电偶源海洋瞬变电磁法三维数值模拟与响应特征研究

由于海底能源资源勘查和其他研究的需要,人工源海洋电磁法已经成为一个研究热点。使用傅里叶伪谱法来模拟瞬变水平电偶极源对不同三维海底模型的响应,与全空间解析解对比,验证算法的正确性。海底低阻体模型响应说明,时间域电磁法可以连续地追踪电磁场扩散及与海底低阻体的响应过程。高阻体模型响应说明,可以通过研究早期电磁场的幅值随收发距的变化来确定高阻体的存在。     

Mathematical modeling of aerosol emission from die sinking electrical discharge machining process

Emission of toxic gases and aerosol is an important hazard associated with the electrical discharge machining (EDM) process, one of the most widely used non-conventional manufacturing processes. These emissions can cause adverse health effects to the operators and has a direct impact on the environment. The emission from this process is directly related to the temperature at the process location. This paper was aimed at developing a model that quantifies the aerosol generated from the die sinking EDM process while machining steel workpiece with copper electrode. The model developed in this paper made use of energy balance and heat transfer equations. The modeling results were then validated using experimentally obtained values of the emission rate of aerosol from this process. The results showed a close correlation of +0.89 with experimental results. The model developed in this paper can predict the level of emissions at different process locations; thereby reducing the direct cost and time associated with experimentation.     

The extended affinity

The deviation from equilibrium is described by the affinity expressed by using the chemical potentials. It leads to difficulties at describing the processes for which the use of the chemical potentials is problematic. The extended affinity suitable to consider the processes in the systems with alloys of compounds with two or more mixed sublattices is represented. This affinity reduces to the conventional affinity for the simpler systems for which the use of the chemical potentials is not problematic. The extended affinity makes possible the consideration of a wider class of processes.     

柱状螺旋线圈电磁超声探头解析建模及分析

针对目前柱状螺旋线圈EMAT建模不完善,可解算度不高的问题。将线圈等效为单匝导线的矩形面积分,并采用区域特征函数截断法(TREE)对其进行完整地解析建模,得到磁感应强度、涡流、线圈阻抗表达式。通过实际搭建EMAT(electromagnetic acoustic transducer)试验平台,测量对比模型的各参数及变化规律,验证了模型的正确性及可行性。     

Understanding the cascading failures in Indian power grids with complex networks theory

Two huge blackouts, occurred separately on 30 and 31 July 2012 in India, spread over half the country when three of its five regional grids collapsed, leaving hundreds of millions of people without government-supplied electricity and ringing once again alarm bells with security problems in electric power grid systems. The first investigation reveals that the outage of the second (backup) 400 kV Bina–Gwalior–Agra line on 29 July 2012 led to the cascading failure through the grid, which can be simulated and explained from the perspective of the complex networks theory. In this paper, a new model of a power grid involving the active and reactive power loads is proposed and then used to analyze the cascading behavior of power grids, which is also used to explain the reason of the blackout happening in India. Furthermore, some strategic advices are given for improving the stability and security of power grids, especially Indian power grids.     

Modal analysis and harmonic response of resonators: An extension of a mapped orthogonal functions technique

A mapped orthogonal functions technique is extended for solving three-dimensional acoustical wave problems with taking into account electrical sources. For validation and illustration purposes, it is applied to the determination of the frequency spectrum of a piezoelectric disc resonator. Formulation is given for the calculation of the electric input admittance along with specializations for open- and short-circuit boundary conditions. In view of validation, normal frequencies and electric input admittance are obtained for specific geometries where a one-dimensional analytical model is working and compared against results from the analytical approach. Illustrative results, dispersion curves for a PZT5A resonator and electromechanical coupling coefficients as a function of the diameter to thickness ratio for the first radial mode of a respectively PZT5A, AlN and SiC resonator are also given.     

A discrete model of a rope with bending stiffness or viscous damping

A discrete model of a rope is developed and used to simulate the plane motion of the rope fixed at one end.Actually,two systems are presented,whose members are rigid but non-ideal joints involve elasticity or dissipation.The dissipation is reflected simply by viscous damping model, whereas the bending stiffness conception is based on the classical curvature-bending moment relationship for beams and simple geometrical formulas.Equations of motion are derived and their complexity is discussed from the computational point of view.Since modified extended backward differentiation formulas(MEBDF)of Cash are implemented to solve the resulting initial value problems,the technique scheme is outlined.Numerical experiments are performed and influences of the elasticity and damping on behaviour of the model are analyzed.Basic energy principles are used to verify the obtained results.     

A numerical study of the assumptions underlying the calculation of the stationary zone mass transfer coefficient in the general plate height model of chromatography in two-dimensional pillar arrays

The present study investigates the validity of one of the key assumptions underlying the general plate height model of chromatography, i.e., the presumed independency of the individual band broadening contributions. More precisely, it is investigated under which conditions the mass transfer inside the stationary zone (e.g., porous pillars) is independent from the axial transport of species outside this zone, and how strongly any such dependency would affect the validity of the general plate height model of chromatography. For this purpose, detailed calculations of the species concentration distribution inside and outside the porous pillars of a computer-mimic of a porous pillar array column have been made. These simulations revealed a clear interplay between the mass transfer inside and outside the pillars, manifesting itself as an asymmetry of the species concentration distribution inside the pillars. The latter is in disagreement with the basic assumption used to calculate the value of the C_s-term of the general plate height model. The asymmetry-effect is largest at low reduced velocities, high retention factors and high intra-pillar diffusion coefficients. Fortunately, these are conditions where the C_s-term is relatively small, which might explain why the general plate height model of chromatography (and based on the symmetry assumption) can represent the band broadening in a porous pillar array within an accuracy on the order of some 1–2%.     

Prediction of gas chromatographic retention time via an additive thermodynamic model

A straightforward group contribution model based on thermodynamic parameters was developed to predict retention times for a series of alcohols and ketones on three different stationary phases. Thermodynamic parameters determined from gas chromatographic retention data for structurally similar compounds via a three-parameter model were used to predict the retention times of test molecules consisting of ketones and alcohols. The model worked well for the compounds tested with a root mean square error of prediction of 5.50 s across all compounds, phases, and temperature ranges studied. Considering just the alcohols, the error of prediction was 2.79 s across all phases and temperatures.