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1.
将具有完备动力学理论的非连续变形分析(DDA)方法应用于块体碰撞研究。基于三维DDA(3D DDA)方法,按时步输出块体碰撞过程速度变化和接触嵌入量,进而得到块体碰撞恢复系数、冲量、冲击力。以此为参考指标,采用斜抛、面-面对心等碰撞模型,验证3D DDA方法模拟块体碰撞的有效性,并将3D DDA方法应用于多米诺骨牌倾倒、滚石边坡成灾及防护等算例分析,探讨了多米诺骨牌倾倒机制、滚石启动及运动行为、滚石灾害防护方案。结果表明:多米诺骨牌间距越大,同一块体被碰撞时间越迟,其最终稳定时间也越迟,与下一块体碰撞的动能越大;滚石运动呈侧向平动及转动三维运动特征,每一次碰撞,均引起动能、轨迹或状态的显著变化;滚石拦挡设施弹簧刚度越大,越先达到最大冲击力,最大冲击力随弹簧刚度的增加而减小;可结合树木阻挡效应,耗散滚石动能,降低滚石飞跃高度,使滚石灾害减轻或控制在防护范围以内。 相似文献
2.
This paper extends the original 2D discontinuous deformation analysis (DDA) method proposed by Shi to 3D cases, and presents
the formulations of the 3D DDA. The formulations maintain the characteristics of the original 2D DDA approach. Contacts between
the blocks are detected by using Common-Plane (C-P) approach and the non-smooth contact, such as of vertex-to-vertex, vertex-to-edge
and edge-to-edge types, can be handled easily based on the C-P method. The matrices of equilibrium equations have been given
in detail for programming purposes. The C program codes for the 3D DDA are developed. The ability and accuracy of the formulations and the program are verified by
the analytical solutions of several dynamic examples. The robustness and versatility of the algorithms presented in this paper
are demonstrated with the aid of an example of scattering of densely packed cubes. Finally, implications and future extensions
are discussed.
The project supported by the National Natural Science Foundation of China (50139010) 相似文献
3.
This paper describes a material model, in which the materials under consideration grow up in a particular direction while re-organizing themselves to the surroundings. The structural reorganization is modeled as the rearrangement of anisotropy. Two models are proposed; one is that the anisotropic vector is embedded just as in fiber-reinforced materials, and the other is that the vector behaves like a float. In order to apply the present model to boundary-value problems, a three-dimensional finite element formulation is obtained with reference to the total-Lagrangian approach. Here we evaluate the performance of the model in terms of anisotropic growth; (a) adaptation behavior of a quasi-isotropy in the initial state, and (b) monotonic growth in helical direction. 相似文献
4.
In this work, a model of the stepped Timoshenko beam in presence of deflection and rotation discontinuities along the span is presented. The proposed model relies on the adoption of Heaviside’s and Dirac’s delta distributions to model abrupt and concentrated, both flexural and shear, stiffness discontinuities of the beam that lead to exact closed-form solutions of the elastic response in presence of static loads. Based on the latter solutions, a novel beam element for the analysis of frame structures with an arbitrary distribution of singularities is here proposed. In particular, the presented closed-form solutions are exploited to formulate the displacement shape functions of the beam element and the relevant explicit form of the stiffness matrix. The proposed beam element is adopted for a finite element discretization of discontinuous framed structures. In particular, by means of the introduction of a mass matrix consistent with the adopted shape functions, the presented model allows also the dynamic analysis of framed structures in presence of deflection and rotation discontinuities and abrupt variations of the cross-section. The presented formulation can also be easily employed to conduct a dynamic analysis of damaged frame structures in which the distributed and concentrated damage distributions are modelled by means of equivalent discontinuities. As an example, a simple portal frame, under different damage scenarios, has been analysed and the results in terms of frequency and vibration modes have been compared with exact results to show the accuracy of the presented discontinuous beam element. 相似文献
5.
A finite element method for highly viscous fluid is used to calculate the velocity and stress fields in the surrounding soft
rock of a tunnel. In order to fit the calculated values with the measured displacement of tunnel wall, we inverted the boundary
forces and the mechanical parameters of the surrounding rocks. 相似文献
6.
建立了一个橡胶复合材料结构有限元分析模型。在该模型中 ,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和物理非线性及橡胶基复合材料的各向异性。此外 ,本文还利用该模型研制的有限元分析软件对全钢丝子午胎的变形轮廓进行了详细的分析。 相似文献
7.
本文采用大变形弹塑性有限元法对金属板条在柱形模中的压弯成形过程进行了数值模拟,并与实验进行了比较。首先给出了纠正的拉格朗日有限元公式和基于弹塑性乘法分解的超弹性塑性本构关系。对接触摩擦问题的处理采用了罚函数法。通过对数值结果的分析得出了一些对弯曲工艺的设计有指导价值的结论。 相似文献
8.
A moving discontinuous Galerkin finite element method with interface condition enforcement is formulated for flows with discontinuous interfaces. The underlying weak formulation enforces the interface condition separately from the conservation law, so that the residual only vanishes upon satisfaction of both. In this formulation, the discrete grid geometry is treated as a variable, so that, in contrast to the standard discontinuous Galerkin method, this method has both the means to detect interfaces, via interface condition enforcement, and to satisfy, via grid movement, the conservation law and its associated interface condition. The method therefore directly fits interfaces, including shocks, preserving a high-order representation up to the interface without requiring shock capturing or an upwind numerical flux to achieve stability. It can be generalized to flows with a priori unknown interfaces with nontrivial topology and curved interface geometry as well as to an arbitrary number of spatial dimensions. Unsteady flows are represented in a manner similar to steady flows using a space-time formulation. In addition to computing flows with interfaces, the method can represent point singularities in a flow field by degenerating cuboid elements. In general, the method works in conjunction with standard local grid operations, including edge collapse, to ensure that degenerate cells are removed. Test cases are presented for up to three-dimensional flows that provide an initial assessment of the stability and accuracy of the method. 相似文献
9.
The theory of generalized functions is used to address the static equilibrium problem of Euler–Bernoulli non-uniform and discontinuous
2-D beams. It is shown that if simple integration rules are applied, the full set of response variables due to end nodal displacements
and to in-span loads can be derived, in a closed form, for most common beam profiles and arbitrary discontinuity parameters.
On this basis, for finite element analysis purposes, a non-uniform and discontinuous beam element is implemented, for which
the exact stiffness matrix and the fixed-end load vector are derived. Upon computing the nodal response, no numerical integration
is required to build the response variables along the beam element. 相似文献
10.
构造了一种在π平面上为椭圆的后续屈服函数,将该屈服函数、“Tresca”及“Misses型”后继屈服函数分别应用于干涉孔及冷胀孔问题的弹塑性有限元分析,并对这三种屈服函数在弹塑性有限元中的应用进行了评估。本文三种屈服函数在弹塑性问题中的应用评估对更有效地解决工程中的弹塑性问题有着实际的应用价值。 相似文献
11.
It is noted that the behavior of most piezoelectric materials is temperature dependent and such piezo-thermo-elastic coupling
phenomenon has become even more pronounced in the case of finite deformation. On the other hand, for the purpose of precise
shape and vibration control of piezoelectric smart structures, their deformation under external excitation must be ideally
modeled. This demands a thorough study of the coupled piezo-thermo-elastic response under finite deformation. In this study,
the governing equations of piezoelectric structures are formulated through the theory of virtual displacement principle and
a finite element method is developed. It should be emphasized that in the finite element method the fully coupled piezo-thermo-elastic
behavior and the geometric non-linearity are considered. The method developed is then applied to simulate the dynamic and
steady response of a clamped plate to heat flux acting on one side of the plate to mimic the behavior of a battery plate of
satelite irradiated under the sun. The results obtained are compared against classical solutions, whereby the thermal conductivity
is assumed to be independent of deformation. It is found that the full-coupled theory predicts less transient response of
the temperature compared to the classic analysis. In the steady state limit, the predicted temperature distribution within
the plate for small heat flux is almost the same for both analyses. However, it is noted that increasing the heat flux will
increase the deviation between the predictions of the temperature distribution by the full coupled theory and by the classic
analysis. It is concluded from the present study that, in order to precisely predict the deformation of smart structures,
the piezo-thermo-elastic coupling, geometric non-linearity and the deformation dependent thermal conductivity should be taken
into account.
Project supported by the National Natural Science Foundation of China (Nos. 10132010 and 50135030) and the Foundation of In-service
Doctors of Xi'an Jiaotong University. 相似文献
12.
A complete three-dimensional FEM model of the Bar-Bar Tensile Impact Apparatus (BTIA) is constructed, in which the slots in
the bars and the glue layers between the bars and the flat-shaped specimen are included. For elastic-plastic specimen material,
Ly12cz aluminum alloy, the process of tensile impact experiments is simulated and the matching relation between the specimen
geometry and the bars is investigated. Based on the FEM analysis, an iterative method is proposed to design a reasonable specimen
geometry for obtaining the true dynamic stress-strain relation for a certain specimen material.
The project supported by the National Natural Science Foundation of China (19272061) 相似文献
13.
The ordinary differential constitutive equations of endochronic theory are extended to simulate elasto-plastic deformation in the range of finite strain using the concept of corotational rate. Different corotational stress rates (Jaumann, Cotter-Rivlin, Truesdell, Dienes and Mandel) are incorporated into the theory. In addition, a new formulation of the plastic spin, which can be used in the Mandel stress rate, is derived. Theoretical simulations of the axial effects for various materials subjected to simple and pure torsional loading cases are discussed in this study. It is shown that the endochronic theory incorporated with the Mandel stress rate yields the most satisfactory result, as indicated from comparison with the experimental data found in literature. Finally, theoretical investigation of the deformation subjected to finite proportional and non-proportional biaxial compression is presented. The true relationship between stress and strain can be converted to a nominal stress-strain relationship for biaxial loading through the explicit transformation equations derived in this paper. Experimental data tested by Khan and Wang [1990] (“An Experimental study of Large finite Plastic Deformation in Annealed 1100 Aluminum During Proportional and Non-proportional Biaxial Compression” Int. J. Plasticity, 6, 485) are suitably described by the theory demonstrated from a comparison with the theoretical prediction according to rigid-plastic and elastic-plastic models employed by Huang and Khan [1991]. “An Analysis of Finite Elastic-Plastic Deformation under Biaxial Compression”, Int. J. Plasticity, 7, 219). 相似文献
14.
Comparing with two-dimensional contact problems, three-dimensional frictional contact problems are more difficult to deal
with, because of the unknown slip direction of the tangential force and enormous computing time. In order to overcome these
difficulties, a combined PQP (Parametric Quadratic Programming) and iteration method is derived in this paper. The iteration
algorithm, which alleviates the difficulty of unknown slip direction, is used along with the PQP method to cut down computing
costs. Numerical example is given to demonstrate the validity of the present algorithm.
The project supported by the Machinary and Electronics Ministry of China 相似文献
15.
A numerical analysis of convective drying of a 3D porous solid of brick material is carried out using the finite element method
and mass lumping technique. The energy equation and moisture transport equations for the porous solid are derived based on
continuum approach following Whitaker’s theory of drying. The governing equations are solved using the Galerkin’s weighted
residual method, which convert the governing equations into discretized form of matrix equations. The resulting capacitance
matrices are made diagonal matrices by following the classical row-sum mass lumping technique. Hence with the use of the Eulerian
time marching scheme, the final equations are reduced to simple algebraic equations, which can be solved directly without
using an equation solver. The proposed numerical scheme is initially validated with experimental results for 1D drying problem
and then tested by application to convective drying of 3D porous solid of brick material for four different aspect ratios
obtained by varying the cross section of the solid. The mass lumping technique could correctly predict the wet bulb temperature
of the solid under evaporative drying conditions. A parametric study carried out for three different values of convective
heat transfer coefficients, 15, 30 and 45 W/m 2 K shows an increased drying rate with increase in area of cross section and convective heat transfer coefficient. The proposed
numerical scheme could correctly predict the drying behavior shown in the form of temperature and moisture evolutions. 相似文献
16.
The problem of interval correlation results in interval extension is discussed by the relationship of interval-valued functions and real-valued functions. The methods of reducing interval extension are given. Based on the ideas of the paper, the formulas of sub-interval perturbed finite element method based on the elements are given. The sub-interval amount is discussed and the approximate computation formula is given. At the same time, the computational precision is discussed and some measures of improving computational efficiency are given. Finally, based on sub-interval perturbed finite element method and anti-slide stability analysis method, the formula for computing the bounds of stability factor is given. It provides a basis for estimating and evaluating reasonably anti-slide stability of structures. 相似文献
17.
本文探讨一种基于半连续半离散思想,适用于复杂结构(如高层框架、剪力墙、桁架、网架等结构系统)工程分析的超级有限元,其结构数值分析是按连续体进行,但又按单个构件进行有限元计算。这种按整体系统进行离散所获得的单元内部包含众多构件,有别于一般常见的实体有限元,称为“超级有限元”。这种方法自由度数比一般有限元法少很多,又与单元内部所含构件数多少无关,并可求取结构内每个构件的内力值。 相似文献
18.
THERANDOMVARIATIONALPRINCIPLEINFINITEDEFORMATIONOFELASTICITYANDFINITEELEMENTMETHODGaoHang-shan(高行山)(NorthwestenPolytechnicalU... 相似文献
19.
在热传导分析中,当热流与温度梯度存在时间延迟时,需采用非傅立叶热传导模型进行分析。生物组织具有较强的热松弛时间系数,承受激光、微波及烧烫等作用时,其呈现出较强的非傅立叶行为。本文对脉冲热源作用下生物组织的非傅立叶热传导进行研究,针对强脉冲引起的温度场在空间域的高梯度变化、波阵面的间断行为以及通用传统时域数值方法会带来虚假数值振荡的特点,提出采用所发展的时域间断Galerkin有限元法(DG-FEM )进行求解计算。对多种脉冲热源作用下的非傅立叶热传导过程进行数值模拟,通过考量强脉冲作用下温度场分布和热致生物组织损伤行为的影响,表明了本文所发展的DGFEM 能够有效、准确地描述温度场空间分布和热传导过程以及非傅立叶行为下的生物热损伤更为明显,在生物组织热行为分析中应该受到重视。 相似文献
20.
An elastic–plastic finite element model is developed for 3D orthogonal cutting of discontinuous chips. The tool is P20 while the workpiece is made of 6-4 brass. Examined under the condition of low cutting speed are the initial crack location, the direction of crack growth and variations of discrete chips. These predictions are made possible by application of the strain energy density (SED) theory. The initial crack was formed above the tool tip and grew progressively along the stationary values of the SED function until the trajectory intersects with the free surface. The plastic deformation and friction result in a high equivalent stress in the secondary deformation zone of the first longitudinal chip. Stresses are also high at the location of crack initiation. The chip node near the tool face is sensitive to the contact of the tool face. As more residual stress prevails after the first longitudinal cut, degradation of the workpiece surface prevails and should be accounted for. 相似文献
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