Numerical Modeling of Inclusion Removal in Electromagnetic Stirred Steel Billets

To investigate the inclusion removal in billets cast under electromagnetic stirring (EMS) influence, a numerical model has been developed to compute the magnetic field, the Lorentz force, the steel flow velocities, and the particle transport within the liquid pool. The electromagnetic field was described by the Maxwell equations and the finite element method was applied using a commercial package. The turbulent fluid flow was described by the Navier‐Stokes equation and by the Reynolds Stress model and the finite volume method was applied using another numerical package. The time average of the Lorentz force was calculated in each element center and this value was applied as a body force in the Navier‐Stokes equation. The magnetic flux density profile was compared with the data obtained in the stirrer of the steel plant. The particle transport model includes the drag force, the buoyancy force and the random walk model, to include the turbulence effects on the particle trajectory. The inclusion removal was calculated and analysed in function of casting speed and stirring current for one size section of mold. The inclusions considered in the calculations have a fixed density and four values of diameter. The numerical results of the electromagnetic model are in agreement with the experimental measurements. A good relationship between the electromagnetic model and the fluid flow model could be shown. An interesting effect is the break of the rotation motion due to the EMS by the jet from the nozzle. The fraction of inclusions removed by the top surface of the mold was improved due to the EMS.     

狭缝式透气砖内气流速度分布规律及阻力研究

建立了狭缝式透气砖内气体流动速度和阻力的数学模型;忽略质量力时,对定常流动不可压缩流体连续方程进行了简化,并进行了数值计算.结果表明,其速度沿狭缝厚度方向按抛物线规律分布,狭缝中心速度最高,流动状态一般为层流;沿程阻力大小与狭缝大小、供气压力、透气砖长度等存在密切关系.为透气砖的设计提供了相关理论依据,可资参考、借鉴.     

小方坯连铸结晶器电磁搅拌的数值模拟

借助有限元分析软件ANSYS,对150mm×150mm小方坯连铸结晶器电磁搅拌在电流为150A,频率变化情况下的钢液内部磁感应强度和电磁力进行了数值分析,并分析了结晶器厚度对钢液内部磁场的影响以及不同时刻钢液内部电磁力的分布。模拟结果表明,在结晶器电磁搅拌时,同一个断面上,4个角部的磁感应强度最大;随着频率的增加,钢液内部磁感应强度降低,钢液边部电磁力在4~5Hz时最大;钢液内部的电磁力在1个周期的不同时刻,形成了同一个方向的力偶,在这个力偶的作用下,完成了对钢液的搅拌;结晶器厚度对钢液内部磁场影响很大,厚度增加,钢液内部磁感应强度降低。     

Finite Element Analysis of 3D Electromagnetic Field in Bloom Continuous Casting Mold

Threedimensional finite element model of electromagnetic stirrer was built to predict magnetic field in a bloom continuous casting mold for steel during operation. The effects of current intensity, current frequency, and mold copper plate thickness on the magnetic field distribution in the mold were investigated. The results show that the magnetic induction intensity increases linearly with the increase in current intensity and decreases with the increase in current frequency. Increasing current intensity and frequency is available in increasing the electromagnetic force. The Joule heat decreases gradually from surface to center of bloom, and a maximum Joule heat can be found on corner of bloom. The prediction of magnetic induction intensity is in good agreement with the measured values.     

搅拌混合机理与设计研究

根据流体动力学理论和试验分析,研究湍流条件下的搅拌混合动力学问题。混合是在强制对流作用下经过主体对流、湍流扩散和分子扩散,最终达到分子级均匀混合。湍流条件下,湍流扩散主导宏观混合,分子扩散主导微观混合,而混合时间由宏观混合主导,G和knT可作为搅拌混合效果的综合设计参数,并通过试验分析进一步证实了该参数的可行性。     

Lag synchronisation of master–slave dynamical systems via intermittent control

In this paper, the problem on lag synchronisation is investigated for a master–slave model. The intermittent control method is used to design controllers, lag synchronisation criteria are proposed. Together with some Lyapunov–Krasovskii functionals and effective mathematical techniques, several conditions are derived. An example is given to illustrate the effectiveness of the proposed methods.     

Constrained intermittent model predictive control

The generalised hold formulation of intermittent control is re-examined and shown to have some useful theoretical and practical properties. It is shown that this provides a foundation for constrained model predictive control in an intermittent context. The method is illustrated using an example and verified with experimental results.     

Power-constrained intermittent control

In this article, input power, as opposed to the usual input amplitude, constraints are introduced in the context of intermittent control. They are shown to result in a combination of quadratic optimisation and quadratic constraints. The main motivation for considering input power constraints is its similarity with semi-active control. Such methods are commonly used to provide damping in mechanical systems and structures. It is shown that semi-active control can be re-expressed and generalised as control with power constraints and can thus be implemented as power-constrained intermittent control. The method is illustrated using simulations of resonant mechanical systems and the constrained nature of the power flow is represented using power-phase-plane plots. We believe the approach we present will be useful for the control design of both semi-active and low-power vibration suppression systems.     

EFFECT OF INTERMITTENT HEATING ON DRYING-INDUCED STRAIN-STRESS OF MOLDED CLAY

ABSTRACT

Parametric analyses of the strain-stress in the drying process are performed to study the influence of the intermittent drying on the behaviors of drying-induced strain-stress and deformation as well as the drying characteristic. The transient three-dimensional problem of strain-stress and heat and moisture transfer in a slab is solved simultaneously by the finite element method. The dimensionless parameters are introduced to generalize the problem in the conservation equations of heat and moisture transfer. The intermittent drying is modeled by applying periodically smaller and larger Biot numbers to the boundary conditions. The maximum tensile and compressive stresses fluctuate, and fall remarkably during the smaller Biot number period when a slab is heated intermittently. The peak stress of the fluctuation exceeds beyond the case in the continuous healing where the overall drying rate is almost equivalent to that in the intermittent beating, but the reduction of the stresses takes place rapidly in the low heating period.     

热水间歇供暖加热过程数理模型

将建筑物供暖过程模拟划分为两个串联工作的热力系统，在假设条件下建立间歇供暖加热过程微分方程组及其关系式，并通过初步的实验加以验证，结果表明假设条件基本符合实际，误差能满足工程需要。