Conservative Models and Numerical Methods for Compressible Two-Phase Flow

The paper presents the computational framework for solving hyperbolic models for compressible two-phase flow by finite volume methods. A hierarchy of two-phase flow systems of conservation-form equations is formulated, including a general model with different phase velocities, pressures and temperatures; a simplified single temperature model with equal phase temperatures; and an isentropic model. The solution of the governing equations is obtained by the MUSCL-Hancock method in conjunction with the GFORCE and GMUSTA fluxes. Numerical results are presented for the water faucet test case, the Riemann problem with a sonic point and the water-air shock tube test case. The effect of the pressure relaxation rate on the numerical results is also investigated.     

Lagrangian data assimilation for river hydraulics simulations

We present a method to use Lagrangian data from remote sensing observation in a variational data assimilation process for a river hydraulics model based on the bidimensional shallow water equations. The trajectories of particles advected by the flow can be extracted from video images and are used in addition to classical Eulerian observations. This Lagrangian data brings information on the surface velocity thanks to an appropriate transport model. Numerical twin data assimilation experiments in an academic flow configuration demonstrate that this method makes it possible to significantly improve the identification of local bed elevation and initial conditions.     

Flutter prediction by an Euler method on non-moving Cartesian grids with gridless boundary conditions

A method is presented for the prediction of transonic flutter by the Euler equations on a stationary Cartesian mesh. Local grid refinement is established through a series of embedded meshes, and a gridless method is implemented for the treatment of surface boundary conditions. For steady flows, the gridless method applies surface boundary conditions using a weighted average of the flow properties within a cloud of nodes in the vicinity of the surface. The weighting is established with shape functions derived using a least-squares fitting of the surrounding nodal cloud. For unsteady calculations, a perturbation of the shape functions is incorporated to account for a fluctuating surface normal direction. The nature of the method provides for efficient and accurate solution of transient flow problems in which surface deflections are small (i.e. flutter calculations) without the need for a deforming mesh. Although small deviations in angle of attack are considered, the mean angle of attack can be large. Results indicate good agreement with available experimental data for unsteady flow, and with computational results addressing flutter of the Isogai wing model obtained using traditional moving mesh algorithms.     

Block-implicit multigrid calculation of two-dimensional recirculating flows

The performance of a recently developed calculation procedure for steady multidimensional fluid flows is assessed in four laminar two-dimensional recirculating flows representative of those in industrial equipment. The calculation procedure is based on a coupled solution of the momentum and continuity equations by the multigrid technique. The rate of convergence of the algorithm is critically assessed by varying the flow Reynolds number, the number of finite difference nodes, and the numerical underrelaxation factor. The procedure is observed to converge rapidly to an acceptable accuracy in all the flow situations.     

医院无线网络信息节点安全性度量方法研究

为了提高医院无线网络信息节点安全性,确保医院无线网络通信的畅通,提出一种基于传感器量化融合跟踪检测的医院无线网络信息节点安全性度量方法。构建医院无线网络信息节点的自适应转发控制模型,采用节点剩余能量融合识别方法进行节点的自适应调度,在物联网环境下实现医院无线网络信息节点的优化定位部署,构建节点的路由探测协议,利用医院无线网络信息节点自身的存活度进行无线传感网络模式下的节点转发链路均衡处理,采用传感器量化融合跟踪测试方法实现医院无线网络信息节点的安全性度量。仿真测试结果表明,采用该方法进行医院无线网络信息节点安全性度量的准确性较高,节点的能量开销较小,提高了节点数据转发的准确率。     

Image Sequence Interpolation Using Optimal Control

The problem of finding an interpolating image between two given images in an image sequence is considered. The problem is formulated as an optimal control problem governed by a transport equation, i.e. we aim at finding a flow field which transports the first image as close as possible to the second image. This approach bears similarities with the Horn and Schunck method for optical flow calculation but in fact the model is quite different. The images are modeled in the space of functions of bounded variation and an analysis of solutions of transport equations in this space is included. Moreover, the existence of optimal controls is proven and necessary conditions are derived. Finally, two algorithms are given and numerical results are compared with existing methods. The new method is competitive with state-of-the-art methods and even outperforms several existing methods.     

Free-boundary method for the numerical solution of gas-dynamic equations in domains with varying geometry

A novel method is proposed for numerical solution of gas-dynamic equations on stationary Cartesian grids in domains containing solid impermeable and, in the general case, moving inclusions (objects). The suggested technique is based on the immersed boundary method, in which the computational domain (including solid objects) is covered by a single Cartesian grid and the calculation is carried out by the shock-capturing method over all cells. Under this approach, the influence of the solid inclusions on the flow of the gas medium is simulated by the introduction of specially selected mass, momentum, and energy fluxes into the right-hand side of the equations. The currently developed methods for the solution of this class of problems are surveyed and the advantages of the proposed approach are discussed. The method is verified by calculating some test problems that admit analytical solutions and it is used to solve the problem of supersonic flow around a blunt body. The results are compared with the calculation findings based on the standard curvilinear grid tied to the geometry of the body.     

基于扩展的低阶多元广义线性模型的脑节点识别方法

针对现有单节点模型识别准确度较低以及低阶多元广义线性模型（LRMGLM）计算时间过长和使用局限性问题，提出基于扩展的低阶多元广义线性模型（ELRMGLM）的脑节点识别方法。首先，建立可以同时处理两次实验所有节点数据的ELRMGLM，以更多的时间空间信息来提高算法的准确度；然后，利用带时空平滑惩罚项的优化函数引入先验信息，并通过迭代函数对模型参数进行求解；最后，使用基于K-means的快速选择策略实现惩罚参数和大脑节点的快速选择。三次样本实验中，ELRMGLM的准确度分别比经典血液动力学响应函数（canonical）方法、平滑有限脉冲响应（SFIR）方法、正则化和广义交叉验证（Tik-GCV）方法的最优结果提升了约20%、8%、20%，略优于LRMGLM，且计算时间是LRMGLM的1/750。实验结果表明，ELRMGLM能有效提高大脑节点的识别准确度，减少计算时间。     

Arrival first queueing networks with applications in kanban production systems

In this paper, we introduce a new class of queueing networks called arrival first networks. We characterise its transition rates and derive the relationship between arrival rules, linear partial balance equations, and product form stationary distributions. This model is motivated by production systems operating under a kanban protocol. In contrast with the conventional departure first networks, where a transition is initiated by service completion of items at the originating nodes that are subsequently routed to the destination nodes (push system), in an arrival first network a transition is initiated by the destination nodes of the items and subsequently those items are processed at and removed from the originating nodes (pull system). These are similar to the push and pull systems in manufacturing systems.

Our characterisation provides necessary and sufficient conditions for the network to possess linear traffic equations, and sufficient conditions for the network to have a product form stationary distribution. We apply our results to networks operating under a kanban mechanism and characterise the rate at which items are pulled as well as the routing and blocking protocols that give rise to a product form stationary distribution.     

利用改进蚁群算法的重叠社团检测分析方法

针对重叠社团检测准确率提升问题,提出了一种基于改进蚁群算法的新型重叠社团检测算法。该算法包含位置初始化、运动和后处理三个阶段,分别通过初始位置识别与标签列表存储、基于节点间相似度的启发式信息重定义、合作保持标签列表等方式,使算法在合成数据集与现实世界数据集中的重叠社团与节点检测方面具有更好的性能。实验结果表明,在合成网络与现实世界网络平台上使用不同检测算法,所提出的方法对重叠社团与重叠节点的检测准确率较传统检测方法来说更高,因而对重叠社区检测问题求解与理解网络功能结构具有重要的参考与借鉴意义。     

Flows of rarefied gaseous mixtures in networks of long channels

A method is presented to calculate the steady flows of rarefied gaseous mixtures in networks of long channels. The approach is based on the kinetic level. First, the McCormack linearized kinetic model is solved to obtain the local flow properties in the channels in a wide range of gaseous rarefaction and mole fraction. Second, the global flow properties including the flow rates and the distribution of the pressure and the mole fraction are deduced. An integral equation is introduced in order to determine the flow rates as functions of the differences of the partial pressures between the two ends of each channel. The conservation of mass at the nodes of the network results into a system of linear algebraic equations. The overall mathematical problem is solved iteratively. Pressure driven flows of He/Xe and He/Ar through an example network of circular tubes are calculated at intermediate values of the gaseous rarefaction. The results of the flow rates and the pressures and the mole fractions at the nodes in the whole system and the representative distributions of the pressure and the mole fraction along the channels are presented and commented on.     

Modeling steady axis-symmetric thermal plasma flow of air by a parallelized magneto-hydrodynamic flow solver

This paper discusses a parallelized magneto-hydrodynamic flow solver for modeling axis-symmetric thermal plasma flow using Cartesian grid system and taking the induced electrical and magnetic effects into account, where the magneto-hydrodynamic equations, including the continuity equation, momentum equations, energy equation, current continuity equation and turbulence transport equations are solved by a finite volume discretization in a segregated manner. The thermal plasma flow of a 476 mm long, transferred well-type plasma torch operating with air is simulated for two power conditions, i.e. I = 432 A and 901 A, to demonstrate the capability of proposed numerical model to analyze the heat and mass transfer characteristics of axis-symmetric thermal plasma flow, where the location of cathode is determined by fixing the measured voltage drop between two electrodes. The numerical calculation suggests that the high-power case can deliver an axial velocity of 400 m/s and 15,000 K in temperature at the center of torch outlet, where a strong jetting vortex is expected emitting from the torch body. The low-power case is predicted with a longer electric arc than that of the high-power one, which clearly results in a large high-temperature region between the gas inlet and cathode and unfavourable to reduce the cathode erosion and to increase thermal efficiency.     

Lattice Boltzmann method for variable density shallow water equations

A lattice Boltzmann method is developed for solution of a form of the shallow water equations that is suitable for flows which are fully mixed in the vertical direction but have variable density in the horizontal plane. In the present approach, double distribution functions are applied: one for the shallow water flows and the other for the mass transport. Direct coupling between the water flow and mass transport is achieved by updating the flow density from the concentration during simulation. Accuracy and applicability of the model are demonstrated by two numerical tests: the stationary hydrostatic equilibrium of liquid of variable density in a tank with non-uniform bed terrain, and the horizontal diffusion of species with an initial Gaussian distribution of concentration in a uniform flow field.     

Gas-mass-flow transfer-rate simulation and experimental evaluation in microchannels

Continuum hydrodynamics accurately describes the flow of fluids over a wide range of systems. However, continuum models are unable to adequately describe the flow of fluid under extreme confinement. In particular, the no-slip boundary condition invoked in continuum flow calculations is violated for low density gases flowing in microtubes or nanoporous materials. The calculation of gas-mass-transfer rate in microtubes using experiments and simulation is investigated in the case of small absolute pressures. Specifically, in the present work, Argon, Helium, and Air gas is considered in a 3D model of two metallic tanks connected through microchannels. The pressure difference between the inlet and the outlet of the structure is monitored as a function of time. Thus the gas- transfer-rate is evaluated and compared with experimental data, in order to verify the departure from the standard Navier–Stokes equations with the no-slip boundary condition.     

综合能源热力潮流节点标幺值模型及算法实现

潮流计算是综合能源能量管理的基础,已有的综合能源潮流计算模型,采用电力网络节点模型与热力网络回路模型组合,实时潮流计算过程中,要在网络拓扑形成节点之后,搜索供热网络回路,形成多个独立的最小热力回路,在最小回路模型的基础上,做牛顿法潮流计算;为了方便与电网潮流的节点模型组合,提高综合能源潮流计算的算法效率和收敛性能,我们采用热力网络潮流节点标幺值模型,用热力节点的供水温度、回水温度、供水压力、回水压力作为热力网络状态量,用回水、供水节点净注入流量为零、回水、供水节点节点的注入能量为零作为基础模型,采用变尺度算法解热力潮流非线性方程组,只计算一次雅可比矩阵并求逆,通过递推来实现潮流计算,克服了牛顿法需要多次求导求逆的缺点,避免了搜索实时网络的最小回路,方便与电力网络节点模型联合求解,更适合大规模热-电联合系统中的潮流计算。     

煤粒瓦斯解吸时变规律实验研究

针对目前瓦斯解吸研究采样范围小、解吸模型计算结果与实测数据之间存在误差等问题,采集多个煤矿的煤样进行解吸实验,扩大煤样采集范围;基于搭建的煤粒瓦斯解吸实验平台,采用控制变量法,分析煤粒在不同吸附平衡压力、不同温度、不同粒度下的瓦斯解吸时变规律。得出以下结论:吸附平衡压力越大,瓦斯解吸量越大;粒度越大,解吸量和解吸速度越小,到达阈值粒度后,粒度对解吸量和解吸速度的影响较小;温度越高,解吸量越大;随着时间的增加,瓦斯解吸量逐渐增加,瓦斯解吸速度逐渐减小。对不同地质条件下的煤样进行解吸实验研究,提高了瓦斯解吸模型的适用性,进一步验证了温度、粒度等主控因素对瓦斯解吸规律的影响。     

Simulation algorithm for piston ring dynamics

Piston ring dynamics play important roles on the lubricant characteristic of reciprocating engines which lead to the consequences of engine wear and vast amount of lubricating oil consumption. Due to the complexity of motion, a study of motions and effects of the piston ring is mostly conducted in a simulation program. This paper shows a theoretical work and a new simulation algorithm of the 3D piston ring motions. The simulation concept is to determine the positions of the piston ring, which are the solutions of the Newton and Euler equations. Well known models like mixed lubrication model, asperity contact model, and blow-by/blow-back flow model were used in this study. The new simulation algorithm consists of four processes: construction of calculation nodes, use of finite different method, determination of the non-linear equation system, use of parallel computational technique.Two sets of the experimental studies were conducted for simulation verification. First, the gas flows through the static rectangular piston ring pack. Second, the blow-by/blow-back gas flow through the piston ring pack of a single cylinder diesel engine. The good agreement between the experimental and simulation results indicates that the developed simulation program can illustrate the piston ring motions and blow-by/blow-back flow. Since there is no algebraic equation in the ring profile, the presented simulation technique is suitable for the complicated surface of the piston and piston rings.     

Numerical investigation of heat and mass transfer flow under the influence of silicon carbide by means of plasma-enhanced chemical vapor deposition vertical reactor

The effect of characteristics flow (contour of velocity), mass transfer (Sherwood number) and heat transfer (Nu number) on the growth rate of silicon carbide by means of plasma-enhanced chemical vapor deposition vertical reactor is investigated. The species transport and thermal fluid transport with chemical reaction are taken into account. The steady-state laminar fluid flow and gas flow having ideal behavior are considered. A mixture of silane and propane (2% molar) as main reactant gases and hydrogen (96% molar) as propellant gas are injected into the reactor. Four different diameters of shower head, three different substrate rotation speeds and five different temperatures of the substrate are used. The finite volume method is employed to solve the problem. The governing equations are solved by upwind differencing scheme. The assumption of speed–pressure coupling leads to use of semi-implicit method for pressure-linked equations to solve the governing equation. It is found that the deposition rate reduces with the shower head diameter and value of substrate temperature and enhances with rotational speed of the substrate. Furthermore, the best shower head diameter to achieve maximum rate of deposition is 1 mm. At the end, a comparison as a limiting case of the considered problem with the existing studies is made. Comparing the results of this experiment with prior studies has shown acceptable consistency.

     

基于感知源的数据驱动信任评测模型

为解决物联网数据源头的可靠问题,构建一种基于感知源的数据驱动信任评测模型.模型以监测模块为评测单元,由中继节点完成其所在监测模块内感知节点的信任评测,通过感知节点自身数据之间的关系实现直接信任的计算,利用监测模块内各邻居节点之间关系实现推荐信任的计算,再结合历史信任,输出感知节点的综合信任.同时与模型预设的可疑阈值和异常阈值进行对比,更新历史信任和信任列表,实现感知节点的异常检测,利用预警检测误差和失信检测误差对模型的检测效果进行评价,统计结果表明模型能够保持较低的平均误差.将信任机制引入到数据融合过程,用综合信任作为加权因子,从而提高了数据融合的准确度.最后,通过实验仿真对信任评测模型进行评价,结果表明引入信任评测模型后延长了节点开始死亡的时间,随着节点的更新迭代,失信节点越来越少,在一定程度上提高了节点的存活率,延长了网络的生命周期.