共查询到20条相似文献,搜索用时 15 毫秒
1.
Will E. Pazner Andrew Nonaka John B. Bell Marcus S. Day Michael L. Minion 《Combustion Theory and Modelling》2016,20(3):521-547
We present a fourth-order finite-volume algorithm in space and time for low Mach number reacting flow with detailed kinetics and transport. Our temporal integration scheme is based on a Multi-Implicit Spectral Deferred Correction (MISDC) strategy that iteratively couples advection, diffusion, and reactions evolving subject to a constraint. Our new approach overcomes a stability limitation of our previous second-order method encountered when trying to incorporate higher-order polynomial representations of the solution in time to increase accuracy. We have developed a new iterative scheme that naturally fits within our MISDC framework and allows us to conserve mass and energy while simultaneously satisfying the equation of state. We analyse the conditions for which the iterative schemes are guaranteed to converge to the fixed point solution. We present numerical examples illustrating the performance of the new method on premixed hydrogen, methane, and dimethyl ether flames. 相似文献
2.
François P. Hamon Marcus S. Day Michael L. Minion 《Combustion Theory and Modelling》2019,23(2):279-309
We present a parallel multi-implicit time integration scheme for the advection-diffusion-reaction systems arising from the equations governing low-Mach number combustion with complex chemistry. Our strategy employs parallelisation across the method to accelerate the serial Multi-Implicit Spectral Deferred Correction (MISDC) scheme used to couple the advection, diffusion, and reaction processes. In our approach, the diffusion solves and the reaction solves are performed concurrently by different processors. Our analysis shows that the proposed parallel scheme is stable for stiff problems and that the sweeps converge to the fixed-point solution at a faster rate than with serial MISDC. We present numerical examples to demonstrate that the new algorithm is high-order accurate in time, and achieves a parallel speedup compared to serial MISDC. 相似文献
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Breakdown voltage analysis of Al0.25Ga0.75N/GaN high electron mobility transistors with partial silicon doping in the AlGaN layer
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In this paper,two-dimensional electron gas(2DEG) regions in AlGaN/GaN high electron mobility transistors(HEMTs) are realized by doping partial silicon into the AlGaN layer for the first time.A new electric field peak is introduced along the interface between the AlGaN and GaN buffer by the electric field modulation effect due to partial silicon positive charge.The high electric field near the gate for the complete silicon doping structure is effectively decreased,which makes the surface electric field uniform.The high electric field peak near the drain results from the potential difference between the surface and the depletion regions.Simulated breakdown curves that are the same as the test results are obtained for the first time by introducing an acceptor-like trap into the N-type GaN buffer.The proposed structure with partial silicon doping is better than the structure with complete silicon doping and conventional structures with the electric field plate near the drain.The breakdown voltage is improved from 296 V for the conventional structure to 400 V for the proposed one resulting from the uniform surface electric field. 相似文献
5.
Breakdown voltage analysis of Al<sub>0.25</sub>Ga<sub>0.75</sub>N/GaN high electron mobility transistors with partial silicon doping in the AlGaN layer
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In this paper,two-dimensional electron gas(2DEG) regions in AlGaN/GaN high electron mobility transistors(HEMTs) are realized by doping partial silicon into the AlGaN layer for the first time.A new electric field peak is introduced along the interface between the AlGaN and GaN buffer by the electric field modulation effect due to partial silicon positive charge.The high electric field near the gate for the complete silicon doping structure is effectively decreased,which makes the surface electric field uniform.The high electric field peak near the drain results from the potential difference between the surface and the depletion regions.Simulated breakdown curves that are the same as the test results are obtained for the first time by introducing an acceptor-like trap into the N-type GaN buffer.The proposed structure with partial silicon doping is better than the structure with complete silicon doping and conventional structures with the electric field plate near the drain.The breakdown voltage is improved from 296 V for the conventional structure to 400 V for the proposed one resulting from the uniform surface electric field. 相似文献
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磁共振成像(Magntic Resonance Imaging,MRI)技术是一种先进的医疗影像技术.在MRI系统中,通过梯度线圈电流快速切换方向,对待测区域施加梯度磁场,产生的梯度磁场会在其周围的金属体内激发出变化的涡旋电场,进而导致金属体内闭合的回路中产生对原来的梯度电流起抑制作用的感生电流,也就是我们所说的涡流.本文介绍了一种测量磁体涡流场的方法,结合电磁感应定律,设计了一种磁体涡流场测量装置,通过硬件采集以及软件处理的方法,将理想梯度场与实际磁场进行相减并将波形实时呈现,实验结果表明该方法可实现对磁体涡流场的测量. 相似文献
8.
Time-Domain Numerical Solutions of Maxwell Interface Problems with Discontinuous Electromagnetic Waves
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Ya Zhang Duc Duy Nguyen Kewei Du Jin Xu & Shan Zhao 《advances in applied mathematics and mechanics.》2016,8(3):353-385
This paper is devoted to time domain numerical solutions of two-dimensional
(2D) material interface problems governed by the transverse magnetic
(TM) and transverse electric (TE) Maxwell's equations with discontinuous electromagnetic
solutions. Due to the discontinuity in wave solutions across the interface, the
usual numerical methods will converge slowly or even fail to converge. This calls for
the development of advanced interface treatments for popular Maxwell solvers. We
will investigate such interface treatments by considering two typical Maxwell solvers
– one based on collocation formulation and the other based on Galerkin formulation. To
restore the accuracy reduction of the collocation finite-difference time-domain (FDTD)
algorithm near an interface, the physical jump conditions relating discontinuous wave
solutions on both sides of the interface must be rigorously enforced. For this purpose,
a novel matched interface and boundary (MIB) scheme is proposed in this work, in
which new jump conditions are derived so that the discontinuous and staggered features
of electric and magnetic field components can be accommodated. The resulting
MIB time-domain (MIBTD) scheme satisfies the jump conditions locally and suppresses
the staircase approximation errors completely over the Yee lattices. In the discontinuous
Galerkin time-domain (DGTD) algorithm – a popular Galerkin Maxwell solver, a
proper numerical flux can be designed to accurately capture the jumps in the electromagnetic
waves across the interface and automatically preserves the discontinuity in
the explicit time integration. The DGTD solution to Maxwell interface problems is explored
in this work, by considering a nodal based high order discontinuous Galerkin
method. In benchmark TM and TE tests with analytical solutions, both MIBTD and
DGTD schemes achieve the second order of accuracy in solving circular interfaces. In
comparison, the numerical convergence of the MIBTD method is slightly more uniform,
while the DGTD method is more flexible and robust. 相似文献
9.
Sona P. Kumar Anju Agrawal Rishu Chaujar Mridula Gupta R.S. Gupta 《Superlattices and Microstructures》2008
A two-dimensional (2-D) analytical model for a Dual Material Gate (DMG) AlGaN/GaN High Electron Mobility Transistor (HEMT) has been developed to demonstrate the unique attributes of this device structure in suppressing short channel effects (SCEs). The model accurately predicts the channel potential, electric field variation along the channel, and sub-threshold drain current, taking into account the effect of lengths of the two gate metals, their work functions, barrier layer thicknesses, and applied drain biases. It is seen that the SCEs and hot carrier effects in DMG AlGaN/GaN HEMT are suppressed due to the work function difference of the two metal gates, thereby screening the drain potential variations by the gate near the drain. Besides, a more uniform electric field along the channel leads to improved carrier transport efficiency. The accuracy of the results obtained from our analytical model has been verified using ATLAS device simulations. 相似文献
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电流变液与电-磁流变液的衍射特性 总被引:5,自引:3,他引:2
本文把电流变液装置作为反射光栅研究其衍射特性,首次提出由电场强度改变来调节光栅常数的概念.并讨论了同时外加电场与磁场的情况下,电磁流变液的衍射特性. 相似文献
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In this paper, the electric field effect on enhancement of the water evaporation rate in a channel is numerically investigated. The coupled equations of electrical field, flow field, temperature field and species concentration fields are discretized using Finite Volume Method (FVM) and the implicit/hybrid difference form. This equations are solved via SIMPLE algorithm and the Kaptsov hypothesis. The turbulent flow is modelled by Large Eddy Simulation (LES). The numerical results show that the water evaporation rate is increased with the presence of electric field, but the effect of electric field is diminished at high Reynolds number. 相似文献
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基于超材料的电磁谐振特性, 设计、制作了一种极化无关的宽带低雷达散射截面 (radar cross section, RCS)超材料吸波体. 通过场分布和反演法分析了其吸波机理, 利用波导法和空间波法测试了其吸波率和RCS特性. 理论分析表明: 在平面波的作用下, 该吸波体对某一吸波频率在不同的位置分别提供电谐振和磁谐振, 对不同的吸波频率, 利用不同的介质层提供主要的能量损耗, 从而有效减弱了电磁耦合, 保证了宽频带的强吸收特性. 实验结果表明: 设计的三层结构吸波体吸波率达90%以上的带宽是单层结构的4.25倍, RCS减缩10 dB以上的带宽为5.1%, 其单元尺寸为0.17λ, 厚度仅为0.015λ. 该吸波体的低RCS特性还具有极化无关、宽入射角的特点, 且通过改变吸波体的夹层结构可以实现工作带宽的灵活调节.
关键词:
超材料吸波体
雷达散射截面
宽带
电磁谐振 相似文献
15.
M. F. Paisley 《Journal of computational physics》2001,170(2):785
The steady incompressible Navier–Stokes equations in three dimensions are solved for neutral and stably stratified flow past three-dimensional obstacles of increasing spanwise width. The continuous equations are approximated using a finite volume discretisation on staggered grids with a flux-limited monotonic scheme for the advective terms. The discrete equations which arise are solved using a nonlinear multigrid algorithm with up to four grid levels using the SIMPLE pressure correction method as smoother. When at its most effective the multigrid algorithm is demonstrated to yield convergence rates which are independent of the grid density. However, it is found that the asymptotic convergence rate depends on the choice of the limiter used for the advective terms of the density equation, and some commonly used schemes are investigated. The variation with obstacle width of the influence of the stratification on the flow field is described and the results of the three-dimensional computations are compared with those of the corresponding computation of flow over a two-dimensional obstacle (of effectively infinite width). Also given are the results of time-dependent computations for three-dimensional flows under conditions of strong static stability when lee-wave propagation is present and the multigrid algorithm is used to compute the flow at each time step. 相似文献
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介绍节块内嵌离散纵标(SN)方法求解三维堆芯中子输运/扩散方程的算法框架.在基于扩散理论的三维粗网节块展开方法(NEM)的算法体系中,用基于输运理论的径向二维细网节块离散纵标方法(NDOM)的内迭代过程,替代节块展开方法(NEM)内迭代的径向求解过程.该算法充分考虑了核电厂反应堆堆芯的三维结构特点,另一方面,也充分利用了已经成熟的三维粗网节块展开方法(NEM)和二维离散纵标方法(SN)的研究成果,同时有效避免了利用离散纵标方法(SN)求解三维中子输运方程所面临的计算内存和计算时间的瓶颈问题.编制开发二维多群节块离散纵标方法(NDOM)模块程序NSNM和三维多群节块展开方法(NEM)模块程序MGNEM,并以此为基础编制开发节块内嵌SN方法的模块程序HANWIND;其中,NSNM为HANWIND求解两维问题的功能模块.针对OECD/NEA-2D C5G7MOX基准问题以及两环路核电厂三维堆芯的数值验算结果表明,节块内嵌SN方法的算法开发及程序编制有效、切实可行. 相似文献
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A numerical model for an electrohydrodynamic (EHD) grooved Flat Miniature Heat Pipe (FMHP) is developed. Two microchannel shapes are considered as axial capillary structures: square and triangle grooves. For both groove shapes, the electric field affects the liquid-vapor radius of curvature which decreases in the condenser and increases in the evaporator under the action of the electric field. The liquid and vapor velocities are also affected by the EHD effects. The electric field effects on the velocities depend on the FMHP zone. It is also demonstrated that the electric field increases the vapor pressure drop; however, it decreases the liquid pressure drop. The liquid-wall and vapor-wall viscous forces as well as the shear liquid-vapor forces are affected by the electric field. The analysis of the electric forces shows that the dielectrophoretic forces which act on the liquid-vapor interface are predominant and their order of magnitude is much higher than the Coulomb forces. Finally, it is also demonstrated that the capillary limit increases with the electric field for both groove shapes. 相似文献
19.
K. Gnanasekar K. Navaneethakrishnan 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,53(4):455-461
Spin-dependent Floquet scattering theory is developed to investigate the
photon-assisted spin-polarized electron transport through a semiconductor
heterostructure in the presence of an external electric field.
Spin-dependent Fano resonances and spin-polarized electron transport through
a laser irradiated time-periodic non-magnetic heterostructure in the
presence of Dresselhaus spin-orbit interaction and a gate-controlled Rashba
spin-orbit interaction are investigated. The electric field due to laser
along with the spin-orbit interactions help to get spin-dependent Fano
resonances in the conductance, whereas the external bias can be
appropriately adjusted to get a near 80% spin-polarized electron
transmission through heterostructures. The resultant nature of the Floquet
scattering depends on the relative strength of these two electric fields. 相似文献
20.
G. Stojmenovik S. Vermael F. Beunis K. Neyts A. R. M. Verschueren 《Opto-Electronics Review》2007,15(1):13-19
A new Monte Carlo algorithm for ion transport in two-dimensional anisotropic media is reported. It is based on physical considerations
of drift and diffusion in anisotropic media with or without an impermeable boundary. Inhomogeneities in the medium and electric
field can be taken into account by averaging along the ion trajectory. The algorithm has been applied to the calculation of
ion transport in liquid crystal displays and has been successfully compared with a finite difference program on a one-dimensional
liquid crystal structure. 相似文献