Numerical study on three-dimensional flow field of continuously rotating detonation in a toroidal chamber

Gaseous detonation propagating in a toroidal chamber was numerically studied for hydrogen/oxygen/nitrogen mixtures. The numerical method used is based on the three-dimensional Euler equations with detailed finiterate chemistry. The results show that the calculated streak picture is in qualitative agreement with the picture recorded by a high speed streak camera from published literature. The three-dimensional flow field induced by a continuously rotating detonation was visualized and distinctive features of the rotating detonations were clearly depicted. Owing to the unconfined character of detonation wavelet, a deficit of detonation parameters was observed. Due to the effects of wall geometries, the strength of the outside detonation front is stronger than that of the inside portion. The detonation thus propagates with a constant circular velocity. Numerical simulation also shows three-dimensional rotating detonation structures, which display specific feature of the detonation- shock combined wave. Discrete burning gas pockets are formed due to instability of the discontinuity. It is believed that the present study could give an insight into the interest- ing properties of the continuously rotating detonation, and is thus beneficial to the design of continuous detonation propulsion systems.

A combined numerical model of three-dimensional tidal motion and sediment transport in tidal current and its application

A calculation scheme, which combines a horizontal upwind finite element method with vertical implicit differences, is used to establish a three-dimensional mathematical model of tidal motion and sediment transport in tidal current. Compared with those of the relative theoretical formula, the results are satisfactory. The model mentioned above has been applied to the water area of the Lianzhou Bay, Guangxi Province. On the basis of the analysis and comparison with the field data, it shows clearly that the model calculation results are reasonable.

Recursive super-convergence computation for multi-dimensional problems via one-dimensional element energy pro jection technique

This paper presents a strategy for computation of super-convergent solutions of multi-dimensional problems in the finite element method （FEM） by recursive application of the one-dimensional （1D） element energy projection （EEP） technique. The main idea is to conceptually treat multi-dimensional problems as generalized 1D problems, based on which the concepts of generalized 1D FEM and its consequent EEP formulae have been developed in a unified manner. Equipped with these concepts, multi-dimensional problems can be recursively discretized in one dimension at each step, until a fully discretized standard finite element （FE） model is reached. This conceptual dimension-by- dimension （D-by-D） discretization procedure is entirely equivalent to a full FE discretization. As a reverse D-by-D recovery procedure, by using the unified EEP formulae together with proper extraction of the generalized nodal solutions, super-convergent displacements and first derivatives for two-dimensional （2D） and three-dimensional （3D） problems can be obtained over the domain. Numerical examples of 3D Poisson＇s equation and elasticity problem are given to verify the feasibility and effectiveness of the proposed strategy.

下颌角骨折坚强内固定后应力遮挡效应的三维有限元分析

目的:分析下颌角骨折坚强内固定时的应力分布,探讨可能发生的应力遮挡效应,为临床应用提供参考。方法:运用三维有限元软件对下颌角骨折采用双小型钛接骨板与小型板+重建板2种内固定方法,分析在骨折愈合的早、中、后3个时期的应力分布,计算各种情况下的应力遮挡率。结果:下颌角骨折采用双小型板固定时,骨折愈合早、中、后3个时期的应力遮挡率分别为88.46%、9.24%、8.99%;采用小型板+重建板固定时,3个时期的应力遮挡率分别为89.67%、11.81%、11.11%。结论:下颌角骨折坚强内固定后应力遮挡效应是始终存在的,随着骨折的愈合,下颌角骨折各种内固定系统的应力遮挡率逐渐减小。且同一骨折愈合时期,小型板+重建板的应力遮挡率大于双小型板,即接骨板的强度越高,应力遮挡作用越明显。

基于等效平面的斜角切削仿真分析

单刃螺旋立铣可视为斜角切削,基于等效平面法分析切削过程更符合斜角切削特性。对斜角切削的二维正交建模方式进行优化,提出了基于等效平面的二维建模方法,在等效平面上将三维斜角切削转化为二维正交切削:推导出等效平面内刀具等效参数,建立基于等效平面的二维正交模型。将其仿真结果与基于主剖面的二维模型的仿真结果进行对比,并结合以往文献中基于主剖面的二维模型的仿真值与试验值进行对比分析,通过研究表明,基于等效平面的二维建模方法可适当提高斜角切削的二维仿真结果的精度,因此,等效平面法可为斜角切削二维建模的优化提供参考。

三维编织复合材料抗侵彻性能——准静态侵彻实验与弹道侵彻有限元计算的对比

用钢制圆柱锥体对四步法三维编织芳纶/环氧复合材料在MTS材料试验机上作准静态侵彻测试,得到准静态侵彻载荷一位移曲线,并由此计算得到侵彻功一位移曲线。在对复合材料侵彻破坏的细观观测中发现,复合材料主要以拉伸断裂方式为主并在受侵彻面伴有压缩和剪切破坏。由于弹道侵彻破坏很难测量侵彻过程中的侵彻功随侵彻位移的变化,这里用有限元程序LS-DYNA960并结合由准静态得到的破坏判据、复合材料力学性质常数模拟动态侵彻,对比准静态侵彻功一位移曲线和弹道侵彻模拟曲线,两者有较好的一致性,表明用该类复合材料的准静态侵彻性能模拟弹道侵彻性能有一定的可行性。

小型挖掘机偏转机构的有限元分析

以GC18型挖掘机偏转机构为研究对象,用Pro/Engineer建立了挖掘机的偏转机构的三维模型,并进行了模拟装配和有限元分析.针对偏转机构2个典型的工况位置的应力和变形,采用有限元法进行了计算分析,计算出2个工况下应力分布和变形,为有限元法在小型挖掘机设计上的应用提供了参考.

脊柱腰段正常及骨质疏松三维有限元数字模型的建立

背景:建立逼真的有限元模型是对脊柱进行有限元力学分析的重要基础,关于骨质疏松有限元模型的报道尚少。目的:建立脊柱腰段各主要结构及骨质疏松腰椎的有限元数字模型,为正常脊柱腰段及骨质疏松患者腰椎的有限元力学分析打下基础。方法:对 1 名健康男性志愿者行脊柱腰段的螺旋 CT 扫描,将所得图像先在 Mimics 中进行分隔和重建,在 Geomagic 中进行优化,在 Ansys 中赋材质及网格划分,建立三维有限元数字模型。结果与结论:建立了包括全部腰椎、椎间盘及主要韧带的正常腰椎及骨质疏松腰椎三维有限元数字模型。该模型外形逼真,几何相似性好,可以随意旋转,方便从多角度观察、采集三维信息,各主要结构材料属性接近实际,适合进行生物力学研究。提示利用 CT 数据及 mimics、geomagic、Ansys 软件可以建立脊柱腰段正常及骨质疏松有限元数字模型。

Herschel-Quincke管用作液压脉动衰减器的滤波特性研究

Herschel-Quincke管(HQ管)广泛用于气体消声系统,且该结构声学特性研究也已成熟。鉴于此,将这种结构引入液压系统,采用一维解析法构建其数学模型,再利用三维有限元法进行验证。两种理论方法传递损失计算结果在平面波域内吻合较好,证明了截止频带内采用一维解析法研究液压脉动衰减器声学特性是可行的。利用一维解析法对HQ管用作液压脉动衰减器的滤波特性进行了研究,结果表明,只要分支管道长度以及横截面积选取合理,HQ管是可以用于液压系统压力脉动衰减的。

包含推杆式矫治器的牙列-颌骨-颞下颌关节的三维有限元模型的建立

目的建立包含推杆式矫治器(Forsus)、牙列、颌骨、颞下颌关节在内的三维有限元模型。方法采用64层螺旋CT,对已经排齐整平的安氏2类1分类患者行常规头部平扫,利用原始DICOM数据,经MIMICS8.0、ABAQUS6.5软件建模。结果建立了包含Forsus在内的完整颅面复合体三维有限元模型,由785 519个单元和238 194个节点组成,探索出一条适用于临床需要的颅面复合体三维有限元建模方法。结论所建三维有限元模型几何相似性和力学相似性较好,使用MIMICS和ABAQUS建模是一种快速有效的方法。

高速永磁涡轮发电机二维饱和涡流场的分析与计算

将弹载电源WF—11涡轮发电机考虑为一个二维饱和涡流场的计算问题,用有限元法对该电机的空载和负载电压进行了计算,并对该电机中所使用的永磁材料进行了适当讨论,提出了材料更新的设想,分析了用NdFeB替代AlNiCo5-3的利弊,从而为该电机性能得以进一步改善提供了一些可行性分析。并在计算的基础上将原电机所用的永磁材料缩短了5mm,在满足性能的要求下,达到了节材的目的,获得了较大的经济效益。

南水北调东线穿黄河工程滩地埋管三维有限元计算分析

滩地埋管是南水北调穿黄河工程主要建筑物,位于黄河南岸子路堤至解山之间的黄河滩地下,全长3 943 m,该埋管为有压埋管,水文地质条件复杂,采用内圆外城门洞型,结构尺寸较大,直径达到7.5 m,结构安全要求高,设计采用三维有限元计算方法完成大型复杂埋管的结构分析。

Numerical simulation of soft palate movement and airflow in human upper airway by fluid-structure interaction method

In this paper, the authors present airflow field characteristics of human upper airway and soft palate movement attitude during breathing. On the basis of the data taken from the spiral computerized tomography images of a healthy person and a patient with Obstructive Sleep Apnea-Hypopnea Syndrome （OSAHS）, three-dimensional models of upper airway cavity and soft palate are reconstructed by the method of surface rendering. Numerical simulation is performed for airflow in the upper airway and displacement of soft palate by fluid-structure interaction analysis. The reconstructed threedimensional models precisely preserve the original configuration of upper airways and soft palate. The results of the pressure and velocity distributions in the airflow field are quantitatively determined, and the displacement of soft palate is presented. Pressure gradients of airway are lower for the healthy person and the airflow distribution is quite uniform in the case of free breathing. However, the OSAHS patient remarkably escalates both the pressure and velocity in the upper airway, and causes higher displacement of the soft palate. The present study is useful in revealing pathogenesis and quantitative mutual relationship between configuration and function of the upper airway as well as in diagnosingdiseases related to anatomical structure and function of the upper airway.

Exact 3D Thermoelastic Solutions for a Penny-Shaped Crack in an Infinite Magnetoelectric Medium

Exact solutions of three-dimensional(3D)crack problems are much less in number than those of two-dimensional ones,especially for multi-field coupling media exhibiting a certain kind of material anisotropy.An exact3Dthermoelastic solution has been reported for a uniformly heated penny-shaped crack in an infinite magnetoelectric space,with impermeable electromagnetic conditions assumed on the crack faces.Exact 3Dsolutions for the penny-shaped crack subjected to uniform or point temperature load are further presented here when the crack faces are electrically and magnetically permeable.The solutions,obtained by the potential theory method,are exact in the sense that all field variables are explicitly derived and expressed in terms of elementary functions.Along with the previously reported solution,the limits or bounds of the stress intensity factor at the crack-tip for a practical crack can be identified.

三维中空复合材料天线罩的有限元结构分析

某类型天线罩外形尺寸较大,减重要求高,三维中空复合材料可满足该类型天线罩透波和结构高强的要求。针对上述使用要求和实际工况,选择三维中空织物复合材料为主体结构,玻璃纤维增强环氧树脂复合材料为补强面层,制备三维中空结构天线罩,采用有限元分析软件建立三维中空结构天线罩的有限元模型,对该类型天线罩在使用工况下的刚度、强度和稳定性进行分析,其计算结果满足刚度、强度和稳定性的要求,并通过压力试验验证中空夹层天线罩的变形量与有限元分析结果保持一致,从而指导该天线罩的铺层设计、优化及材料的选用。

环境荷载下智能变电站预制舱有限元仿真研究

为了验证环境荷载下高性能纤维双层立体组合预制舱的结构强度,以四川省乐山市某110kV智能变电站新建工程高性能纤维双层立体组合预制舱为抗环境荷载性能评估对象,采用有限元动力时程分析方法,并应用SolidWorks、Hypermesh、Ansys等非线性有限元仿真软件,分析并校核了该立体组合预制舱结构在雪荷载及屋面活荷载、10级强风、8级抗震设防烈度荷载作用下是否发生破坏,舱体结构强度是否满足环境荷载要求,是否满足相应服役地区的使用要求。提出了强化双层立体组合预制舱结构强度的建议措施,对确保智能变电站预制舱设备安全稳定运行提供了有价值的借鉴和参考。研究方法可用于复杂框架式结构的强度与刚度计算和评估。

某抽蓄电站厂房蜗壳结构保压值选定分析

结合某抽水蓄能电站厂房蜗壳外围混凝土结构配筋计算过程,运用三维有限元计算软件对该蜗壳结构保压值进行选定分析。根据计算结果并依照规范得出各种保压值方案下蜗壳外围混凝土配筋结果,通过各种因素的对比分析选定相对合理的蜗壳保压值。同时,通过该工程蜗壳保压值的选定分析过程,总结经验和规律,供参考。

Accuracy of Low-level Surface in Hierarchical Construction of Potential Energy Surface

The effects of low-level PES on the overall accuracy of the final surface constructed by using hierarchical construction were investigated with the constructions of a number of global surfaces for the H3 system at UHF （UMP2, DFT-B3LYP, UCCSD（T））/vtz, and UCCSD（T）/avqz levels of theory. The total reaction probabilities for the H＋H2 reaction calculated on these surfaces revealed that the accuracy of UCCSD（T）/avqz surface is very close to the well-known BKMP2 surface, while the UCCSD（T）/vtz PES has a slightly higher barrier. In contrast, the low-level theories （UHF, UMP2, DFT-B3LYP） with vtz basis set can only provide a qualitative description of this simplest reaction despite the fact that they are widely used to study reactions in complex systems. On the other hand, although these theories are not accurate on describing the reaction, they can be used to provide the low- level PESs for hierarchical construction of the UCCSD（T）/avqz PES with the number of UCCSD（T）/avqz energies substantially reduced.

高速铁路低矮路堤灰土桩复合地基的动力特性分析

利用有限元软件MIDAS/GTS,分别建立了灰土桩复合地基和未经处理的黄土地基上铁路路基的三维有限元模型,用轨道不平顺法模拟列车荷载,分析计算了在不同速度列车荷载作用下不同路堤高度下地基土中动应力的分布,得出了桩土应力比的变化规律和地基瞬时变形规律。

无避让二层车库开发设计

随着人们生活水平的提高,轿车数量快速增长,城市商业区和旅游区存车场拥挤严重,新开发无避让二层车库应运而生。在车库机构和结构设计方面,充分利用三维建模和有限元分析软件,综合考虑现有无避让立体车库技术的优势和不足,对新开发的二层车库结构进行分析设计,保证结构的安全实用性和经济合理性,设计了一款便于使用的二层车库。