、动量方程和能量方程进行离散。对方腔内的流体受迫对流换热进行数值模拟,主要分析了方腔顶部流体在不同速度的情况下,对方腔内部流体的温度场和速度场以及对流换热量的影响,结果表明随着方腔顶部流速的增大方腔底部的温度场和换热量也增大。     

超导悬浮系统中电磁力的有限元分析

利用超导体宏观电磁场的Bean模型和有限元方法对由超导体和超导悬浮线圈所组成的悬浮系统进行了分析计算,通过定量计算与模拟,得到了超导体感应的屏蔽电流分布,从而得到了悬浮间隙及悬浮线圈中的电流对悬浮力的影响规律,同时分析了悬浮线圈尺寸与最大悬浮力之间的关系。这些数值计算结果为优化超导悬浮系统的结构设计提供了理论依据。     

A Stiffness Reduction Method for efficient absorption of waves at boundaries for use in commercial Finite Element codes

Commercially available Finite Element packages are being used increasingly for modelling elastic wave propagation problems. Demand for improved capability has resulted in a drive to maximise the efficiency of the solver whilst maintaining a reliable solution. Modelling waves in unbound elastic media to high levels of accuracy presents a challenge for commercial packages, requiring the removal of unwanted reflections from model boundaries. For time domain explicit solvers, Absorbing Layers by Increasing Damping (ALID) have proven successful because they offer flexible application to modellers and, unlike the Perfectly Matched Layers (PMLs) approach, they are readily implemented in most commercial Finite Element software without requiring access to the source code. However, despite good overall performance, this technique requires the spatial model to extend significantly outside the domain of interest. Here, a Stiffness Reduction Method (SRM) has been developed that operates within a significantly reduced spatial domain. The technique is applied by altering the damping and stiffness matrices of the system, inducing decay of any incident wave. Absorbing region variables are expressed as a function of known model constants, helping to apply the technique to generic elastodynamic problems. The SRM has been shown to perform significantly better than ALID, with results confirmed by both numerical and analytical means.     

弯曲圆盘驱动的双Helmholtz共振腔换能器

使用双面同相振动的弯曲圆盘换能器驱动双Helmholtz共振腔,既放大了弯曲圆盘换能器弯曲共振频率以下频段的声输出,又利用两个Helmholtz共振腔的同相声源辐射模型实现了在Helmholtz共振频率处的"∞"字形垂直指向性,实现了低频指向性声发射。阐述了换能器实现"∞"字形低频指向性发射的机理,研究了腔体长度、金属圆片厚度及弯曲圆盘边缘简支厚度等关键结构参数对Helmholtz共振频率的影响,求解了换能器的发送电压响应、指向性等参数。依据仿真结果制作了实验样机,在消声水池中进行了电声性能测试。测试结果显示,指向性形状及液腔共振频率与仿真结果基本相符。这种由弯曲圆盘驱动的双Helmholtz共振腔水声换能器为实现水声换能器小尺寸、低频指向性发射提供了一种技术手段。      

Comparison of 1D transfer matrix method and finite element method with tests for acoustic performance of multi-chamber perforated resonator

Multi-chamber perforated resonator (MCPR) is a kind of typical silencer element which can both attenuate broadband noise and satisfy specific installation requirements. The one-dimensional transfer matrix method (TMM) and finite element method (FEM) are widely used to predict the transmission loss of the resonators. This paper mainly focuses on the comparison between 1D TMM and FEM in which detailed perforation modeling is applied for the acoustic modeling of MCPRs. Five resonators with different acoustic attenuation frequency ranges are built for simulation and test. In order to verify the results of the above methods, a transmission loss test facility is designed based on two-load method. Through adjusting the distance between microphones, the facility’s effective measurement frequency can be changed. The results show that despite of the complex modeling and calculation, FEM with detailed perforation modeling shows good consistency with test results in both frequency and amplitude within entire frequency range. In comparison, TMM is limited by the cut-off frequency when calculating transmission losses. Besides, accuracy of TMM in low frequency range is also affected by perforation conditions. However, TMM is time-saving in calculation and structure optimization. In MCPRs’ development process, TMM can be used to quickly design and optimize structure parameters while FEM can be used to verify the acoustic performance before prototyping.