基于弯矩等效的装载机外载荷当量与载荷谱编制

为了编制装载机工作装置载荷谱进行结构疲劳性能研究,提出了一种基于动臂截面弯矩等效的装载机外载荷当量方法,将装载机铲装物料时所受外载荷简化为一个作用在铲斗上的集中载荷并进行载荷谱编制。以动臂前后两端铰点连线为基准构建动臂局部坐标系,将铲斗铰点实测载荷转化为局部坐标系下动臂铰点载荷,研究铲掘姿态下动臂截面弯矩和装载机外载荷的同步对应关系,确定了外载荷作用点位置和作用方向,利用动臂最大弯矩截面的弯矩等效建立了装载机外载荷的当量数学模型。由实测的铲斗铰点载荷时间历程和装载机外载荷当量模型得到ZL50G装载机当量外载荷的时间历程,采用雨流计数得到典型作业介质下当量外载荷均值、幅值、频次的统计特性,编制多工况合成的工作装置疲劳试验程序载荷谱。结果表明:基于动臂截面弯矩等效方法能够获取固定姿态下装载机当量外载荷作用位置和作用方向;利用动臂最大弯矩截面的弯矩得到当量载荷时间历程,且在当量载荷与实测载荷下动臂截面弯矩变化规律和大小保持一致;当量载荷均值服从正态分布、幅值服从三参数威布尔分布,利用雨流计数和参数外推法编制的适用于工作装置疲劳试验的变均值加速加载程序载荷谱,缩短了疲劳台架试验的加载时间。提出的基于动臂截面弯矩等效的装载机外载荷当量模型以及载荷谱编制方法,可为装载机工作装置疲劳寿命评估和台架试验规范的制定提供依据。     

双频载荷等效计数法

本文提出双频载荷等效计数的两种方法:其一,首先对载荷进行雨流计数,利用应力-应变(ε-σ)滞回环,使雨流计数前、后的双频载荷具有一一对应关系,从而推导出叠加在大载荷基础上的小载荷的等效循环计数公式。其二,将大载荷的雨流计数结果转化为脉动载荷,再将小载荷叠加上去,使转换后的载荷与原载荷有其对应区间,然后,依据等级载荷累加原理得出双频载荷等效计数公式。最后根据等效应力公式和疲劳累积线性损伤公式得到双频载荷疲劳寿命估算公式。     

宽带随机载荷谱下结构疲劳寿命的计算

以目前国际上普遍认可的一种雨流循环计数应力范围概率密度函数为依据,采用结构危险部位疲劳寿命曲线,利用不完全Gamma函数,建立了一种宽带随机载荷谱下结构疲劳寿命计算的一种解析解法,为在宽带随机载荷谱下服役的结构在设计阶段用频域法进行疲劳寿命计算提供了一种快捷方法。     

改进雨流计数法在拖拉机零部件疲劳寿命估算中的应用

本文介绍了传统的载荷数据统计处理方法和改进的雨流计数法,着重强调以三峰谷计数原则代替一般的四峰谷计数原则。提出了在用改进雨流计数法进行载荷数据统计时结合载荷分布参数估计的变差系数法,可简化统计处理过程,提高计算速度。并且采用改进雨流计数法编制了上海-50拖拉机驾驶室骨架载荷谱,对骨架的随机疲劳寿命进行估算。     

一种修正的基于临界平面多轴循环计数法

进行多轴随机载荷下的结构疲劳寿命分析时,需选择合适的循环计数方法提取损伤事件.结合疲劳寿命预测方法中的临界平面法,对Langlais多轴循环计数法进行了讨论,并在此基础上完成了对Langlais多轴循环计数法的修正.修正后的多轴循环计数法可以精确地考虑到1个主通道循环内辅助通道的全部载荷信息;同时发展了修正Langlais法新的实现方法,可以用于封闭曲面法计算有效载荷;对三点雨流计数法的循环计数起始点选择进行了改进,提高了循环计数效率.     

装载机工作装置随机载荷统计特性分析

装载机工作装置随机载荷的统计分析是工作装置载荷谱编制及结构疲劳分析的基础。文章实测了装载机工作装置在大石方、原生土、小石方和沙子4种物料工况下铲斗的受力载荷时间历程,采用统计方法对信号中的毛刺进行甄别与剔除,按照工况时间比例对载荷进行分段拼接,检验分段载荷的平稳性和各态历经性;利用数理统计的方法分析分段实测随机载荷的统计特性,采用峰谷抽取和雨流计数法统计载荷均值和幅值的频次,得到了均值频次和幅值频次分别服从正态分布和三参数威布尔分布的拟合分布数学模型,且载荷均值分布和幅值分布相互独立。随机载荷统计分析的方法和结果为装载机工作装置疲劳载荷谱编制以及可靠性台架试验提供了依据。     

装载机工作装置的疲劳试验及疲劳可靠性评估

为了对装载机工作装置进行抗疲劳设计和疲劳可靠性评估,在获得ZL50G装载机工作装置固定姿态当量外载荷二维载荷谱的基础上,对载荷谱进行了等寿命加速处理,设计疲劳试验台进行加速加载疲劳试验研究,并对工作装置进行了极小子样疲劳可靠性评估。结果表明:利用加速加载谱加载35.88 h可以等效装载机连续作业495.67 h,实现了工作装置快速疲劳试验的目的;工作装置试件的实际疲劳寿命的平均值为9 132.20 h,疲劳破坏起始于销轴衬套与动臂焊接处,靠近动臂板处的焊趾裂纹源是造成疲劳断裂的主要因素;基于给定工作寿命和疲劳寿命试验结果的极小子样疲劳可靠性评估,获得了工作装置寿命与可靠度为3次多项式的数学关系。     

基于动载荷谱的齿轮弯曲疲劳寿命预测

为了探讨齿轮弯曲疲劳寿命计算问题,将齿轮疲劳总寿命分为两个阶段,即疲劳裂纹萌生寿命和裂纹扩展寿命。通过 ADAMS 软件仿真实验齿轮的工作情况,使其接近真实状况,得到齿轮载荷谱。根据齿轮载荷谱,利用有限元ANSYS 软件分析在齿轮齿根危险截面处的最大应力。采用断裂力学、雨流法和 Miner 疲劳损伤累积模型,对考虑动载荷情况下的齿轮弯曲疲劳寿命进行预测,推导了齿根裂纹萌生期和扩展期的疲劳寿命计算公式。在高频疲劳试验机上对算例齿轮进行了双齿脉动加载齿根弯曲疲劳寿命实验研究,理论计算结果与实验结果基本吻合,验证了本文理论分析的正确性。     

近海风电机组单桩式支撑结构疲劳分析

用WAsP分析风场数据得到风速的分布情况,统计各工况的风、浪、流等环境参数.基于支撑结构所受的疲劳载荷,用ABAQUS对结构建模并通过振型叠加法求出应力响应的时间历程.根据S-N曲线、雨流计数法以及线性累积损伤理论,用Fe-safe计算出支撑结构的疲劳寿命并分析各种载荷对结构疲劳寿命的影响.结果表明：支撑结构的疲劳寿命满足要求;风机载荷是结构疲劳的主要影响因素,合理的发电机控制策略有助于提高结构的疲劳寿命.以风向和10 min平均风速为依据划分工况的方法可为海上风力发电结构的疲劳分析提供参考.     

基于虚拟迭代的空调管路疲劳寿命预估方法

文章采用试验与仿真相结合的手段,提出了对时变工况下变频空调管路疲劳寿命进行估算的新方法。在对变频空调器转子压缩机排、回气管口进行振动测试的基础上,采用虚拟迭代的方法对时变工况下的转子压缩机载荷激励进行识别,并使用迭代算法逐步修正载荷激励,保证反求载荷的准确性与可靠性;基于识别的载荷激励,采用瞬态动力学分析求取危险节点的应力谱,使用雨流计数法、基于Miner累积损伤理论估算出危险节点的疲劳寿命。     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

Features of Women's language

Language is a means of verbal communication. People use language to communicate with each other. In the society, no two speakers are exactly alike in the way of speaking. Some differences are due to age, gender, statue and personality. Above all, gender is one of the obvious reasons. The writer of this paper tries to describe the features of women＇s language from these perspectives： pronunciation, intonation, diction, subjects, grammar and discourse. From the discussion of the features of women＇s language, more attention should be paid to language use in social context. What＇s more, the linguistic phenomena in a speaking community can be understood more thoroughly.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-     

Density Functional Theory for the Response of Periodic Systems to Electric Fields Based on the Vector Potential Approach

正The electronic and nuclear(structural/vibrational)response of 1D-3D nanoscale systems to electric fields gives rise to a host of optical,mechanical,spectral,etc.properties that are of high theoretical and applied interest.Due to the computational difficulty of treating such large systems it is convenient to model them as infinite and periodic(at least,in first approximation).The fundamental theoretical/computational problem in doing so is that     

On the Thermodynamic Limit for Responses to Static Electromagnetic Fields

For molecular systems,the quantum-mechanical treatment of their responses to static electromagnetic fields usually employs a scalar-potential treatment of the electric field and a vector-potential treatment of the magnetic field.Although the potential for each field separately is associated with the choice of an(unphysical)origin,the precise choice of the origin for the electrostatic field has little consequences for the results.This is different for the     

Call for Papers

<正>"The Journal of Shanghai Normal University:Mathematics"is published by Shanghai Normal University as regular issues of The Journal of Shanghai Normal University each year from 2014 in English.The editors-in-chief of the issues are professors Yuhao Cong and Maoan Han.The Journal of Shanghai Normal University was started in 1958 with     

Journal of Donghua University ( English Edition) Contents of Volume 31

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