Investigation on Skidding of Rolling Element Bearing in Loaded Zone

Skidding which occurs when rolling element entering into the loaded zone is prone to cause wear and incipient failure to the raceways and rolling elements. This paper presents a dynamic model to investigate the skidding of a rolling element bearing under radial load when the rolling element is entering into the load zone. In this dynamic model, the effects of the contact forces, friction forces on the rolling element-race and rolling element-cage interfaces, gravity, and the centrifugal forces of rolling elements are taken into consideration. The Hertzian contact theory is applied to calculate the non-linear contact forces. The Coulomb friction law is used to calculate the friction forces. The differential equations of rotational motion of the rolling element with regard to its central axis and the central axis of the outer ring are established respectively. The dynamic equations are then solved by using a fourth-order Runge-Kutta algorithm. The skidding characteristics of rolling element at the entry into the loaded zone are exposed, and the effects of the operating parameters on skidding behavior are carefully investigated.

High-precision solution to the moving load problem using an improved spectral element method

In this paper, the spectral element method(SEM)is improved to solve the moving load problem. In this method, a structure with uniform geometry and material properties is considered as a spectral element, which means that the element number and the degree of freedom can be reduced significantly. Based on the variational method and the Laplace transform theory, the spectral stiffness matrix and the equivalent nodal force of the beam-column element are established. The static Green function is employed to deduce the improved function. The proposed method is applied to two typical engineering practices—the one-span bridge and the horizontal jib of the tower crane. The results have revealed the following. First, the new method can yield extremely high-precision results of the dynamic deflection, the bending moment and the shear force in the moving load problem.In most cases, the relative errors are smaller than 1%. Second, by comparing with the finite element method, one can obtain the highly accurate results using the improved SEM with smaller element numbers. Moreover, the method can be widely used for statically determinate as well as statically indeterminate structures. Third, the dynamic deflection of the twin-lift jib decreases with the increase in the moving load speed, whereas the curvature of the deflection increases.Finally, the dynamic deflection, the bending moment and the shear force of the jib will all increase as the magnitude of the moving load increases.

Discrete element modeling of ice loads on ship hulls in broken ice fields

Ice loads on a ship hull affect the safety of the hull structure and the ship maneuvering performance in ice-covered regions. A discrete element method （DEM） is used to simulate the interaction between drifting ice floes and a moving ship. The pancake ice floes are modelled with three-dimensional （3-D） dilated disk elements considering the buoyancy, drag force and additional mass induced by the current. The ship hull is modelled with 3D disks with overlaps. Ice loads on the ship hull are determined through the contact detection between ice floe element and ship hull element and the contact force calculation. The influences of different ice conditions （current velocities and directions, ice thicknesses, concentrations and ice floe sizes） and ship speeds are also examined on the dynamic ice force. The simulated results are compared qualitatively well with the existing field data and other numerical results. This work can be helpful in the shil3 structure design and the navigation securitv in ice-covered fields.

A multiscale 3D finite element analysis of fluid/solute transport in mechanically loaded bone

The transport of fluid, nutrients, and signaling molecules in the bone lacunar-canalicular system （LCS） is critical for osteocyte survival and function. We have applied the fluorescence recovery after photobleaching （FRAP） approach to quantify load-induced fluid and solute transport in the LCS in situ, but the measurements were limited to cortical regions 30-50 μm underneath the periosteum due to the constrains of laser penetration. With this work, we aimed to expand our understanding of load-induced fluid and solute transport in both trabecular and cortical bone using a multiscaled image-based finite element analysis （FEA） approach. An intact murine tibia was first re-constructed from microCT images into a three-dimensional （3D） linear elastic FEA model, and the matrix deformations at various locations were calculated under axial loading. A segment of the above 3D model was then imported to the biphasic poroelasticity analysis platform （FEBio） to predict load-induced fluid pressure fields, and interstitial solute/fluid flows through LCS in both cortical and trabecular regions. Further, secondary flow effects such as the shear stress and/or drag force acting on osteocytes, the presumed mechano-sensors in bone, were derived using the previously developed ultrastructural model of Brinkman flow in the canaliculi. The material properties assumed in the FEA models were validated against previously obtained strain and FRAP transport data measured on the cortical cortex. Our results demonstrated the feasibility of this computational approach in estimating the fluid flux in the LCS and the cellular stimulation forces （shear and drag forces） for osteocytes in any cortical and trabecular bone locations, allowing further studies of how the activation of osteocytes correlates with in vivo functional bone formation. The study provides a promising platform to reveal potential cellular mechanisms underlying the anabolic power of exercises and physical activities in treating patients with skeletal deficiencies.

Influence of load capacity on hydrostatic journal support deformation in finite element calculation

Based on the application of the four-oil-pad radial hydrostatic bearing in heavy equipments, the deformation of the four-oil-pad radial hydrostatic bearing was calculated by using the finite element method. The formula of film stiffness, film thickness and carrying capacity were established; the influence of the main parameters, such as load, load area and deformation on the supportability was analyzed; and the capacity of the two kinds of bearings was compared. The result shows that the carrying capacity of typeⅠ is prior to that of type Ⅱ . Calculations provide a theoretical basis for the bearing choosing and structure designing in the actual project.

Strength reduction and step-loading finite element approaches in geotechnical engineering

The finite element limit analysis method has the advantages of both numerical and traditional limit equilibrium techniques and it is particularly useful to geotechnical engineering.This method has been developed in China,following well-accepted international procedures,to enhance understanding of stability issues in a number of geotechnical settings.Great advancements have been made in basic theory,the improvement of computational precision,and the broadening of practical applications.This paper presents the results of research on（1） the efficient design of embedded anti-slide piles,（2） the stability analysis of reservoir slopes with strength reduction theory,and（3） the determination of the ultimate bearing capacity of foundations using step-loading FEM（overloading）.These three applications are evidence of the design improvements and benefits made possible in geotechnical engineering by finite element modeling.

The finite element analysis of articular cartilage fiber-reinforced composite model under rolling load

Articular cartilage is a layer of low-friction,load-bearing soft hydrated tissue covering bone-ends in diarthrosis,which plays an important role in spreading the load,reducing the joint contact stress,joint friction and wear during exercise.The vital mechanical function

温度与荷载共同作用下钢筋混凝土桩的细观损伤

为探究港口码头不同环境因素对码头桩身材料特性的劣化影响而降低桩身承载能力,通过颗粒流分析程序(particle flow code 3D,PFC3D)建立三维颗粒流离散元钢筋混凝土桩模型开展研究。对温度-应力模型进行建立,选取热学参数,构建了温度热管模型,通过分级加热,得到了钢筋混凝土桩的横向拉伸应变、纵向压缩应变以及微裂缝生长数量随温度变化曲线;调整模型混凝土粗骨料占比与强度等级,研究其对钢筋混凝土桩受热损伤的影响;通过施加温度场的模型进行水平加荷载后,得到的应力应变曲线;基于模型微裂隙数量的损伤变量,并构建了损伤变量-轴向应变曲线,进一步分析了温度-荷载共同作用的损伤规律。结果表明:混凝土轴向压缩应变和横向拉伸应变会随温度的增加而逐渐升高,细观微裂隙数量会随温度的升高而增长;粗骨料占比升高会使受热初始损伤增加;温度的升高,材料的宏观力学性能出现了不同程度的降低。

装配式槽钢组合梁中开孔钢板连接件力学性能

为研究新型装配式双拼槽钢-混凝土组合梁中开孔钢板剪力连接件(PSP剪力连接件)的力学性能,设计7组标准试件并开展推出试验,对比分析不同参数PSP剪力连接件的受剪承载力和破坏模式。利用ABAQUS非线性有限元模型对PSP剪力连接件的破坏模式和受力机制进行数值模拟,并与试验结果对比验证计算结果的可靠性。在此基础上,进一步分析开孔钢板厚度、开孔直径、混凝土强度、穿孔钢筋及连接件间距对PSP剪力连接件力学性能的影响。结果表明:除10 mm厚度的PSP剪力连接件外,所有4 mm与6 mm厚度的PSP剪力连接件均发生明显弯曲变形,试件破坏时连接件周围混凝土均出现斜向裂缝;开孔直径和穿孔钢筋对受剪承载力和抗剪刚度影响较小,而增加开孔钢板厚度、混凝土强度能提高剪力连接件受剪承载力和抗剪刚度;对于双排PSP剪力连接件,增大连接件间距能够显著提高单排PSP剪力连接件平均承载力,当间距为250 mm时,单排平均承载力达到单个PSP剪力连接件的91.2%。根据试验及有限元荷载滑移曲线提出装配式双拼槽钢-混凝土组合梁中单个PSP连接件荷载滑移曲线计算公式,为装配式双拼槽钢混组合梁的设计提供参考。

基于三维有限元模型的人体全腰椎振动特性研究

振动暴露被认为是诱发腰椎退行性病变和下腰痛的重要原因,本研究旨在探寻振动载荷对腰椎生物力学的影响。基于人体腰椎L1节段至骨盆(L1-pelvis)的CT扫描数据,重构L1-Pelvis三维几何模型。对该几何模型进行网格划分和材料特性赋值,建立L1-Pelvis三维有限元模型,并利用可获得的实验数据对模型的有效性进行验证。基于该有限元模型,通过瞬时动态分析计算出腰椎各运动节段在幅值40 N,频率5 Hz轴向正弦振动载荷作用下的力学响应,并与-40 N和+40 N轴向静态载荷作用下的结果进行对比,响应参数包括椎体轴向位移、纤维环膨出变形和纤维环基质冯·米塞斯应力。研究结果表明,相比于静态载荷,振动载荷下腰椎各运动节段的椎体轴向位移、纤维环膨出变形、纤维环基质冯·米塞斯应力的幅值分别增加了0.550~1.020 mm、0.124~0.251 mm、0.043~0.099 MPa,最大增幅分别可达195.0%、175.7%、151.4%。从量化角度说明振动载荷下腰椎发生损伤的风险更高。

木塑空心柱轴压力学性能试验与有限元分析

为探究木塑复合材料用作低密度装配式建筑承重柱的可行性,通过材性测试和轴压试验评估共挤出木塑空心柱的轴压力学性能,并利用ABAQUS有限元分析软件模拟探究木塑空心柱壁厚、长细比和内置薄壁圆钢管壁厚对其极限承载力、变形能力和破坏模式的影响。模拟分析结果与试验测试数据高度一致,验证了模拟方法的有效性。试验研究表明,木塑空心柱主要通过局部压溃破坏,并表现出明显的弹塑性阶段。有限元分析结果表明,增加壁厚能提高木塑空心柱的初始刚度和极限承载力,其中8 mm厚度在成本、重量及承载能力方面具有最佳性价比。随着长细比的增加,木塑空心柱的承载力和刚度逐渐降低,破坏模式也从强度破坏转向失稳破坏。内置3 mm薄壁钢管显著增强了木塑空心柱的承载力和延性,其力学性能能够满足建筑对抗压承重构件的要求。

芯轴悬挂器高强度螺纹结构设计及评价研究

为了防止芯轴下端连接螺纹强度不足而造成失效事故,采用高温高压套管柱设计计算方法、有限元数值模拟和实验手段,对芯轴材料进行了力学性能实验,开发了一种用于芯轴悬挂器高强度螺纹结构,并在极限复合载荷下对该螺纹进行了三维有限元计算。研究结果表明,拉扭压复合载荷对外螺纹强度影响较大,压缩载荷对内螺纹内台肩第一牙应力影响较大,内外螺纹其余部位相对安全。拉伸载荷在一定程度缓解了上扣扭矩对内外螺纹台肩部位的影响。从计算结果得到内外螺纹整体上应力小于材料允许的屈服极限,且螺纹接头接触压力均大于外在流体压力,可以形成有效密封,研究结果为芯轴悬挂器螺纹结构的选型和使用提供理论基础。

地基中混凝土排桩主动隔振研究

为了探究地基中设置混凝土排桩后,排桩的各参数变化对近场主动隔振的影响规律,在有限元软件中建立与试验场地一致的三维有限元模型,通过计算与分析验证了有限元计算结果的有效性;参考TB 10621—2014《高速铁路设计规范》建立了足尺寸的有限元模型,分析在列车荷载作用下排桩的各参数变化对隔振效果的具体影响规律。研究结果表明:桩长参数对隔振效果影响较为明显,随着参数增大,隔振效果越理想,当桩长参数为10.5以后,继续增加比值,隔振效果提升不显著;随着桩间距参数越大,隔振效果越不理想,较小的桩间距可获得理想的隔振效果;埋深参数对隔振效果影响显著,参数越大,隔振效果越不理想,当参数为3.5时,隔振效果已很不理想,较浅埋深能获得较理想的隔振效果。

横向冲击载荷下齿形双螺母防松性能

针对螺栓连接结构在舰船爆炸冲击中容易发生松动的现象,设计了一种齿形双螺母的防松结构。利用局部滑移理论分析齿形双螺母的防松原理,采用有限元仿真法,通过预紧力和微滑移的变化量对其防松性能进行分析,并研究了齿形双螺母防松性能的影响因素及其影响规律。研究结果表明:横向冲击载荷下,齿形双螺母预紧力下降慢,微滑移变化小,具有较好的防松性能;当楔形角与螺纹升角相同时,防松效果最差;楔形角越大,齿形数量越多,齿形双螺母的防松效果越好。

新型钢节点装配式混凝土梁力学性能及破坏机制研究

由于传统装配式混凝土梁运输和施工难度大,提出了一种新型钢节点装配式混凝土梁,并试制了1根现浇梁试件与3根装配式梁试件,通过抗弯静载试验,对比研究了新型钢节点对装配式梁试件力学性能及其破坏机制的影响。根据试验情况,采用ABAQUS有限元软件进行了试件破坏模拟,并与试验结果进行了对比分析。结果表明:装配式梁试件可达到现浇梁的承载力水平;新型钢节点的钢端板厚度对装配式梁试件的整体承载力影响较大,当钢端板尺寸在一定范围内时,装配式梁试件的承载能力优于现浇梁;新型钢节点对混凝土的破坏形式影响较大,其梁纯弯段裂缝不同于现浇梁的受弯竖向裂缝,表现为弯剪斜向裂缝;有限元模拟结果与试验结果相吻合,可用于装配式梁试件的后续研究。

基于格宾石笼的隧道支护构件静力加载模型试验设计

尽管格宾石笼在边坡、护岸工程、路基加固等工程中已有了一定的应用,但鲜有研究提及格宾石笼在隧道支护中的应用。由于格宾石笼具有一定的承载力和良好的变形适应能力,在应对隧道围岩大变形和高地应力等方面具有一定应用前景,因此,对基于格宾石笼的隧道支护构件静力加载模型进行试验设计具有一定的实际意义。为了方便学生更好地了解格宾石笼作为隧道支护结构的力学作用机理,设计了一种简化的格宾石笼构件成形方法和与之配套的试验加载装置,并提出了基于离散元计算的格宾石笼隧道局部构件数值建模方法,进而对比和揭示了组成格宾石笼构件的两大主要参数(格宾网抗拉强度和填石有效模量)对格宾石笼建构的隧道支护构件静力力学特性差异的影响规律。通过该试验,为学生演示了基于格宾石笼建构的隧道支护局部构件的设计、拼装、试验加载以及数据采集的全过程,旨在为学生深入学习和掌握格宾石笼建构的隧道支护局部构件的试验静力力学行为及其建模方法提供一种新思路。

移动荷载下道路病害的弯沉盆特性

移动荷载作用下道路弯沉盆蕴含路基、路面的病害信息,充分利用移动弯沉盆信息开展道路病害快速无损检测受到行业重要关注。该文通过分析道路病害的弯沉盆特性,为移动弯沉车开发道路病害检测方法提供技术参考。首先建立半刚性基层沥青路面有限元模型,通过设置不同类型和程度的病害有限元模型,分析在移动荷载作用下路表弯沉盆的连续变化情况。结果表明:荷载移动到病害区域时,各病害模型中路表弯沉盆的中心弯沉值均会变大;路面结构层出现横向裂缝时,弯沉盆的形状会发生明显变化,贯通性横向裂缝对弯沉盆形状的影响最明显;基层与底基层局部松散对弯沉盆形状的影响比面层松散对弯沉盆的影响更明显;土基顶部出现空洞时,弯沉盆形状变化不明显;路基唧泥病害会严重影响路表弯沉盆形状与大小。

移动荷载作用下沥青路面的力学响应数值模拟

掌握沥青路面在移动荷载作用下的力学响应,是更为合理地进行路面结构设计的重要基础。该文基于有限元建立了移动荷载作用下沥青路面力学响应的数值模拟方法,讨论了移动荷载作用下沥青路面结构不同层位的竖向位移、应力与应变等力学响应特征,系统研究了轴载、车速及温度对沥青路面力学响应的影响,为优化路面结构设计提供参考。结果表明:移动荷载作用下,沥青路面各层的竖向位移随路面深度增加逐渐增大,且随轴载与温度增加而增大,而受车速影响较小;沥青路面各层所受应力包括竖向压应力与剪切应力,其压应力与剪切应力均随着轴载增加而显著增加,而受温度与车速的影响较小;相应的各层竖向压应变与剪切应力均随轴载与温度增加而增加,受车速影响较小。路面结构内部的应力与应变情况复杂,在设计中,应控制各结构层最不利应力及应变,满足设计要求。

深厚软土区桩柱式桥墩临界荷载简化计算方法

现有桩柱式桥墩临界荷载简化计算方法在大多数情况下计算误差较大,适用性有限.在利用软土区现场桩基屈曲实验结果标定的基础上,采用基于特征值屈曲分析的有限元方法对有典型桩柱式桥墩的临界荷载进行了计算并与现有简化计算方法结果进行了对比,指出了现有简化计算方法的适用范围,发现现有简化方法不适用于软土区桩柱式桥墩计算.在大量桩柱式桥墩有限元特征值屈曲分析数据的基础上,采用随机森林算法对计算结果进行分析,得到可以计算桩柱式桥墩计算长度的随机森林模型以及各影响参数重要性指数分析结果.最后以现常用简化公式为基本形式,纳入随机森林算法给出的重要参数,通过回归分析,提出了深厚软土区桩柱式桥墩临界荷载的简化计算方法.

考虑风载因素的玻璃幕墙清洁机器人设计

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