ODTLES: A multi-scale model for 3D turbulent flow based on one-dimensional turbulence modeling

A novel multi-scale approach for extending the one-dimensional turbulence (ODT) model of [A.R. Kerstein. One-dimensional turbulence: model formulation and application to homogeneous turbulence, shear flows, and buoyant stratified flows, J. Fluid Mech. 392 (1999) 277] to treat turbulent flow in three-dimensional (3D) domains is described. In this model, here called ODTLES, 3D aspects of the flow are captured by embedding three, mutually orthogonal, one-dimensional ODT domain arrays within a coarser 3D mesh. The ODTLES model is obtained by developing a consistent approach for dynamically coupling the different ODT line sets to each other and to the large scale processes that are resolved on the 3D mesh. The model is implemented computationally and its performance is tested by performing simulations of decaying isotropic turbulence at two different Reynolds numbers and comparing to the experimental data of [H. Kang, S. Chester, C. Meneveau. Decaying turbulence in an active-grid-generated flow and comparisons with large-eddy simulations, J. Fluid Mech. 480 (2003) 129; G. Comte-Bellot, S. Corrsin, Simple Eulerian correlation of full-and narrow band velocity signals in grid-generated ’isotropic’ turbulence, J. Fluid Mech. 48 (1971) 273].     

颗粒动力学与湍动能耦合的稠密两相流动数学模型

在气相湍流流动的k-ε模型基础上,建立了颗粒动力学与湍动能耦合的稠密两相流动数学模型。颗粒相的有效粘性系数取决于颗粒之间相互碰撞而引起的层流粘性以及颗粒微团的湍流脉动而形成的湍流粘性,其中颗粒的碰撞行为以及所形成的颗粒的层流特性用颗粒动力学模型来描述,颗粒的湍流特性采用颗粒湍动能输运方程模型来描述。利用所建立的模型对提升管内气固两相流动过程进行了数值模拟,可以合理地预报出提升管内气固两相的环核流动结构。     

颗粒动力学与湍动能耦合的稠密两相流动数学模型

在气相湍流流动的κ-ε模型基础上，建立了颗粒动力学与湍动能耦合的稠密两相流动数学模型。颗粒相的有效粘性系数取决于颗粒之间相互碰撞而引起的层流粘性以及颗粒性以及颗粒微团的湍流脉动而形成的湍流粘性，其中颗粒的碰撞行为以及所形式的颗粒的层流特性用颗粒动力学模型来描述，颗粒的湍流特性采用颗粒湍动能输运方程模型来描述。利用所建立的模型对提升管内气固两相流动过程进行了数值模拟，可以合理地预报出提升管内气固两相的环核流动结构。     

Estimation of the kinetic energy dissipation in fall-arrest system and manikin during fall impact

Fall-arrest systems (FASs) have been widely applied to provide a safe stop during fall incidents for occupational activities. The mechanical interaction and kinetic energy exchange between the human body and the fall-arrest system during fall impact is one of the most important factors in FAS ergonomic design. In the current study, we developed a systematic approach to evaluate the energy dissipated in the energy absorbing lanyard (EAL) and in the harness/manikin during fall impact. The kinematics of the manikin and EAL during the impact were derived using the arrest-force time histories that were measured experimentally. We applied the proposed method to analyse the experimental data of drop tests at heights of 1.83 and 3.35 m. Our preliminary results indicate that approximately 84-92% of the kinetic energy is dissipated in the EAL system and the remainder is dissipated in the harness/manikin during fall impact. The proposed approach would be useful for the ergonomic design and performance evaluation of an FAS. STATEMENT OF RELEVANCE: Mechanical interaction, especially kinetic energy exchange, between the human body and the fall-arrest system during fall impact is one of the most important factors in the ergonomic design of a fall-arrest system. In the current study, we propose an approach to quantify the kinetic energy dissipated in the energy absorbing lanyard and in the harness/body system during fall impact.     

Numerical modeling of rarefied gas flow through a slit into vacuum based on the kinetic equation

A rarefied gas flow through a thin slit into vacuum is calculated on the basis of the kinetic model equations applying the discrete velocity method. The calculations are carried out for the whole range of the gas rarefaction from the free-molecular regime to the hydrodynamic one. Numerical data on the flow rate and distributions of density, bulk velocity and temperature along the symmetry axis are reported. A comparison with the corresponding results obtained previously by the direct simulation Monte Carlo method is performed. A good agreement between these results shows a reliability of the model equations which require less computational effort than the Monte Carlo method.     

基于预期剩余能量模型的聚焦爬行方法

如何确定搜索的方向和深度是聚焦爬行的核心问题。为此,提出了链接的预期剩余能量概念及其计算方法。该方法利用当前页面的信息计算链接的立即回报能量,利用到达同一链接不同历史路径给予的历史回报知识不断迭代更新链接的预期剩余能量。利用预期剩余能量作为链接的优先级和搜索深度限制,设计了基于预期剩余能量模型的聚焦爬行算法,并给出了关键模块的实现。实验结果显示该方法具有更强的主题网站发现能力。     

Analysis of the energy budget in turbulent channel flow using orthogonal wavelets

The spatial and scale statistics of turbulence kinetic energy are examined in turbulent channel flow at Re_τ = 300 using the orthonormal wavelet transform. The behaviour of the production, viscous and transfer terms is examined in terms of their variation with both space and scale. All terms are numerically large at wavenumbers at which a −5/3 slope is apparent in the velocity spectra, and they all exhibit significant spatial variability as evidenced by large flatnesses which increase with decreasing scale size. The flatness of terms involving transfer are particularly large. Attention focusses primarily on the sublayer and local-equilibrium regions: in the former, scale-to-scale flux is large and negative and consistent with conventional “backscatter” in Fourier space. In the linear sublayer, the flux is positive, consistent with Couette-like vortex stretching. The present work paves the way for close scrutiny of those components of the subgrid-scale stress that contribute most to the subgrid energy flux in large-eddy simulation of near-wall turbulent flows.     

基于剩余能量的局部更新路由算法

为了延长无线传感器网络(WSNs)的寿命,提出了一种基于剩余能量的局部更新路由算法(RE-RouA)。算法将节点的剩余能量融入到原算法过程中,在算法的虚拟汇聚节点选取阶段、数据收集树的构造阶段、路由更新阶段均进行了有效改进,增加了选取以及更新的条件,通过加权函数调整节点位置。实验结果表明:改进算法在保证网络延时不变的基础上,有效延长了WSNs的生命周期,实验效果显著。     

Density based topology optimization of turbulent flow heat transfer systems

The focus of this article is on topology optimization of heat sinks with turbulent forced convection. The goal is to demonstrate the extendibility, and the scalability of a previously developed fluid solver to coupled multi-physics and large 3D problems. The gradients of the objective and the constraints are obtained with the help of automatic differentiation applied on the discrete system without any simplifying assumptions. Thus, as demonstrated in earlier works of the authors, the sensitivities are exact to machine precision. The framework is applied to the optimization of 2D and 3D problems. Comparison between the simplified 2D setup and the full 3D optimized results is provided. A comparative study is also provided between designs optimized for laminar and turbulent flows. The comparisons highlight the importance and the benefits of full 3D optimization and including turbulence modeling in the optimization process, while also demonstrating extension of the methodology to include coupling of heat transfer with turbulent flows.     

基于多粒度的自适应UDP流检测

针对用户数据报协议(UDP)流检测研究不足,其准确率和效率不高等问题,提出一种基于多粒度的自适应UDP流检测方法。通过分析UDP流的特征,设计两种不同粒度的动态超时策略,对短流使用“细粒度”方法,对长流采用多粒度结合的方法。与其他超时策略比较,其准确率与固定超时相近,内存约占其他方法的75%。结果证实了方法适用于UDP流检测。     

Classification of turbulent flow patterns with fuzzy clustering

A pattern recognition technique for the identification of critical points in turbulent flows based on fuzzy C-means clustering is presented. The technique deals with, in particular, the problem that experimental data is normally obtained with coarsely spaced sensors making the identification of critical points uncertain. The technique was applied to hot-wire data from two different turbulent flows; one is the highly ordered wake of a mesh strip, while the second is the wake of a circular cylinder, which has a higher level of disorder. Foci and saddle points in the velocity fields were accurately detected and classified.     

利用多颜色信息融合的自适应肤色建模

客观世界中存在不同的光照、肤色和人种等因素,通常情况下难以建立一个通用的肤色模型进行各种裸露皮肤的检测。研究了一种自适应肤色建模方法,即利用AdaBoost算法检测人脸,通过这些人脸区域进行肤色建模。为了取得较好的肤色建模效果,适当缩小了由AdaBoost算法检测到的人脸区域;利用多颜色空间信息融合技术,即通过选取多个颜色空间的若干颜色分量,计算待检测图像中这些分量的各自SPM（肤色概率图）,经过“与”运算融合获得最终检测的肤色区域。该算法不需要考虑光照、肤色和人种等因素,是一种自适应的建模过程。实验表明,该算法可以有效解决绝大多数情况下的彩色图像肤色检测问题。     

一种基于流数约减的非线性公平采样算法

针对现有采样算法存在可扩展性和公平性差的问题,提出一种基于流数约减的非线性公平采样算法(adaptive fair sampling based on reducing flow numbers,AFS-RFN).AFS-RFN算法首先采用均匀抽样的方法对要统计流数进行约减,获得样本流集合;然后,对属于样本流集合的分组采用非线性的方法进行公平采样,实现控制统计流数目的同时保证统计流信息的准确性.仿真表明,与ANLS(adaptive non-linear sampling)算法相比,AFS-RFN算法大幅降低了存储开销,同时,将算法的公平性提高了60％.算法具有良好的可扩展性和公平性.     

一种基于剩余能量的无线传感器网络分簇协议

在无线传感器网络中,分簇技术可以实现高效的能量利用、方便的数据融合、灵活的网络扩展。簇首作为簇的中心,负责收集簇成员的数据,簇首消耗的能量远大于簇成员,因此,簇首的选择至关重要。提出了一种基于剩余能量的分簇协议（CPRE）,该协议优先选择剩余能量较多的节点作为簇首,并采用簇间转发的方式将数据发送到基站。仿真结果表明：该协议能够显著地延长网络的生存时间,其性能明显优于LEACH协议。     

基于低功耗技术的10kV电能记录仪的研究与开发

介绍了一种10kV用电户电能记录仪的设计。此装置由太阳能供电，采用低功耗嵌入式技术，完成电量数据的精确采集、存储，并具有红外通讯功能，实现10kV用户电能考核目的。该记录仪成本较低，结构简单，易于安装和拆卸。     

Finite element computation of turbulent flows with the discontinuity-capturing directional dissipation (DCDD)

The streamline-upwind/Petrov-Galerkin (SUPG) and pressure-stabilizing/Petrov-Galerkin (PSPG) methods are among the most popular stabilized formulations in finite element computation of flow problems. The discontinuity-capturing directional dissipation (DCDD) was first introduced as a complement to the SUPG and PSPG stabilizations for the computation of incompressible flows in the presence of sharp solution gradients. The DCDD stabilization takes effect where there is a sharp gradient in the velocity field and introduces dissipation in the direction of that gradient. The length scale used in defining the DCDD stabilization is based on the solution gradient. Here we describe how the DCDD stabilization, in combination with the SUPG and PSPG stabilizations, can be applied to computation of turbulent flows. We examine the similarity between the DCDD stabilization and a purely dissipative energy cascade model. To evaluate the performance of the DCDD stabilization, we compute as test problem a plane channel flow at friction Reynolds number Re_τ = 180.     

基于光流优化的堆叠Unet背景建模神经网络

针对现有背景建模算法难以处理复杂前景及间歇性运动前景的问题,提出了一种基于非监督学习的背景建模算法（改进的BM-Unet算法）。该算法结合光流法和Pearson相关系数在视频帧上提取背景关注区域,以此优化网络训练集和损失函数,从而有效提高了该算法在复杂前景情况和前景停留情况下的适应性;在此基础上,为进一步提高背景生成的精确度,又提出了一种堆叠Unet网络架构BM-SUnet（background modelling stacked Unet）。在SBMnet数据集上与现有算法在可视化效果和评估参数两方面的比较结果表明,所提算法在复杂前景和间歇运动前景情况下建模准确性好且鲁棒性高的结论。     

基于节点位置与剩余能量的LEACH协议优化

LEACH协议在簇头选举产生、能耗控制还存在许多问题,为此,对其产生方式提出改进.在原LEACH协议中加入网络中节点的具体位置信息和网络节点当前的剩余能量信息,在簇头选定阶段引入了备选簇头节点间距和模拟退火算法.在NS2上的仿真结果表明:改进的LEACH协议使簇头节点的选择更为合理,整个网络的寿命延长了50％,网络基站的接收数据量提高了175％.     

Adaptive finite-volume solution of complex turbulent flows

This paper describes an automatic local grid adaptation procedure driven by an evaluation of the differential residuals of the RANS equations computed using a higher-order reconstruction operator. A suitable data structure is developed for the local mesh adaptation process to be flexible and low CPU time consuming. The whole procedure is designed in the framework of finite-volume methods on unstructured grids. To avoid the appearance of ill-conditioned near-wall cells in the vicinity of curved surfaces of bodies a global mesh deformation technique is used. The whole procedure is applied to a complex turbulent flow around a high-lift multiple element airfoil in take-off configuration using the Spalart-Allmaras turbulence model. The adaptation is controlled by as many indicators as there are equations involved in the problem. It is demonstrated that the proposed methodology performs rigorous local adaptive mesh refinement and automatically achieves grid independent results. Thus, interesting gains are obtained in terms of CPU time, memory requirement and user effort compared to single mesh computations.