Robust Nonlinear Current Sensorless Control of the Boost Converter with Constant Power Load

The boost converter feeding a constant power load (CPL) is a non-minimum phase system that is prone to the destabilizing effects of the negative incremental resistance of the CPL and presents a major challenge in the design of stabilizing controllers. A PWM-based current-sensorless robust sliding mode controller is developed that requires only the measurement of the output voltage. An extended state observer is developed to estimate a lumped uncertainty signal that comprises the uncertain load power and the input voltage, the converter parasitics, the component uncertainties and the estimation of the derivative of the output voltage needed in the implementation of the controller. A linear sliding surface is used to derive the controller, which is simple in its design and yet exhibits excellent features in terms of robustness to external disturbances, parameter uncertainties, and parasitics despite the absence of the inductor’s current feedback. The robustness of the controller is validated by computer simulations.

A New Fracture Criterion for a Crack under Combined Mode Loading

A new fracture criterion was proposed. The physical explanation of the criterion is that crack will propagate when the minimum strain energy density in iso hoop stress curve reach a critical strength of the material considered. The resulting curve of critical fracture of mixed mode cracks shows that the present fracture is efficient and more accurate than the previous criteria.

Computational Fracture Analysis of an AFM-Specimen under Mixed Mode Loading Conditions

Fracture processes in ship-building structures are in many cases of a 3-D character. A finite element （FE） model of an all fracture mode （AFM） specimen was built for the study of 3-D mixed mode crack fracture behavior including modes Ⅰ,Ⅱ, and Ⅲ. The stress intensity factors （SIFs） were calculated by the modified virtual crack closure integral （MVCCI） method, and the crack initiation angle assessment was based on a recently developed 3-D fracture criterion--the Richard criterion. It was shown that the FE model of the AFM-specimen is applicable for investigations under general mixed mode loading conditions, and the computational results of crack initiation angles are in agreement with some available experimental findings. Thus, the applicability of the FE model of the AFM-specimen for mixed mode loading conditions and the validity of the Richard criterion can be demonstrated.

Effect of loading point position on fracture mode of rock

Anti symmetric four point bending specimen with different loading point positions was used to study effect of loading point position on fracture mode of rock in order to explore a feasible method for achieving Mode Ⅱ fracture and determining Mode Ⅱ fracture toughness of rock, K ⅡC . Numerical and experimental results show that the distance between the inner and outer loading points, L 1+ L 2, has a great influence on stresses at notch tip and fracture mode. When L 1+ L 2>0.5 L or 0.1 L < L 1+ L 2<0.5 L , maximum principal stress σ 1 exceeds the tensile strength σ t. The ratio of τ max / σ 1 is relatively low or high and thus Mode Ⅰ or mixed mode fracture occurs. When L 1+ L 2< 0.1 L , σ 1 is smaller than σ t and the ratio of τ max / σ 1 is much higher, which facilitates the occurrence of Mode Ⅱ fracture.

A HALF PLANE CRACK UNDER THREE-DIMENSIONAL COMBINED MODE IMPACT LOADING

The dynamic stress intensity factor history for a half plane crack in an otherwise unbounded elastic body, with the crack faces subjected to a traction distribution consisting of two pairs of suddenly-applied shear line loads is consid- ered. The analytic expression for the combined mode stress intensity factors as a function of time is obtained. The method of solution is based on the application of integral transforms and the Wiener-Hopf technique. Some features of the solutions are discussed and graphical numerical results are presented.

EFFECT OF TEMPERATURE ON THE FRACTURE MODES OF BHW-35 STEEL UNDER MODE-Ⅱ LOADING

Finite element method(FEM)has been used to analyze the stress and strain fields and the stress tri-axial levels around the tip of the crack under mode-Ⅱ loading.The results show that: under mode-Ⅱ loading,the direction of the maximum tensile stress and that of the maximum tri-axial levels(R_ )exist at an angle of-75.3°from the original crack plane:the maximum shear stress and R_ =0 exist along the original crack plane. Mode-Ⅱ loading experiment using BHW-35 steel at different temperatures show that there are two kinds of fracture mode.opening mode(or tensile mode)and sliding mode(or shear mode).A de- crease in temperature causes the fracture mode to change from shear mode to tensile mode.For BHW- 35 steel,this critical temperature is about-90C.Actually.under any kind of loading mode(mode Ⅰ,mode Ⅱ,mode Ⅲ or mixed mode),there always exist several kinds of potenital fracture modes (for example,opening mode.sliding mode.tearing mode or mixed mode).The effect of temperature under mode-Ⅱ loading is actually related to the change of the elastic-plastic properties of the material.

Failure modes of PDC cutters under different loads

The capability of several types of flat PDC cutters to withstand combined loads were tested and evaluated by the impact and cutting of single PDC cutter on granite in a linear impact cutting table. The primary failure modes of PDC cutters withstanding different combined loads were investigated and analyzed. The suggestions of enhancing PDC cutters to be suitable for drilling very hard rock have been made.

A THEORETICAL MODEL OF MATRIX CRACKING IN COMPOSITE LAMINATES UNDER THERMOMECHANICAL LOADING

A theoretical approach is presented for analyzing the ply crackingin general symmetric lami- nates subjected to any combination ofin-plane mechanical loading and uniform temperature changes. Theequivalent constraint model proposed by the authors in a previouswork is used to account for the cracking in- teraction betweenlaminae in the laminates. By using a superposition schemce and thestress field solutions the energy release rate for a ply cracking isexplicitly as a function of stiffness reduction parameters of thelaminates. The ratio of mode Ⅰ to mode Ⅱ is introduced formconstruction of the fracture criterion. The effects of the laminateparameters and the crack spacing on the energy release rate and themode mixity are illustrated. Finally, the model is used to predictthe thermomechanical load for the first-ply-cracking.

落石被动柔性防护网非线性静力设计方法及验证

被动柔性防护网是一种常见的落石灾害防治措施。针对当前落石被动柔性防护网尚无适用的工程化设计方法的现状,以非线性计算过程中结构内能与设计防护能级相等作为加载完成的判别准则,建立了落石被动柔性防护网的非线性静力设计方法。基于LS-DYNA对250~5000 kJ共8种常用能级的被动柔性防护网开展非线性动力分析,明确了冲击力的分布范围及相对大小,形成了适用于不同能级落石被动柔性防护网非线性静力设计的荷载模式。为了有效模拟被动柔性防护网特殊的受力特征,开发了由索单元与受拉弹簧单元组成的非线性耗能单元用于耗能器模拟,开发了内部由多段索单元组成的滑移索单元用于滑移边界以及网环单元模拟。基于对网片冲击试验的反演和3500 kJ被动柔性防护网的设计及足尺冲击试验检验,验证了所提出的落石被动柔性防护网非线性静力设计方法的有效性。

基于温升特性的强迫导向油循环风冷结构变压器负荷能力评估

针对强迫导向油循环风冷(oir directrd air forced,ODAF)结构变压器负荷能力受温升约束影响的问题,提出了3种负荷类型情况下变压器负荷能力评估方法。首先,考虑风扇与油泵的运行状态以及油粘度变化对热阻的影响等因素,基于热电类比法建立了变压器热路模型,以计算绕组热点与顶部油温度;其次,采用粒子群优化(particle swarm optimization,PSO)算法拟合热路模型参数,并基于2台不同型号变压器的运行数据,对热路模型的计算精度与拟合参数适用性进行有效性验证;最后,参考GB/T1094.7负载导则给出的温升限值,基于温升特性提出了负荷能力评估模型。分析结果表明,该研究所提热路模型计算热点温度的误差不大于2.35℃,在工程允许范围内;正常周期性负荷下当环境温度低于1℃时,关闭1组子散热器后仍满足温升约束。

软硬不均地层盾构隧道荷载模式研究

系统考虑隧道埋深、滑移面形式、侧压力系数与地层的关联,提出一种适用于软硬不均地层的盾构隧道荷载模式。对于浅埋隧道,基于椭球体理论推导极限状态下滑移面为椭圆的侧压力系数及竖向松动土压力表达式,并构建力学平衡方程推导侧压力计算式;对于深埋隧道,考虑软硬不均地层突变性并对太沙基理论滑移面宽度进行合理修正,推导对应的围岩压力计算式;再结合软硬不均地层分界线位于隧道水平中线上方、下方2类典型工况,推导出隧底反力表达式;最后结合工程实例对所提荷载模式进行验证。结果表明:与修正惯用法荷载体系相比,所提方法得到的软土-硬土隧道顶部、下半拱竖向土压力与实测值的误差分别缩小74%和172%;相较于软土-硬土隧道,该方法应用于土层-岩层隧道时,计算得到的下半拱竖向土压力、隧底侧向土压力与实测值的误差更小,即所提荷载计算模式更符合隧道实际受荷状态,且当隧道埋深与开挖直径之比较大以及下部地层越坚硬时,其适用性越强。

Geiger型索穹顶冲击动力响应与失效机理研究

针对当前索穹顶结构缺乏冲击荷载作用下结构动力响应和失效机理的研究现状,该文基于ANSYS/LS-DYNA分析软件,提出了Geiger型索穹顶结构冲击动力分析模型,详细分析了冲击作用下结构的节点位移和杆件内力响应,并进一步结合美国规范UFC4-023-03的倒塌准则,对结构的失效模式进行评价,提出了三种失效模式,即结构轻微损伤、结构局部损伤和结构整体失效。随后,基于冲击破坏杆件数和杆件内力损伤程度,提出了结构整体损伤指数的概念,通过参数分析,探索了索穹顶结构在不同冲击物参数下整体损伤指数的变化特点及不同设计参数下的抗冲击性能。研究发现了整体损伤指数与三种失效模式之间的关系:当失效模式为结构轻微损伤时,其整体损伤指数小于0.3;当失效模式为结构局部损伤时,其整体损伤指数位于0.3~0.8之间;当失效模式为结构整体失效时,其整体损伤指数大于0.8。基于此提出了失效模式控制方程。冲击荷载越靠近结构中心,结构发生整体失效概率越大,反之则局部损伤和轻微损伤概率越大。提高初始预应力水平和杆件截面面积能有效提高结构的抗冲击性能。

湿热老化对FRP-钢胶接节点力学性能的影响

为进一步研究湿热老化对纤维增强复合材料(FRP)-钢胶接节点力学性能的影响,在现有试验的基础上,采用轮盘加载装置,分别从6个加载条件对湿热老化处理后的FRP-钢胶接节点进行一系列加载测试,研究了湿热老化对FRP-钢胶接节点的极限破坏荷载、破坏模式、刚度以及强度破坏准则的影响,并将结果与未老化胶接节点进行比较。试验结果表明:在剪切和拉伸荷载作用下,湿热老化显著降低了FRP-钢胶接节点的极限破坏荷载,分别降至11.0 kN和41.9 kN;在组合荷载作用下,湿热老化对极限破坏荷载的影响较小;老化与未老化FRP-钢胶接节点的强度破坏准则曲线彼此接近;对于拉伸和拉伸/剪切组合荷载条件,湿热老化改变了FRP-钢胶接节点的破坏模式,即从FRP夹芯板和结构胶粘贴层之间的部分界面破坏到覆盖整个结构胶粘结区域的FRP分层破坏和纤维断裂破坏的组合;在6个加载条件下,湿热老化均明显降低了FRP-钢胶接节点的刚度。因此,在设计及使用FRP-钢胶接节点时,应该充分考虑湿热老化对FRP-钢胶接节点力学性能的影响,避免其发生结构破坏。

嵌入式操作系统加载模式选择方法研究

针对现有嵌入式操作系统加载模式选择方法会增加额外硬件开销和牺牲加载速度的问题,提出了一种基于链路状态信息的嵌入式操作系统加载模式选择方法。该方法利用上电后先复位PHY等外设再复位CPU,CPU运行BootLoader读取并判断PHY的链路建立指示信号确定加载模式,若链路建立指示信号指示网络已连接好,则选择以太网远程加载模式,其他情况下都选择本地存储器加载模式。工程应用实测结果表明,该方法稳定可靠。

海上液压修井机承载模式优化及应用

液压修井机自从在国内海上平台用于修井以来,已经进行了多次作业。在作业过程中,如何提高液压修井机的抗风能力、安全快速高效地实现液压修井机在海上平台槽口间的转换,一直是一项重要的课题。通过对承载模式的创新,优化设计出了适用于渤海各采油平台的滑移导轨,承载模式由传统的井口承载优化成为滑移底座承载,增加了液压修井机的稳定性,提高了修井作业效率,降低了修井作业成本,是对液压修井作业模式的再一次创新。

基于工作模态辨识的高速飞行器运输约束动载荷辨识技术研究

在运输振动测量数据基础上,本文提出了基于工作模态辨识的高速飞行器运输约束动载荷辨识方法。首先,详细介绍了ERA(Eigensystem Realization Algorithm)环境激励模态辨识方法的理论和载荷辨识时域方法的理论;其次,给出了飞行器结构动力学建模方法;再次,提出了基于工作模态辨识的高速飞行器运输约束动载荷辨识计算工作流程,详细分析了各操作步骤;最后,通过算例验证了方法的可行性,其中,基于振动测量数据,采用环境激励模态辨识方法辨识各时刻的模态,包括模态频率和模态振型,再利用振动响应的模态叠加原理和模态正交理论,获取各时刻飞行器低阶模态的响应,再结合模态剪力和模态弯矩进行动载荷识别,采用载荷识别方法获取了高速飞行器约束点的约束载荷时域历程。

退变及加载方式对于高加载速率下椎间盘力学行为的影响

腰椎间盘退变导致了整个腰椎间盘粘弹性特性的变化,但是对于腰椎间盘退变的确切机制目前仍知之甚少,特别是在加载方式和高加载速率方面。利用胰蛋白酶溶液制备退变牛腰椎间盘模型,应用数字图像相关技术对退变椎间盘进行轴向压缩实验,研究加载方式对于高加载速率下腰椎间盘内部位移分布及弹性模量的综合影响。结果表明:无论退变前后,高加载速率下腰椎间盘的弹性模量均显著高于准静态加载时。退变对于弹性模量的影响及高加载速率下腰椎间盘内部位移分布的影响均与加载方式有关。组织切片染色结果表明,椎间盘的髓核和纤维环组织在注射胰蛋白酶后产生了不同程度的结构破损。

偏差电量考核机制下聚合温控负荷群控制策略

为降低售电公司在电力交易中的偏差考核电量和惩罚成本,以在用户负荷中占比较高的温控负荷为控制对象,建立配电网监测控制系统,收集电力市场和居民负荷数据,再根据这些数据设计基于聚合温控负荷群双层优化调度模型的直接负荷控制策略。仿真结果表明,该策略能降低配电网功率不平衡性,有效增加温控负荷的可调度容量,减少温控负荷的调度次数,降低售电公司的偏差考核电量,提高售电公司利润。

地震荷载下边坡大变形失稳破坏形式研究

采用物质点法分析边坡失稳破坏模式,通过改变土体参数,确定浅层、中层与深层破坏形式边坡模型,进而分析在考虑土体应变软化模型及不同地震荷载作用下,三种边坡破坏模式的破坏过程和变化规律.研究表明,在静态计算中考虑应变软化时,边坡破坏过程较为复杂,滑体沿着滑面整体滑移后,浅层破坏滑体会持续破坏成碎散块体,中层破坏滑体持续分裂成小块体,深层破坏滑体出现新的层状失效区.动态计算中不考虑应变软化时,地震荷载不改变边坡的破坏形式,但加剧边坡的滑移和变形,且随着地震荷载峰值加速度的增加而增加.在考虑应变软化时,地震荷载峰值加速度的增加会改变边坡破坏形式,摩擦角在这个过程中起着重要作用.研究结果可为边坡治理、预防滑坡提供参考.