Electromagnetic Lorentz Force Research Articles

Comparative numerical analysis of electromagnetic forces in DC and HFPC TIG welding

The paper presents a detailed theoretical analysis of the electromagnetic forces in the arc plasma and the weld pool metal in Tungsten Inert Gas (TIG) welding at direct current (DC) and high-frequency pulse current (HFPC) modulation with a frequency of 10 kHz. The electromagnetic (Lorentz) force, acting on arc plasma and metal is presented via potential (magnetic pressure) and rotational (equivalent electromagnetic force) force components. This approach allows us to substantially simplify the analysis of the Lorentz force effect on the arc plasma and weld pool metal under different arc burning modes. It was shown that in HFPC TIG welding with a given frequency, the effect of modulated current on the arc plasma is inherently non-stationary, whereas the effect on the weld pool metal is determined by the time-averaged magnitude of electromagnetic force throughout the period of current modulation. The proposed approach serves as a basis for numerical analysis of the electromagnetic forces in arc plasma and weld pool metal during DC and HFPC modes of the welding process. We established that the application of HFPC modulation promotes a greater intensity of both the gas-dynamic processes in the welding arc, thereby significantly increasing the pressure on the weld pool surface, and convective heat transfer from the most heated central region near the weld pool surface towards the weld pool bottom. Both these factors lead to an increase of the arc penetrability in the case of the HFPC mode compared with the DC mode, all other conditions being equal.

Phase-field simulation of the dendrite growth in aluminum alloy AA5754 during alternating current electromagnetic stirring laser beam welding

Electromagnetic stirring is known to promote material flow, reduce porosity, uniform elements distribution, and refine grain in laser beam welding (LBW), which enhances the applicability of LBW in various industries. In this study, a phase-field model of dendrite growth in AA5754 Al alloy electromagnetic stirring laser beam welding was established. The model considered the thermal electromagnetic Lorentz force resulting from the interaction between the electric field generated by the Seebeck effect and the magnetic field, as well as the temperature gradient and solidification rate of the solidification interface obtained from the computational fluid dynamics electromagnetic stirring LBW model. The variation rules of dendrite growth with different magnetic parameters and effects are analyzed. Comprehensively, the magnetic field promotes the solidification rate, thus promoting interfacial instability and a large magnetic flux density leads to a faster interface instability. The solidification rate as well as the temperature gradient affect the growth rate, and the accelerated growth caused by the solidification rate with a high frequency and a large magnetic flux density effectively inhibits the slow growth caused by the temperature gradient. The thermal electromagnetic Lorentz force is the main factor for the branch increment at low frequencies, while both thermal electromagnetic Lorentz force and temperature gradient increase the number of branches at high frequencies. The calculated average branch numbers considering various factors in the stable stage under different magnetic parameters were consistent with the results of the scanning electron microscope tests.

Simulation of Electromagnetic Forming Process and Optimization of Geometric Parameters of Perforated Al Sheet Using RSM

Electromagnetic forming (EMF) is a kind of high-speed forming technology that can be useful for materials like aluminum. EMF helps to overcome the limitations of traditional forming. Due to this ability, the use of EMF in automotive applications has risen in recent years. The application of finite element software packages such as ANSYS 22 gives numerical modelling capabilities to simulate the EMF process and to design the forming process. Hence, the aim of this research work is to build and study the three-dimensional finite element model for the electromagnetic forming process and analyze the geometric parameters influencing the deformation of the perforated sheet with a design of experiments (DOE) approach. The finite element simulation is used in two stages. In the first stage, the electromagnetic force or Lorentz force striking the workpiece (i.e., Al sheet) is predicted using the ANSYS 22 Emag module. In the second stage, the predicted Lorentz force is then applied on an Al sheet to calculate the sheet deformation. The deformation of the sheet is predicted for different combinations of the geometric parameters of the sheet, such as open area percentage, ligament ratio (LR) and size of the hole, using ANSYS 22 Structural. In the DOE, response surface methodology (RSM) is used by considering the geometric parameters of perforated sheet such as open area percentage, ligament ratio (LR) and size of the hole. To minimize the number of experiments, an RSM model named central composite design (CCD) is employed. Further, the optimization study finds that the maximum deformation 0.0435 mm is calculated for the optimized combination of 25% open area, 0.14 LR and 4 mm hole size.

Self-consistent scaling of amplitude and pitch of ripples on a solidified surface

Amplitude and pitch of ripples on a solidified surface during arc welding or electron beam welding are self-consistently and realistically scaled. Defects of surface rippling or humping after solidification usually accompany solute segregation, porosity, etc. Surface ripples have also been contemporarily used to excite surface plasmon with wavelength less than that of incident laser and local concentrated energy near the surface to enhance efficiencies of LEDs, solar energy absorption and medical detections, etc. This work modified the previous scaling of the amplitude and pitch of surface ripples induced by Marangoni or thermocapillary flow in the molten pool by further accounting for joule heat and electromagnetic Lorentz force due to electric current from the top electrode. Combining the modified scaling of surface ripples with surface velocity in the pool, the results find that amplitude and pitch of surface ripples depend on modified Marangoni, Peclet, Prandtl numbers, loss coefficient and current frequency parameter. The loss coefficient and current frequency play a role in amplitude and pitch, respectively. Predicted surface amplitudes and pitches affected by electromagnetic, fluid, energy and concentration transport variables using COMSOL code are in good agreement with available experimental data.

Width-bending characteristic of REBCO HTS tape and flat-tape Rutherford-type cabling

The width-bending behaviors for a rare earth barium copper oxide (REBCO) high-temperature superconducting (HTS) tape have been investigated. It has been found experimentally that the width-bending strain of a Yttrium Barium Copper Oxide (YBCO) tape does not degrade the critical current as much as is expected from the axial strain. The critical current is not directly affected by the width-bending strain but by the axial strain, which the width-bending strain generates by the Poisson effect. Since Poisson’s ratio is about 0.3, the axial strain effective on the critical current is about 30% of the width-bending strain. Therefore, the width-bending strain of even 1.5% degrades the critical current by only 15% if the REBCO layer side is bent inward. However, the critical current degraded by more than 70% when the REBCO layer is outward. The width-bending effects on the critical current have been further examined, considering Poisson’s ratio changes and the neutral plane shift of the REBCO tape substrate. Those changes would occur when the material yields due to severe width-bending. Based on the width-bending of REBCO tapes, flat-tape Rutherford-type cabling is discussed. A REBCO Rutherford-type cable can provide various advantages, especially for narrow-tape cabling. The flat-tape Rutherford-type cable has better characteristics against an electromagnetic transverse Lorentz force. Furthermore, the tape length of the cable can be approximately the same as the cable length allowing for excellent tape usage. REBCO Rutherford-type cabling will be a promising high-current, high-field cabling method using thin substrate REBCO tapes. It will be useful for AC ramp-field and pulse-field applications with low AC losses and low shield currents. It notes that the filaments in the cable are symmetrically distributed in parallel. Therefore, each filament’s inductance is uniform, and a uniform current distribution among the filaments can be obtained.

An Electromagnetic Energy Harvester of Large-Scale Bistable Motion by Application of Stochastic Resonance

Abstract Vibrational energy harvesting has attracted considerable research attention for electrical power collection from ambient vibrations. Thereby, this study first developed an electromagnetic energy harvester of large-scale bistable motion by application of stochastic resonance, to enhance energy harvesting efficiency at a broadly low frequency. The electromagnetic energy harvester is fabricated by a magnet-coil generator and an oblique-supported spring-mass system. In the beginning, a weighting function is originally proposed considering mutual position relationship of the magnet and coil, and a motion equation and an electromagnetic induction equation are simultaneously established considering both elastic spring recovery force and electromagnetic induction Lorentz force. Subsequently, numerical analysis is processed to resolve the simultaneous equations to obtain systematic response displacement and the induced voltage, and the numerical solutions are accurately consistent with the measuring results in validation experiments. Furthermore, a damping coefficient is identified considering the mutual effectiveness of the damping forces from the normal friction and electromagnetic induction, and the influence of electromagnetic induction damping on systematic response displacement is carefully discussed. Eventually, experimental results clarified that the stochastic resonance phenomenon actually occurred as a large-scale bistable motion, and it is further validated that power generation efficiency can be noticeably enhanced following amplitude amplifications of systematic response displacement.

Magnetostructural assessment of DEMO TF coils with ENEA Winding Pack configuration

The present paper deals with a multiphysics study of the DEMO Toroidal Field (TF) coils with Winding Pack (WP) layout proposed by the Italian agency ENEA. The latest WP configuration, so far designed adopting the Wind&React technique, is composed of 202 Nb3Sn rectangular conductors, with steel jacket thickness progressively increased from the plasma-facing side, arranged in 6 double layers. Each conductor is designed to carry an operative current of 73.4 kA (14.8 MAt for one TF coil) and to ensure the requirement of 12 T of magnetic peak field. The electromagnetic (EM) Lorentz forces have been preliminary evaluated with a magnetostatic 3D analysis at different instants of plasma scenario and then used to perform the 3D structural assessment of the TF coil. For both models (i.e., electromagnetic and mechanical), the WP has been represented as a homogenized material with the cyclic symmetry boundary conditions, allowing to reduce the computational effort. In the structural model, a preliminary design of outer inter-coil structures and gravity support have been included allowing them to identify critical locations in a reliable way. In addition to the EM loads at different plasma scenario instants also the cooling down has been considered as loading condition. The stress assessment on the steel Casing was performed, exploiting the stress linearization along several paths chosen in the most critical locations.

The Effects of Solar Wind Structure on Nanodust Dynamics in the Inner Heliosphere

AbstractSeveral interplanetary spacecraft have inferred the presence of nanometer‐sized dust grains in the inner heliosphere accelerated to near‐solar wind velocities based on observations by radio wave antennas. These “nanodust” grains exhibit unique behavior in interplanetary space as they are strongly affected by both the solar gravitational force and the electromagnetic Lorentz force from the convecting interplanetary magnetic field. Here, we study the dynamics of nanodust grains in the inner heliosphere via a combination of background electromagnetic fields from the coupled Wang‐Sheeley‐Arge/Enlil heliospheric model and a nanodust grain charging and dynamics model. The model results predict strong time variability in the nanodust velocity and flux distributions at 1 au within a single Carrington rotation (CR) driven by a combination of nanodust grain size, heliospheric current sheet tilt, and varying heliospheric plasma parameters. In contrast, the general character of nanodust dynamics does not drastically change from one CR to the next. Despite including observationally driven heliospheric plasma conditions, the modeled nanodust impact rates do not agree with in situ observations by the STEREO A and B WAVES instruments, especially with regard to CR‐to‐CR variability. We interpret this data‐model disagreement as evidence that additional time variability must be present in the production rate of nanodust grains in the inner heliosphere. We discuss possibilities for this time variability, including non‐steady‐state collisional cascades, variability in nanodust trapping regions, and the impulsive disruption of inner solar system comets and/or asteroids.

Array of nanostrings electromagnetically interacting through repelling Lorentz forces

The collective stability behavior of a planar array of parallel nanostrings interacting through electromagnetic Lorentz forces is analyzed. The repelling coupling forces between the neighboring strings, organized in a snake-like arrangement and designed to deflect in a vertical, perpendicular to the array plane, direction, are generated solely by an electric current of alternating directions, which also results in the Joule heating of the strings. The analysis of the associated linearized eigenvalue problem provides the critical current corresponding to a push-out buckling with an intrinsic out-of-plane “zig-zag” mode. This bifurcation-type buckling is shown to precede the string loosening due to Joule heating, and to occur, in nano strings of realistic dimensions, at current density lower than the melting- or electromigration-related limits. The postbuckling behavior, governed by the inherent structural geometric and electromagnetic nonlinearities, is studied analytically and numerically. The results demonstrate the competing effects of the initial string tension and of the Joule heating on the array responses. In arrays constituting of finite numbers of strings, the critical buckling current is confined in a region bounded by the values obtained for the single string and infinite arrays.

Experimental and numerical study on the influence of process parameters in electromagnetic compression of AA6061 tube

ABSTRACTHigh velocity forming (HVF) technique is a forming process that deforms tubes and sheets with added advantages like less springback, wrinkling, improved strain distribution, better surface finish, and improved product quality. Electromagnetic forming is one of the HVF processes that work on the principle of electromagnetic induction and Lorentz force. In the present study, electromagnetic compression of AA6061 tube has been studied experimentally and analytically using finite element method simulation. Aluminum alloy AA6061 tubes of 56 mm outer diameter (OD) and 1 mm thickness were compressed using a four-turn bitter coil with the help of 40 kJ capacitor bank. A range of energy generated from a single and/or double capacitor banks was applied and gap between coil inner diameter and tube OD was varied to study their effect on deformation. Resultant velocity, magnetic field, effective plastic strain, displacement, and current density were calculated numerically and their effect on compression is compared. A regression equation has been developed using a factorial design of experiment method to calculate the rib depth at various energy and gap. A correlation was established between discharge energy and gap with deformation of tube, and variation of various numerically calculated parameters was analyzed.

An Introduction to Space–Time Exterior Calculus

The basic concepts of exterior calculus for space–time multivectors are presented: Interior and exterior products, interior and exterior derivatives, oriented integrals over hypersurfaces, circulation and flux of multivector fields. Two Stokes theorems relating the exterior and interior derivatives with circulation and flux, respectively, are derived. As an application, it is shown how the exterior-calculus space–time formulation of the electromagnetic Maxwell equations and Lorentz force recovers the standard vector-calculus formulations, in both differential and integral forms.

Edge-Based Finite Element Modeling of Magnetogasdynamic-Based Propulsion Systems

The paper presents an edge-based finite element method formulation for the coupled magnetohydrodynamic equations used for the simulation of magnetogasdynamic propulsion systems. The flow is modeled by the Reynolds-averaged Navier–Stokes equations along with the electromagnetic Lorentz force and joule heating resulting from the magnetic/electric interactions represented by source terms, whereas the electromagnetic phenomena are modeled through the magnetic induction equation. Turbulence is treated through the one-equation Spalart–Allmaras model. Both the flow and the electromagnetic problems are transformed into their pseudo-unsteady forms, and a segregated solution strategy is employed for the coupled system. The algebraic systems are solved by applying the generalized minimum residual with an incomplete lower upper factorization as a right preconditioner. After using the Hartmann flow as a validation test, results have been obtained for an magnetohydrodynamic converging channel accelerator, a two-dimensional inviscid flow in a scramjet, and a three-dimensional viscous flow in the same scramjet. The numerical results are compared against published numerical ones and show good agreement.

Wideband electromagnetic dynamic acoustic transducers (WEMDATs) for air-coupled ultrasonic applications

Achieving sufficient energy transmission over a wide frequency range is a challenge which has restricted the application of many types of air-coupled ultrasonic transducers. Conventional transducer configurations such as the piezoelectric micromachined or flexural ultrasonic transducers can be considered as narrowband. This study reports a type of ultrasonic transducer, the wideband electromagnetic dynamic acoustic transducer (WEMDAT), which operates through a combination of electromagnetic induction and Lorentz force with dynamic behaviour of a micro-scale-thick conductive film. WEMDAT prototypes have been designed, fabricated, and tested, showing their compatibility with both low and high power inputs, operating efficiently as a wideband transmitter from 46.4 kHz to 144.6 kHz with a good directivity. The WEMDAT has also been shown to operate effectively as a wideband ultrasonic receiver through the measurement in a pitch-catch configuration. The WEMDAT prototypes possess an adjustable drive coil lift-off distance from the active membrane, providing flexibility for optimizing the sensitivity of the transducers for different input levels. The performance of the WEMDATs can be optimized, showing significant potential for air-coupled ultrasonic applications.

Experimental study of liquid metal magnetohydrodynamic flows near gaps between flow channel inserts

The flow of the electrically conducting lead lithium, foreseen in liquid metal blankets as breeder and coolant, under the influence of the plasma-confining magnetic field induces electric currents that create strong electromagnetic Lorentz forces and high magnetohydrodynamic pressure drop. Electrically insulating flow channel inserts (FCI) may be applied for electrically decoupling the liquid metal flow from the well-conducting channel walls. This reduces currents and associated Lorentz forces that are responsible for the major contribution to pressure drop in the blankets. For fabrication reasons, it is unavoidable that gaps between inserts are present. Gaps will interrupt the electrical insulation, thus providing unwanted local short circuit for electric currents. For experimental investigations of 3D effects at junctions of FCIs, a test section has been manufactured and experiments have been performed in the MEKKA facility at the Karlsruhe Institute of Technology (KIT). The present experimental study shows the benefits of FCIs for pressure drop reduction in fully developed flows and quantifies the deterioration of pressure drop reduction by the presence of uninsulated gaps between FCIs.

Fabrication Issues of Sandwich-Like Flow Inserts for Circular Pipes

The dual-coolant lead lithium (DCLL) blanket in which the eutectic lead-lithium alloy is used as tritium breeder and coolant is a promising concept for applications in fusion power plants. The interaction of the moving electrically conducting liquid metal with the plasma-confining magnetic field induces electric currents and creates strong electromagnetic Lorentz forces opposing the flow. This may lead to high magnetohydrodynamic (MHD) pressure drops. Efficient cooling requires a sufficiently high flow velocity and, under these conditions, if currents find a shortcut through electrically conducting walls, the pressure drop will be very large. One way to reduce the MHD pressure drop in ducts is to decouple electrically the coolant flow from the load-carrying walls by insulating flow channel inserts (FCI). In order to demonstrate the capability of pressure drop reduction by FCIs in 3D MHD flow, a test section is currently being designed and manufactured for experiments in the MEKKA laboratory at the Karlsruhe Institute of Technology. The used FCIs are of sandwich-type with a ceramic layer protected from both sides by thin sheets of steel to prevent direct contact of the insulator with liquid metal. This technical note focuses on fabrication issues of sandwich-type flow channel inserts for circular pipes and shows methods and techniques for successful manufacturing.

Characteristics of welding and arc pressure in TIG narrow gap welding using novel magnetic arc oscillation

Tungsten inert gas (TIG) narrow gap welding using magnetic arc oscillation is one of the most important methods for joining thick components. Today’s developments are aimed at increasing a sophisticated process understanding, especially concerning the physical effect of arc behavior, which can provide many strategies to enhance weld prediction and joint quality. In this article, the arc behaviors studied by its arc pressure, static characteristic, and arc profile in terms of arc force are presented. With the help of the forces acting on the welding arc, arc profile can be considered separately to allow an improved investigation of narrow gap welding involved. Measurements of arc pressure distribution are used to validate the weld formation and the final welding result. Under the same conditions, the uniformity of arc pressure distribution in both the bottom and sidewall improved with the increase in magnetic flux density. Furthermore, a comparative study of arc static characteristic with magnetic field and non-magnetic field has also been carried out. The reduction in the difference of arc static characteristic is attributed to the inverse effect between electromagnetic pinch force and Lorentz force with the increasing welding current.

Defects and Correction Theories of Electromagnetics

<p class="1Body">Experiments show that, there is the electrostatic field around the permanent magnet; since the electromagnetics can not explain this phenomenon, it can be concluded that there are some defects in electromagnetics. This paper makes an analysis of the defects of electromagnetics from fourteen aspects. It is noted that, the basic defect of electromagnetics is that there is no explanation of any inherent causes and physical processes of electromagnetic induction, displacement current, Lorentz force and other surface phenomena. Moreover, it may also lead us to make incorrect inferences in the theoretical analysis of electromagnetics, e.g. the same direction of action and reaction, infinitely high kinematic velocity of magnetic field, etc. It can be seen from analysis of all electromagnetic phenomena that, all the electromagnetic phenomena will be inevitably accompanied by an electron motion; and the electron motion is bound to take effect through an electric field; therefore, the analysis of motion in an electric field is the basis for analysis of all electromagnetic phenomena. This paper proposes seven rules for analysis of motion in an electric field, analyzes the uniform motion and variable motion in an electric field on the basis of such rules, clarifies the inherent causes of Lorentz force, theoretically qualitatively and quantitatively demonstrates why there exists the electrostatic field at some locations around the permanent magnet, and considers that all the magnetic phenomena are resulted from the contraction of electric field in the direction of motion, which is derived from the natural law of constant velocity of light, and therefore all the electromagnetic phenomena is rooted in the constant velocity of light. Through the analysis of variable motion in an electric field, this paper proves the law of displacement current and electromagnetic induction, clarifies the physical processes of such phenomena, deduces the law of total current, explains why electric field strength and magnetic field strength of electromagnetic wave must be in same phase and why a plane wave has the electric and magnetic fields only with a certain length but no source, and considers that neither fast nor slow propagation velocity of electromagnetic wave is good and that the actual velocity of light is the ideal velocity of light.</p>

Velocity and flow rate measurement of liquid metal by contactless electromagnetic Lorentz force technique

Providing flow analysis in case of aggressive and hot liquids is a complicated task, especially when liquid's composition and, hence, its physical properties, are unknown. Contactless techniques are the most promising methods for liquid metal flow rate control and some of these methods are based on electromagnetic induction of breaking force acting on an electrically conductive fluid which is moving through a magnetic field. One of the techniques is time-of-flight Lorentz force velocimetry (LFV). By using the method one can estimate volumetric flow rate without knowing of electrical conductivity, magnitude of magnetic field or characteristic dimension. The most important and crucial challenge within the technique is detection of small fluctuations of Lorentz force value. In this article we will focus on application and investigation of time-of-flight LFV.

Experimental study of an electromagnetic flow meter for liquid metals based on torque measurement during pumping process

This paper presents a detailed experimental study on an electromagnetic flow measurement technique to measure the flow rate of liquid metals. The experimental setup consists of a contactless electromagnetic pump with a torque sensor mounted on the pump shaft. The electromagnetic pump is composed of two rotating steel discs having embedded permanent magnets with alternating poles. The rotation of the discs creates a travelling sinusoidal magnetic field and eddy currents within the liquid metal. The metal is contained inside the duct located between the discs of the pump. The interaction of the magnetic field and the induced eddy currents generates an electromagnetic Lorentz force providing the pumping effect. The flow rate is proportional to this force. The torque sensor measures the moment of the discs due to the Lorentz force, which is converted to a flow rate value. We name the method Lorentz torque velocimetry (LTV). The full calibration procedure and experimental investigation of the LTV are described. The method can be used as a non-contact flow rate control technique for liquid metals.

Revisiting Arc, Metal Flow Behavior in Flux Activated Tungsten Inert Gas Welding

Tungsten inert gas (TIG) welding is commonly used for quality joining of ferrous and non-ferrous materials. But lower depth of penetration is one major shortcoming of TIG and more numbers of passes are required for thick plate joining. Use of activated flux layer on workpiece remarkably enhances penetration. In the present work, arc and metal flow behavior are studied to revisit and validate the presence and role of governing forces responsible for higher penetration in flux activated TIG (ATIG) welding. Arc behavior, material flow patterns are studied during conventional and activated TIG welding for AISI 304 stainless steel using four different activated fluxes by carrying out welding (when arc is moving) as well as keeping the arc halted (stationary arc) for all cases. Results clearly demonstrate the presence of electromagnetic Lorentz force and surface tension induced reverse Marangoni flow (strongly centripetal). These forces also push the metal flow downward near the center region of the molten pool and in many occasions penetration reaches beyond plate thickness in ATIG welding.