共查询到20条相似文献，搜索用时 31 毫秒
1.
The problem of a liquid conductor confined between two concentric cylindrical electrodes and driven electromagnetically is considered. The steady, three-dimensional viscous case is treated asymptotically in the limit of small magnetic Prandtl numbers. The zeroth-order solution to the coupled hydrodynamic and Maxwell equations yields the trivial solution of no motion in the limit of vanishing conductivity. Results for the first-order solution indicate two-dimensional effects in the electromagnetic field quantities while the first-order velocity is one dimensional in the circumferential direction. Due to secular effects the solution is limited to values of small Hartmann numbers. The formulation of the second order and a limited solution for the velocity distribution indicates that the velocity field is three-dimensional having a cell-type structure. 相似文献
2.
The diffusion of the magnetic field due to a step current in an infinitely long ideal conductor, through infinite media is discussed. An analytical solution of the field diffusion through two concentric cylinders of different conductivity is derived using a generalized Ohm's law which considers both solid and fluid conductors. A rigorous mathematical treatment which can be generalized to any number of conducting cylinders is presented.The limiting case of an external superconducting medium is discussed and it is shown that with all the other parameters fixed it represents a lower limit in diffusion time. 相似文献
3.
A.A. Raptis 《Journal of The Franklin Institute》1983,316(6):445-449
This paper investigates the effects of a magnetic field on the free convective flow of a viscous, incompressible, dissipative fluid through a porous medium, occupying a semi-infinite region of the space bounded by an infinite vertical and porous plate. The plate is subjected to a normal suction velocity and the heat flux at the plate is constant. The magnetic field is of uniform strength and is applied perpendicular to the plate. An analytical solution to the problem is obtained. The influence of the magnetic parameter (M) and permeability parameter (K) is discussed for the case of air (P = 0.71) when the plate is subjected to a constant suction velocity and is being cooled by free convection currents. 相似文献
4.
David B. Geselowitz 《Journal of The Franklin Institute》1973,296(6):379-391
The first magnetocardiogram was published one decade ago. Subsequent development of magnetocardiography is discussed. A general expression is developed for the quasi-static magnetic field outside a nonmagnetic volume conductor containing internal electromotive forces. The multipole expansion for the magnetic field is derived and an expression is obtained for the magnetic field of a dipole current source in a sphere. The heart is modelled by 20 current dipoles in a homogeneous conducting sphere. Electric and magnetic scalar potentials at the surface of the sphere are calculated. These data, perturbed by noise, are used to solve the inverse problem, i.e. to determine the moments of the multiple dipole array which would generate the external potentials. The accuracy of the inverse solution is improved when a combination of electric and magnetic data is used rather than electric data alone. 相似文献
5.
一些单位或企业在数据库产品更新换代的过段中,经常会碰到由于不同数据库、不同数据表、不同字段属性的原因,数据之间在导入或转换时会出现错误,导致以前的数据不能及时升级;另一方面由于数据量非常大,手工输入不太可能,容易出错,而又没有什么好的解决办法,这给单位带来了极大的麻烦。本文使用程序实现不同数据库之间数据的转换,成千上万的数据在极短时间内转换完成,简单、安全、高效地完成任务,使数据库顺利升级。 相似文献
6.
Tunable pores (TPs) have been used for resistive pulse sensing of 1 μm superparamagnetic beads, both dispersed and within a magnetic field. Upon application of this field, magnetic supraparticle structures (SPSs) were observed. Onset of aggregation was most effectively indicated by an increase in the mean event magnitude, with data collected using an automated thresholding method. Simulations enabled discrimination between resistive pulses caused by dimers and individual particles. Distinct but time-correlated peaks were often observed, suggesting that SPSs became separated in pressure-driven flow focused at the pore constriction. The distinct properties of magnetophoretic and pressure-driven transport mechanisms can explain variations in the event rate when particles move through an asymmetric pore in either direction, with or without a magnetic field applied. Use of TPs for resistive pulse sensing holds potential for efficient, versatile analysis and measurement of nano- and microparticles, while magnetic beads and particle aggregation play important roles in many prospective biosensing applications. 相似文献
7.
《Journal of The Franklin Institute》1986,321(6):299-307
A special matrix is introduced, the elements of which are zero or first-order operators. This matrix is used to define the initial boundary value problem which covers a wide class of engineering applications. To bring the solution of the problem within the realm of integral transform theory, a new finite integral transform and the corresponding inversion formula are developed. The necessary orthogonality relations is derived using an extension of the Gauss-Green theorem. The formal solution obtained here can be applied to study heat conduction problems, elasticity problems, etc. 相似文献
8.
By use of the multiple Laplace transform a partial differential equation and its associated boundary conditions characterizing a boundary value problem in n independent real variables can be transferred directly into an algebraic equation in n independent complex variables. This algebraic equation can be solved for the multiple transform of the solution of the boundary value problem. Multiple inversion of this transform then gives the desired solution. The general theory underlying such solution of boundary value problems in two and three independent variables is advanced in detail. Use of this theory is illustrated by solution of two specific problems. 相似文献
9.
In this paper, we first develop an adaptive shifted Legendre–Gauss (ShLG) pseudospectral method for solving constrained linear time-delay optimal control problems. The delays in the problems are on the state and/or on the control input. By dividing the domain of the problem into a uniform mesh based on the delay terms, the constrained linear time-delay optimal control problem is reduced to a quadratic programming problem. Next, we extend the application of the adaptive ShLG pseudospectral method to nonlinear problems through quasilinearization. Using this scheme, the constrained nonlinear time-delay optimal control problem is replaced with a sequence of constrained linear-quadratic sub-problems whose solutions converge to the solution of the original nonlinear problem. The method is called the iterative-adaptive ShLG pseudospectral method. One of the most important advantages of the proposed method lies in the case with which nonsmooth optimal controls can be computed when inequality constraints and terminal constraints on the state vector are imposed. Moreover, a comparison is made with optimal solutions obtained analytically and/or other numerical methods in the literature to demonstrate the applicability and accuracy of the proposed methods. 相似文献
10.
A numerical modeling of natural convection under the influence of either axial (Bz) or radial (Br) magnetic field in a cylindrical configuration filled with a low-Prandtl number electrically conducting fluid, is studied. The finite volume method is used to discretize the equations of continuity, Navier Stokes and energy. A computer program based on the SIMPLER algorithm is developed. The flow and temperature fields are presented by stream function and isotherms, respectively. Stability diagrams are established according to the numerical results of this investigation. These diagrams put in evidence the dependence of the critical Grashof number, Grcr with the increase of the Hartmann number, Ha. The strongest stabilization of the convective flows occurs when the magnetic field is applied in the radial direction. This study confirms the possibility of stabilization of a liquid metal flow in natural convection by application of a radial magnetic field. 相似文献
11.
用已发展的双倒易边界元和Laplace变换、反变换相结合的方法求解非傅立叶导热 ,对于一类等温进口条件下的问题 ,数值预示了热波导热、非傅立叶导热和傅立叶扩散的温度场随时间推进的不同特征 ,并且发现了温度变化前缘的推进速度存在着明显的差异 相似文献
12.
D. Schieber 《Journal of The Franklin Institute》1973,295(3):249-261
In many technical devices an a.c.-supplied “primary” magnetic field induces eddy-current flow in a “secondary” armature. Exact calculation of the overall field distribution is difficult, hence, the secondary field is often neglected in practice and only an estimate of the interaction is obtained. This paper outlines a general solution of the problem with both fields taken into account, and the specific model discussed shows how to proceed in more complicated cases. 相似文献
13.
The Graph-Theoretical Field Model provides a unifying approach for developing numerical models of field and continuum problems. The methodology examines the field problem from the first stages of conceptualization without recourse to the governing differential equations of the field problem; this is accomplished by deriving discrete statements of the physical laws which govern the field behaviour. There are generally three laws, and these are modelled by the “cutset equations”, the “circuit equations”, and the “terminal equations”. In order to establish these three sets of equations it is expedient first to spatially discretize the field in a manner similar to the finite difference method and then to associate a linear graph (denoted as the field graph) with the spatial discretization. The concept of “through” and “across” variables, which underlies the cutset and circuit equations respectively, enables one to define the graph in an unambiguous manner such that each “edge” of the graph identifies a pair of complementary variables. From a knowledge of the constitutive properties and the boundary conditions of the field it is possible to associate terminal equations with sets of edges. Since the resulting sets of equations represent the field equations, these equations provide the basis for a complete (but approximate) solution to the field or continuum problem. In fact, this system approach uses a two part model: one for the components and another for the interconnection pattern of the components which renders the formulation procedures totally independent of the solution procedure.This paper presents the theoretical basis of the model and several graph-theoretic formulations for steady-state problems. Examples from heat conduction and small- deformation elasticity are included. 相似文献
14.
《Journal of The Franklin Institute》2023,360(14):10582-10604
In this paper, the optimal model reference adaptive control (MRAC) problem is studied for the unknown discrete-time nonlinear systems with input constraint under the premise of considering robustness to uncertainty. Through an input constraint auxiliary system, a new adaptive-critic-based MRAC algorithm is proposed to transform the above problem into the optimal regulation problem of the auxiliary error system with lumped uncertainty. In order to realize the chattering-free sliding model control for the auxiliary error system, an action-critic variable is introduced into the adaptive identification learning. In this case, the closed-loop control system is robust to the disturbance and the neural network approximation error. The uniformly ultimate bounded property is proved by the Lyapunov method, and the effectiveness of the algorithm is verified by a simulation example. 相似文献
15.
《Journal of The Franklin Institute》2022,359(2):859-869
In this paper, we considered a time-optimal control problem for a new type of linear parameter varying (LPV) system which is obtained through data identification in the process of dealing with actual problems. The addition of non-linear terms is compensation for the method that does not require linear expansion at the equilibrium point. Since the objective function is the terminal time which is an implicit function concerning decision variables, it is a non-standard optimal control problem with uncertain terminal time. To find the global optimal solution to this problem, firstly, the control parameterization method is used to transform it into a nonlinear optimization problem of parameter selection, and then the modifed particle swarm optimization (PSO) algorithm is combined to solve the equivalent nonlinear programming problem. Numerical examples are used to illustrate the effectiveness of the proposed algorithm. 相似文献
16.
从社会资本视角来看,创新网络中知识扩散的实质是一种社会交换,网络中的知识扩散受社会关系网络中个体位势的影响。研究从微观视角切入,探讨科研网络中的知识主体对其知识扩散的动态影响机制。选取度中心度、Bonacich Power中心度、效率结构洞、中介中心度四种SNA算法,从知识的多样性、传递路径的非确定性和平行复制三个属性对比各SNA算法所暗含的知识扩散特征,对科研网络中知识扩散机制提出假设,选取国内知识管理领域发表于1998-2011年的CSSCI数据,利用Cox比例风险模型构建生存分析模型,研究各SNA算法对该领域知识扩散演化机制的解释程度。研究发现占据"结构洞"位置和度数中心度高的权威个体在知识管理领域知识扩散中发挥最为重要的作用;该领域主要通过团队成员间的平行复制和不同团队间的知识多样化融合来实现知识的扩散与创新。 相似文献
17.
《Journal of The Franklin Institute》2022,359(8):3979-3999
This paper addresses an active fault diagnosis problem for a class of discrete-time closed-loop system with stochastic noise. By introducing the theories of system identification, a novel active fault diagnosis method is developed to detect and isolate the faults. An important advantage of the proposed method is that there is no need to cut off the original input signal, which is necessary in most active fault diagnosis methods. Firstly, due to the features of the faults, we transform the problem of fault diagnosis into a problem of model selection by estimating model parameters. Then, the sufficient condition for active fault diagnosability is analysed, and the property that auxiliary input signal can enhance the fault diagnosability is given. Finally, simulation studies are carried out to demonstrate the effectiveness and applicability of the proposed method. 相似文献
18.
M. Sami Fadali 《Journal of The Franklin Institute》2011,348(2):239-260
In this paper, we use input and output maps to develop simple procedures to obtain minimal realizations for linear continuous-time systems. The procedures developed are numerically efficient and yield explicit formulae for the state-space matrices of the realization in terms of the system parameters, notably the system eigenvalues. Both systems with distinct eigenvalues and repeated eigenvalues are treated. We also present a procedure for transforming a realization obtained through the input or output map to Jordan canonical form. The transformation matrices required to transform the realization to Jordan canonical form are specified entirely in terms of the system eigenvalues. We illustrate the results obtained with several examples. 相似文献
19.
《Journal of The Franklin Institute》2006,343(4-5):480-494
The maximum principle developed by Sloss et al. [Optimal control of structural dynamic systems in one space dimension using a maximum principle, J. Vibr. Control 11 (2005) 245–261] is used to determine the optimal control functions for a class of one-dimensional distributed parameter structures. The distributed parameter structures are governed by systems of fourth order hyperbolic equations with constant coefficients. A quadratic performance index is formulated as the cost functional of the problem and can be used to represent the energy of the structure and the force spent in the control process. The developed maximum principle establishes a theoretical foundation for the solution of the optimal control problem and relates the optimal control vector to an adjoint variable vector. The method of solution is outlined which involves reducing the original problem to a system of ordinary differential equations. The solution of the general problem is given and a structural control problem is solved to illustrate the solution procedure. The effectiveness of the proposed control solution is shown by comparing the behavior of controlled and uncontrolled systems. 相似文献
20.
《Information processing & management》2005,41(5):1175-1192
Block-sorting is an innovative compression mechanism introduced in 1994 by Burrows and Wheeler. It involves three steps: permuting the input one block at a time through the use of the Burrows–Wheeler transform (bwt); applying a move-to-front (mtf) transform to each of the permuted blocks; and then entropy coding the output with a Huffman or arithmetic coder. Until now, block-sorting implementations have assumed that the input message is a sequence of characters. In this paper we extend the block-sorting mechanism to word-based models. We also consider other recency transformations, and are able to show improved compression results compared to mtf and uniform arithmetic coding. For large files of text, the combination of word-based modeling, bwt, and mtf-like transformations allows excellent compression effectiveness to be attained within reasonable resource costs. 相似文献