Fabrizio Ferraioli

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.

Effective Exploitation of Prior Information in Electrical Impedance Tomography for Thermal Monitoring of Hyperthermia Treatments

Real-time monitoring of hyperthermia treatments for liver cancers by noninvasive techniques was investigated in the last two decades. Among the proposed techniques, Electrical Impedance Tomography (EIT) arises particular interest for its low cost and sensitivity to tissues parameter changes to be detected. In this paper, an approach based on the intensive but critical exploitation of prior information is proposed and a preconditioning method of the impedance measurements based on a sensitivity analysis is assessed.

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

Electromechanical analysis of end windings in turbo generators

Purpose – The purpose of this paper is to present a numerical approach for the computation of 3D magnetic fields in rotating electrical machines. The technique is suitable for the computation of flux densities and forces in the end windings of large synchronous turbo generators (TG).Design/methodology/approach – The magnetostatic FEM model of the generator end windings is carried out for different displacements of the rotor axis to the stator magnetomotive force (MMF) axis. The method is based on a parallel integral formulation allowing to substantially reduce the computational effort.Findings – The computational model requires only the discretization of magnetic materials and conductors and is fast enough for carrying out 3D analyses on a time scale fast enough for the needs of the designer. As far as the present application is concerned, the analysis of a synchronous generator in the class of 300‐400 MVA has shown that the most stressed elements of the armature conductors are those closer to the stator ...

Criteria for the optimal design of magneto-encephalography measurement system

Magneto-encephalography is a promising technique for the in vivo monitoring of brain activity. The information about neural activity is reconstructed from the electrical current map of the brain, which is in turn deduced, via an inverse problem resolution, from the magnetic field map measured by superconductive quantum interference devices placed around the head. In this paper, a possible strategy to improve the detection ability of the procedure by optimally designing the representation system is proposed and discussed

Computation of end-winding inductances of rotating electrical machinery through three-dimensional magnetostatic integral FEM formulation

Purpose – The paper aims to illustrate a numerical technique to calculate fields and inductances of rotating electrical machines. Design/methodology/approach – The technique is based on an integral formulation of the nonlinear magnetostatic model in terms of the unknown magnetization. The solution is obtained by means of a Picard-Banach iteration whose convergence can be theoretically proved. Findings – The proposed method has been used to build a model of a large turbine generator. In particular, the influence of end effects on flux linkages has been computed. It has been demonstrated that the 2D solution underestimates the flux linkages as well as the no load voltage of 2 per cent, while the leakage fluxes are computed by the 2D solution with errors as high as 20 per cent. Originality/value – The method is advantageous in comparison to standard methods.

Three dimensional optimal current patterns for radiofrequency ablation treatments

Purpose – The purpose of this paper is to propose a planning strategy for the radio frequency ablation (RFA) treatment of hepatic tumors. The goal is to give to the surgeon the opportunity of controlling the shape and the size of the treated volume and preserving the healthy tissues.Design/methodology/approach – A FEM model of the human torso is built from radiographic and MRI scans of the patients, and then the RFA treatment “dynamically optimized” by controlling currents in multiple external electrodes, in such a way to drive currents in the desired regions, burning the tumor while trying to preserve healthy regions. A suitable cellular death model is considered in order to achieve an effective description of the biological modifications in the tumor volume.Findings – A numerical method to plan the RFA treatment of hepatic tumors has been defined, aiming to preserve as much as possible healthy tissues.Research limitations/implications – The method depends on the knowledge of inner structure and properti...

Adaptive Ablation Treatment Based on Impedance Imaging

The application of thermal ablation technique and, in particular, of the radiofrequency ablation (RFA), has become widely used in the treatment of solid tumors. The use of optimization methods to plan the therapy is among the emerging fields of interests. Monitoring of the ablative treatment by using electrical impedance tomography (EIT), allowing real time observations with no ionizing radiations and at low cost, is also considered a relevant goal. In this paper, a proposal for an adaptive RFA treatment based on multiple external electrodes and EIT images is presented. In particular, the distribution of Ohmic power deposition is optimized by controlling the current pattern on multiple external electrodes in such a way to achieve a suitable temperature rise in the tumour volume limiting it at the same time in healthy tissues. The optimization of the RFA heating is based on the knowledge of the electric properties of living tissues; the well known uncertain knowledge of this parameter is at least partially resolved by generating online EIT images.

A circuital formulation for direct electrical resistive tomography problems

Purpose – Electrical resistive tomography (ERT) is a non‐destructive testing technique based upon the reconstruction of the electrical conductivity profile inside a body from measurement made on its boundary. In the literature about the inverse problems the ERT is considered still challenging being both non‐linear, ill‐posed and very limited in resolution. Purpose of the paper is to assess the performances of an approach exploiting the circuital behaviour of a particular class of problems, highlighting its advantages in terms of simplicity and reduction of the computer burden.Design/methodology/approach – In this paper, an electrical property of a particular class of problems is pointed out; the same property is used to formulate in terms of a circuital model the ERT problem. The proposed methodology consists basically of combining properly simplified data previously evaluated and collected. The overall procedure is presented with reference to an underground structure diagnostics problem.Findings – The ef...

Strategies for brain sources and tissues properties identification from EEG/MEG and EIT signals

The estimation of human brain cellular activity from EEG/MEG signals requires a rather accurate knowledge of the living tissues electrical properties. The identification of these properties from joint EEG/MEG measurements as well as from impedance tomography has been thoroughly investigated in literature. In this paper, an assessment of the information content coming from each diagnostics, and their possible interactions, will be presented and discussed.