基于三维细观随机模型的碳纳米颗粒/聚合物力电响应模拟

针对碳纳米颗粒聚合物内部导电颗粒随机分布且结构复杂的特点,本研究提出一种结合细观有限元分析与材料微观等效电路电阻计算的方法,对其力电响应行为进行模拟。首先,借助ABAQUS二次开发及改进型最近距离算法,建立碳纳米颗粒聚合物材料的代表性体积单元模型,通过有限元分析得到不同加载条件下相邻导电聚集体的间距变化。其次,通过转换矩阵法及隧穿电阻公式,对该复合材料所简化的随机电阻网络进行等效电阻的计算。最终以相邻导电聚集体间距为纽带,将导电聚合物电阻与全局应力相关联,得到其力电响应曲线。为验证该方法的有效性,以CB3100/硅橡胶材料为例,分别计算了不同轴向压缩应力下导电复合材料的电阻,并与文献中的数据进行对比。结果表明,该方法不仅能够有效模拟碳纳米颗粒聚合物的力电响应,且从细观尺度揭示了其应变传感机制。

压电悬臂梁的力电响应及疲劳寿命分析

压电悬臂梁的力电响应与疲劳寿命是制约振动能量收集器深层次应用的关键。基于分布式参数建模方法,建立了压电悬臂梁的动力学模型,求解了压电悬臂梁的力电响应的解析解;借助有限元方法,开发了压电悬臂梁的仿真模型;通过实验验证了理论模型与有限元模型的准确性;应用仿真模型,分析了压电悬臂梁的几何尺寸、基体层厚度、陶瓷层厚度对力电响应的影响;基于估算的压电材料S-N曲线,探讨了各参数对压电悬臂梁疲劳寿命的影响。结果表明:当宽度、基体层和陶瓷层厚度分别从16~24 mm、0.16~0.24 mm线性增加时,压电悬臂梁的疲劳寿命近乎呈现指数形式增加,而压电悬臂梁的长度由48 mm增加到56 mm,其疲劳寿命显著降低。

基于力电响应的压电悬臂梁疲劳寿命预测

针对压电振动能量收集器的疲劳问题,旨在研究基于力电响应的压电悬臂梁振动疲劳寿命预测方法。结合压电悬臂梁振动疲劳试验测得的试验结果,以剩余刚度理论和“两段式”疲劳寿命分析模型为基础提出一种基于谐振频率的压电悬臂梁疲劳寿命预测方法;进一步分析振动疲劳过程中谐振频率变化与负载功率变化的关系模型,提出一种基于负载功率的压电悬臂梁疲劳寿命预测方法。结果表明:基于谐振频率的压电悬臂梁疲劳寿命预测方法的平均误差在10%~20%之间,其误差范围控制在1.5倍误差线以内;而基于负载功率的压电悬臂梁疲劳寿命预测方法的平均误差集中于25%左右,误差范围均控制在2倍误差线以内且属于偏安全的预测效果。

双激励压电悬臂梁的力电响应分析

压电能量收集器因其结构简单、能量密度高、不受电磁干扰、能够在较低的频率收集振动能等优点,在机械、电子和航空航天等领域具有良好的应用前景。针对提高压电振动能量收集器发电效率的动力学设计,旨在研究双激励环境下压电悬臂梁的力电响应特性。根据Euler-Bernoulli梁理论、压电材料本构关系以及克希霍夫定律,建立双激励压电悬臂梁的机电耦合动力学模型。在此基础上,应用Galerkin法与模态叠加原理推导压电悬臂梁的力电响应表达式,建立根部应变与输出电压的关系模型。测试不同参数下单/双激励压电悬臂梁的力电响应特性,验证理论推导的合理性。最后,分析相位对双激励下压电悬臂梁输出电压的影响。结果表明:压电悬臂梁在双激励下的应变幅频响应变化规律与电压响应规律基本吻合;双激励下压电悬臂梁的力电响应曲线均呈现先增大,在接近共振频率达到极值时减小的变化趋势;激励幅值的增大导致压电悬臂梁的刚度和共振频率降低,试验测得的压电悬臂梁最大频率降为1.5 Hz;调节2种激励信号的相位,会影响输出电压响应,而且在一个周期内呈先减小后增大的趋势。

基于ANSYS的1-3型水泥基压电复合材料力电响应分析

运用ANSYS有限元方法,分别对PZT5H压电陶瓷和1-3型水泥基压电复合材料的力电响应进行了模拟分析。分析结果表明:在位移约束和面载荷下,PZT5H压电陶瓷和1-3型水泥基压电复合材料上的最大位移和最大电势均发生在压电陶瓷(柱)上表面,且产生的最大电压均发生在最大位移处,陶瓷在垂直方向上的电势与位移分层明显且一致。

PVDF/GO柔性复合薄膜的制备及力电响应性能

采用Hummers法制备氧化石墨烯纳米粒子(GO),并通过静电纺丝技术制备不同含量的聚偏氟乙烯/氧化石墨烯(PVDF/GO)柔性纳米纤维复合薄膜,探究了GO含量对PVDF/GO复合薄膜材料的结晶行为,以及力电响应性能的影响。通过差示量热扫描法和X射线衍射法分析PVDF/GO复合薄膜材料的结晶行为,采用力电响应测试装置对PVDF/GO复合薄膜材料的力电响应性能进行分析。结果表明:当GO添加量为0.4 wt.%时,PVDF/GO复合薄膜材料的结晶度和结晶中的β相含量分别为54.66%和81.44%,材料表现出优异的力电响应性能,在频率为1 Hz,2 N的作用力下,其开路电压为0.59 V,短路电流为0.12 nA,响应信号稳定清晰,为电活性高分子及其复合材料在柔性智能可穿戴器件中的应用提供了新路径。

循环荷载下1-3型水泥基压电复合材料的力电响应

利用MTS810万能材料试验机,对1-3型水泥基压电复合材料开展了准静态单轴压缩试验和循环加载试验。结果表明:在循环荷载下,试件输出电压与施加荷载之间呈现出一一对应的响应特性;在较高应力比下,随循环周次增加,试件输出电压幅值无明显变化;在较低应力比下,随循环周次增加,试件输出电压幅值呈现递减规律,加载前期电压幅值下降较快,后期逐渐趋于平稳;相同应力比时,随循环周次增加不同加载频率下,试件输出电压幅值变化规律与输出电压幅值随应力比的变化规律一致。

冲击载荷下2-2型水泥基压电复合材料力电响应特性

研究2-2型水泥基压电复合材料在冲击载荷下的力电响应特征,利用分离式Hopkinson压杆装置进行冲击加载,借助超高速摄影技术观察试样在冲击载荷下的破坏形貌。结果表明:冲击载荷下,压电复合材料具有明显的应变率效应,是应变率敏感材料;压电复合材料的力电响应存在一个临界值,当应力小于该临界值时,试样的电信号与施加载荷之间具有良好的线性关系;动态增强因子可以有效描述压电复合材料压缩强度的率效应规律,在线性范围内,随着应变率的增大,试样的动态增强因子也增大,且具有稳定的增长率;由Maxwell模型得到的压电复合材料应力松弛时间随应变率增大单调递减;冲击载荷下,2-2型水泥基压电复合材料与压电陶瓷的电学失效发生在力学失效之前,且均呈现“爆炸式”破碎,压电陶瓷还伴随着明显的电弧放电现象。

1-3型水泥基压电复合材料在冲击载荷下的电学响应

采用切割-浇注法制备1-3型水泥基压电复合材料,并利用分离式霍普金森压杆测量装置(SHPB),对PZT5压电陶瓷和1-3型水泥基压电复合材料在冲击载荷作用下的力电响应进行实验研究与分析。研究表明:在冲击载荷作用下,PZT5压电陶瓷和1-3型水泥基压电复合材料的电位移与应力具有较好的动态响应;在相同荷载作用下,两者的电位移随应变率的增加而增加,且产生相同应变所对应的应力值也随着应变率的增加而增加,表现出"率相关"的材料特征。

Involvement of cyclic electron flow in irradiance stress responding and its potential regulation of the mechanisms in Pyropia yezoensis

Pyropia yezoensis, belongs to the genus of P orphyra before 2011, inhabit on intertidal zone rocks where irradiation changes dramatically, implying that the seaweed has gained certain mechanisms to survive a harsh environment. Based on the photosynthetic parameters with or without the inhibitors determined by a Dual-PAM-100 apparatus, we investigated the photosynthetic performance and the changes in electron fl ow that occurred during the algae were stressed with dif ferent light intensities previously. When the irradiation saturation was approaching, the CEF around PS I became crucial since the addition of inhibitors usually led to an increase in non-photochemical quenching. The inhibitor experiments showed that there were at least three dif ferent CEF pathways in Py. yezoensis and these pathways compensated each other. In addition to maintaining a proper ratio of ATP/NAD(P)H to support effi cient photosynthesis, the potential roles of CEF might also include the regulation of dif ferent photoprotective mechanisms in Py. yezoensis. Under the regulation of CEF, chlororespiration is thought to transport electrons from the reduced plastoquinone(PQ) pool to oxygen in order to mitigate the reduction in the electron transfer chain. When irradiation was up to the high-grade stress conditions, the relative value of CEF began to decrease, which implied that the NADP+ pool or PQ + pool was very small and that the electrons were transferred from reduced PS I to oxygen. The scavenging enzymes might be activated and the water-water cycle probably became an ef fective means of removing the active oxygen produced by the irradiation stressed Py. yezoensis. We believe that the dif ferent mechanisms could make up the photoprotective network to allow Py. yezoensis for survival in a highly variable light stress habitat, which may enlighten scientists in future studies on irradiance stress in other algae species.

Mechanical response of transmission lines based on sliding cable element

In order to study the sliding characteristics when the cable is connected with the other rods in the transmission line structures,a linear sliding cable element based on updated Lagrangian formulation and a sliding catenary element considering the out-of-plane stiffness coefficient are put forward.A two-span and a three-span cable structures are taken as examples to verify the sliding cable elements.By comparing the tensions of the two proposed cable elements with the existing research results,the error is less than 1%,which proves the correctness of the proposed elements.The sliding characteristics should be considered in the practical engineering because of the significant difference between the tensions of sliding cable elements and those of cable element without considering sliding.The out-of-plane stiffness coefficient and friction characteristics do not obviously affect the cable tensions.

Study on Improvement of Seismic Performance of Transmission Tower Using Viscous Damper

The earthquake resistance of transmission tower has been often discussed from the viewpoint of reinforcing the foundation of steel tower, but there are also few studies considering the damping characteristics of the tower. This paper focuses on the viscous damper which has been adopted for seismic reinforcement of bridges in recent years. The purpose of this study is to improve the seismic performance of steel tower by giving the high damping to the tower. We construct a single tower model considering the influence of transmission line, and then simulate the vibration characteristics and seismic behavior of the tower by the eigenvalue analysis and the dynamic response analysis. The results show that the transmission tower with viscous damper can reduce its own response effectively and drastically. This research concludes that it is necessary to consider the extreme increase of steel tower＇s response depending on the seismic wave and the collapse of steel tower can be avoided by using the optimum damper in the design of the transmission tower.

Riser VIV and its numerical simulation

This paper summarizes some of the typical riser vortex-induced vibration （VIV） problems in subsea oil and gas developments, and presents the corresponding computational fluid dynamics （CFD） time domain simula- tion results to address these problems. First, the CFD time domain simulation approach was applied to analyze the wake field behind a stationary cylinder and a vibrating cylinder. Then a vertical riser VIV response under uniform current was studied. The VIV response time histories revealed some valuable clues that could lead to explanation of the higher harmonics. After that, a vertical riser VIV response under shear current was investigated. A 3 000 ft （1 ft=-0.304 8 m） water depth top tensioned riser was sized, and its VIV responses under uniform and shear current were studied. Then this paper continues to discuss one catenary flexible riser VIV response during normal lay. Last, the time domain simulation approach was applied to a partially submerged flexible jumper, to study the jumper VIV behavior, and dynamic motion envelopes. It was demonstrated that the time domain simulation ap- proach is able to disclose details of the flow field, vortex shedding pattern, and riser dynamic behavior, and han- dle different tvoes of risers under different Woe of currents.

Nonlinear static response of piezoelectric plates considering electro-mechanical coupling

Nonlinear static analysis of piezoelectric plates has been carried out using nonlinear finite element method considering electro-mechanical coupling,The geometrical nonlinearity has been taken into account and electric potential is assumed to be quadratic across the plate thickness,The governing equations are obtained using potential energy and Hamilton's principle that includes elastic and piezoelectric effects.The finite element model is derived based on constitutive equation of piezoelectric material accounting for coupling between elasticity and electric effect using higher order plate elements,Results are presented for piezoelectric plate under different mechanical boundary conditions,Numerical results for the plate are given in dimensionless graphical forms.Effects of boundary conditions on linear and nonlinear response of the plate are also studied.The numerical results obtained by the present model are in good agreement with the available solutions reported in the literature.

Impact of Weather Conditions and Dynamic Load Models on Steady State and Dynamic Response of Power System

This paper gives an insight on the effect of transmission line temperature variations, resulting from loading and weather conditions changes, on a power system＇s steady state and dynamic performance. The impact of dynamic load models on system stability is also studied. The steady-state and dynamic stability simulation results of a 39 bus system for constant line impedance （the traditional simulation practice） are compared to the results with estimated, but realistic, temperature varied line impedances using PSLF （positive sequence load flow） software. The modulated line impedances will affect the thermal loading levels and voltage profiles of buses under steady state response, while the dynamic results will show improved damping in electro-mechanical oscillations at generator buses.

Research and Application of Probability Distribution of Wind Power Fluctuation Characteristics

The fluctuation characteristics is the inherent property of wind power.Through analysis of a large number of wind t＇anns based on measured data,we find it describes the best probability distribution of wind power fluctuation for the mixed Gauss distribution of two components,and try to carry out the physical interpretation of two components.Further discussion is between the probability distribution of fluctuating wind power time difference and whole relationship.It is found that the two have basic similarity.Through comparing the different time level data quantified losses the information of wind power fluctuation,quantitative determination of the degree of impact prediction.We can summarize and understand of wind power fluctuation,constructing instance from the wind farm construction and monitoring prediction two aspect recommendations to overcome the adverse effects of wind power fluctuations on the power grid operation.

Power ＂Smart Pricing＂ with and without Smart Meters

Over the past several years, the Taiwan Power Company has launched two smart pricing programs to assess the demand response of residential customers： the TOU （time-of-use） rate scheme and the DRI （demand reduction incentive） scheme. This paper discusses these two programs and evaluates their respective performances. We develop an efficient approach based on marginal cost pricing to redesign the TOU rate scheme. In our finding, the TOU price levels could be revised to encourage more customers to participate by enlarging the price gap. Moreover, the DRI scheme can be further improved in order to reach an efficient win-win solution among customers, the utility and society. This can be achieved via a careful design of incentive tariff discounts to take account of the time-of-use or location-specific features of the power supply/demand condition.

Fault Current Limiters and Impacts on the System Protection Behavior

A deregulated power market is making short-circuit currents likely to exceed the thermal or mechanical permissible limits of switchgear. Consequently fault current limiters （FCL） become more necessary in power systems. The use of FCLs has an impact on the protection schemes and functions in power systems. Thus, before FCLs can be applied in the network, the impacts on existing protection system must be understood. Depending on the current limiting technique used, today＇s protection concepts may have to be adapted or revised to ensure proper network protection selectivity. A relationship between fault current limiters and protection schemes should be established by taking into account both protection and network specific issues, such as the impact of different FCL technologies, existing and new protection concepts, selectivity and innovative network. This paper is presenting a frame work for accomplishing this task.

功能梯度压电界面层在球形压头作用下的接触问题

材料参数的不连续变化是导致界面处裂纹萌生和分层现象的重要原因。将材料参数连续变化的功能梯度压电材料用作界面层是抑制界面处裂纹萌生和分层的重要方法。主要研究了压电涂层-功能梯度压电界面层-压电基底结构在刚性绝缘球形压头作用下的轴对称无摩擦接触问题。首先,假设涂层和基底为均匀压电材料,建立材料参数沿厚度方向按照指数函数形式变化的功能梯度压电界面层的接触力学分析模型;其次,利用Hankel积分变换方法,将刚性球形压头作用下压电涂层-功能梯度压电界面层-压电基底结构的轴对称无摩擦接触问题转化为奇异积分方程并求解;最后,得到材料非均匀参数对涂层、梯度压电界面层、基底结构内部及界面处的力电响应的影响。研究结果表明:功能梯度压电材料作为界面层连接压电涂层和基底时,可以消除界面处的材料参数不连续导致的界面应力不连续;梯度压电材料参数的变化对界面层的应力与电位移分量有显著影响。

压电涂层-功能梯度压电界面层-基底结构的二维接触问题研究

在多层压电元件中,由于界面处材料成分和性质的突变,常常导致界面处应力集中,使得界面处出现开裂或蠕变现象,从而大大缩短了压电元件的使用寿命.功能梯度压电材料作为界面层,可有效的缓解界面材料不匹配导致的破坏.论文主要研究利用功能梯度压电材料界面层连接压电涂层和基底,分析三层结构在圆柱型压头作用下的力电响应.利用傅里叶积分变换方法,论文将压电涂层-功能梯度压电层-基底结构在刚性圆柱压头作用下的二维平面应变接触问题转化为带有柯西核的奇异积分方程.运用高斯-切比雪夫积分公式,将奇异积分方程转化为线性方程组并对其进行数值求解,得到压电涂层-功能梯度压电层-基底结构在圆柱形压头作用下的应力分布和电位移分布.数值结果表明,梯度压电材料参数的变化对结构中的力电响应具有重要的影响.论文研究结果对于利用功能梯度压电界面层消除界面处的应力不连续导致的界面破坏具有重要的理论指导意义,研究结果可为功能梯度压电材料界面层的设计提供帮助.