A simple algorithm to improve the performance of the WENO scheme on non-uniform grids

This paper presents a simple approach for improving the performance of the weighted essentially nonoscillatory(WENO) finite volume scheme on non-uniform grids. This technique relies on the reformulation of the fifthorder WENO-JS(WENO scheme presented by Jiang and Shu in J. Comput. Phys. 126:202–228, 1995) scheme designed on uniform grids in terms of one cell-averaged value and its left and/or right interfacial values of the dependent variable.The effect of grid non-uniformity is taken into consideration by a proper interpolation of the interfacial values. On nonuniform grids, the proposed scheme is much more accurate than the original WENO-JS scheme, which was designed for uniform grids. When the grid is uniform, the resulting scheme reduces to the original WENO-JS scheme. In the meantime,the proposed scheme is computationally much more efficient than the fifth-order WENO scheme designed specifically for the non-uniform grids. A number of numerical test cases are simulated to verify the performance of the present scheme.

Control Strategy of DC Link Voltage Flywheel Energy Storage for Non Grid Connected Wind Turbines Based on Fuzzy Control

The large-scale development of wind power is an important means to reduce greenhouse gas emissions, alleviate environmental pollution and improve the utilization rate of renewable energy. At the same time, large-scale non grid connected wind power generation theory avoids the technical difficulties of wind power integration [1]. However, due to the randomness and uncontrollability of wind energy, the output power of the wind power generation system will fluctuate accordingly [2]. Therefore, the corresponding energy storage devices are arranged in the non-grid-connected wind power generation system to ensure the power quality, and it has become the key to full utilization of renewable energy. In the case of wind speed fluctuation, the DC bus control strategy of the wind turbine is proposed in this paper. It can reduce the impact on the unit converter and the power load;this ensures safe and stable operation of non-grid connected wind turbines.

Partition of Unity for a Class of Nonlinear Parabolic Equation on Overlapping Non-Matching Grids

A class of nonlinear parabolic equation on a polygonal domain Ω R2 is inves- tigated in this paper. We introduce a finite element method on overlapping non-matching grids for the nonlinear parabolic equation based on the partition of unity method. We give the construction and convergence analysis for the semi-discrete and the fully discrete finite element methods. Moreover, we prove that the error of the discrete variational problem has good approximation properties. Our results are valid for any spatial dimensions. A numerical example to illustrate the theoretical results is also given.

SEISMIC PROPAGATION SIMULATION IN COMPLEX MEDIA WITH NON-RECTANGULAR IRREGULAR-GRID FINITE-DIFFERENCE

This paper presents a finite-difference(FD)method with spatially non-rectangular irregular grids to simulate the elastic wave propagation.Staggered irregular grid finite difference oper- ators with a second-order time and spatial accuracy are used to approximate the velocity-stress elastic wave equations.This method is very simple and the cost of computing time is not much.Complicated geometries like curved thin layers,cased borehole and nonplanar interfaces may be treated with non- rectangular irregular grids in a more flexible way.Unlike the multi-grid scheme,this method requires no interpolation between the fine and coarse grids and all grids are computed at the same spatial iteration.Compared with the rectangular irregular grid FD,the spurious diffractions from'staircase' interfaces can easily be eliminated without using finer grids.Dispersion and stability conditions of the proposed method can be established in a similar form as for the rectangular irregular grid scheme.The Higdon's absorbing boundary condition is adopted to eliminate boundary reflections.Numerical simu- lations show that this method has satisfactory stability and accuracy in simulating wave propagation near rough solid-fluid interfaces.The computation costs are less than those using a regular grid and rectangular grid FD method.

Finite difference calculation of traveltime on non-orthogonal grid

Finite difference methods have been widely employed in solving the eikonal equation so as to calculate traveltime of seismic phase. Most previous studies used regular orthogonal grid. However, much denser grid is required to sample the interfaces that are undulating in depth direction, such as the Moho and the 660 km discontinuity.Here we propose a new finite difference algorithm to solve the eikonal equation on non-orthogonal grid（irregular grid）.To demonstrate its efficiency and accuracy, a test was conducted with a two-layer model. The test result suggests that the similar accuracy of a regular grid with ten times grids could achieve with our new algorithm, but the time cost is only about 0.1 times. A spherical earth model with an undulant660 km discontinuity was constructed to demonstrate the potential application of our new method. In that case, the traveltime curve fluctuation corresponds to topography. Our new algorithm is efficient in solving the first arrival times of waves associated with undulant interfaces.

Pseudoelastic effect in autoparametric non-ideal vibrating system with SMA spring

In this paper a three degrees of freedom autoparametric system with limited power supply is investigated numerically. The system consists of the body, which is hung on a spring and a damper, and two pendulums connected by shape memory alloy （SMA） spring. Shape memory alloys have ability to change their material properties with temperature. A polynomial constitutive model is assumed to describe the behavior of the SMA spring. The non-ideal source of power adds one degree of freedom, so the system has four degrees of freedom. The equations of motion have been solved numerically and pseudoelastic effects associated with the martensitic phase transformation are studied. It is shown that in this type system one mode of vibrations might excite or damp another mode, and that except different kinds of periodic vibrations there may also appear chaotic vibrations. For the identification of the responses of the system＇s various techniques, including chaos techniques such as bifurcation diagrams and time histories, power spectral densities, Poincare maps and exponents of Lyapunov may be used.

Non-linear Maps on Borel Subalgebras of Simple Lie Algebras Preserving Abelin Ideals

Let g be a complex simple Lie algebra of rank ι, b the standard Borel subalgebra. An invertible map on Ь is said to preserve abelian ideals if it maps each abelian ideal to some such ideal of the same dimension. In this article, by using some results of Chevalley groups, the theory of root systems and root space decomposition, the author gives an explicit description on such maps of Ь.

Solving Schrodinger Equation with Non-Uniform Grids by Scale Transformation Method

A new scale transformation method is used in solving the Schrodinger equation. With it, the uniform grids in the discretization in conventional metho d are changed into non-uniform grids. Consequently, in some cases, the computing quantity will be greatly reduced at keeping the required accuracy. The calcul ation of the quantized inversion layer in MOS structure is used to demonstrate t he efficiency of the new method.

Confinement Effect and Diameter Effect on the Non-ideal Detonation Parameters of Small Charge

An expanding model of the confinement of non-ideal detonation of small charge is established on the basis of the nozzle theory.Making use of the expanding model,the analytic relationship of small charge detonation velocity and the semi-empirical relationship of detonation pressure that both change with charge diameter and confinement condition are established.The detonation velocity and pressure of small charges are calculated and experimentally verified,and the detonation velocity deviation is less than 7% while the detonation pressure deviation is less than 9%.

Investigation of Shock Waves in Non-Ideal Gas under the Action of Magnetic Field

In present paper, certain aspect of shock wave in non-ideal gas, when magnetic field is orthogonal to the trajectories of the gas particles and electrical conductivity is taken to be infinite, is investigated. Considering one-dimensional unsteady non-planer motion, basic equations, its general solution and formation of shock-wave, conservation laws and jumps conditions, variation of area of non-uniform cross section and analytical solution of strong non planer shock is obtained.

Frequency-Concentration Dependence of Optical Activity of a Non-Ideal 1D-Superlattice

In the present work the widths of layers constituting the non-ideal superlattice are much bigger then the characteristic scales of space dispersion. In such a case the contribution of individual layers to gyrotropy can be regarded as independed. Thus the corresponding optical quantities can be expressed through the layers’ gyrotropic characteristics. This approach is applied to calculate the specific rotation angle of plane of polarization of light propagating through a nonideal 1D-superlattice, which varies in composition as well as in layers’ width. We carry out numerical calculation of the frequency dispersion of optical activity of a non-ideal superlattice, which includes impurity layers with point defects.

计及经济性和低碳性的光储充一体化电站多目标优化配置

为充分挖掘光储充一体化电站经济效益及碳减排效益,实现站内组成单元合理配置,文中提出一种计及经济性和低碳性的光储充一体化电站多目标优化配置方法。首先,根据充电站内各模块的功能及需求,探究光储充电站中碳排放的来源,建立站内各模块成本、碳排放的数学模型。然后,以系统年投资运行成本和碳排放量最小为目标,使用基于三黑洞捕获策略的多目标粒子群算法,对不同负荷场景下电站各组成模块进行优化配置,得出各场景下电站各组成模块的最优配置方案。对比结果表明,文中所提方法可有效降低规划运行时的成本和碳排放量,提高电站经济及环境效益。最后,采用逼近理想解排序法得出最优场景下的折衷优化方案,可为当前光储充一体化电站的投资建设提供参考。

非均匀格网下的耕地集中连片等级划分方法

耕地细碎化导致农业生产成本高、效率低,为了提高耕地利用效率,需实现耕地集中式管理。针对均匀网格在对耕地面积进行表达时数据量冗余和格网尺度选择问题,本文提出了根据斑块平均面积和面积表达误差确定格网最适宜起始和终止尺度的方法,构建基于四叉树的非均匀格网,建立了耕地集中连片分析规则、评价指标体系和技术流程,实现非均匀格网下的耕地集中连片等级划分。以江苏省徐州市为试验区开展耕地集中连片分析。结果表明:①与均匀网格相比,非均匀格网减少了43.8%数据冗余,实现了耕地面积最小误差表达,适用性更强。②徐州耕地连片区域占耕地总面积88.6%,其中50%耕地集中连片等级处于中等偏上水平。③连片区域中有21.4%耕地集中连片等级处于中等以下水平,应将其作为提高区域整体连片等级优先优化的耕地。

电网电压跌落下基于二分迭代和NITA法的同步调相机全域瞬态流热分析

同步调相机安装在特高压输电系统换流站内用于稳定输电系统的电压,输电系统可能发生电压跌落故障决定其需要具备工作在极限运行状态的能力。温升是制约调相机极限调节能力的重要因素之一,因此,对同步调相机极限运行时的瞬态流热分析非常必要。该文建立调相机与输电系统耦合的暂态分析模型,研究电网电压跌落时调相机的瞬态响应特性。为综合评价电网电压跌落故障对调相机热表征的影响,建立300 Mvar同步调相机全域内流固耦合瞬态分析模型;提出一种二分迭代的流固耦合模型边界确定方法,通过数以亿计的多面体网格离散(共1.4亿网格单元),同时,基于非迭代时间推进法对全域复杂传热模型进行求解,研究调相机多风腔内流体和温度相互影响机理;探讨极限运行状态下温度约束对调相机安全运行的影响。为对该文所提研究方法进行验证,开展调相机总装温升实验,证明其可行性与准确性。

非均匀网格有限差分法大地电磁测深法正演模拟

为解决有限差分法大地电磁正演模拟中模拟精度与计算效率之间的矛盾,采用非均匀网格有限差分进行了大地电磁响应计算。基于二维大地电磁方程,推导出非均匀网格剖分下的TM极化模式的大地电磁方程的差分格式。通过均匀半空间模型和低阻异常体模型的正演模拟,验证了非均匀网格差分法的正确性,非均匀网格差分法可以准确反映出复杂模型的大地电磁响应特征,识别异常体分布范围。

复杂大电网非预设性运行工况下的继电保护动作适应性仿真分析

非预设性运行工况下的突发事件多,导致继电保护逻辑的适应性较差,不合理区域较多,为此,进行复杂大电网非预设性运行工况下继电保护动作适应性仿真分析。分析历史常规故障,标记故障点最常发生位置,构建零序、负序方向元件模型、距离元件模型、纵联电流差动元件模型,观察复杂大电网非预设性运行工况下的电网参数变化情况,第一时间掌握电网的耦合性,不断选择电网所需的继电保护动作逻辑,确认继电保护动作适应性。仿真实验表明,将故障点设置在保护区域内和区域外,继电保护动作能够根据故障选择不同保护模型进行故障母线切除或者保护不动作,适应性好。

基于组合基元法的非理想模型装配偏差预测算法研究

基于模型定义(model-based definition,MBD)体系的装配偏差算法适用于赛博空间中理想数模的装配场景,但不适用于物理空间中非理想状态的装配场景,导致现场产生大量修配工作。针对这一问题,文章模拟真实的装配场景,基于零件的非理想状态,并将配合特征之间的拓扑关系考虑在内,对装配偏差的传递与累积过程展开研究,给出一种装配偏差预测算法。首先,针对孔轴配合与槽轴配合,将装配约束转化为定位点约束,依据最大实体原则,构造柱面点云的最小包围圆,确定接触状态,给出串行装配偏差算法,并将以上两种配合定义为两种基元,对应的装配偏差算法定义为两种独立基元算法。其次,基于平面贴合、孔轴配合与槽轴配合给出并行装配偏差算法,并将其定义为组合基元算法。最后,基于非理想模拟数据进行实例验证,达到了准确预测装配偏差的目标,为后续在赛博空间基于实测数据的装配偏差计算提供理论依据,以促进高精度装配。

基于MMC闭锁与负直流电压无闭锁的综合直流故障限流策略

基于模块化多电平换流器(MMC)的柔性直流电网存在抗直流故障扰动能力弱的问题。为此,在无闭锁和闭锁限流的基础上,提出了一种适用于柔性直流电网的无闭锁与闭锁的综合直流故障限流策略。故障发生后,各换流站首先根据直流侧出口电流进行基于负直流电压控制的无闭锁限流,若某换流站由于无闭锁降压限流失效而发生过流,则主动将该换流站闭锁。故障消失或隔离后,无闭锁换流站第一时间恢复正常工作模式,而无须等待重启过程较长的闭锁换流站,以尽量减小系统功率损失。基于MATLAB/Simulink的仿真结果表明,所提综合直流故障限流策略可快速阻断故障电流,并兼顾限流过程的安全性和快速性,最大限度保证系统功率传输,提高了直流电网的抗故障扰动能力。

我国电网智能安全技术的关键专利分析

新安全格局下,为促进电网安全管理由传统模式向安全生产全过程数字化、信息化、智能化模式的转变,基于2008—2023年我国电网智能安全专利数据,采用网络中心度分析和主路径分析等方法,描绘专利地图;提取关键专利技术子群,并系统分析电网智能安全的技术发展情况、技术发展重点;基于专利地图和专家意见,运用熵权-优劣解距离法(TOPSIS),就我国既有智能安全技术社群对电网安全智能化的支撑度进行评价。结果表明:我国电网智能安全技术已形成11类关键技术社群,其中,电网智能安全过程技术是最丰富的知识群组。11类电网智能安全技术社群中,对电网智能安全支撑度较高的技术是智能控制技术、智能调度技术和网络通信安全技术。智能安全技术对电网传统安全目标中的安全管控能力和安全稳定能力有较好的支撑度,并对电网的现代安全目标中的安全治理能力和主动安全能力有较好的支撑度,但对安全韧性能力的支撑度不高。

NFTSM控制的光伏并网系统低压穿越控制策略

针对现有PI与ISMC控制下光伏并网系统LVRT过程响应速度慢、不对称故障时控制效果较差或抖振效果明显等问题,提出一种NFTSM控制的LVRT控制策略。考虑光伏并网系统外部条件多变的特性,采用双指数滑模超平面与控制率,选取指数趋近律加速趋近速率,构造出具有调节有功、无功输出的非奇异快速滑模控制器,并验证其稳定与收敛性,简单且有效地实现了光伏并网LVRT。Matlab/Simulink仿真结果表明,NFTSM控制的光伏并网LVRT具有收敛速度快、谐波含量低、抗外界干扰与抖振抑制能力强等优点。