低耗散非结构网格多维限制器

基于极值原理分析非结构网格多维限制器的构造准则，通过引入约束位置和约束模板的定义，将非结构网格多维限制器构造方法统一化，并以此为基础提出一种新型非结构网格多维限制器.通过典型算例计算与已有限制器进行比较.结果表明：对于包含激波、接触间断等复杂波系干扰流动，新型多维限制器在保证数值稳定的条件下具有更低的数值耗散，对于复杂波系结构具有更高的流动分辨率.     

On the optimization of flux limiter schemes for hyperbolic conservation laws

A classic strategy to obtain high‐quality discretizations of hyperbolic partial differential equations is to use flux limiter (FL) functions for blending two types of approximations: a monotone first‐order scheme that deals with discontinuous solution features and a higher order method for approximating smooth solution parts. In this article, we study a new approach to FL methods. Relying on a classification of input data with respect to smoothness, we associate specific basis functions with the individual smoothness notions. Then, we construct a limiter as a linear combination of the members of parameter‐dependent families of basis functions, and we explore the possibility to optimize the parameters in interesting model situations to find a corresponding optimal limiter. © 2012 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2013     

基于磁流体热透镜效应的阈值可调光学限幅器的理论设计

理论模拟了激光束通过磁流体样品后产生的远场光斑图样,提出了一种阈值可调光学限幅器的实现方案.计算了不同光阑孔径半径和不同光阑样品距离情况下,系统的出射光功率与入射光功率的关系.得出了系统的光学限幅阈值随光阑孔径半径的增大以及光阑样品距离的减小而向高功率方向转移的结论,且限幅阈值与光阑孔径半径之间呈线性关系.定义了描述磁流体样品特征的参量f,发现了系统的光学限幅阈值随f的绝对值增加而减小.本文的结论能为实际的磁流体基可调谐光学限幅器的设计与制作提供有益的参考.     

Z-扫描技术与非线性光学材料性质的测量

介绍了Z-扫描技术的基本原理，以及Z-扫描技术在测量非线性光学介质的非线性折射率、非线性吸收系数和光学限制器等方面的应用，以细菌视紫红质(bR膜)、碘的酒精溶液和偶氮材料CN2为例，分别介绍了它们的测量结果，给出了提高Z-扫描灵敏度的改进方法，介绍了其发展装状况。     

A simple weighted essentially non-oscillatory limiter for the correction procedure via reconstruction (CPR) framework on unstructured meshes

In this paper, we adapt a simple weighted essentially non-oscillatory (WENO) limiter, originally designed for discontinuous Galerkin (DG) schemes on two-dimensional unstructured triangular meshes [39], to the correction procedure via reconstruction (CPR) framework for solving nonlinear hyperbolic conservation laws on two-dimensional unstructured triangular meshes with straight or curved edges. This is an extension of our earlier work [4] in which the WENO limiter was designed for the CPR framework on regular meshes. The objective of this simple WENO limiter is to simultaneously maintain uniform high order accuracy of the CPR framework in smooth regions and control spurious numerical oscillations near discontinuities. The WENO limiter we adopt in this paper uses information only from the target cell and its immediate neighbors. Hence, it is particularly simple to implement and will not harm the conservativeness and compactness of the CPR framework. Since the CPR framework with this WENO limiter does not in general satisfy the positivity preserving property, we also extend the positivity-preserving limiters [36], [33] to the CPR framework. Numerical results for both scalar equations and Euler systems of compressible gas dynamics are provided to illustrate the good behavior of this procedure.     

A physically based flux limiter for QUICK calculations of advective scalar transport

Transient, advective transport of a contaminant into a clean domain will exhibit a moving sharp front that separates contaminated and clean regions. Due to ‘numerical diffusion’—the combined effects of ‘cross‐wind diffusion’ and ‘artificial dispersion’—a numerical solution based on a first‐order (upwind) treatment will smear out the sharp front. The use of higher‐order schemes, e.g. QUICK (quadratic upwinding) reduces the smearing but can introduce non‐physical oscillations in the solution. A common approach to reduce numerical diffusion without oscillations is to use a scheme that blends low‐order and high‐order approximations of the advective transport. Typically, the blending is based on a parameter that measures the local monotonicity in the predicted scalar field. In this paper, an alternative approach is proposed for use in scalar transport problems where physical bounds C_Low?C?C_High on the scalar are known a priori. For this class of problems, the proposed scheme switches from a QUICK approximation to an upwind approximation whenever the predicted upwind nodal value falls outside of the physical range [C_Low, C_High]. On two‐dimensional steady‐state and one‐dimensional transient test problems predictions obtained with the proposed scheme are essentially indistinguishable from those obtained with monotonic flux‐limiter schemes. An analysis of the modified equation explains the observed performance of first‐ and second‐order time‐stepping schemes in predicting the advective transport of a step. In application to the transient two‐dimensional problem of contaminate transport into a streambed, predictions obtained with the proposed flux‐limiter scheme agree with those obtained with a scheme from the literature. Copyright © 2007 John Wiley & Sons, Ltd.     

Lower hybrid current drive experiments with graphite limiters in the HT-7 superconducting tokamak

Recent progress of lower hybrid (LH) experiments with new graphite limiters configuration in the HT-7 tokamak is presented. The lower hybrid current drive (LHCD) efficiency can be determined by fitting based on experimental data. Improved particle confinement was observed via LHCD (P_LHW>300 kW) characterized by the particle confinement time τ_p increased about 1.56 times. It is found that runaways are suppressed during loop voltage is decreasing at the flat-top phase of LH discharges. The main limitations of pulse length are presented in long-pulse experiments with new limiter configuration.     

守恒型双曲方程的中心差分TVD格式研究

研究了如何利用迎风格式的耗散性构造中心差分ＴＶＤ格式的方法，给 相应的定理，构造出新的耗散表达式。新格式既保留了二阶中心差分格式灵活方便的优点，又吸收了迎风格式耗散项比较精细的特点，同时具有ＴＶＤ性质，使得新格式具有较同的激波分辨率。     

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在HT-7装置上采用红外热像仪测量了活动限制器的表面温度,显示了第一壁温度与等离子体水平位移、波加热参数的关系,一定程度上反映了等离子体与壁相互作用的程度。采用ANSYS计算了活动限制器表面大致的能流分布,其结果与方法可为EAST装置等第一壁温度的测量和能流的计算分析提供一定的参考。     

PIN限幅器电磁脉冲效应数值模拟与验证

基于电磁脉冲对半导体器件效应的电-热多物理场模型,利用Sentaurus-TCAD仿真器建立了PIN限幅器电磁脉冲效应数值模型,研究了不同峰值功率的电磁脉冲作用下限幅器的输入/输出特性,以及大功率电磁脉冲注入PIN器件热损伤阈值与脉冲宽度的关系。模拟与实验结果表明:基于器件热效应影响载流子输运过程的电-热多物理模场型,模拟限幅器在大功率电磁脉冲注入下输入/输出功率的结果与实验结果吻合较好;模拟大功率电磁脉冲注入PIN器件热损伤阈值与脉冲宽度的关系式,与Wunsch-Bell半经验关系式符合较好。