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Antonio MASSARINI

Professore Associato
Dipartimento di Ingegneria "Enzo Ferrari"

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Pubblicazioni

- Feed-forward control of aircraft bus dc boost converter [Brevetto]
J. A., Weimer; M. K., Kazimierczuk; Massarini, Antonio; R. C., Cravens II
abstract

An open loop control arrangement for an electrical energy flow-controlling circuit coupling the varying terminal voltage of an energy storing capacitor to a fixed voltage direct current aircraft energy supply bus in order to supplement bus voltage transients. the open loop controlarrangement allows energy flow from the varying terminal voltage of the capacitor to the fixed bus voltage by providing a time varying pulse modulation cycle in an energy conveying and voltage changing inductive element located in the energy coupling path. The open loop control arrangement senses input voltage rather output voltage of the coupling circuit in what is termed "feed forward" output regulation algorithm. A transistorized and itegrated circuit inclusive preferred embodiment of the invention is disclosed in which a disconnect of the inductance from the aircraft supply bus is accomplished during shunt path inductance energy charging portions of an operating cycle.

2018 - Analytical Approach to the Calculation of Parasitic Capacitance between Winding Turns [Relazione in Atti di Convegno]
Massarini, A.
abstract

At high frequencies, winding components behave differently than at low frequencies. Therefore, suitable models are required which can predict coil performances over the whole possible range of frequencies they can be operated. Inductors used in power electronic conversion, magnetic sensors, EMC equipments, and also motor windings can experience frequency levels above several hundreds of kHz where parasitic resistance and capacitance can affect significantly their intended operation. One of the main problems is modeling turn-to-turn capacitance of coils both for single- and multiple-layer windings. The lumped parameter models used in literature for HF inductor simulation are based on simplified approaches to the turn-to-turn and turn-to-core capacitance calculation. In this paper, an analytical approach based on conformal mapping to calculate the exact solution for the turn-to turn and turn-to-core capacitances for coils with different geometrical structures is introduced.

2004 - Electromgnetic coupling between wires and loops inside a rectangular cavity using multiple-mode transmission line theory [Relazione in Atti di Convegno]
A., Nanni; D. W. P., Thomas; C., Christopoulos; T., Konefal; J., Paul; L., Sandrolini; U., Reggiani; Massarini, Antonio
abstract

The efficiency and reliability of the multiple-mode transmission line theory applied to predict the electromagnetic coupling between electric monopoles with conducting planes inside a metallic enclosure is assessed in this paper. The planes are represented with an equivalent impedance through a transmission line analogy. Particularly critical coupling configurations, such as close monopole-to-plane and plane-to-plane configurations are tested. The results obtained with the proposed method are compared to experimental measurements and transmission-line modelling method (TLM) numerical simulations. The proposed model is attractive due to its rapidity and good accuracy in predicting the coupling configurations examined.

2004 - Model of laminated iron-core inductors for high frequencies [Articolo su rivista]
Grandi, G; Kazimierczuk, Mk; Massarini, Antonio; Reggiani, U; Sancineto, G.
abstract

We propose a model with frequency-dependent lumped parameters to represent the behavior of laminated iron-core inductors that are used in switching converters, i.e., for excitation frequencies above several kilohertz. The model applies to laminated iron cores with air gaps. We show that the core parameters can be calculated by using the same analytical expressions as those valid for gapless cores if a properly defined equivalent magnetic permeability is introduced instead of the iron sheet permeability. We compare the inductor model parameters calculated as functions of frequency with those obtained by measurements for two test inductors. The behavior of the inductors showed that the effects due to the eddy currents in the laminated iron core and the turn-to-turn and turn-to-core stray capacitances become significant in different frequency ranges.

2004 - Non linear ciruit model of a polymer electrolyte membrane fuel cell [Relazione in Atti di Convegno]
U., Reggiani; L., Sandrolini; G. L., Giuliattini Burbui; A., Melotti; Massarini, Antonio
abstract

A nonlinear circuit model of a polymer electrolyte membrane (PEM) fuel cell stack is presented. The model considers the time dimension, allowing the simulation of both steady-state and dynamic behaviour of the stack. The circuit parameters can be obtained by means of simple experimental tests and calculations. The PEM stack is modeled as seen from the power conditioning system side, without requiring parameters necessary for complex mathematical models and not easily obtainable by the majority of users. A procedure of parameter determination is developed and a comparison between the simulated and experimental results for both steady-state and dynamic behaviour of the PEM stack is shown.

2004 - Review of simple electromagnetic models for predicting radiated emissions from PCBs [Relazione in Atti di Convegno]
G. L., GIULIATTINI BURBUI; Massarini, Antonio; U., Reggiani; L., Sandrolini
abstract

This paper reviews the basic mechanisms through which voltage and currents signals in printed circuit boards (PCBs) produce unwanted radiated emissions and some analytical models that can be used to predict these radiated emissions. Three models are applied to a simple PCB and the results are compared to those obtained with the electromagnetic analysis carried out with a Finite-Difference Time-Domain (FDTD) computer code. Although the models are not likely applicable to real-life problems, the comparison is useful to underline their assumptions and limitations.

2003 - Analysis of design solutions for a GTEM cell [Relazione in Atti di Convegno]
G. L., GIULIATTINI BURBUI; Massarini, Antonio; U., Reggiani; L., Sandrolini
abstract

Gigahertz Transverse Electromagnetic (GTEM) cells are among the standard environments used for radiated emission and immunity tests on electrical and electronic equipment and systems at frequencies from DC up to over 1 GHz. In this paper, an analysis of different cross sections for a GTEM cel is presented. The aim of this work is to find possible new shapes for GTEM cells suitable to obtain a more uniform electric field distribution inside an unloaded cell.

2003 - Experimental verification of predicted electromagnetic field radiated by straight connecting cables carrying high-frequency currents [Relazione in Atti di Convegno]
U., Reggiani; Massarini, Antonio; L., Sandrolini; M., Ciccotti; X., Liu; D. W. P., Thomas; C., Christopoulos
abstract

This paper provides an experimental verificationof analytical expressions for predicting radiated electromagneticfields from straight interconnect cables carrying high-frequencycurrents. These analytical expressions are derived through twodifferent models. The former model is based on the assumptionthat a radiating two-wire transmission line can be considered astwo Hertzian dipoles, while in the latter one each radiating wireis treated as a chain of short radiating dipoles. The radiated fieldis calculated and measured at selected locations and the resultsare compared in order to verify the agreement among them.Different configurations (two parallel cables at various distancesfrom a conducting ground plane) are considered.

2003 - Experimental verification of predicted electromagnetic fields radiated by straight interconnect cables carrying high-frequency currents [Relazione in Atti di Convegno]
Reggiani, U.; Massarini, A.; Sandrolini, L.; Ciccotti, M.; Liu, X.; Thomas, D. W. P.; Christopoulos, C.
abstract

This paper provides an experimental verification of analytical expressions for predicting radiated electromagnetic fields from straight interconnect cables carrying high-frequency currents. These analytical expressions are derived through two different models. The former model is based on the assumption that a radiating two-wire transmission line can be considered as two Hertzian dipoles, while in the latter one each radiating wire is treated as a chain of short radiating dipoles. The radiated field is calculated and measured at selected locations and the results are compared in order to verify the agreement among them. Different configurations (two parallel cables at various distances from a conducting ground plane) are considered. © 2003 IEEE.

2003 - Lumped circuit models of PCB lands in switching converters [Relazione in Atti di Convegno]
Massarini, Antonio; U., Reggiani; L., Sandrolini
abstract

This paper deals with circuit models that can be used to represents printed circuit lands of Switched-ModePower Supplies (SMPS). These circuit models are useful forthe prediction of the electromagnetic emissions radiatedfromsuch converters. Representations of SMPS built on printedcircuit board (PCB) in terms of lumped circuits and lumped-circuit iterative structures are considered and comparedunder different SMPS load conditions. These circuit modelsare also validated against measurements.

2003 - Radiated emissions from switching converters [Relazione in Atti di Convegno]
Massarini, Antonio; U., Reggiani; L., Sandrolini
abstract

This paper presents an attempt to solve the problem of predicting radiated emissions from a Switched-Mode Power Supply (SMPS). The model for the emission is based on the assumption that each conductor (land) of the printed circuit board (PCB) of which the SMPS is composed can be considered as a Hertzian dipole. The currents in the lands are determined by means of approximate lumped circuits connected in different ways and using a circuit simulator like PSPICE.

2002 - Frequency dependence of shielding effectiveness of multilayered magnetic shields [Relazione in Atti di Convegno]
Massarini, Antonio; U., Reggiani; L., Sandrolini
abstract

An analysis of magnetic shielding effectiveness of multilayered structures versus frequency is presented. It is shown that the quasistatic field approximation is accurate until several MHz depending on the source-to-observation-point distance, characteristic dimensions of the source, and physical and geometrical properties of layers. The accuracy is assessed by means of comparisons with the solution of the wave equation in a wide frequency reange. This study can be useful for the shield design and also for predicting the shielding effectiveness of multilayered magnetic shields in a source of non sinusoidal periodic magnetic fields.

2002 - Multifrequency optimization of multilayered shields [Articolo su rivista]
Massarini, A.; Reggiani, U.; Sandrolini, L.
abstract

A procedure for the optimization of planar multilayered shielding structures for magnetic fields, at frequencies for which the quasimagnetostatic description can be adopted, is presented in this paper. The optimum thickness of multilayered shields is found under the constraint of a minimum threshold value for the magnetic shielding effectiveness (SE) at a certain distance from a given source. The design of the shield with respect to the number and type of layers is carried out adopting the particle swarm optimization (PSO) method. Multilayered shields composed of selected materials are considered, and the optimal configuration in a source of a periodic triangular-wave current at the frequency of 10 kHz is investigated.

2002 - Shielding effectiveness of multilayered shields for magnetic field nonsinusoidal sources [Relazione in Atti di Convegno]
Massarini, Antonio; U., Reggiani; L., Sandrolini
abstract

The magnetic field generated by a nonsinusoidal periodic source is shielded by a planar infinite multilayered shield composed of high permeability and high conductivity materials. By means of a transform analytical approach the shielding effectiveness is calculated.

2001 - An efficient algorithm for the formulation of state equations and output equations for networks with ideal switches [Relazione in Atti di Convegno]
Massarini, A.; Reggiani, U.
abstract

A novel algorithm for the computer formulation of state equations and output equations for linear dynamic networks containing ideal switches is proposed. The state equation and output equation are obtained directly from each topology of the network and its element laws for all cases with no restriction and without the necessity to resort to an iterative procedure. The proposed method is efficient and easy to be implemented in a computer code.

2001 - Laminated iron-core inductor model for time-domain analysis [Relazione in Atti di Convegno]
Grandi, G.; Massarini, A.; Reggiani, U.; Sancineto, G.
abstract

The development of new power electronic components and soft switching techniques has allowed an increase in the switching frequency reducing the size of inductors and capacitors. Magnetic components are employed in most switching converters so a renewed attention is paid to inductors and transformers with particular emphasis to the high-frequency behavior of the winding and core, and the effects of parasitic capacitances. Laminated iron-core inductors are largely used in the medium to high power range as choke coils, filtering devices and link coils. In this paper, a model for laminated iron-core inductors is developed for studying electromagnetic transients. The proposed model allows time-domain analysis to be performed by means of standard circuit-oriented simulation programs.

2001 - Optimization of magnetic multilayered shields [Relazione in Atti di Convegno]
Massarini, A.; Reggiani, U.; Sandrolini, L.
abstract

In this paper a procedure for the optimization of multilayered shields for low-frequency magnetic fields is presented. The shield is optimized with respect to the total volume of the composing materials, being the magnetic flux density magnitude at test points in the shielded region smaller than a given threshold value. For simplicity, shields composed of two different materials only are considered. The number and thickness of the shield layers belong to the set of the control variables. Only one layer thickness at a time is allowed to vary. The procedure is repeated for the different multilayered shield configurations, starting from the single-layer ones for each material, until the optimum shield volume is reached.

2000 - A solution to the problem of determining X-points in magnetic induction fields [Articolo su rivista]
Massarini, Antonio; U., Reggiani; L., Sandrolini
abstract

A procedure which exploits a sufficient condition for determining X-points in quasi-static magnetic induction fields characterized by traditional or axisymmertical geometry is presented. The validity of the procedure and usefulness of the theorem are illustrated via a numerical example.

2000 - High-frequency behavior of laminated iron-core inductors for filtering applications [Relazione in Atti di Convegno]
Reggiani, U.; Grandi, G.; Sancineto, G.; Kazimierczuk, M. K.; Massarini, A.
abstract

Laminated iron-core inductors are largely used in power electronics applications. In particular, coupling reactors and filtering devices employ such a type of inductors in the medium-high power range. In this paper, a model is proposed to represent the behavior of these inductors that are used in switching converters, i.e., for excitation frequencies above several kHz.

2000 - Magnetic Shielding of Long Wires with Multilayered Cylinders [Relazione in Atti di Convegno]
Massarini, Antonio; U., Reggiani; L., Sandrolini
abstract

An efficient approach for evaluating the low-frequency magnetic shielding effectiveness of long cylindrical multilayered structures enclosing a system of straight wires is presented. No restriction is imposed on the number of both conductors and shielding layers and on the conductor locations inside the shell. The quasi-static shielded magnetic field is related to the unshielded one by means of a transmission matrix whose elements depend only on the geometry and material properties of each layer. the method is extremely flexible and the ruselts obtained are in good agreement with those derived from a finite element analysis.

2000 - Transform method for calculating low-frequency shielding effectiveness of planar linear multilayered shields [Articolo su rivista]
L., Sandrolini; Massarini, Antonio; U., Reggiani
abstract

A two-dimensional analytical solution for quasistatic magnetic field shielding with planar infinite multilayered shields is presented. The magnetic field source is a system of long straight mires parallel to the shield, carrying sinusoidal currents. The analysis assumes that material media can be considered linear under the applied source fields. The spatial Fourier cosine and sine transforms are applied to the analytical expressions of the magnetic field intensity and flux density is obtained by solving the diffusion equation in each layer. Using transfer relations for every layer in terms of transformed variables allows one to obtain the shielded field, and thus the shielding effectiveness, with no need to determine the integration functions explicitly, The results obtained with both this approach and a finite-element computer code are in good agreement, The method seems to be also suited for the analysis of problems with more complex geometries and source distributions.

1999 - Feedforward Control of DC-DC of PWM Buck Converters with Reference Voltage Modulation [Relazione in Atti di Convegno]
M. K., Kazimierczuk; Massarini, Antonio; M. A., Izadi
abstract

A feedforward control technique with reference voltage modulation is introduced for PWM buck converter operated in continuous conduction mode (CCM). the reference voltage is proportional to the dc converter input voltage. A steady-state analysis is performed. experimental results are given. the measured open-loop line voltage regulation was 1.32%/V.

1999 - Feedforward control with reference voltage modulation [Relazione in Atti di Convegno]
Kazimierczuk Marian, K.; Massarini, Antonio; Izadi Mohammad, Ali
abstract

A feedforward control technique with reference voltage modulation is introduced for PWM buck converter operated in the continuous conduction mode (CCM). The reference voltage is proportional to the dc converter input voltage. A steady-state analysis is performed. Experimental results are given. The measured open-loop line voltage regulation was 1.32%/V.

1999 - High-frequency small-signal model of ferrite core inductors [Articolo su rivista]
M. K., Kazimierczuk; G., Sancineto; G., Grandi; U., Reggiani; Massarini, Antonio
abstract

A circuit model of ferrite core inductors is presented. The behavior of the model parameters versus frequency is considered. The total power loss in inductors consisting of the winding resistance loss and the core loss, is modeled by a frequency-dependent equivalent series resistance. The total inductance given by the sum of the main inductance and the leakage inductance is obtained as a function of frequency. In order to study the core equivalent resistance and main inductance versus frequency, the magnetic field distribution in the core is derived from Maxwell's equations for a long solenoid. The complex permeability and permittivity of the ferrite core are introduced in the electromagnetic field equations, Experimental results are also given.

1999 - Stray capacitances of single-layer solenoid air-core inductors [Articolo su rivista]
G., Grandi; M. K., Kazimierczuk; Massarini, Antonio; U., Reggiani
abstract

This paper presents a method for predicting parasitic capacitances of solenoid NF inductors made of one layer of turns with circular cross sections, uniformly wound around a cylindrical nonconductive core. The method is based on an analytical approach to obtain the turn-to-turn and turn-to-shield capacitances of coils. The influence of the wire insulation is taken into account. An equivalent lumped parallel capacitance is derived. The method was tested by experimental measurements. The calculated and measured values were in good agreement in the considered cases. The derived expressions are useful for designing HF inductors and can also be adopted for modeling and simulation purposes.

1998 - Conditions for the existence of an X-point in a magnetic field [Articolo su rivista]
Massarini, Antonio; U., Reggiani
abstract

A sufficient condition for the existence of a node (i.e. an X-point) in lines of a quasi-static magnetic induction field is proved. The theoretical approach is developed for two-dimensional fields. The problem of obtaining an X-point in a magnetic induction field is encountered in toroidal devices (tokamaks) for controlled thermonuclear fusion experiments. The proposed method is capable of identifying possible X-point locations through the knowledge of field variables which are easy to calculate and/or measure.

1997 - Analysis of networks with ideal switches by state equations [Articolo su rivista]
Massarini, Antonio; U., Reggiani; M. K., Kazimierczuk
abstract

A new computer-oriented method for a large-signal time-domain analysis of networks containing ideal switches is presented. The method is based on a state variable approach that exploits an efficient novel algorithm developed for the systematic formulation of state equations and output equations for linear active networks, Switched networks consisting of linear elements and both externally and internally controlled switches can be investigated, Dirac's delta impulses are permitted in the analysis in order to find out the correct topology after switching, A new simple and convenient method for representing Dirac's delta impulses is also introduced, An example is both discussed in detail and analyzed with a computer code.

1997 - Feedforward control of DC-DC PWM boost converter [Articolo su rivista]
M. K., Kazimierczuk; Massarini, Antonio
abstract

A new feedforward control circuit suitable for applications in the de-de pulsewidth modulated (PWM) boost converter operated in the continuous conduction mode (CCM) is proposed, Its principle of operation is described, analyzed for steady state, and experimentally verified, The peak value of the sawtooth voltage at the noninverting input of a PWM modulator is held constant and the voltage at the inverting input of the PWM modulator varies in proportion to the converter de input voltage, As a result, the complement of the on-duty cycle (1 - D) is proportional to the de converter input voltage, yielding the converter output voltage theoretically independent of the converter input voltage, The circuit is very simple and significantly improves line regulation of the output voltage, The measured open-loop line regulation at fixed loads was less than 5% for the converter de input voltage change by 400%. The load regulation was also good even without a negative feedback loop.

1997 - Optimal design of single-layer solenoid air-core inductors for high frequency applications [Relazione in Atti di Convegno]
G., Grandi; U., Reggiani; M. K., Kazimierczuk; Massarini, Antonio
abstract

This paper deals with the optimized design of single-layer solenoid air-core inductors for HF applications. The presence of shields or other conductive materials in the neighborhood of the inductor is neglected. Optimum design is obtained with respect to weight, resistance, and losses of inductors, whose highest operating frequency is determined by the first self-resonant frequency. The optimization procedure is formulated as a nonlinear programming problem. A Sequential Quadratic Programming (SQP) algorithm is used for the solution. The influence of different geometrical parameters on the optimum design is highlighted and guidelines for the design are given.

1997 - Self capacitance of inductors [Articolo su rivista]
Massarini, Antonio; M. K., Kazimierczuk
abstract

A new method for predicting the stray capacitance of inductors is presented. The method is based on an analytical approach and the physical structure of inductors. The inductor winding is partitioned into basic celles many of which are identical. An expression for the equivalent capacitance of basic cell is derived. Using this expression, the stray capacitance is found for both single- and multiple-layer coils, including the presence of the core. The method was tested with experimental measurements. The accuracy of the result is good. The derived expressions are useful for designing inductors and can be used for simulation purposes.

1996 - A new representation of Dirac impulses in time-domain computer analysis of networks with ideal switches [Relazione in Atti di Convegno]
Massarini, Antonio; M. K., Kazimierczuk
abstract

A novel method for representing Dirac impulses in switched networks is presented. This method can be applied in the analysis and simulation of switched networks when the ideal switch model is used. The Dirac impulses in the time domain are not approximated by large values wich can give problems with conditioning and overflows. A logical representation of impulsive quantities is introduced. This representation did prove to be reliable and efficient in handling impulses which can be present at some of the switching transitions. Influence of impulses on the state of switches in the network can be easily accessed. No prior knowledge of circuit operation is needed to find the correct circuit topology after switching. The use of a state space description of the switched network allows to predict the possibly impulsive transitions. Therefore, the impulse analysis can be performed only for a limited number of transitions.

1996 - Computer-aided time-domain large-signal analysis of networks with switches [Relazione in Atti di Convegno]
Massarini, Antonio; U., Reggiani
abstract

A computer-oriented method for a large-signal time-domain analysis of switched networks is presented. The method is based on a state variable approach which exploits an efficient algorithm developed for the systematic formulation of state equations and output equations for linear active networks. Switched networks consisting of linear elements and both externally and internally controlled switches can be investigated. Every switching element is modeled as an ideal switch and the evolution of the network is represented by a sequence of linear circuit topologies. State equations for each topology are systematically obtained through a simple interchange of columns of a reduced tableau matrix. The elements of this matrix are calculated only once at the initial stage of the procedure. Dirac impulses are permitted in the analysis in order to find the correct topology after switching.

1996 - Feedforward control of PWM Buck converter with sawtooth peak value modulation [Relazione in Atti di Convegno]
M. K., Kazimierczuk; M. A., Izadi; Massarini, Antonio
abstract

This paper presents an analysis and experimental results for a feedforward control circuit suitable for applications in pulse-width modulated (PWM) buck derived converters. Line regulation can be improved using feedforward control techniques. The analysis is given for the buck converter operated in continuous conduction mode (CCM). The experimental results are performed at Vi = 17 to 42 V, V0=14 V, and the switching frequency of 100 kHz. The measured line regulation of the buck converter without negative feedback loop was less than 0.2% per 1 V of imput voltage.

1996 - Lumped parameter models for single- and multiple-layer inductors [Relazione in Atti di Convegno]
Massarini, A.; Kazimierczuk, M. K.; Grandi, G.
abstract

A method for modeling inductors at high-frequency operation is presented. The method is based on analytical approaches which can predict turn inductances, turn-to-turn and turn-to-core capacitances using physical structure of windings. Turn inductances, turn-to-turn and turn-to-core capacitances of coils are then introduced into suitable lumped parameter equivalent circuits of inductors. The overall inductance and stray capacitance can be obtained through the use of the equivalent circuits. Both single- and multiple-layer inductors are considered. The method was tested with experimental measurements. The accuracy of the results was good in most cases. The derived expressions can be useful for the design of HF inductors and can also be used for simulation purposes.

1996 - Stray capacitances of single-layer air-core inductors for high-frequency applications [Relazione in Atti di Convegno]
G., Grandi; M. K., Kazimierczuk; Massarini, Antonio; U., Reggiani
abstract

A method for predicting stray capacitances of HF inductors dependent on their geometry is presented. The analysis is performed for inductors made of one layerof turns with circular and rectangular cross sections. The wire is uniformly wound around a cylindrical non-ferromagnetic core. The method is based on an analytical approach to obtain the turn-to-turn and turn-to-shield capacitances of coils. The influence ofn insulating coatings of the wire is also taken into account. An overall equivalent stray capacitance is derived according to the typical HF equivalent lumped parameter circuit of inductors. The method was tested with experimental measurements and the accuracy of the results was good in most cases. The derived expressions are useful for designing of HF inductors and can be also used for simulation purposes.

1995 - Computer-aided time-domain analysis of switched networks [Articolo su rivista]
Massarini, Antonio; L., Foschini
abstract

A new computer-oriented method for an efficient and accurate large-signal time-domain analysis of switched networks consisting of strictly linear elements and of a wide class of switches can be investigated. The switching elements are assumed ideal and the state equation method is adopted for the network description. When a network topology changes, state equations are derived systematically by means of a generalized formulation of the p-port contraint matrices. Each set of equations holds from a switching instant to the next one which is calculated through a Newton-type algorithm. Numerical results are compared with experimental data and SPICE simulations.

1994 - Computer-aided time-domain analysis of switched networks [Relazione in Atti di Convegno]
L., Foschini; Massarini, Antonio
abstract

A new computer-oriented method for an efficient and accurate large-signal time-domain analysis of switched networks is presented. Switched networks consisting of strictly linear elements and of a wide class of switches can be investigated. The switching elements are assumed ideal and the state equation method is adopted for the network description. When network topology changes, the equations are derived systematically by means of a generalized formulation of the p-port constraint matrices. Each set of equations holds from a switching instant to the next one which is calculated through a Newton-type algorithm. Numerical results are compared with experimental data and SPICE simulations.

1993 - Electrical stresses during transients in linear MHD channels [Articolo su rivista]
Borgi, K. A.; Massarini, A.; Madzanti, D.
abstract

Electrodynamical (electric field, current density, electrical power density), hydrodynamic (shear stress) and thermal (heat flux density towards the walls) stresses in a linear segmented Faraday MHD channel have been investigated by means of numerical methods for the startup procedure, a transient from the open circuit (k=1) conditions to loads with K=0.5 (optimum load) and 0.3. The main characteristics of the MHD channel were chosen corresponding to a sample having been investigated before. It has been found that the hydrodynamical and thermal stresses manifest no increase due to the transient when compared with their steady state values. However, at k≠0.5 these can be larger than at k=0.5. In contrary to this, the electrical stresses show unwanted increases at k=0.3. Therefore, it is important to work at k=0.5. Several results of the calculations have been plotted graphically. Some recommendations for the channel design have been given.

1993 - Electrical strsses during transients in linear MHD channels [Articolo su rivista]
C. A., Borghi; Massarini, Antonio; G., Mazzanti
abstract

A quasi-onedimensional time dependent model capable of treating MHD compressible flows in linear channels has been adopted. shear stresses and heat losses are taken into account by means fo integral expressions. Electrial boundary conditions related to channel connections (segmented Faraday channels or diagonal conducting sidewall channels) are considered. Three finite difference numerical schemeshave been implemented for the solution of the model equations. MHD supersonic, transonic and subsonic flows can be treated. Variations of the elecric field and current density distribution during transients are calculated in order to evaluate high electrical field locations and current concentrations resulting in occurence of inter-electrode breakdown, local enhance of wall temperature, thermal stresses, corosion and erosion.

1993 - Transport phenomena in boundary layer two-dimensional analysis of an MHD generator channel [Articolo su rivista]
C. A., Borghi; Massarini, Antonio; G., Mazzanti
abstract

An analysis of transport processes and turbulence in MHD generator flows has been carried out bymeans of a steady-state two-dimensional MHD model. The calculations are made in the plane containing the axis of the flow and perpendicular to the magnetic induction. ùan evaluation of the influence of turbulence has been made. In order to do this, the description of the turbulence behavior of the plasma flow has been made through the k-epsilon model extended to low Reynolds numbers (this model considers tha balance of the turbulent kinetic energy k and of the turbulence dissipation epsilon).

1992 - Fault generated transients in MHD channels [Relazione in Atti di Convegno]
C. A., Borghi; Massarini, Antonio
abstract

Flow transient in MHD linear channels are analyzed by means of a quasi-one-dimensional time dependent model. Medium size MHD channelsboth in segmented Faradayandin diagonal connection are utilized for the present study. Plasma flows derived from the natural gas combustion with a mass flow rate of 25 kg/s in the subsonic regime and with a mass flow rate of 45 kg/s in the supersonic regime, are considered. Transients generated by the transition from the nominal operating condition to short circuit, by the transition from the nominal operating condition to open circuit and by a sudden interruption of the seed supply are analyzed.

1992 - Magnetohydrodynamic transients in MHD generators [Relazione in Atti di Convegno]
C. A., Borghi; Massarini, Antonio
abstract

Models for the investigation of transients MHD flows are presented in this paper. Both the study of transients caused by the finite flow time of the plasma through the channel and by transitions between different operating conditions of the generator are considered. The analysisof physical phenomena as plasma relaxation and non-uniformities belong to the first case. Transients originated by changes of the operating conditions and faults are of the second case. In order to perform the mentioned study, one-dimensional and two-dimensional time dependent models have been set up. The models are presented in this note. The analysis of the transient during the start up of a linear gas fired generator is shown.

1992 - Multidimensional models for the analysis of linear MHD generator plasma flows [Articolo su rivista]
C. A., Borghi; Massarini, Antonio; G., Mazzanti
abstract

Mathematical models for the analysis of the linear MHD generator channel operation are described. The local phenomena are analyzed through a steady-state two-dimensional model which is based on a description of both the fluid dynamic and the electrodynamic behavior of the plasma. The transients caused by variations of the loading and by faults are studied by means of a time-dependent quasi-one-dimensional model.

1992 - One- and two-dimensional model for the linear MHD generator channel design [Articolo su rivista]
C. A., Borghi; Massarini, Antonio; G., Mazzanti; P. L., Ribani
abstract

Mathematical models for the design of the linear channel of an MHD generator, are described. By means of a quasi-one-dimensional optimization's model the main design parameters of the channel, are calculated. The local phenomena effects are analyzed through a steady state two-dimensional model. This model is based on the description both of the fluid dynamic and of the electrodynamic in the plane containing the channel axis and normal to the magnetic induction. The transients caused by variations of the loading and by faults, are studied by means of a time dependent quasi-one-dimensional model.

1992 - Steady state descriptions of MHD plasma flows [Relazione in Atti di Convegno]
C. A., Borghi; Massarini, Antonio; G., Mazzanti; P. L., Ribani
abstract

An analysis of one-dimensional and multi-dimensional models of the steady state regime of the flow in an MHD channel has been done. A one-dimensional model is obtained from the balance of the fluxes of the fluid dynamic quantities in volume elements of the channel. The boundary layer effects on the fluid dynamics and on the electrodynamics are taken into account by means of a semi-empirical formulation. A two-dimensional model is described. It considers both the fluid dynamics and the electrodynamics. The effect of turbulence is described by means of the Lauder-Jones eddy viscosity model. The models are utilized for the analysis of a 3 m length diagonal channel. The results are compared with those of a three dimensional model reported in the literature. A good agreement is obtained. Furthermore the effect of turbulence on the results of the two-dimensional model is studied. Turbulence results to dominate the fluid dynamic behavior of the flow.

1992 - Time-dependent quasi-onedimensional flow models for linear magnetohydrodynamic generator channels [Articolo su rivista]
Massarini, Antonio; C. A., Borghi
abstract

A time-dependent quasi-one-dimensional approximation of a magnetohydrodynamic (MHD) compressible flow in a linear channel has been considered. for the numerical solution of the problem three different algorithms have been utilized (MacCormack's, Godunov's and Casulli's algorithms). they are based on the finite-difference method. these models are utilized for the prediction of the behavior of electrical, thermal, and dynamic quantities during transients and during the occurrence of faults in MHD channels. A comparison of the methods when analyzing a load variation for a Faraday channel is considered.