Design and Structural Analysis of Flexible Wearable Chair Using Finite Element Method

The flexible wearable chair is like a light weight mobile exoskeleton that allows people to sit any-where in any working position. The traditional chair is difficult to move to different working locations due to its large size, heavy weight (~5 - 7 kg) and rigid structure and thus, they are inappropriate for workplaces where enough space is not available. Flexible wearable chair has a gross weight of 3 kg as it utilizes light-weight aluminium alloy members. Unlike the traditional chair, it consists of kinematic pairs which enable taking halts between continuous movements at any working position and thus, it is capable of reducing the risk of the physical musculoskeletal disorder substantially among workers. The objective of this paper is to focus on the mechanical design and finite element analysis (FEA) of the mechanism using ANSYS® software. In the present work, all the parts of the mechanism are designed under static load condition. The results of the analysis indicate that flexible wearable chair satisfies equilibrium and stability criterion and is capable of reducing fatigue during working in an assembly line/factory.

Enhanced Multi-Layer Fatigue-Analysis Approach for Unbonded Flexible Risers

This paper proposes an enhanced approach for evaluating the fatigue life of each metallic layer of unbonded flexible risers. Owing to the complex structure of unbonded flexible risers and the nonlinearity of the system, particularly in the critical touchdown zone, the traditional method is insufficient for accurately evaluating the fatigue life of these risers. The main challenge lies in the transposition from global to local analyses, which is a key stage for the fatigue analysis of flexible pipes owing to their complex structure. The new enhanced approach derives a multi-layer stress-decomposition method to meet this challenge. In this study, a numerical model validated experimentally is used to demonstrate the accuracy of the stress-decomposition method. And a numerical case is studied to validate the proposed approach. The results demonstrate that the multi-layer stress-decomposition method is accurate, and the fatigue lives of the metallic layers predicted by the enhanced multi-layer analysis approach are rational. The proposed fatigue-analysis approach provides a practical and reasonable method for predicting fatigue life in the design of unbonded flexible risers.

Dynamic analysis of spatial parallel manipulator with rigid and flexible couplings

The dynamics of spatial parallel manipulator with rigid and flexible links is explored. Firstly, a spatial beam element model for finite element analysis is established. Then, the differential equation of motion of beam element is derived based on finite element method. The kinematic constraints of parallel manipulator with rigid and flexible links are obtained by analyzing the motive parameters of moving platform and the relationships of movements of kinematic chains, and the overall kinetic equation of the parallel mechanism with rigid and flexible links is derived by assembling the differential equations of motion of components. On the basis of abovementioned analyses, the dynamic mechanical analysis of the spatial parallel manipulator with rigid and flexible links is conducted. After obtaining the method for force analysis and expressions for the calculation of dynamic stress of flexible components, the dynamic analysis and simulation of spatial parallel manipulator with rigid and flexible links is performed. The result shows that because of the elastic deformation of flexible components in the parallel mechanism with rigid and flexible links, the force on each component in the mechanism fluctuates sharply, and the change of normal stress at the root of drive components is also remarkable. This study provides references for further studies on the dynamic characteristics of parallel mechanisms with rigid and flexible links and for the optimization of the design of the mechanism.

Analysis of the Rigidity of a Straight Beam Flexible Hinge with Different Geometrical Parameters

Flexible hinges are widely used in micro motion robotics. Its rigidity directly influences an organization＇s terminal localization. Its actual structure geometry size cannot satisfy the theoretical analysis completely in a theoretical supposition condition. In this paper, we analyzed the rotation rigidity of a corner-filleted straight beam flexible hinge in different parameters using finite element software ANSYS. The errors are discovered and compared with theoretical results. Through the graph of the flexible hinge parameters and its performance, an analysis of changes of parameters on the performance of a corner-filleted flexible hinge was carried out. The key manufacture parameters that affect the performance of a corner-filleted flexure hinge the most and rules of design are given, which can provide directions of design precision for the flexure hinge.

Mechanical analysis of flexible integrated energy storage devices under bending by the finite element method

Although a great deal of studies focus on the design of flexible energy storage devices(ESDs),their mechanical behaviors under bending states are still not sufficiently investigated,and the understanding of the corresponding structural conversion therefore still lags behind.Here,we systematically and thoroughly investigated the mechanical behaviors of flexible all-in-one ESDs under bending deformation by the finite element method.The influences of thicknesses,Young’s moduli and Poisson’s ratios of electrodes and electrolyte were taken into account.Visualized and quantified results including displacement,strain energy,von Mises stress,and tensile,compressive,and interfacial shear stress are demonstrated and analyzed.Based on these results,significant conclusions are drawn for the design of flexible integrated ESDs with robust mechanical properties.This work will provide guidance for the design of ESDs with high flexibility.

Influence of structure and material on the vibration modal characteristics of novel combined flexible road wheel

Aiming at the independent development of tracked vehicles,it is urgent to improve its mobility,passability and ride comfort,a new type of flexible road wheel with a“wheel-hinge-hub”combined structure is proposed in this study.The vibration model characteristics of the flexible road wheel were studied by the combination of numerical simulation and experiments.The superelasticity of rubber is obtained through uniaxial tensile experiment of the material and a detail three-dimensional nolinear finite element model of the flexible road wheel is established through finite element software ABAQUS.The free vibration equation of the flexible road wheel is solved by Lanczos vector direct superposition method,and its predicted modes and natural frequencies are compared with experimental results,which verifies the accuracy and reliability of the established finite element model.On this basis,the effects of various key structural or material factors on the natural frequencies of the flexible road wheel are studied using orthogonal experimental design method.Besides,the vibration modal characteristics of the flexible road wheel are also compared with those of the rigid road wheel.The research results provide a theoretical basis for the vibration and noise reduction of flexible road wheel.

Simulation and Analysis of Spatial Weft Insertion Mechanism Considering Flexibility and Clearance

A 3D model of the spatial four-bar weft insertion mechanism was built with unigraphics NX(UG) according to the actual requirement,and dynamics simulation was carried out by importing the model into ADAMS.Without considering the clearance,the motion characteristic curve of the sword belt was generated through ADAMS combined with MATLAB.In this paper the hinge between the rod and the sector gear was selected as an example with different values of clearance,outputting the motion characteristic curve of the sword belt.Finite element analysis(FEA)was conducted,the flexible body was generated by importing the forked frame into ANSYS,and flexible dynamics simulation was carried out by importing the flexible body into ADAMS to replace the rigid rod.A comprehensive comparison of the output characteristics of the sword belt was conducted in the consideration of the clearance or flexible.Analysis of the force on the left hinge of the rod was carried out with the ADAMS post processing module.With the same clearance,considering the flexibility,amplitude of fluctuation of the force on the hinge increased obviously.

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.

Parametric analysis of wheel wear in high-speed vehicles

In order to reduce the wheel profile wear of highspeed trains and extend the service life of wheels, a dynamic model for a high-speed vehicle was set up, in which the wheelset was regarded as flexible body, and the actual measured track irregularities and line conditions were considered. The wear depth of the wheel profile was calculated by the well-known Archard wear law. Through this model, the influence of the wheel profile, primary suspension stiffness, track gage, and rail cant on the wear of wheel profile were studied through multiple iterafive calculations. Numerical simulation results show that the type XP55 wheel profile has the smallest cumulative wear depth, and the type LM wheel profile has the largest wear depth. To reduce the wear of the wheel profile, the equivalent conicity of the wheel should not be too large or too small. On the other hand, a small primary vertical stiffness, a track gage around 1,435-1,438 mm, and a rail cant around 1：35-1：40 are beneficial for dynamic performance improvement and wheel wear alleviation.

Reinforcing a Dangerous Rock Mass Using the Flexible Network Method

Because the main failure type of a dangerous rock mass is collapse, the treatment of such a mass should focus on controlling collapse failure. When treating dangerous rock masses, disturbing the mass （e. g. by blasting） needs to be avoided, as this new damage could cause collapse. So the self-bearing capacity of the mountain mass must be used to treat the dangerous rock mass. This article is based on a practical example of the control of a dangerous rock mass at Banyan Mountain, Huangshi, Hubei Province. On the basis of an analysis of damage mechanism and the stability of the dangerous rock mass, a flexible network reinforcement method was designed to prevent the collapse of the rock mass. The deformations of section Ⅱ w of the dangerous rock mass before and after the flexible network reinforcement were calculated using the two-dimensional finite element method. The results show that the maximum deformation reduced by 55 % after the application of the flexible network reinforcement, from 45.99 to 20.75 ram, which demonstrates that the flexible network method is effective, and can provide some scientific basis for the treatment of dangerous rock masses.

Coupled Element Modeling Scheme for the Global Dynamic Analysis of Unbonded Flexible Risers

A coupled element modeling method is proposed for global dynamic analyses of unbonded flexible risers.Owing to the multi-layer structure of unbonded flexible risers, the global-dynamic-analysis method applied to the steel rigid risers is insufficient for flexible risers. The main challenges lie in the enormous difference between the anti-tension and anti-binding capacity of unbonded flexible risers which results in serious ill-conditional calculation in global dynamic analysis. In order to solve this problem, the coupled element modeling approach was proposed in this study. A time domain fatigue analysis was applied to illustrate the necessity of the proposed approach.A dynamic benchmark case is used to demonstrate the accuracy of the coupled element method respectively.Subsequently the validated coupling element method is employed to conduct the global dynamic analyses for a free hanging flexible riser. The results demonstrate that the proposed approach can give the accurate global dynamic response under the guidance of the fatigue failure mode for unbonded flexible riser. The parametric influence analyses also provide a practical and effective way for predicting the global dynamic response.

Comparison Between Different Finite Element Analyses of Unbonded Flexible Pipe via Different Modeling Patterns

Three kinds of models based on the same flexible pipe with 8 layers have been separately created to investigate the effects of different modeling approaches on numerical simulation results of finite element(FE)models for unbonded flexible pipes.Then the mechanical property of the unbonded flexible pipe under tension,torsion and bending load has been analyzed and compared via ABAQUS software on the basis of three created models.The research shows that different modeling methods of flexible pipes make a great difference in the results.Especially,modeling simplifications of the carcass and pressure armor have a great impact on the accuracy of the results.Model 3,in which the carcass is simulated by spiral isot ropic shell and other layers are Simula ted by solid element,possesses good adaptability,which has been proved by comparing the experiment data and other models.This paper can offer a reference for the FE modeling methods,selection and mechanical property analysis of unbonded flexible pipe.

柔性连接填充墙RC框架结构非线性有限元分析

为了研究橡胶作为新型柔性连接材料对填充墙钢筋混凝土(RC)框架结构抗震性能的影响,在7榀1/2缩尺填充墙RC框架结构低周反复加载试验的基础上,采用DIANA有限元软件分析了填充墙与框架之间的连接方式、砌块材料、柔性连接材料以及砂浆强度对填充墙RC框架结构抗震性能的影响。结果表明:与刚性连接相比,以橡胶作为新型柔性连接材料,能减缓结构的强度和刚度退化,极大降低结构的破坏程度,显著提高结构的抗震性能;高弹性橡胶和高阻尼橡胶作为柔性连接材料均表现出优异的抗震性能,而聚苯板(EPS)作为柔性连接材料的抗震性能要比橡胶差;刚性连接方式下不同砌块材料对结构抗震性能影响很大,当使用强度较高的砌块材料时建议采用柔性连接方式以减弱墙-框相互作用;合理降低砂浆的强度等级,可以改变填充墙的破坏模式,对抗震有利。

基于能量有限元的薄板结构多目标拓扑优化

拓扑优化设计是结构设计中降低成本和实现轻量化的关键环节。能量有限元法(energy finite element analysis,EFEA)是高频动响应分析的有力工具。在高频动力学拓扑优化中,用能量有限元法代替有限元法(finite element analysis,FEA)进行动响应计算可以获得较高的计算效率和计算精度。为了使能量有限元求解和拓扑优化过程能够有效衔接,促进基于能量有限元法的高频动力学拓扑优化的工程应用,建立了基于能量有限元法的多目标拓扑优化模型。基于能量有限元法,以最小能量柔度和感兴趣单元最小能量密度作为高频动力学拓扑优化的目标函数,采用“线性加权法”,建立多目标情况下的拓扑数学模型;再对模型进行离散化,进而对其进行灵敏度计算,通过灵敏度过滤和最优化准则得到多目标拓扑优化构型。最后通过算例,分析不同激励频率对拓扑构型的影响,揭示不同目标权重系数对拓扑构型的交叉影响规律。结果表明,当权重系数相同,激励频率不同时,中高频的减重百分比较低频大;当频率相同,权重系数比为1∶1时,减重百分比最大。基于能量有限元的高频动力学拓扑优化模型有利于发展飞行器等易诱发高频振动的结构的优化设计理论,优化设计结果对实际的结构设计具有一定的参考价值。

多连杆刚柔机械手设计与手指减振分析

针对陶瓷易碎零件分拣过程中难以稳定抓取的问题,设计了一种能够有效稳定抓取的新型多连杆刚柔机械手。首先,以机械传动为基础,将刚性关节与柔性材料相结合,设计机械手的传动方式与柔顺关节的最优结构,并在三维软件上构建刚柔机械手的整体结构;其次,通过对机械手手指结构进行简化,采用拉格朗日理论和有限元离散方法,构建出具有尖端质量的手指多连杆刚柔耦合动力学模型;最后,求解出机械手手指在运动过程中的动力学方程。在此基础上,通过设计减振方案,对机械手手指结构做出优化和改进。仿真实验结果表明:在外激力为2 N的条件下,改进结构后的刚柔机械手手指其振动的幅度降低8 mm,且恢复稳定的时间缩短了4 s以上,在一定程度上提高了分拣和抓取过程中的抗冲击力,保证了对陶瓷易碎零件抓取过程的稳定性。

振动辅助抛光装置设计与性能研究

为了解决传统抛光技术及机床在过程中存在的加工效率低、表面质量差、周期性抛光纹理等问题,基于柔性机构理论,采用中心对称的方式,设计一个二维振动辅助装置;基于柔度矩阵法,建立二维振动辅助装置的理论模型。对二维振动辅助装置进行性能测试及有限元仿真。结果表明:此装置的最大行程约为46μm,放大比约为1.21,固有频率约为933 Hz,耦合误差率约为2.5%,最大应力不超过83 MPa,输入刚度为23.52 N/μm,输出刚度为12.29 N/μm。并通过振动辅助加工实验及有限元仿真,证明了振动辅助抛光装置具有改善实际抛光效果的能力。

基于有限元柔性体理论的起落架落震仿真分析

以某飞机起落架为研究对象,研究落震动力学问题。根据前起落架的结构特性,利用多体动力学建模技术,建立前起落架多柔性体动力学(MFBD)模型,并进行落震仿真分析及非线性接触研究。采用落震试验数据对模型进行校验,仿真结果与试验数据较为吻合。通过分析缓冲器零件的变形,考虑接触因素的多柔体动力学模型能更真实反应实际情况,以最大降落速度工况进行落震仿真,同时对起落架关键零件进行强度校核,以及缓冲器内部零件进行非线性接触计算,求得不同材质的下凸轮及底托受到的垂向力与摩擦力,获得在物理试验中难以测量的数据,分析结果对起落架设计具有重要意义。

精密导向膜片设计与优化

针对微振动模拟器中精密导向机构行程小、精度高的要求,提出了一种具有精密导向作用的柔性膜片。首先,基于柔度矩阵法对柔性膜片的轴向与径向柔度进行建模;其次,基于柔性膜片的结构参数对其轴向和径向柔度进行参数化分析;接着,以高轴向柔度、高轴向/径向柔度比和低应力为目标,建立了优化设计模型,并对其进行优化,优化结果表明轴向柔度优化率为233%,轴向/径向柔度比优化率为172%,最大应力优化率为32%。优化后柔性膜片的各目标性能都得到较大提升;最后,通过有限元分析与实验进行验证。有限元分析与实验结果相对于理论分析的相对误差分别为6.7%和7.8%。理论分析与优化方法为柔性膜片提供了一个简单有效的设计思路。

精密柔性角度调节机构的几何非线性建模分析

为同步辐射关键光学设备,文中优化设计了一种精密圆盘式柔性角度调节机构,柔性铰链采用直梁圆角形,既可以实现微纳弧度级的高精度,又能有较大的转角范围。对该角度调节机构在较大转角时产生几何非线性的因素进行分析,建立分段式边界约束模型,采用数值分析方法求解。同时,建立了增量型更新拉格朗日法的非线性平衡方程,采用牛顿-拉普森方法对平衡方程进行迭代求解。采用两种方法分析了机构的输出角度与输入载荷的非线性关系,以及考虑非线性时柔性铰链中心的漂移,并通过有限元的非线性与线性分析对比,研究了非线性对机构输出角度和最大应力的影响。结果表明:建立两种模型分析吻合度较好,该角度调节机构呈强非线性,可实现的最大安全调节角度为1.6°,分析证明了为机构设计建立的非线性模型的准确性和有效性。

原生喙锁韧带及柔性重建后有限元仿真和实验测试

背景:对于以喙锁韧带断裂造成的肩锁关节脱位,单束和双束重建为常见修复方式,深化研究对比二者修复的应力分布和骨折风险具有重要意义。目的:研究喙锁韧带的生物力学性能,对比单束和双束重建肩锁关节的固定效果、应力分布和破坏形式。方法:①有限元仿真分析:利用Mimics、Wrap和SolidWorks软件分别建立正常喙锁韧带、单束重建和双束重建肩锁关节模型,利用Ansys软件分析锁骨垂向受载时各模型肩胛骨和锁骨的应力和变形情况;②标本实验:取15个完整的人体肩胛骨-锁骨标本,随机分为5组处理,每组3个:A组切断肩锁韧带,保留完整的喙锁韧带;B组切断肩锁和斜方韧带,保留完整的锥状韧带;C组切断肩锁和锥状韧带,保留完整的斜方韧带;D组切断肩锁和喙锁韧带,采用单束重建修复喙锁韧带;E组切断肩锁和喙锁韧带,采用双束重建修复喙锁韧带。利用力学试验机进行力学实验,分析肩胛骨和锁骨的生物力学状态、应力分布和破坏形式。结果与结论:①有限元仿真分析:正常喙锁韧带附着标本喙突的平均应力最小,其相对于单束和双束重建模型喙突骨折的风险较小;单束和双束重建模型的喙突平均应力相当,二者骨折风险接近;②标本实验:A-E组标本的刚度分别为(26.4±3.5),(19.8±2.8),(21.3±3.2),(57.7±4.1),(46.2±2.8)N/mm,极限载荷分别为(545.5±53.7),(360.1±42.1),(250.9±44.4),(643.5±39.1),(511.9±31.7)N,D、E组标本的整体刚度高于A组(P=0.00006,0.0003),D组极限承载高于A组(P<0.05),E组极限承载和A组无差异(P>0.05);A-C组为韧带断裂,D、E组为喙突骨折;③结果显示:从生物力学角度分析,对于肩锁关节脱位中的喙锁韧带断裂,单束和双束重建均为有效的治疗技术,但均增加了骨折风险,其中双束重建分散了钢板应力、减小了钢板和骨质的接触力,但稍微降低了极限承载力,应根据临床实际情况选用单束或双束重建。