Forward and inverse problems in fundamental and applied magnetohydrodynamics

This Minireview summarizes the recent efforts to solve forward and inverse problems as they occur in different branches of fundamental and applied magnetohydrodynamics. As for the forward problem, the main focus is on the numerical treatment of induction processes, including self-excitation of magnetic fields in non-spherical domains and/or under the influence of non-homogeneous material parameters. As an important application of the developed numerical schemes, the functioning of the von-K\'{a}rm\'{a}n-sodium (VKS) dynamo experiment is shown to depend crucially on the presence of soft-iron impellers. As for the inverse problem, the main focus is on the mathematical background and some first practical applications of the Contactless Inductive Flow Tomography (CIFT), in which flow induced magnetic field perturbations are utilized for the reconstruction of the velocity field. The promises of CIFT for flow field monitoring in the continuous casting of steel are substantiated by results obtained at a test rig with a low melting liquid metal. While CIFT is presently restricted to flows with low magnetic Reynolds numbers, some selected problems of non-linear inverse dynamo theory, with possible application to geo- and astrophysics, are also discussed.Comment: 15 pages, 4 figures, accepted for publication in European Physical Journal Special Topic

Inverse Problems in Magnetohydrodynamics: Theoretical and Experimental Aspects

We consider inverse problems related to the velocity reconstruction in electrically conducting fluids from externally measured magnetic fields. The underlying theory is presented in the framework of the integral equation approach to homogeneous dynamos in finite domains, which can be cast into a linear inverse problem in case that the magnetic Reynolds number is not too large. Some mathematical problems of the inversion, including the uniqueness problem in the sphere and a paradigmatic isospectrality problem for mean-field dynamos, are touched upon. For practical purposes, the inversion is carried out with the help of Tikhonov regularization using a quadratic functional of the velocity field as penalty function. For the first time, we present results of an experiment in which the three-dimensional velocity field of a propellor driven flow in a liquid metal is reconstructed by a contactless inductive measuring technique.Comment: 8 pages, submitted to "Inverse Problems in Engineering

Urbanisme et économie de marché socialiste

China is currently moving from a centralized and planned economy to a socialist market economy. In such a context, urbanism sees its influence and role transformed. The urbanists must continue to direct town organization but they must now come to terms with economic players and factors outside their control. The master plans must now abandon the rigid zoning inherited from earlier plans and encourage — according to the value of land and the competition — a combination of economic functions on common ground.La Chine passe actuellement d'une économie centralisée et planifiée à une économie de marché socialiste. Dans un tel contexte, l'urbanisme voit son influence et son rôle transformés. Les urbanistes doivent continuer à orienter l'ordonnancement de la ville, mais il leur faut dorénavant composer avec des acteurs et des facteurs économiques qui échappent à leur pouvoir. Les schémas directeurs doivent désormais abandonner le zonage rigide hérité des plans d'autrefois et encourager — en fonction de la valeur du sol et de la concurrence — une combinaison des fonctions économiques sur un même terrain.Xu Mingtian, Dong Yang. Urbanisme et économie de marché socialiste. In: Villes en parallèle, n°23-24, décembre 1996. Villes chinoises. pp. 274-291

IHTC14-22243 BALLISTIC-DIFFUSIVE HEAT CONDUCTION MODEL

ABSTRACT In the present work, the heat flux and high order fluxes as well as their time derivatives are taken as independent variables and a new type of extended irreversible thermodynamics is developed. In the framework of this extended irreversible thermodynamics, the size dependence of the effective conductivity is investigated and a generalized single phase lagging heat conduction model including the size effect is established. Theoretically, it covers the diffusive to ballistic regime of heat conduction. The comparison with the experimental and theoretical results of silicon nanowires and thin films shows a good agreement in nano-scale regime. INTRODUCTION The fundamental law of the heat transfer is the classical Fourier law which has been widely and successfully applied in the conventional engineering heat conduction problems, in which the system has large spatial dimension and the emphasis is on the long time behavior. However, the Fourier law suffers from some drawbacks. Firstly, it assumes the infinite speed of heat propagation Much effort has been devoted to the improvement of the Fourier law. Cattaneo and Vernotte proposed the following heat conduction model (CV model

Multiscale transport of mass, momentum and energy

published_or_final_versionMechanical EngineeringDoctoralDoctor of Philosoph

The application of field synergy number in shell-and-tube heat exchanger optimization design

In the present work the field synergy principle is applied to the optimization design of the shell-and-tube heat exchanger with segmental baffles. The field synergy number which is defined as the indicator of the synergy between the velocity field and the heat flow is taken as the objective function. The genetic algorithm is employed to solve the heat exchanger optimization problems with multiple design variables. The field synergy number maximization approach for heat exchanger optimization design is thus formulated. In comparison with the initial design, the optimal design leads to a significant cost cut on the one hand and an improvement of the heat exchanger performance on the other hand. The comparison with the traditional heat exchanger optimization design approach with the total cost as the objective function shows that the field synergy number maximization approach is more advantageous.Heat exchanger Field synergy principle Field synergy number Optimization design

polar leo satellite constellation measurement by delay probing

IEEELow Earth Orbit (LEO) satellite networks are capable of providing wireless connectivity seamlessly and continuously to any part of the world with guaranteed short round-trip propagation delay. As a key part of Next Generation Network (NGN) in