基于流形覆盖的岩体宏细观破裂的颗粒离散元法

本文基于流形覆盖的思想,结合颗粒接触模型,构造一种新的颗粒离散元数值方法即MPD(Manifold Particle Discrete),该方法可以从宏细观角度分析岩体破裂的全过程.通过分析流形覆盖和球颗粒模型,构造三维流形覆盖的四面体单元,得到MPD模型的平衡方程和相容方程.通过数值算例,验证了所提出的数值方法的正确性和分析岩石破裂的可行性.     

布拉格光纤光栅传感器在非均匀应变场中的响应分析

在非均匀应变场的作用下,布拉格光纤光栅的主要参数有效折射率和光栅周期都会发生非均匀的变化,导致光纤光栅的反射光光谱结构发生变化。在光波导耦合模理论的基础上,建立了布拉格光纤光栅在非均匀应变场下反射光谱的分析数学模型,利用龙格 库塔法对其进行了数值求解。给出了几种典型应变场下的布拉格光纤光栅的反射光谱,并分析了它们的特点。     

煤粒均相着火规律的研究

煤粒均相着火规律的研究张军，傅维标（清华大学工程力学系北京１０００８４）关键词均相着火，简化模型，预报１前言煤粉颗粒既能发生均相着火，又能发生非均相着火山。对非均相着火，许多学者进行了研究，取得了很多有价值的成果。均相着火由于比较复杂，一直发展缓慢。...     

多失效模式光电系统可靠性建模分析方法北大核心CSCD

系统可靠性建模分析是开展可靠性分配、预计、故障树分析及可靠性优化设计的基础。介绍了一种光电系统可靠性建模分析方法,针对光电系统中部分分系统具有多种失效模式且各失效模式均服从指数分布的特点,依据齐次马尔科夫理论,采用马尔科夫状态转移图方法建立了产品的可靠性模型,并给出解析表达式、数值计算方法和Monte Carlo仿真方法。最后,将其应用于某机载光电系统供电回路的实例分析中。采用两种计算方法及Monte Carlo仿真方法分别进行计算,并将结果进行对比分析,证明了该方法的正确性及可行性。     

气幕对潜艇声屏蔽作用的数值计算

本文利用惠更斯-菲涅尔原理和虚源方法建立了均匀海水中障碍物后声传播损失的计算模型,对模型进行了数值实验验证,并与海上试验数据对比,得到了较为合理的结果。     

激光束照射下内压柱壳热爆破数值模型

建立了研究内压柱壳在激光束照射下的破坏实验的热弹塑性数值模型。采用了与应变速率有关的耦合热传导分析,考虑了材料物理性质随温度的变化,考虑了内压是预先加载,考虑了热变形对结构刚度和荷载的几何非线性效应;采用子结构方法把耦合热传导分析和热弹塑性分析的区域局限在一个较小的范围内。数值结果与文献[1]的实验大致吻合,这表明本文建立的数值模型可以有效地描述这种“热软化”破坏的全过程。     

Brightness Temperature Emitted by Radiometer Calibration Load at Millimeter Wave Band

In this paper, the DVRT (vector radiative transfer theory of densely distributed random discrete scatters) model to calculate the brightness temperature emitted by radiometer calibration load is presented. It takes the multiple scattering of isolation layer into account, which is neglected by the incoherent homogeneous model often used in calibration. Hence, it works much better than incoherent homogeneous model at millimeter wave band. Furthermore, the iteration of DVRT model is presented, and it proves that the incoherent homogeneous model is just the zero-order solution of DVRT model. Some numerical results are provided in the end.     

Cascading failure in Watts-Strogatz small-world networks

In this paper, we study the cascading failure in Watts-Strogatz small-world networks. We find that this network model has a heterogeneous betweenness distribution, although its degree distribution is homogeneous. Further study shows that this small-world network is robust to random attack but fragile to intentional attack, in the cascading failure scenario. With comparison to standard random graph and scale-free networks, our result indicates that the robust yet fragile property in the cascading failure scenario is mainly related to heterogeneous betweenness, rather than the network degree distribution. Thus, it suggests that we have to be very careful when we use terms such as homogeneous network and heterogeneous network, unless the distribution we refer to is specified.     

混凝土HJC、RHT本构模型的失效强度参数

通过对LS-DYNA、AUTODYN数值软件中混凝土HJC、RHT本构模型失效强度参数的分析计算,发现原始失效强度参数在较高静水压下将导致混凝土失效强度降低.提出了利用混凝土的特征强度确定HJC、RHT失效强度参数的方法,并通过计算得出了校验后的失效强度参数值.最后,使用校验前后的失效强度参数进行了混凝土侵彻实验的数值...     

Mathematical modeling of the evolution of polaron states

The evolution of polarons in a homogeneous medium is studied depending on model parameters and initial conditions that are chosen in the form of various combinations of stationary polaron states. A computational scheme and results of numerical modeling are presented.     

Simulation study of the inhomogeneous Olami-Feder-Christensen model of earthquakes

Statistical properties of the inhomogeneous version of the Olami-Feder-Christensen (OFC) model of earthquakes is investigated by numerical simulations. The spatial inhomogeneity is assumed to be dynamical. Critical features found in the original homogeneous OFC model, e.g., the Gutenberg-Richter law and the Omori law are often weakened or suppressed in the presence of inhomogeneity, whereas the characteristic features found in the original homogeneous OFC model, e.g., the near-periodic recurrence of large events and the asperity-like phenomena persist.     

激光束照射下内压柱壳热爆破数值模型

 建立了研究内压柱壳在激光束照射下的破坏实验的热弹塑性数值模型。采用了与应变速率有关的耦合热传导分析，考虑了材料物理性质随温度的变化，考虑了内压是预先加载，考虑了热变形对结构刚度和荷载的几何非线性效应；采用子结构方法把耦合热传导分析和热弹塑性分析的区域局限在一个较小的范围内。数值结果与文献[1]的实验大致吻合，这表明本文建立的数值模型可以有效地描述这种“热软化”破坏的全过程。     

Numerical model of dual-wavelength erbium-doped fiber ring laser based on gain-equilibrium method

A novel numerical model of the dual-wavelength fiber ring lasers utilizing gain-equilibrium method is presented by developing the two level, homogeneous Giles model. To obtain the simulation method, the gain equilibrium condition is derived and modified to adapt to the iterative procedure in simulations. This condition is confirmed by both the numerical and experimental results, which indicate that the cavity losses of both wavelength channels play important roles in maintaining stable dual-wavelength emitting. The tolerant loss-bias is 0.05 dB in simulations and 0.4 dB in experiments, respectively. The difference between numerical and experimental results reveals that the inhomogeneous linewidth broadening of EDF contributes mostly to the improved power stability, but the loss vibrations play an important role in this effect.     

考虑中子泄漏修正的快堆蒙特卡罗少群截面参数制作与验证方法

一种基于B1均匀化方程的泄漏修正模型在连续能量蒙特卡罗程序TRIPOLI4中得以实现并且用于制作少群截面参数。此蒙卡泄漏修正模型通过在连续能量的蒙卡模拟以及求解B1均匀化方程之间迭代,最终得到蒙卡模拟下的临界状态。通过此方法得到的少群截面参数较其他蒙卡以及确定论方法有两点显著优势：用于求解B1均匀化方程的少群常数是用通过临界状态的通量谱得到的;考虑了泄漏效应的蒙卡模拟可以更真实地反映组件计算时的能谱状态。为验证此泄漏修正模型,一个由连续能量的TRIPOLI4模拟而得到的数值临界实验被用于分析与比较。通过与其他蒙卡程序SERPENT以及确定论程序ECCO进行结果对比,可证明此B1泄漏修正方法能够给出更精确的用于堆芯计算的少群截面参数。     

The weakly nonlocal limit of a one-population Wilson-Cowan model

We derive the weakly nonlocal limit of a one-population neuronal field model of the Wilson-Cowan type in one spatial dimension. By transforming this equation to an equation in the firing rate variable, it is shown that stationary periodic solutions exist by appealing to a pseudo-potential analysis. The solutions of the full nonlocal equation obey a uniform bound, and the stationary periodic solutions in the weakly nonlocal limit satisfying the same uniform bound are characterized by finite ranges of pseudo energy constants. The time dependent version of the model is reformulated as a Ginzburg-Landau-Khalatnikov type of equation in the firing rate variable where the maximum (minimum) points correspond stable (unstable) homogeneous solutions of the weakly nonlocal limit. Based on this formulation it is also conjectured that the stationary periodic solutions are unstable. We implement a numerical method for the weakly nonlocal limit of the Wilson-Cowan type of model based on the wavelet-Galerkin approach. We perform some numerical tests to illustrate the stability of homogeneous solutions and the evolution of the bumps.     

Exact solution of three-dimensional acoustic field in a wedge with perfectly reflecting boundaries

An exact approach is presented to compute the three-dimensional(3D) acoustic field in a homogeneous wedge-shaped ocean with perfectly reflecting boundaries. This approach applies the Fourier synthesis technique, which reduces a 3D point-source ideal wedge problem into a sequence of two-dimensional(2D) line-source ideal wedge problems, whose analytical solution is well established. A comparison of numerical efficiency is provided between this solution and the solution proposed by Buckingham,which is obtained by a sequence of integral transforms. The details of numerical implementation of these two solutions are also given. To validate the present approach and at the same time compare numerical efficiency between this approach and Buckingham's analytical solution, two numerical examples are considered. One is the Acoustical Society of America(ASA) benchmark wedge problem and the other is a wide-angle wedge problem. Numerical results indicate that the present approach is efficient and capable of providing accurate 3D acoustic field results for arbitrary receiver locations, and hence can serve as a benchmark model for sound propagation in a homogeneous wedge-shaped ocean.     

Conformal invariance and perturbations in the two-dimensional Ising model: Surface defects

The influence of homogeneous surface perturbations on the surface critical behavior of the two-dimensional Ising model is studied through finite-size scaling and conformal invariance. Quantum chains of up to 2000 spins are studied in the fermionic version of the model. The results are deduced from the numerical solution of an eigenvalue equation for the excitation spectrum and show that conformal invariance still works for irrelevant surface perturbations.     

非弹性散射对水体遥感反射率影响的数值模拟

基于矩阵算法建立了一个可用于模拟水体非弹性散射过程的水体辐射传输数值模型.该模型采用单个均匀介质层中辐射能量随深度增大而呈指数衰减的假设,将非弹性散射作为源矩阵算子引入到矩阵算法当中进行解算.通过Mobley水体辐射传输标准问题7的验证以及与Hydrolight 5.0结果的比较,说明该模型对多次散射和非弹性散射的处理...     

Frequency Characteristics of the Satureted Gain in Nonequilibrium Gas Flow and Doppler-Broadened Chemical Laser Amplifiers

We present "convection-nonequilibrium cross relaxation" model for a gas flow and chemical lasers, Teh experessions of the saturated gain spectrum are obtained for the two-type flow models with layer or turbulent flow mixture respectively. The numerical results show that the gain profile of a saturated amplifier with Doppler-broadening is a mixture of inhomogeneous and homogeneous profiles