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.

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.

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.

Three-Dimensional Thermo-Elastic-Plastic Finite Element Method Modeling for Predicting Weld-Induced Residual Stresses and Distortions in Steel Stiffened-Plate Structures

The objective of the present paper is to develop nonlinear finite element method models for predicting the weld-induced initial deflection and residual stress of plating in steel stiffened-plate structures. For this purpose, three-dimensional thermo-elastic-plastic finite element method computations are performed with varying plate thickness and weld bead length (leg length) in welded plate panels, the latter being associated with weld heat input. The finite element models are verified by a comparison with experimental database which was obtained by the authors in separate studies with full scale measurements. It is concluded that the nonlinear finite element method models developed in the present paper are very accurate in terms of predicting the weld-induced initial imperfections of steel stiffened plate structures. Details of the numerical computations together with test database are documented.

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.

新型空心管状翼缘钢板组合梁设计理念与力学性能

工字钢组合梁桥正朝着少主梁、精简横向联系的方向发展。与传统多主梁复杂横向联系组合梁桥相比,双主梁桥由于采用了开口截面的结构形式,极大地削弱了其抗扭能力,在偏载作用下会产生较大的变形及翘曲应力,使钢主梁处于弯扭耦合的受力状态。空心管状翼缘钢板组合梁采用空心钢管取代传统的平板上翼缘,提升了稳定性,改善了结构性能。本文通过理论分析和实体有限元法的计算,研究了单梁在自重与横向风荷载作用下的稳定性;对非组合截面的组合体系下的稳定性能进行了分析与比较,并分离出扭转翘曲应力和纵向正应力,研究了不同跨径下扭转效应的影响。最后,对横向联系、加劲肋的影响进行了分析。研究结果表明,空心管状翼缘钢板组合梁桥扭转刚度大于传统工字形截面组合梁扭转刚度,自身横向稳定性好,并且需要较少的横向联系与加劲肋,可实现单梁吊装,避免采用过多临时加固及支撑措施,提高施工效率。

不同锈蚀程度下栓钉连接件的抗剪性能分析

为研究栓钉连接件锈蚀条件下的抗剪性能退化规律,建立ABAQUS有限元模型进行数值模拟.针对均匀圆环、受压区半环、受拉区半环及拉压区半环4种不同的锈蚀分布形态,考虑不同的锈蚀高度、锈蚀深度进行数值分析.结果表明,当锈蚀深度相同时,4种锈蚀分布形态的栓钉抗剪承载力随锈蚀高度的增加而降低,在锈蚀高度为10 mm时降到最小,且锈蚀深度越大,承载力降低程度也越大;当锈蚀高度相同时,随着锈蚀深度的增加,抗剪承载力和抗剪刚度基本上呈线性下降趋势;当锈蚀高度和深度相同时,均匀圆环锈蚀的抗剪承载力和刚度的降低程度最大,相比其他3种情况降低60%左右,受压区半环锈蚀的抗剪承载力和刚度的降低程度最小.研究成果可为钢混组合结构栓钉连接件耐久性设计提供参考.

梁桁组合结构高铁斜拉桥的收缩徐变分析——以西十高铁汉江特大桥为例

梁桁组合结构高铁斜拉桥中,混凝土收缩徐变对桥面线性的平顺性及行车的舒适性有直接影响,是桥上能够铺设无砟轨道的关键因素。因此,为分析收缩徐变对梁桁组合结构受力和变形的影响,依托新建西安至十堰高铁汉江特大桥工程,采用CEB-FIP90徐变计算模型,通过建立有限元模型分析收缩徐变影响下主要构件的内力和变形,评价各主要受力构件刚度变化对徐变变形的贡献程度,研究改善收缩徐变变形措施。结果表明:(1)收缩徐变引起主梁跨中下挠、桥塔向跨中侧偏移,同时引起主梁和桥塔的压缩变形,5年完成的收缩徐变变形占前10年的70%以上,且主梁产生的收缩徐变贡献超过50%;(2)收缩徐变引起斜拉索索力松弛,运营30年的最大变化率在5%以内;(3)收缩徐变引起主梁应力及上下缘应力差变化,随着运营时间增加主梁跨中区域应力差增大明显,主要表现在下缘压应力储备降低;(4)随着桥塔刚度、主梁刚度、加劲钢桁刚度增大,收缩徐变引起的变形有所减小,而斜拉索刚度则产生相反的趋势。(5)延长铺轨时间、适当增加底板钢束面积、增加斜拉索索力以及在跨中加劲钢桁上弦灌注混凝土可有效降低主梁跨中徐变下挠。

螺栓联接结合面三维分形刚度模型与实验研究

为更准确地分析螺栓联接体的静动态特性,根据三维分形理论,考虑微凸体弹塑性接触在内的4种变形阶段,分别得到螺栓联接结合面的法向载荷与切向载荷,进而建立了螺栓联接结合面法向刚度与切向刚度模型,并分析了各参数对螺栓联接结合面刚度模型的影响关系。开展了有限元分析与实验研究,应用所建立的法向刚度与切向刚度模型,将考虑结合面影响的螺栓联接体有限元分析结果分别与忽略结合面影响的螺栓联接体有限元分析结果以及实验结果对比。研究结果显示,增大预紧力、工作载荷、分形维数、材料特性参数,或是减小分形尺度参数,可增大螺栓联接结合面的刚度;应用所建立结合面刚度模型的螺栓联接体有限元分析结果与实验结果误差在8%以内,远小于忽略结合面影响的有限元分析误差。

个性化髋关节假体设计及其生物力学性能研究

通用型髋关节假体和个人股骨匹配度不足,易导致应力遮挡率过大。为制备与个人股骨相匹配的髋关节假体,基于人体下肢电子计算机断层扫描(computed tomography,CT)数据,通过逆向工程技术建立股骨实体模型,利用提取的关键特征参数逆向建模,建立个性化髋关节假体模型,采用步态试验确定股骨受力情况,进行有限元分析和电测实验研究其生物力学性能。结果显示,在站立中期的步态载荷下个性化髋关节假体的应力遮挡率在7.64%~38.71%之间,通用型髋关节假体应力遮挡率在16.66%~49.32%之间。个性化髋关节假体可以减小应力遮挡率,可为髋关节假体研究人员提供参考。

装配式槽钢-混凝土组合梁受弯性能研究

为研究采用螺栓连接的装配式槽钢-混凝土组合梁(PSCCB)的受弯性能,制作了7个不同宽跨比、梁高和剪切连接间距的PSCCB试件,对其进行四点弯曲测试。基于ABAQUS软件建立PSCCB有限元模型,通过试验结果验证模型的可靠性,并分析螺栓间距、螺栓预紧力、抗剪连接件间距、剪跨比、宽跨比、槽钢强度和混凝土强度对PSCCB受弯性能的影响。试验结果表明:高强度螺栓能确保PSCCB具有较高的整体性和良好的强度和延性;随着宽跨比增大,PSCCB抗弯承载力和延性分别提高8%~19%和11%~21%;穿孔钢板剪力连接件在槽钢和混凝土板之间提供高效的组合作用,部分抗剪连接与完全抗剪连接PSCCB的延性、强度、刚度差异少于10%;与梁高320 mm的PSCCB相比,梁高400 mm的PSCCB的抗弯承载力提高96%,但延性降低10%。分析结果说明:有限元分析结果与试验结果较吻合,所建立的模型能准确反映PSCCB的受弯性能;随着螺栓间距和预紧力的增大,PSCCB受弯承载力和初始刚度基本保持不变;适当增加抗剪连接程度和宽跨比能有效提升PSCCB的受弯承载力和初始刚度;增加槽钢强度能显著提高PSCCB的受弯承载力,而混凝土强度变化对其受弯承载力影响较小。根据试验和有限元参数分析,提出PSCCB受弯性能设计方法,受弯承载力和跨中挠度计算值与试验及有限元分析结果吻合良好,可为PSCCB的工程设计提供参考。

纳米TiO_(2)改性纤维素纸板在油流环境下的带电特性研究

经纳米TiO_(2)改性纤维素纸板可以增强其击穿场强与抗老化性能,是当前电气绝缘领域研究的热点。纸板中添加纳米粒子对于变压器油流带电影响仍不明确;因此,为了揭示纳米粒子对油流带电影响与抑制机理,需测量与分析纳米改性纸板中的油流带电特性。文中以TiO2改性纸板与未改性矿物油为研究对象,通过旋转圆盘系统测量其摩擦产生的静电电流。根据控制变量法研究了温度、纳米粒子质量分数和流速等因素对带电程度的影响,分析了纳米粒子对于油流带电影响机理;采用有限元分析方法分析了变压器油道仿真模型,对比了不同质量分数下的纳米TiO_(2)改性纸板制作的油道模型内部电场分布情况。研究结果表明:与未改性纸板相比,纤维素基体中添加质量分数为1%的纳米TiO_(2)粒子可以抑制油流带电程度,使得油道内部积累电荷后的电场分布畸变程度最小。研究结果可以为抑制变压器中的油流带电提供新方法。

基于有限元软件海水置换泵连接管线机械激励振动分析

受动设备产生机械激励的影响,管道往往会出现振动问题,对海上平台的安全生产造成严重威胁。通过分析产生机械激励的原因,探究了管道产生机械激励振动的机理,可将其分为动设备自身问题和管道系统设计缺陷两种类型。对当前机械激励振动有限元分析方法进行了梳理,总结出完整且可靠的机械激励振动分析流程,并以某海上平台海水置换泵连接管线为例,采用有限元分析软件进行管线三维建模、模态分析和谐波响应分析。通过对计算结果进行分析评估,得到了共振频率下管道的振动结果,并针对振动较大位置采取了减振措施。经有限元软件再次分析检验,验证了处理机械激励振动问题时对振幅较大管段添加约束形式支架方案的切实可行性,为实际管道振动中处理机械激励振动的相关问题提供了参考。

重型锻造液压机理论设计与实际变形对比研究分析

重型锻造液压机的精度是保证制件精度的一个重要指标,而设备机架的刚度指标是横梁设备整个精度保持性的一个标准。本文利用ANSYS有限元分析软件对重型锻造液压机的框架变形情况进行了分析,并与现场实际测量的变形值进行了对比研究。通过对比,得出数据差值,为后续同类型设备的刚度设计提供相应的设计依据。

非对称荷载下内撑式基坑支护结构参数分析及设计优化探讨

非对称荷载作用下,内撑式基坑会向荷载小侧整体偏移,这将不利于基坑的稳定,因此有必要对支护结构进行设计优化。本研究以某偏压综合管廊基坑为例,通过有限元软件PLAXIS 2D对该基坑进行了仿真模拟,模拟结果与实测数据吻合良好,验证了模型的有效性。进一步对该基坑进行参数分析,研究了支护结构长度、等效厚度和弹性模量对支护结构变形和基坑安全性的影响。研究结果表明,在两侧支护结构均按偏压侧进行设计的基础上,增大某侧支护结构长度,会使该侧支护结构水平位移最大值增大,分别增大两侧支护结构等效厚度、弹性模量,均可以减小该侧支护结构水平位移最大值和非偏压侧支护结构顶部逆向位移。基于参数分析,提出一种针对非对称荷载基坑的简单有效、经济可行的优化思路,并通过数值模拟对优化效果进行了分析,证明了该优化思路的可行性。

9.6m厢式货车铝合金厢体的轻量化设计和刚度研究

交通领域作为最大排放源之一,汽车轻量化成为实现双碳目标的有效途径。将9.6m中型厢式货车厢体设计变更为铝合金材料,建立该车厢的三维模型及有限元模型,针对厢体不同构件特点划分不同网格,并在国家及行业标准的测试工况下进行结构分析,确保厢体所受应力及残余变形满足标准。仿真结果表明:该车厢既满足原有安全可靠的要求,也具有更小体积质量、更耐腐蚀、更大冲压塑性等特点。

考虑结合面特性影响的机床整机有限元静力学分析模型

针对机床数字化设计中典型结合面建模精度误差较大的问题,提出了一种采用虚拟材料等效结合面静力学特性的方法,建立了考虑结合面特性影响的机床整机有限元静力学分析模型,并完成了相应的静刚度测试实验。首先,综合考虑了弹塑性变形机制和摩擦力的影响,提出了一种新的结合面法向和切向刚度的分析模型;其次,根据不同类型结合面的特点,采用虚拟材料模拟结合面的刚度特性,建立了刚度特性与虚拟材料弹性模量和泊松比的关系,并将其应用于精密数控机床整机的静刚度分析;最后,开展了整机工艺系统的静刚度测试实验,得到了主轴末端X、Y、Z三个方向的刚度分别为26.60 N/μm、41.87 N/μm和40.17 N/μm,并将其与仿真数据进行了对比。研究结果表明:不考虑结合面影响的模型相对误差将近17%,而考虑结合面影响的模型相对误差在5%以内,验证了考虑结合面特性影响的机床整机有限元静力学分析模型的有效性;采用虚拟材料等效结合面静力学特性的方法可作为机床数字化设计的一种可行的方法。

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。

基于渐近均匀化方法的准周期梁结构等效刚度数值实现方法研究

相比周期梁结构,准周期梁结构沿轴向梯度变化,具有更大的设计自由度,能够获得更好的结构性能。由于其非均质性,一般将其均匀化为具有等效性质的均质梁结构,但现有工作很少涉及准周期梁结构等效性质的计算。本文针对由周期梁结构映射而成的准周期梁结构,通过引入雅可比矩阵,基于渐近均匀化方法推导的单胞方程及其等效性质计算列式,并建立了其单胞方程及等效刚度的有限元求解列式。该方法可以处理沿轴向变形的任意微单胞构型,数值算例验证了其正确性和有效性。