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Hierarchical material property representation in finite element analysis: Convergence behavior and the electrostatic response of vertical fracture sets

2018 SEG International Exposition and Annual Meeting, SEG 2018

Weiss, Chester J.; Beskardes, G.D.; van Bloemen Waanders, Bart G.

Methods for the efficient representation of fracture response in geoelectric models impact an impressively broad range of problems in applied geophysics. We adopt the recently-developed hierarchical material property representation in finite element analysis (Weiss, 2017) to model the electrostatic response of a discrete set of vertical fractures in the near surface and compare these results to those from anisotropic continuum models. We also examine the power law behavior of these results and compare to continuum theory. We find that in measurement profiles from a single point source in directions both parallel and perpendicular to the fracture set, the fracture signature persists over all distances. Furthermore, the homogenization limit (distance at which the individual fracture anomalies are too small to be either measured or of interest) is not strictly a function of the geometric distribution of the fractures, but also their conductivity relative to the background. Hence, we show that the definition of “representative elementary volume”, that distance over which the statistics of the underlying heterogeneities is stationary, is incomplete as it pertains to the applicability of an equivalent continuum model. We also show that detailed interrogation of such intrinsically heterogeneous models may reveal power law behavior that appears anomalous, thus suggesting a possible mechanism to reconcile emerging theories in fractional calculus with classical electromagnetic theory.

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TYPE Conference Poster YEAR 2018
DOIOSTIScopus

Magnetic Methods for Tracking Particle Motions and Temperatures within Opaque Vessels

Nemer, Martin N.; van Bloemen Waanders, Bart G.; Mazumdar, Yi C.; Guba, Oksana G.; Mazumdar, Anirban; Bond, Stephen D.; Brooks, Carlton F.; Roberts, Christine C.; Dodd, Amanda B.; Miller, Stephen S.

A three year LDRD was undertaken to look at the feasibility of using magnetic sensing to determine flows within sealed vessels at high temperatures and pressures. Uniqueness proofs were developed for tracking of single magnetic particles with multiple sensors. Experiments were shown to be able to track up to 3 dipole particles undergoing rigid-body rotational motion. Temperature was wirelessly monitored using magnetic particles in static and predictable motions. Finally high-speed vibrational motion was tracked using magnetic particles. Ideas for future work include using small particles for measuring vorticity and better calibration methods for tracking multiple particles.

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TYPE SAND Report YEAR 2017
DOIOSTI

Remote Temperature Distribution Sensing Using Permanent Magnets

IEEE Transactions on Magnetics

Mazumdar, Yi C.; Guba, Oksana G.; Brooks, Carlton F.; Roberts, Christine C.; van Bloemen Waanders, Bart G.; Nemer, Martin N.

Remote temperature sensing is essential for applications in enclosed vessels, where feedthroughs or optical access points are not possible. A unique sensing method for measuring the temperature of multiple closely spaced points is proposed using permanent magnets and several three-axis magnetic field sensors. The magnetic field theory for multiple magnets is discussed and a solution technique is presented. Experimental calibration procedures, solution inversion considerations, and methods for optimizing the magnet orientations are described in order to obtain low-noise temperature estimates. The experimental setup and the properties of permanent magnets are shown. Finally, experiments were conducted to determine the temperature of nine magnets in different configurations over a temperature range of 5 °C to 60 °C and for a sensor-to-magnet distance of up to 35 mm. To show the possible applications of this sensing system for measuring temperatures through metal walls, additional experiments were conducted inside an opaque 304 stainless steel cylinder.

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TYPE Journal Article YEAR 2017
DOIOSTIScopus
Results 76–100 of 185
Results 76–100 of 185