路面平整度的时间序列模型

介绍非标准道路的路面平整度的时间序列模型,研究道路实测数据的时间序列模型.通过对实际路段的数据采集,进行道路平整度实例分析和道路平整模型的平稳性检验、模型的识别和估计,确定了模型参数,检验模型的适用性.实例表明了模型的置性度和合理性.     

灰色GM(1,1)模型研究综述

GM(1,1)是灰色预测理论的核心模型和基础模型.从累加生成方法、初值优化、背景值优化、参数估计方法、模型性质和模型拓展的视角,梳理了GM(1,1)模型的研究进展.明确了有待进一步研究的问题,对GM(1,1)模型的未来研究方向提出了建议.     

路面平整度的时间序列模型

介绍非标准道路的路面平整度的时间序列模型,研究道路实测数据的时间序列模型.通过对实际路段的数据采集,进行道路平整度实例分析和道路平整模型的平稳性检验、模型的识别和估计,确定了模型参数,检验模型的适用性.实例表明了模型的置性度和合理性.     

成比例附加故障混合模型

Frailty模型和可加故障模型在研究各种风险因素与疾病发生原因的关系中提供了两种重要的方法.在不知哪个模型更适合数据时,涵盖这两个模型的成比例附加故障模型提供了一个备选模型.Frailty基本上是观察不到的,需要考虑对应的混合模型.本文研究了成比例附加故障混合模型的年龄性质、相依性质.并对该模型中的那些随机变量进行了随机比较.     

ARCH族模型及其对深圳股票市场的实证分析

ARCH族模型是动态非线性的股票定价模型,它在金融和经济领域具有广阔的应用前景.在短短二十年时间里取得了迅速的发展,先后提出了GARCH、ARCH-M、TARCH、EGRACH等模型丰富了ARCH族模型.本文从ARCH族模型出发,简要介绍了其主要形式和特点,然后将ARCH族模型运用于我国深圳股票市场的实证分析,从实证结果中总结深圳股市的总体特征.     

基于改进BP神经网络的电力负荷预测

在现有文献研究的基础上,对BP神经网络进行了深入研究,提出了一种新的LAFBP模型,给出了模型的标准BP算法、改进BP算法、权值和阈值的初始化方法.在此基础上,用新的LAFBP模型与传统的标准BP模型对黑龙江省巴彦县的电力负荷进行了预测.预测结果表明,新的LAFBP模型不仅克服了传统的BP模型外推效果不好的缺点,而且在模型的拟合精度、学习时间和学习次数方面明显优于传统的BP模型.     

多元失效时间数据的一般边际半参数危险率模型研究

在生物医学研究中,多元失效时间数据非常常见.该文提出用一般边际半参数危险率回归模型来分析多元失效时间数据.此模型包括了三种常用边际模型:边际比例风险模型、边际加速失效时间模型和边际加速危险模型作为子模型.对于模型中的回归系数,可以通过估计方程的方法来估计它,同时也给出了基准累积危险率函数的估计.得到的估计可以证明是相合的和渐近正态的.     

动态供应链网络均衡模型构建与分析

基于单一商品流,考虑了时间变量和库存问题,建立了三层动态供应链网络结构模型.对制造商、零售商和需求市场的多期独立决策行为及其相互作用进行了分析,应用变分不等式构建了各层均衡模型和整个供应链网络均衡模型.最后与相关文献的模型进行了比较.     

考虑外部效应与风险因素的多项目优化模型及应用

多项目的组合优化与资源分配优化,实质上是经济学中资源配置与利用问题.运用经济学与管理学的相关理论和定量研究方法,建立了外部效应估算模型、项目评价模型、风险估算模型、多项目组合优化模型和关于资源分配优化的两层决策模型.相关模型的应用实例研究,说明了该模型的有效性.     

基于光的波粒二象性猜想的数学仿真

从现有的经典物理光学理论和专业实验结果出发,运用数学思维,综合光子理论,建立了基于光的波粒二象性猜想的四种数学模型.针对光微子碰撞猜想,建立了基于光子碰撞后概率分布的模型.针对光子作为电磁场自我旋转的猜想,分别从专业证明和数学模型分析方面建立了电磁场偏转模型和光子旋转模型.最后建立了我们自己的猜想模型——光子蜂窝网络模型.该模型引入了"光子域"、"光子电力"、"光子磁力"、"光子键"等概念,从五个子模型出发,定性解释了四个光学现象,合理回答了题目提出的三大问题,并定量证明了衍射光强分布.     

Numerical modelling of shear-thinning non-Newtonian flow in compliant vessels

We present recent results on numerical modelling of non-Newtonian flow in two-dimensional compliant vessels with application in hemodynamics. Two models of the shear-thinning non-Newtonian fluids are considered and compared with the Newtonian model. For the structure problem the generalized string equation for radial symmetric tubes is used and extended to a stenosed vessel. A global iterative approach is used to approximate the fluid-structure interaction. At the end we present numerical experiments for selected non-Newtonian models, comparisons with the Newtonian model and the hemodynamic wall parameters: the wall shear stress and the oscillatory stress index. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Buckling analyses of three characteristic-lengths featured size-dependent gradient-beam with variational consistent higher order boundary conditions

In this work, a three characteristic-lengths featured size-dependent gradient-beam is constructed by adopting the modified nonlocal model, resulting in much more general constitutive equation with stress gradient up to four-order and strain gradient to two-order. The six-order differential governing equation for transverse displacement is formulated. All boundary conditions especially variational consistent higher order boundary conditions of the present model are derived with the aid of weighted residual approach. The closed-form solutions to critical buckling loads under different sets of boundary conditions are systematically formulated with higher order boundary conditions incorporated. The numerical results show that both nonlocal parameters have significant effect on the buckling behaviors. Meanwhile, if two nonlocal parameters are taken as same, the present results cannot always reduce to that from Eringen's nonlocal model. Due to its clear physical meaning, the present model is expected to be widely adopted in mechanical analyses of nano-structures.     

Constitutive equations of non-isothermal polymer melt

Constitutive equations of non-isothermal polymer melt are presented by the analysis of entropic free energy contribution of the macromolecular chains, which are treated as elastic dumbbell models. With describing non-isothermal dumbbell spring, as the function of temperature, the non-linear elastic coefficient expression causes the appearance of temperature gradient in stress constitutive equations. Following the constitutive equation of Hookean dumbbell model, non-isothermal stress constitutive equations of FENE and FENE-P models are derived. In deriving process of constitutive equations, the second moment approximation is used to closure FENE model. Using the non-isothermal constitutive equations, numerical simulations of polymer flow through shear cavity and planar contraction cavity are presented. And the distributions of correlative stress functions and the effects of different temperatures on stress functions are discussed. The present results are shown to explore the non-isothermal constitutive equations of elastic dumbbell models, and to search more accurately describing way of non-isothermal polymer melt.     

Power law fluid model for blood flow through a tapered artery with a stenosis

In the present paper, blood flow through a tapered artery with a stenosis is analyzed, assuming the flow is steady and blood is treated as non-Newtonian power law fluid model. Exact solution has been evaluated for velocity, resistance impedance, wall shear stress and shearing stress at the stenosis throat. The graphical results of different types of tapered arteries (i.e. converging tapering, diverging tapering, non-tapered artery) have been examined for different parameters of interest. Some special cases of the problem are also presented.     

Analytical and numerical techniques for predicting the interfacial stresses of wavy carbon nanotube/polymer composites

By introducing a new simplified 3D representative volume element for wavy carbon nanotubes, an analytical model is developed to study the stress transfer in single-walled carbon nanotube-reinforced polymer composites. Based on the pull-out modeling technique, the effects of waviness, aspect ratio, and Poisson ratio on the axial and interfacial shear stresses are analyzed in detail. The results of the present analytical model are in a good agreement with corresponding results for straight nanotubes. Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 45, No. 2, pp. 299-306, March-April, 2009.     

GFV solution on UTE mesh for transient modeling of concrete aging effects on thermal plane strains during construction of gravity dam

Considering variation of the material properties during early ages of construction, the strain–stress fields due to cement hydration induced transient temperature field in a section of a concrete dam are computed. The 2D matrix free Galerkin Finite Volume (GFV) method is utilized to solve temperature and plane-strain equations in a sequential manner on an Unstructured Triangular Elements (UTE) meshes. For the computed temperature field at each time step some iterative solutions are performed until the force equilibrium equations are converged. In the developed numerical model, a novel method to impose gradient boundary condition is introduced that is suitable for the GFV solution on UTE meshes. The results of the developed model is verified by comparing the computed results with the experimental measurements of some bench mark test cases, and good agreement is observed. To present the ability of the introduced model to model real problems, modeling time dependent thermal stress profiles during gradual construction of a concrete dam on a natural foundation is performed for both constant and variable mechanical properties conditions.     

A comparison of strain gradient theories with applications to the functionally graded circular micro-plate

The strain gradient theory of Zhou et al. is re-expressed in a more direct form and the differences with other strain gradient theories are investigated by an application on static and dynamic analyses of FGM circular micro-plate. To facilitate the modeling, the strain gradient theory of Zhou et al. is re-expressed in cylindrical coordinates, and then the governing equation, boundary conditions and initial condition for circular plate are derived with the help of the Hamilton's principle. The present model can degenerate into other models based on the strain gradient theory of Lam et al., the couple stress theory, the modified couple stress theory or even the classical theory, respectively. The static bending and free vibration problems of a simply supported circular plate are solved. The results indicate that the consideration of strain gradients results in an increase in plate stiffness, and leads to a reduction of deflection and an increase in natural frequency. Compared with the reduced models, the present model can predict a stronger size effect since the contribution from all strain gradient components is considered, and the differences of results from all these models are diminishing when the plate thickness is far greater than the material length-sale parameter.     

Functional Fatigue in polycrystalline Shape Memory Alloys

Shape memory alloys show the well known effect of pseudo-elasticity associated with the formation of two stress plateaus in the stress/strain diagram for tension tests. Due to cyclic loading, the stress plateaus decrease with every load cycle, particularly the upper one. This important effect of functional fatigue results from plastic deformations that are produced during solid-solid phase transformations between the austenitic and martensitic state. Outgoing from a polycrystalline approach for shape memory alloys we develop a micromechanical material model that is based on the Principle of the Minimum of the Dissipation Potential and predicts the evolution of plastic strains. Therefore, only a small number of material parameters is necessary and additionally, only a few assumptions are sufficient to model the effect of functional fatigue. We present yield functions as well as evolution equations for the volume fractions of austenite and martensite, and the plastic strains. Furthermore, we show an exemplary calculation for Nickel Titanium and compare it with experimental measurements to demonstrate the ability of our model. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Predicting initial erosion during the hole erosion test by using turbulent flow CFD simulation

CFD simulation with enhanced modeling of turbulence and near-wall treatment is used to model water–clay mixtures flowing through a cylindrical pipe domain. Effects on the wall-shear stress resulting from varying water clay content and applied hydraulic gradient are analyzed. Various parametric studies were performed and had shown that the two-dimensional modelling introduced in the present study does not yield a uniform wall-shear stress along the pipe wall and that clay concentration affects significantly the wall-shear stress value. This is in contrast with the common hypothesis used in one-dimensional modeling approaches where this stress is assumed constant and which gives rise to uniform erosion along the pipe wall. The obtained results had enabled predicting more realistically erosion amount and had allowed for understanding the irregular eroded hole wall shape as observed experimentally after performing the standard hole erosion test.     

An improved dynamic subgrid-scale model and its application to large eddy simulation of stratified channel flows

In the present paper, a new dynamic subgrid-scale (SGS) model of turbulent stress and heat flux for stratified shear flow is proposed. Based on our calculated results of stratified channel flow, the dynamic subgrid-scale model developed in this paper is shown to be effective for large eddy simulation (LES) of stratified turbulent shear flows. The new SGS model is then applied to the LES of the stratified turbulent channel flow to investigate the coupled shear and buoyancy effects on the behavior of turbulent statistics, turbulent heat transfer and flow structures at different Richardson numbers.