压力容器设计标准中外压圆筒初始几何偏差规定的讨论

分别由简化傅里叶级数模型与一致缺陷模态模型构造带初始几何偏差的外压圆筒,采用ANSYS有限元进行非线性模拟,当模拟得到的临界压力为理想圆筒临界压力的80%时,得到这两种模型对应的几何偏差e值曲线。将上述曲线以及ASMEⅧ-1(或GB 150)、ASMEⅧ-2所规定的e值、Annaratone所著一书中理论公式求得的e值进行比较分析,结果表明:一致缺陷模态法所得结果偏保守;在L/Do较小时,采用ASMEⅧ-1中规定的e值,其结果可能是冒进的;在Do/t与L/Do相同时,由简化傅里叶级数模型得到的e值,明显高于一致缺陷模态模型得到的e值。WRC公报(443号)提到了试验值(p-Test)大于理论值(p-Theory)的现象,这与初始几何偏差在实际情况下和理论模型所假设的初始几何偏差不同有关;由ASMEⅧ-2规定得出的e值均大于简化傅里叶级数模型得到的e值,说明ASMEⅧ-2对于e值的规定是可行的。     

外压圆筒临界压力的双非线性ANSYS有限元模拟与讨论

利用有限元模拟软件ANSYS的几何/材料双非线性分析技术对外压圆筒临界压力进行模拟计算,将模拟结果与文献试验结果、GB 150、ASMEⅧ-2及EN 13445等压力容器设计标准中计算结果进行比较分析。结果表明:若ANSYS软件中偏差系数按外压圆筒实际最大偏差考虑,与文献中试验值和Mises公式计算结果的材料非线性修正值相比,ANSYS的模拟结果普遍偏低。模拟值按ASMEⅧ-2第5章设计系数考虑后,得到许用外压力,在弹性失稳阶段时,有的略高于ASMEⅧ-2公式法的,也有的略低于GB 150所得的。在非弹性失稳阶段,模拟所得的许用外压低于ASMEⅧ-2公式法、EN 13445规范计算结果,高于GB 150规范计算结果。     

初始几何缺陷对履带起重机桁架臂临界失稳载荷影响分析

针对履带起重机桁架臂初始几何缺陷对其承载能力影响问题,对相关规范和企业标准进行统计整理,将初始几何缺陷分为两类:臂节几何缺陷和臂节组装产生的几何缺陷.对一致缺陷模态法进行改进,在线性屈曲分析的基础上,考虑了缺陷分布的随机性,建立了模态参与系数的概率模型,提出了多阶模态随机耦合法模拟臂节几何缺陷,并采用等效载荷法模拟臂节组装产生的几何缺陷.算例分析表明,理想臂架的临界失稳载荷为392 t,本文所提方法模拟臂架几何缺陷所得最不利临界失稳载荷为361 t,相比降低了7.9％;考虑前四阶单阶模态作为臂节几何缺陷所得最不利临界失稳载荷为368 t.综合上述结果,本文所提几何缺陷模拟方法可以模拟出最不利的缺陷,并且获得最不利缺陷分布下的临界失稳载荷,为桁架臂初始几何缺陷模拟提供一些借鉴和参考.     

外壁受刚性约束的外压圆筒的稳定性试验研究

本文重点研究了内外壁间的间隙、几何形状偏差及残余应力对外壁受刚性约束外压圆筒失稳临界压力的影响。试验表明,间隙是影响临界压力大小的决定性因素,且存在一个临界间隙值。对于钢制圆筒,在间隙小于临界值时,随着间隙的减小,临界压力可大幅度地升高至达拉姆公式计算值的1.8～3.3倍;当间隙大于临界值时,临界压力升高不明显,且随着间隙的增大减小至外壁无刚性约束外压圆筒的临界压力而恒定不变。试验还表明,几何形状偏差会使临界压力严重下降。类似化工设备中的卷焊钢制圆筒松衬里,在其焊缝附近无直边、局部椭圆度不大于0.36%,且间隙小于某值时,其临界压力均可达拉姆公式计算值的2倍以上。     

轴心受压高强钢圆管稳定承载性能研究

对770MPa级高强钢管件的初始几何缺陷、残余应力和本构关系进行了测试，完成了66根770MPa级不同规格高强钢管件的轴压极限承载力试验，结合仿真分析，验证了添加初始缺陷的一致模态法分析高强钢管件极限承载力的准确性。     

含初始缺陷的加强复合材料圆柱壳的非线性屈曲分析

综合考虑几何非线性、材料非线性、横向剪切效应以及初始几何缺陷等因素，对带有加强筋和加强环的复合材料圆柱壳的屈曲问题进行了分析研究。所得数值结果与有关试验值及其它已知解吻合良好，因而可用于实际工程中加强复合材料圆柱壳的设计计算，同时表明这里给出的本构关系对于弹塑性屈曲分析是适用的，并提出保证结构完整性、改善结构整体屈曲性能的关键是控制制造加工质量，减少初始缺陷。     

弹性边界条件下圆板横向自由振动特性分析

采用谱几何法(spectro-geometric method,简称SGM)分析了弹性边界条件下圆板横向自由振动特性。首先,将圆板的振动位移容许函数描述为一种谱形式的改进三角级数,并采用沿边界均匀分布的约束弹簧来模拟弹性边界条件;然后,将未知级数展开系数看作广义变量,应用瑞利-里兹法从能量的角度推导弹性边界条件下圆板结构横向自由振动系统特征矩阵方程;最后,设计搭建了相关实验台架,对圆板结构横向自由振动模态参数进行测试。将文中方法计算结果与文献解、有限元计算结果和实验结果进行对比,验证了谱几何法求解圆板横向自由振动问题的正确性和计算精度。     

含加强肋(环)的非完善复合材料圆柱壳的稳定性分析

综合考虑几何非线性、材料非线性、横向剪切效应及初始几何缺陷等因素，对带有加强肋和加强环的复合材料圆柱壳的稳定性问题进行了分析研究。所得结果与有关试验值及其他已知解吻合良好，因而可用于实际工程中复合材料加强肋(环)圆柱壳的设计计算，同时表明所给出的本构关系对于弹塑性稳定性分析是适用的，并提出保证结构完整性、改善结构整体稳定性的关键是控制制造加工质量，减少初始缺陷。     

含冲击凹坑缺陷的ZM6材料疲劳试验与寿命预估方法研究

制备了ZM6镁合金材料的光滑试样、缺口试样以及含冲击凹坑缺陷的试验件,并对这些试验件进行了疲劳试验测试,获得了含冲击缺陷时不同应力水平下试验件的疲劳寿命.基于连续损伤力学理论,在高周疲劳损伤演化模型的基础上,提出了一种新的多轴疲劳的损伤演化模型,用于描述凹坑局部材料的疲劳损伤.采用Abaqus软件对凹坑缺陷的形成过程进行模拟,得到了凹坑缺陷的几何形状和局部的残余应力应变场.通过Abaqus子程序Usdfld将材料本构和损伤演化进行耦合,从而实现含凹坑缺陷结构件疲劳寿命的计算.结果 显示,预测的中值寿命结果与试验中值寿命结果一致,误差在两倍误差带内,符合工程使用的要求.     

点焊试件中兰姆波传播的有限元模拟及其应用

提出兰姆波评价汽车钢板点焊质量的理论依据及试验方法,评价对象包括点焊焊核的直径及最大拉伸载荷.兰姆波中的多模态频散特性及在复杂结构中的模式转换导致超声检测信号难于区分,通过解析方法难以获得兰姆波在点焊试样中的传播规律,因此采用有限元法模拟兰姆波在点焊试样中的传播.有限元法的模拟结果显示:经焊核传播的A0模态兰姆波特征峰值随焊核直径的增大而减小、随凹痕深度的增大而增大.因此,A0模态兰姆波的特征幅值可望用于评价焊核的形状及力学性能.试验通过调整斜探头入射角度激励A0模态兰姆波对高强度镀锌钢板的点焊试件进行检测试验,结果显示:A0模态兰姆波特征峰值随焊核直径及焊核最大拉伸载荷的增大而减小,该规律与有限元模拟的结果一致,可以用于实际结构点焊质量的无损评价.     

Minimal Realization of Linear Graph Models for Multi-physics Systems

An engineering system may consist of several different types of components,belonging to such physical"domains"as mechanical,electrical,fluid,and thermal.It is t...     

INTEGRAL EQUATION METHOD＇S APPLICATION IN HOLE-EDGE STRESS OF COMPOSITE MATERIAL PLATE WITH DIFFERENT SHAPED HOLES

The strength of composite plate with different hole-shapes is always one of the most important but complicated issues in the application of the composite material. The holes will lead to mutations and discontinuity to the structure. So the hole-edge stress concentration is always a serious phenomenon. And the phenomenon makes the structure strength decrease very quickly to form dangerous weak points. Most partial damage begins from these weak points. According to the complex variable functions theory, the accurate boundary condition of composite plate with different hole-shapes is founded by conformal mapping method to settle the boundary condition problem of complex hole-shapes. Composite plate with commonly hole-shapes in engineering is studied by several complex variable stress fimction. The boundary integral equations are founded based on exact boundary conditions. Then the exact hole-edge stress analytic solution of composite plate with rectangle holes and wing manholes is resolved. Both of offset axis loadings and its influences on the stress concentration coefficient of the hole-edge are discussed. And comparisons of different loads along various offset axis on the hole-edge stress distribution of orthotropic plate with rectangle hole or wing manhole are made. It can be concluded that hole-edge with continuous variable curvatures might help to decrease the stress concentration coefficient; and smaller angle of outer load and fiber can decrease the stress peak value.     

Non-monotonic material contrast in scanning ion and scanning electron images

30 keV Ga⁺ focused ion beam induced secondary electron (iSE) imaging was used to determine the relative contrast between several materials. The iSE signal compared from C, Si, Al, Ti, Cr, Ni, Cu, Mo, Ag, and W metal layers does not decrease with an increase in target atomic number Z₂, and shows a non-monotonic relationship between contrast and Z₂. The non-monotonic relationship is attributed to periodic fluctuations of the stopping power and sputter yield inherent to the ion–solid interactions. In addition, material contrast from electron-induced secondary electron (eSE) and backscattered electron (BSE) images using scanning electron microscopy (SEM) also shows non-monotonic contrast as a function of Z₂, following the periodic behavior of the stopping power for electron–solid interactions. A comparison of the iSE and eSE results shows similar relative contrast between the metal layers, and not complementary contrast as conventionally understood. These similarities in the contrast behavior can be attributed to similarities in the periodic and non-monotonic function defined by incident particle–solid interaction theory.     

Application of Feature Extraction through Convolution Neural Networks and SVM Classifier for Robust Grading of Apples

This paper proposes a novel grading method of apples,in an automated grading device that uses convolutional neural networks to extract the size,color,texture,an...     

分布动态载荷识别的抗噪处理

针对正交多项式频域法在用多种响应对矩形薄板进行载荷识别中抗噪性较差的问题,综合运用平均法、矩阵预处理和奇异值截断法等方法对之进行改善,并引入空间映射的思想,将该方法的应用范围拓展为复杂的模型.利用仿真算例,证实了该方法具有较好的抗噪性.     

基于MELTAC-N平台的核电厂安全级DCS环网研究与测试

针对工程实践中环网通讯相关问题的处理缺乏理论基础及国产化安全级DCS平台的开发缺乏成熟经验借鉴问题,对基于MELTAC-N平台核电厂安全级DCS环网的软硬件实现进行了研究。提出了安全级DCS环网双环网冗余设计、光切换开关设计等硬件设计方法,以及以RPR协议为基础,采用全数据收发策略的软件设计方法。在CPR1000安全级DCS平台上对安全级DCS环网的可靠性及实时性进行了评价,并进行了容错能力、响应时间及响应时间稳定性测试验证实验。结果表明,基于MELTAC-N平台安全级DCS环网软硬件设计具有较好的容错能力及响应时间稳定性。     

Short-Term Relay Quality Prediction Algorithm Based on Long and Short-Term Memory

The fraction defective of semi-finished products is predicted to optimize the process of relay production lines, by which production quality and productivity ar...     

End-to-End Multiview Gesture Recognition for Autonomous Car Parking System

The use of hand gestures can be the most intuitive human-machine interaction medium.The early approaches for hand gesture recognition used device-based methods....     

The laboratory simulation of abrasive wear

Abrasive wear has long been recognised as one of the most potentially serious tribological problems facing the operators of many types of plant and machinery; several industrial surveys have indicated that wear by abrasion can be responsible for more than 50% of unscheduled machine and plant stoppages. Locating the operating point of a tribological contact in an appropriate operational ‚map’︁ can provide a useful guide to the likely nature and origins of the surface degradation experienced in use, though care must be exercised in choosing the most suitable parameters for the axes of the plot. Laboratory testing of materials and simulations of machine contacts are carried out for a number of purposes; at one level for the very practical aims of ranking candidate materials or surface hardening treatments in order of their wear resistance, or in an attempt to predict wear lives under field conditions. More fundamentally, tests may be aimed at elucidating the essential physical mechanisms of surface damage and loss, with the longer term aim of building an analytical and predictive model of the wear process itself. In many cases, component surface damage is brought about by the ingress of hard, particulate matter into machine bearing or sealing clearances. These may be running dry although, more usually, a lubricant or service fluid is present at the interface. A number of standardised wear test geometries and procedures have been established for both two- and three-body wear situations, and these are briefly described. Although abrasive wear is often modelled as following an ‚Archard’︁ equation (i.e. a linear increase in material loss with both load and time, and an inverse dependence on specimen hardness) both industrial experience and laboratory tests of particularly lubricated contacts show that this is not always the case: increasing the hardness differential in an abrasively contaminated lubricated pair may not always reduce the rate of damage to the harder surface.     

Limits of topographic measurement by the scanning tunnelling and atomic force microscopes

Parameters describing the topographic character of a surface (height, surface wavelength, slope and curvature) can be derived from equivalent sinusoidal profiles. The response of a surface-measuring instrument may be modelled in terms of instrument parameters such as stylus radius, and scanning range and resolution. The performance of the instrument may then be mapped as a zone in amplitude-wavelength (AW) space to show the sinusoidal profiles it is capable of measuring. In a first-order analysis the STM and AFM are considered as equivalent to contact-stylus instruments with a notional stylus radius equal to the tip radius plus the gap. Comparisons between different instruments and types of instrument are readily made by mapping in AW space. The error arising from convolution of the sinusoidal profile with that of the finite tip may be quantified and plotted as contours in AW space.