桥梁结构挠度-温度-车辆荷载监测数据相关性模型

运营状态下桥梁结构挠度、车载和温度的相关性复杂,高精度的车载、温度与挠度相关性模型对桥梁结构健康监测具有重要意义。为此,提出了基于门控循环单元(gated recurrent unit, GRU)神经网络的桥梁挠度监测数据建模方法。为解决车辆荷载监测数据在时域内离散分布的问题,提出了基于挠度影响线的车载影响参数计算方法;在此基础上建立了基于GRU神经网络的车载影响参数、环境温度和桥梁挠度相关性模型。以一座悬索桥为例,分别建立了短时段、中长时段的相关性模型,考察了相关性模型对加劲梁挠度的预测能力,并利用相关性模型提出了一种温度和车载挠度分量的分离方法。悬索桥实例研究表明：短时段相关性模型的挠度预测值与实时监测数据基本吻合,而中长时段相关性模型则对一定时间窗口内的挠度极值具有精确的预测能力;采用相关性模型计算得到的温度与车载挠度分量与小波分解结果具有良好的一致性。     

UML时间顺序图的自动验证技术

UML顺序图反映对象之间的消息交互顺序,在系统建模中应用十分广泛.对顺序图进行时间扩展得到UML时间顺序图,使其具备对实时系统建模的能力.在此基础上研究了UML建模工具和模型验证工具UPPAAL的接口信息,将UML时间顺序图模型转化为时间自动机模型,并对该系统模型进行形式化验证.设计和实现了基于XML的UML时间顺序图自动验证工具.     

某型爪极发电机的模态仿真与试验分析

爪极发电机固有频率和模态振型的准确计算是降低电机振动和噪声的基础。基于某型车用爪极发电机,噪声试验显示其存在结构共振导致的电磁噪声偏大问题。首先建立定子铁芯整体模型,在考虑端部绕组的情况下对线圈进行等体积式建模,并完成了整机模型的建立。对材料参数等效处理,通过数值软件进行零部件和整机的自由模态仿真,自由模态试验结果与仿真结果的最大误差为7.1%,二者具有较好的一致性。最后完成整机约束模态试验和仿真,验证建模方法和模态分析的有效性。可为同类型爪极发电机建模和模态计算提供参考。     

基于WITNESS的看板生产系统建模仿真与优化研究

基于WITNESS对看板生产系统进行了PetriNet建模,对wITNESS看板生产系统的基本假设、系统绩效指标选取、模型参数优化与仿真结果进行了分析,应用WITNESS建立了一个单产品、多阶段、混联的JIT生产系统仿真模型,通过仿真实验,研究分析了在安全系数和变异系数两方面的随机变量在不同的组合下对系统绩效指标的影响．     

Variable-structure control of gas collector pressure based on smooth switching strategy for coke ovens

针对基于专家切换策略的焦炉集气管压力变结构控制方法具有动态切换特性差的缺点和集气管压力在不同工况切换时容易导致压力出现振荡和超调的现象,提出了一种基于平滑切换策略的集气管压力变结构控制方法.该方法根据集气管分管压力在不同工况下具有的动态特性,选用基于满意聚类的T-S模糊模型建立相应的动态子模型,并采用相应的模糊子控制器进行控制.为保证子模型切换过程状态轨迹的平滑性,采用监督级控制器动态切换子模型及相应的子控制器.仿真和实际效果说明了该算法的有效性.     

田口方法在冲压仿真建模参数优化中的应用研究

利用现有的有限元软件ABAQUS,建立了V形件冲压加工的有限元仿真模型。结合田口方法,通过实验数据和仿真结果对比,分析了各建模参数对仿真模型鲁棒性的影响,最终找出有利于提高鲁棒性的建模参数组合,建立了可运用于实际分析的鲁棒性有限元模型。给出了V形冲压件基于田口方法的有限元建模参数优化的计算实例。结果表明,所提方法是有效且实用的,为提高有限元建模的鲁棒性提供了依据。     

多单元柔性制造系统的人机比建模与仿真

人机比是指在一定工作时间内一个工人所能操作的机器数量,代表工人的工作效率。本文主要研究多单元柔性制造动态复杂系统的建模与仿真,建立了人机比的通用仿真模型。进一步,基于所建立的仿真模型,本文对影响人机比的关键因素的灵敏度等指标进行了深入分析和研究。     

基于虚拟样机的某车载转管机枪在不同激励下振动特性研究

为研究某型车载转管机枪在外部激励作用下的振动特性,利用虚拟样机技术对该武器系统进行强迫振动分析。分析该型机枪系统拓扑结构及所受载荷,利用ADAMS软件建立车载转管机枪的刚柔耦合模型及武器振动方程,用所建立虚拟样机模型对车载状态下转管机枪的振动特性进行仿真测试,主要研究路面激励与车辆行驶速度激励,获得机枪系统在不同激励下的振动。计算结果为车载机枪试验与进一步参数匹配优化及提高机枪射击精度奠定基础。     

基于预制体边界反射方法的三维四向编织复合材料几何建模

针对预制体中纱线路径复杂,几何建模耗时较长的问题,提出了一种预制体边界反射(PBR)方法,有效地缩短了几何建模过程中建立纱线运动模型的计算时间.在此基础上,开发了基于SolidWorks软件的CAD仿真建模系统,可模拟不同编织参数下的三维编织预制体整体结构.与传统建模方法相比,PBR方法可在不影响预制体几何建模精度的前提下,明显缩短仿真时间.因此,可明显提高编织工艺设计的效率.该方法为复杂几何结构预制体的细观结构和机械性能研究奠定了基础.     

垂直热发射过程弹架耦合作用研究

研究裸弹垂直热发射过程系统的动态响应及其对导弹运动的影响。对车载导弹发射系统进行了简化和等效建模,进行了导弹起飞过程的理论分析,基于动力学和有限元软件建立了系统刚柔耦合多体动力学模型,对发射过程展开了动力学仿真与分析,并进行了多刚体与刚柔耦合两类模型计算结果对比。数值模拟结果表明,导弹起飞过程与发射车的耦合作用明显,系统振动对导弹起飞姿态产生影响,发射车振动衰减特性良好,柔性发射台模型能够较好反映发射过程系统动态响应以及弹架耦合特性。     

Experimental and theoretical study of light scattering by individual mature red blood cells by use of scanning flow cytometry and a discrete dipole approximation

Elastic light scattering by mature red blood cells (RBCs) was theoretically and experimentally analyzed by use of the discrete dipole approximation (DDA) and scanning flow cytometry (SFC), respectively. SFC permits measurement of the angular dependence of the light-scattering intensity (indicatrix) of single particles. A mature RBC is modeled as a biconcave disk in DDA simulations of light scattering. We have studied the effect of RBC orientation related to the direction of the light incident upon the indicatrix. Numerical calculations of indicatrices for several axis ratios and volumes of RBC have been carried out. Comparison of the simulated indicatrices and indicatrices measured by SFC showed good agreement, validating the biconcave disk model for a mature RBC. We simulated the light-scattering output signals from the SFC with the DDA for RBCs modeled as a disk-sphere and as an oblate spheroid. The biconcave disk, the disk-sphere, and the oblate spheroid models have been compared for two orientations, i.e., face-on and rim-on incidence, relative to the direction of the incident beam. Only the oblate spheroid model for rim-on incidence gives results similar to those of the rigorous biconcave disk model.     

Modeling the hygroexpansion of aligned wood fiber composites

The effect of wood fiber ultrastructure and cell wall hygroelastic properties on wood fiber composite hygroexpansion has been analyzed. An analytical concentric cylinder model extended to include also free hygroexpansion of orthotropic phase materials has been used on several length scales. Using properties of the three main wood polymers, cellulose, hemicellulose and lignin the longitudinal and transverse hygroexpansion coefficients for the microfibril unit cell were obtained and the volume fraction change of the wood polymers in the microfibril unit cell depending on relative humidity was calculated. The fiber cell wall was modeled regarding each individual S1, S2 and S3 layer and the cell wall longitudinal hygroexpansion coefficient was determined depending on microfibril angle in the S2 layer. A homogenization procedure replacing the S1, S2 and S3 layers with one single layer was found not to influence the results significantly for low microfibril angles. Finally the hygroexpansion coefficients of an aligned softwood fiber composite were calculated.     

Optimization of ring magnet geometry for field harmonic control inelectric motors

An optimization algorithm for shaping a multipole, continuous magnet for elimination of one or more harmonics is presented. The magnet is modeled as a continuous ring portion and an optimized section, modeled as a series of thin layers, at each pole. The analytical model investigated consisted of a radially magnetized four-pole motor with a solid ring stator. The algorithm successfully shaped the poles to eliminate selectively the 8th, the 12th, or the 16th harmonic, at the expense of increasing the amplitudes of the other harmonics. The solutions were not unique. A tradeoff in effectiveness existed between the minimum thickness of the continuous ring and the minimum sector angle of the outer pole layer. For thin rings and small outer layer sector angles, an optimum pole shape was readily found. However, if one parameter was too large, then the other had to be decreased for an effective solution to exist     

High crystallinity oligo(3-methylthiophenes) for p-channel organic field-effect transistors

A new type of oligo(3-methylthiophenes) with highly regiosymmetric chemical structure was presented for developing high performance and solution-processable organic field-effect transistors (OFETs). The representative molecule Br4MT, tetramer of the oligo(3-methylthiophenes), was synthesized through the oxidative cross-coupling reactions using Cu(II)-catalyst and fully characterized. The Br4MT exhibited remarkably high crystallinity and great ionization potential due to its unique molecular structure, evidenced by differential scanning calorimetry, electrochemical and X-ray diffraction studies. The solution-processed OFETs based on Br4MT achieved high hole mobility of up to 0.24 cm²/V/s with reasonable ambient stability, suggesting that the Br4MT had great potential for application in low-cost OFETs.     

Interface stress redistribution in FRP-strengthened reinforced concrete beams using a three-parameter viscoelastic foundation model

External bonding of FRP plates or sheets has become a popular method for strengthening reinforced concrete structures. Stresses along the FRP–concrete interface are critical to the effectiveness of this technique because high stress concentration along the FRP–concrete interface can lead to the FRP debonding from the concrete beam. In this study, a novel analytical solution has been developed to predict the interface stress redistribution of FRP-strengthened reinforced concrete beams induced by the viscoelastic adhesive layer. Both the FRP plate and the RC beam are modeled as Timoshenko’s beams, connected through the adhesive layer. The adhesive layer is modeled as a three-parameter viscoelastic foundation (3PVF) using Standard Linear Solid model. The 3PVF model satisfies the equilibrium equation of the adhesive layer and the zero shear-stress boundary condition at the free edge. Closed-form expressions of the time-dependent interface stresses and deflection of the beam are obtained using Laplace transform. Finite element analysis is also conducted to verify the analytical solution using a subroutine UMAT based on the Standard Linear Solid model. Numerical results suggest that the stress concentrations within the FRP–concrete interface relax with time. The axial force in the FRP plate also reduces with time due to the creep of the adhesive layer. However, this relaxation is limited to a small zone close to the end of the FPR plate.     

A data-driven maintenance policy for railway wheelset based on survival analysis and Markov decision process

Wheelsets absorb a significant part of the maintenance budget of any train operating company. Although wheel wear has been an extensively discussed topic in the literature, wear rates are very rarely characterized by using degradation data in a real-world case study aimed at identifying optimal maintenance policies including both degradation and recovery modeling. Furthermore, wheel defects, which impose an additional challenge to the modeling of the lifecycle of the wheels, are usually considered separately in the literature. In this study, conducted at a Portuguese train operating company, 17 years of inspection data are used to estimate wheel wear rates and survival curves, which are further incorporated into a Markov decision process (MDP) model. A bidimensional framework considering discrete intervals of wheel diameter along with a quantitative variable (kilometers since last turning/renewal) is used to represent the possible wheel states, while the probability of a defect interfering with the wheel maintenance schedule is modeled by contemplating survival curves derived from a Cox proportional-hazards model. Optimal results in terms of minimal cost policy are discussed in the context of the MDP, but a more realistic and easy-to-implement policy fixing one of the parameters is compared with the optimal policy. Results showed that in practice train operating companies might benefit from using the easy-to-implement policy, which has an associated long-run average cost only about 1% higher than the one suggested by the optimal decision map.     

包装人机工程学课程教学改革探索

为培养应用型人才,以包装工程专业人才知识结构对人机工程学的需求为前提,分析了以产品设计为核心的人机工程学课程的适用性,并结合包装工程专业对人机工程学课程内容进行适当地删减、调整和转换,形成了适用于包装工程专业的人机工程学课程教学体系。在教学内容和教学方法上,提出应从理论讲解为中心转向以案例分析为中心;在教学环节设置上,提出了“理论阐述,研究案例／章节讨论＋设计实践”的“3＋1”教学模式。     

基于动态故障树的CTCS-3级ATP系统可靠性分析简

 针对传统的可靠性分析方法分析CTCS-3级ATP系统动态失效问题的不足,提出采用动态故障树分析其可靠性。首先,分析系统的结构和功能建立动态故障树模型;其次,采用深度优先最左遍历算法搜索动态故障树模型,得到独立的子树;最后,在引入可修系统可靠性指标基础上,采用解析法和马尔科夫矩阵迭代法求解子树,结合分层迭代方法对动态故障树分析法改进,以减小运算量,使得上述可靠性指标能用于CTCS-3级ATP系统的可靠性评估。计算所得可靠性指标与可靠性框图分析得到的结果对比表明：动态故障树能够更好地描述系统的冗余性和容错性等特点,提高了可靠性指标的精度。     

Fracturing behaviors of FRP-strengthened concrete structures

In this paper, we focus on the study of concrete cracking behavior and interfacial debonding fracture in fiber reinforced polymer (FRP)-strengthened concrete beams. An experimental program is systematically reviewed according to the observed failure modes, in which it is found that the interfacial debonding may propagate either within the adhesive layer or through concrete layer in the vicinity of bond interface. A finite element analysis is performed to investigate the different types of debonding propagation along FRP-concrete interface and crack distribution in concrete. For the numerical fracture models, interfacial debonding that initiates and propagates in adhesive layer is modeled by fictitious interfacial crack model. And concrete cracking, including the debonding fracture through interfacial concrete, is modeled by smeared crack model. Properties of the interfacial adhesive layer and concrete are considered to significantly influence the debonding propagation types and crack distribution. The interactions between interfacial bond strength, interfacial fracture energy of bond adhesive layer and tensile strength, fracture energy of concrete are discussed in detail through a parametric study. According to the results, the effects of these properties on different types of interfacial debonding, concrete cracking behavior and structural load-carrying capacity are clearly understood.