Federico Moro

A novel h-ϕ approach for solving 3-D time-harmonic eddy current problems is presented. It makes it possible to limit the number of degrees of freedom required for the discretization such as the T-method, while overcoming topological issues related to it when multiply connected domains are considered. Global basis functions, needed for representing magnetic field in the insulating region, are obtained by a fast iterative solver. The computation of thick cuts by high-complexity computational topology tools, typically required by the T-method, is thus avoided. The final matrix system turns out to be symmetric and full-rank unlike the more classical A-A method, which requires gauging of magnetic vector potential to ensure uniqueness. Numerical tests show that the proposed method is accurate and the field problem solution is obtained in a reasonable computational time even for 3-D models with millions of mesh elements. INDEX TERMS Eddy currents, finite element method, cell method, multiply connected, cut.

Purpose – The purpose of this paper is to optimize the performance of direct methanol fuel cells for portable applications by combining a non-linear, fully coupled circuit model and a stochastic optimization procedure. Design/methodology/approach – A novel non-linear equivalent circuit that accounts for electrochemical reactions and charge generation inside catalyst layers, electronic and protonic conduction, methanol crossover through the membrane, mass transport of reactants inside diffusion layers is presented. The discharge dynamic of the fuel cell, depending on the initial methanol concentration and on the load profile, is modelled by using the mass conservation equation. The equivalent circuit is interfaced to a stochastic optimization procedure in order to maximize the battery duration while minimizing fuel crossover. Findings – In the proposed circuit scheme, unlike semi-empirical models, lumped circuit parameters are derived directly from mass transport and electric equations in order to fully describe the dynamic performance of the fuel cell. Physical and geometrical parameters are optimized in order to improve the system runtime. It is shown that a combined use of fuel cells and lithium batteries can improve the runtime of portable electronic devices compared to traditional supply systems based on lithium batteries only. Research limitations/implications – The one-dimensional model of the micro fuel cell does not take into account possible transverse mass and electric charge flows in the fuel cell layers; most of the geometric and physics model parameters cannot be estimated from direct in situ or ex situ measurements. Practical implications – Direct methanol fuel cells are nowadays a promising technology for replacing or complementing lithium batteries due to their high energy density. Most limiting features of direct methanol fuel cells are the fuel crossover and its slow oxidation kinetics. By using the proposed approach, fuel cell parameters can be optimized in order to enhance the discharge runtime and to reduce the methanol crossover. Originality/value – The equivalent circuit model with optimized lumped non-linear parameters can be used when designing power management units for portable electronic devices.

ABSTRACT A three-dimensional (3D) domain decomposition method for analyzing electrical-thermal contact problems is presented. The computational domain is subdivided into non-overlapping regions discretized according to the Cell Method. Voltage and temperature drops at the contact interfaces are modelled by means of boundary constitutive operators. Continuity between sub-domains is enforced with Lagrange multipliers. The final non-linear algebraic system is solved by an iterative Newton procedure combined to a Schur’s complement approach in order to reduce the problem size and improve the condition number. Potential and temperature jumps across the contact interface depend on the local surface conditions according to Holm’s theory. Surface roughness and a-spot density in the contact area are modelled by means of statistical parameters that can be easily embedded into a CM formulation. The developed code has been validated by a 3D FEM commercial software package.

Developments in computational methods for solving boundary value problems, coupled with the advances in computer hardware, has led to the commercial availability of very efficient computer aided engineering (CAE) tools. The aim of this work is to define a suitable criterion for the shape design optimization of HV shielding electrodes for reducing the radio interference. The experimental part of the

The electromagnetic environment related to electric power installations is typically evaluated by numerical integration methods. Numerical techniques, although powerful, are not well suited for assessing the dependence of the field strength on electric and geometric parameters. In this paper, a fast procedure to analytically evaluate power-line magnetic fields, based on complex vectors, is proposed. The use of complex algebra greatly

All-Vanadium Redox Flow Batteries (VRFBs) are emerging as a novel technology for  stationary  energy  storage.  Numerical  models  are useful  for  exploring  the  potential performance of such devices, optimizing the structure and operating condition of cell stacks, and studying its interfacing to the electrical grid. A one-dimensional steady-state multiphysics
model of a single VRFB, including mass, charge and momentum transport and conservation, and coupled to a kinetic model for electrochemical reactions, is first presented. This model is
then  extended,  including  reservoir  equations,  in  order  to  simulate  the  VRFB  charge  and discharge dynamics. These multiphysics models are discretized by the finite element method in a commercial software package (COMSOL). Numerical results of both static and dynamic 1D models are compared to those from 2D models, with the same parameters, showing good agreement. This motivates the use of reduced modelsfor a more efficient system simulation.

The existence of complementary energy bounds for magnetostatic problems discretized by the Finite Integration Technique (FIT) is proved, when material matrices are constructed according to the so–called energetic approach. A numerical example shows that complementarity provides fast and accurate estimates of global quantities such as the inductance.

Novel basis functions are proposed for enforcing continuity constraints in 3-D elliptic problems discretized by
non-conforming domain decomposition methods. The major advantage over standard coupling methods is that the projection matrix, mapping degrees of freedom from master to slave surface, can be constructed with minimum computing effort since the slave matrix is diagonal. The accuracy of matching conditions and convergence properties of the method are tested on a benchmark problem.

Abstract Purpose – The purpose of this paper is to optimize the performance of direct methanol fuel cells for portable applications by combining a non-linear, fully coupled circuit model and a stochastic optimization procedure. Design/methodology/approach –A novel non-linear ...

A 3-D domain decomposition method for fully coupled electrothermomechanical contact problems is presented. The formulation is based on the cell method. Contacting domains are linked together by introducing a new reference frame (i.e., the mortar surface). Field discontinuities across contact interfaces are simulated by suitable constitutive operators. It is shown that the same coupling strategy can be adopted for the electrical, thermal, and mechanical contact problems. Compatibility constraints are imposed by means of dual Lagrange multipliers defined on the mortar surface. Coupled nonlinear algebraic equations are finally cast into a saddle-point problem, which is resolved by combining the Schur complement method with the Newton-Raphson method. The proposed mortar approach is validated with a commercial 3-D finite-element method multiphysics software package.

Abstract Purpose – The purpose of this paper is to simulate passive proton exchange membrane fuel cells (PEMFCs) for portable electronic devices by means of a non-linear lumped circuit based on electrical, mass transfer and electro-kinetic equations. Design/methodology/approach ...

The design of a magnetic shielding arrangement for an indoor substation is considered. The aim of the intervention is to reduce the magnetic field intensity inside a room above the substation. Stray fields are mitigated by using metallic screens and by rearranging LV cables in order to limit intervention costs. A three-dimensional electromagnetic analysis of stray fields is performed by means of an original integral code, whereas a two-dimensional FEM software is used for assessing the shielding performance locally, in proximity of LV cables. Simulations show that the highest field attenuation levels are attained when phases of conductors and transformers are arranged in optimised configurations. The developed procedure is then applied to design a magnetic shield for a MV/LV substation. It is shown that measured and computed field r.m.s. values of the magnetic flux density are in good agreement.