Case Studies

Electromagnetic Wave Propagation over a Corrugated Cylinder

April 2005 | Westlake Village, CA Contributed by Touraj Sahely Member Technical Staff HyPerComp, Inc.

HyPerComp is using Tecplot to develop a higher order discretization procedure for modeling scattering and radiation problems of interest to both the defense and commercial electromagnetics community. The animation shows an electromagnetic pulse moving over a grooved cylinder.

The input for this animation consisted of 250 data files each representing a different time step in the simulation. A macro was created to operate on every data file one at a time creating the animation. The macro did the following for each time step:

• 8 Value blanking was used to peel away the outer boundary and expose the center tube
• Blanking was then turned off in the original volume zone
• A constant y plane slice was activated and added to the original zone
• The image was exported

The Engineer
Touraj Sahely is a member of the 15-person technical staff at HyPerComp, Inc. The Westlake Village, California-based company develops, implements, validates and disseminates user-friendly, high-performance computational technologies combining advances in physics-based numerical algorithms and parallel computing hardware for cost-effective simulations of complex, multidisciplinary physical processes in support of defense, energy, and commercial product design.

Founded in 1998, HyPerComp's vision is to continue being the best developer of high performance computing tools for time and space-dependent physical processes while expanding to serve more clients. Among the company's leading clients are government research & development organizations (Air Force Research Laboratory, Air Force Office of Scientific Research, Army Research Laboratory, NASA, DARPA); private industry (Rockwell, Boeing, Lockheed Martin, SAIC); and research institutions (Brown University, UCLA, University of Texas-Arlington).

The animation shows an electromagnetic pulse moving over the cylinder from right to left. As it moves over the corrugated part, the surface discontinuity of the grooves sets up scattered waves that get reflected at the end of the corrugation and move left to right as seen in the animation.

How HyPerComp Uses Tecplot
"Plots we generate with Tecplot help us to visualize electric and magnetic fields," explained Sahely, a six-year veteran of HyPerComp. "They include volume and surface fields. We look at electromagnetic wave strength and distribution inside a volume domain. We extract slices from volume domain and plot field contours, and also extract XY plots. Surface current contours are also generated and are key to understanding a given target's response to radar illumination."

Just like in computational fluid dynamics (CFD) simulations where he plots pressure, density, temperature and other quantities for flow visualization, in electromagnetics (EM) Sahely uses Tecplot to plot electric and magnetic fields, surface currents and other parameters to better understand the scattering and radiation of EM fields that lead to final postprocessed quantities such as radar cross section, range profiles and SAR imagery.

This physics-based scattering can be very complex and occur in many different forms such as: a) specular reflection, b) creeping waves, c) traveling waves, d) slow moving surface waves, e) edge diffraction, f) singular currents at surface discontinuities, g) resonating gaps and waveguides, and h) general material response. "It is a formidable challenge to be able to accurately simulate the various scattering phenomena," Sahely said. "For waves traveling over long distances, the relationship between the phase and amplitude of various scattered waves and the incident illumination is very critical for accurate representation of the near fields and the resulting farfield. Tecplot greatly assists us in understanding the physical phenomenon related to these simulations."

Analytically it has been shown that the nature of the slow moving wave is a function of the groove geometry (depth and width of the groove and the number of grooves per wavelength). The higher order time-domain Maxwell solver developed by HyPerComp is applied to study the corrugated cylinder to establish the presence and behavior of slow moving surface waves.

Plotting and Data Visualization
HyPerComp is using Tecplot to develop a higher order discretization procedure for modeling scattering and radiation problems of interest to both the defense and commercial electromagnetics community. Visualization of computed solutions provides two very important benefits, according to Sahely. First, Tecplot-generated visualizations provide a debugging mechanism. Since the mathematics of higher order formulations are complex, only through visualization is Sahely able to identify coding errors and formulation errors. Second, electromagnetics physics cannot be visualized in the real world, as can flow field behavior in a wind tunnel, because EM phenomena occurs at the speed of light. Visualization of computer generated EM fields, therefore, provides a very valuable understanding of some of the complex physics being modeled.

Film flow in MTOR Experiment. Open channel MHD flow in strong magnetic fields and conducting walls

Magnetohydrodynamics Creates Challenges
In the area of incompressible free surface magnetohydrodynamics (MHD) flows, HyPerComp frequently is required to visualize the free surface shape and compare them with experimental observations. The electric current generated in MHD flows is an important quantity that can only be physically understood with proper visualization. Sahely said Tecplot-generated animations of both free surface and velocity profiles greatly help in troubleshooting numerical simulation errors, while also providing customers with an intuitive feel for the results.

"This is particularly true in MHD or other forms of EM simulations, where the regular engineering curricula do not provide adequate background in order to truly understand the physical issues involved," Sahely said. "We routinely use Tecplot to simulate high Hartmann number flows in MHD where minor numerical discrepancies in boundary conditions are amplified greatly and cause serious errors in core flow quantities. With the aid of Tecplot, these errors are properly identified by visualizing current streamlines, potential distributions and so forth, often on a complex geometry with multiple material regions."

When asked what life would be like without Tecplot, Sahely had a simple answer. "It would be almost impossible to troubleshoot our simulation tools."

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