Alessandro Formisano

Optimal magnetic probes location for current reconstruction in multistrands superconducting cables

The critical current in multistrand superconducting (SC) cables is usually lower than expected due to current imbalance among strands and early current sharing. It is thus crucial to be able to detect the current distribution in SC cables to assess their stability properties. Due to the ill-conditioning of the problem, the reconstruction accuracy may prove very sensitive to measurement noise and to the uncertainty of the numerical data. In this work, a possible allocation strategy for the magnetic probes is discussed, aimed at optimization of the reconstruction process.

Coupled Three Dimensional Numerical Calculation of Forces and Stresses on the End Windings of Large Turbo Generators via Integral Formulation

A novel numerical approach to calculate the time evolution of the three dimensional distribution of the magnetic field and forces in the end winding regions of large turbine generators is presented. The proposed approach is based on an integral formulation for nonlinear magnetostatic problems. Its main advantage is the reduction of the discretization to only the conductors and magnetic materials. In this paper the solution of a coupled magnetostructural problem consisting in the calculation of the mechanical stresses and deformations caused by the electrodynamic forces is presented. The analysis is based on a time stepping simulation where the currents are derived from the integration of a lumped parameter model.

Robust design of high field magnets through Monte Carlo analysis

An effective approach to the optimal design of electromagnetic devices should take into account the effect of mechanical tolerances on the actual devices performance. A possible approach could be to match a Pareto optimality study with a Monte Carlo analysis by randomly varying the constructive parameters. In this paper it is shown how such an analysis can be used to allow an expert designer to select among different Pareto optimal designs.

A genetic algorithm approach to the design of split coil magnets for MRI

Innovative, open magnet designs for Magnetic Resonance Imaging (MRI) of parts of human body have been recently proposed. These open configurations require notable skill in the design phase to obtain satisfactory performance in terms of compactness and field homogeneity; optimization techniques thus seems adequate to assist the designer of such devices. A novel optimization scheme, based on a genetic algorithm (GA) has been implemented for the resolution of this problem. The GA seems well suited for this applications thanks to its ability in exploring the whole design parameters space, not being trapped by local minima, but some improvements have been implemented, namely floating point parameter representation, introduction of a directional mutation operator and adaptive probability of operators action.

A Lagrangian approach to shape inverse electromagnetic problems

This paper presents a completely Lagrangian approach which is able to solve shape inverse (optimization and identification) electromagnetic problems. A first order deterministic minimization technique combined with Lagrangian finite element approach is used. Theoretical and numerical advantages and drawbacks of such a method are discussed, and some applications are presented.

Stochastic handling of tolerances in robust magnets design

Due to construction tolerances, the performances of actual electromagnetic devices differ from those of the nominal design. A strategy for the search of design solutions robust against construction tolerances is presented. The approach is based on the statistical analysis of the tolerances impact on the design objective function to be evaluated. The application of the proposed strategies to the optimal design of magnetic resonance imaging magnets by a genetic algorithm shows the possibility to direct the search toward robust solutions.

Effectiveness in 3-D Magnetic Field Evaluation of Complex Magnets

Numerical high-accuracy evaluation of 3-D magnetic field generated by complex magnetic structures can be a quite demanding task. In order to save the computational effort, while preserving the accuracy level, a number of simple magnetic elements able to model complex 3-D structures are available. In this paper, a critical comparison of different modeling has been carried out in the perspective of a graphical processing unit implementation.

Tolerance Analysis of NMR Magnets

Due to manufacturing and assembly variations, there are tolerances associated with the nominal dimensions of complex electromagnetic devices. A possible approach to take into account such tolerances in the early design phases is the “worst case tolerance analysis,” whose goal is to determine the effect of the largest variations on assembly dimensions on the product performance. On the other hand, when many tolerances must be considered, locating the worst case with combinatorial effects could get very time consuming, since performance assessment of such devices may require numerical field analysis. In this paper, a fast approach based on the performance sensitivity with respect to design parameters is presented, and applied to the tolerance analysis of nuclear magnetic resonance (NMR) magnets.

An Approach to the Electrical Resistance Tomography Based on Meshless Methods

Electrical resistance tomography is a noninvasive diagnostic technique based on the identification of the conductivity profile inside a control volume using injected low-frequency currents. Possible advantages in clinical applications coming from a numerical approach based on the combination of meshless method and finite element method are discussed

Increasing design robustness in evolutionary optimisation

The role of the parameters uncertainness in the optimal design of electromagnetic devices is discussed and an efficient strategy to look for robustness of feasible solutions is proposed. A suitable modification of the objective function (OF) is used to rank different device configurations on the basis of their ability to maintain the required performances against small parameters modifications due to construction tolerances. In the frame of a genetic algorithm approach, the modified OF has been able to address the evolutionary optimisation towards more robust solutions.