Space vector modulation strategy for an eight-switch three-phase NPC converter

A three-phase neutral point clamped (NPC) converter is presented for power factor correction and dc-link voltage regulation. A simplified space vector pulsewidth modulation scheme (SVPWM) is adopted to track line current commands. Using a simplified SVPWM algorithm, the calculated time for the time duration of voltage vector is reduced. The adopted NPC converter has less power switches compared with the conventional three-level NPC converter. Only eight power switches and four clamping diodes with voltage stress of half the dc bus voltage are used in the circuit configuration. Based on the proposed control algorithm, a reference voltage vector is generated on the ac terminal for drawing the sinusoidal line currents with unity power factor. Computer simulation and experimental results based on a laboratory prototype are presented to verify the validity and effectiveness of the proposed control strategy.     

Simplified procedure for controlling pressure distribution of a scramjet combustor

Scramjet engines are used at extreme temperatures and velocity. New control problems involving distributed parameter control have been found concerning investigations of the control of scramjet engines whose physical states are spatially interacted. Succeeding the existing theoretical studies on the distributed parameter control for scramjet engines, this paper puts forward a simplified distributed parameter control approach for scramjet engines aimed at engineering application. The simplified control procedure uses the classical proportional-integral（PI） compensation to control the target pressure distribution of scramjet engines, which is effective and applicable for practical implements. Simulation results show the validation of the simplified distributed parameter control procedure.     

简化微小液滴在超声速气流横向喷射中的运动探索

从研究超声速气流中简化液滴(刚性小球)的气动力着手,比较分析使用CFD方法与使用两相流理论中已有的颗粒阻力系数模型得到的简化液滴气动力结果,得出Charles B.Henderson给出的阻力系数经验关系式适用于计算简化液滴在超声速气流中的运动。进一步,对不同直径简化液滴的运动开展工程方法的计算。在来流Ma=2.7的二维平板超声速流场中选取一个截面,作为气相流场,结果显示:(1)简化液滴与主气流存在相对超声速运动,当简化液滴直径dk≤0.12mm时,纵向相对超声速运动区域约为0.15m~0.4m,当dk0.12mm时,作用区域明显增大;(2)以10m/s喷射出的简化液滴,其横向穿透深度与纵向运动距离比约为0.004m/1m~0.021m/1m;(3)以100m/s的速度喷射出的30~120μm直径简化液滴,其横向穿透深度与纵向运动距离比约为0.02m/1m~0.055m/1m,实际过程中,小尺寸简化液滴的汽化很快,其穿透深度很小。     

耦合多螺旋桨滑流影响的低雷诺数机翼设计

以某型手抛式太阳能无人机(UAV)模型为对象进行考虑多螺旋桨滑流影响的低雷诺数机翼平面形状设计研究。首先,基于升力面理论发展了准定常求解多螺旋桨/机翼相互气动干扰问题的涡格法(VLM)程序,并采用建立参考翼型气动特性数据库的形式发展了相关低雷诺数修正(LRC)方法;然后,通过对翼型、低雷诺数机翼及单螺旋桨/机翼算例的数值模拟及与相关实验结果的对比,验证了本文数值方法具备模拟低雷诺数复杂流动问题的可靠性及准确性;最后,对某型手抛式太阳能无人机简化拉力多螺旋桨/机翼模型进行了直接优化设计及反设计,并通过具有较高精度的CFD准定常求解技术对优化结果进行了验证。结果表明:以CFD方法计算结果为参考,本文涡格法程序及低雷诺数修正方法能够准确高效地计算相关低雷诺数复杂流动问题;传统未考虑多螺旋桨滑流影响的设计机翼在实际螺旋桨工作状态下将偏离设计点,机翼气动特性得不到提高;考虑螺旋桨滑流影响的优化设计方法能够有效改善机翼阻力特性,相对应地,在设计状态下优化机翼总阻力能够降低19.52counts。     

脉冲耦合神经网络在图像分割中的应用研究

系统研究了脉冲耦合神经网络在图像分割中的应用。首先研究了标准PCNN和简化的PCNN模型在图像分割中的应用,对分割结果进行了比较分析,结果表明,两种PCNN模型都能得到较好的分割结果。其次研究了最大熵、最小交叉熵和区域特征一致性准则在PCNN最优分割结果确定中的应用。最后探讨了PCNN参数变化对图像分割结果的影响,并给出了仿真试验结果。     

液体火箭发动机喷管简化建模及模型修正

为了准确掌握喷管的动力学特性,提出了一种等效简化建模结合试验数据的模型修正方法。首先,将喷管的原始几何模型经过几何处理成简化模型,建立了喷管的有限元模型,对有限元模型在自由条件下进行模态计算,将得到的计算数据与测试数据对比分析,再利用测试数据对有限元模型的弹性模量参数进行修正,修正后的喷管有限元模型前9阶模态计算结果与测试结果频差在5%以内,MAC值(模态置信准则)在0.8以上。表明此方法是一种高效可行的喷管简化建模方法,既保证了精度又提高了计算效率,对其动力学特性分析、振动响应预测等方面具有重要应用价值,对于液体火箭发动机其他部件的动力学建模及分析也具有普适性。     

战斗机综合设计仿真系统中的飞控系统模型

通过分析飞控系统各环节对飞机动态特性的影响及第三代战斗机控制律的特点,为战斗机综合设计仿真系统建立了飞控系统模型。该模型是能够反映飞控系统功能的简化模型。通过对飞控系统各项功能与特点的检验,对飞控系统简化模型进行了验证。验证结果表明,所建立的简化飞控系统模型能够满足战斗机综合设计仿真系统的需要。     

反射面天线的双站雷达截面

 本文导出了任意旋转反射器天线在任意双站角的散射场和雷达截面(RCS),其中反射场由几何光学法(GO)求得,绕射场则利用基于物理绕射理论(PTD)与等效线电流辐射积分公式导出的等效电磁流法求得。分别计算了轴向入射和偏轴向入射时在任意散射方向上水平极化与垂直极化两种情况下的双站RCS,并给出了这些结果的立体图形式。方法简化为单站情况时的计算结果与实验值大致相符。     

Finite data performance of MUSIC and minimum norm methods

In the direction of arrival (DOA) estimation problem, we encounter both finite data and insufficient knowledge of array characterization. It is therefore important to study how subspace-based methods perform in such conditions. We analyze the finite data performance of the multiple signal classification (MUSIC) and minimum norm (min. norm) methods in the presence of sensor gain and phase errors, and derive expressions for the mean square error (MSE) in the DOA estimates. These expressions are first derived assuming an arbitrary array and then simplified for the special case of an uniform linear array with isotropic sensors. When they are further simplified for the case of finite data only and sensor errors only, they reduce to the recent results given previously (1989, 1991). Computer simulations are used to verify the closeness between the predicted and simulated values of the MSE     

Detection of Changes in the Characteristics of a Gauss-Markov Process

By an extension to the theory of sequential detection with dependent measurements, it is possible to develop a sequential probability ratio test (SPRT) to detect changes in regime in a Gauss-Markov process rather than detecting which of the two regimes exists. It is shown how a posterior form of this extended SPRT may be simplified to reduce computational complexity. The simplified SPRT's are in fact modifications of the original SPRT detecting the regime and not the change. The tests are applied to the problem of fault detection in a gyro navigational system; the results of a detailed computer simulation are given.     

Simulation of unsteady combustion in a LOX-GH2 fueled rocket engine

This paper presents results from an investigation of unsteady combustion inside a small-scale, multi-injector liquid rocket engine. A time-accurate approach in an axisymmetric geometry is employed to capture the unsteady flow features, as well as the unsteady heat transfer to the walls of the combustion chamber. Both thermally perfect gas (TPG) and real gas (RG) formulations are evaluated for this LOX-GH₂ system. The Peng–Robinson cubic equation of state (EoS) is used to account for real gas effects associated with the injection of oxygen. Realistic transport properties are computed but simplified chemistry is used in order to achieve a reasonable turnaround time. Results show the importance of the unsteady dynamics of the flow, especially the interaction between the different injectors. The RG EoS, despite a limited zone of influence, is shown to govern the overall chamber behavior. The sensitivity of the results to changes in the system parameters is studied and some general trends are discussed. Although several features of the simulations agree well with past experimental observations, prediction of heat flux using a simplified flux boundary condition is not completely satisfactory. Reasons for this discrepancy are discussed in the context of the current axisymmetric approach.     

RP-3航空煤油三组分替代燃料简化机理验证

利用机理自动简化程序ReaxRed对航空煤油RP-3三组分替代燃料半详细化学反应动力学模型采用两种方案分别进行了简化。方案一采用直接关系图（directed relation graph,DRG）法构建了109组分423步基元反应,方案二在方案一的结果上采用基于误差传播的DRG（directed relation graph based on error propagation,DRGEP）方法和计算奇异摄动（computational singular perturbation,CSP）法构建了84组分271步基元反应。结合点火延迟试验数据对方案二所构建的简化机理进行了验证,并且采用层流火焰速度、温度和重要产物等方面的数值计算结果进行对比分析,结果表明:方案二所构建的简化机理在简化过程中保留一定的计算精度前提下更加经济实用,其中在各种工况下方案二简化机理和半详细机理的点火延迟时间之间的平均误差在6%以内并且它们在火焰传播速度方面平均误差在不超过8%。采用本生灯预混燃烧器为物理模型,以RP-3航空煤油为燃料,进行相应的试验研究来验证方案二的简化机理,结果表明该简化机理数值计算结果与试验数据较吻合。      

ROBUST ADAPTIVE BANK-TO-TURN MISSILE AUTOPILOT DESIGN USING FUZZY CMAC NEURAL NETWORKS

ＲＯＢＵＳＴＡＤＡＰＴＩＶＥＢＡＮＫ┐ＴＯ┐ＴＵＲＮＭＩＳＳＩＬＥＡＵＴＯＰＩＬＯＴＤＥＳＩＧＮＵＳＩＮＧＦＵＺＺＹＣＭＡＣＮＥＵＲＡＬＮＥＴＷＯＲＫＳＺｈａｎｇＹｏｕａｎ（张友安）,ＣｕｉＰｉｎｇｙｕａｎ（崔平远）,ＷａｎｇＳｈｏｕｂｉｎｇ（王守斌...     

初始疲劳质量的一种简化模型

提出描述结构细节初始疲劳质量的简化模型。此模型只需一种应力水平下的耐久性试验结果和细节Ｓ－Ｎ曲线之指数值ｍ,即可描述初始疲劳质量,进行耐久性分析。用一套耐久性试验数据验证了简化简模型的可用性。最后,还给出了由裂纹尺寸和裂纹超过数概率定义的Ｓ－ｔ关系,使结构耐久性分析简单易行。     

超声速气流中简化微小液滴横向喷射的汽化过程探索

为研究超声速气流中简化液滴的汽化过程问题,本文分析了两相流计算中已有的两相传热模型,并对简化液滴绕流开展数值计算.在来流Ma≤0.6的条件下,数值计算得到的简化液滴-气流之间的传热速率与已有模型得到的结果相一致,而在来流Ma≥0.9的条件下,数值计算得到的简化液滴-气流之间的传热速率与已有模型得到的结果存在很大偏差.由此建立了考虑简化液滴与气流相对超声速相互作用的两相传热模型.进一步,采用Charles B.Henderson阻力系数关系式与新建立的传热模型,对不同直径简化液滴的运动与汽化开展工程计算.在来流2.7Ma的二维平板超声速流场中选取一个截面,作为气相流场,结果显示,(1)简化液滴与主气流存在相对超声速作用.当简化液滴直径dk≤0.12mm时,作用区域约为0.1m～0.4m,当dk>0.12mm时,作用区域明显增大,(2)简化液滴的穿透尺度不超过0.011m/m(深度/长度),时间尺度约为0.28ms～3ms,(3)简化液滴完成汽化的空间尺度约为0.1m(dk>=0.03mm)、0.45m(dk>=0.05mm)与1.24m(dk>=0.075mm),而当dk>0.09mm时,简化液滴完成汽化的空间尺度则大于1.9m.使用考虑简化液滴与气流相对超声速相互作用的两相传热模型与使用传统的传热模型对简化液滴的运动轨迹没有影响,而对简化液滴的汽化过程有较大影响.     

永磁同步电机有限控制集模型预测转矩控制系统研究

建立了基于定子磁链xy坐标系的永磁同步电机(PMSM)有限控制集模型预测转矩控制(FCSMPTC)系统,仿真验证了系统的有效性和可行性。针对磁链和转矩预测模型较为复杂的问题,提出了磁链和转矩的简化预测模型。理论分析、仿真和试验结果验证了FCSMPTC的简化模型与常规模型控制效果相当,可明显减小计算负担,提高系统实时性能。将电压矢量幅值和角度作为FCSMPTC的控制变量,设计了变幅值变角度的备选电压矢量集合。仿真结果表明该备选电压矢量集合可有效减小稳态转矩脉动,但动态性能不及传统备选电压矢量集合。基于不同备选电压矢量的特点,提出了根据系统状态自适应动态变化的备选电压矢量策略。仿真结果表明,该控制策略在静动态下均可取得良好的控制性能。     

与空时二维自适应滤波兼容的单脉冲测角新方法

针对机载相控阵雷达系统提出了一种空时二维自适应单脉冲测角方法 ,当存在阵元和通道幅相误差时它仍具有较高的测角精度。还给出了一种稳健的自适应和、差波束增益归一化方法 ,并讨论了所提方法的简化兼容实现方案。最后给出了基于高保真雷达杂波模拟数据的仿真实验结果     

套齿连接转子简化建模及动力特性分析

在进行转子和整机计算时建立套齿结构接触模型会增加计算量，降低计算效率，直接将套齿结构省略又无法体现其刚 度特性变化对转子动力特性的影响。针对该问题，基于航空发动机单圆柱面套齿连接的结构和力学特征，建立了考虑构件间界面 接触状态的力学特征分析模型，提出了考虑套齿结构刚度随参数变化的简化建模方法，并与套齿接触模型进行了对比分析。建立 了单圆柱面套齿连接结构转子简化模型，开展了相应的转子动力特性试验，对比分析了拧紧力矩对转子模态频率的影响。结果表 明：转子简化模型与试验模型最大计算误差小于5%，证明套齿结构简化建模方法具有较高的可靠性和准确性，可为工程实践中高 效开展含套齿结构转子及整机动力学准确计算分析提供方法与参考。     

Robust sliding-mode control for the uncertain MIMO aircraft model F-18

Robust flight control laws based on variable structure control (VSC) theory and Lyapunov V-function method are designed for a simplified aircraft model F-18. A min-max control (MMC) and VSC laws are derived, for multi-input multi-output (MIMO) systems with plant uncertainties and input disturbance. Two types of robust feedback controllers MMC and VSC for uncertain MIMO systems are considered. For both cases the existence conditions of a stable sliding mode and the robust asymptotic stability in uncertain MIMO systems by MMC and VSC are investigated. For the design of an MMC and VSC, measurable states and sliding surface are chosen so that the zero dynamics of the system are stable. An application of tracking and positioning of VSC of longitudinal dynamics is presented. Finally, simulation results are presented to show the effectiveness of the design methods.     

Loopy belief propagation based data association for extended target tracking

The data association problem of multiple extended target tracking is very challenging because each target may generate multiple measurements. Recently, the belief propagation based multiple target tracking algorithms with high efficiency have been a research focus. Different from the belief propagation based Extended Target tracking based on Belief Propagation (ET-BP) algorithm proposed in our previous work, a new graphical model formulation of data association for multiple extended target tracking is proposed in this paper. The proposed formulation can be solved by the Loopy Belief Propagation (LBP) algorithm. Furthermore, the simplified measurement set in the ET-BP algorithm is modified to improve tracking accuracy. Finally, experiment results show that the proposed algorithm has better performance than the ET-BP and joint probabilistic data association based on the simplified measurement set algorithms in terms of accuracy and efficiency. Additionally, the convergence of the proposed algorithm is verified in the simulations.