Solution of the time-dependent,three-dimensional resistive magnetohydrodynamic equations

Resistive magnetohydrodynamics (MHD) is described by a set of eight coupled, nonlinear, three-dimensional, time-dependent, partial differential equations. A computer code, IMP (Implicit MHD Program), has been developed to solve these equations numerically by the method of finite differences on an Eulerian mesh. In this model, the equations are expressed in orthogonal curvilinear coordinates, making the code applicable to a variety of coordinate systems. The Douglas-Gunn algorithm for Alternating-Direction Implicit (ADI) temporal advancement is used to avoid the limitations in timestep size imposed by explicit methods. The equations are solved simultaneously to avoid synchronization errors. While the continuity and magnetic field equations are expressed as conservation laws, the momentum and energy equations are nonconservative. This is to: (1) provide enhanced numerical stability by eliminating errors introduced by the nonvanishing of τ · B on the finite difference mesh; and, (2) allow the simulation of low β plasmas. The resulting finite difference equations are a coupled system of nonlinear algebraic equations which are solved by the Newton-Raphson iteration technique. We apply our model to a number of problems of importance in magnetic fusion research. Ideal and resistive internal kink instabilities are simulated in a Cartesian geometry. Growth rates and nonlinear saturation amplitudes are found to be in agreement with previous analytic and numerical predictions. We also simulate these instabilities in a torus, which demonstrates the versatility of the orthogonal curvilinear coordinate representation.     

Self-sensing for electromagnetic actuators. Part I: A coupled reluctance network model approach

A self-sensing arrangement in active magnetic bearings (AMBs) comprises a single electromagnetic transducer to realize the actuation and sensing functions concurrently. Minimizing the number of sensing devices and associated interfacing directly reduces possible failure points, system costs, and system complexity. Currently, self-sensing performance is degraded due to problems such as magnetic cross-coupling, eddy currents, saturation, and high losses. This first paper in a two part series presents an integrated model for self-sensing of an 8-pole heteropolar magnetic bearing. The proposed self-sensing approach addresses mechanisms that contribute to modelling error and uncertainty by using several techniques in an integrated structure. A coupled reluctance network model (RNM) is developed which models the coil impedance at the switching frequency. The accuracy of the model is improved by incorporating terms for air gap fringing, complex permeability, and magnetic material nonlinearity. The RNM is verified and refined through a process of iteration using finite element method (FEM) results and experimental AMB measurements. The results demonstrate that a RNM with only 40 nodes can achieve high levels of accuracy when compared to an 80 000 node FEM analysis.In Part II of the series, the refined RNM is incorporated into a multiple input multiple output (MIMO) parameter estimation self-sensing scheme.     

Numerical solution of laplace's equation on non-simply connected regions on R 2

We consider the interior Dirichlet problem for Laplace's equation on a non-simply connected two-dimensional regions with smooth boundaries.The solution is sought as the real part of a holomorphic function on the region, given as Cauchy-type integral.The approximate double layer density function is found by solving a system of Fredholm integral equations of second kind.Because of the non-uniqueness of the solution of the system we solve it using a technique based on the solution of the “Modified Dirichlet problem”.The Nystrom's method coupled with the trapezoidal rule is used as numerical integration scheme.The linear system derived from the integral equation is solved using the conjugate gradient applied to the normal equation.Theoretical and computational details of the method are presented.     

The use of high-resolution airborne magnetic,ASTER and Landsat 7 ETM+ images for identification of kimberlite pipes in the northwestern Free State Province,South Africa

Airborne magnetic, Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and Landsat Thematic Mapper images were used for the detection of detailed exploration targets for kimberlite pipes located around the Kimberley and Boshof regions in the Northern Cape Province of South Africa. In order to achieve the objectives, the magnetic data and the satellite images were processed using various algorithms.

The magnetic signatures of 25 previously known kimberlite pipes in the study area were used as a guide to identify new potential targets. Based on this approach, 30 kimberlite-like bodies were identified, of which 11 were given high ranks for detailed exploration. The ranking was based on a comparison of the strength of magnetic intensity and the size and geometry of the magnetic signatures (isolated sharp and circular high/low magnetic values), which are distinct from the magnetic response of the surrounding host rocks. The most prospective areas are located southeast of Kimberley Mine, east of Boshof and the central parts of the study area. In addition, the spectral angle mapping (SAM) method was applied to the first nine ASTER bands, and this enabled us to distinguish kimberlite indicator minerals (ilmenite, serpentine, olivine and phlogopite). The results of the SAM algorithm show that the images classified as ilmenite and phlogopite form linear patterns, which coincide with palaeo-channels in the northern part and mafic dikes in the southeastern part of the area. The thematic map derived from a classification of the image shows the presence of significant amounts of serpentine in the western part of the area around Kimberley Mine, which is consistent with the composition of the soil derived from the altered and weathered ultramafic rocks. In general, the SAM technique was successful in supplementing the identification of detailed exploration targets.     

Design of a hybrid optical image stabilization actuator to compensate for hand trembling

In this paper, a novel hybrid optical image stabilization (OIS) actuator for digital camcorder is proposed. Image stabilization for this hybrid type consists of both radially and tangentially moving components to compensate for hand trembling. The proposed OIS actuator, which uses a voice coil motor method, is divided into two parts: a structure and a magnetic circuit. For the structural part, the driving mechanism consists of two systems: one system is based on a ball guide with a magnetic spring, and the other system is based on a pivot bearing. The former system is typically used as a driving mechanism in mobile devices, whereas the latter system has advantages such as mechanical stability and reduced friction. Overall, a magnetic spring between the magnet and yoke should be considered to select the best magnetic circuit part design and mechanism design. Regarding the electro-magnetic (EM) circuit, two types of EM circuits were designed to satisfy each direction: one circuit is a moving magnet circuit for the radial direction, and the other circuit is a moving coil for the tangential direction. In a digital camcorder, the space for the OIS actuator is limited, and thus, optimized actuator with adequate performances is required. To solve these problems, a sensitivity analysis was performed using the design of experiment procedure. Based on these results, an objective function was defined for the optimization procedure. Finally, the actuator was fabricated, and the dynamic characteristics and feasibility of adapting two types of mechanisms of the suggested OIS actuator were verified. The experimental results indicate that the proposed OIS actuator exhibits sufficient performance for the sensitivity.     

A quintic spline collocation procedure for solving the falkner-skan boundary-layer equation

A quintic spline collocation method is used to numerically solve the Falkner-Skan similarity boundary-layer equation for a wide range of pressure gradient parameter, both favorable and adverse, and wall mass transfer, both injection and suction. Through proper choice of the parameter in a constant ratio interval variable-grid system, extremely accurate solutions are obtained with as few as 7 grid points across the boundary layer. It is suggested that perhaps the method and grid system can be coupled to yield an optimal node distribution technique which will allow highly accurate solutions with few grid points and minimum discretion on the part of the user.     

磁悬浮系统的双环自适应控制器设计与仿真

研究了基于机械和电气两种结构的磁悬浮系统的自适应控制方案，实现了双环磁悬浮控制系统的稳定悬浮。根据电磁铁动力学方程和电磁线圈的电压平衡方程，建立了磁悬浮系统基本模型。对系统中的电气部分和机械部分采用不同的控制方法：电气部分采用模型参考自适应控制的方法，加快电流上升的速度，使电流环性能达到设定指标；机械部分简化模型建立在电气自适应控制的基础上，针对系统参数的慢变特点而采用自校正控制方法，给出了能够自动跟踪系统参数，尤其是悬浮质量变化的稳定悬浮自适应控制算法。仿真和实验结果均证明这种控制方法能够使电流环快速跟踪给定信号，保证此悬浮系统能够很好地适应悬浮质量发生突变的情况，具有一定的实用价值。     

On the entanglement and engineering phase gates without dynamical phases for a two-qubit system with Dzyaloshinski-Moriya interaction in magnetic field

We calculate Berry phases and entanglement of adiabatic states for a two spin-1/2 system described by the Heisenberg model with Dzyaloshinski-Moriya (DM) interaction; one of the spins is driven by a time-varing rotating magnetic field and the other is coupled with a static magnetic field. This static magnetic field can be used for controlling as well as vanishing the Berry phases and entanglement of the system state. Besides, we show that the Berry phase and entanglement are not always exact but useful to detect energy levels approach. Additionally, we find that a nontrivial two-spin unitary transformation, purely based on Berry phases, can be obtained by using two consecutive cycles with the opposite direction of the static magnetic field, opposite signs of the exchange constant as well as DM interaction, and a phase shift of the rotating magnetic field. This unitary transformation presents a two-qubit geometric phase gate.     

An optimal design of magnetic actuators using topology optimization and the response surface method

The magnetic actuator is a device that transforms electric energy to mechanical energy. By mechanical energy transformation, some part of the electric energy creates force, and the other part is stored within the ferrous material. An actuator with improved magnetic force can be designed by reducing the stored energy within the ferrous material at the core or the armature. Topology optimization based on the homogenization design method (HDM) is used for the initial design by determining the porous hole size of each element created. The homogenized magnetic permeability is applied in calculation of the magnetic energy stored. The magnetic energy is calculated by finite element analysis and the sensitivity is calculated mathematically by determining the effects of the magnetic energy according to the permeability change at each element. Repeating the process of the porous hole size determination by the sequential linear programming (SLP), eventually leads to a design of an actuator that makes the most improved magnetic force within the limited volume. The initial actuator model derived from topology optimization uses parameter optimization for detail designs. In parameter optimization design, the response surface method (RSM) based on the central composite design is used to obtain a clear final design.     

Transfer efficiency optimal control of magnetic resonance coupled system of wireless power transfer based on frequency control

In order to suppress the fast decrease of the transfer efficiency of magnetic resonance coupled wireless power transfer system(MRCWPTS) with distance increase,this paper investigates the impact factors of the system transfer efficiency and is,then formulates a new efficiency optimal control method based on frequency control.Based upon this control method two optimal control schemes are designed to achieve transfer efficiency control of the system.Simulations and experiments show that the proposed efficiency...     

磁悬浮飞轮储能系统机电耦合非线性动力学研究

针对磁悬浮飞轮储能系统的"磁悬浮飞轮-发电机"机电耦合非线性动力学特性进行研究.通过推导磁悬浮飞轮储能系统在偏心条件下的动能、势能、发电机系统的磁场能以及系统的耗散函数,由Lagrange-Maxwell方程建立磁悬浮飞轮系统和两相四极永磁发电机系统的机电耦合动力学方程.采用数值法对0.6MW磁悬浮飞轮储能系统进行了仿真分析,研究结果表明,系统机电耦合非线性方程存在稳定的与转速同频的基频和三倍频周期运动解,且基频振动幅值比三倍频振动幅值大.对于稳定的磁悬浮储能飞轮机电耦合系统,飞轮转速增大,或磁轴承系统刚度减小或阻尼增大,或磁场能(电枢反应磁场能或永磁励磁磁场能)减小,可使系统的非线性振动幅值减小.而增大磁轴承系统的刚度,或减小磁轴承系统的阻尼,或增大系统的磁场能有可能破坏机电耦合系统的稳定性,使飞轮失稳.     

Coding, analysis, interpretation, and recognition of facialexpressions

We describe a computer vision system for observing facial motion by using an optimal estimation optical flow method coupled with geometric, physical and motion-based dynamic models describing the facial structure. Our method produces a reliable parametric representation of the face's independent muscle action groups, as well as an accurate estimate of facial motion. Previous efforts at analysis of facial expression have been based on the facial action coding system (FACS), a representation developed in order to allow human psychologists to code expression from static pictures. To avoid use of this heuristic coding scheme, we have used our computer vision system to probabilistically characterize facial motion and muscle activation in an experimental population, thus deriving a new, more accurate, representation of human facial expressions that we call FACS+. Finally, we show how this method can be used for coding, analysis, interpretation, and recognition of facial expressions     

Dynamic motion analysis of magnetic particles in microfluidic systems under an external gradient magnetic field

To gain an insightful understanding of motion behavior of paramagnetic particles suspended in a nonmagnetic fluid under a gradient magnetic field, a coupled fluid–structure model based on a direct numerical scheme is developed in this work. The governing equations of magnetic field, fluid flow field and particle motion are simultaneously solved using an Arbitrary Lagrangian–Eulerian method, taking into account magnetic and hydrodynamic interactions between particles in a fully coupled manner. The accuracy of the proposed method is validated using the magnetic particulate flows of two particles under a uniform magnetic field as the test problem and is then applied to investigate effects of magnetic and hydrodynamic interactions between particles on the particle motion behavior. Results show that neighboring magnetic particles are easy to form chain-like clusters along field direction due to magnetic interactions between particles and then move together toward the surface of magnetic source under the action of gradient magnetic force. More importantly, it has been found that both magnetic and hydrodynamic interactions between particles are conducive to the acceleration of particles and the chain formation of particles. The present method and results could help in understanding the basic mechanism underlying the low-gradient magnetophoretic separation process and designing magnetic aggregate-based microfluidic devices.     

基于磁耦合谐振的无线电能传输系统的研究

分析并设计实现了一种基于磁耦合谐振的无线电能传输系统.介绍了无线电能传输技术,阐述了磁耦合谐振式无线电能传输技术原理及其优越性,分析了磁耦合谐振无线电能传输系统中传输距离d及负载阻值RL等相关参数对系统传输功率、效率的影响.对所提出的无线电能传输系统进行实验测试,实验结果表明,需综合考虑上述相关参数,以达到传输效率、传...     

Model-based autonomous system for performing dexterous, human-level manipulation tasks

This article presents a model based approach to autonomous dexterous manipulation, developed as part of the DARPA Autonomous Robotic Manipulation Software (ARM-S) program. Performing human-level manipulation tasks is achieved through a novel combination of perception in uncertain environments, precise tool use, forceful dual-arm planning and control, persistent environmental tracking, and task level verification. Deliberate interaction with the environment is incorporated into planning and control strategies, which, when coupled with world estimation, allows for refinement of models and precise manipulation. The system takes advantage of sensory feedback immediately with little open-loop execution, attempting true autonomous reasoning and multi-step sequencing that adapts in the face of changing and uncertain environments. A tire change scenario utilizing human tools, discussed throughout the article, is used to described the system approach. A second scenario of cutting a wire is also presented, and is used to illustrate system component reuse and generality.     

A time-adaptive fluid-structure interaction method for thermal coupling

The thermal coupling of a fluid and a structure is of great significance for many industrial processes. As a model for cooling processes in heat treatment of steel we consider the surface coupling of the compressible Navier-Stokes equations bordering at one part of the surface with the heat equation in a solid region. The semi-discrete coupled system is solved using stiffly stable SDIRK methods of higher order, where on each stage a fluid-structure-coupling problem is solved. For the resulting method it is shown by numerical experiments that a second order convergence rate is obtained. This property is further used to implement a simple time-step control, which saves considerable computational time and, at the same time, guarantees a specified maximum error of time integration.     

小型无人直升机纵横角动态耦合辨识建模

针对小型无人直升机耦合建模问题提出了一种频域解耦辨识建模方法,该方法通过处理针对耦合辨识的实验数据得到指定频域范围内被辨识耦合的频域特性,对频域特性进行拟合从而获得耦合模型.提出了适用于多输入输出(MIMO)系统的频域特性计算方法,定义了一种复合相干函数并证明其能够用于表达在耦合通道辨识中输入输出的相关性.基于该方法,对一种小型无人直升机在悬停状态的纵横角动态耦合模型进行了辨识,并将耦合模型加入到直升机仿真模型中考察其对模型预测精度的影响.模型预测输出与实际输出的比较表明,相较于普通模型,考虑了耦合动态的仿真模型能够更为精确地预测实际输出.     

磁传感器特性测试中标准磁场发生装置的设计

磁传感器作为传感器的重要组成部分,在航空航天、生物医学、材料科学等领域得到了广泛应用,但目前却缺乏对其特性进行全面测试的手段,特别是传感器的频率特性。针对这个难题,在分析了Helm-holtz空心圆柱线圈、电磁铁、永磁铁、通流导线等磁场发生装置的特性与优缺点后,设计出一种实用性较强的磁场发生装置,能够产生较宽频率、较宽幅度的标准磁场,通过对磁场发生装置多项参数的仿真计算,验证了设计的可行性,最后给出了磁场发生装置的系统实现框图。     

磁悬浮控制系统工程设计方法研究

磁悬浮装置是典型的非线性系统,其模型随悬浮对象的变化而显著变化。控制器设计的复杂性和非通用性制约了磁悬浮的广泛应用。本文致力于探讨一种简单的工程设计方法,其目的是在没有受控对象的精确数学模型和负载不明确的情况下,根据简单实验的数据即可设计控制器参数。文中提出根据电流变化率设计控制器参数的方法,并以一个一自由度磁悬浮装置作为实验对象,对所提出的设计方法进行了验证,得到满意的实验结果。     

体内植入装置的磁耦合谐振无线电能传输分析

体内植入医疗装置已被广泛应用,然而使用传统的供电方法为其供电却极为不便。磁耦合谐振式无线电能传输通过近场区强耦合谐振实现能量的高效传输,为体内植入医疗装置的供电提供了有效途径。介绍了体内植入式医疗装置的磁耦合谐振式无线电能传输原理,阐述了无线电能传输技术的理论基础耦合模理论（ CMT）,并基于该理论仿真研究了磁耦合谐振式无线电能传输技术高效传输的必要条件。