Dynamical structure of the turbulent boundary layer on rough surface

The experiments on structure of turbulent boundary layer on the plane rough wall without pressure gradient are presented. Sand roughness of the wall is considered. Measurements are carried out using Time-Resolved PIV technique in planes parallel and perpendicular to the wall. The results on rough wall are compared with the base case of boundary layer on smooth wall. Hairpin vortices have been detected. Topology and typical size of those structures substantially differ in the cases in question. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Analysis of melting behavior of PCMs in a cavity subject to a non-uniform magnetic field using a moving grid technique

Melting flow and heat transfer of electrically conductive phase change materials subjecting to a non-uniform magnetic field are addressed in a square enclosure. The top and bottom walls of the cavity are adiabatic, and the sidewalls are isothermal at different temperatures. The temperature of the hot wall is higher than the fusion temperature of PCM (T_f), and the cold wall is at the fusion temperature or lower. At the initial time, the cavity is filled with a solid saturated PCM. In the vicinity to the hot wall, there is an external line-source magnet, inducing a magnetic field. The location of the magnetic source (Y₀) can be changed along the hot wall. The cavity domain is divided into two parts of the liquid domain and the solid domain. The moving grid method is utilized to track the phase change interface at the exact fusion temperature of T_f. The governing equations for continuity, flow and heat transfer associated with the Arbitrary Lagrangian–Eulerian (ALE) moving mesh technique are solved using the finite element method. The results are investigated for the melting behavior of PCM by the study of Hartmann number (0 ≤ Ha ≤ 50) and the location of the magnetic source (0 ≤ Y₀ ≤ 1). Outcomes show that the effect of the magnetic field on the melting behavior of PCM is negligible at the initial stages of the melting (Fo < 1.15). However, after the initial stages of the melting, the effect of the presence of a magnetic field becomes significant. Moreover, the location of the magnetic source induces a feeble effect on the melting front at the initial melting stages, but its effect on the shape of the melting front increases by the increase of the non-dimensional time. The location of the magnetic source also significantly affects the streamlines patterns. Changing the position of the magnetic source from the bottom of the cavity (Y₀ = 0.2) to the almost middle of the cavity (Y₀ = 0.6) would decrease the required non-dimensional time of full melting from Fo = 10.4 to Fo = 9.0.     

On the Cardiovascular Effects of Whole-Body Vibration Part I. Longitudinal Effects: Hydrodynamic Analysis

For a given direction of whole-body vibration and a given piece of blood vessel, the local vibration has in general both a longitudinal (parallel) component and a lateral (perpendicular) component. The longitudinal and lateral effects are treated in Part I and Part II, respectively. In Part I, detailed hydrodynamic analysis shows that the maximal shear stress at the wall of the vessel is considerably increased by the longitudinal component of vibration for big vessels. For example, for high frequency range 40–50 Hz, the maximal shear stress at the wall of coronary artery could increase by 35–49% even if the local longitudinal amplitude is as small as 50 μm. Potential benefits and risks associated with this effect are discussed. In Part II, statistical analysis is carried out based on the results of specially designed experiments, where accelerations at different body locations and some cardiovascular parameters were measured simultaneously. Some changes of body mode were arranged during the vibration experiments in a way that the transmissibility of vibration increased considerably during each change of body mode. Statistical analysis of the results suggests with high level of confidence (>97%) that arterioles were dilated during such changes of body mode. Potential benefits associated with this effect are discussed.     

Numerical investigation into a liquid displacing a gas in thin porous layers

To examine the filling process in a lithium-ion battery, a numerical model to characterize the displacing flow of a liquid in air-filled pores of thin heterogeneous porous materials is elaborated. The investigation is based on the volume-averaged Navier-Stokes equations for small Reynolds numbers, using a volume-of-fluid method to cover the multiphase flow. The flow is investigated with respect to the wall effect and to capillary action within the porous matrix. On the one hand, model experiments with similar particle-size distributions as in the battery layers are conducted to extract the porosity as function of the wall distance. On the other hand, experiments with the three different porous layers of the battery are performed to receive mean values for the most important properties related to the two-phase flow. Results for the displacement flow in parts of the battery are presented and discussed, showing a considerable influence of the modeled effects onto the flow characteristics. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Hierarchical and conditional combination of belief functions induced by visual tracking

In visual tracking, sources of information are often disrupted and deliver imprecise or unreliable data leading to major data fusion issues. In the Dempster-Shafer framework, such issues can be addressed by attempting to design robust combination rules. Instead of introducing another rule, we propose to use existing ones as part of a hierarchical and conditional combination scheme. The sources are represented by mass functions which are analysed and labelled regarding unreliability and imprecision. This conditional step divides the problem into specific sub-problems. In each of these sub-problems, the number of constraints is reduced and an appropriate rule is selected and applied. Two functions are thus obtained and analysed, allowing another rule to be chosen for a second (and final) fusion level. This approach provides a fast and robust way to combine disrupted sources using contextual information brought by a particle filter. Our experiments demonstrate its efficiency on several visual tracking situations.     

Modeling of individual coherent structures in wall region of a turbulent boundary layer

Models for individual coherent structures in the wall region of a turbulent boundary layer are proposed. Method of numerical simulations is used to follow the evolution of the structures. It is found that the proposed model does bear many features of coherent structures found in experiments.     

A method of calculating ice loads when ice piles up on a fixed wall

A model for calculating ice loads on a shelf ice-resistant platform is developed which corresponds to a cyclic scenario of the interaction of ice with the wall of a platform observed in laboratory experiments. Using relations which follow from the laws of conservation of mass, momentum and energy written for ice which fills a ridge formed at the wall of the platform, an explicit formula is obtained for the ice load on the wall. The generalized forces characterizing the dependence of the energy dissipation accompanying ridging on the dimensions of the sail and keel of the ridge and on the shape of the wall are parametrized. It is shown that the calculated loads obtained using the assumption of hydrostatic equilibrium of the sail and the keel of the ridge correspond to the lower boundary of the experimentally measured loads. The calculated loads obtained using the assumption that the keel of a ridge is of constant size yield an upper estimate of the ice loads. In order to estimate the limit loads at which collapse of the ice into the water occurs, a problem on the formation of a flexural crack in an ice floe which is thrust onto the wall is considered. The average and maximum ice loads on the wall of a platform are calculated on a real scale.     

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)     

基于Huber正则化的红外与可见光图像融合

图像融合通常是指从多源信道采集同一目标图像,将互补的多焦点、多模态、多时相和/或多视点图像集成在一起,形成新图像的过程.在本文中,我们采用基于Huber正则化的红外与可见光图像的融合模型.该模型通过约束融合图像与红外图像相似的像素强度保持热辐射信息,以及约束融合图像与可见光图像相似的灰度梯度和像素强度保持图像的边缘和纹理等外观信息,同时能够改善图像灰度梯度相对较小区域的阶梯效应.为了最小化这种变分模型,我们结合增广拉格朗日方法(ALM)和量身定做有限点方法(TFPM)的思想设计数值算法,并给出了算法的收敛性分析.最后,我们将所提模型和算法与其他七种图像融合方法进行定性和定量的比较,分析了本文所提模型的特点和所提数值算法的有效性.     

Open-surface MHD flow over a curved wall in the 3-D thin-shear-layer approximation

3-D thin-shear-layer equations for flows of conducting fluids in a magnetic field have been derived in orthogonal body-oriented coordinates and then applied to the analysis of MHD open-surface flows over a curved wall. Unlike the classic boundary-layer-type equations, present ones permit information to be propagated upstream through the induced magnetic field. Another departure from the classic theory is that the normal momentum equation keeps the balance between the pressure gradient term, and those related to gravity, centrifugal forces, and Lorentz force. Thus, the normal pressure variations are allowed. The model describes basic 3-D effects due to the wall curvature and spatial variations of the applied magnetic field. As a particular case, equations for flows with rotational symmetry have been derived. Numerical calculations were performed for open-surface flows over a body of revolution under conditions relevant to a fusion reactor (Hartmann number is 8500). Some specific flow patterns, such as flow thickening and spiral-type flows, have been observed and discussed. A special attention has been paid to the analysis of the magnetic propulsion as a tool for the active flow control by applying an electric current. It has been shown that depending on the applied current, the axial pressure gradient can act as an adverse pressure gradient or propulsion force.     

周期压力驱动下管壁局部不规则的圆管Poiseuille流感受性问题

采用渐近分析方法,建立了在周期压力驱动下,完全发展的圆管Poiseuille流当管壁存在局部不规则几何形状时的感受性问题模型．通过特征函数的双正交系统,应用Chebyshev配点法进行数值求解．通过算例计算,获得周期压力和矩形突起激发起的流体系统中的各种空间发展模态以及相应的感受性系数．从计算和分析可以知道,在流场的不同发展阶段不同的模态起着主导作用,这与在试验中观察到的扰动流场在不同位置的特性是一致的．     

Modeling of individual coherent structures in wall region of a turbulent boundary layer

Models for individual coherent structures in the wall region of a turbulent boundary layer are proposed. Method of numerical simulations is used to follow the evolution of the structures. It is found that the proposed model does bear many features of coherent structures found in experiments. Project supported by the National Natural Science Foundation of China (Grant No. 19732005) and National Climbing Project.     

Ab-initio molecular dynamics simulation on nano-system under external pressure

A new constant-pressure molecular dynamics (MD) method is developed to simulate the dynamic behavior and structure transition of finite system under external pressure. In this method, no artificial parameter is introduced and the computation overheads are very small. As an application, a hard-soft transition of single wall carbon nanotube     

固壁近旁Stokes流中粘性液滴的运动和变形

发展了一种模拟固壁近旁轴对称Stokes流中粘性液滴的运动和变形及直接计算固壁上应力的边界积分方法．用此方法对不同的液滴-固壁初始相对间距、粘度比、表面张力和浮力联合参数以及环境流动参数情况进行了数值实验．数值结果显示,由于环境流动和浮力的作用,随着时间的推进,液滴在轴向压缩,在径向拉伸．当环境流动的作用弱于浮力作用时,随着时间的推移,液滴上升并向上弯,固壁上由液滴运动所引起的应力不断减小．当环境流动的作用强于浮力作用时,随着时间的推移,液滴变得越来越扁．在这种情形,当大初始间距时,壁面上的应力随液滴的演变而增大;当小初始间距时,由环境流动、浮力及壁面对流动的较强作用的联合影响,此应力随液滴的演变而减小．由于液滴运动所引起的壁面应力的有效作用仅限于对称轴附近的一个小范围内,且此范围随液滴与固壁的初始间距增大而增大．应力的大小随初始间距增大而大为减小．表面张力对液滴变形有阻止作用．液滴粘性会减小液滴的变形和位置迁移．     

基于多特征信息自适应融合的视频目标跟踪算法

针对单一视觉特征跟踪的局限性,提出一种根据场景变化动态建立目标模型的粒子滤波视觉跟踪算法,方法首先选择简单且具有互补性的色彩与纹理特征描述表示当前图像,然后在粒子滤波框架下,利用民主融合策略进行信息融合,从而提高目标观测模型的鲁棒性;分析和实验表明, 算法对视频运动目标的任意平移、转动、部分遮挡、光照变化以及相似物干扰等情况下的跟踪均具有较好的效果.     

Ab-<Emphasis Type="Italic">initio</Emphasis> molecular dynamics simulation on nano-system under external pressure

A new constant-pressure molecular dynamics (MD) method is developed to simulate the dynamic behavior and structure transition of finite system under external pressure. In this method, no artificial parameter is introduced and the computation overheads are very small. As an application, a hard-soft transition of single wall carbon nanotube (SWCNT) under external pressure is found, which is in agreement with the experiments.     

Approximate solution to the nonlinear problem of an underground pipeline deformation

Some geometrically nonlinear mathematical model is constructed of a pipeline as a shell in a strongly viscous medium. We find a universal procedure for reducing the two-dimensional equations of motion to the one-dimensional equations for long bent pipes. We also constructed a difference scheme and propose a software complex for numerical analysis of the equations under study. Some numerical experiments are conducted for a particular case of a bent pipeline, the deformations of the pipe wall are found, and the displacement of its centerline is calculated.     

X-ray absorption spectra of plasmas

In this paper we present a theoretical method to calculate the absorption spectra of hot dense plasmas. Based on our fully relativistic treatment incorporated with the quantum defect theory to handle the huge number of transition arrays from many configurations with high principal quantum number, we can calculate the absorption spectra for any element or multi-element plasmas with little computational efforts. We calculate the absorption spectra of C10H1605 plasmas, which are in good agreement with the experimental spectra. We can then provide diagnostic analysis for plasmas in relevant inertial confinement fusion (lCF) experiments; namely not only to determine plasmas' temperatures and densities, but also to provide the population densities of various ionic stages. Our theoretical method verified by "benchmark experiments" will be a basic tool to provide "precise" opacity data for the ICF research.``     

Ab-initio molecular dynamics simulation on nano-system under external pressure

A new constant-pressure molecular dynamics (MD) method is developed to simulate the dynamic behavior and structure transition of finite system under external pressure. In this method, no artificial parameter is introduced and the computation overheads are very small. As an application, a hard-soft transition of single wall carbon nanotube (SWCNT) under external pressure is found, which is in agreement with the experiments.

     

One singularly perturbed Stefan problem describing destruction of the fuel layer in a laser target

A mathematical model of degradation of a deuterium-tritium (D-T) fuel layer located on the interior wall of a spherical shell is proposed. Such a shell with a solid layer frozen on it is a laser target that is employed in controlled thermonuclear fusion. As the laser target is delivered from the cryogenic chamber to the focus of the laser beam, the chamber stays, during a certain time interval, in a warm-gas cloud. During this time interval, the D-T layer degrades, and, in particular, its surface becomes nonideal. The mathematical model is formulated as a Stefan problem for a system of parabolic equations with nonlinear initial-boundary conditions. Small-parameter methods are applied to obtain an analytic solution to this problem, and the time during which the changes in the geometric parameters of the target’s fuel layer do not exceed technologically admissible values is estimated.