Application of improved equivalent edge currents in synthetic aperture radar imaging

Target modeling and scattering function calculating are important prerequisites and groundwork for the synthetic aperture radar（SAR） imaging simulation.According to the difficult problems that normal methods cannot calculate the scattering function of electrically large object under the condition to wideband,an effective method of improved equivalent edge currents is presented and applied to SAR imaging simulation for the first time.This method improves calculating velocity and has relatively high precision.The concrete steps of applying the method are given.By way of the simulation experiment,the effectiveness of the method is verified.

Research on Equivalent Modeling Method of AC-DC Power Networks Integrating with Renewable Energy Generation

Along with the increasing integration of renewable energy generation in AC-DC power networks,investigating the dynamic behaviors of this complex system with a proper equivalent model is significant.This paper presents an equivalent modeling method for the AC-DC power networks with doubly-fed induction generator(DFIG)based wind farms to decrease the simulation scale and computational burden.For the AC-DC power networks,the equivalent modeling strategy in accordance with the physical structure simplification is stated.Regarding the DFIG-based wind farms,the equivalent modeling based on the sequential identification of multi-machine parameters using the improved chaotic cuckoo search algorithm(ICCSA)is conducted.In light of the MATLAB simulation platform,a two-zone four-DC interconnected power grid with wind farms is built to check the efficacy of the proposed equivalentmodelingmethod.Fromthe simulation analyses and comparative validation in different algorithms and cases,the proposed method can precisely reflect the steady and dynamic performance of the demonstrated system under N-1 and N-2 fault scenarios,and it can efficiently achieve the parameter identification of the wind farms and fulfill the equivalent modeling.Consequently,the proposed approach’s effectiveness and suitability are confirmed.

An improved equivalent beam model of large periodic beam-like space truss structures

Space truss structures are essential components for space-based remote sensing loads with high spatial and temporal resolutions.To achieve high-precision vibration control,an accurate and efficient dynamics model is essential.In addition to the current equivalent beam model(EBM)based on the classical continuum theory,an improved equivalent beam model(IEBM)is proposed that considers the impact of the distinction between trusses and beams on torsional and shear deformations,as well as the impact of shear deformation on flexural rigidity.According to the displacement expressions of spatial beams,torsional,shear,and bending correction coefficients are introduced to derive expressions of strain energy and kinetic energy.The energy equivalence principle is then utilized to calculate the elasticity and inertia matrices,and dynamics equations are established using the finite element method.Subsequently,an IEBM is constructed by employing the particle swarm optimization approach to determine the correction coefficients with the truss natural frequency as the optimization target.The natural vibration characteristics of the structure are estimated for various material properties.Compared with the full-scale finite element model,the EBM reaches a maximum error of 80%for a low modulus of elasticity,while the maximum error of the IEBM is less than 2%for any given parameters,indicating its superior accuracy to the EBM.

采用改进等价极值法的钢网架动力可靠性分析

为比较动力作用下航站楼钢网架结构可靠性的空间分布差异,基于等价极值原理中的极值(P),推导并改进了以逼近极值(ΔPi)为特征变量的结构失效概率计算方程。结合某机场航站楼钢网架优化案例,数值模拟分析了指廊钢屋盖在不同有效峰值加速度(effective peak acceleration,简称EPA)作用下的结构可靠性变化规律,总结了改进等价极值法在预测结构失效时的优越性。结果表明:利用改进等价极值法得到的结构失效概率上下界曲线能准确表征不同EPA作用下结构失效的“三阶段”变化趋势,且计算阈值区间随EPA增加而收敛,并在EPA大于0.22 g时趋于0;在结构设计优化指标满足规范要求时,改进等价极值法既能有效预测其可靠性变化趋势又具有较高预测精度;指廊结构区段内的支座节点失效概率与整体失效概率接近,EPA小于0.295 g时误差不超过4%,可通过监测代表节点实现结构整体可靠度监测。

一种基于ISBO算法的锂离子电池等效电路模型辨识方法研究

锂离子电池等效电路模型的参数辨识方法对模型精度有较大的影响。针对缎蓝园丁鸟优化SBO(satin bowerbird optimization)算法收敛精度低和收敛速度慢的问题,提出一种改进的缎蓝园丁鸟优化ISBO(improved satin bowerbird optimization)算法。采用惯性权重、柯西变异、高斯变异和贪婪选择策略来提高ISBO算法的收敛精度,并利用标准测试函数对其收敛性能进行验证。结合电池充放电数据,将提出的ISBO算法用于锂离子电池等效电路模型的参数辨识。实验结果表明,与SBO和自适应权重粒子群优化算法相比,ISBO算法参数辨识精度较高且辨识精度不受电池工况的影响。

基于改进粒子群算法的分散式电采暖负荷模型参数辨识

分散式电采暖负荷是一种具有巨大调节潜力的需求响应资源,但是,用户行为差异、太阳辐照度等随机因素为建立精确的分散式电采暖负荷模型增加了一定难度。首先,结合具体应用场景,搭建基于气候模拟平台的分散式电采暖负荷实验平台,采集负荷建模实验数据。然后,针对分散式电采暖负荷二阶等效热参数模型方程较为复杂的问题,以仿真温度与实测温度之间的误差最小为目标,提出基于改进粒子群算法的模型参数辨识方法,建立分散式电采暖负荷模型。最后,通过改变数据采样周期,对负荷模型进行优化。结果表明,所提参数辨识及建模优化方法可以有效地提高分散式电采暖负荷二阶等效热参数模型精度。

强夯加固粉土地基的竖向附加动应力传递特性

强夯法在各类地基处理项目中得到了广泛应用,但其加固机理仍落后于实践,特别是强夯引起的地基内部竖向附加动应力传递特性。鉴于此,先基于Boussinesq应力解和动量定理推导强夯竖向附加动应力和附加剪应力拟静力解。然后,以新疆维吾尔自治区乌鲁木齐市机场北区扩建项目为工程背景,运用夯锤速度法,模拟1000~4000 kN·m能级间强夯引起的动力波传播过程、竖向附加动应力传递特性和夯后土体位移场。最后,将拟静力解与动力数值解的计算结果进行对比分析。研究结果表明:强夯引起的动力波传播呈半圆弧形,竖向附加动应力传递呈半椭圆形。动力波的传播距离决定了强夯影响范围,竖向附加动应力显著区边界决定了强夯有效加固区。由拟静力解得到的竖向附加动应力相比数值解沿深度方向的衰减更快。该研究结果可为强夯法地基处理工程提供重要参考。

基于土地利用变化的温州市生态系统服务价值评价

【目的】通过对温州市近20年间土地利用变化和生态系统服务价值的研究,掌握温州市的生态综合整治效果,为温州市的空间规划、生态综合保护与政策制定提供科学基础,助力温州市的城市发展。【方法】本研究基于2000、2010、2020年的土地利用数据,采用面积转移矩阵、土地利用动态度等方法对温州市2000—2020年土地利用的动态变化进行模拟分析,并基于改进的谢高地生态系统服务价值当量表,对研究时段内温州市的生态系统服务价值进行定量的分析。【结果】①温州市的林地面积最大,林地和水域面积均处于上升的态势,建设用地大幅扩张,周边耕地大幅减少;②2000—2020年,温州市的生态系统服务价值整体始终处于上升的趋势,其中林地的贡献度最为显著,占比超过80%;③在研究时段内,单项生态系统服务均表现为调节服务>支持服务>供给服务>文化服务。【结论】近20年间温州市的生态保护成效显著,生态环境得到了明显改善。

An improved model of Robinson equivalent circuit analytical model

The Robinson equivalent circuit analytical model can be used only in calculating shielding effectiveness of enclosure with the same multi-holes in one wall, but cannot be used in different multi-holes in two walls. According to the practical requirement, this article uses Konefal's and Farhana's characteristic impedance of apertures to improve the equivalent circuit analytical model in different multi-holes in two walls. The improved equivalent circuit analytical model is more useful than Robinson equivalent circuit analytical model. In the article, all kinds of enclosures are simulated by TLM (Transmission-Line Matrix method) to prove that this improved model is feasible in multimode.

Equivalent model of multi-type distributed generators under faults with fast-iterative calculation method based on improved PSO algorithm

There are various types of distributed generators (DGs) with different grid integration strategies. The transient characteristics of the fault currents provided by the DGs are different to those of conventional synchronous generators. In this paper, a distribution network with multi-type DGs is investigated, including consideration of DG low-voltage ride through (LVRT). The fault current characteristics of two typical DGs, i.e. an inverter-interfaced distributed generator (IIDG) and a doubly-fed induction generator (DFIG), are analyzed, considering the specific operation modes. Based on analysis of the fault characteristics, an equivalent model of the multi-type DGs under symmetrical/asymmetrical fault conditions is established. A fast-iterative fault calculation method for enhancing the calculation efficiency while avoiding local convergence is then proposed using an improved particle swarm optimization (PSO) algorithm. A simulation system of the distribution network with multi-type DGs is established in PSCAD/EMTDC. The simulation results validate the high accuracy and calculation efficiency of the proposed calculation method of the fault components. This can assist in the settings of the protection threshold.

Improved method to derive equivalent current systems from global MHD simulations

Derivation of equivalent current systems(ECS)from a global magnetospheric magnetohydrodynamics(MHD)model is very useful in studying magnetosphere-ionosphere coupling,ground induction effects,and space weather forecast.In this study we introduce an improved method to derive the ECS from a global MHD model,which takes account of the obliqueness of the magnetic field lines.By comparing the ECS derived from this improved method and the previous method,we find that the main characteristics of the ECS derived from the two methods are generally consistent with each other,but the eastward-westward component of the geomagnetic perturbation calculated from the ECS derived from the improved method is much stronger than that from the previous method.We then compare the geomagnetic perturbation as a function of the interplanetary magnetic field(IMF)clock angle calculated from the ECS derived from both methods with the observations.The comparison indicates that the improved method can improve the performance of the simulation.Furthermore,it is found that the incomplete counterbalance of the geomagnetic effect produced by the ionospheric poloidal current and field-aligned current(FAC)contributes to most of the eastward-westward component of geomagnetic perturbation.

An improved single-π equivalent circuit model for on-chip inductors in GaAs process

An improved single-π equivalent circuit model for on-chip inductors in the GaAs process is presented in this paper. Considering high order parasites, the model is established by comprising an improved skin effect branch and a substrate lateral coupling branch. The parameter extraction is based on an improved characteristic function approach and vector fitting method. The model has better simulation than the previous work over the measured data of 2.5r and 4.5r on-chip inductors in the GaAs process.

基于改进生态绿当量的城市绿色空间要素配置优化——以北京市中心城区为例

生态文明背景下的新型城镇化建设着重强调生态、高效的内涵式发展来实现经济-社会-生态效益的综合增长。以北京市中心城区为研究对象,基于改进生态绿当量进行现状绿色空间的量化评价,采用线性规划模型进行生态系统服务最大化目标下的要素结构调整,为各区域提供可行的实施建议。结果表明:(1)研究区内除西城区和石景山区满足生态绿当量要求外,其他区域均不满足。(2)采用线性规划模型进行优化调整后,东城区的生态绿当量满足要求,生态系统服务水平提高了4.23%;朝阳区、丰台区和海淀区生态绿当量分别提高到了0.77、0.73、0.90,生态系统服务水平分别提高了6.79%、10.49%和5.76%。(3)朝阳、海淀、丰台等区域优先完善自然山水要素,加强西部浅山区绿化、增补温榆河、永定河、清河、南沙河等滨河绿色空间,大力推进两道绿化隔离带增量提质建设;东城区着重改善大面积斑块形成生态源地。研究探究了高密度建设的中心城区绿色空间配置的量化方法和优化路径,为北京市中心城区高质量发展提供了科学参考。

基于改进混沌布谷鸟算法的风电场多机等值参数辨识方法

针对风电场的参数准确辨识问题,提出了一种基于改进混沌布谷鸟算法的风电场多机等值参数辨识方法。首先,阐述了风电场的系统结构与多机等值建模思路,设计了混沌布谷鸟算法的改进方案。然后,通过综合使用解析法与辨识法,建立了基于改进混沌布谷鸟算法的风电场多机等值参数依次辨识流程。最后,利用Matlab平台搭建了风电场多机等值仿真模型,比较了所提依次辨识方法与同时辨识方法在风电场参数辨识中的效果,分析了改进混沌布谷鸟算法与传统粒子群算法、布谷鸟算法的性能差异。结果表明:所提方法将风机参数辨识平均误差由11.07%降低至2.41%,提高了风电场动态特性拟合度,验证了其用于风电场多机等值参数辨识的有效性。

大电流弧爆激波的改进等离子炬聚束性能研究

具有高温高压特性的大电流弧爆激波,在材料加工与军工领域有着巨大的应用前景。为实现定向热冲击,需要对弧爆激波聚束,通过改进等离子炬,设计了一种聚束原型机。采用等效电弧爆炸的方法,利用Autodyn-2D和高精度多物质求解器Euler-2D对9组设计方案进行数值模拟,分析了原型机的聚束管、管仰角和电极距离等对弧爆激波聚束性能的影响规律。研究结果表明:等离子炬通过加装聚束管改进后,能将弧爆激波射流速度与压强峰值分别提升300%、500%;管仰角γ对出口出处射流速度有很大的影响;弧倾角λ为45°时,聚束波的速度和能量最大;电极距离主要影响弧爆激波速度和压强的变化率。

面向不同电流工况的锂离子电池改进EECM研究

锂离子电池是新能源汽车动力系统的核心,基于模型的电池管理系统(battery management system,BMS)是保证电池性能充分发挥的关键。然而现有BMS主要采用等效电路模型(equivalent circuit model,ECM),尚未考虑放电倍率对可用容量的影响机制,导致模型在不同放电倍率下以及低荷电状态(state of charge,SOC)区域会存在明显的端电压仿真误差,影响算法精度;尤其是BMS无法准确估计电池放电截止条件,剩余放电电量(remaining discharge capacity,RDC)估计误差大,可能导致电池电压骤降甚至整车抛锚等严重后果。针对以上问题,文中以考虑内部扩散机制的扩展等效电路模型(extended equivalent circuit model,EECM)为基础,对不同倍率的放电电压容量增量(incremental capacity,IC)曲线进行对比分析,利用能斯特方程构造不同放电倍率下的容量-开路电压曲线,提出改进的EECM。所提改进EECM在不同电流倍率和动态工况下的端电压仿真误差均小于传统ECM和EECM,可以提高RDC估计的准确性,有应用于实际BMS的潜力。

智能网联混合动力汽车分层式节能优化控制

针对智能网联环境下混合动力汽车的能量优化控制,提出一种基于智能网联分层式能量管理策略。为减少红灯停车次数并降低制动能量损失,提出了上层控制器的预减速滑动控制以求解初始目标车速范围,进而采用PSO算法优化寻优,求解最优目标车速序列;为提高能量管理实时性,提出了下层控制器的基于逻辑门限规则改进等效燃油消耗最小策略。MATLAB与CRUISE的联合仿真结果表明,所提出的分层控制策略可避免车辆碰撞、闯红灯,并有效减少红灯停车次数,提高燃油经济性。在城市道路限速条件下,采用相同下层控制算法,上层控制算法较交通信号灯正时(SPAT)算法降低8.4%等效燃油消耗;采用相同上层控制算法,下层控制算法有着与等效燃油消耗最小策略(ECMS)相近的燃油经济性,但分层控制总计算时间成本降低21.7%。

双参数优化的混合动力汽车能量管理策略研究

为了挖掘新型功率分流式混合动力汽车能量管理策略的节能潜力,设计了一种双参数优化的等效油耗最低策略(AD-ECMS)。首先,提出并验证了发动机起停规则对整车经济性的影响。基于此,优化出一种改进型粒子群算法(ISPSO),根据对等效油耗和电量的实时跟踪,实现对最优等效因子及发动机起停规则的双参数求解。随后,提出了一种双参数优化的等效油耗最低策略,利用模糊控制器识别当前工况特征,通过在线更新等效因子和发动机起停规则,实现经济性能量管理。最后,与ECMS策略、A-ECMS策略进行仿真对比及实验验证,结果表明:AD-ECMS策略在整车经济性和电量平衡性上,都具备更好的控制效果。

艉轴承刚度等效形式对轴系横向振动特性的影响

[目的]由于船舶艉轴承的长径比较大,将其简化为传统的单点支撑等效模型难以反映出轴承的实际运行情况,因此有必要探讨艉轴承等效形式对轴系横向振动特性的影响。[方法]首先,基于能量原理,引入改进傅里叶级数方法描述推进轴系的横向振动位移,构建可用于单点、多点和连续分布式支撑的多种等效形式的推进轴系横向振动特性计算模型;然后,分别分析由液膜压力等效的支撑刚度变化对轴系横向振动特性以及螺旋桨激励对轴系振动响应的影响;最后,与文献和采用有限元方法(FEM)计算的结果进行对比,验证所提模型的正确性。[结果]结果显示,多点支撑的计算结果收敛于连续分布式支撑计算结果,螺旋桨激励下轴系响应受转速影响。[结论]研究表明,可采用三点支撑等效形式研究液膜压力分布对推进轴系横向振动特性的影响,所构建的计算模型收敛性好、计算精度高、代价低。