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This study presents a novel technique to inactivate coccidian oocysts in an aqueous solution. The technique consists of treating the contaminated liquid by using an atmospher- ic-pressure air dielectric barrier discharge (DBD) plasma in contact with it. Many experiments in several operating conditions were performed. The discharge was supplied by sinusoidal and nanosecond-pulsed voltages with a constant average power of ~7 W in both cases. Biological effects due to the plasma were investigated by performing tests with increasing treatment time. A sudden ~40% drop in the number of survived oocysts was reached in 4 min and a two-fold reduction was detected after 12 min of exposure. No significant differences in the biocidal efficacy were detected between the AC-driven and the nanosecond-pulsed discharge. Chi-squared statistical analysis on the treated samples showed significant statistical difference (with a statistical significance P value parameter less than 0.01) and nonrandomness warranty of the results, opening interesting scenarios for fimire developments.

This paper reports on the effects of a series of fluid-dynamic dielectric barrier discharge plasma actuators on a NACA0015 airfoil at high angle of attack. A set of jet actuators able to produce plasma jets with different directions (vectoring effect) and operated at different on/off duty cycle frequencies are used. The experiments are performed in a wind tunnel facility. The vectorized jet and the transient of the flow induced by unsteady duty cycle operation of each actuator are examined and the effectiveness of the actuator to recover stall condition in the range of Reynolds numbers between 1.0 × 105 and 5.0 × 105 (based on airfoil chord), is investigated. The actuator placed on the leading edge of the airfoil presents the most effective stall recovery. No significant effects can be observed for different orientations of the jet. An increase of the stall recovery is detected when the actuator is operated in unsteady operation mode. Moreover, the frequency of the on/off duty cycle that maximizes the stall recovery is found to be a function of the free stream velocity. This frequency seems to scale with the boundary layer thickness at the position of the actuator. A lift coefficient increase at low free stream velocities appears to linearly depend on the supply voltage.

In this study we examine both the effect of changing the applied voltage waveform shape and the modulation on-time on the amount of ozone dissolved within a liquid in a dielectric barrier discharges (DBD) bubble reactor. In this device, the discharge forms at the gas–liquid interface allowing for effective transfer of the plasma effluent into the liquid. To produce different voltage waveforms, a multilevel inverter power supply capable of generating arbitrary waveforms without switching-on and switching-off transients has been used. Of the four waveforms used in the study (sinusoidal, sawtooth, square and short-pulse), the square waveform was found to be the most efficient at producing the highest ozone concentration for a fixed peak voltage and average power. To determine the effect of the modulation on-time, the number of cycles during the on-time were increased from 1 up to 1000, adjusting the off-time accordingly to maintain the same duty cycle. Shorter on-time periods were found to be more efficient. Experimental and computational results indicate that the time between subsequent discharges is critical for increased ozone generation efficacy, as this needs to be long enough for ozone produced in one discharge event to diffuse away from the discharge region before the next discharge event occurs, thereby avoiding its partial destruction in the plasma. This insight provides a valuable criterion for the optimization of DBD reactors used in novel biomedical, agricultural and environmental applications.

Charge particles can increase the biocidal efficacy of nonthermal plasmas in indirect treatments. The aim of this study is to increase the amount of free charges produced and delivered by a surface dielectric barrier discharge fluid‐ dynamics actuator. Different linear actuators and supplying conditions have been considered. Actuators were utilized to produce an ionic wind impinging an insulating target surface. Charged particles' distribution over the target was measured with and without a metallic mesh between the actuator and target itself. Linear actuators have proven to be more effective in charge delivery with respect to an annular one previously studied by our research team. A two‐ dimensional electrostatic finite‐element analysis has been carried out to get a better insight into this physical behavior.

In this paper, an investigation on an annular Plasma Synthetic Jet Actuator (PSJA) utilizing a Surface Dielectric Barrier Discharge (SDBD) is reported. The work is focused at an investigation of the electric charges transported by the jet produced by the actuator and deposited on a target. Particularly, an assessment of the various factors that may affect the charge deposit process has been carried out. Experiments have been performed in a controlled environment with different electric configurations. This allowed to evaluate how the humidity rate affects and the dynamics of the electric charge build-up process. It was observed that humidity rate weakly affects the charge deposition, being the most notable effect an increase of the deposition time for higher humidity rate. Moreover, the performances of two different power supply systems, working at different voltage and frequency conditions, were compared. The two supplies have been set up do feed the actuator with the same power, in order to assess which voltage-frequency condition is more efficient at depositing electric charge on the target. It was observed that a higher applied electric field produces higher charge deposition rates.

This paper reports the characterization of a low-power, atmospheric pressure plasma source developed for and successfully tested in applications of plasma medicine. The source produces plasma by ionizing a helium flow containing traces of air. The effluent gas is thus enriched in reactive oxygen and nitrogen species as well as helium metastable excited states. Electrical measurements, Schlieren imaging, OES and various chemical analyses and probes enabled us to fully characterize the plasma source and to determine some fundamental parameters for treating living samples such as the power feeding the discharge, the optimal source to target distance, the maximum exposure time, and to identify the major chemical species responsible for the biological action on exposed living matter.

Annular plasma synthetic jet actuators demonstrated their ability to produce a tubular flow normal to the surface where the dielectric barrier discharge (DBD) is ignited. These fluid-dynamic actuators enhance the delivery of reactive species towards the target to be treated. In these actuators, long life charged particles are generated within the plasma region and then carried on by the induced flow. In this work, the potential distribution induced by charges deposited over an insulating target has been measured. Surface DBD actuators, made with different dielectric materials, have been supplied by different sinusoidal voltages at a constant average power supplying the discharge. Actuators with the exposed electrode connected to both the high voltage potential and grounded have been tested. The charge distribution accumulated on a target surface perpendicular to the flow has been measured at different time intervals with the plasma on. Charges advected by the flow are always positive. The potential distribution on the target surface generated by the charges has been measured. For both configurations, firstly an M-shaped distribution develops and, later on, it becomes bell-shaped. A charge build-up mechanism has been found to be faster when the exposed electrode is connected to the high voltage terminal. The target has been placed at a variable distance from 1 to 5 cm from the actuator surface. At a distance of 5 cm, induced potentials are two times smaller than those with the target at 1 cm. Measurements allow us to estimate a charge flux toward the target on the order of 1011 particles (cm2 s)−1. The results presented in this work show that the presence of charged particles in the jet flow outside the plasma could be an important factor to be accounted for when these plasma actuators are used for treatment purposes (indirect plasma treatment).

In this work ozone concentration in a plane-to-plane Dielectric Barrier Discharge (DBD) reactor has been evaluated both experimentally and numerically. The reactor geometry has been chosen to generate a homogenous discharge. Therefore, simplified approaches for both experiments and numerical simulations have been utilized. The discharge was excited for 20 s in atmospheric-pressure quiescent air by means of a sinusoidal voltage of 15 kV peak at a frequency of 5 kHz in continuous operation. Electrical and optical measurements have been done to estimate the input parameters for the kinetics model. The ozone density within the discharge gap was measured by using the UV absorption method. The optical path travelled by the UV beam inside the reactor gap was estimated by means of Schlieren imaging. Within the time intervals and the dimensions considered, plasma was assumed to be uniform. This assumption was confirmed experimentally by iCCD images of the discharge. Numerical simulations have been performed by means of the zero-dimensional open-source code ZDPlasKin. A set of 622 reactions among 62 chemical species has been implemented, accounting for a 1% water vapour fraction. Reduced electric field, electron density and gas temperature were the input parameters of the code. Ozone density presented a production peak of about 1.3 ⋅ 1017 cm−3 half a second after discharge ignition. A steady state value of 6 ⋅ 1016 cm−3 was reached after a transient of about 12 s. Numerical simulation delivered ozone concentrations in good agreement with experimental data. Graphical abstract: [Figure not available: see fulltext.].

Plasma synthetic jet actuators (PSJAs) demonstrated their ability to produce a tubular flow normal to the surface where the dielectric barrier discharge (DBD) is ignited. These fluid dynamics actuators enhance the delivery of reactive and charged species toward the target to be treated. In this work, the efficacy of an octagonal PSJA used to indirectly treat Candida guilliermondii, both in agar substrate and in saline solution, was experimentally studied. The inactivation effect of free charges advected by the induced flow has been investigated as well by interposing a metallic mesh between the actuator surface and the treated sample. Therefore, the passage of charges and their migration toward the sample can either be allowed or prevented simply by having the mesh floating or connected to the ground, respectively. A 4 log and a 2 log colony-forming unit (CFU) reduction were observed for agar substrate and saline solution, respectively, at the highest energy dose treatment with the grid grounded. Under the same conditions but with the grid at floating potential, the presence of advected charges gives an additional 1 log CFU. In addition to biological tests, chemical analyses have been carried out to identify the most important modifications produced by the induced flow into treated water. Results presented in this work demonstrate the efficacy of PSJAs in indirect treatment of C. guilliermondii, both on agar substrate and saline solution, and the inactivation properties of free charges advected by this type of fluid dynamics actuator.

In this work several planar dielectric barrier discharge fluid-dynamics actuators have been experimentally investigated. The actuator is made by an electrode pair separated by a dielectric. It is characterized by a planar geometry and it induces a volume force on the gas above it which modifies the fluid-dynamics within the aerodynamic boundary layer. Several actuator geometries, dielectric materials, a.c. supply voltages and supply frequencies have been used. Rotational and vibrational temperatures have been determined by means of spectroscopic measurements. Vibrational temperatures have been found to be one order of magnitude higher than the rotational ones, confirm-ing the non-thermal behavior of the discharge. The translational temperature has been evaluated by thermographic observations of the dielectric surface heated by the plasma. The values of the translational temperature are in a very good agreement with those of the rotational temperature. Electric measurements have been carried out to determine the average power delivered to the discharge and to estimate the average electron number density. In the plasma induced by the discharge above the actuator an average electron density of 4 ÷ 15 · 1017 m-3 has been determined. The gas speed of the induced wall jet has been measured with a Pitot tube. The average power delivered to the electrodes increas-es with a power law of the applied voltage (exponent ≈ 3 ÷ 5) and linearly with the supply frequency. The induced speed increases with the increase of the average power until a plateau is reached. The efficiencies of the different actuators have been compared by evaluating the relation between average power and induced gas speed.

The electrohydrodynamic (EHD) interaction induced in atmospheric air pressure by a surface dielectric barrier discharge (DBD) actuator has been experimentally investigated. Plasma synthetic jet actuators (PSJAs) are DBD actuators able to induce an air stream perpendicular to the actuator surface. These devices can be used in the field of aerodynamics to prevent or induce flow separation, modify the laminar to turbulent transition inside the boundary layer, and stabilize or mix air flows. They can also be used to enhance indirect plasma treatment effects, increasing the reactive species delivery rate onto surfaces and liquids. This can play a major role in plasma processing and chemical kinetics modelling, where often only diffusive mechanisms are considered. This paper reports on the importance that different electrode geometries can have on the performance of different PSJAs. A series of DBD aerodynamic actuators designed to produce perpendicular jets has been fabricated on two-layer printed circuit boards (PCBs). Both linear and annular geometries were considered, testing different upper electrode distances in the linear case and different diameters in the annular one. An AC voltage supplied at a peak of 11.5 kV and a frequency of 5 kHz was used. Lower electrodes were connected to the ground and buried in epoxy resin to avoid undesired plasma generation on the lower actuator surface. Voltage and current measurements were carried out to evaluate the active power delivered to the discharges. Schlieren imaging allowed the induced jets to be visualized and gave an estimate of their evolution and geometry. Pitot tube measurements were performed to obtain the velocity profiles of the PSJAs and to estimate the mechanical power delivered to the fluid. The optimal values of the inter-electrode distance and diameter were found in order to maximize jet velocity, mechanical power or efficiency. Annular geometries were found to achieve the best performance.

Surface dielectric barrier discharges (S-DBDs) have received renewed attention in recent years for their potential application in emerging biomedical, environmental and agricultural applications. In most of these applications, the plasma is not in direct contact with the substrate being treated and the transport of reactive species from the plasma to the substrate is typically assumed to be controlled by diffusion. Here, we demonstrate that generally this is not the case and that electrohydrodynamic (EHD) forces can produce jets that enhance the delivery of these species, thereby influencing the efficacy of the S-DBD device. In particular, we have studied the degradation of potassium indigotrisulfonate solutions exposed to S-DBDs generated in devices with annular electrodes of diameters varying between 10 mm and 50 mm. All the devices were driven at constant linear power density (watts per cm of plasma length) and although local plasma properties remained the same in all the devices, a three-fold efficacy enhancement was observed for devices of diameter ∼30 mm due to EHD effects.

The magnetohydrodynamics interaction around a conical test body in a hypersonic argon flow is experimentally investigated. The hypersonic flow is realized in the high-enthalpy arc-heated wind tunnel of Alta Societa per Azioni (S.p.A.) (Pisa, Italy) at Mach 6. The aim of experimental activity is to produce an experimental data base to be used for the validation of numerical codes for the analysis of the magnetohydrodynamics interaction. The magnetohydrodynamics interaction is obtained in the shock layer of the conical test body at the exit of the hypersonic nozzle. The electrical configuration realized allows one to enhance the effect of the magnetohydrodynamics interaction on the plasma parameters. This is done using the Hall field to generate the magnetohydrodynamics interaction and by short-circuiting the Faraday current inside the plasma of the shock layer. The magnetic flux density is produced by an array of three magnets located in the test body. Tests are performed at three different stagnation pressures. Fluid-dynamic, electrical, and optical observations have been done. The experiment showed a considerable effect of the magnetohydrodynamics interaction on the values of the quantities measured.

— The MHD interaction around a conical test body in a hypersonic argon flow was experimentally investigated. The aim of the experiment was to produce a data base to be used for the validation of numerical codes for the analysis and the simulation of the magneto-fluid dynamics in hypersonic flows. In these ex-periments the flow was obtained in the high-enthalpy arc-heated hypersonic wind tunnel – HEAT - of Alta (Pisa-Italy). Speeds at Mach 6 were reached. In the present experiment the flow and the plasma characteristics have been determined. The MHD interac-tion was obtained in the shock layer of a conical test body placed at the exit of the hypersonic nozzle. The realized electrical con-figuration allowed to enhance the effect of the MHD interaction on the plasma parameters. This was done by utilizing the Hall field to generate the MHD interaction and by short-circuiting the Faraday current inside the plasma of the shock layer. The mag-netic flux density was produced by an array of three magnets located in the test body. Test runs were performed at three differ-ent stagnation pressures. Fluid-dynamic, electrical and optical observations have been done. The experiment showed a large effect of the MHD interaction on the values of the measured quan-tities. In order to have a test body entirely contained in the region where a uniform hypersonic flow has been measured, a test body of smaller sizes has been constructed and tested. The results ob-tained in this case confirm the results of the tests with the larger body.

none 13 si In this contribution, a poly(butylene succinate)-based copolymer containing thioether linkages (P(BS85BTDG15)) has been synthesized and characterized from the molecular, thermal and mechanical point of view. The results have been compared to the parent homopolymer. Films obtained both by PBS and P(BS85BTDG15) have been subjected to surface modification by means of non-thermal plasma surface treatment and the effect on physic/mechanical properties has been considered. Hydrolytic degradation rate under physiological conditions and in vitro biocompatibility of treated and non-treated polymeric films have been also investigated. The introduction of thioether linkages and the plasma etching enhanced the polymer surface wettability, thus resulting in an increased hydrolytic degradation rate. On the other hand, bulk properties were not significantly affected. Biocompatibility assays highlighted the absence of potentially cytotoxic products into the culture medium and proved that the investigated polymeric films can support cell adhesion and proliferation. mixed Fabbri, Martina; Gigli, Matteo; Costa, Michela; Govoni, Marco; Seri, Paolo; Lotti, Nadia; Giordano, Emanuele; Munari, Andrea; Gamberini, Rita; Rimini, Bianca; Neretti, Gabriele; Cristofolini, Andrea; Borghi, Carlo A Fabbri, Martina; Gigli, Matteo; Costa, Michela; Govoni, Marco; Seri, Paolo; Lotti, Nadia; Giordano, Emanuele; Munari, Andrea; Gamberini, Rita; Rimini, Bianca; Neretti, Gabriele; Cristofolini, Andrea; Borghi, Carlo A

In magnetohydrodynamic (MHD) regimes of plasmas with magnetic Reynolds number comparable to one, electrodynamics exhibits a nonlinear characteristic. In the present paper, the electrodynamics has been discretized utilizing a finite-element method. The problem unknown is the electric scalar potential. Nonlinearity is caused by the dependence of the electric transport parameters and of the source terms on the magnetic flux density. Different approaches are evaluated to deal with the nonlinearity. The model has been coupled with a solver of the Navier-Stokes equations. The MHD interaction in the boundary layer of an hypersonic flight has been analyzed.

Inexact Newton solvers offer many attractive features for the solution of nonlinear problems in the field of electromagnetics. A critical point for the optimal setup of the solver is the choice of the best algorithm for the evaluation of the approximate solution of the linear systems at each Newton step and the most effective preconditioning strategy. In this paper, the Newton iterative solver method is proposed for the solution of a nonlinear magnetostatic problem. The problem is discretized by means of a finite-element approach. The generalized minimum residuals (GMRES) method is adopted as linear solver, and three preconditioners are tested. The performance of this procedure is evaluated for different magnetostatic problems and compared to the results obtained by means of a Newton–Raphson method.

The paper discusses the generation of a family of neural models for spiral inductors and MIM capacitors, and their use in broadband nonlinear circuit optimization by evolutionary algorithms. It is shown that the resulting optimization process is fast and well behaved, and can achieve the same circuit performance produced by a design approach based on lumped passive components. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 38: 46–52, 2003

A model for the analysis of the magnetoplasmadynamic regime, devoted to magnetohydrodynamics (MHD) systems in a hypersonic flight vehicle, is presented. In the model, the discrete formulation of fluid dynamics and electrodynamics are coupled. The Navier-Stokes equations are discretized by means of a finite volume formulation. The electrodynamics is discretized by means of a finite-element method. The model has been utilized for the analysis of MHD interaction for the fluid control over a hypersonic body. Calculations have shown that MHD interaction can strongly affect the boundary layer fluid dynamic regime.

The paper presents a method for determining the main design parameters of a permanent magnet (PM) motor that will reduce the total torque ripple. First, the magnet arrangement is derived by one-dimensional field analysis coupled with a multiobjective minimization technique. Then, a two-dimensional model is used to further optimize the magnet arc width and minimize the cogging torque. The analysis mainly focuses on a rotor that is completely covered by the permanent magnets. In this configuration, the permanent magnets can be made from a tube of polymer-bonded magnet, and manufacture of the motor is greatly simplified. We present experimental tests of a machine manufactured on the basis of our design procedure.

Many aspects of magnetohydrodynamics (MHD) have been studied at the Department of Electrical Engineering of the University of Bologna (MHD power generators, plasmadynamics in a Tokamak machine, superconducting magnetic separators, arc discharge in circuit breakers, meniscus shaping in casting machines). The recent activities developed with the aim to analyze different electric power applications of MHD Sciences, are reported in the paper.

This work reports an experimental investigation performed in wind tunnel facility on a NACA0015 airfoil equipped with a set of vectorizable fluid-dynamic DBD plasma actuators. The ability of the actuators to recover the stall condition with free stream velocities in the range 5-23 m/s has been investigated. The discharge has been generated by feeding the actuators with a sinusoidal voltage waveform with a frequency of 15 kHz and voltages up to 7.5 kV peak. The actuator positioned on the leading edge exhibits highest ability in the stall recovery. Unsteady actuation obtained by alternatively switching on and off the discharge is more effective in the stall recovery when compared with a steady actuation. The frequency that optimizes the stall recovery has been found to be a function of the velocity with the power of 1.5. This result leads to the determination of a constant Strouhal number if the boundary layer thickness is used as characteristic length. Finally the lift coefficient, obtained when the plasma actuator has been turned on, has been found to be a linear function of the applied voltage.

The global optimisation of Loney’s solenoid, aiming at minimizing the level of inhomogeneity of the main field, was proposed and solved as a first benchmark for single criterion optimisation. Accordingly, the TEST (Testing Electromagnetic Synthesis Techniques) environment has been set up. Based on Loney’s solenoid even in the unshielded configuration, a multicriteria optimisation problem has been then formulated: to identify the coil geometry producing a main field with the minimum inhomogeneity within the solenoid and, at the same time, a minimum level of stray field around the solenoid. The scope of this contibution is to compare different methodologies for the solution of the multicriteria design problem.

In this work a low-temperature plasma source for the generation of plasma activated water (PAW) is developed and characterized. The plasma reactor was operated by means of an atmospheric-pressure air dielectric barrier discharge (DBD). The plasma generated is in contact with the water surface and is able to chemically activate the liquid medium. Electrodes were supplied by both sinusoidal and nanosecond-pulsed voltage waveforms. Treatment times were varied from 2 to 12 min to increase the energy dose released to the water by the DBD plasma. The physics of the discharge was studied by means of electrical, spectroscopic and imaging diagnostics. The interaction between the plasma and the liquid was investigated as well. Temperature and composition of the treated water were detected. Images of the discharges showed a filamentary behaviour in the sinusoidal case and a more homogeneous behaviour in the nanosecond-pulsed one. The images and the electrical measurements allowed to evaluate an average electron number density of about 4 × 1019 and 6 × 1017 m-3 for the sinusoidal and nanosecond-pulsed discharges respectively. Electron temperatures in the range of 2.1÷2.6 eV were measured by using spectroscopic diagnostics. Rotational temperatures in the range of 318-475 K were estimated by fitting synthetic spectra with the measured ones. Water temperature and pH level did not change significantly after the exposure to the DBD plasma. The production of ozone and hydrogen peroxide within the water was enhanced by increasing the plasma treatment time and the energy dose. Numerical simulations of the nanosecond-pulsed discharge were performed by using a self-consistent coupling of state-to-state kinetics of the air mixture with the Boltzmann equation of free electron kinetics. Temporal evolution of the electron energy distribution function shows departure from the Maxwellian distribution especially during the afterglow phase of the discharge. When limited deviations from Maxwellian distribution were observed, calculated electron temperature is in good agreement with the one measured by means of spectroscopic diagnostics. Computed temporal evolution of the energy delivered to the discharge is comparable with the one obtained from electrical measurements. The electrical discharges supplied by both voltage waveforms produce plasma activated water with negligible thermal effects and pH variations.

A fully implicit method for the solution of the magneto-hydrodynamic problem in an SF/sub 6/ circuit breaker is presented. The self induced magnetic field is considered in order to analyze the magnetohydrodynamic interaction in the plasma. The effects of the interaction between the magnetic field and the flow velocity on electrodynamics are evaluated. The model discretizes the Navier-Stokes equations by means of a finite volume formulation and the electrodynamics by means of a finite element method. Time integration is performed separately by means of a multistep method.

A theoretical investigation of the expansion of the plasma, produced by a nanosecond laser pulse hitting a titanium metallic target, has been carried out. The study is oriented to understand the interaction of the plasma plume with the surrounding gas (air) not only from the fluid dynamic point of view, but also considering the effects of chemical reactions. To this purpose, a 2-D solver of the Euler equations has been developed and self-consistently coupled with the local thermodynamic equilibrium calculation. The results show the plasma confinement due to the ambient gas and the appearance of metallic oxides in proximity of the plume border.

In the present work, magnetohydrodynamics (MHD) power generation based on the T-layer regime has been investigated both experimentally and numerically. The experimental investigation has been carried out in a shock tunnel MHD facility. There, the plasma layer characteristics have been studied. The layers have been produced by means of electrical discharges at the entrance of a segmented Faraday MHD channel. Streak photography pictures and charge coupled device (CCD) camera snap shots are used to observe the layers. The effect of the layers on the local electrical power production is studied through the response of the currents of individual electrode pairs. The performance characteristic of the T-layer MHD generation has been investigated in a channel of commercial size (active length of 14 m) by means of numerical simulations performed by means of a two-dimensional time dependent (2-Dt) model. In the commercial size channel, when using ideal gas and neglecting loss mechanisms, an enthalpy extraction larger than 30% has been obtained. The effects of a real gas and of loss mechanisms on the T-layer MHD conversion have been studied by means of the 2-Dt numerical analysis in a 4-m channel. In this channel, when an ideal gas is used, a reduction of about 20% of the electrical power output is caused by the loss mechanisms. When loss mechanisms and combustion gas in the 4-m channel are considered, an increase of the power stored in the plasma T-layer is observed. This power is of the order of the electrical power extracted from the MHD channel.

A multi-objective optimization problem for Loney's solenoid consists of the determination of the current system which produces a uniform magnetic field within a domain of finite extent inside the solenoid and a low stray field outside it. In order to solve the multi-objective problem, four different approaches have been utilized and compared. In all cases evolution strategy (ES) techniques are utilized for the minimization procedure.

The design of a superconducting magnetic energy storage (SMES) device requires the determination of a current system that produces a magnetic field of a given magnetic energy and a low stray field outside the device. To optimize the design, the amount of conductor and the device volume is minimized. High-temperature superconductor technology is utilized. Quench conditions must be fulfilled. In order to solve the multiobjective optimization problem, two different methods have been used: the objective weighting method, which combines the two objective functions (conductor volume and device volume) into a new cost function by means of penalty coefficients, and one based on fuzzy logic. In both methods the (1+1) evolution strategy minimization algorithm has been utilized. Moreover, in order to improve the solution of the objective weighting method, the results given by the evolution strategy algorithm are used as the starting point of a deterministic method (standard SQP method). The results are compared and discussed.

The design of the main current systems of an actively shielded and of an iron shielded MRI device for nuclear resonance imaging, is considered. The model for the analysis of the magnetic induction produced by the current system, is based on the combination of a Boundary Element technique and of the integration of two Fredholm integral equations of the first and the second kind. The equivalent current magnetization model is used for the calculation of the magnetization produced by the iron shield. High field uniformity in a spherical region inside the device, and a low stray field in the neighborhood of the device are required. In order to meet the design requirements a multi-objective global minimization problem is solved. The minimization method is based on the combination of the filled function technique and the (1+1) evolution strategy algorithm. The multi-objective problem is treated by means of a penalty method. The actively shielded MRI system results to utilize larger amount of conductor and produce higher magnetic energy than the iron shield device.

In this paper a minimization technique is used to reduce the torque ripple of permanent magnet actuators. In order to do this a global stochastic (1+1) evolution strategy algorithm coupled to a filled function acceleration technique is utilized. The cost function is defined as a combination of the e.m.f. harmonics induced in the stator windings and the harmonic components of the magnet permeance. The relative importance of the different contributions are taken into account by penalty coefficients. The method described is used for a 3-phase, 6-pole Permanent Magnets (PM) synchronous motor.

In the present work a model for the two-dimensional time dependent description of the magneto-fluid dynamics in the channel of an MHD (magnetohydrodynamic) generator is described. The numerical code obtained from it can be used for the analysis of the MHD channel operation, during the design procedure and for numerical experiments. The model is based on a time dependent two-dimensional description of the fluid dynamics iteratively coupled to a steady state two-dimensional description of the electrodynamics. In the plasma flow considered the magnetic field diffusion dominates over the magnetic field convection. A semi-implicit finite difference pressure scheme has been utilized for the solution of the fluid dynamic problem. The turbulence behavior is taken into account. The electrodynamics is described by a second order elliptic partial differential equation, obtained from the Maxwell equations and generalized Ohm’s law, and solved by means of an exponential fitting finite difference method. The model has ...

A method for finding the global optimum of the electromagnetic inverse problem solution is presented. The problem consists in the determination of the current system which produces a given magnetic field within a domain of finite extent. An infinite class of solutions exists. In order to find the solution of the synthesis problem obtained, a global optimization technique, based on the combination of the filled function (FF) method and the evolution strategy (ES) method, is developed. The FF method is utilized to find a sequence of regions containing decreasing minima. The minimization inside this region is done by means of the ES method. The technique described has been utilized for the poloidal magnetic system of a toroidal device for thermonuclear fusion experiments and for the main coil system of a nuclear magnetic resonance (NMR) device.

In the present work, a time-dependent two-dimensional model based on a pressure scheme is presented. It is able to take real gas thermodynamics and loss mechanisms due to friction, heat transport, and turbulence into account. The MHD generation in a current-carrying nonuniform (STCC) regime has been studied by means of it. In order to see what the effects of the loss mechanisms on the STCC-MHD generation are, the results of three different approximations are compared. In the first case, the model analyzes the MHD operation in an ideal gas approximation without losses. In the second case, the ideal gas with losses is studied, in the last one, a combustion gas with loss mechanisms is considered. In all three cases, the same starting conditions and boundary conditions are assumed. Passing from the first to the second case, a reduction of the electrical power output of 20% is calculated. In the third case, with similar plasma conditions, small differences of the power output are obtained. In this case, the energy needed for the formation of the plasma nonuniformity results to be much larger than the energy used in the ideal gases. This is due to the specific heat of the combustion gas, which increases with the temperature.

The determination of the current system which produces a given magnetic field in a region of finite extent, is considered. The magnetic field synthesis problem arisen from this, is solved by means of a global optimization method. The method is based on search trajectories. This technique utilizes the expression of the gradient of the cost functional and allows one to save calculation time when the expression of it is known. The algorithm for the solution of the problem is developed for an axisymmetric electromagnetic configuration. Two applications for the determination of the poloidal current system in toroidal devices for thermonuclear fusion experiments, are considered.

A finite difference method and a finite element method have been developed for the solution of a two-dimensional steady state electrodynamic problem in magnetohydrodynamic flows for a magnetic Reynolds number much lower than one. The finite different method is based on an exponential fitting scheme. The finite element method is obtained from a variational formulation. The two methods have been applied for the solution of the electrodynamic problem in the plasma fow of an MHD generator. The results obtained are discussed and compared.

A system study of a combined cycle MHD-steam thermal power plant electrical station with zero stack emission through recirculation of CO/sub 2/, is presented. The design of the MHD generator of the topper is done by means of a quasi-one dimensional optimization model. The technology of the components is conventional. An overall efficiency larger than 40% for power plants with thermal power inputs above 1000 MWth, is obtained.

A difference method for the solution of the two-dimensional electrodynamic problem in a magnetohydrodynamic field is presented. An exponential fitting is utilised for the discrete formulation of the problem. A multigrid technique is adopted. The method developed converges fastly and yields an accurate approximation of the solution of the problem. >

A numerical experiment in a plasma vane (current carrying plasma nonuniformity) MHD generator is presented. The numerical calculations are based on a time-dependent two-dimensional model. The gas constituting the plasma is assumed to be ideal. Viscosity and heat losses are neglected. In order to optimize the generator performance, a parametric analysis is carried out. The results of the calculations indicate that enthalpy extractions larger than 30% can be obtained. >

Summary form only given. The paper considers the charge deposited on the surface of a plasma dielectric barrier discharge (DBD) actuator. The actuator is utilized to induce the electro-hydro-dynamic (EHD) interaction in the aerodynamic boundary layer of one atmosphere air [1,2]. The effect on the EHD interaction of the charge distribution on the actuator surface is studied both experimentally and numerically.

This paper deals with the measurements performed to characterize the jet produced by the plasma wind tunnel SCIROCCO. The measurements are aimed to determine the vibrational temperature and the electron density of the plasma flow. A numerical rebuilding of the expansion trough the nozzle has then been performed. The work is part of an experimental activity funded by the European Space Agency and by the Italian Space Agency in the framework of a conjunct research project on the MHD interaction in an unseeded hypersonic air flow.

These paper deals with the numerical rebuilding of the experimental data from the experimental campaing on blunt body equipped with an electromagnet made in CIRA at SCIROCCO facility. A set resticted set of experimental condition have been considered for numerical rebuilding. Two different CIRA codes have been used, CAST and EMC3NS. Codes, whose structure is generally similar, are different is some modeling aspects. Their results compared with experimental data have been analized and criticallycompared, and gives a guidelines for further developments and analysis in this field.

The operation of a surface dielectric barrier discharge actuator for airflow control has been experimentally investigated. The actuator is constituted by an electrode pair separated by a dielectric Teflon sheet. Several ac supply conditions have been utilized. An electrohydrodynamics interaction was induced in still air, and several fluid-dynamic regimes were obtained. Visualization of the plasma boundary layer during the discharge ignition phase and during the steady state regime was obtained by utilizing a Schlieren diagnostic technique. The vortex morphology and propagation velocities at all supply conditions utilized have been evaluated. Velocity profiles perpendicular to the actuator surface, obtained from Pitot tube measurements, and line intensity profiles, determined by means of Schlieren imaging, have been determined for the steady regime operation. The integral along a line perpendicular to the actuator surface of the light intensity of the Schlieren image has been calculated. The profile obtained is in good agreement with the Pitot velocity profile in all the supply conditions investigated. Numerical simulations were also performed. The calculations confirm the relation between the flow velocity distribution in the boundary layer and the gas density distribution, which is the cause of the Schlieren image.

The Electro-Hydro-Dynamics (EHD) interaction, induced by a dielectric barrier discharge (DBD) in the aerodynamic boundary layer induced in a one atmosphere still air, has been studied both numerically and experimentally. Three different geometrical actuator configurations have been used. The first one is constituted by an electrode pair separated by a 2 mm dielectric teflon sheet. The second and the third configuration have been obtained by adding a third electrode on the upper dielectric surface. This electrode has been placed downstream of the upper electrode and has been connected to the ground or has been left floating. The high voltage electrode has been fed by an a.c. electrical signal. Measurements of the dielectric surface potential generated by the charge deposition have been obtained by using an electrostatic voltmeter. Numerical simulations allowed to determine the charge distribution on the dielectric surface. The discharge has been switched off after positive and negative values of the plasma current. The measurements have been carried out after both phases. Surface potential distributions show that the charge build up takes place several centimeters downstream the upper electrode after the end of the plasma extension. The charge distribution strongly depends on the switching off phase and is heavily affected by the geometrical configuration. Velocity profiles are obtained by using a Pitot probe. They show that the third electrode limits the fluid dynamics performance of the actuator. A relation between the charge surface distribution and the EHD interaction phenomenon has been found. Images of the plasma have been taken to evaluate the discharge structure and the extension of the plasma in the different geometrical configurations studied.

A surface dielectric barrier discharge (DBD) actuator has been experimentally investigated. An electrode pair separated by a dielectric sheet constitutes the actuator. Two types of dielectric materials and several a.c. supply conditions have been utilized to generate a surface dielectric barrier discharge with different characteristics. An Electro Hydro Dynamics (EHD) interaction was induced into still air and several fluid-dynamic regimes were obtained. Using electric and fluid dynamics measurements, the energy transfer mechanisms caused by the EHD interaction have been investigated. The visualization of the plasma boundary layer during the discharge ignition phase, characterized by hot vortexes, and during the steady regime has been obtained by means of Schlieren diagnostics technique. Vortex morphology and propagation velocities for both actuator types at all supply conditions have been evaluated. Pitot velocity profiles have been taken in the steady regime operation at several distances along a line perpendicular to the actuator surface. Along this line and as a function of the position the integral of the pixel intensities of the Schlieren image has been calculated. The function obtained matches with a good agreement the Pitot velocity profile for all distances and in all the supply conditions investigated. Numerical simulations were performed to validate theoretically this result. The calculations confirm the relationship between flow velocity distribution in the boundary layer and the gas density distribution.

An advanced flow control experiment, concerning magnetohydrodynamics (MHD) interaction over a blunt body, has been designed by Alta, CIRA and Department of Electrical Engineering (DIE) of University of Bologna and to be realized in CIRA's plasma wind tunnel "Scirocco" under a technology research program (TRP) funded by the European Space Agency (ESA). This work is a further step of the researches performed during the last decade by Alta and DIE in the field of MHD interaction. This experimental campaign foresees the employment of a 50 kW electromagnet, enclosed into an insulated blunt-shaped metallic TPS convectively cooled and electrically insulated by a ceramic coating. The test article has been designed for an air flow with nominal stagnation conditions of p0=2 bar and h0=22 MJ/kg, but several other conditions are planned to be investigated. The aim of the experimental campaign, along with a better understanding of the physical phenomena occurring within an highly ionized shock layer with an applied magnetic field, is the comparison of the collected data with the numerical predictions of CFD codes developed by CIRA. © 2011 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

This paper presents a technique for improving the convergence rate of a generalized minimum residual (GMRES) algorithm applied for the solution of a algebraic system produced by the discretization of an electrodynamic problem with a tensorial electrical conductivity. The electrodynamic solver considered in this work is a part of a magnetohydrodynamic (MHD) code in the low magnetic Reynolds number approximation. The code has been developed for the analysis of MHD interaction during the re-entry phase of a space vehicle. This application is a promising technique intensively investigated for the shock mitigation and the vehicle control in the higher layers of a planetary atmosphere. The medium in the considered application is a low density plasma, characterized by a tensorial conductivity. This is a result of the behavior of the free electric charges, which tend to drift in a direction perpendicular both to the electric field and to the magnetic field. In the given approximation, the electrodynamics is described by an elliptical partial differential equation, which is solved by means of a finite element approach. The linear system obtained by discretizing the problem is solved by means of a GMRES iterative method with an incomplete LU factorization threshold preconditioning. The convergence of the solver appears to be strongly affected by the tensorial characteristic of the conductivity. In order to deal with this feature, the bandwidth reduction in the coefficient matrix is considered and a novel technique is proposed and discussed. First, the standard reverse Cuthill–McKee (RCM) procedure has been applied to the problem. Then a modification of the RCM procedure (the weighted RCM procedure, WRCM) has been developed. In the last approach, the reordering is performed taking into account the relation

In this work several plane dielectric barrier discharge actuators had been experimentally investigated. Each actuator is constituted by a planar electrode pair separated by a dielectric. Several actuator geometries, dielectric materials, and a.c. supply voltages and frequencies have been utilized. Rotational and vibrational temperatures have been appraised through spectroscopic measurements. Translational temperatures have been evaluated by thermographic investigations, and the fluid speed has been obtained by using a Pitot tube. Electric measurements have been performed to determine the average power and the electron number density. All these parameters have been correlated to evaluate the best configuration and operating conditions for the considered actuators.

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 [AIAA Hypervelocity Impact Conference (American Institute of Aeronautics and Astronautics, Washington, DC, 1969), AIAA Paper No. 69–354], Godunov’s [Numerical Methods in Fluid‐Dynamics (Springer‐Verlag, New York, 1977), pp. 28–38], and Casulli’s [Int. J. Numer. Methods Fluids 4, 1001 (1984)] 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.