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高分子材料的极限断裂强度和破坏性能的研究——Ⅱ.蠕变持久强度的动力学模型理论 总被引:1,自引:0,他引:1
本文对当前蠕变持久强度的表征进行了系统总结,指出了它是高分子材料的可形变性、分子链应力集中情况和应力集中链断链滑移动力学三者统一的体现。基于这种破坏概念,推导出一种能表征半晶态、玻璃态和弹性体等聚合物的蠕变持久强度动力学模型理论和一般化断裂状态方程。当该方程引入一、二级近似条件后,该式就分别还原为准脆性状态下粘弹性蠕变断裂方程,受迫高弹性状态下蠕变断裂方程和高弹性状态下蠕变断裂方程。 相似文献
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本文对当前蠕变持久强度的表征进行了系统总结,指出了它是高分子材料的可形变性、分子链应力集中情况和应力集中链断链滑移动力学三者统一的体现。基于这种破坏概念,推导出一种能表征半晶态、玻璃态和弹性体等聚合物的蠕变持久强度动力学模型理论和一般化断裂状态方程。当该方程引入一、二级近似条件后,该式就分别还原为准脆性状态下粘弹性蠕变断裂方程,受迫高弹性状态下蠕变断裂方程和高弹性状态下蠕变断裂方程。 相似文献
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众所周知,在复微分方程和复差分方程领域中,Malmquist型方程是比Painlev′e方程和Riccati方程形式更一般的非线性方程.在本文中,我们运用Nevanlinna理论的差分模拟结果和微分域理论对一类具指数函数系数的Malmquist型复差分方程进行了研究.当上述Malmquist型复差分方程的有限级超越亚纯解具有较少的零点和极点时,我们得到其增长性和指数函数ez的增长性一致.该结果是对复微分Malmquist定理和复差分Malmquist定理的推广和补充. 相似文献
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基于一个六自由度的位移场和电势场, 建立了压电复合材料层板的控制方程。在简支边界条件下, 得到了正交矩形压电复合材料层板的解析解。该理论是一个等效单层理论, 控制方程的变量仅六个, 且不随层数变化, 使解的数学过程简洁。在该理论中, 决定精度的位移分布函数和电势分布函数由三维应力和静电平衡方程的特解来确定, 使之满足压电层板界面连续条件与板面力及电条件。算例验证了本文中等效单层理论的高精度。 相似文献
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针对一类由交流电机驱动的弹性连杆式振动机械,研究了该非理想振动系统中的Sommerfeld效应。基于拉格朗日方程,引入交流电机的数学模型,建立了该振动系统的机电耦合动力学方程。应用平均法,推导了系统一次近似解析解及稳态运动时的电机运动方程。根据一次稳定性判别法,获得该系统的三个稳定性条件。通过对理论结果进行数值分析发现,交流电机驱动的非理想振动系统必须考虑机电耦合作用,因为其幅频特性曲线也具有硬式非线性特征。对存在转速跳跃现象的案例进行分析发现,其产生原因均是电机运动方程本身是超越方程,存在多根现象。需要将参数代入稳定性条件判断哪个状态是稳定的。上述理论结果通过时域仿真得到了验证。对质量、主振刚度、传动刚度、偏心半径和电机阻尼等系统参数进行了定量的数值讨论,可以为该类振动机械参数设计提供依据。 相似文献
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In this paper we consider generalized nonlinear discontinuity equation and try to obtain second-order approximation solution. In order to obtain these solutions we used modified Lindstedt-Poincare method. Then we extract solitonic solution from special case of generalized nonlinear discontinuity equation. These solution behave as particle like in the cold black holes and low temperature dark matter. Other application of these solution is in superfluid and superconductivity. 相似文献
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Sassaroli A Martelli F Fantini S 《Journal of the Optical Society of America. A, Optics, image science, and vision》2006,23(9):2105-2118
We approach the perturbative solution to the diffusion equation for the case of absorbing inclusions embedded in a heterogeneous scattering medium by using general properties of the radiative transfer equation and the solution of the Fredholm equation of the second kind given by the Neumann series. The terms of the Neumann series are used to obtain the expression of the moments of the generalized temporal point-spread function derived in transport theory. The moments are calculated independently by using Monte Carlo simulations for validation of the theory. While the mixed moments are correctly derived from the theory by using the solution of the diffusion equation in the geometry of interest, in order to obtain the self moments we should reframe the problem in transport theory and use a suitable solution of the radiative transfer equation for the calculation of the multiple integrals of the corresponding Neumann series. Since the rigorous theory leads to impractical formulas, in order to simplify and speed up the calculation of the self moments, we propose a heuristic method based on the calculation of only a single integral and some scaling parameters. We also propose simple quadrature rules for the calculation of the mixed moments for speeding up the computation of perturbations due to multiple defects. The theory can be developed in the continuous-wave domain, the time domain, and the frequency domain. In a companion paper [J. Opt. Soc. Am. A23, 2119 (2006)] we discuss the conditions of applicability of the theory in practical cases found in diffuse optical imaging of biological tissues. 相似文献
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Jian-Yu Lu Hehong Zou Greenleaf J.F. 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1995,42(5):850-853
Limited diffraction beams could have applications in medical imaging, tissue characterization, and nondestructive evaluation, as well as other wave related areas such as electromagnetics and optics. In this paper, we develop a novel approach that can convert any diffracting solution of the isotropic-homogeneous wave equation to a limited diffraction solution. As an example, this approach was applied to an n-dimensional wavelet solution that we generalized from the three-dimensional solution obtained by Kaiser et al. (1992). This example establishes a relationship between localized limited diffraction beams and the wavelet theory. The resulting limited diffraction beam was compared with those discovered previously 相似文献
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T. V. Hromadka G. L. Guymon 《International journal for numerical methods in engineering》1984,20(1):25-37
A generalized boundary integral equation method for the solution of the Laplace equation is developed based on the Cauchy integral theorem for analytical complex variable functions. Although the approach is complicated by the utilization of complex variable theory, the resulting model involves direct integration along straight-line boundary segments (elements) rather than using quadrature formulae that are required in current real variable boundary element formulations. Previously published boundary integral equation methods based on the Cauchy integral theorem are shown to be a subset of the generalized model theory developed in this paper. 相似文献
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Summary In the context of the generalized thermoelasticity theory, a mixed problem for the temperature equation is constructed by starting with a mixed problem for the coupled governing equations for the displacement and temperature fields. The uniqueness of solution of the former problem is established. A method of deducing a solution of the latter problem from that of the former problem is presented. 相似文献
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在全球气候变暖的极端反常的情形下,大气尘埃的扩散现象会带来巨大的灾害.本文研究了大气尘埃等离子体扩散的一类广义非线性孤立子波模型.首先对非扰动情形下利用待定系数法得到孤立子波解的解析表示式.其次用广义变分迭代的方法求出对应的变分乘子并构造变分迭代式,依次求出孤子波的各次迭代解.然后用行波变换得到广义非线性尘埃等离子体扰动模型的孤立子波的各次近似解.最后,由得到解的近似函数序列据变分理论知,在自变量的一定区域内此序列为一致收敛的.因此便证明了迭代解的极限函数是尘埃等离子体低频振动非线性方程的精确解.本文得到的近似解是尘埃等离子体的低频振动孤立子波的近似解析解,据它可用解析运算来求出相关量的物理性态,如孤立子波的波峰值.可以根据本文理论采取相应措施,避免出现电荷超高密度的聚集而导致放电击穿现象等. 相似文献