Starting from a previously developed lightning return stroke representation, the electric field p... more Starting from a previously developed lightning return stroke representation, the electric field propagating into a dissipative soil is considered as incident field for embedded earth electrodes. Then the method of Moments is applied to investigate transient performances of earth electrodes of large size and complex shape. So, primary and secondary currents, field transferred to separate electrodes, electric field on the surface of the soil and voltages arising between different parts of earthed electric equipment can be evaluated. Some application examples are reported.
ABSTRACT In this paper, a first application of the method of fundamental solutions in estimating ... more ABSTRACT In this paper, a first application of the method of fundamental solutions in estimating the electric potential and the spatial current density distribution in the brain due to transcranial stimulation, is presented. The coupled boundary value problems for the electric potential are solved in a meshless way, so avoiding the use of grid based numerical methods. A multi-spherical geometry is considered and numerical results are discussed.
ABSTRACT The estimation of neuronal activity in the human brain from electroencephalography (EEG)... more ABSTRACT The estimation of neuronal activity in the human brain from electroencephalography (EEG) and magnetoencephalography (MEG) signals is a typical inverse problem whose solution process requires an accurate and fast forward solver. In this paper the method of fundamental solutions is, for the first time, proposed as a meshfree, boundary-type, and easy-to-implement alternative to the boundary element method (BEM) for solving the M/EEG forward problem. The solution of the forward problem is obtained by numerically solving a set of coupled boundary value problems for the three-dimensional Laplace equation. Numerical accuracy, convergence, and computational load are investigated. The proposed method is shown to be a competitive alternative to the state-of-the-art BEM for M/EEG forward solving.
L'attività di ricerca si prefigge di dare un contributo alla modellistica numerica nel contesto d... more L'attività di ricerca si prefigge di dare un contributo alla modellistica numerica nel contesto della MEG. In questa prima fase è stata affrontata la modellizzazione numerica del problema diretto avvalendosi di un approccio particellare, basato sulla tecnica meshless Smoothed Particle Hydrodynamics (SPH). Con tale schema numerico, una funzione incognita e le sue derivate si possono valutare per mezzo di una appropriata rappresentazione integrale. La intrinseca natura del metodo consente di modellizzare efficientemente problemi multi-sorgente, anche puntiformi, in domini con diffuse inomogeneità ed anisotropie. I primi risultati ottenuti riguardano la simulazione di domini sferici anche multistrato con sorgenti tipo dipolo: il confronto con analoghi risultati presenti in letteratura mostra la validità del metodo proposto.
... New Delhi 110 002 35-36 Creams Road, Thousand Lights, Chennai 600 006 306 Shiv Centre, DBC Se... more ... New Delhi 110 002 35-36 Creams Road, Thousand Lights, Chennai 600 006 306 Shiv Centre, DBC Sector 17, KU Bazar PO, Navi Mumbai 400 705 2F-2G Shivam Chambers, 53 ... Consumption-Investment Decisions on Fixed Income 503 Radha Panini and Ram P. Srivastav ...
In this paper a field approach to investigate the transient performance of long grounding electro... more In this paper a field approach to investigate the transient performance of long grounding electrodes is presented. The method is based on the spectral analysis and, as a great advantage in comparison with circuit approach, it enables us to calculate electrical and magnetic fields in the surrounding soil. As a particular matter, this paper, after having investigated the behaviour of a single electrode, is devoted to study fields transferred from an electrode to a separate one, in any mutuai position. As examples, time behaviour of main electric quantities are reported assuming a lightning stroke injected current.
This paper deals with the application of wavelets in a computational tool, based on a modified ve... more This paper deals with the application of wavelets in a computational tool, based on a modified version of the thin-wire electric field integrai equation (EFIE) in frequency domain, devoted to analyse transient performances of electric power substations grounding systems in a homogeneous soil. Time profiles of the electromagnetic quantities can be evaluated via discrete fast Fourier transform. In the numerical scheme, after having discretized the electromagnetic problem by applying the method of moments in a direct formulation, wavelet filter coefficients are directly employed to build a wavelet-matrix transform by using the concept of wavelet decomposition and reconstruction algorithms. The application of the wavelet-matrix transform to the moment matrix generated by the modified EFIE, produces a sparse matrix equation which can be efficiently solved by the conjugate gradient method. Moreover, a preconditioner which strongly reduce the number of iterations of the iterative solver adopted, has been built by using the same wavelet-matrix transform. The computational results obtained by running a complex earthing structure are discussed. I. INTRODUCTION Wavelet theory [1] is a relatively new and emerging area in mathematical research. It has been applied in a wide range of engineering disciplines. Recently, the use of wavelets and wavelet-like basis functions in computational electromagnetics has received considerable attention for the numerical analysis of integrai equations. The integrai equation approaches have the merit of reducing the solution domain to a small finite region containing boundary conditìons implicitly. However, the major drawback of this method is that the integrai equation formulation specifies the global interactions among sources, object and fields; by usually applying the method of moments in a direct formulation, this leads to a dense matrix equation. For small to medium scale problems, the integrai equation approach enables efficient numerical solutions. But, for large scale problems, the dense matrix equation leads to computations which are often prohibitive.
In this paper a method to accurately simulate the human body under a high voltage overhead line o... more In this paper a method to accurately simulate the human body under a high voltage overhead line or in proximity to substation's equipment is proposed, in order to evaluate the electric field and currents on the human body surface. Based on the charge simulation and Maxwell subareas methods, the computer program developed allows to consider complex systems, including three-dimensional multiple overhead lines, bus-bar system, grounding wires, supporting lattice towers and metallic elements as reinforcing bars.
This paper proposes a Maxwell's equations finite difference time domain (FDTD) approach for elect... more This paper proposes a Maxwell's equations finite difference time domain (FDTD) approach for electromagnetic transients in ground electrodes in order to take into account the non linear effects due to soil ionization. A time variable soil resistivity method is used in order to simulate the soil breakdown, without the formulation of an a priori hypothesis about the geometrical shape of the ionized zone around the electrodes. The model has been validated by comparing the computed results with available data found in technical literature referred to concentrated earths. Application examples are also reported in order to show the computational capability. Streszczenie. (Zastosowanie FTDT przy efektach nieliniowych w elektrodach uzlemiafacych), W ailykule zaproponowano zastosowanie rownan Maxwella do modelowanie metodq roznic skonczonych zagadnienia przebiegow czasowych pola elektromagnetycznego koto elektrody uziemiafacej (FTDT). Zostaty uwzgl^dnione nieliniowe efekty zwia^zane z jonizacjfi ziemi. Zastosowano metod$ zmiennej w czasie rezystywnosci gleby bez okreslenia geometiycznego ksztatiu jonizowanego obszaru wokof elektrody. Model zostal zweryfikowany poprzez porownanie wynikow obliczen z danymi literaturowymi dla zage_szczonej ziemi. Przyktadowe zastosowania pokazujq mozliwosci obliczeniowe melody.
Starting from a previously developed lightning return stroke representation, the electric field p... more Starting from a previously developed lightning return stroke representation, the electric field propagating into a dissipative soil is considered as incident field for embedded earth electrodes. Then the method of Moments is applied to investigate transient performances of earth electrodes of large size and complex shape. So, primary and secondary currents, field transferred to separate electrodes, electric field on the surface of the soil and voltages arising between different parts of earthed electric equipment can be evaluated. Some application examples are reported.
ABSTRACT In this paper, a first application of the method of fundamental solutions in estimating ... more ABSTRACT In this paper, a first application of the method of fundamental solutions in estimating the electric potential and the spatial current density distribution in the brain due to transcranial stimulation, is presented. The coupled boundary value problems for the electric potential are solved in a meshless way, so avoiding the use of grid based numerical methods. A multi-spherical geometry is considered and numerical results are discussed.
ABSTRACT The estimation of neuronal activity in the human brain from electroencephalography (EEG)... more ABSTRACT The estimation of neuronal activity in the human brain from electroencephalography (EEG) and magnetoencephalography (MEG) signals is a typical inverse problem whose solution process requires an accurate and fast forward solver. In this paper the method of fundamental solutions is, for the first time, proposed as a meshfree, boundary-type, and easy-to-implement alternative to the boundary element method (BEM) for solving the M/EEG forward problem. The solution of the forward problem is obtained by numerically solving a set of coupled boundary value problems for the three-dimensional Laplace equation. Numerical accuracy, convergence, and computational load are investigated. The proposed method is shown to be a competitive alternative to the state-of-the-art BEM for M/EEG forward solving.
L'attività di ricerca si prefigge di dare un contributo alla modellistica numerica nel contesto d... more L'attività di ricerca si prefigge di dare un contributo alla modellistica numerica nel contesto della MEG. In questa prima fase è stata affrontata la modellizzazione numerica del problema diretto avvalendosi di un approccio particellare, basato sulla tecnica meshless Smoothed Particle Hydrodynamics (SPH). Con tale schema numerico, una funzione incognita e le sue derivate si possono valutare per mezzo di una appropriata rappresentazione integrale. La intrinseca natura del metodo consente di modellizzare efficientemente problemi multi-sorgente, anche puntiformi, in domini con diffuse inomogeneità ed anisotropie. I primi risultati ottenuti riguardano la simulazione di domini sferici anche multistrato con sorgenti tipo dipolo: il confronto con analoghi risultati presenti in letteratura mostra la validità del metodo proposto.
... New Delhi 110 002 35-36 Creams Road, Thousand Lights, Chennai 600 006 306 Shiv Centre, DBC Se... more ... New Delhi 110 002 35-36 Creams Road, Thousand Lights, Chennai 600 006 306 Shiv Centre, DBC Sector 17, KU Bazar PO, Navi Mumbai 400 705 2F-2G Shivam Chambers, 53 ... Consumption-Investment Decisions on Fixed Income 503 Radha Panini and Ram P. Srivastav ...
In this paper a field approach to investigate the transient performance of long grounding electro... more In this paper a field approach to investigate the transient performance of long grounding electrodes is presented. The method is based on the spectral analysis and, as a great advantage in comparison with circuit approach, it enables us to calculate electrical and magnetic fields in the surrounding soil. As a particular matter, this paper, after having investigated the behaviour of a single electrode, is devoted to study fields transferred from an electrode to a separate one, in any mutuai position. As examples, time behaviour of main electric quantities are reported assuming a lightning stroke injected current.
This paper deals with the application of wavelets in a computational tool, based on a modified ve... more This paper deals with the application of wavelets in a computational tool, based on a modified version of the thin-wire electric field integrai equation (EFIE) in frequency domain, devoted to analyse transient performances of electric power substations grounding systems in a homogeneous soil. Time profiles of the electromagnetic quantities can be evaluated via discrete fast Fourier transform. In the numerical scheme, after having discretized the electromagnetic problem by applying the method of moments in a direct formulation, wavelet filter coefficients are directly employed to build a wavelet-matrix transform by using the concept of wavelet decomposition and reconstruction algorithms. The application of the wavelet-matrix transform to the moment matrix generated by the modified EFIE, produces a sparse matrix equation which can be efficiently solved by the conjugate gradient method. Moreover, a preconditioner which strongly reduce the number of iterations of the iterative solver adopted, has been built by using the same wavelet-matrix transform. The computational results obtained by running a complex earthing structure are discussed. I. INTRODUCTION Wavelet theory [1] is a relatively new and emerging area in mathematical research. It has been applied in a wide range of engineering disciplines. Recently, the use of wavelets and wavelet-like basis functions in computational electromagnetics has received considerable attention for the numerical analysis of integrai equations. The integrai equation approaches have the merit of reducing the solution domain to a small finite region containing boundary conditìons implicitly. However, the major drawback of this method is that the integrai equation formulation specifies the global interactions among sources, object and fields; by usually applying the method of moments in a direct formulation, this leads to a dense matrix equation. For small to medium scale problems, the integrai equation approach enables efficient numerical solutions. But, for large scale problems, the dense matrix equation leads to computations which are often prohibitive.
In this paper a method to accurately simulate the human body under a high voltage overhead line o... more In this paper a method to accurately simulate the human body under a high voltage overhead line or in proximity to substation's equipment is proposed, in order to evaluate the electric field and currents on the human body surface. Based on the charge simulation and Maxwell subareas methods, the computer program developed allows to consider complex systems, including three-dimensional multiple overhead lines, bus-bar system, grounding wires, supporting lattice towers and metallic elements as reinforcing bars.
This paper proposes a Maxwell's equations finite difference time domain (FDTD) approach for elect... more This paper proposes a Maxwell's equations finite difference time domain (FDTD) approach for electromagnetic transients in ground electrodes in order to take into account the non linear effects due to soil ionization. A time variable soil resistivity method is used in order to simulate the soil breakdown, without the formulation of an a priori hypothesis about the geometrical shape of the ionized zone around the electrodes. The model has been validated by comparing the computed results with available data found in technical literature referred to concentrated earths. Application examples are also reported in order to show the computational capability. Streszczenie. (Zastosowanie FTDT przy efektach nieliniowych w elektrodach uzlemiafacych), W ailykule zaproponowano zastosowanie rownan Maxwella do modelowanie metodq roznic skonczonych zagadnienia przebiegow czasowych pola elektromagnetycznego koto elektrody uziemiafacej (FTDT). Zostaty uwzgl^dnione nieliniowe efekty zwia^zane z jonizacjfi ziemi. Zastosowano metod$ zmiennej w czasie rezystywnosci gleby bez okreslenia geometiycznego ksztatiu jonizowanego obszaru wokof elektrody. Model zostal zweryfikowany poprzez porownanie wynikow obliczen z danymi literaturowymi dla zage_szczonej ziemi. Przyktadowe zastosowania pokazujq mozliwosci obliczeniowe melody.
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