A mixed-timescale SGS model for thermal field at various Prandtl numbers

A new subgrid-scale (SGS) model for the thermal field is proposed. The model is an extended version of the mixed-timescale (MTS) SGS model for velocity field by Inagaki et al. (2005), which has been confirmed to be a refined SGS model for velocity field suited to engineering-relevant practical large eddy simulation (LES). In the proposed model for the thermal field, a hybrid timescale between the timescales of the velocity and thermal fields is introduced in a manner similar to velocity-field modeling. Thus, the present model dispenses with an ambiguous SGS turbulent Prandtl number, like the dynamic SGS model. In addition, the wall-limiting behavior of turbulence is satisfied, which is not in the original MTS model, by incorporating the wall-damping function for LES based on the Kolmogorov velocity scale proposed by Inagaki et al. (2010). The model performance is tested in plane channel flows at various Prandtl numbers, and the results show that this model gives the ratio of the timescales between the velocity and thermal fields similar to that obtained using the dynamic Smagorinsky model with locally calculated model parameters. It is also shown that the proposed model predicts better mean and fluctuating temperature profiles in cooperation with the revised MTS model for the velocity field, than the Smagorinsky model and the dynamic Smagorinsky model. The present model is constructed with fixed model parameters, so that it does not suffer from computational instability with the dynamic model. Thus, it is expected to be a refined and versatile SGS model suited for practical LES of the thermal field.     

基于最小概率DWO的激光陀螺温度误差模型辨识

鉴于激光陀螺温度误差模型的非线性和时变性,从提高模型辨识质量的需要出发,运用基于最小概率DWO（直接加权优化）的非线性系统辨识方法进行激光陀螺温度误差模型辨识研究,提出了一种精度更高的激光陀螺温度误差模型。该模型以带宽作为唯一需要确定的模型参数,避免了以往温度误差模型研究中的结构与参数辨识等复杂问题,从而在保证模型辨识质量的基础上,也相应提高了模型的适应能力,并通过两种温度误差特性有显著区别的激光陀螺（四频差动激光陀螺和二频机抖激光陀螺）的温度实验数据验证了该模型的正确性和适应性。     

汽车液压阻尼器的四段线性化模型

通过对现有某车用液压阻尼器的实验研究和车辆悬架系统动力学仿真研究，发现这种阻尼器的动力学特性存在复杂的非线性行为。为准确描述这类阻尼器的动力学特性和进行汽车悬架系统的动力学仿真研究，本文根据阻尼器的实验数据，提出一种新型四段线性化阻尼器模型，并建立其相应的数学模型。通过汽车悬架系统的动力学仿真研究表明，采用四段线性化阻尼器模型，汽车悬架系统簧载质量在不同路面不平度函数作用下的加速度响应和均方根加速度响应随频率变化不会出现大的波动。与等效线性化阻尼器模型相比，四段线性化阻尼器模型，能较好降低汽车悬架系统簧载质量的加速度响应和均方根加速度响应，有利于提高汽车乘坐舒适性和行驶稳定性，并为新型阻尼器设计提供一个新的思路。     

非完整系统动力学中的Vakonomic模型和Четаев模型

综述了非完整系统动力学中Чｅтａｅв模型和Ｖａｋｏｎｏｍｉｃ模型．论证了Ｈｅｒｔｚ,Ｃａｐｏｎ和Ｌｉｎｄｅｌｏｆ的工作与Ｖａｋｏｎｏｍｉｃ模型相吻合,而Ｈｏｌｄｅｒ,Ｐａｒｓ和Чаплыгин的工作与Четаев模型相吻合;Ｖａｋｏｎｏｍｉｃ模型和четаев模型两类模型并存的局面可以追溯到非完整力学发展的初期．说明了伴随两类模型并存的现象而出现的两个问题:ｄ－δ交换性问题和∫－δ交换性问题．综述了我国学者为统一两类模型作出的贡献．最后,展望了该领域的研究方向．      

基于最优加权组合模型及高斯－牛顿法的滑坡变形预测研究

在对最优加权组合理论和高斯－牛顿法优化非线性模型参数的方法研究的基础上,依托于洒勒山滑坡的实际变形监测资料,建立了该滑坡变形预测的3个非线性预测模型：指数模型、Verhulst模型和灰色GM（1,1）模型;利用最优加权组合理论建立了洒勒山滑坡的最优加权组合预测模型,并运用高斯－牛顿法对各单一模型和组合模型的参数进行了优化。通过对比分析得出：组合模型的预测精度高于任何单一模型的预测精度;参数优化后各单一模型的预测精度都有不同程度的提高;参数优化后的组合模型预测精度是最高的。因此,综合运用最优组合理论和高斯－牛顿法处理滑坡预测预报模型,是提高滑坡预测预报精度的行之有效的方法。     

结构动力学有限元模型修正的发展——————模型确认

结构动力学有限元建模精度问题是力学分支中受到广泛关注的研究课题之一. 以提高建模精度为目标的有限元模型修正技术的发展日臻完善, 并已逐步在工业界得到应用. 然而模型修正技术未能全面解决建模精度中存在的问题. 近几年以美国三大国家实验室为代表的科技人员提出了模型确认技术, 以希望全面解决结构动力学建模精度问题. 本文以模型修正为基础, 讨论模型确认的相关问题以及与模型修正的关系.      

基于多重子域代理模型的结构可靠性分析

基于合理子域概念，构建多重代理模型。多重代理模型在合理子域内采用经典响应面模型，在合理子域外采用经典Kriging模型，能够充分利用两种经典模型各自的优势。多重代理模型能够合理规避经典响应面模型中响应函数采取事先假定形式带来的可靠度评估风险，同时能够有效避免经典Kriging模型中试验点组合爆炸的问题。相比经典响应面模型，多重代理模型所需试验点数量并未增加，计算效率与经典响应面模型大体相同。算例表明，本文方法的计算结果与MCS的计算结果几乎一致，具有较好的计算精度。     

Gravitational forces in dual-porosity systems: II. Computational validation of the homogenized model

Three models are considered for single component, single phase flow in naturally fractured porous media. The microscopic model holds on the Darcy scale, and it is considered to govern the system. The macroscopic, dual-porosity model was derived in Part I of this work from the microscopic model by two-scale mathematical homogenization. In this paper, we show that the dual-porosity model predicts well the behavior of the microscopic model by comparing their computed solutions in certain reasonable test cases. Homogenization gives a complex formula for a key parameter in the dual-porosity model; herein a simple approximation to this formula is presented. The third model considered is a single-porosity model with averaged parameters. It is shown that this type of model cannot predict the behavior of the microscopic flow.This work was supported in part by the National Science Foundation and by the State of Texas Governor's Energy Office.     

混凝土损伤组合模型

在AUTODYN软件中成功嵌入了TCK模型,并总结了TCK模型中各参数的确定方法.结合TCK模型的嵌入,对AUTODYN中材料模型的二次开发进行了简要的介绍.应用AUTODYN中二次开发文件的调用规则,实现了TCK模型和RHT模型的组合,得到了组合模型,并指出了组合模型中TCK部分发生的一些变化和组合模型存在的一些问题.应用该组合模型对高速动能杆侵彻混凝土进行了仿真研究,仿真结果与试验结果符合的很好,说明该模型在高速冲击领域有很好的应用前景.     

CFD modeling using heterogeneous reaction kinetics for catalytic dehydrogenation syngas reactions in a fixed-bed reactor

A comprehensive 2D computational fluid dynamics （CFD） model was developed to simulate the flow behavior and catalytic dehydrogenation reaction of syngas in a heterogenous fixed-bed reactor （FBR）. The model combined the porous medium CFD model with a reaction kinetics model. To acquire an accu- rate reaction kinetics model, a comprehensive reaction mechanism was studied for the heterogeneous catalytic dehydrogenation reaction ofsyngas over a supported metal catalyst. Based on the reaction mech- anism and a statistical test, a reliable kinetics model was proposed. The CFD model combined with the above kinetics model was validated with one set of experimental data. The CFD model was also used to predict key reaction variable distributions such as the temperature and the component concentrations in the reactor.     

薄膜多层滚压的表面粗糙度晶体学分析

提出了晶体学模型来研究多层薄膜滚压的表面粗糙度。研究了单层滚压模型,提出滚压的三维模型和二维模型（平面应变）,讨论了晶粒大小和应力状态的影响。把单个单层滚压和多层滚压模型、三维模型和平面应变模型进行了比较,发现对于所涉及的二维和三维模型来说,单层滚压和多层滚压模型并无明显的差别。因此在这些情况下,可以用单个单层滚压模型来代替多层滚压模型从而节省CPU时间。     

多孔格栅均匀化模型平压仿真分析

为了研究均匀化方法在一种多孔格栅结构中的应用,从格栅单胞尺度入手,建立了一种适用于有限元仿真分析的三维周期性边界条件.以ABAQUS作为分析平台,对周期性边界条件下的格栅单胞模型进行了平压仿真分析,并将仿真结果与文献实验结果对比,验证了该边界条件的可靠性.利用均匀化理论建立了格栅单胞力学平衡方程,得到了格栅均匀化模型....     

A NON-ISOTROPIC MULTIPLE-SCALE TURBULENCE MODEL

This paper describes a newly developed non-isotropic multiple-scale turbulence model(MS/ASM)for complex flow calculations.This model focuses on the direct modeling of Reynolds stresses and utilizes split-spectrum concepts to model multiple-scale effects in turbulence.Validation studies on free shear flows,rotating flows and recirculating flows show that the current model performs significantly better than the single-scale k-εmodel.The present model is relatively inexpensive in terms of CPU time which makes in suitable for broad engineering flow applications.     

Calculation procedure to determine average mass transfer coefficients in packed columns from experimental data for ammonia–water absorption refrigeration systems

The ammonia purification process is critical in ammonia–water absorption refrigeration systems. In this paper, a detailed and a simplified analytical model are presented to characterize the performance of the ammonia rectification process in packed columns. The detailed model is based on mass and energy balances and simultaneous heat and mass transfer equations. The simplified model is derived and compared with the detailed model. The range of applicability of the simplified model is determined. A calculation procedure based on the simplified model is developed to determine the volumetric mass transfer coefficients in the vapour phase from experimental data. Finally, the proposed model and other simple calculation methods found in the general literature are compared.     

Photoelastic model measurement with rotated principal axes by scattered-light photoelasticity

The method of measurement of a three-dimensional photoelastic model with rotated principal axes has not yet been fully experimentally established. It is known that a three-dimensional photoelastic model can be reduced to an optically equivalent model. In this paper, the optically equivalent model is realized from a stratified model consisting of two layers of the frozen stress model. The secondary principal stress direction and the relative phase retardation of the frozen disk model in the stratified frozen stress model are determined for the entire field from Stokes parameters obtained by scattered-light photoelasticity using unpolarized light. The accuracy of these values is confirmed by a comparison with results only from the frozen stress disk model.     

孔隙网络模型在渗流力学研究中的应用

孔隙网络模型广泛地用于同多孔介质有关的微观模拟中. 本文简介了利用网络模型研究储层渗流规律的基本思想、主要步骤以及网络模型同其它微观模型相比较的优缺点, 总结了在微观渗流研究中使用的两大类网络模型(准静态网络模型和动态网络模型)的特征及其适用范围, 综述了目前网络模型在研究渗流中的应用现状以及国内外研究比较活跃的几个方面,最后分析了网络模型今后的发展趋向.      

Principles of Integrated Flow Modeling

Integrated flow modeling is the combination of a traditional flow simulator with a petrophysical model. By combining a petrophysical model with a traditional flow model, it is possible to perform calculations that improve our ability to monitor fluid movement in porous media. This paper outlines the formulation of an integrated flow model IFLO and its multi-variable, Newton–Raphson IMPES solution procedure. The benefits of integrated flow modeling and the underlying principles involved in the integration of a flow model with a petrophysical model are presented. Results from the IFLO model are used to illustrate the principles.     

Multi-layer analytic solution for k-ω model equations via a symmetry approach

Despite being one of the oldest and most widely-used turbulence models in engineering computational fluid dynamics (CFD), the k-ω model has not been fully understood theoretically because of its high nonlinearity and complex model parameter setting. Here, a multi-layer analytic expression is postulated for two lengths (stress and kinetic energy lengths), yielding an analytic solution for the k-ω model equations in pipe flow. Approximate local balance equations are analyzed to determine the key parameters in the solution, which are shown to be rather close to the empirically-measured values from the numerical solution of the Wilcox k-ω model, and hence the analytic construction is fully validated. The results provide clear evidence that the k-ω model sets in it a multilayer structure, which is similar to but different, in some insignificant details, from the Navier-Stokes (N-S) turbulence. This finding explains why the k-ω model is so popular, especially in computing the near-wall flow. Finally, the analysis is extended to a newly-refined k-ω model called the structural ensemble dynamics (SED) k-ω model, showing that the SED k-ω model has improved the multi-layer structure in the outer flow but preserved the setting of the k-ω model in the inner region.     

Comparison of a Rapidely Converging Phase Field Model for Interfaces in Solids with the Allen-Cahn Model

We compare two phase field models for interfaces in elastic solids carrying low surface energy. One model has hybrid properties of a Hamilton-Jacobi and a parabolic equation, the other is the Allen-Cahn model. For vanishing width of the interface we construct asymptotic solutions of second order for the hybrid model and of first order for the Allen-Cahn model. These constructions show that the width of the diffused interface necessary for tracking accurately the sharp interface can be chosen much larger for the hybrid model than for the Allen-Cahn model, and that moreover the hybrid model can describe interfaces with nonlinear kinetic relation. This explains why numerical simulations based on the hybrid model are considerably more effective. These simulations are discussed in the last section.     

关于二相流、多相流、多流体模型和非牛顿流等概念的探讨

本文分析了单相流、二相流和多相流等概念上的差异,也分析了单流体模型、双流体模型和多流体模型等概念上的差异,指出前面三种概念是按流动介质的客观物理构成划分的,而后者是按主观采用的研究方法划分的．目前这些概念在使用中存在一些混乱,如二相流与多相流,多相流与多流体模型等．本文还研究了扩散模型、非牛顿流模型和颗粒流模型等,指出前两种模型在分类上属于单流体模型,分析了非牛顿流模型、扩散模型和双（多）流体模型的特点和应用范围,最后,以泥石流为例讨论了以上概念的应用．