基于GAP单元的车架有限元分析

利用Hyperworks软件对某重型货车车架进行了有限元分析,研究了采用GAP单元模拟车架钢结构之间接触的方法,并采用壳单元离散车架纵梁和横梁、多点约束单元(MPC)模拟铆钉和螺栓的传力、以及梁单元和弹簧单元模拟前后悬架.对比了利用GAP单元和等效实体单元来模拟接触以及不考虑接触的3种建模方法,分析了该车架的弯曲工况,并对计算结果进行了试验验证.分析结果表明:GAP单元能够有效地模拟车架各层钢结构之间的接触,提高车架有限元分析精度和分析效率,从而为重型货车车架有限元分析提供了一种有效方法.

基于GAP单元的滚动轴承应力分析

利用有限元分析软件MSC.Marc/Mentat对某一滚动轴承进行有限元分析,采用GAP单元代替滚动体模拟轴承内外圈间的接触,在某组载荷工况下,计算该简化模型的应力结果;在同组工况下,对比实体轴承模型与GAP单元简化模型的有限元分析结果,对比各自的最大应力值;同时用理论计算方法计算轴承在相同工况下的最大应力值,来验证有限元结果的正确性。结果表明:GAP单元可以有效的模拟滚动轴承内外圈之间的接触,从而为滚动轴承建模及与轴承连接的组合件之间的建模提供了一种简便且有效的方法。

Effect of Radial Resistance Gap on the Pressure Drop of a Compact Annular-Radial-Orifice Flow Magnetorheological Valve

A compact annular-radial-orifice flow magnetorheological(MR)valve was developed to investigate the effects of radial resistance gap on pressure drop.The fluid flow paths of this proposed MR valve consist of a single annular flow channel,a single radial flow channel and an orifice flow channel through structure design.The finite element modelling and simulation analysis of the MR valve was carried out using ANSYS/Emag software to investigate the changes of the magnetic flux density and yield stress along the fluid flow paths under the four different radial resistance gaps.Moreover,the experimental tests were also conducted to evaluate the pressure drop,showing that the proposed MR valve has significantly improved its pressure drop at 0.5 mm width of the radial resistance gap when the annular resistance gap is fixed at 1 mm.

Numerical study of resonance induced by wave action on multiple rectangular boxes with narrow gaps

By introducing a source term into the Laplace equation, a two-dimensional fully nonlinear time-domain numerical wave flume （NWF） is developed to investigate the resonance induced by the interaction between waves and multiple objects with narrow gaps. In the numerical model, the fully nonlinear kinematic and dynamic boundary conditions are satisfied on the instantaneous free surface and the constant artificial damping is employed in the gaps to approximate the viscous dissipation due to vortex motion and flow separation. The computational domain is discretized using a higher-order boundary element method （HOBEM）. The proposed model is firstly validated against the published experimental data and numerical results of the wave height in the narrow gap between two boxes, the wave heights in the two gaps of three boxes, and wave loads on the boxes. Then, the extensive numerical experiments are performed to study the influences of the number of the boxes and the gap spacing on the resonant frequency, reflected and transmitted wave heights and wave loads on the boxes.

Time-dependent Ginzburg–Landau equations for multi-gap superconductors

We numerically solve the time-dependent Ginzburg–Landau equations for two-gap superconductors using the finite-element technique. The real-time simulation shows that at low magnetic field, the vortices in small-size samples tend to form clusters or other disorder structures. When the sample size is large, stripes appear in the pattern. These results are in good agreement with the previous experimental observations of the intriguing anomalous vortex pattern, providing a reliable theoretical basis for the future applications of multi-gap superconductors.

Study on Band Gap Characteristics of Boat-Shaped Phononic Crystal

In this paper, we analyze the two-dimensional Boat-shaped structure based on the finite element method. We calculated its energy band structure and vibration transmission properties and found that the structure has band gaps at both high and low frequencies. Compared with common traditional two- dimensional phononic crystals, the boat-shaped phononic crystal has the advantage of larger bandgap design and modulation parameter space due to their structural complexity. In order to obtain better bandgap characteristics, we studied the influence of four key parameters, such as the rod length and the angle between the rods, on the bandgap. The results show that: for low frequency band gaps, the width of the band gap can be effectively changed by changing the size of the angle between the rods while rod length greatly affects the bandgap position;for high band gaps, the length of rods has a large effect on the band gap position. These laws have guiding significance for the bandgap regulation of boat-shaped phononic crystal.

Numerical Estimation of the Thermal Response of Thermal Protective Clothing-Air Gap-Human Skin Micro-system

Thermal protective clothing has been recognized as the primary shielding against emergency fire hazard and inflammable gas leakage. Therefore,the thermal response of human covered with thermal protective clothing under high temperature is the key work to investigate the thermal insulation of thermal protective clothing. A coupling model composed of thermal protective clothing,air gap and human skin is established and the temperature of the micro-system is numerically solved via the finite element method( FEM).Especially,the heat transfer of air gap located between clothing and human skin considering conduction and radiation is established while the human skin layers involve the effect of blood perfusion. Then the effect of thermophysical properties( thermal conductivity and volumetric capacity) of fabric and thickness of fabric and air on the thermal response of the micro-system is elucidated and compared.The results indicate that the volumetric heat capacity of fabric is the key parameter to affect the thermal shielding performance of thermal protective clothing,and the thicker fabric thickness and air gap thickness can improve the thermal protective properties of the micro-system.

Numerical investigation of solitary wave action on tworectangular boxes with a narrow gap

Based on the time-domain higher-order boundary element method(HOBEM), a two-dimensional numerical wave flume is developed to investigate solitary wave interaction with two rectangular boxes with a narrow gap.In the numerical model, the fully nonlinear boundary conditions are satisfied on the free surface, the mixed Eulerian-Lagrangian method is adopted to track the transient water surface and the fourth-order Runga-Kutta method is used to predict the velocity potential and wave elevation on the free surface. The acceleration potential technique is used to compute the transient wave forces along the wetted object surface. A piston-type wavemaker is used to generate solitary waves. The proposed model is validated by comparing the simulated wave run-up and the wave loads with the published experimental and numerical results of the reflection of a solitary wave from a vertical wall. Then, numerical experiments are performed to study the effects of the narrow gap and the size of each box on the wave run-ups at the two sides of the two-box system and in the narrow gap between two boxes, and the wave loads on the two boxes. The interaction between double solitary waves with a time interval between them with a two-box system is also investigated.

Some Implications of an Alternate Equation for the BCS Energy Gap

A set of generalized-BCS equations (GBCSEs) was recently derived from a temperature-dependent Bethe-Salpeter equation and shown to deal satisfactorily with the experimental data comprising the Tcs and the multiple gaps of a variety of high-temperature superconductors (SCs). These equations are formulated in terms of the binding energies W1(T),W2(T),… of Cooper pairs (CPs) bound via one- and more than one-phonon exchange mechanisms;they contain no direct reference to the gap/s of an SC. Applications of these equations so far were based on the observation that for elemental SCs |W01|=△0 at T = 0 inthe limit of the dimensionless BCS interaction parameter λ→0. Here △0 is the zero-temperature gap whence it follows that the binding energy of a CP bound via one-phonon exchanges at T = 0 is 2|W01|. In this note we carry out a detailed comparison between the GBCSE-based W1(T) and the BCS-based energy gap △(T) for all 0≤T≤Tc and realistic, non-vanishingly-small values of λ. Our study is based on the experimental values of Tc Debye temperature , and ?0 of several selected elements including the “bad actors” such as Pb and Hg. It is thus established that the equation for W1(T) provides a viable alternative to the BCS equation for △(T). This suggests the use of, when required, the equation for W2(T) which refers to CPs bound via two-phonon exchanges, for the larger of the two T-dependent gaps of a non-elemental SC. These considerations naturally lead one to the concept of T-dependent interaction parameters in the theory of superconductivity. It is pointed out that such a concept is needed both in the well-known approach of Suhl et al. to multi-gap superconductivity and the approach provided by the GBCSEs. Attention is drawn to diverse fields where T-dependent Hamiltonians have been fruitfully employed in the past.

数字经济时代背景下城乡收入差距的新变化及破解路径

城乡收入差距是我国现代化道路上的突出问题之一。随着我国数字经济发展转向普惠共享的新阶段,讨论数字经济时代背景下我国城乡收入差距变化的理论逻辑与实践表现、明确缩小城乡收入差距的破解路径,成为推进全体人民共同富裕的迫切需要。数字经济时代背景下数字技术、数据要素与数字基础设施多层次赋能农业农村,形成缩小城乡收入差距的潜在路径。结合城镇地区看,数字技术、数据要素与数字基础设施会对城乡收入差距产生非对称性影响,总体形成矛盾化的变动趋势。改革开放后,我国城乡收入差距整体呈现波动上升后持续下降的动态变动态势;2010年后,我国城乡收入差距的持续缩小与推动农业农村部门信息化、数字化转型等政策存在高度相关性。数字经济时代背景下缩小城乡收入差距的破解路径集中表现为完善农业数字技术应用基础、促进数据要素加速渗透、推进数字基础设施普及应用。

高静压下两间隙气体开关结构及电场优化设计

为解决可控冲击波设备的两间隙气体火花开关在非常规页岩油开发中结构强度不够的问题,提出了一种适用于高静压、有限空间中的气体火花开关结构强度与电场分布同步优化的设计方法。基于有限元模拟与理论分析,评估了50 MPa外部高静压对气体火花开关结构强度的影响,针对结构强度足够的气体火花开关模型,通过高斯定理对开关内部的电场分布进行了优化分析,给出了两电极气体火花开关结构强度与电场分布同步优化的设计方案。研究结果表明:开关结构强度主要与腔室壁厚正相关,而壁厚的增加会提高开关异常放电概率,在特定的壁厚参数下,电极半径存在最佳值使得绝缘子表面电场强度最低。在保证结构强度的前提下,对现有开关电场分布进行了优化分析,优化后的开关间隙电场的不均匀度有轻微提高,而高压绝缘子内、外表面电场强度分别衰减了59.6%与31.0%。通过先增加结构强度、后优化电场分布的方法,实现了对冲击波设备的两电极气体火花开关结构强度与电场分布的同步优化。

有限元模拟仿真在压力容器对接接管焊缝相控阵超声检测工艺设计中的研究与验证

针对大壁厚压力容器接管焊缝多为窄间隙对接焊接头,超声检测中存在扫查路径复杂、定量定性精度差和检出率相对较低等难点,引入有限元模拟仿真技术。通过建立工件3D模型和不同类型的缺陷,模拟各缺陷在压力容器筒体外壁和接管内壁相控阵超声检测时的响应情况,优化相控阵超声探头、楔块设计和探头运动轨迹,最终实现检测工艺的理论设计。在带有自然缺陷的模拟试块上,验证检测工艺的准确性和可靠性。对比有限元模拟仿真和在模拟试块上的实际检测情况表明,经过仿真设计过的相控阵超声检测工艺可有效提高接管窄间隙焊缝中缺陷的检出率和检测精度。

土地流转与劳动力转移的要素互动对城乡收入差距的影响

要素流动对于破解城乡融合发展难题,建立均衡增长和良性循环的城乡关系具有重要影响。基于2005—2020年31个省级宏观面板数据,考察土地制度综合配套改革下土地流转与劳动力转移的互动关系及对城乡收入差距的影响与作用机制。研究发现:土地流转与劳动力转移之间具有显著的正向互动效应。土地流转与劳动力转移的互动有助于缩小城乡收入差距。土地流转与劳动力转移的互动,通过促进城市化水平、提高产业高级化程度,间接缩小城乡收入差距。此外,土地流转与劳动力转移的互动对城乡收入差距的影响具有异质性,对工资性收入差距存在显著的负向影响。为进一步缩小城乡收入差距,需要推动土地和户籍制度联动改革,扩大人地要素的权利开放程度,强化城乡土地、劳动力要素的流动性,完善土地流转和劳动力市场,引导农村转移劳动力参与土地流转。

骨质对右上第一磨牙种植修复体咬合调整影响的有限元分析

背景:骨组织改建与应力加载密切相关,目前就骨质与种植修复体咬合调整关系的研究或指南较少,并且缺乏科学的证据。目的:通过有限元方法探究不同种植修复体咬合间隙在Ⅰ-Ⅳ类骨质条件下时对种植体-骨界面应力分布、应力峰值、位移的影响。方法:通过光学扫描仪扫描等比例牙齿模型后,使用Solidworks 2022构建等比例右上第一磨牙Straumann 4.8×8 mm BL RC种植体及其相关部件模型,再利用Mimics、Geomagic、Solidworks软件,依据文献ZARB和LEKHOLM提出的骨质分类、NORTON和TRISI骨质密度分类,建立Ⅰ-Ⅳ类骨质的上下颌骨模型。以0,20,40,60,80,100μm为修复体咬合间隙完成模型的装配,并且额外构建一组未进行密度比设置的均质模型作为对比。将上述模型导入Hypermesh进行网格划分后,进行有限元分析的材料赋值、边界约束以及参数设定,最后以250 N为加载力模拟上下颌受力情况,分析比较各组模型中种植体-骨界面的应力分布、应力峰值和位移情况。结果与结论:①相同荷载条件下,种植修复体应力随咬合接触点均匀分布,当咬合间隙达80μm和100μm时,Ⅰ类骨质和Ⅱ、Ⅲ、Ⅳ类骨质下的种植牙冠分别出现应力中断现象。②种植体-骨界面的位移主要集中在种植体周围的皮质骨区并沿种植体长轴向下传导至底部的松质骨区域。随着Ⅰ-Ⅳ类颌骨骨质的减弱,各组模型皮质骨区产生的位移、Von Mises应力均呈现增加趋势,且均较松质骨区大。而松质骨区Von Mises应力除自Ⅱ类骨起则呈下降趋势外,其余均与皮质骨区相类似,但当咬合间隙增大时,皮质骨及松质骨区产生的应力及位移峰值则呈现逐渐减小趋势。③在咬合间隙为0-40μm的Ⅱ-Ⅳ类骨质条件下以及60μm的Ⅳ类骨质条件时,种植体-骨组织界面应力均介于20-60 MPa之间,其余各组应力均<20 MPa。④种植体Von Mises应力主要集中于种植体颈部,在咬合间隙为20μm的Ⅱ-Ⅳ类骨质条件下,种植体应力峰值均大于咬合间隙为0μm、Ⅰ类骨质条件下的144.10 MPa。⑤在不同弹性模量的均质模型中,其应力及位移分布较非均质模型更加均匀。⑥结论:实验结果从生物力学的角度证明种植义齿修复的咬合调整应该将牙槽骨骨质纳入考虑因素,临床工作中咬合间隙应随着颌骨密度的下降而增加,单颗种植牙与对颌天然牙的咬合间隙在20-40μm是一个相对合适的咬合调整方案。但由于有限元分析法的特殊性,还有待结合临床进行进一步的深入研究。

长白山温带森林生态系统关键要素耦合及演替过程动态模拟

认识生态系统内和生态系统间耦合机制,揭示复合生态系统功能规律,对促进我国山水林田湖草沙项目一体化修复和保护实践具有重要的意义。针对目前修复和保护工程中出现的缺乏系统性、连续性等问题,以拥有丰富生态资源的长白山温带森林生态系统为研究区域,对其关键要素“水土气生”进行耦合建模。通过分析模型的运行机理,探究重要子模块之间的相互作用以及子模块内部生态关键要素的耦合机制,并以长白山温带落叶阔叶林的组成树种和环境因素为对象构建模型参数,通过运行林窗模型1000次,得出长白山温带森林的动态演替过程。结果表明:在森林生态系统的演替过程中,“水土气生”体现为模型中有效积温、干旱天数(低于土壤凋萎点的天数)、土壤可利用氮以及可利用光,这些关键要素之间相互影响,综合决定着每棵树木的更新、生长、死亡过程。模拟结果显示在长白山温带针阔混交林的动态演替过程中0—70 a, 70—170 a, 170—280 a, 280—400 a四个阶段分别有不同的树种组成特征,与真实演替过程比较发现模拟林具有明显的阶段性。白桦、山杨为演替先锋树种,0—70 a期间生物量共占比为55%,70 a后生物量减少最后消失;紫椴、蒙古栎、水曲柳等为过渡树种,这些树种进一步改变了生长环境。红松在170 a前生物量占比仅为3%左右,随演替的发展生物量持续增加,170—280 a期间生物量占比15%,280 a之后红松生物量占总林分的50%。该结果模拟森林动态过程符合演替规律,充分说明多关键要素“水土气生”耦合机制的合理性,对于促进生态系统尺度上多生态要素耦合的相关研究提供了科学理论基础以及方法技术。

定子间隙宽度对拼块式永磁电机电磁性能的影响

为探究定子间隙宽度对不同槽极配置及不同拼块式结构永磁电机电磁性能的影响,通过有限元仿真软件建立12槽10极和12槽14极定子一体式、E型拼块式、C型拼块式永磁电机的仿真模型,通过改变定子间隙宽度,得出定子间隙宽度与各电磁性能间的关系,并进行理论分析验证。结果表明:12槽10极电机更适合采用C型2 mm/4 mm拼块式结构降低齿槽转矩和转矩脉动;12槽14极电机更适合采用E型4 mm拼块式结构提高输出转矩或采用C型2 mm降低齿槽转矩和转矩脉动。

功能梯度材料声子晶体低频带隙特性研究

声子晶体作为一种减振降噪的结构已经在建筑、土木等领域被广泛应用。基于局域共振声子晶体理论在前期研究的基础上对一种含二维变化功能梯度材料的声子晶体进行优化设计,并通过有限元数值仿真研究该声子晶体的减振性能。结果表明:功能梯度材料声子晶体能带结构在0~1000Hz内共有3条完全带隙,其第一禁带的起始频率约为0,第三禁带截止频率为991.36Hz,总禁带宽度为990.85 Hz,在该带隙范围内占比为99.08%,并且在X方向上对该声子晶体10×5个周期进行传输特性分析,分析结果完全验证了禁带的存在,证明含二维变化功能梯度材料的声子晶体能有效抑制0~1000 Hz的弹性波,最后将含功能梯度材料声子晶体与传统声子晶体进行对比分析,验证了功能梯度材料声子晶体的减振性能。研究结果可为土木交通工程减振降噪提供一种新的设计方法。

带球冠形脱空缺陷的圆钢管混凝土T型相贯节点的滞回性能研究

为研究球冠形脱空缺陷对圆钢管混凝土T型相贯节点抗震性能的影响,以脱空率、支主管直径比和主管径厚比为主要试验参数,完成了18个圆钢管混凝土T型节点试件在主管承受恒定轴向拉力和支管承受往复轴向荷载作用下的滞回性能试验,考察了球冠形脱空缺陷对其失效模式、滞回曲线、骨架曲线、承载力、刚度和耗能的影响规律。建立了有限元分析模型,分析了球冠形脱空缺陷对主管钢管与核心混凝土之间接触应力发展的影响规律,开展了脱空率、支主管直径比、主管径厚比、混凝土强度、钢材强度和轴拉比等参数对节点受拉承载力影响的参数分析。结果表明:球冠形脱空缺陷的存在会改变节点的失效模式,导致节点的承载力、刚度和耗能能力均有不同程度的降低,并削弱主管钢管与混凝土之间的相互作用,影响节点的荷载传递机制。最后,提出了考虑球冠形脱空缺陷影响的圆钢管混凝土T型节点受拉承载力折减公式。

改进气隙磁导计算的混合励磁电机建模与分析

针对等效磁路(EMC)模型中气隙磁导分段建模复杂、容易引入误差的问题,将槽漏磁磁路集中在气隙中,通过计算等效气隙长度的空间分布,将气隙磁导计算转化为与等效气隙长度相关的积分。此外,通过分析混合励磁开关磁链永磁(HESFPM)电机导磁桥饱和现象的机制,采用分子区域建模的方法,提出一种考虑槽漏磁、永磁体极间漏磁及导磁桥不均匀饱和的EMC模型。以一台12槽10极的HESFPM电机为例,将所提EMC模型分别与有限元分析(FEA)法、实验结果进行对比。结果表明:所提EMC模型在保证电机电磁性能计算精度的前提下,计算时长仅为FEA仿真的0.12%,极大地提高了计算速度。

数字普惠金融能否缩小地区包容性绿色增长差距

本文深入考察数字普惠金融发展影响地区包容性绿色增长差距的内在机理,并利用2012—2022年中国277个地级城市的面板数据构建空间收敛模型,实证检验地区包容性绿色增长差距的变动特征以及数字普惠金融的影响效应。研究发现:在考虑空间效应的情形下,中国包容性绿色增长存在条件β收敛特征,即地区包容性绿色增长差距逐渐缩小;数字普惠金融及其空间溢出效应加快了包容性绿色增长速度,有利于缩小地区包容性绿色增长差距;资本要素流动是数字普惠金融缩小地区包容性绿色增长差距的内在机制。进一步异质性分析表明,在数字普惠金融的三个维度中,覆盖广度对地区包容性绿色增长差距的缩小作用更强,同时数字普惠金融对地区包容性绿色增长差距的缩小作用在中西部更加显著。