Modeling tippers on a sphere

<p>In the past three decades, a huge amount of long-period magnetic data (from weeks to years of measurements) has been collected around the world either inland or at sea bottom. It makes tempting to estimate from these data magnetotelluric (MT) vertical transfer functions - tippers – in as wide  period range as practicable and further probe with them the three-dimensional (3-D) distribution of electrical conductivity in the upper mantle on a global or semi-global/continental scale. Such problem setup requires modelling MT responses in spherical geometry. It is known that MT impedances in spherical coordinates can be modelled using different polarizations of a uniform external magnetic field. As for tippers, one cannot compute them on a sphere using this type of excitation, because the uniform external magnetic field of any polarization contains a non-zero vertical component. To overcome the problem, we elaborate a model of the source, which leads to valid MT tippers on a sphere or a part thereof. To compute tippers in spherical Earth models with 3-D conductivity distribution we use a novel accurate and computationally efficient solver called GEMMIE. The solver is based on nested integral equations, allowing researchers to calculate high-resolution MT tippers globally and regionally taking into account realistic oceans, sediments, and Earth’s conductivity.</p>

Modeling magnetotelluric tippers on a sphere with particular emphasis on ocean induction effect and effect from oceanic sediments

In the past three decades, an immense amount of long-period magnetic field data (with periods of measurements from months to years) has been collected worldwide, either inland or at sea bottom. This makes it tempting to estimate from the data magnetotelluric (MT) vertical transfer functions -tippers - and further probe with them the three-dimensional distribution of electrical conductivity on a global or semi-global/continental scale. Such problem setup requires modeling MT responses in spherical geometry. It is known that MT impedances in spherical coordinates can be modeled using different polarizations of a uniform external magnetic field. As for tippers, one needs another type of excitation because the uniform external magnetic field of any polarization contains a non-zero radial component. In the paper, we elaborate a model of the source, which leads to valid tippers on a whole sphere. We also present an accurate and computationally efficient solver to calculate the electromagnetic field and responses in a spherical shell or a part thereof. The solver, based on nested integral equations, was used to calculate high-resolution tippers regionally and globally, taking into account realistic oceans and Earth’s conductivity. In particular, we investigate an effect in tippers from bathymetry and oceanic sediments, both at the Earth's surface and sea bottom sediments.

Depletion-Induced Chiral Chain Formation of Magnetic Spheres

Experimental evidence is presented for the spontaneous formation of chiral configurations in bulk dispersions of magnetized colloids that interact by a combination of anisotropic dipolar interactions and isotropic depletion attractions. The colloids are superparamagnetic silica spheres, magnetized and aligned by a carefully tuned uniform external magnetic field; isotropic attractions are induced by using poly(ethylene oxide) polymers as depleting agents. At specific polymer concentrations, sphere chains wind around each other to form helical structures–of the type that previously have only been observed in simulations on small sets of unconfined dipolar spheres with additional isotropic interactions.

The Performance of Squeeze Film between Parallel Triangular Plates with a Ferro-Fluid Couple Stress Lubricant

The present study aims at investigating a couple stress ferrofluid lubricant effects on the performance of the squeezed film when a uniform external magnetic field is applied. For this purpose, Shliomis ferrohydrodynamic and couple stress fluid models are employed. The considered geometry is parallel triangular plates. The effects of couple stress, volume concentration, and Langevin parameters on squeeze film characteristics including time vs. height relationship and load-carrying capacity are investigated. According to the results, employing couple stress ferrofluid lubricant in the presence of the magnetic field leads to an increased performance of the squeeze film.

Method of Measuring Deformations of Magnetoactive Elastomers under the Action of Magnetic Fields

Magnetic deformation is a change in the size and shape of a sample under the action of a uniform external magnetic field. The study of this effect in various materials provides deep understanding of the nature of magnetic and mechanical interactions. Moreover, magnetic deformation is of great interest from an engineering point of view for designing new devices. In magnetoactive elastomers containing magnetic microparticles in the polymer matrix, a giant deformation is detected under the action of an external magnetic field. The generally accepted methods for measuring magnetic deformation in magnetoactive soft materials are now practically absent. The article describes the installation for the study of the magnetomechanical characteristics of magnetoactive elastomers and demonstrates its experimental capabilities. The installation allows to measure deformations in the range from 0 to 12.5 mm with a resolution of 1 micron. The deformation curves obtained using these installations are required for developing actuators and sensors based on magnetoactive elastomers, and also for improving their manufacturing technologies.

Hartmann and Reynolds Numbers Effects in the Newtonian Blood Flow of a Bifurcated Artery with an Overlapping Stenosis

Blood flow through a bifurcated artery with the presence of an overlapping stenosis located at parent’s arterial lumen under the action of a uniform external magnetic field is studied in this paper. Blood is treated as an electrically conducting fluid which exhibits the Magnetohydrodynamics principle and it is characterized by a Newtonian fluid model. The governing equations are discretized using a stabilization technique of finite element known as Galerkin least-squares. The maximum velocity and pressure drop evaluated in this present study are compared with the results found in previous literature and COMSOL Multiphysics. The solutions found in a satisfactory agreement, thus verify the source code is working properly. The effects of dimensionless parameters of Hartmann and Reynolds numbers in the fluid’s velocity and pressure are examined in details with further scientific discussions.

Effect of temperature on the MHD stagnation-point flow past an isothermal plate for a Boussinesquian Newtonian and micropolar fluid

Purpose This paper aims to analyze the steady two-dimensional stagnation-point flow of an electrically conducting Newtonian or micropolar fluid when the obstacle is uniformly heated. Design/methodology/approach The governing boundary layer equations are transformed into a system of ordinary differential equations using appropriate similarity transformations. Some analytical considerations about existence and uniqueness of the solution are obtained. The system is then solved numerically using the bvp4c function in MATLAB. Findings If the temperature of the obstacle Tw coincides with the environment temperature T0, then the motion reduces to the usual orthogonal stagnation-point flow; if Tw = T0, then it is necessary to include in the similarity function describing the velocity an oblique part due to the temperature. Also, the presence of a uniform external magnetic field orthogonal to the obstacle is examined. In all cases, the motion is reduced to a system of nonlinear ordinary differential equations with boundary conditions, whose solution is discussed numerically when the Prandtl and the Hartmann number varies. Originality/value The present results are original and new for the problem of magnetohydrodynamic mixed convection in the plane stagnation-point flow of a Newtonian or a micropolar fluid over a vertical flat plate. At infinity, the motion approaches the orthogonal stagnation-point flow of an inviscid fluid; the effect of an uniform external magnetic field is considered, and the obstacle has a uniform temperature.