Numerical simulation of tire/soil interaction using a verified 3D finite element model

The compaction and stress generation on terrain were always investigated based on empirical approaches or testing methods for tire/soil interaction.However,the analysis should be performed for various tires and at different soil strengths.With the increasing capacity of numerical computers and simulation software,finite element modeling of tire/terrain interaction seems a good approach for predicting the effect of change on the parameters.In this work,an elaborated 3D model fully complianning with the geometry of radial tire 115/60R13 was established,using commercial code Solidwork Simulation.The hyper-elastic and incompressible rubber as tire main material was analyzed by Moony-Rivlin model.The Drucker-Prager yield criterion was used to model the soil compaction.Results show that the model realistically predicts the laboratory tests outputs of the modeled tire on the soft soil.

Real-time determination of sandy soil stiffness during vibratory compaction incorporating machine learning method for intelligent compaction

An emerging real-time ground compaction and quality control, known as intelligent compaction(IC), has been applied for efficiently optimising the full-area compaction. Although IC technology can provide real-time assessment of uniformity of the compacted area, accurate determination of the soil stiffness required for quality control and design remains challenging. In this paper, a novel and advanced numerical model simulating the interaction of vibratory drum and soil beneath is developed. The model is capable of evaluating the nonlinear behaviour of underlying soil subjected to dynamic loading by capturing the variations of damping with the cyclic shear strains and degradation of soil modulus. The interaction of the drum and the soil is simulated via the finite element method to develop a comprehensive dataset capturing the dynamic responses of the drum and the soil. Indeed, more than a thousand three-dimensional(3D) numerical models covering various soil characteristics, roller weights, vibration amplitudes and frequencies were adopted. The developed dataset is then used to train the inverse solver using an innovative machine learning approach, i.e. the extended support vector regression, to simulate the stiffness of the compacted soil by adopting drum acceleration records. Furthermore, the impacts of the amplitude and frequency of the vibration on the level of underlying soil compaction are discussed.The proposed machine learning approach is promising for real-time extraction of actual soil stiffness during compaction. Results of the study can be employed by practising engineers to interpret roller drum acceleration data to estimate the level of compaction and ground stiffness during compaction.

Finite-Element Simulation and Experimental Research of the Hot-Press Sintering of Nano-Sized Ceramic Powders

Numerical simulation of hot-press sintering of nano-sized ceramic powders was introduced by the commercial finite element code MSC.MARC. The powder plastic model and the thermo-mechanical coupled quadrilateral element were developed and adopted in the simulation. The mechanical and thermal properties of the nano-sized alumina based powders were determined.In addition, the experimental research and numerical simulation of the sintering process of different initial densities were carried out. The stress state in sintering of green compacts with different initial densities was analyzed by the densification theory.The reason for the density fluctuations of as-sintered ceramic bulks was found out.

Coupled mechanical and thermal simulation of warm compaction

Warm compaction process of pure iron powder was investigated. Due to the existence of elastic, plastic and thermal strains, a coupled mechanical and thermal model was applied. The elasto-plastic constitutive equations for powder material were developed based on ellipsoidal yield criterion and continuum theory. The constitutive equations were integrated into the constitutive integral arithmetic and solved employing incremental iterative solution strategy. The yield strength of iron powder was obtained according to the tensile experiments. When the compaction temperature was raised to 130 ℃, the yield strength of iron powder metal drops to 85% of room temperature value. Modified coulomb friction law is applied and the simulation results show that friction was an important factor resulting in the inhomogeneous relative density and reverse-density distribution phenomena in the regions near the die wall and the symmetrical axis.

Simulation of die wall friction's effect on density distribution in metallic powder compaction

A computer simulation procedure for metal powder die compaction was described. Friction behavior of metal powder during cold compaction was simulated by the finite element method. The movement of powder relative to the die wall was taken into consideration by utilizing the shear friction model. Friction between the powder and the rigid die wall leads to inhomogeneous density distribution during the compaction process. The floating die technique and double punch pressing can attain more homogenous compacts than the fixed die technique can do. The results obtained from numerical analysis agree well with the experimental results. Simulation model was built in MSC.Mentat, and MSC.Marc software was used to calculate the powder compaction process.

Research of PDC Bit Compact Die With FEM and Optimum Method

In mould design, it is necessary for a designer to ensure that the cylinder has enough intensity in both the prestressed and synthesis states. An individual layer cylindrical mould cannot withstand a very high pressure needed in polycrystalline diamond composite (PDC) production. So, multi-layer prepressure combination assemble moulds are often used. The analysis conducted here is to study the interaction of cylindrical layers and to explain how to obtain enough load capability with the lowest requirement of material performance. The ratio of the pressure cylinder radius of synthetic diamond is 3.27, which is close to the optimal value and can be used as structure size in a design for PDC bit compact die. There is a linear relationship between the internal and external pressures under a special tangent stress on the inner wall of the pressure cylinder. So, when two of the three parameters (the internal pressure, external pressure, and the requirement value of the tangent stress on the inner wall of the pressure cylinder) are given, the third can be obtained. The sleeve acts as a bridge?between the pressure cylinder and the steel belts. The optimum model developed in this paper can be used in PDC bit compact die design and other similar prestressed cold extrusion die design.

The Compactions of Elasto-Plastic and Visco-Plastic Granular Assemblies

In this paper, the compactions of the elasto-plastic and the visco-plastic granular assemblies are simulated using the finite element method. Governing equations for motion and deformation for particles, including coupling of rigid body motion and deformation for deformable bodies, are investigated. An implicit discrete element method for block systems is developed to make visco-plastic analysis for the assemblies. Among particles, three different contact types, cohering, rubbing and sliding, are taken into account. To verify accuracy and efficiency of the numerical method, some numerical example is simulated and the results are in a satisfactory agreement with the solutions in literatures. The effects of frictional condition, the initial solid volume ratio, the number of particles in the assembly, and different types of compact- tion on the compaction of the elasto-plastic and the visco-plastic aggregates are investigated. It is demonstrated that the effect of frictional condition, the initial solid volume ratio, the number of particles in the assembly, and different types of compaction on the global behavior of the elasto-plastic the visco-plastic granular assemblies under compacting are considerable. The numerical model is extended to simulate the compaction of aggregates consisting of mixed particles of different viscous incompressible materials. It is indicated that, with minor modification, the method could be used in a variety of problems that can be represented using granular media, such as asphalt, polymers, aluminum, snow, food product, etc.

某水库大坝挡水坝段坝后渗漏探测及有限元分析

混凝土坝坝体渗漏影响大坝的安全性和耐久性,危及电器设备正常运行,应及时探查渗漏位置,消除渗漏隐患。为查明某混凝土挡水坝坝后渗漏原因,采用自然电位、跨孔声波、单孔声波、钻孔电视、钻孔取芯、注水试验、压水试验等多种方法对坝体混凝土质量进行检测,并基于检测成果开展有限元分析。检测发现:4号—5号坝段横缝存在渗漏异常,挡水坝段混凝土渗透系数不满足设计抗渗要求,各坝段混凝土存在不同程度蜂窝、离析、空洞和不密实现象,4号坝段520廊道与494廊道存在垂向渗漏通道,5号坝段钻孔之间混凝土存在渗漏通道,且廊道以下及向下游方向混凝土存在渗漏通道。有限元分析结果表明:515 m高程碾压混凝土与常态混凝土交界处为主要渗漏通道。

翁结水库碾压混凝土重力坝动力特性及其抗滑稳定分析

重力坝是水利工程中最常用的主要水工建筑物之一,混凝土重力坝在地震作用下的动力稳定是坝工设计中的重要问题.本文以翁结碾压混凝土重力坝为对象,取位于河谷中的7、8号溢流坝段和9号非溢流坝段,建立三维有限元模型,通过计算分析了碾压混凝土重力坝在不同工况下的应力变形规律及抗滑稳定性.结果表明:静力荷载作用下,坝体位移符合重力坝一般规律,坝踵主拉应力范围较小;动力荷载作用下,位移等响应在坝顶达到最大,符合鞭鞘效应特征,同时坝体残余位移较小,坝体在一些部位出现瞬时拉应力超标现象,坝基塑性区未发生贯通;对7、8号坝段和9号坝段在建基面及碾压层面进行抗滑稳定验算,坝体坝基均满足稳定要求.

基于遗传算法的碾压混凝土重力坝温度场多测点反演

由于碾压混凝土重力坝施工现场条件复杂,实验获得的参数与实际参数存在一定的差异。为获得高精度的温度场仿真结果,根据某碾压混凝土重力坝现场实测温度数据,利用遗传算法反演该碾压混凝土坝的绝热温升Q 0、温升常数n和导热系数λ,并运用所得的反演参数进行温度场仿真模拟分析,对比不同测点个数下反演所得参数的可靠性和精确性。结果表明:通过遗传算法进行参数反演可有效提高反演的速度与精度,并且反演所依据的测点个数越多反演结果越接近实测数据,9个测点反演比3个测点反演误差减少了1.43%,比6个测点反演误差减少了0.44%。因此,在利用遗传算法进行参数反演时应尽量选择较多的测点个数,以提高仿真计算的精度。研究结果可为碾压混凝土重力坝热学参数反演提供理论指导和依据。

基于PFEM法的黄土地基振杆密实过程大变形分析

采用粒子有限元方法(PFEM)及结构性土的本构模型,对振杆密实法加固砂质黄土地基的大变形过程进行了数值模拟研究,分析了振杆贯入过程中周围土体的位移场、应力场、速度场以及塑性体应变等分布规律,揭示了砂质黄土地基深层振动密实机理.结果表明:现场实测和数值模拟获得的地面垂直振动速度峰值变化趋势较为一致,验证了粒子有限元方法的可靠性;垂直激振的振杆能够同时引起土体垂直方向和水平方向上位移场、应力场和速度场的变化;在距振源水平距离5R(R为振杆半径)范围内,土颗粒以半梭形向外扩展并趋于密实,同时水平应力大幅增加并产生预压效果;以塑性体应变作为加固范围的评价标准,结果表明土体径向加固范围随振杆贯入深度增加而略有增大,最大径向加固范围约为3.2R,且振杆底端以下1R~2R范围亦有密实效果.

基于碾压混凝土破坏特征研究

以目前碾压混凝土重力坝坝体破坏特点为背景,利用扩张有限元数值方法,对碾压层厚度对大坝应力分布规律和裂缝扩展的影响进行了研究,并将在同一超载系数下的计算结果进行了比较,其中,超载系数从1.04~3.04,一共9种。在同样的过载条件下,裂缝的垂直延伸长度随碾压层的加厚而略有下降,裂缝的垂直延伸长度比正常情况下要小,仅在K=2.29、K=2.79两个位置与正常情况相当。大坝的压应力和物质的抗压强度相近,表明大坝在这个时候会出现总体失稳,而且裂缝的发展会转向沿河流的流向;在坝体各部位的材料达到对应的强度后,裂缝的横向发展速率会迅速增加,直至整个坝体的断裂。通过对4种不同荷载作用下坝体裂缝扩展深度、坝顶位移、坝踵及坝址处的受力情况进行了比较,结果显示,不同荷载作用下坝体裂缝呈现出脆性突发性破坏特征;结果表明:在荷载作用下,坝体裂缝扩展深度和坝顶位移均有一定程度的降低。

数值模拟在粉末压制细观分析中的应用与发展

数值模拟技术已经成为研究粉末压制过程的重要手段。研究人员运用离散单元法(discrete element method,DEM)从细观角度研究粉末颗粒的力学行为,分析力链特性及力链演化过程,揭示细观结构对宏观性质的影响;使用多粒子有限元法(multi-particle finite element method,MPFEM)从颗粒层面对不同粉末的压制变形机理进行研究。本文对离散单元法和多粒子有限元法两种数值模拟方法在粉末压制中的应用及发展进行综述,总结了多粒子有限元法在粉末压制数值模拟中的难点,分析得到在动态载作用下对粉末力链演化规律及颗粒致密机理的研究可作为未来探索方向的展望。

碾压混凝土大坝6m升层通水冷却的温度场研究

伴随着国内筑坝技术的不断提高和发展,碾压混凝土大坝由于其优良的特性和便捷的施工方法成为工程建设者比较青睐的坝型,施工期的温控防裂措施也得到了高度重视。布置冷却水管通入制冷水降温是混凝土大坝施工期的主要温控措施,其布置形式对坝体内混凝土温度场的影响比较显著,通过建立坝体河床坝段三维有限元模型,模拟计算6 m升层施工过程坝内混凝土冷却水管的不同布置形式的温度场,结果显示:冷却水管布置间距的加密变小,能够有效降低碾压混凝土坝体内温度,使坝体内部最大温度达到设计要求的范围,同时也能减小坝体的温度应力,为碾压混凝土拱坝的温控防裂起到显著的作用,为类似工程的设计和施工提供一定的参考依据。

不同压制工艺对粉末冶金制品性能影响的有限元模拟

利用MSC/MARC有限元分析软件对金属粉末压制过程进行模拟分析。采用基于更新拉格朗日方法的热—力耦合分析不同工艺条件(温度、摩擦条件和压制方式等)对压坯性能的影响规律,同时对压制过程中的力学特征(压制力、脱模力、侧压力和应力分布等)进行分析。结果显示,摩擦条件是影响压坯密度大小及分布的关键因素,通过采用双向压制方法可以有效地改善单向压制压坯密度分布不均、差值较大的现象。温度的提高有利于提高粉末颗粒的塑性变形能力,但效果不明显。另外,由于温度影响润滑剂润滑性能,因此在制定压制工艺时需考虑温度对压坯性能的影响。此外温度的提高、摩擦的降低均有利于降低压制力,提高压坯密度均匀性,改善压坯应力集中现象。

新型外转子磁齿轮复合电机的设计与研究

提出一种新型外转子磁齿轮复合电机,该电机将磁齿轮和无刷直流电机进行整合,电机的外转子和磁齿轮的内转子共同构成复合电机的内转子,实现了低速大转矩的直接驱动方式,同时充分利用了磁齿轮的内部空间,从而提高了整个传动系统的效率。采用时步有限元法对复合电机的磁场进行分析,充分考虑了谐波磁场的相互耦合问题,并得出复合电机的相关动态特性。这些特性揭示了复合电机非常适合与低速大转矩的直接驱动场合,但是不适合于对舒适度和位置精度要求较高的场合。制造了一台1200W原型机,并对原型机进行试验,验证了电磁理论分析结果的正确性。

特高压紧凑型输电线路工频电场强度计算

为研究特高压交流输电线路的工频电场强度,通过建立二维静电场有限元模型,计算了LGJ-400/65、LGJ-500/45、LGJ-630/45 3种型号导线,子导线根数分别为6、8、10、12的导线表面场强、相导线平均场强最大值、线路下方距地面1 m处最大场强和线路走廊宽度,分析了导线截面、子导线根数、线路最低对地高度和走廊宽度的选取。结果表明特高压交流线路选取大截面导线、紧凑型倒三角布置方式在导线表面场强、杆塔高度和线路走廊方面可满足要求。

链传动啮合冲击理论分析及有限元模拟

啮合冲击是引发链传动产生振动、噪声以及链条零部件发生疲劳损坏的主要原因,因此,精确地分析与计算啮合冲击载荷是进行轮齿强度计算以及链传动系统动力学研究的重要内容.为此,建立了链轮轮齿滚子间啮合冲击动力学模型,计算了啮合冲击力幅值;采用赫兹接触理论,对齿面接触应力进行了静态条件下的理论计算;建立了套筒滚子链传动系统有限元模型,采用三维弹性接触问题有限元分析方法,对轮齿滚子间的啮合冲击效应进行了精确模拟,分析了具有标准齿廓形状轮齿滚子瞬时啮合时,冲击载荷变化规律及应力分布情况.计算结果表明:在动态条件下轮齿滚子作为弹性体发生冲击接触时,接触区域变形并非理想的长方形区域;轮齿齿面的冲击接触力分布是不均匀的;在理论接触区域两侧冲击应力较大;在考虑了链轮齿形、间隙及弹性变形等多种影响因素的条件下,动态冲击载荷远大于静态条件下的理论计算值.

强夯大变形冲击碰撞数值分析

本文采用动力接触有限元法分析了强夯对地基土的冲击碰撞过程。夯击过程中 ,夯点周边地基土存在局部大变形现象。采用无限小应变度量将不能消除刚体位移的影响 ,必须采用大变形理论。为了保证显示算法的网格稳定性 ,计算模型中考虑了侵蚀分析。锤底接触力和夯沉量在计算过程中直接求得 ,模型考虑了夯锤自重 ,能够模拟夯锤与地基土的多次接触分离过程 ,适应于各种复杂的地基土结构。文章最后给出了一个工程实例 ,以验证本文计算模型。

500kV紧凑型线路悬垂复合绝缘子均压环电晕抑制分析

500kV紧凑型输电线路部分均压环由于结构设计和安装方式不合理,电晕现象严重,需要对其结构进行优化和改造以抑制电晕放电。为此,使用紫外成像仪沿线观测导线和杆塔金具,找出了有明显电晕现象的均压环,确定了放电位置和强度,运用三维有限元方法建立了紧凑型直线塔模型,计算了该均压环的电场分布,分析了其球头和环体产生电晕的原因,提出了均压环的结构优化方案,将环表面最大场强由3868V/mm降低至2475V/mm。根据优化方案制造的新均压环挂网运行后的结果表明,球头和环体无电晕,防晕效果显著。该研究可为今后超、特高压线路防晕金具的设计、制造和安装提供研究经验和思路。