STIFFNESS ANALYSIS OF THE MAIN MODULE FOR PARALLEL MACHINE TOOLS BY FINITE ELEMENT ANALYSIS

With the aid of commercial finite element analysis software package ANSYS,investigations are made on the contributions of main components to stiffness of the main module for parallel machine tools,and it is found that the frame is the main contributor.Then,influences of constraints,strut length and working ways of the main module have also been investigated.It can be concluded that when one of the main planes of the frame without linear drive unit is constrained,the largest whole stiffness can be acquired.And,the stiffness is much better when the main module is used in a vertical machine tool instead of a horizontal one.Finally,the principle of stiffness variation is summarized when the mobile platform reaches various positions within its working space and when various loads are applied.These achievements have provided critical instructions for the design of the main module for parallel machine tools.

Finite element analysis of stiffness and static dent resistance of aluminum alloy double-curved panel in viscous pressure forming

The static dent resistance performance of the aluminum alloy double-curved panel formed using viscous pressure forming (VPF)was studied by finite element analysis,which mainly considers the forming process conditions.The whole simulation consisting of three stages,i.e.,forming,spring-back and static dent resistance,was carried out continuously using the finite element code ANSYS.The influence of blank holder pressure(BHP)and the drawbead on the stiffness and the static dent resistance of the panels formed using VPF was analyzed.The results show that the adequate setting of the drawbead can increase the plastic deformation of the double-curved panel,which is beneficial to the initial stiffness and the static dent resistance.There is an optimum BHP range for the stiffness and the static dent resistance.

A FINITE ELEMENT METHOD FOR STRESS ANALYSIS OR ELASTOPLASTIC BODY WITH POLYGONAL LINE STRAIN——HARDENING

In this paper, the stress-strain curve of material is fitted by polygonal line composed of three lines. According to the theory of proportional loading in elastoplasticity, we simplify the complete stress-strain relations, which are given by the increment theory of elastoplasticity. Thus, the finite element equation with the solution of displacement is derived. The assemblage elastoplastic stiffness matrix can be obtained by adding something to the elastic matrix, hence it will shorten the computing time. The determination of every loading increment follows the von Mises yield criteria. The iterative method is used in computation. It omits the redecomposition of the assemblage stiffness matrix and it will step further to shorten the computing time. Illustrations are given to the high-order element application departure from proportional loading, the computation of unloading fitting to the curve and the problem of load estimation.

Assessment of natural frequency of installed offshore wind turbines using nonlinear finite element model considering soil-monopile interaction

A nonlinear finite element model is developed to examine the lateral behaviors of monopiles, which support offshore wind turbines(OWTs) chosen from five different offshore wind farms in Europe. The simulation is using this model to accurately estimate the natural frequency of these slender structures, as a function of the interaction of the foundations with the subsoil. After a brief introduction to the wind power energy as a reliable alternative in comparison to fossil fuel, the paper focuses on concept of natural frequency as a primary indicator in designing the foundations of OWTs. Then the range of natural frequencies is provided for a safe design purpose. Next, an analytical expression of an OWT natural frequency is presented as a function of soil-monopile interaction through monopile head springs characterized by lateral stiffness KL, rotational stiffness KRand cross-coupling stiffness KLRof which the differences are discussed. The nonlinear pseudo three-dimensional finite element vertical slices model has been used to analyze the lateral behaviors of monopiles supporting the OWTs of different wind farm sites considered. Through the monopiles head movements(displacements and rotations), the values of KL, KRand KLRwere obtained and substituted in the analytical expression of natural frequency for comparison. The comparison results between computed and measured natural frequencies showed an excellent agreement for most cases. This confirms the convenience of the finite element model used for the accurate estimation of the monopile head stiffness.

PHYSICAL VALUE MAPPING ALGORITHM OF MESH IN FINE CAE ANALYSIS OF AUTOMOBILE BODY STRUCTURE

A physical value mapping （PVM） algorithm based on finite element mesh from the stamped part in stamping process to the product is presented, In order to improve the efficiency of the PVM algorithm, a search way from the mesh of the product to the mesh of the stamped part will be adopted. At the same time, the search process is divided into two steps： entire search （ES） and local search （LS）, which improve the searching efficiency. The searching area is enlarged to avoid missing projection elements in ES process. An arc-length method is introduced in LS process. The validity is confirmed by the results of the complex industry-forming product.

Mass-Stiffness Templates for Cubic Structural Elements Dedicated to Professor Karl Stark Pister for his 95th birthday

1 This paper considers Lagrangian finite elements for structural dynamics constructed with cubic displacement shape functions.The method of templates is used to investigate the construction of accurate mass-stiffness pairs.This method introduces free parameters that can be adjusted to customize elements according to accuracy and rank-sufficiency criteria.One-and two-dimensional Lagrangian cubic elements with only translational degrees of freedom(DOF)carry two additional nodes on each side,herein called side nodes or SN.Although usually placed at the third-points,the SN location may be adjusted within geometric limits.The adjustment effect is studied in detail using symbolic computations for a bar element.The best SN location is taken to be that producing accurate approximation to the lowest natural frequencies of the continuum model.Optimality is investigated through Fourier analysis of the propagation of plane waves over a regular infinite lattice of bar elements.Focus is placed on the acoustic branch of the frequency-vs.-wavenumber dispersion diagram.It is found that dispersion results using the fully integrated consistent mass matrix(CMM)are independent of the SN location whereas its lowfrequency accuracy order is O(κ8),whereκis the dimensionless wave number.For the diagonally lumped mass matrix(DLMM)constructed through the HRZ scheme,two optimal SN locations are identified,both away from third-points and of accuracy order O(κ8).That with the smallest error coefficient corresponds to the Lobatto 4-point integration rule.A special linear combination of CMM and DLMM with nodes at the Lobatto points yields an accuracy of O(κ10)without any increase in the computational effort over CMM.The effect of reduced integration(RI)on both mass and stiffness matrices is also studied.It is shown that singular mass matrices can be constructed with 2-and 3-point RI rules that display the same optimal accuracy of the exactly integrated case,at the cost of introducing spurious modes.The optimal SN location in two-dimensional,bicubic,isoparametric plane stress quadrilateral elements is briefly investigated by numerical experiments.The frequency accuracy of flexural modes is found to be fairly insensitive to that position,whereas for bar-like modes it agrees with the one-dimensional results.

Stochastic analysis of excavation-induced wall deflection and box culvert settlement considering spatial variability of soil stiffness

In this study, a three-dimensional (3D) finite element modelling (FEM) analysis is carried out to investigate the effects of soil spatial variability on the response of retaining walls and an adjacent box culvert due to a braced excavation. The spatial variability of soil stiffness is modelled using a variogram and calibrated by high-quality experimental data. Multiple random field samples (RFSs) of soil stiffness are generated using geostatistical analysis and mapped onto a finite element mesh for stochastic analysis of excavation-induced structural responses by Monte Carlo simulation. It is found that the spatial variability of soil stiffness can be described by an exponential variogram, and the associated vertical correlation length is varied from 1.3 m to 1.6 m. It also reveals that the spatial variability of soil stiffness has a significant effect on the variations of retaining wall deflections and box culvert settlements. The ignorance of spatial variability in 3D FEM can result in an underestimation of lateral wall deflections and culvert settlements. Thus, the stochastic structural responses obtained from the 3D analysis could serve as an effective aid for probabilistic design and analysis of excavations.

Cartwheel型双轴柔性铰链设计

针对精密光学仪器对光学元件柔性支撑的需求,提出了由带圆角的短直梁复合组成的Cartwheel型双轴柔性铰链,并利用无量纲设计图研究了设计方法。首先,基于对Cartwheel双轴柔性铰链的参数化有限元分析进行多项式拟合,建立了其刚度、应力等力学指标的无量纲设计图。针对光学仪器的工程需要,利用该无量纲设计图进行了实例设计,并利用有限元分析对其进行了实验验证。搭建了光学测试平台,对设计实例的转动刚度进行了测量。结果显示:有限元分析结果、实验测量数据与设计结果符合得较好,最大相对误差为10.1%。使用无量纲设计图方法作为设计工具,设计者可根据对带圆角短直梁复合组成的Cartwheel型双轴柔性铰链的刚度、转角行程、最大应力与结构重量等要求,确定其几何尺寸,从而方便、快速、准确地满足设计要求。

不同内固定系统治疗股骨转子间骨折的力学稳定性

背景:股骨转子间骨折的骨折类型和固定方式多样,各固定系统间的力学稳定性相差较大。使用有限元分析方法对各固定系统开展生物力学研究具有科学的临床意义。目的:通过有限元方法对比分析多种内固定应用于股骨A031-A2.1型转子间骨折的力学稳定性。方法:在已验证有效性的股骨有限元模型基础上,对模型进行必要的切割,造模成股骨A031-A2.1型转子间骨折,模拟临床手术方法置入不同的内固定系统,分别建立股骨近端防旋髓内钉、动力髋螺钉、经皮加压钢板和股骨近端锁定钢板固定模型。约束4组模型股骨远端下所有节点,在股骨头上施加700,1400和2100N的压缩载荷,通过计算分析,观察各组模型的等效应力分布和压缩刚度,比较各组模型之间的力学稳定性。结果与结论:①通过计算分析,对比各组模型的变形量计算压缩刚度后,在各级载荷作用下,各组模型上压缩刚度呈现的趋势:生理组>股骨近端防旋髓内钉组>股骨近端锁定钢板组>经皮加压钢板组>动力髋螺钉组;完整的生理组模型的压缩刚度明显高于所有的手术组模型;②观察应力指标,因存在应力遮挡效应,致使各固定组的应力峰值均高于生理组,最大峰值均集中分布于各内固定上;其中股骨近端防旋髓内钉固定组应力峰值最小,动力髋螺钉固定组应力最高,应力分布趋势呈现:生理组<股骨近端防旋髓内钉固定组<经皮加压钢板固定组<股骨近端锁定钢板固定组<动力髋螺钉固定组;③分布于骨质模型的应力,因内固定置入位置不同呈现不同的分布结果;④提示对于股骨转子间骨折,各种内固定均能起到有效的固定,结合有限元分析结果得出股骨近端防旋髓内钉组是较好的一种内固定选择,呈现变形量小、应力峰值低,应力分布均匀的特性;经皮加压钢板组和股骨近端锁定钢板组的力学效果优良,固定效果接近股骨近端防旋髓内钉固定;动力髋螺钉固定效果欠佳,同比于其他内固定,其力学稳定性较差。

基于ANSYS与ADAMS/Car联合仿真的轿车副车架结构分析

以制动工况为例,利用ANSYS与ADAMS/Car联合仿真的方法对某轿车副车架进行结构强度计算和模态分析。静力计算结果与材料许用强度的分析以及模态频率与激振频率的分析表明:采用联合仿真的方法可以快速有效的验证副车架的强度及动态性能是否满足使用要求。该方法可为缩短副车架开发周期及相关改进设计提供参考。

基于AnyBody骨骼肌肉多体动力学分析的有限元仿真

目的研究AnyBody骨骼肌肉多体动力学仿真技术的建模和有限元建模相结合的方法,进行临床骨外科生物力学分析。方法根据志愿者身高、体质量及CT数据,利用AnyBody软件建立志愿者个性化上肢的骨骼肌肉运动力学模型,模拟正常人肘关节屈曲运动,导出肱骨在屈曲运动过程中所受肌肉力、关节力、力矩及约束条件,作为有限元分析的边界条件。根据CT数据在MIMICS软件中进行三维重建,在Geomagic Studio软件中完成肱骨曲面化和位置坐标匹配,并在HyperMesh软件中进行网格划分和材料赋值。把三维重建的肱骨有限元模型导入ABAQUS软件中,施加AnyBody软件导出的边界条件数据并执行应力计算分析。结果在ABAUQUS软件中计算得到肘关节屈曲运动过程中肱骨的应力、位移结果,肘关节屈曲运动约90°时肱骨受到的应力和位移最大,分别为0.76 MPa、20μm。结论实现了肘关节屈曲运动过程中肱骨应力、位移的一个连续动态的分析,更符合人体生理解剖要求,为研究临床骨外科问题提供一个高效的分析平台及新的方法。

基于AnyBody仿真及有限元建模下的八段锦运动生物力学研究

以AnyBody仿真骨骼肌多体逆向动力学三元素肌肉收缩力模型及有限元法构建八段锦动作的三维胫骨模型,全面、客观地计算不同动作最大肌力峰值时刻的积分肌电、力矩、肌肉收缩等生物力学特性.将10例健康青年八段锦志愿者的身高、体质量、髋宽、髋深、膝宽、踝宽等形态学数据作为约束条件,用AnyBody7.1.2软件导出八段锦8个动作下肢最大肌力指标,依据胫骨最大应力约束条件,用Minics 10.01、Geomagic studio 2013、ANSYS 19.2软件建构三维数据,添加AnyBody中的3个方向数据,分析并计算不同动作最大力的应力传导大小、分布规律.研究结果表明:八段锦是左右对称性运动,双侧同块肌肉积分肌电值、肌肉力值无显著性差异,有利于锻炼双下肢稳定性及协调性,运动中人体需要通过移动来保持平衡,膝关节在垂直轴方向力最大,伸展力矩值最大;做八段锦运动过程中,髋关节主导发力肌肉为臀中肌,膝关节主导发力肌肉为比目鱼肌、股外侧肌、腓肠肌,踝关节主导发力肌肉为拇长屈肌;表面肌电验证是评价人体肌肉激活程度的主要方式,八段锦运动中胫骨前肌、腓肠肌、股直肌、股二头肌的肌肉活性仿真结果与积分肌电值具有较高的一致性.以AnyBody软件分析下肢动作特征和有限元软件建构的胫骨模型,适用于八段锦动作的动态研究,可为计算八段锦运动时动力学变化提供新思路与实践价值参考.

Age- and direction-related adaptations of lumbar vertebral trabecular bone with respect to apparent stiffness and tissue level stress distribution

The objective of this study was to study the age-related adaptation of lumbar vertebral trabecular bone at the apparent level, as well as the tissue level in three orthogonal directions. Ninety trabecular specimens were obtained from six normal L4 vertebral bodies of six male cadavers in two age groups, three aged 62 years and three aged 69 years, and were scanned using a high-resolution micro-computed tomography （micro-CT） system, then converted to micro- finite element models to do micro-finite element analyses. The relationship between apparent stiffness and bone volume fraction, and the tissue level yon Mises stress distribution for each trabecular specimen when compressed separately in the longitudinal direction, medial-lateral and anterior-posterior directions （transverse directions） were derived and compared between two age groups. The results showed that at the apparent level, trabecular bones from 69-year group had stiffer bone structure relative to their volume fractions in all three directions, and in both age groups, changes in bone volume fraction could explain more variations in apparent stiffness in the longitudinal direction than the transverse directions; at the tissue level, aging had little effect on the tissue von Mises stress distributions for the compressions in all the three directions. The novelty of the present study was that it provided quantitative assessments on the age and direction- related adaptation of Chinese male lumbar vertebral trabecular bone from two different levels： stiffness at the apparent level and stress distribution at the tissue level. It may help to understand the failure mechanisms and fracture risks of vertebral body associated with aging and direction for the prevention of fracture risks in elder individuals.

LOADS INFLUENCE ANALYSIS ON NOVEL HIGH PRECISION FLEXURE PARALLEL POSITIONER

A large workspace flexure parallel positioner system is developed, which can attain sub-micron scale accuracy over cubic centimeter motion range for utilizing novel wide-range flexure hinges instead of the conventional mechanism joints. Flexure hinges eliminate backlash and friction, but on the other hand their deformation caused by initial loads influences the positioning accuracy greatly, so discussions about loads＇ influence analysis on this flexure parallel positioner is very necessary. The stiffness model of the whole mechanism is presented via stiffness assembly method based on the stiffness model of individual flexure hinge, And the analysis results are validated by the finite element analysis （FEA） simulation and experiment tests, which provide essential data to the practical application of this positioner system.

Analysis of Frequency Characteristics and Sensitivity of Compliant Mechanisms

Based on a modified pseudo-rigid-body model,the frequency characteristics and sensitivity of the large-deformation compliant mechanism are studied.Firstly,the pseudo-rigid-body model under the static and kinetic conditions is modified to enable the modified pseudo-rigid-body model to be more suitable for the dynamic analysis of the compliant mechanism.Subsequently,based on the modified pseudo-rigid-body model,the dynamic equations of the ordinary compliant four-bar mechanism are established using the analytical mechanics.Finally,in combination with the finite element analysis software ANSYS,the frequency characteristics and sensitivity of the compliant mechanism are analyzed by taking the compliant parallel-guiding mechanism and the compliant bistable mechanism as examples.From the simulation results,the dynamic characteristics of compliant mechanism are relatively sensitive to the structure size,section parameter,and characteristic parameter of material on mechanisms.The results could provide great theoretical significance and application values for the structural optimization of compliant mechanisms,the improvement of their dynamic properties and the expansion of their application range.

DYNAMICS OF FLEXIBLE MULTIBODY SYSTEMS WITH TREE TOPOLOGIES

The dynamic equations of flexible multibody systems with tree topological configuration are de- rived by using the Jourdain's principle.The independent joint coordinates are introduced to describe the large displacements of the bodies,and the modal coordinates are used to describe small deformations of flexible bodies based on the consistent mass finite element method and normal vibration mode analysis.The mini- mum differential equations are developed,which are compatible with the equations of multi-rigid body sys- tems or structural dynamics.The stiff problem in the numerical integration is thus alleviated effectively.The method used in this paper can be extended to deal with systems with other topological configurations. Finally,the validity and feasibility of the presented mathematical model are demonstrated by a numerical ex- ample of a manipulator with two elastic links.

Structural Reliability Analysis and Design Optimization of Hot-Rolled H-beam Steel Universal Mill

The structure of a hot-rolled H-beam steel universal mill was optimized,including bearing chocks( upper and lower) and mill frame. To verify the reliability of the optimized structure, the parameters of rolling mill and parts were analyzed by finite element,including the maximum stress,strain and maximum displacement.The results showed that the maximum displacement of the mill frame and the bearing chock was 0. 049 mm,and the maximum stress was2. 659 MPa. The maximum stress of the mill was 3. 181 MPa. There were no obviously elastic deformation and plastic deformation,which satisfied the structural requirements. The reliability of the optimized mill structure was verified.

LARGE EDDY SIMULATION AND SPECTRUM ANALYSIS OF FLOW AROUND TWO SQUARE CYLINDERS ARRANGED SIDE BY SIDE

Large eddy simulation cooperated with the second order full extension ETG(Euler-Taylor-Galerkin) finite element method was applied to simulate the flow around two square cylinders arranged side by side at a spacing ratio of (1.5.) The second order full extension ETG finite element method was developed by Wang and He. By means of Taylor expansion of terms containing time derivative, time derivative is replaced by space derivative. The function of it is equal to introducing an artificial viscosity term. The streamlines of the flow at different moments were obtained. The time history of drag coefficient, lift coefficient and the streamwise velocity on the symmetrical points were presented. Furthermore, the symmetrical problem of the frequency spectrum of flow around two square cylinders arranged side by side were studied by using the spectral analysis technology. The data obtained at the initial stage are excluded in order to avoid the influence of initial condition on the results. The power spectrums of drag coefficient, lift coefficient, the streamwise velocity on the symmetrical points were analyzed respectively. The results show that although the time domain process of dynamic parameters is non-symmetrical, the frequency domain process of them is symmetrical under the symmetrical boundary conditions.

Method to analyze wrinkled membranes with zero shear modulus and equivalent stiffness

To solve the problems of divergence,low accuracy and project application of membrane wrinkling analysis,an analysis method of zero shear modulus and equivalent stiffness was proposed.This method is an improvement to the previous method (Method I) of local coordinate transposition and stiffness equivalence.The new method is derived and the feasibility is theoretically proved.A small-scale membrane structure is analyzed by the two methods,and the results show that the computational efficiency of the new method (Method II) is approximately 23 times that of Method I.When Method II is applied to a large-scale membrane stadium structure,it is found that this new method can quickly make the second principal stress of one way wrinkled elements zero,and make the two principal stresses of two-way wrinkled elements zero as well.It could attain the correct load responses right after the appearance of wrinkled elements,which indicates that Method II can be applied to wrinkling analysis of large-scale membrane structures.

Bionic stab-resistant body armor based on triangular pyramid structure

A stab-resistant substrate was designed and realized with a triangular pyramidal structure, inspired by the biological armor model in nature. The stab-resistance behavior and dynamic response mechanisms were studied through numerical simulation and experimental testing of a knife impacting a substrate,and an optimal structural design was obtained accordingly, with a tilted angle of 22.5and optimal thickness of 1.2 mm. It was shown that the triangular pyramidal structure generated twice the internal energy of the knife than the flat substrate due to the dispersing effect of the structure. The force parallel to the inclination caused a significant scratch on the substrate surface, while the force perpendicular caused obvious substrate deformation. A new riveting method was used to form the total layer, which passed the GA 68-2008 standard. The stab-resistant clothing coupled with the reduced wearing burden could provide effective protection and avoid fatal injuries on security personnel working in dangerous environments. The method provided may enlighten the future design and manufacturing of stabresistant clothing.