饱和铁芯型超导限流器对距离保护的影响

饱和铁芯型超导限流器SCFCL(Saturated Core Superconducting Fault Current Limiter)是一种较为理想的高电压限流器,利用其技术特点可以实现无时限的明显限流作用,有着广泛的运用前景。距离保护能够很好的满足高电压复杂网络快速、精确切除故障的要求,其主要元件阻抗继电器是现阶段普遍应用的高性能继保装置。SCFCL在高压输电网络的接入会对距离保护产生很大影响,运用PSCAD搭建500kV输电线路模型,详细分析限流器接入前后不同短路故障类型及故障距离对线路距离保护的影响。     

Runaway electron generation decrease during a major disruption by limiter biasing in tokamaks

The high-energy current of runaway electrons during a major disruption in tokamak reactors can cause serious damage to the first wall of the reactors and reduce their life time. Therefore, finding a method to minimize runaway electron generation during a major disruption is much needed. Tokamak limiter biasing is one of the methods that can be used for controlling the radial electric field and can induce a transition to an improved confinement state. This paper attempts to examine the effect of limiter biasing on the generation of runaway electrons during a major disruption. To do so, a horizontal biased limiter placed on the tokamak was used. Main parameters such as plasma current, loop voltage, emitted hard X-ray intensity, magnetohydrodynamic (MHD) oscillation and H_α radiation and spectrum of hard X-rays, in the presence and absence of negative and positive limiter biasing, were measured. The results show that the application of limiter biasing during a major disruption can reduce runaway electron generation.     

Two positivity preserving flux limited,second‐order numerical methods for a haptotaxis model

Two numerical methods for a one‐dimensional haptotaxis model, which exploit the use of van Leer flux limiter, are developed and analyzed. Sufficient conditions time step size and flux limiting are given for such formulation to ensure the non‐negativity of the discrete solution and second‐order accuracy in space. Another advantage is that we avoid solving large nonlinear systems of algebraic equations. The discrete preservation of total conservation of cell density, concentration, and logarithmic density is also verified for the numerical solution. Numerical results concerning accuracy, convergence rate, positivity, and conservation properties are presented and discussed. Similar approach could be applied efficiently in the corresponding two‐ and three‐dimensional problems. © 2012 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 2013     

温度对PIN二极管限幅器功率响应特性的影响

 通过求解PIN二极管基区双极载流子扩散方程得到了限幅器Pspice等效电路模型, 根据PIN二极管物理参数与温度的关系, 数值计算得到了PIN二极管限幅器在多个温度点的功率响应特性, 发现温度的升高会使限幅器内部损耗增加, 加剧限幅器内部热损伤。并利用恒温控制系统进行了实验验证, 实验结果与数值计算结果相符合。实验还发现高温热冲击可能使限幅器限幅能力大幅下降, 可能成为通信系统的重大安全隐患。     

超导故障限流器的数学模型研究

文中总结了几种超导故障限流器的模型。在数学模型的基础上 ,阐述了超导材料的温升、失超传播速度和临界电流密度对超导故障限流器性能的影响     

高分辨率差分格式的数值分析与限制因子的构造

本文利用差分方法余项效应理论,分析比较了一些典型的限制因子.对不同的限制因子,格式的表现明显差异主要是由其数值耗散性、色散性强弱不同所致.在分析比较格式的数值耗散性、色散性之后,本文提出了一种新的限制因子,得到的格式在解的剧烈变化区具有更高的分辨率,在光滑区避免了由于数值色散性较强导致的失真.数值试验表明该格式具有较好的性质.     

EAST液态锂限制器分配盒参数对锂流动性影响

为考察溢流孔结构几何参数及壁面电导率对液态锂流动的影响,通过数值模拟方法对不同尺寸、形状及壁面电导率的溢流孔中液态锂的流动进行了数值模拟。结果表明：溢流孔的截面宽度越小,其出口的速度分布越均匀,速度峰值也越小,但溢流孔进出口之间的压力降会显著增加;且随着壁面电导率增大,MHD压降也随之增大。对于圆形及椭圆形截面的溢流孔,其出口的速度分布远比矩形溢流孔均匀。另外,关于限制器热平衡的计算有助于保证限制器的安全稳定运行。结果对分配盒几何参数的设计、电磁泵及冷却系统的设计具有重要的指导意义。     

Flux Limiter Lattice Boltzmann Scheme Approach to Compressible Flows with Flexible Specific-Heat Ratio and Prandtl Number

We further develop the lattice Boltzmann (LB) model [Physica A 382 (2007) 502] for compressible flows from two aspects. Firstly, we modify the Bhatnagar--Gross-Krook (BGK) collision term in the LB equation, which makes the model suitable for simulating flows with different Prandtl numbers. Secondly, the flux limiter finite difference (FLFD) scheme is employed to calculate the convection term of the LB equation, which makes the unphysical oscillations at
discontinuities be effectively suppressed and the numerical dissipations be significantly diminished. The proposed model is validated by recovering results of some well-known benchmarks, including (i) The thermal Couette flow; (ii) One- and two-dimensional Riemann problems. Good agreements are obtained
between LB results and the exact ones or previously reported solutions. The flexibility, together with the high accuracy of the new model, endows the proposed model considerable potential for tracking some long-standing problems and for investigating nonlinear nonequilibrium complex systems.     

Extension of the DSMC method to high pressure flows

A collision-limiter method, designated as equilibrium direct simulation Monte Carlo (eDSMC), is proposed to extend the DSMC technique to high pressure flows. The method is similar to collision-limiter schemes considered in the past with the important distinction that for inviscid flows, equilibrium is enforced in the entire flow by providing a sufficient number of collisions, based on pre-simulation testing. To test the method with standard DSMC and Navier–Stokes (NS) methods, axi-symmetric nozzle and embedded-channel flows are simulated and compared with experimental temperature data and pre-existing calculations, respectively. The method is shown to agree with third-order Eulerian nozzle flows and first-order channel flows. Chapman–Enskog theory is utilized to predict the range of initial conditions where eDSMC is potentially useful for modeling flows that contain viscous boundary layer regions. Comparison with supersonic nozzle data suggests that the eDSMC method is not adequate for capturing the large variation in flow length scales occurring in supersonic expansions into a vacuum. However, when eDSMC is used in combination with the baseline-DSMC method a near-exact solution is obtained with a considerable computational savings compared to the exact DSMC solution. Viscous flow channel calculations are found to agree well with an exact Navier–Stokes (NS) calculation for a small Knudsen number case as predicted by Chapman–Enskog theory.     

液态锂限制器的铺展性测试平台设计及初步实验

为研究液态锂在电磁驱动限制器表面的铺展特性,设计了与EAST限制器接口相同的限制器测试平台。该平台运行时真空环境可达10^-4Pa,对被测限制器可加热至350℃。在限制器锂回路管道上,利用外部2T水平磁场以及竖直方向施加的最大为200A的直流电流,形成电磁驱动力驱动下的锂液循环回路。测试平台设有顶部和正面两个观察窗,能够在可视化条件下,完成液态锂限制器的铺展性测试实验。基于该测试平台,对首次设计的双通路液态锂限制器,研究了不同实验温度和驱动电流下液态锂在限制器表面的流动铺展情况。结果发现,锂的流量和限制器表面结构是影响锂液铺展的主要因素。