Influence of Initial Value of Transient Time Step on Numerical Simulation of Blow Molding Balloon

The correlation between the initial time value of transient iterative parameters and the blowing pressure in the numerical simulation process of blowing balloon is investigated by POLYFLOW. The results show that: 1) As the blow molding pressure increases, the boundary value of the iterative time step decreases rapidly at first and then slowly. At the end of the first step of iterative calculation for each boundary value, the balloon parison is in the mold core cavity. 2) If the initial time value of transient iterative parameters is smaller than the boundary value of the iterative time step, the balloon parison is still in the mold core cavity at the end of the first iteration. However, if the iterative calculation continues, the calculation process may be interrupted when the time step is smaller than the initial time value of the transient iterative parameters, which makes the blow molding simulation of balloon unable to continue. 3) It is suggested that the initial time value of transient iterative parameters is one order of magnitude smaller than the boundary value of the iterative time step to complete smoothly the simulation of blow molding balloon.

Time Domain Simulation of Transient Responses of Very Large Floating Structures Under Unsteady External Loads

A time domain finite element method （FEM） for the analysis of transient elastic response of a very large floating structure （VLFS） subjected to arbitrary time-dependent external loads is presented. This method is developed directly in time domain and the hydrodynamic problem is formulated based on linear, inviscid and slightly compressible fluid theory and the structural response is analyzed on the thin plate assumption. The time domain finite element procedure herein is validated by comparing numerical results with available experimental data. Finally, the transient elastic response of a pontoon-type VLFS under the landing of an airplane is computed by the proposed time domain FEM. The time histories of the applied force and the position and velocity of an airplane during landing are modeled with data from a Boeing 747-400 jumbo jet.

Time-domain solution for transient dynamic response of a large-diameter thin-walled pipe pile

The propagation of stress waves in a large-diameter pipe pile for low strain dynamic testing cannot be explained properly by traditional 1D wave theories. A new computational model is established to obtain a wave equation that can describe the dynamic response of a large-diameter thin-walled pipe pile to a transient point load during a low strain integrity test. An analytical solution in the time domain is deduced using the separation of variables and variation of constant methods. The validity of this new solution is verifi ed by an existing analytical solution under free boundary conditions. The results of this time domain solution are also compared with the results of a frequency domain solution and fi eld test data. The comparisons indicate that the new solution agrees well with the results of previous solutions. Parametric studies using the new solution with reference to a case study are also carried out. The results show that the mode number affects the accuracy of the dynamic response. A mode number greater than 10 is required to enable the calculated dynamic responses to be independent of the mode number. The dynamic response is also greatly affected by soil properties. The larger the side resistance, the smaller the displacement response and the smaller the refl ected velocity wave crest. The displacement increases as the stress waves propagate along the pile when the pile shaft is free. The incident waves of displacement and velocity responses of the pile are not the same among different points in the circumferential direction on the pile top. However, the arrival time and peak value of the pile tip refl ected waves are almost the same among different points on the pile top.

A HIGH ACCURATE TIME-DOMAIN-ADVANCE INTEGRATION METHOD FOR TRANSIENT ELASTODYNAMIC PROBLEMS

All step-by-step integration methods available at present for structural dynamic analysis use the displacement, velocity, and acceleration vectors computed at a previous interval for evaluating those at an advanced time step. Hence, an accumulated error will be definitely introduced after such integration. This paper presents a novel time-domain-advance integration method for transient elastodynamic problems in which the exact initial conditions are strictly satisfied for the solutions for each time step. In this way, the accumu- lated error can be eliminated and the approximate solutions will converge to the exact ones uniformly on the whole time domain. Therefore. the new method is more accurate. When applying to a structural dynamic problem, the present mehtod does not have to use the initial acceleration as is required by most other algorithms and the corresponding computation can be avoided. The present method is simple in representation, easy to be programmed, and especially suitable for accurate analyses of long-time problems. The comparison of numerical results with exact ones shows that the present method is much more accurate than some most widely used algorithms.

Real-Time Computer Analytical Application in Pressure Transient Analysis of Petroleum Reservoirs

Today with certainty, the petroleum industry is fostering sanguinely the fields’ development programs for the optimization of reservoir characterization through worth-full appliances of computer analysis techniques. The time element is of prime importance for optimistic petroleum development projects. Therefore, the frontline of “Real-time Analysis” is added into the applications of computer solving techniques for achieving and sketching up the real-time cost effectiveness in analyzing field development programs. It focuses on the phases of real-time well test data acquisition system, real-time secure access to the well test data either on field or in office and real-time data interpretation unit. This interface will yield the productive results for the field of reservoir’s pressure transient analysis and wells’ systems analysis by following the up-to-date preferred, accurate and effective well test analytical principles with modern real-time computer applications and techniques. It also lays emphasis for the comfort and reliability of data in creating best interpersonal working modes within a reputable and esteemed petroleum development organization.

中性点柔性接地配电网故障相恢复电压暂态时域特征分析

配电网接地故障过零熄弧后的电压暂态恢复特性决定了系统过电压水平及电弧重燃特性,目前,中性点柔性接地配电网故障熄弧后暂态恢复电压变化机理尚不明确,为此建立柔性接地配电网接地故障暂态等值电路,理论解析故障过零熄弧后故障恢复电压的时域表达式。在此基础上,对比分析配电网谐振接地与柔性接地方式下,系统参数变化对故障相恢复电压暂态峰值与恢复速度的影响,揭示暂态时间尺度下故障相恢复电压特征随注入零序电流值与电流注入时机的变化规律,阐明通过中性点注入可控零序电流抑制故障暂态过电压的机理。在PSCAD/EMTDC仿真环境与10 kV真型配电网实验场中模拟各种运行和故障工况,仿真与真型实验结果均验证柔性接地配电网故障相恢复电压时域解析特征与变化规律的正确性。

Exact Time Domain Solutions of 1-D Transient Dynamic Piezoelectric Problems with Nonlinear Damper Boundary Conditions

Novel exact solutions of one-dimensional transient dynamic piezoelectric problems for thickness polarized layers and disks, or length polarized rods, are obtained. The solutions are derived using a time-domain Green’s function method that leads to an exact analytical recursive procedure which is applicable for a wide variety of boundary conditions including nonlinear cases. A nonlinear damper boundary condition is considered in more detail. The corresponding nonlinear relationship between stresses and velocities at a current time moment is used in the recursive procedure. In addition to the exact recursive procedure that is effective for calculations, some new practically important explicit exact solutions are presented. Several examples of the time behavior of the output electric potential difference are given to illustrate the effectiveness of the proposed exact approach.

LONG-TIME BEHAVIOR OF TRANSIENT SOLUTIONS FOR CELLULAR NEURAL NETWORK SYSTEMS

By establishing concept an transient solutions of general nonlinear systems converging to its equilibrium set, long-time behavior of solutions for cellular neural network systems is studied. A stability condition in generalized sense is obtained. This result reported has an important guide to concrete neural network designs.

基于数据-模型混合驱动的电力系统机电暂态快速仿真方法

数据驱动建模方法改变了发电机传统的建模范式,导致传统的机电暂态时域仿真方法无法直接应用于新范式下的电力系统。为此,该文提出一种基于数据-模型混合驱动的机电暂态时域仿真(data and physics driven time domain simulation,DPD-TDS)算法。算法中发电机状态变量与节点注入电流通过数据驱动模型推理计算,并通过网络方程完成节点电压计算,两者交替求解完成仿真。算法提出一种混合驱动范式下的网络代数方程组预处理方法,用以改善仿真的收敛性;算法设计一种中央处理器单元-神经网络处理器单元(central processing unit-neural network processing unit,CPU-NPU)异构计算框架以加速仿真,CPU进行机理模型的微分代数方程求解;NPU作协处理器完成数据驱动模型的前向推理。最后在IEEE-39和Polish-2383系统中将部分或全部发电机替换为数据驱动模型进行验证,仿真结果表明,所提出的仿真算法收敛性好,计算速度快,结果准确。

风电不确定性输入下电力系统仿真的区间仿射算法

大规模的风电机组并网改变了以同步发电机为主的传统电力系统的暂态特性,此外风电出力的随机性会影响电力系统的暂态稳定性。为此,文中提出了基于仿射算术的电力系统不确定性时域仿真算法,以考虑风电出力的波动性。在双馈风电机组机电暂态模型的基础上,扩展电力系统机电暂态模型,建立考虑双馈风电机组输入功率波动下的电力系统机电暂态仿射模型,通过隐式梯形积分法将仿射模型转化为的仿射雅克比矩阵方程迭代求解。仿真结果表明,文中所提出的仿射方法在不假设输入不确定量概率分布的情况下,能够较蒙特卡洛仿真更快地获得电力系统暂态响应的区间边界。

时间分辨动态LIBS测量方法

针对激光诱导击穿光谱(LIBS)研究对时间分辨动态光谱测量方法的需求,建立了基于多通道光纤束的动态LIBS测量方法。该方法首先利用不同长度的光纤组成多通道光纤束,对瞬态LIBS信号进行差异延迟,使按照特定时间序列发射的光谱信号同步到达探测器,而后采用面阵ICCD相机对同步到达的多通道光谱信号进行高时间分辨探测。该方法单次测量即可获得LIBS辐射不同时刻的时间分辨光谱。为了验证基于多通道光纤束的动态LIBS测量方法,研制了具有19个通道的光纤束,光纤束中包含的各个单根光纤长度呈等差数列排布,长度差设置为10 m,对应测量的时间间隔约为50 ns,单次测量记录的总时间长度近900 ns。分别基于短脉冲激光光源和标准光源,开展了系统时间响应和光谱响应特性研究,获得了系统的时间响应数据和光谱响应曲线。用YAG激光器的二倍频激光(532 nm)诱导Si产生等离子体辐射光谱,在线测量了辐射光谱的时间演化历程,获得了Si等离子体辐射过程中SiⅠ390.52 nm,SiⅡ385.51 nm,SiⅡ413.12 nm谱线从0~898 ns时间范围内19个时刻的光谱信息,获得了特征光谱的演化规律,验证了该测量方法的可行性。结果表明,利用该测量方法,单次测量可以获得瞬态LIBS辐射过程中19个时刻的光谱参数,具有很高的测量效率。对于实验成本较高、运行频率低的激光诱导等离子体实验研究,采用该方法可以大大降低了测量成本,有效提升等离子体时间分辨动态光谱测量能力。

Time-of-Flight透散射介质成像技术综述

Time-of-Flight (ToF)成像是利用光在目标和相机之间的飞行时间来获取场景的深度信息,具有体积小、成本低、实时成像等优势。在散射环境中,由于散射介质对光的散射作用,ToF成像受到多径干扰的影响,深度测量误差较大,限制了ToF相机在散射场景中的应用。ToF透散射介质成像技术是校正因散射光引起的多径干扰效应,从传感器接收到的混叠信号中分离出目标分量,实现散射场景中的深度信息恢复,其在雾天自动驾驶、水下勘测、生物医学等领域具有广阔的应用前景。依据ToF成像系统的不同,详细介绍了PL-ToF和CW-ToF成像的基本原理,阐述和分析了散射场景中ToF稳态成像和瞬态成像的机理和特点,分别回顾和总结了ToF稳态成像和瞬态成像的透散射介质成像研究现状,并介绍了ToF透散射介质成像的应用前景,最后依据现有ToF透散射介质成像技术的优缺点,对未来发展趋势进行了展望。

自适应可调恒定导通时间Buck型直流电压变换器设计

为提高开关电源输出纹波电压、负载调整率、线性调整率和瞬态响应时间等性能指标,采用纹波控制的方法,研究出一款自适应可调恒定导通时间(adjustable-constant-on-time,ACOT)Buck型直流电压变换器。基于TSMC0.18μmCMOS工艺完成了电路设计,并用Cadence平台Spectre仿真器进行了仿真验证。结果表明:该电路的恒定导通时间可以精准灵活调节,纹波电压、线性调整率和瞬态响应时间均较低,与相关文献对比可知,本文设计在负载调整率上具有明显优势。

A Real-Time Transient Analysis of a Functionally Graded Material Plate Using Reduced-Basis Methods

Based on the hybrid numerical method (HNM) combining with a reduced-basis method (RBM), the real-time transient response of a functionally graded material (FGM) plates is obtained. The large eigenvalue problem in wavenumber domain has been solved through real-time off-line/on-line calculation. At off-line stage, a reduced-basis space is constructed in sample wavenumbers according to the solved eigenvalue problems. The matrices independent of parameters are projected onto the reduced-basis spaces. At on-line stage, the reduced eigenvalue problems of the arbitrary wavenumbers are built. Subsequently, the responses in wavenumber domain are obtained by the approximated eigen-pairs. Because of the application of RBM, the computational cost of transient displacement analysis of FGM plate is decreased significantly, while the accuracy of the solution and the physics of the structure are still retained. The efficiency and validity of the proposed method are demonstrated through a numerical example.

一种高速A/D转换器时域重构技术研究

A/D转换器在航空航天系统中的重要元器件,随着器件转换时钟频率不断提高而其工作环境不断恶化,如何准确测试其时间参数对于全面评价A/D转换器性能特别重要。目前对于高速A/D转换器时间参数测试,主流方法是通过示波器直接测试其输出,该方法对于示波器采样速度要求比较高。文章提出一种高速A/D转换器时域重构技术,可以通过计算机数字信号处理方法来实现高速A/D转换器时间参数测试,同时避免对示波器采样速度的依赖。同时,在研究高速A/D转换器时域重构技术方法及其应用的基础上,通过了相关试验验证。

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。

末次间冰期全球气候瞬变模拟与平衡态模拟的对比研究

采用水平分辨率约1°的地球系统模式CESM,本研究开展了末次间冰期129~124 ka的瞬变模拟试验(TGCS-LIG)和127 ka的平衡态切片模拟试验(127ka-LIG),量化了数值试验方案对模拟的末次间冰期全球气候的影响,以期加深理解造成模拟结果与重建数据之间分歧的可能原因。TGCS-LIG试验和127ka-LIG试验均表明:末次间冰期全球年平均温度较工业革命前低,降温幅度分别为0.4℃和0.2℃;在夏季,北半球升温(1.2/1.5℃),而南半球降温(0.9/0.7℃)。就年降水而言,末次间冰期北半球季风区降水增加,南半球季风区降水减少,但存在显著的区域差异。与重建数据相比,TGCS-LIG试验和127ka-LIG试验的模拟-数据符号一致性与均方根误差均相近,但127ka-LIG试验模拟效果略好。TGCS-LIG试验与重建的全球年平均(夏季)海温符号一致性为34.9%~44.7%(36.8%~42.5%),较127ka-LIG偏差约2%~4%(约5%~7%);均方根误差为2.9~3.2℃(2.9~3.4℃),较127ka-LIG试验偏差小于约0.1℃。对于全球年平均降水,TGCS-LIG试验与重建数据的符号一致性为63.8%,略高于127ka-LIG试验(63.1%)。相较于模拟和重建之间的绝对偏差而言,数值试验方案对于改进两者分歧的作用十分有限。需要注意的是,TGCS-LIG试验表明:末次间冰期全球关键气候模态的年际变率在129~124 ka间存在显著的内部变化,其中ENSO年际变率随时间逐渐增强,北半球环状模与南半球环状模的年际变率呈现千年尺度波动的特征;而127ka-LIG试验无法刻画气候模态的时间演变特征。总之,本文研究结果表明,采用平衡模拟试验或是瞬变模拟试验并不是造成末次间冰期模拟-数据分歧的主要原因,但开展高时空分辨率的瞬变模拟试验对研究末次间冰期气候变率具有重要的科学价值。

一种双控制模式的同步降压型DC/DC转换器

为突破转换器在输出电容选型上的局限性,保证转换器快速的负载瞬态响应,基于自适应恒定导通时间控制的两种控制模式,提出一种可根据输出电容类型选择控制模式的同步降压型DC/DC转换器。在D-CAP模式下,支持具有适当等效串联电阻的电容等作为输出电容;在电流模式下,支持等效串联电阻较低的陶瓷电容作为输出电容。基于0.35μm BCD工艺,使用Cadence软件对转换器进行瞬态仿真。结果表明,该设计在两种模式下都具有快速的瞬态响应。

基于多核CPU的风光新能源场站全拓扑实时仿真建模方法

风光新能源场站在构建新型电力系统中占据重要地位,其电磁暂态实时仿真愈发受到关注。由于新能源场站网络解算十分复杂,串行逻辑冗长,难以在目前开发较为成熟的多核CPU仿真机上实时仿真。因此提出了一种基于多核CPU的风光新能源场站全拓扑实时仿真建模方法。该方法基于电网络等效原理,建立发电单元四端子等效模型,依据该模型的仿真流程设计适用于多核CPU的并行仿真架构,实现新能源场站的实时仿真。所建场站模型利用内部电压的计算可保留高精度的全拓扑信息,同时通过降阶有效降低网络解算资源占用,缩短串行逻辑。经仿真测试,相较于RTDS模型,该方法所建模型在保证精度误差小于4%的同时可实时仿真的场站规模扩大3倍,有效降低实时仿真硬件成本。

基于非线性解耦方法的交直流配电系统暂态稳定性分析

随着柔性交直流配电系统的迅速发展,电力电子装置和恒功率负载等非线性元件的大规模接入使系统的暂态稳定性问题日趋严重。首先,建立了双环控制下AC/DC与DC/DC换流器并联的具有恒功率负载的交直流配电系统数学模型,并进行非线性泰勒展开。其次,根据非线性解耦理论将原始高阶系统解耦成一系列低阶子系统,确定主导解耦子系统并采用相平面法和逆轨迹法对其进行暂态稳定性分析,通过实物仿真验证理论分析的有效性。然后,基于非线性解耦原理引入非线性参与因子概念,对状态变量进行参与因子的计算,提出恒功率负载扰动下控制参数影响稳定性的分析方法,进一步给出控制参数的可行域。最后,利用PLECS软件搭建了恒功率负载下双环控制的交直流配电系统,仿真及实验验证了所提方法的有效性。