磁致伸缩材料Terfenol-D非线性耦合有限元分析

为了研究巨磁致伸缩材料Terfenol-D的非线性耦合磁力特性及响应,提出一种增量显式有限元列式及其在通用有限元软件中的实现方法.该显式增量方法基于实验测得材料性质或非线性本构计算所得材料参数,通过分段插值函数描述磁致伸缩材料的材料参数随磁场和预应力的非线性变化关系,采用耦合方程的弱形式给出相应有限元列式及增量算法,并在通用有限元软件ABAQUS中执行数值算例.该方法通过显式插值避免大多数数值方法求解非线性方程组的迭代过程,只需要先进行稳定性验证来标定合适的增量步长即可保证结果的可靠性.数值分析结果表明,该方法具有较好的精度和稳定性,能够准确有效地模拟不同预应力水平和偏磁场强度下的磁致伸缩非线性耦合响应,同时能够反映预应力对最大磁致伸缩的影响,即“反转效应”.该方法对磁致伸缩器件的设计应用及力磁耦合非线性分析具有一定的理论和实际意义.     

用大变形壳元数值模拟薄钣的深冲成形

开发了大变形弹塑性壳单元有限元程序．为了改进增量计算的收敛性,程序中采用Ｃ１连续的几何非线性──材料非线性三角形浅壳单元．为了有效计算广泛存在于薄板成形过程中的接触问题,提出了混合半道解法有限元解法计算接触问题．并给出了若干计算结果,验证了计算方法的有效性．     

Deformation mechanism and excavation process of large span intersection within deep soft rock roadway

The FLAC3D software was used to simulate and analyze numerically the displacement, stress and plastic zone distribution characteristics of a large span intersection in a deep soft rock roadway after the surrounding rock was excavated. Our simulation results show that there are two kinds of dominating factors affecting roadway stability at points of intersection, one is the angle between horizontal stress and axial direction of the roadway and the other are the angles at the points of intersection. These results are based on a study we carried out as follows: first, we analyzed the failure mechanism of a large span intersection and then we built a mechanical model of a rock pillar at one of the points of intersection. At the end of this analysis, we obtained the failure characteristics of the critical parts on the large span intersection. Given these failure characteristics, we proposed a new supporting method, i.e., a Double-Bolt Control Technology (DBCT). By way of numerical simulation, DBCT can effectively control the deformation of the surrounding rock at the points of intersection in roadways.     

不对称带束层11.00R20全钢载重子午线轮胎有限元分析

借助ABAQUS有限元软件,建立一个带束层不对称的轮胎结构有限元分析模型,考虑了轮胎变形的几何非线性、轮胎与地面和轮胎与轮辋的大变形非线性接触,轮胎材料的非均匀性、橡胶材料的不可压缩性和物理非线性及橡胶基复合材料的各向异性。通过有限元分析,得到了带束层不对称的子午线轮胎在充气压力下的变形和应力分布情况,带束层和胎体帘线的受力状况和分布特征,并对计算结果进行了分析,以期验证二维模型,为轮胎设计提供参考。     

冷弯薄壁型钢四肢拼合立柱轴压承载力设计方法

建立了考虑材料、几何和接触非线性的有限元模型,在对冷弯薄壁型钢四肢拼合截面立枉的轴压性能试验试件进行模拟分析,验证有限元方法正确性的基础上,对考虑长细比、截面翼缘宽厚比等因素的一系列试件进行了数值分析,并得到其轴压承载力。在相关规范“有效宽度法”和“直接强度法”的基础上,提出了冷弯薄壁型钢四肢拼合截面立柱轴压承载力的设计方法：有效计算长度法和修正系数法。研究结果表明：试件最终破坏均呈现局部屈曲和畸变屈曲的破坏模式;在未考虑计算长度系数折减的情况下,当长细比小于50时,各规范公式计算值均略低于试验值和有限元值,吻合较好,当长细比大于50时,公式计算结果过于保守。     

带缀板的开口薄壁杆件的约束扭转

根据薄壁杆件结构约束扭转的一致性理论,并在符拉索夫刚周边假定及库尔布鲁纳和哈丁对翘曲位移的假定下,考虑缀板的弯曲与剪切变形,得到带缀板的开口薄壁杆件的总势能及相应的拉格朗日函数。通过引入对偶变量,建立了缀板加强的开口薄壁杆件的哈密顿对偶体系,并采用两端边值问题的精细积分法求得高精度数值解。算例证明,本方法具有较高的精度,且计算过程简单清晰,为缀板加强的开口薄壁杆件的约束扭转分析提供了一种新的思路。     

强夯加固机理的大变形数值分析

强夯过程的动力响应问题非常复杂,理论上难以用解析方法进行分析和求解,目前已有的数值分析方法多为小变形分析方法.考虑到强夯过程中实际土体的变形基本上属于大变形,因此采用大变形几何非线性有限元法分析强夯加固机理.在强夯计算模型中,引入P波阻尼和S波阻尼的概念来说明土体的材料阻尼特性,同时运用改进人工边界法来模拟波在人工边界上的传播.为了保证模型的网格稳定,计算程序中增加了液化单元分析.通过一个工程实例,对其加固深度、变形特征、应力分布进行了数值分析,对比结果验证了强夯大变形分析的正确性     

不可压缩超弹性材料大变形接触分析

列出了增量求解方案和基于完全拉格郎日描述的有限元方程。给出了用间隙元法分析接触问题的基本思路,以及Mooney-Rivlin不可压缩超弹性材料的应力应变关系。由上述理论编制了ADINA－GAP程序并对橡胶材料的大变形接触进行了有限元分析。绘出了橡胶护舷在大变形下的位移反力关系曲线。计算结果与实验结果相吻合较好,表明本方法是实用有效的。     

Buckling analysis of super-long rock-socketed filling piles in soft soil area by element free Galerkin method

In order to discuss the buckling stability of super-long rock-socketed filling piles widely used in bridge engineering in soft soil area such as Dongting Lake, the second stability type was adopted instead of traditional first type, and a newly invented numerical analysis method, i.e. the element-free Galerkin method (EFGM), was introduced to consider the non-concordant deformation and nonlinearity of the pile-soil interface. Then, based on the nonlinear elastic-ideal plastic pile-soil interface model, a nonlinear iterative algorithm was given to analyze the pile-soil interaction, and a program for buckling analysis of piles by the EFGM (PBAP-EFGM) and arc length method was worked out as well. The application results in an engineering example show that, the shape of pile top load-settlement curve obtained by the program agrees well with the measured one, of which the difference may be caused mainly by those uncertain factors such as possible initial defects of pile shaft and the eccentric loading during the test process. However, the calculated critical load is very close with the measured ultimate load of the test pile, and the corresponding relative error is only 5.6%, far better than the calculated values by linear and nonlinear incremental buckling analysis (with a greater relative error of 37.0% and 15.4% respectively), which also verifies the rationality and feasibility of the present method.     

Analysis on nonlinear wind-induced dynamic response of membrane roofs with aerodynamic effects

Based on the characteristics of membrane structures and the air influence factors, this paper presented a method to simulate the air aerodynamic force effects including the added air mass, the acoustic radiation damping and the pneumatic stiffness. The infinite air was modeled using the acoustic fluid element of commercial FE software and the finite element membrane roof models were coupled with fluid models. A comparison between the results obtained by FE computation and those obtained by the vibration experiment for a cable-membrane verified the validity of the method. Furthermore, applying the method to a flat membrane roof structure and using its wind tunnel test results, the analysis of nonlinear wind-induced dynamic responses for such geometrically nonlinear roofs, including the roof-air coupled model was performed. The result shows that the air has large influence on vibrating membrane roofs according to results of comparing the nodal time-history displacements, accelerations and stress of the two different cases. Meantime, numerical studies show that the method developed can successfully solve the nonlinear wind-induced dynamic response of the membrane roof with aerodynamic effects.     

沥青混合料粘弹塑性本构关系及大变形有限元分析一般理论

应用Perzyna’s理论和Mises屈服准则建立沥青混合料粘弹塑性本构方程,并扩展到三维方程;应用Newton-Raphson迭代程序的逐步积分方法,获得了小变形粘弹塑性本构理论增量形式和有限元数值方程。基于小变形本构理论,把其应力应变、应力偏量和等效应力分别改用Cauchy应力的Jaumann导数、变形率、应力偏量和等效应力,推导出大变形粘弹塑性增量形式的本构方程和数值方程,建立了沥青混合料粘弹塑性理论体系。     

Comparisons between centrifuge and numerical modeling results for slope toppling failure

This paper presents series studies on the toppling mechanism by centrifuge tests and numerical simulations. Two different discrete element methods, i.e., the continuum-based discrete element method(CDEM) and the discontinuous deformation analysis(DDA), are adopted. The modeling results show that both the methods can accurately capture the failure modes of the centrifuge tests, including three distinct zones and two failure surfaces. Comparisons are made between the physical test and numerical simulation results. The critical inclination angle of the tilting table where the slope models are fixed on can be moderately predicted by the two methods, with different degrees of precision. The error between the test results and the simulated results is within 1% for the slope models without rock-bridges by both CDEM and DDA. However, it is amplified for the staggered-joint models that simulate the rock-bridges. With DDA, the average error is about 5%, and the maximum error is up to 17%. While with CDEM, the errors for the aligned-joint models are ranged from 1% to 6%, and it is from 10% to 29% for the staggered-joint models. The two numerical methods show the capability in simulating toppling failure of blocky rock mass with and without rock-bridges. The model with rock-bridges which provides a certain bending resistance is more stable than the one without any rock-bridge. In addition, the two failure surfaces were observed, which is different from the common understanding that only one failure surface appears.     

当前刚度系数在前屈曲分析中的应用

在有限元分析中,非线性问题最终都归结为求解非线性代数方程组.基于增量法的当前刚度系数,具有趋零特性.即随着载荷向临界点靠近,当前刚度系数单调收敛于零.利用这一特性,可以用以确定载荷增量步长,并利用前屈曲分析各解点上当前刚度系数值构造拉格朗日插值,用以确定临界载荷.最后,通过算例验证了本算法的有效性.     

双层连续组合梁弹塑性状态的界面滑移

考虑了上层混凝土开裂及钢筋与混凝土之间滑移对梁变形的影响.根据剪力连接件的实际力学特性,采用简化后的线弹性弹簧来模拟钢筋 混凝土界面以及钢梁 混凝土界面的剪切滑移,并结合内力-变形关系推导出双层钢 混凝土组合梁的上下层界面滑移微分方程.在分析过程中偏保守地假设负弯矩截面上缘混凝土板抗拉刚度降为零.为验证该解析法的合理性,采用非线性较强的有限元软件Abaqus建立了空间模型,模型考虑了剪力连接件和材料的非线性.有限元计算结果表明,通过2种方法所得的界面滑移数值和趋势比较吻合,该解析法用于分析双层连续组合梁的滑移变形是可行的.     

爆炸载荷作用下混凝土板的塑性动力响应

采用能量守恒原理,对假设四边为固定约束的地下浅埋混凝土方板,忽略材料的弹性变形能,同时考虑土-结构的接触界面上两种介质相互作用对界面压应力分布的影响,在非接触爆炸载荷作用下的塑性大变形响应进行了理论分析,运用Lagrange方程,建立板的运动响应微分方程,得到固支混凝土方板塑性大变形的理论计算公式．结果表明：理论计算与试验及程序分析结果吻合较好,表明该方法可应用于地下混凝土板类结构在非接触爆炸载荷作用下的毁伤或人防结构的工程预测．     

层间黏结性能对夹层管屈曲传播的影响机理

为了研究层间黏结性能对夹层管屈曲传播的影响,通过深海压力舱小比例模型试验,测得不同层间黏接情况下夹层管试件的变形形态和压力-体积变化曲线.利用有限元软件ABAQUS,建立外压作用下夹层管的三维数值模型,采用非线性弹簧单元模拟轴向和环向层间黏结性能,数值模拟分析夹层管试件的局部屈曲失稳和屈曲传播过程,得到试件的变形形态和压力-体积变化曲线,与试验结果吻合较好.采用建立的数值模拟方法,分析不同层间黏接情况下夹层管的屈曲传播过程.结果表明：良好的层间黏结性能可以使夹层管各层间有效传力和协调变形,显著提升结构的整体受力性能,提高夹层管的屈曲传播压力,具有更好的承压和变形能力.     

Development and verification of large deformation model considering stiffness deterioration and shear dilation effect in FLAC~(3D)

The existing constitutive models of rock with strain softening cannot successfully reflect the damageinduced anisotropy and nonlinearity of the post-peak failure behavior under progressive loading. In order to better reflect the nonlinear stress-strain behavior of rock, especially for the post-peak failure behavior,with expected stiffness degradation and large deformation, a modified constitutive model of rock considering stiffness degradation and dilatation behavior at large deformation was proposed in this study. This study analyzes and discusses various attenuation parameters in the proposed nonlinear plastic constitutive model using FLAC~(3D) software. The excavation-induced stress in rocks was calculated by FLAC~(3D) using the Mohr-Coulomb model, conventional strain model, and the proposed modified model. The obtained results of these models were analyzed and compared with field data. This study shows that the simulated results using the proposed new constitutive model matched much more closely with the measured field data, with an average error less than 5%. This new model can successfully reflect the damage-induced stiffness degradation at large deformation, and can provide a theoretical basis for stability design and evaluation of underground excavation.     

双包络蜗轮蜗杆的现代设计与检测方法(邀请论文)

针对目前齿轮工业中存在的2种不同类型双包络蜗轮蜗杆,即加工时蜗杆轴线与机床转台轴线正交型和不正交型,为研发双包络蜗轮蜗杆,将这2种不同的类型统一在一个计算机程序中,包含了现代齿轮设计中根切线与接触线包络界线、相对曲率、瞬时接触线与接触带、啮合角、相对滑动、齿面接触分析(tooth contact analysis,TCA)、齿面测量、单-双线接触区及其重合系数分析等最新技术,以及蜗杆螺旋齿面在三坐标测量机(coordinate measuring machine,CMM)上的测量方法,通过2个算例设计分析了2种不同双包络蜗轮蜗杆,展示了齿轮设计的现代方法.     

利用转动不协调确定煤矿覆岩断裂带高度

基于非线性大变形几何场论，建立了覆岩断裂带高度预计的差分余量法，使得地表移动预计和覆岩断裂带的确定统一为一个有机整体；证明了介质变形连续性的协调条件可以用转动协调方程等价表示，微观转动不协调是导致岩石类材料颗粒与夹杂接触边界产生微裂纹的原因。算例的计算结果表明，该方法简单、快速，有望在放顶煤开采和水体下采煤中得到应用。