一种螺栓结合部刚度四点等效方法

螺栓结合部是机床结构中应用最普遍的固定结合部之一,直接影响着机床整机性能。应用有限元软件分析机床整机结构性能时,为了保证计算精度,需要精细划分螺栓结合部网格,导致计算规模大、耗时,因此探索简单有效的机床螺栓结合部有限元模型的处理方法具有重要意义。基于实验获取结合面基础特性参数,通过解析方法得到螺栓结合部中每个单元螺栓结合部的六项刚度,然后基于刚度等效原则将每个单元螺栓结合部等效成对称分布的四个弹簧单元,给出了等效弹簧刚度及位置的计算方法,在机床整机结构有限元分析时,以等效弹簧单元代替单元螺栓结合部,直接将其等效刚度代入有限元模型求解,可大大简化有限元计算模型。实验验证该等效方法是可行的。     

基于结合部刚度特性的滚珠丝杠进给系统动态特性分析

滚珠丝杠进给系统的动态特性对数控机床的定位精度、加工性能和振动等特性具有重要影响。针对滚珠丝杠进给系统理论建模中结合部刚度难以确定的问题,以自行设计制造的滚珠丝杠进给系统为研究对象,基于吉村允效法计算进给系统固定结合部的刚度;根据滚珠丝杠副、滚动导轨副和轴承结合部的共同特点,提出基于Hertz接触理论的进给系统滚动结合部刚度计算方法,建立进给系统的有限元模型。在此基础之上,对进给系统进行理论和试验模态分析,通过模态振型和固有频率的对比验证了有限元模型和滚动结合部刚度计算方法的正确性。根据所建立的有限元模型,着重分析工作台的质量和位置、滚珠丝杠副的刚度、滚动导轨副的刚度和轴承的刚度等参数对进给系统动态特性的影响。所提出的方法为机床滚动结合部刚度的识别提供了参考,研究结论为滚珠丝杠进给系统的改进设计和动态性能优化提供了依据。     

带滚珠丝杠副的直线导轨结合部动态刚度特性

借助弹性力学中的赫兹接触理论,分析计算直线滚动导轨的线刚度、滚珠丝杠副和角接触球轴承的轴向刚度,建立带滚珠丝杠副的机床直线导轨结合部的动力学特性理论模型,开发了计算软件;以一款立式加工中心为研究对象,分析计算带滚珠丝杠副直线导轨结合部动态刚度,着重讨论工作载荷对结合部动态刚度的影响规律,基于有限元法分析含结合部动态参数的加工中心整机动态特性。研究结果不仅突破了目前机床直线导轨结合部刚度模型不考虑滚珠丝杠副之缺陷,而且与传统的参数识别法和有限元法相比,具有物理概念清晰、计算过程简单等特点。     

基于能量分布的机床整机动态特性优化方法

基于机床结构中的能量分布,在准确建立立式加工中心整机有限元模型的基础上提出一种整机动态性能优化方法。采用弹簧阻尼系统等效结合部的接触特性,基于辨识的结合部等效刚度和阻尼值在Ansys中建立了立式加工中心整机有限元模型,对整机进行模态分析和谐响应分析。通过整机模态试验验证了该有限元模型的准确性,并根据有限元分析与试验结果确定整机的薄弱模态。计算薄弱模态下整机、结合部的弹性能以及结合部在整机中的弹性能分布率,以分布率较高的结合部作为薄弱结合部。基于薄弱结合部的等效接触刚度提出优化方案,优化后薄弱结合部的弹性能分布率明显降低,主轴轴端的动态响应幅值降低,从而使整机动态性能得到改善,验证了该优化方法的可行性。     

膜片弹簧力学性能有限元分析

为分析具有对称结构的膜片弹簧的载荷特性曲线,利用ABAQUS软件建立了膜片弹簧单分离指结构的有限元模型,通过施加位移载荷模拟了膜片弹簧的压紧行程和分离行程,得到膜片弹簧的载荷-位移非线性特性曲线,并与Almen-Laszlo公式计算结果对比。结果显示,有限元计算得到特性曲线与理论公式计算结果趋势接近,验证了有限元模型的准确性。     

高速HSK热装工具系统结合部的参数辨识

HSK工具系统的动态特性直接影响机床的加工效率与质量,获得准确的工具系统结合部参数又是精确预测HSK工具系统动态特性的基础。将热装刀柄-刀具结合部简化为弹簧-阻尼模型,基于Timoshenko梁理论建立了HSK热装刀柄-刀具结合部的有限元模型,采用弹塑性理论辨识结合部的刚度和阻尼,获得了HSK热装刀柄-刀具结合部内沿轴向不同位置的刚度和阻尼。进而建立了HSK热装工具系统的有限元动力学模型,分析工具系统刀尖点的频响函数。最后进行了HSK热装工具系统频响函数的实验测量,与理论频响函数相比较,验证了将结合部等效为弹簧-阻尼的辨识方法的合理性和有效性。     

高速列车空气弹簧横向特性动力学建模与应用

为了优化高速列车空气弹簧的横向动力学特性,以含附加气室与节流阻尼孔的高速列车空气弹簧为研究对象,分析了橡胶气囊在横向变形下的受力状态,采用橡胶材料的本构关系对橡胶气囊的摩擦力、线弹力进行了描述,建立了空气弹簧横向非线性模型。基于实测数据和有限元方法辨识了摩擦力、线弹力和其他动力学参数,试验验证了该模型的准确性,探究了空气弹簧横向刚度特性的影响因素。将该模型直接导入到车辆动力学模型中进行联合仿真,计算空气弹簧模型对车辆运行平稳性、曲线通过性的影响。结果表明：考虑橡胶气囊特性的空气弹簧模型能描述出刚度回滞曲线的两端尖角效应,且与试验曲线更接近;该模型在动力学计算中能降低高速列车的横向平稳性指标,并提高列车通过曲线时的计算精度。     

铰接车橡胶弹簧悬挂系统非线性特性建模分析

橡胶弹簧悬挂系统结构简单减振性能良好,在非公路车辆、大型载重车辆和工程车辆中有广阔的应用前景。对铰接式自卸车悬挂系统进行了研究,对前悬沙漏式橡胶弹簧、后悬的复合橡胶弹簧等进行静、动态实验及分析,在试验的基础上,基于有限元方法对橡胶弹簧的非线性刚度特性进行理论建模与分析,并分析橡胶弹簧结构参数对其刚度特性的影响。对其非线性刚度进行分析,对比分析表明模型仿真与试验分析结果曲线具有一致性,表明所用理论方法和所建模型的准确性;采用非线性有限元接触模型对橡胶弹簧特性进行分析,可有效提高分析的时效性;橡胶弹簧的静态特性试验研究表明,结构的刚度与系统的载荷呈现正相关特征;橡胶弹簧的动态特性试验研究表明,其动刚度和阻尼损耗因子与振动频率和振幅有很大的关系;试验结果和分析模型可作为设计选用橡胶弹簧的依据。     

机车车辆用橡胶弹簧的静动态性能分析

通过选用合适的橡胶本构模型,用有限元数值方法对不规则大变形的橡胶弹性元件进行了分析,充分考虑橡胶和钢板直接的接触以及耦合,得到了橡胶元件的载荷一位移曲线,并计算出等效刚度,与实际情况相符.采用超弹性材料模型对橡胶弹簧进行了有限元数值冲击的定性分析,得出其动刚度的变化情况,为今后橡胶弹簧进一步研究打下基础.     

基于汽车座椅导轨试验模态的结合部刚度优化

汽车座椅导轨结合部的刚度决定着导轨的主要动态特性。以某型号汽车座椅导轨为研究对象,运用有限元分析和模态试验方法对导轨结合部刚度进行优化。在导轨有限元模型中,用刚度阻尼单元模拟钢珠与导轨内外轨之间的接触。以试验模态固有频率作为目标,弹簧刚度作为设计变量,运用优化软件OptiStruct优化接触部的等效刚度。用优化后的等效刚度参数对导轨进行重新建模,结果表明该方法能够提高有限元动力学模型的建模精度,较好地解决了结合部建模时动力学参数的获取问题。     

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.     

ANGULAR DISTORTION ALLOWABLE VALUE AND ASSESS METHOD OF WELD ON COKE TOWER

A graph as the new engineering method for estimate the safety of bulging deformation of coke tower is proposed. Through stresses analysis of circumferential weld of coke tower and comparing the stresses produced by pressure with heat stress of steady state, residual stress, bending stress produced by both itself weight and wind loads, it showed that the stresses produced by pressure on the angle distortion are the main factor of equivalent stress of the combined stress. After comparing four kinds of stress controlling conditions, the relation to stress with depth of angular distortion, grade of curvature of angular distortion and half of region of angular distortion has been inferred. Graph of deformation allowable value of coke tower for different condition by angular distortion and half of region of angular distortion has been plotted. The five steps for its engineering use have been explained. The lighter the grade of curvature is, the larger of bulge allowance, may be, and the bigger of depth of angular distortion may pose too. For the coke tower with a popular structure of Dg 5 400 mm×28 mm, the result by graph is nearly more than the result of two formulas formed by other research, the error is less than 7.0%. But, the graph can be easily applied to different size of angular distortion.