首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 781 毫秒
1.
韩文娟  刘海 《力学与实践》2010,32(4):109-111
对《力学》中的物体自由度进行多方面分析,以深化教学、提高学生正 确分析物理问题的能力.使用实际教学分析的研究方法,在《力学》范围内讨论自由度与坐标、 自由与约束的关系并得以下结论: (1) 同一物体的自由度随其所在的``空间'不同而不同, 不因坐标系的选取不同而 异, 在同类参考系中不因参考系的动静而有别;(2)自由度遵循叠加原理. 讨论了质点系的总自由度及相关计算问题,并指出研究《力学》中自由度的意义.  相似文献   

2.
When the state and input matrices of a multivariable linear time-invariant system are perturbed, the problem of the estimation of pole perturbance of closed-loop system is considered by making use of the theory of branching of solutions for nonlinear equations.  相似文献   

3.
两自由度振动系统的斜碰撞分析   总被引:3,自引:0,他引:3  
韩维  胡海岩  金栋平 《力学学报》2003,35(6):723-729
研究斜碰撞振动系统动力学的一个关键问题是对系统在碰撞前后的状态进行合理描述和正确计算.针对两弹性体斜碰撞问题,基于瞬间碰撞假设,提出了采用步进冲量来分析和求解斜碰撞前后的状态关系;并以弹簧摆和振子组成的两自由度斜碰撞振动系统为例,具体介绍了该算法如何实现.用解析方法讨论了该系统在斜碰撞过程中可能出现的各种力学现象,将冲量步进算法得到的数值解与解析结果进行对比,取得了完全一致的结果.该数值方法能适应多种斜碰撞问题的计算.  相似文献   

4.
沙漠地貌演化过程的湍流大涡模拟研究   总被引:1,自引:1,他引:0  
采用大涡模拟和混合粒径群体沙粒运动算法结合内置边界方法来模拟沙波纹与沙丘的演化和发展,在平坦沙区形成沙波纹的同时,在沙丘上同样也出现了沙波纹的结构,即沙波纹的发展出现了多尺度现象.此外,还分析了粒径对沙波纹与沙丘自身形态演化和发展的影响,以及沙丘对平坦沙区沙波纹形成发展的作用.  相似文献   

5.
1.IntroductionThestudyofoscillator}'behaviorofneutraldifferentialequationsisarelativealnewfieldandisveryinterestinginapplications.Inrecentyears.theoscillatorytheoryfortheseequationshasbeenextensivelydeveloped.WerefertotherecentbookbyGyoriandLadaSI'I,Baino…  相似文献   

6.
贾彦武  张萌  周晓平  张勇勇  宋丽  武朋飞 《应用力学学报》2020,(2):866-872,I0028,I0029
以汉中市综合管廊为工程背景,通过有限元软件,首先模拟分析综合管廊早龄期温度场,随后将温度场结果附加到管廊结构中求解温度应力,从而分析综合管廊早龄期混凝土温度应力与浇筑长度的关系。模拟分析发现:综合管廊在混凝土浇筑早期,温度场沿长度方向变化不显著,且随着浇筑长度的增加,温度场不变;在墙体温度上升阶段,墙体内部沿长度方向的应力主要为压应力,当墙体混凝土内部温度达到最高,混凝土开始降温,结构内变形由膨胀逐渐变为收缩,内力由压应力逐渐变为拉应力,随着时间的变化,墙体内外温差趋于稳定,墙体温度应力也逐渐平稳,此时温度应力主要受外界环境变化影响;当综合管廊浇筑长度在60m范围内,浇筑长度越大,温度应力越大,但当浇筑长度超过60m,温度应力不再增加。  相似文献   

7.
本文通过纳米压痕实验技术得到混凝土材料细观各相参数,基于渐进均匀化理论,采用蒙特卡洛方法和双向游走方法建立了含孔隙混凝土的胞元模型.分析了孔隙在冻融循环次数增加情况下对混凝土有效弹性模量的影响,同时与有限元模拟分析进行了比较.结果表明:随着冻融循环次数增加,孔隙体积分数增大,界面与砂浆压痕模量相对降低,但对骨料影响较小,导致混凝土宏观弹性模量随之降低;理论分析预测的混凝土有效弹性模量与有限元模拟结果吻合良好.应用含孔隙混凝土胞元模型能有效地预测混凝土宏观弹性模量,进而也为其在冻融作用下老化演变机理的研究评估提供了基础.  相似文献   

8.
IntroductionTheone_dimensionalMHDequationsunderLagrangecoordinateare τ t- u x=0 , u t P x 18π x(H2 y H2 z) =0 , Hy t Hyτ u x =0 , Hz t Hzτ u x=0 , S t=0 ,( 1 )whereu ,τ,Hy,HzandSthevelocity ,specificvolume,thecomponentsofmagneticfieldiny_andz_diectionsandtheentropyrespectively .T…  相似文献   

9.
We consider the system of elastostatics for an elastic medium consisting of an imperfection of small diameter, embedded in a homogeneous reference medium. The Lamé constants of the imperfection are different from those of the background medium. We establish a complete asymptotic formula for the displacement vector in terms of the reference Lamé constants, the location of the imperfection and its geometry. Our derivation is rigorous, and based on layer potential techniques. The asymptotic expansions in this paper are valid for an elastic imperfection with Lipschitz boundaries. In the course of derivation of the asymptotic formula, we introduce the concept of (generalized) elastic moment tensors (Pólya–Szegö tensor) and prove that the first order elastic moment tensor is symmetric and positive (negative)-definite. We also obtain estimation of its eigenvalue. We then apply these asymptotic formulas for the purpose of identifying with high precision the order of magnitude of the diameter of the elastic inclusion, its location, and its elastic moment tensors.  相似文献   

10.
This paper presents the effect of non-homogeneity of the material of plate structures on the vibration frequencies. The non-homogeneity of the plate is characterized by taking a variety of combinations of linear as well as quadratic variations in the Young’s modulus and density of the material. Boundary characteristic orthogonal polynomials using Gram-Schmidt procedure have been employed in the Rayleigh Ritz method. The results have been included for the first few frequencies of the plate element for all the boundary conditions viz. clamped, simply supported and free. Related Tables and graphs are incorporated to show the effect of the non-homogeneity parameter on the frequencies of the vibration of elliptic and circular plates.  相似文献   

11.
This paper reports a type of laws which governs action poten-tial of nervous impulses,and it is discussed by general form-nonlinear dispersive process.We find that the nervous wave is aslowly varying amplitude solitary wave in the small dispersivecase.we prove that the solitary wave is not generated in the or-dinary dispersion,but a travelling wave with varying amplitudesmay be obtained.The stability of various possible action poten-tials and bifurcation in overdamped case are also discussed inthis paper.  相似文献   

12.
Simultaneous measurements of the components of dynamic modulus at the set of frequencies were made by Fourier-Transform Mechanical Spectroscopy (FTMS) to investigate the curing process of a segmented polyurethane.The whole process of curing is treated as consisting of three stages. In the first stage, the material can flow and this stage is complete at the gel-point. In the second stage, the curing proceeds in the network and ends with phase separation of aggregating segments (blocks) of polymeric chains. In the third stage, the curing continues in the two-phase system. The object of investigation was the transition from the second to the third stage. It was shown that the position of the maximum of loss tangent depends on frequency and does not coincide with different characteristic points marking the time dependencies of G and G. This is due to the formation of micro-particles of the newly formed phase. The FTMS method is used for separation of the modulus changes into parts related to formation of chemical and physical networks.Special means of treating calorimetric measurements identified a weak maximum heat output at the moment corresponding to the transition point.  相似文献   

13.
14.
For periodic arrays of spheres the permeability is obtained numerically as a function of the dimensionless wave number kD in the flow direction, where D is the sphere diameter, k = 2π/λ is the wave number, and λ is the distance between the spheres in the flow direction. Our numerical results for the solids fraction of 0.45 show that for kD < 6.5 the permeability increases with increasing kD. But, it decreases for 6.5 < kD < 8.5 and reaches a local minimum at kD  8.5, and then increases again with increasing kD. Since the Fourier spectrum of the area fraction is zero for kD = 8.98, this result suggests that the area fraction plays an important role in determining the dependence of permeability on the distance between the spheres in the flow direction. For smaller solids fractions, the positions of the local maximum and minimum of permeability shift to slightly smaller kD’s.  相似文献   

15.
建立了考虑瞬态油膜压力影响的热稳定性分析模型 ,用求解系统周期解分岔的 PNF法对推力轴承系统的热稳定性进行了研究 ,结合 Poincare映射与胞映射法思想 ,提出了用于分析系统周期稳态解全局特性的数值计算 PCM方法 ,并对推力轴承热系统周期稳态解的全局特性进行了考察  相似文献   

16.
A method is proposed for determining the stiffness and rheological characteristics of composite materials, which is based on minimizing the disagreement between experimental data and results of numerical simulations of deformation of hemispherical shells under explosive loading. The damping characteristics of randomly reinforced polymer materials are analyzed with the use of this method. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 3, pp. 126–133, May–June, 2006.  相似文献   

17.
An elastic fluid-saturated porous medium is modeled as a bundle of parallel cylindrical tubes aligned in a direction parallel to the fluid movement. The pore space is filled with viscous compressible liquid. A cell model and the theory of transient pipe flow are used to derive one-dimensional governing equations in such media. All macroscopic constants in these equations are defined by the individual material constants of the fluid and solid. The interaction force includes an additional term not found in Biot's theory.  相似文献   

18.
19.
The problem of stability of equilibria of a physical pendulum with a nonstretchable thread attached to it is considered from the standpoint of the Lagrange theorem on stability and its inversion. Specific difficulties which one faces when studying an infinite dimensional mechanical system are discussed. A new approach to the study of stability with respect to two metrics is suggested. The influence of resonant phenomena on the motion of the shortened (linearized) system is considered.
Sommario Si considera il problema di stabilità di punti di equilibrio di un pendolo fisico con un filo inestensibile appeso ad esso dal punto di vista del teorema di Lagrange sulla stabilità e sulla sua inversione. Difficoltà specifiche relative allo studio di un sistema meccanico di dimensione infinita sono discusse. Si suggerisce un nuovo metodo per lo studio della stabilità rispetto a due metriche. L'influenza di fenomeni di risonanza sul moto del sistema ridotto (linearizzato) è considerata.
  相似文献   

20.
The cyclic deformation of aluminium bicrystals was numerically simulated by using a crystalline micromechanical approach to study the effects of crystallographic orientation and deformation properties of constituent grains. Both the macro-and micro-stress-strain responses were analyzed. It was shown that the whole Bauschinger effect and cyclic hardening behavior of bicrystals is primarily controlled by the corresponding properties of the constituent grains, and that the effects of internal stresses induced by the grain boundary and the interaction between grains are secondary. The crystallographic orientation of constituent grains was also shown to have significant influence on the macro-and micro-mechanical behavior of the bicrystals. There were smaller symmetry in the orientation or greater difference in the strength between grains and more remarkable GB effects.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号