瞬态载荷下L4/L5椎间盘内流固耦合效应

中医正脊治疗通过对腰椎施加瞬态拉伸和旋转来治疗腰椎间盘退变, 本文采用考虑流固耦合效应的数值模拟研究其生物力学机制. 通过实验测量和文献调研, 确定了合理的拉伸和旋转的载荷参数; 发展了使用人体断层扫描图像结合解剖学数据建立详细腰椎几何模型的方法; 将松质骨、终板、椎间盘考虑为多孔弹性介质, 其他组织考虑为线性弹性介质, 进而建立了考虑生物组织中流固耦合效应的物理模型; 通过数值模拟得到了不同瞬态载荷及其组合作用下椎间盘内应力?应变与流体流动的变化规律. 研究发现, 瞬态载荷通过改变L4/L5椎间盘基质应力和髓核内外压力梯度, 在髓核中产生流体流动; 拉伸加载引起流体先流出髓核、再流入髓核, 产生含水量变化; 顺时针旋转加载在髓核左右产生相反的流动, 髓核右侧的含水量变化较左侧大. 本研究所采用的方法为流动过程相关的人体椎间盘退变病理生理机制研究提供了新的方法, 为中医正脊研究提供科学化思路, 也为相关的力学-生物学耦合研究和髓核再生的基础研究提供了一个切入点.      

Thick Lévy plates re-visited

This paper is concerned with the bending problem of Lévy plates which are simply supported on two opposite edges with any combination of simply supported, clamped or free conditions at the remaining two edges. This study attempts to solve thick Lévy plate problems in a novel way by establishing bending relationships that allow the prediction of Mindlin plate results using the corresponding Kirchhoff solutions. Based on the concept of load equivalence, these relationships obviate the need for complicated thick plate analyses that involve significant computation time and effort. Numerical plate solutions are then determined from these relationships and the validity of these results is verified using other known results and those generated using the abaqus software. It is through this study that the only analytical Mindlin plate solutions by Cooke and Levinson (Int. J. Mech. Sci. 25 (1983) 207) are found to contain errors. In this study, it is found that there are important distinctions between the Mindlin and Reissner plate theories. These differences will also be substantiated by numerical comparison.     

On the hyperchaotic complex Lü system

The aim of this paper is to introduce the new hyperchaotic complex Lü system. This system has complex nonlinear behavior which is studied and investigated in this work. Numerically the range of parameter values of the system at which hyperchaotic attractors exist is calculated. This new system has a whole circle of equilibria and three isolated fixed points, while the real counterpart has only three isolated ones. The stability analysis of the trivial fixed point is studied. Its dynamics is more rich in the sense that our system exhibits both chaotic and hyperchaotic attractors, as well as periodic and quasi-periodic solutions and solutions that approach fixed points. The nonlinear control method based on Lyapunov function is used to synchronize the hyperchaotic attractors. The control of these attractors is studied. Different forms of hyperchaotic complex Lü systems are constructed using the state feedback controller and complex periodic forcing.     

L积分的显函数表达式

对均质各向同性材料,各向异性材料和两相各向同性材料中的裂纹问题各提出一种辅助的位移应力场,证明积分和Ｂｕｅｃｋｎｅｒ功共轭积分之间有一种固有的简单关系。这个关系在线弹性材料中与材料特征根无关,也不受界面裂纹尖端应力振荡奇性的影响。     

桁架L型梁组合渡槽的优化设计

桁架钢筋混凝土L型梁组合渡槽是我国八十年代初出现的一种新型渡槽。其特点是结构简单,受力明确,两个L形梁拼成的矩形组合槽,既是输水构件,又是主要的受力构件,刚度大,挠度小,抗裂性能好,予制容易,吊装方便。它的优化设计是着重解决在已知水     

316L不锈钢随动强化模型改进研究

本文对316L不锈钢进行了单轴与多轴非比例路径下的应力控制棘轮试验,考察了应力幅值、平均应力和加载历程对棘轮特性的影响。同时进行了应变控制循环试验以研究材料的应力松弛特性。试验结果表明轴向棘轮效应在对称剪切荷载下效果明显,同时棘轮应变随应力幅值和平均应力的增加而增加。研究了Chen-Jiao随动强化模型与Jiang-Sehitoglu随动强化模型采用的单轴与多轴参数对背应力分量增量方向的影响,将Chen-Jiao模型中的多轴系数替换为界面饱和率,并在此基础上引入新的参数对塑性模量系数进行修正,计算结果表明修正后的模型能提升应力控制下多轴棘轮的预测精度,并能很好的预测应力松弛现象,表明了新模型的正确性与有效性。     

基于分段分裂基FFT的GPS L1辅助L2C信号快速捕获算法（英文）

为了缩短GPS L2C CM/CL长码的搜索捕获范围进而提高捕获速度,提出了一种基于分段分裂基FFT的L1辅助L2C信号快速捕获算法,可以有效降低计算量和节省存储空间,因而适合在嵌入式系统中实现。首先根据捕获到的L1信号的多普勒频率将L2C信号的多普勒搜索范围缩至一个固定的值,然后综合利用S-SFFT、补零和重叠舍弃算法快速准确地确定L2C CM/CL码的码相位。利用本文设计的L2C信号产生器产生L2C信号对该算法进行了仿真验证。实验结果表明,当L2C信号强度较强时,该算法可以以显著降低的计算量完成对码相位的准确快速捕获。     

Nachweis periodischer Lösungen bei gewissen nichtlinearen Schwingungsdifferentialgleichungen

Ohne ZusammenfassungEinige der hier vorgetragenen Ergebnisse sind bereits in meiner Dissertation, Existenzsätze für periodische Lösungen bei eingliedrigen nichtlinearen Schwingern, enthalten; Hamburg, Juli 1954, Hauptreferent Professor Dr. L. Collatz, dem ich auch hier für einige wertvolle Ratschläge danke. Vorgelegt von L. Collatz     

Viskosit?t der L?sungen von Polyelektrolyten

Ohne Zusammenfassung     

CONTROLLING (Lü-SYSTEM) USING PARTIAL LINEARIZATION

IntroductionSince 1 963 ,Lorenzfoundthefirstchaoticattractorinathree_dimensionalautonomoussystem[1],chaoshasbeenintensivelystudiedduringthelastdecades.Ithasbeendetectedinalargenumberofdynamicssystemofphysicalnature.However,manyeffectsareusuallyundesirableinpracticeforthesensibilityofchaos.Controllingchaoticsystemhasbeeninthefocusofattentionintheengineeringsociety[2～ 4 ].Manytechniquesandapproacheshavebeenstudiedtocontrolthechaoticsystem .Forinstance,OGYmethod[5 ],linearstatespacefeedback[6…     

Buckling of steel bars with Lüders bands

Experiments and simulations are presented for the study of interaction between material and structural instabilities that occur in mild steel bars under axial compression. The material instability consists of Lüders bands that nucleate and propagate along the specimens. The structural instability involves lateral deflections of the bar leading to collapse. The study includes an investigation of bars of several different lengths. The mechanical response in the experiments were monitored through measurements of axial load, axial and midspan lateral displacements, and full field imaging of a brittle coating showing the Lüders deformation. Interesting interactions exist between the localized deformation due to the material-level instabilities and the global collapse of the bars. Finite element simulations, using a constitutive model with a nonmonotonic stress–strain behavior, showed good agreement with the experiments and helped to explain the variety of collapse modes seen in the experiments. The symmetry of imperfections and/or loading misalignments have dramatic effects on the evolution of Lüders deformation and the eventual collapse mode. Certain imperfections lead to deformation modes that delay structural collapse.     

Die Torsionsspannungen in Wellen mit tiefen Längsnuten

Übersicht MitF(x, y) als Spannungsfunktion einer Welle ohne Nut und(, y) als Potentialfunktion des Quelle-Senke-Systems erhält man Spannungsfunktionen(, y) =F(x, y) –(, y) für Wellen mit tiefen Längsnuten. Es wird gezeigt, daß sich damit die Schubspannungen in den Läufern von Schraubenverdichtern ermitteln lassen.

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Shearing stresses in shafts with deep longitudinal grooves

Summary The stress functions(, y) of shafts with deep longitudinal grooves may be represented by(, y) =F(x, y) –(, y) whereF(x, y) is the stress function of a cylindrical shaft without grooves and(, y) denotes the potential function of the source-sink system. It is shown that the shearing stresses in rotors of screw-compressors may be obtained in this way.

     

Entmischung makromolekularer Lösungen in Scherströmungen

Zusammenfassung Es wird theoretisch hergeleitet und anschließend experimentell bestätigt, daß in einer Scherströmung eine feste Wand auf Makromoleküle hydrodynamisch abstoßend wirkt.     

316L不锈钢不同取向压痕应变率敏感性研究

本研究探讨了不同取向对激光选区熔化(SLM)成形316L不锈钢力学性能的影响．使用纳米压痕测试系统对SLM成形316L不锈钢扫描平面方向和叠加成形方向两个取向的试样进行测试,并通过相关计算得出了材料在这两个方向的弹性模量、硬度、应变率敏感性指数等力学参数．实验结果表明,扫描平面方向的弹性模量和叠加成形方向的弹性模量基本相同;在相同的压入应变率下,扫描平面方向的硬度大于叠加成形方向的硬度;而对于不同的压入应变率,在高应变率下的压痕硬度相对较大;随着压入深度的增加,硬度逐渐减小并趋于稳定值．此外,本研究分析了不同压入应变率下硬度和应变率敏感性指数m的压痕尺寸效应,并得到与尺寸无关的硬度和应变率敏感性指数m．最后,通过引入扫描平面方向准静态宏观压缩工况下的应变率敏感性指数m加以验证本研究的合理性,揭示了SLM成形316L不锈钢在不同取向上应变率敏感性的差异,进而为研究准静态宏观压缩下叠加成形方向的应变率敏感性提供了支撑．     

单个弹丸撞击316L不锈钢引起的变形场

运用金属材料表面纳米化试验机对单个弹丸撞击316L不锈钢表面进行了撞击实验;采用激光共聚焦显微镜观察了弹坑的三维形貌,测量不同振动频率下弹坑的直径及离面位移;采用云纹干涉法对弹坑周围的面内应变场进行测量,并分析振动频率及撞击方式对弹坑尺寸、塑性应变大小以及塑性应变区范围的影响;采用有限元方法对单个弹丸垂直撞击试件表面的应变场进行数值模拟,与实验结果进行比较,分析了弹坑周围残余应力的分布。结果表明:随振动频率的增加,弹坑直径和离面位移都增加,频率在50~55Hz,弹坑直径有突变,离面位移和振动频率呈线性关系;振动频率越大,塑性应变越大,塑性应变分布范围均大于弹坑直径的2倍;同一振动频率下弹丸垂直撞击比倾斜撞击的塑性应变大,而塑性应变分布范围相差不大;面内残余应变场的数值模拟结果和实验结果吻合较好,最大误差小于10%。     

含预制裂纹L形梁柱试件动态断裂过程

针对含预制裂纹L形梁柱试件,为研究预制裂纹动态扩展的力学特征及其对梁柱试件破坏模式的影响,采用数字动态焦散线实验系统,对距节点核心区不同距离l处含有预制裂纹的试件进行落锤冲击实验,得到预制裂纹的扩展轨迹、速度、动态应力强度因子的变化规律。结果表明,l值增大,扩展裂纹在梁下边缘的贯通点与预制裂纹的夹角逐渐增大,曲裂程度变大。裂纹扩展速度随着l的增大振荡性增强,裂纹扩展平均速度逐渐降低。l值为2 mm时,裂尖表现为Ⅰ型断裂,l值增大,裂尖受到剪应力作用增强,Ⅰ型动态应力强度因子减小,Ⅱ型动态应力强度因子增大,断裂逐渐转变为Ⅰ-Ⅱ复合型。