Longitudinal Flux Research Articles

MULTI-PARAMETRIC STUDY OF RISING 3D BUOYANT FLUX TUBES IN AN ADIABATIC STRATIFICATION USING AMR

We study the buoyant rise of magnetic flux tubes embedded in an adiabatic stratification using two-and three-dimensional, MHD simulations. We analyze the dependence of the tube evolution on the field line twist and on the curvature of the tube axis in different diffusion regimes. To be able to achieve a comparatively high spatial resolution we use the FLASH code, which has a built-in Adaptive Mesh Refinement (AMR) capability. Our 3D experiments reach Reynolds numbers that permit a reasonable comparison of the results with those of previous 2D simulations. When the experiments are run without AMR, hence with a comparatively large diffusivity, the amount of longitudinal magnetic flux retained inside the tube increases with the curvature of the tube axis. However, when a low-diffusion regime is reached by using the AMR algorithms, the magnetic twist is able to prevent the splitting of the magnetic loop into vortex tubes and the loop curvature does not play any significant role. We detect the generation of vorticity in the main body of the tube of opposite sign on the opposite sides of the apex. This is a consequence of the inhomogeneity of the azimuthal component of the field on the flux surfaces. The lift force associated with this global vorticity makes the flanks of the tube move away from their initial vertical plane in an antisymmetric fashion. The trajectories have an oscillatory motion superimposed, due to the shedding of vortex rolls to the wake, which creates a Von Karman street.

Correction of homogenized lamination stacks via a subproblem finite element method

Purpose – The purpose of this paper is to develop a subproblem finite element method for progressive modeling of lamination stacks in magnetic cores, from homogenized solutions up to accurate eddy current distributions and losses. Design/methodology/approach – The homogenization of lamination stacks, subject to both longitudinal and transversal magnetic fluxes, is first performed and is followed by local correction subproblems in certain laminations separately, surrounded by their insulating layers and the remaining laminations kept homogenized. The sources for the local corrections are originally defined via interface conditions to allow the coupling between homogenized and non-homogenized portions. Findings – The errors proper to the homogenization model, which neglects fringing effects, can be locally corrected in some selected portions via local eddy current subproblems considering the actual geometries and properties of the related laminations. The fineness of the mesh can thus be concentrated in the...

Plasmon polaritons at the boundary between a dielectric and a nanocomposite with metallic inclusions

Properties of surface plasmon polaritons at the interface formed in a dielectric matrix by a region without inclusions and by a region with metallic nanoinclusions have been investigated. The region with inclusions is a nanocomposite in which the dielectric constant has resonance behavior caused by the plasmon resonance of metallic nanoinclusions. The frequency dependences of the propagation constant and the transverse components of the wave vector, depth of penetration, mean free path, group velocity, and longitudinal energy flux have been obtained based on the solution to the boundary-value problem and numerical analysis. A substantial influence of the dielectric constant of the matrix of the structure on the wave characteristics of surface polaritons has been shown.

The breathability of compact cities

Breathability in dense building arrays with packing densities similar to those of typical European cities is investigated using laboratory measurements and numerical simulations. We focus on arrays made up by regularly spaced square buildings forming a network of streets with right-angle intersections. It is shown that breathability can be evaluated using building ventilation concepts (mean flow rate and age of air) and from vertical mean and turbulent fluxes quantifiable through a bulk exchange velocity. Mean age of air reveals that varying wind angles result in different ventilation, which we explain through mean flow streamlines and exchange velocity. For low wind angles (wind direction almost parallel to the axes of half of the streets of the network), vertical transfer and mean transversal transfers are at minimum and removal of pollutants is associated with mean longitudinal fluxes. Larger wind angles result in better ventilation due to an increase of transversal fluxes and vertical exchange. The latter, for which a formulation is derived, shows a non-negligible contribution of the mean flow which increases with increasing wind angle. Ventilation conditions can be further altered by small differences in the array geometry. These observations are useful for the development of simple urban dispersion models.

Standards for fired heater design: An assessment based on computational modelling

Fired heaters are used all over the World for refinery processes. Many of them are designed according to American Petroleum Institute (API) Standard 560. Among these, some have suffered significant tubes deformation and other defects related to heat loads in high tube walls. This observation motivated the present investigation into the design parameters used by API standard 560. Key design parameters are related to non-uniformity factors, which represent wall heat flux distribution over the length and circumference of a tube. Since sufficiently detailed measurements in operating units are almost impossible, numerical flow simulations were used instead. 3D simulations of combustion and heat transfer in the radiant chamber of a vertical cylindrical fired heater were carried out. The results are reported in the form used by furnace designers, i.e. in terms of circumferential and longitudinal heat flux factor. Additionally, this paper reports 2D parametric analyses of the effect of commonly encountered types of tube deformations on heat flux uniformity. In this manner, the research presented here provides important information on the effect, which tubes deformations may have on heat flux non-uniformity over the lifespan of a furnace. In conclusion, we found that standard 1D design calculations of fired heaters are significantly underestimating real heat flux variability.

Nonlinear Model of Tape Wound Core Transformers

Recently, tape wound cores due to their excellent magnetic properties, are widely used in different types of transformers. Performance prediction of these transformers needs an accurate model with ability to determine flux distribution within the core and magnetic loss. Spiral structure of tape wound cores affects the flux distribution and always cause complication of analysis. In this paper, a model based on reluctance networks method is presented for analysis of magnetic flux in wound cores. Using this model, distribution of longitudinal and transverse fluxes within the core can be determined. To consider the nonlinearity of the core, a dynamic hysteresis model is included in the presented model. Having flux density in different points of the core, magnetic losses can be calculated. To evaluate the validity of the model, results are compared with 2-D FEM simulations. In addition, a transformer designed for series-resonant converter and simulation results are compared with experimental measurements. Comparisons show accuracy of the model besides simplicity and fast convergence.

Surface plasmon polaritons at the interface between dielectric and anisotropic nanocomposite

Specific features of surface-wave propagation along the interface between an isotropic dielectric and an anisotropic nanocomposite containing ellipsoidal metal inclusions whose axes of rotation are perpendicular to the interface between the media have been studied. Frequency dependences of the propagation constant and wave-vector transverse components, of the penetration depths and propagation lengths in each of the media, and of the longitudinal and transverse energy fluxes have been obtained. The effect of the shape of the inclusions on the wave and energy characteristics of the surface waves is shown.

A Budget Analysis of Bottom-Water Dissolved Oxygen in Chesapeake Bay

A coupled hydrodynamic-dissolved oxygen model is developed to simulate the seasonal cycle of dissolved oxygen (DO) in Chesapeake Bay and investigate processes regulating summer hypoxia in the estuary. A budget analysis of DO in the bottom water reveals a balance between physical transport and biological consumption. In addition to the vertical diffusive flux, the longitudinal and vertical advective fluxes are important suppliers of DO to the bottom water. The longitudinal advective flux is affected not only by gravitational circulation but also by wind-driven currents. The vertical advective flux is affected by wind-driven lateral circulation and shows a strong dependence on wind speed and direction. Up-estuary winds weaken the landward bottom flow and generate a clockwise lateral circulation that exchanges DO between the deep channel and adjacent shoals, thereby reducing the longitudinal advective flux and increasing the vertical advective flux. In contrast, down-estuary winds amplify the longitudinal flux and reduce the vertical flux. During the summer, water column respiration contributes to about 74 % of the total biological consumption and sediment oxygen demand accounts for about 26 %. Sensitivity analysis model runs are conducted to analyze how changing river flows and winds affect the hypoxia prediction and oxygen budget balance. Due to the compensating changes in longitudinal and vertical fluxes, the hypoxic volume is relatively insensitive to changes in the river flow. In contrast, the timing and size of hypoxic volume changes with wind speed. Sensitivity analysis also shows that plankton oxygen production, water column respiration, and sediment oxygen demand all affect the hypoxia prediction and bottom oxygen balance.

A performance comparison of conventional and transverse flux linear switched reluctance motors

This paper presents a comprehensive comparison between conventional (longitudinal flux) linear switched reluctance machines (CLSRMs) and transverse flux linear switched reluctance machines (TLSRMs) so as to enable engineers to choose a structure suitable for their applications. A commonly-used single-sided CLSRM and 4 different TLSRM structures are considered for the comparison. For a fair comparison of the 2 types of LSRMs, equal dimensions, including equal length and magnetomotive force, are applied as much as possible. The analytical approach and 3-dimensional finite element analysis (FEA) are employed to obtain the performance of these machines. It is proven analytically that the CLSRM has a higher force capability compared to TLSRMs by as much as 6 times under linear B-H characteristic operating points. The results are reinforced by the FEA-based performance results. Furthermore, the CLSRMs are simpler to construct, resulting in lower manufacturing cost and thus paving an easier path for their market acceptance than TLSRMs. These results make CLSRMs the structure of choice for linear-switched reluctance motors.

How is topographic simplicity maintained in ephemeral dryland channels?

The lack of topographic complexity in ephemeral dryland channels, despite large variations in hydraulic controls and sediment texture, presents an unexplained paradox that limits understanding of their long-term evolution. In dryland basins, spatially and temporally discontinuous channel flow transports and sorts sediment along the bed intermittently and irregularly. The cumulative effect of these processes counterintuitively produces simple topography, manifest in straight longitudinal profiles and symmetrical cross sections, in contrast with perennial channels. This paper presents numerical modeling experiments based on field measurements to investigate dryland channel topographic development through the responses of bed-material flux and net sediment storage to variations in channel hydrology. We show that spatially variable flow creates and subsequently destroys incipient topography along ephemeral reaches, and that large flood events above a threshold overcome hydraulic and grain-size controls to dampen fluctuations in longitudinal sediment flux through a smoothing of the incipient channel bar forms. The results provide a physical explanation for emergent topographic simplicity in ephemeral dryland channels despite higher variability in streamflow and sedimentary characteristics compared to perennial systems.

Field-enhanced electronic specific heat of carbon nanotubes

The tight-binding model including curvature effects is used to study the effect of transverse electric field on the low-temperature electronic specific heat (Cv) for armchair and zigzag carbon nanotubes (ACNTs and ZCNTs). Electric field could effectively modulate energy dispersions of CNTs and cause a shift of electronic states toward the Fermi energy. As field strength reaches to a critical value (Fc), it induces special structures in the density of states near the Fermi energy and thus the giant specific heat. At Fcs, Cv has a value comparable to that of the phonon specific heat and reveals strongly non-linear dependence on temperature. The critical field strength and giant specific heat are closely related to nanotube's geometry. Moreover, under Fcs, the extra longitudinal magnetic flux could cause a re-enhancement in Cv for ZCNTs, whereas Cv is always diminished for ACNTs.

Measurements of thermal properties of crystals CaF2: Ce3+ activated Yb3+ and Lu3+ ions

Aim of this work was to investigate parameters of thermal expansion, thermal conductivity, and the temperature coefficient of the refractive index. These data are very important in the development of optical systems of lasers. Measurements of thermal conductivity were carried out using absolute stationary method of longitudinal heat flux. Parameters of thermal expansion and temperature coefficient of the refractive index were obtained by Jamin and Michelson interferometers.

Calculation of AC Resistance for Stranded Single-Core Power Cable Conductors

The ac resistance of power cable conductors is an important parameter for accurately estimating the ampacity of power cable and optimally designing power cable. Although international standard IEC-60287 has recommended a simplified formula for calculating the ac resistance, it is not capable of taking into account the effect of stranded conductor parameters, such as the direction and the length of lay, on the ac resistance because the stranded conductor is simplified as a solid conductor. In this paper, the method which has been used for analyzing the ac resistance of aluminum-conductor steel-reinforced overhead power lines is applied to single-core power cable conductors. Basically, the magnetic fluxes around each layer of the stranded wires are divided into circular magnetic fluxes and longitudinal magnetic fluxes, and thus each layer is equivalent to a circuit with resistor and inductor in series. Then, the ac resistance of single-core power cable conductors is calculated from the paralleled equivalent circuits representing all layers. A case study of 800 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> single-core power cable is given to investigate the effect of the parameters of the stranded wires on the ac resistance. Results show that the ac resistance for bidirectional stranding of copper wires is a few percentage points higher than that for unidirectional stranding. Such difference will be significant in the optimization of cable design as even a slight decrease in ac resistance can save considerable copper in large-scale industrial application.

Surface polaritons in a dielectric – anisotropic nanocomposite system

We have studied the peculiarities of propagation of surface polaritons at a planar interface between an isotropic dielectric and anisotropic nanocomposite with metal inclusions of ellipsoidal shape. For the case when the axes of all nanoellipsoids of revolution are perpendicular to the propagation direction and parallel to the medium interface, we have obtained frequency dependences of the propagation constant and transverse wave vector components, penetration depth and path length, longitudinal and transverse energy fluxes for surface polaritons. The shape of nanoellipsoids is shown to have an effect on the wave characteristics of surface polaritons.

Eilenberger and London theories for transverse components of flux line lattice form factors in uniaxial superconductors

We theoretically study the magnetic field orientation dependence of longitudinal and transverse flux line lattice form factors in uniaxial superconductors with anisotropy ratio corresponding to ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$. We discuss influences of the anisotropy ratio of coherence length and differences between the $s$-wave and the ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$-wave pairings. The calculations are performed by two methods, the Eilenberger theory and the London theory comparatively, and we study the cutoff function of the extended London theory, which will be helpful in the analysis of the small angle neutron scattering in the vortex states.

The impact of climate and reservoirs on longitudinal riverine carbon fluxes from two major watersheds in the Central and Intermontane West

AbstractA nested sampling network on the Colorado (CR) and Missouri Rivers (MR) provided data to assess impacts of large‐scale reservoir systems and climate on carbon export. The Load Estimator (LOADEST) model was used to estimate both dissolved inorganic and organic carbon (DIC and DOC) fluxes for a total of 22 sites along the main stems of the CR and MR. Both the upper CR and MR DIC and DOC fluxes increased longitudinally, but the lower CR fluxes decreased while the lower MRs continued to increase. We examined multiple factors through space and time that help explain these flux patterns. Seasonal variability in precipitation and temperature, along with site‐level concentration versus discharge relationships proved to be significant factors explaining much of the difference among sites located below reservoirs as compared to sites located in more free‐flowing segments of the river. The characterization of variability in carbon exports over space and time provides a basis for understanding carbon cycling and transport within river basins affected by large reservoir systems, particular in arid‐to semi‐arid ecosystems.

Subexponential decay in Fermi-LAT pulsar spectra: The case for tachyonic Cherenkov radiation

Tachyonic Cherenkov fits are performed to the Fermi-LAT γ-ray spectra of the Vela pulsar, PSR J1709 − 4429 and Geminga. The high-energy spectral tails of these pulsars exhibit pronounced subexponential Weibull decay, which can be modeled in a permeable spacetime by a frequency-dependent tachyon mass. The scaling exponent of the tachyon mass defines the Weibull shape parameter of the energy flux, and it also determines whether the radiation is sub- or superluminal. The negative mass-square in the tachyonic Maxwell-Proca equations gives rise to a longitudinal flux component. The radiation is generated by an ultra-relativistic thermal electron plasma via the inertial Cherenkov effect. The transversal and longitudinal γ-ray emission from Geminga is slightly superluminal, whereas γ-rays from the Vela pulsar and PSR J1709 − 4429 are subluminal despite the negative tachyonic mass-square in the dispersion relations.

Implementation of diffuse-reflection boundary conditions using lattice Boltzmann models based on half-space Gauss-Laguerre quadratures.

The Gauss-Laguerre quadrature method is used on the Cartesian semiaxes in the momentum space to construct a family of lattice Boltzmann models. When all quadrature orders Qx, Qy, Qz equal N+1, the Laguerre lattice Boltzmann model LLB(Qx,Qy,Qz) exactly recovers all moments up to order N of the Maxwell-Boltzmann equilibrium distribution function f(eq), calculated over any Cartesian octant of the three-dimensional momentum space. Results of Couette flow simulations at Kn=0.1, 0.5, 1.0 and in the ballistic regime are reported. Specific microfluidic effects (velocity slip, temperature jump, longitudinal heat flux) are well captured up to Kn=0.5, as demonstrated by comparison to direct simulation Monte Carlo results. Excellent agreement with analytic results is obtained in the ballistic regime.

Separated magnet yoke for permanent magnet linear generator for marine wave energy converters

In this paper the performance of a longitudinal flux permanent magnet linear generator (PMLG) for wave energy converters (WEC) is investigated. The influence of the number of slots per pole, phase q and the number of stator's winding sections are analysed. The power output and the cogging forces in the PMLG are calculated and reviewed with respect to the above design parameters. In addition, an optimised PMLG model is designed and simulated. Three-dimensional Finite Element Method (FEM) is used for solving the combined field and circuit equations of the generator.

Performance evaluation of alternative tunnel longitudinal ventilation systems using two inclined jets

This paper advances a novel design for providing longitudinal ventilation which utilizes the principle of induction while ensuring energy efficiency and allowing a better use of space. The induced longitudinal flow is generated by two inclined jets located about the midpoint between the floor and the ceiling allowing jets to entrain stagnant air freely necessary to guarantee the longitudinal air flux in tunnel. A mono-dimensional model and a CFD model have been developed in a parametric study to investigate the influence of inclination and the effect of confinement on the installation efficiency. It was found that by controlling the pitch angle of the two jets, the induction effect and then the installation efficiency are enhanced in order to achieve a successful use of the new ventilation system. Results show also that there exists an optimal confinement ratio assuring a better use of the longitudinal systems by producing the maximum induced air flow rate.