16,143 research outputs found

    Accelerated Steady-State Torque Computation for Induction Machines using Parallel-In-Time Algorithms

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    This paper focuses on efficient steady-state computations of induction machines. In particular, the periodic Parareal algorithm with initial-value coarse problem (PP-IC) is considered for acceleration of classical time-stepping simulations via non-intrusive parallelization in time domain, i.e., existing implementations can be reused. Superiority of this parallel-in-time method is in its direct applicability to time-periodic problems, compared to, e.g, the standard Parareal method, which only solves an initial-value problem, starting from a prescribed initial value. PP-IC is exploited here to obtain the steady state of several operating points of an induction motor, developed by Robert Bosch GmbH. Numerical experiments show that acceleration up to several dozens of times can be obtained, depending on availability of parallel processing units. Comparison of PP-IC with existing time-periodic explicit error correction method highlights better robustness and efficiency of the considered time-parallel approach

    Parallel-In-Time Simulation of Eddy Current Problems Using Parareal

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    In this contribution the usage of the Parareal method is proposed for the time-parallel solution of the eddy current problem. The method is adapted to the particular challenges of the problem that are related to the differential algebraic character due to non-conducting regions. It is shown how the necessary modification can be automatically incorporated by using a suitable time stepping method. The paper closes with a first demonstration of a simulation of a realistic four-pole induction machine model using Parareal

    Spectral/hp element methods: recent developments, applications, and perspectives

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    The spectral/hp element method combines the geometric flexibility of the classical h-type finite element technique with the desirable numerical properties of spectral methods, employing high-degree piecewise polynomial basis functions on coarse finite element-type meshes. The spatial approximation is based upon orthogonal polynomials, such as Legendre or Chebychev polynomials, modified to accommodate C0-continuous expansions. Computationally and theoretically, by increasing the polynomial order p, high-precision solutions and fast convergence can be obtained and, in particular, under certain regularity assumptions an exponential reduction in approximation error between numerical and exact solutions can be achieved. This method has now been applied in many simulation studies of both fundamental and practical engineering flows. This paper briefly describes the formulation of the spectral/hp element method and provides an overview of its application to computational fluid dynamics. In particular, it focuses on the use the spectral/hp element method in transitional flows and ocean engineering. Finally, some of the major challenges to be overcome in order to use the spectral/hp element method in more complex science and engineering applications are discussed

    Nonlinear dynamics of attractive magnetic bearings

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    The nonlinear dynamics of a ferromagnetic shaft suspended by the force of attraction of 1, 2, or 4 independent electromagnets is presented. Each model includes a state variable feedback controller which has been designed using the pole placement method. The constitutive relationships for the magnets are derived analytically from magnetic circuit theory, and the effects of induced eddy currents due to the rotation of the journal are included using Maxwell's field relations. A rotor suspended by four electro-magnets with closed loop feedback is shown to have nine equilibrium points within the bearing clearance space. As the rotor spin speed increases, the system is shown to pass through a Hopf bifurcation (a flutter instability). Using center manifold theory, this bifurcation can be shown to be of the subcritical type, indicating an unstable limit cycle below the critical speed. The bearing is very sensitive to initial conditions, and the equilibrium position is easily upset by transient excitation. The results are confirmed by numerical simulation

    Collaboration among teachers in inclusive special education program classrooms

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    Collaboration between teachers and special education teachers is a vital factor in ensuring the success of the implementation of the Inclusive Education Programs especially in the teaching and learning aspects. Until 2016, there is no detailed document or information regarding how the collaboration is conducted or implemented in the inclusive classrooms. Therefore, this study is aimed to explore how collaboration is conducted and implemented in the Inclusive Special Education Program classrooms, particularly identifying the stage of collaboration the school are at and approach used in the inclusive classrooms. To achieve this, a survey questionnaire was used as an instrument for this study and it is conducted on 53 schools and 441 participants including headmasters, senior assistant principals for special education teachers, subject teachers and special education teacher. Results showed that most of the participants are at the “Starting a partnership” stage (mean score = 4.165, SD = 0.797). The type of collaboration approach that are usually being used is the “collaboration-consultation” approach (mean score = 4.10, SD = 0.721). This suggests that more action is needed to ensure the successful implementation of an inclusive program. This is because without done the recommended steps of collaboration, the inclusive may not carried out effectively. A successful inclusive classroom also can be achieved through multiple approaches of collaboration are implemented. Therefore, knowledge about steps and approaches of collaboration should be knowledgeable to general, special education teacher and also school administrators

    Determination of efficiencies, loss mechanisms, and performance degradation factors in chopper controlled dc vehical motors. Section 2: The time dependent finite element modeling of the electromagnetic field in electrical machines: Methods and applications

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    The time dependent solution of the magnetic field is introduced as a method for accounting for the variation, in time, of the machine parameters in predicting and analyzing the performance of the electrical machines. The method of time dependent finite element was used in combination with an also time dependent construction of a grid for the air gap region. The Maxwell stress tensor was used to calculate the airgap torque from the magnetic vector potential distribution. Incremental inductances were defined and calculated as functions of time, depending on eddy currents and saturation. The currents in all the machine circuits were calculated in the time domain based on these inductances, which were continuously updated. The method was applied to a chopper controlled DC series motor used for electric vehicle drive, and to a salient pole sychronous motor with damper bars. Simulation results were compared to experimentally obtained ones
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