Direct numerical simulations of transverse and spanwise magnetic field effects on turbulent flow in a 2:1 aspect ratio rectangular duct

Magnetic fields are used extensively to direct liquid metal flows in material processing. Continuous casting of steel uses different configurations of magnetic fields to optimize turbulent flows in rectangular cross-sections to minimize defects in the solidified steel product. Realizing the importance of a magnetic field on turbulent flows in rectangular cross-sections, the present work is aimed at understanding the effect of a magnetic field on the turbulent metal flow at a nominal bulk Reynolds number of ∼5300 (based upon full duct height) (Re_τ = 170, based upon half duct height) and Hartmann numbers (based upon half duct height) of 0, 6.0 and 8.25 in a 2:1 aspect ratio rectangular duct. Direct numerical simulations in a non-MHD 2:1 aspect ratio duct followed by simulations with transverse and span-wise magnetic fields have been performed with 224 × 120 × 512 cells (∼13.7 million cells). The fractional step method with second order space and time discretization schemes has been used to solve the coupled Navier-Stokes-MHD equations. Instantaneous and time-averaged natures of the flow have been examined through distribution of velocities, various turbulence parameters and budget terms. Spanwise (horizontal) magnetic field reorganizes and suppresses secondary flows more strongly. Turbulence suppression and velocity flattening effects are stronger with transverse (vertical) magnetic field.     

Existence of optimal controls for systems driven by FBSDEs

We prove the existence of optimal relaxed controls as well as strict optimal controls for systems governed by non linear forward-backward stochastic differential equations (FBSDEs). Our approach is based on weak convergence techniques for the associated FBSDEs in the Jakubowski S-topology and a suitable Skorokhod representation theorem.     

固定区间Kalman平滑新算法

用现代时间序列分析方法,基于ＡＲＭＡ新息模型和白噪声估值器,提出了一种正向固定区间稳态Ｋａｌｍａｎ平滑新算法和两种反向固定区间稳态Ｋａｌｍａｎ平滑新算法,并给出了保证算法最优性的最优初值公式。算法简单,便于实时应用。仿真例子说明了它们的有效性。     

Delay-dependent exponential stability of the backward Euler method for nonlinear stochastic delay differential equations

Recently, several scholars discussed the question of under what conditions numerical solutions can reproduce exponential stability of exact solutions to stochastic delay differential equations, and some delay-independent stability criteria were obtained. This paper is concerned with delay-dependent stability of numerical solutions. Under a delay-dependent condition for the stability of the exact solution, it is proved that the backward Euler method is mean-square exponentially stable for all positive stepsizes. Numerical experiments are given to confirm the theoretical results.     

The improved split-step backward Euler method for stochastic differential delay equations

A new, improved split-step backward Euler method is introduced and analysed for stochastic differential delay equations (SDDEs) with generic variable delay. The method is proved to be convergent in the mean-square sense under conditions (Assumption 3.1) that the diffusion coefficient g(x, y) is globally Lipschitz in both x and y, but the drift coefficient f(x, y) satisfies the one-sided Lipschitz condition in x and globally Lipschitz in y. Further, the exponential mean-square stability of the proposed method is investigated for SDDEs that have a negative one-sided Lipschitz constant. Our results show that the method has the unconditional stability property, in the sense, that it can well reproduce stability of the underlying system, without any restrictions on stepsize h. Numerical experiments and comparisons with existing methods for SDDEs illustrate the computational efficiency of our method.     

基于前推回代法的20kV配电网的研究与应用

目前,我国城市电力负荷及负荷密度日益增长的情况和城市配电网现状,10kV电压等级供电暴露出许多不足,供电能力将无法满足需要。10kV电压等级将逐渐向20 kV电压等级过渡。对于10kV升压为20kV电压质量的分析,本文采用前推回代法进行配电网潮流计算。     

Combined quasi-static backward modeling and look-ahead fuzzy control of vehicles

Vehicle modeling can play an important role in vehicle power train design, control and energy management investigation. This paper presents a method for vehicle power train modeling. The key feature of the method is its presentation of the dynamic of vehicle based on the road information. This ability makes the method suitable for look-ahead energy management and fuel economy optimal control problems. With the aid of a road slope database, road geometry ahead of the vehicle is extracted. A fuzzy controller is developed that receives this information and controls the velocity of the vehicle with respect to its fuel consumption. In order to maintain the operation of the combustion engine near its efficient region, the fuzzy controller commands a continuously variable transmission. Simulations are carried out using real road data. The results are presented and discussed.     

灰尘在风管中运动轨迹的数值模拟

对通风管道中的气固两相流动流场进行数值模拟，是研究颗粒在通风管道中的运动轨迹。计算中将气相作为连续介质，采用RSM湍流模型。并用SIMPLE算法对流场进行数值模拟；将固相作为离散体系，采用随机轨道法计算其运动轨迹。计算时，分别选用6种颗粒直径为计算工况，计算结果显示出颗粒运动轨迹，指出其与气流速度和颗粒直径相关。     

FEM Simulation of Large Diameter Pipe Bending Using Local Heating

 With the aid of elastic plastic large deformation finite element method (FEM), an elastic plastic and coupling thermo mechanical model was built to calculate the bending process of the bent pipe, combining with local heating or cooling of the bent pipe. Based on the FEM simulation, the metal deformation during the bending process was analyzed in detail. The thinning and thickening ratio of the pipe wall thickness, the ovality of the cross section of the pipe and the spring back angle, etc, are presented.