Evolution of domain structure and frequency effect on ferroelectric properties in BIT ferroelectrics

Based on the time-dependent Ginzburg-Landau(TDGL) equation,the temporal evolution of the domain structure and hysteresis loops of polarization versus electric field were simulated by a phase-field model for Bi4Ti3O12(BIT) ferroelectric single crystal under an applied electric field. In the static electric energy induced by an applied alternating electric field,the effects of field frequency on the ferroelectric properties of BIT ferroelectrics were investigated. The results show that the evolution of ferroelectric domain structure is a gradual process including domain nucleation,domain wall motion,domain growth and domain combination. In the boundary regions of ferroelectric domain,the new domain nucleations occur and the old domains disappear. The coercive field increases with the field frequency,and it is in good agreement with the previous experiment.

Instability of OTSG in movable NPP by using multivariable frequency domain method

The instability occurring in OTSG (Once-Through Steam Generator) of movable nuclear power plants is presented by a multivariable frequency domain theory.As concerning coupling interactions of OTSG tubing,it is more efficient for analyzing the instability of OTSG compared the common single variable method.A mathematical model for the system is derived from the fundamental equations by using the perturbation,Laplace-transform and the nodalization techniques.The stable boundary and parameters which influence the stability of the system are evaluated through computer simulation.Numerical examples are given in the paper and the predictions of the model agree with the experimental results well.

预测规则波浪中船舶运动和载荷的频域三维计算机程序

The development of an in-house computer program for determining the motions and loads of advancing ships through sea waves in the frequency domain,is described in this paper.The code is based on the potential flow formulation and originates from a double-body code enhanced with the regular part of the velocity potential computed using the pulsing source Green function.The code is fully developed in C++language with extensive use of the object-oriented paradigm.The code is capable of estimating the excitation and inertial radiation loads or arbitrary incoming wave frequencies and incidence angles.The hydrodynamic responses such as hydrodynamic coefficients,ship motions,the vertical shear force and the vertical bending moment are estimated.A benchmark container ship and an LNG carrier are selected for testing and validating the computer code.The obtained results are compared with the available experimental data which demonstrate the acceptable compliance for the zero speed whereas there are some discrepancies over the range of frequencies for the advancing ship in different heading angles.

基于地质模型的无井区复频域地震反演方法

对基于模型的反演方法而言,合理的初始模型不仅可以补偿缺失的地震低频信息,也能提高地震反演精度和稳定性。然而,在无井或少井区,地球物理反演面临数据匮乏、资料品质不高的问题,难以直接从井数据中得到较丰富的低频信息,因此获取低频模型是无井区地球物理反演和油藏特征描述的关键。为此,针对新区勘探探索了一种基于地质模型的无井区复频域地震反演方法。首先,在考虑断层影响的基础上,参考地震相定性指导宏观趋势,融合了道积分的低频相对变化,充分运用无井区的地质、地震数据,为无井区反演提供可靠的低频信息。之后,根据复频域反演挖掘地震数据低频信息,将无井初始模型作为复频域反演的低频模型,结合盲信号理论提取地震盲子波,最终得到补充低频信息的复频域无井低频模型,可在一定程度上缓解无井区地震反演的低频成分缺失问题。最后,利用模型和实际工区数据测试了新方法的效果。结果表明,复频域无井反演弹性阻抗与井上弹性阻抗曲线拟合良好,与有井稀疏脉冲反演结果相比,尽管局部精度略低,但复频域无井反演结果的总体趋势及储层展布特征与有井反演结果基本一致,证明了所提方法在无井区的有效性。

山区大跨度窄梁悬索桥静风稳定及抖振性能研究

某山区钢-混组合窄梁悬索桥采用水平导流板对其颤振、驰振性能进行了优化,为了解该桥各类风致静、动力效应,以确保施工安全性和行车安全性,进一步研究优化后加劲梁在平均风作用下的静风稳定性和在脉动风作用下的抖振性能。基于全桥有限元模型结构自振特性分析结果及节段模型风洞试验测得的加劲梁断面静风三分力系数和颤振导数,采用三维非线性数值模拟方法对优化前、后加劲梁的静风临界发散风速进行求解,并与基于小变形假定的二维线性理论分析方法计算结果进行对比;采用抖振响应频域分析方法,结合规范中的桥址区风场特性,计算脉动风作用下的加劲梁抖振位移及内力。结果表明:该桥设置水平导流板前、后,加劲梁静风稳定性均满足规范要求且性能良好;设置水平导流板后,加劲梁扭转方向抖振位移有一定程度增大,同时,加劲梁竖向剪力最大值出现位置发生改变,跨中断面扭矩显著增大,该气动措施对抖振性能的提升较为有限。

“自动控制原理”中频域串联校正的教学探讨

基于系统期望开环伯德图,阐述了滞后环节和超前环节的有利和不足。以一个系统的完整校正过程为例,给出补偿环节的类型和幅穿频率的选择,提供环节参数的公式计算,使读者能够对系统串联校正这个复杂工程问题获得更深入和全面理解。通过对“自动控制原理”课程中频域串联校正的教学内容和思路、改革措施和实践效果进行探讨,为频域串联校正教学提供一个参考。

Multivariable Decoupling Predictive Control Based on QFT Theory and Application in CSTR Chemical Process

A novel method of incorporating generalized predictive control GPC algorithms based on quantitative feedback theory QFT principles is proposed for solving the feedback control problem of the highly uncertain and cross-coupling plants. The quantitative feedback theory decouples the multi-input and multi-output MIMO plant and is also used to reduce the uncertainties of the system, stabilize the system, and achieve tracking performance of the system to a certain extent. Single-input and single-output SISO generalized predictive control is used to achieve performance with higher performance. In GPC, the model is identified on-line, which is based on the QFT input and the plant output signals. The simulation results show that the performance of the system is superior to the performance when only QFT is used for highly uncertain MIMO plants.

大跨度铁路桥梁变形弦测法评价的频域理论

为保障行车舒适性,需严格控制大跨度铁路桥梁的变形。从车辆加速度频响函数与弦测法频响函数相似性出发,提出桥上轨道线形评价的最优弦长选定原则,为大跨桥梁变形控制的弦测法提供理论依据。根据随机振动理论,推导弦测法矢度峰值与车辆加速度峰值之比(峰值比)的理论公式;然后,分析弦测法矢度与车辆加速度时程样本间的波形相似性,以及峰值比对轨道不平顺波长范围和功率谱函数的敏感性;最后,采用一座大跨度斜拉桥上的轨道线形实测数据检验峰值比的理论解。结果表明,最优弦长的弦测法矢度与车辆加速度波形相似性最高;二者峰值比对轨道不平顺的波长范围和功率谱函数都不敏感;以文中车速250 km/h的高速车辆为例,推荐以40 m作为最优弦长,弦测矢度和车辆加速度的峰值比平均值为11 mm·s^(2)/m。

燃气轮机1.5级轴流压气机气动噪声预测

针对多排叶片旋转机械气动声源的复杂性,本文研究了一种预测多排叶轮气动噪声的数值模拟方法。基于混合计算方法研究了燃气轮机1.5级压气机的气动噪声特性,采用剪切应力传输湍流模型对1.5级轴流压气机的三维非定常流场进行全通道计算并获得声源,基于变分形式的Lighthill声类比耦合声源信息预测了压气机噪声,并在压气机动态实验台开展了流场和噪声实验研究。结果表明:非定常压力脉动傅里叶变换后峰值主要出现在叶片通过频率及其谐波处,且压力幅值随着叶频阶数的升高而降低;前传噪声有明显的声学指向性,具有明显的偶极子特征,离散噪声包含可传播的高阶模态;数值仿真的结果与实验吻合较好,本文研究的数值计算方法对多排叶轮的气动噪声预测具有较高的精度。

Transformations between Aeromagnetic Gradients in Frequency Domain

Aeromagnetic gradients are often used to enhance details or add new insights for interpretation. The gradients may be measured or derived from the total field or from transformation between horizontal and vertical gradients. At present, vertical, horizontal, and triaxial aeromagnetic gradiometers are in operation throughout the world, while the first two are used more widely. Transformations between horizontal and vertical gradients are needed for acquiring three gradient components or for checking the validity of measured gradients. Transformation of potential field by fast Fourier transform technique in frequency domain is popularly used; however, when applied to transforming between gradients, there is a problem that needs resolving. Because those expressions of transform operators are undefined when u or v is equal to zero or u and v are simultaneously equal to zero （u is the frequency in x-direction, and v is the frequency in y-direction）, the operators cannot be sampled at these frequencies. Consequently, the transformation cannot be implemented by fast Fourier transform technique directly. In this article, shift sampling theory is employed for resolving this problem. Model test results show that the technique has good accuracy, and the real case of transformation indicates that the computed results agree better with the measured gradients; it demonstrates not only the effective- ness of method but also the reliability of the measured gradients.

拉普拉斯变换在控制理论中的应用

自动控制原理中的拉普拉斯变换理论的引入使得系统建模后复杂的微分方程转化为代数方程,并在分析稳定性、系统校正方面有着重要的作用。选用球杆系统进行建模,结合拉普拉斯变换的性质,进而求出其相应的代数方程,并对系统进行时域、根轨迹、频域3个方法的稳定性分析。在此基础上,对不稳定的系统进行校正,使其达到预期的效果,并利用Matlab的Simulink工具对系统进行了多信号测试,检验系统稳定性。

基于脉诊仪研究肥胖、超重人群与正常人群脉象频域特征的差异性

目的基于王唯工共振理论,通过脉诊仪研究肥胖、超重人群与正常人群脉象频域特征的差异性,为肥胖、超重人群脉象参数提供量化依据。方法将280例受试者按体质量指数(BMI)进行分组,分为体质量超重组(肥胖、超重)、正常组、体质量过轻组。通过脉诊仪采集脉诊参数,并收集身体指标等相关信息,将脉诊参数进行快速傅里叶变换(FFT)展开为频域图,获得其脉象频域参数。对比这3个组别脉图频域特征的差异,提取不同BMI人群的特征点。结果体质量过重组C3谐波强度低于正常组及体质量过轻组(P<0.05)。结论肥胖、超重人群C3(脾部)的谐波强度低于正常人群及体质量过轻人群,考虑与肥胖、超重人群脾虚相关。

Periodic response analysis of a misaligned rotor system by harmonic balance method with alternating frequency/time domain technique

A dynamic model is established for an offset-disc rotor system with a mechanical gear coupling, which takes into consideration the nonlinear restoring force of rotor support and the effect of coupling misalignment. Periodic solutions are obtained through harmonic balance method with alternating frequency/time domain(HB-AFT) technique, and then compared with the results of numerical simulation. Good agreement confirms the feasibility of HB-AFT scheme. Moreover, the Floquet theory is adopted to analyze motion stability of the system when rotor runs at different speed intervals. A simple strategy to determine the monodromy matrix is introduced and two ways towards unstability are found for periodic solutions: the period doubling bifurcation and the secondary Hopf bifurcation. The results obtained will contribute to the global response analysis and dynamic optimal design of rotor systems.

规则波条件下的多液舱浮体动力响应特性研究

为了研究多液舱浮体的动力响应特性,基于势流理论进行多液舱浮体动力响应的频域分析。首先考虑不同的网格尺寸开展网格敏感性分析,随后针对规则波中单液舱浮体开展建模计算并与相关试验结果进行对比验证。最后分析多液舱浮体的动力响应特性,并探讨载液量及载液类型对浮体动力响应的影响。研究发现:液舱对浮体横荡的影响较小,对横摇的影响较大,垂荡响应与全系统自重有关;横摇响应曲线的峰值大小及峰值数量与液舱的载液类型存在一定关联。

不同航速下某浅吃水船耐波性分析

采用Hydro Star软件,系统分析某浅吃水船在不同航速时的耐波性能。研究结果表明:零航速、设计吃水工况下,横浪时垂荡和横摇运动最为显著。随着波浪偏移至艏/艉附近(±30°),横摇响应幅值算子(RAO)迅速减小;对于左舷处的监测点,纵向、垂向加速度RAO曲线关于左右舷浪向呈不对称分布,差异在横浪附近表现得尤为明显,横向运动的对称性则与此无关;横浪下1阶波浪力矩表现为双峰构型,相较于斜浪更大,导致横摇运动加剧;而斜浪下,低频波浪力矩对横摇起主要作用,且更高的航速对应了更大的等效黏性阻尼,从而一定程度上抑制了横摇响应;根据4级海况的短期预报结果,垂向加速度沿船长不同位置分布不均,随浪向、航速的变化规律也各不相同,在实际营运中应予以综合考虑,以避免不利因素的影响。

浅海波导中目标散射的简正波-Kirchhoff近似混合方法

提出了计算浅海波导中复杂目标散射的数值方法:简正波Kirchhoff近似混合方法。通过把目标散射的Kirchhoff近似方法和简正波声传播模型相结合,可对大尺寸复杂目标在浅海波导中的散射声场进行计算。以浅海波导中刚性球体散射的解析解为标准解验证了本方法,说明简正波Kirchhoff近似混合方法是有一定计算精度的工程预报方法。数值计算Pekeris浅海波导中球体目标散射声场在深度频率平面和距离频率平面上的二维干涉结构及其与自由空间中的差异。进而通过FFT获得目标时域回波随深度的分布图,分析浅海波导中目标姿态、声速剖面对Benchmark潜艇目标散射的影响。

定量反馈理论发展综述

定量反馈理论是一种基于频域的鲁棒控制理论,可以用于具有高度不确定性的单变量线性/非线性系统、多变量线性/非线性系统控制器设计.本文概述了定量反馈理论的基本原理、设计过程以及特点.总结了近年来QFT在提高系统性能、鲁棒稳定性、自动设计以及应用等方面的最新研究进展,并且给出了一些已有的理论应用成果.最后讨论了进一步的研究方向.

三相Boost型PWM整流器输出误差无源性控制

提出将无源性控制与频域理论相结合来控制三相Boost型PWM整流器,得到无源性电流控制器、输出误差补偿控制器和闭环系统的频域模型。仿真结果表明,在电路参数变化和负载扰动时,无源性电流控制器和输出误差补偿控制器可以实现输入单位功率因数和输出直流电压恒定,采用频域方法设计参数的输出误差补偿控制器提高了系统的动态性能。

基于小波分析的大型齿轮箱低速轴故障诊断

针对大型齿轮箱低速轴故障信息难以提取的问题,采用小波分析方法对故障数据进行处理以实现信号在时/频域的局域性分析,将其无冗余、无泄漏地分解到一组具有紧支撑性的小波基上.文中采用小波分层突变系数作为判别故障隐患的特征值,并对该特征值进行趋势分析.结果表明:小波变换能有效捕捉冲击信号的时域特征和故障发生的时间历程,用小波分层突变系数所做的趋势图能有效地预测故障发展趋势,避免突发故障.

一种基于电力系统在线平台的广域阻尼协调控制方法

实现广域阻尼控制与就地阻尼控制间的协调控制可以更为有效地抑制大型互联电网的低频振荡,具有重要理论意义和工程应用价值。为实现二者的协调控制,该文提出一种基于电力系统仿真平台的广域阻尼协调控制方法。首先,针对大电网广域协调阻尼控制问题,从多变量系统频域角度建立广域协调阻尼控制研究结构,进而借助于小增益理论研究广域控制与就地控制的影响关系,以及多广域控制间的影响关系;然后,提出广域控制器间的柔性协调因子指标,该指标能够量化广域控制与就地控制协调运行能力以及多广域控制间的协调运行能力,并提出基于电力系统实时仿真平台的柔性协调因子指标实时计算方法,以利于文章协调控制方法在实际电网中的应用。在上述研究基础上提出基于柔性协调因子的广域协调阻尼控制流程,借助电力系统实时仿真平台,实时计算系统中广域控制与就地控制间的协调运行情况,及多台广域控制间的协调运行情况,并根据电网的运行方式变化实时形成控制策略,从而实现系统的广域协调阻尼控制。通过实际电网实例验证了提出方法的有效性及在实际电网中应用的可行性。