hp-Finite element solution of coupled stationary magnetohydrodynamics problems including magnetostrictive effects

We extend our existing hp-finite element framework for non-conducting magnetic fluids (Jin et al., 2014) to the treatment of conducting magnetic fluids including magnetostriction effects in both two- and three-dimensions. In particular, we present, to the best of our knowledge, the first computational treatment of magnetostrictive effects in conducting fluids. We propose a consistent linearisation of the coupled system of non-linear equations and solve the resulting discretised equations by means of the Newton–Raphson algorithm. Our treatment allows the simulation of complex flow problems, with non-homogeneous permeability and conductivity, and, apart from benchmarking against established analytical solutions for problems with homogeneous material parameters, we present a series of simulations of multiphase flows in two- and three-dimensions to show the predicative capability of the approach as well as the importance of including these effects

Resolving the sign conflict problem for hp–hexahedral Nédélec elements with application to eddy current problems

The eddy current approximation of Maxwell’s equations is relevant for Magnetic Induction Tomography (MIT), which is a practical system for the detection of conducting inclusions from measurements of mutual inductance with both industrial and clinical applications. An MIT system produces a conductivity image from the measured fields by solving an inverse problem computationally. This is typically an iterative process, which requires the forward solution of a Maxwell’s equations for the electromagnetic fields in and around conducting bodies at each iteration. As the (conductivity) images are typically described by voxels, a hexahedral finite element grid is preferable for the forward solver. Low order Nédélec (edge element) discretisations are generally applied, but these require dense meshes to ensure that skin effects are properly captured. On the other hand, hp–Nédélec finite elements can ensure the skin effects in conducting components are accurately captured, without the need for dense meshes and, therefore, offer possible advantages for MIT. Unfortunately, the hierarchic nature of hp–Nédélec basis functions introduces edge and face parameterisations leading to sign conflict issues when enforcing tangential continuity between elements. This work describes a procedure for addressing this issue on general conforming hexahedral meshes and an implementation of a hierarchic hp–Nédélec finite element basis within the deal.II finite element library. The resulting software is used to simulate Maxwell forward problems, including those set on multiply connected domains, to demonstrate its potential as an MIT forward solver

An hp-fem framework for the simulation of electrostrictive and magnetostrictive materials

The physical understanding of coupled electro-magneto-mechanics has long been a topic of particular importance for scientists. However, it is only in more recent times that the computational mechanics community has been involved, due to the particularly demanding nature of these coupled problems. In this paper, we extend our previous work (Gil AJ, Ledger PD. A coupled hp finite element scheme for the solution of two-dimensional electrostrictive materials. Int J Numer Methods Eng 2012;91:1158–1183) to make it possible to capture more complex coupled phenomena, namely electrostriction and magnetostriction of elastic solids and incompressible Newtonian viscous fluids. From the formulation standpoint, a total Cauchy stress tensor is introduced combining the effects of the mechanical deformation and the ponderomotive force and, for the case of conservative materials, the weak form is obtained from the stationary points of a suitable enthalpy energy formulation. In order to ensure accuracy of results hp-finite elements are employed. Moreover, for computational efficiency, the scheme is implemented in a monolithic manner via a Newton–Raphson strategy with consistent linearisation. A series of well known numerical examples are presented to demonstrate the influence of the electromagnetic phenomena when fully coupled with fluid and solid fields

Characterisation of multiple conducting permeable objects in metal detection by polarizability tensors

Realistic applications in metal detection involve multiple inhomogeneous-conducting permeable objects, and the aim of this paper is to characterise such objects by polarizability tensors. We show that, for the eddy current model, the leading order terms for the perturbation in the magnetic field, due to the presence of N small conducting permeable homogeneous inclusions, comprises of a sum of N terms with each containing a complex symmetric rank 2 polarizability tensor. Each tensor contains information about the shape and material properties of one of the objects and is independent of its position. The asymptotic expansion we obtain extends a previously known result for a single isolated object and applies in situations where the object sizes are small and the objects are sufficiently well separated. We also obtain a second expansion that describes the perturbed magnetic field for inhomogeneous and closely spaced objects, which again characterises the objects by a complex symmetric rank 2 tensor. The tensor's coefficients can be computed by solving a vector valued transmission problem, and we include numerical examples to illustrate the agreement between the asymptotic formula describing the perturbed fields and the numerical prediction. We also include algorithms for the localisation and identification of multiple inhomogeneous objects

An accurate and efficient three‐dimensional high‐order finite element methodology for the simulation of magneto‐mechanical coupling in MRI scanners

Transient magnetic fields are generated by the gradient coils in an magnetic resonance imaging (MRI) scanner and induce eddy currents in their conducting components, which lead to vibrations, imaging artefacts, noise, and the dissipation of heat. Heat dissipation can boil off the helium used to cool the super conducting magnets and, if left unchecked, will lead to a magnet quench. Understanding the mechanisms involved in the generation of these vibrations, and the heat being deposited in the cryostat, are key for a successful MRI scanner design. This requires the solution of a coupled physics magneto-mechanical problem, which will be addressed in this work. A novel computational methodology is proposed for the accurate simulation of the magneto-mechanical problem using a Lagrangian approach, which, with a particular choice of linearisation, leads to a staggered scheme. This is discretised by high-order finite elements leading to accurate solutions. We demonstrate the success of our scheme by applying it to realistic MRI scanner configurations

Parameterised electromagnetic scattering solutions for a range of incident wave angles

This paper considers the numerical simulation of 2D electromagnetic wave scattering problems and describes the construction of a reduced--order approximation which enables the rapid prediction of the scattering width distribution for a range of incident wave directions. Associated certainty bounds ensure confidence in the results of the computed approximation. Numerical examples are included to demonstrate the performance of the proposed procedure