Changes

The Mirage III has approximate dimensions (length,wingspan,height) of 15m x 8m x 4.5m. Or, measured in terms of freespace wavelength at 850 MHz, 42.5 lambda λ x 22.66 lambda λ x 12.75 lambdaλ. Thus, for the purposes of [[EM.Tempo]], we need to solve a region of about 12,279 cubic wavelengths. For problems of this size, a great deal of CPU memory is needed, and a high-performance, multi-core CPU is desirable to reduce simulation time.

[https://aws.amazon.com/ Amazon Web Services ] allows one to acquire high-performance compute instances on demand, and pay on a per-use basis. To be able to log into an Amazon instance via Remote Desktop Protocol, the [[EM.Cube]] license must allow terminal services (for more information, see [[http://www.emagtech.com/content/emcube-2016-licensing-purchasing-options EM.Cube]] Pricing]). For this project, we used a c4.4xlarge instance running Windows Server 2012. This instance has 30 GiB of memory, and 16 virtual CPU cores. The CPU for this instance is an Intel Xeon E5-2666 v3 (Haswell) processor.

The CAD model used for this simulation was found on [https://grabcad.com/ GrabCAD], an online repository of user-contributed CAD files and models. [[EM.Cube]]'s IGES import was then used to import the model. Once we import the model, we move the Mirage to a new PEC material group in [[EM.Tempo]].

<div><ul> <li style="display: inline-block;"> [[Image:glass.png ‎‎|thumb|left|200px|Selecting glass as cockpit material for the Mirage model.]]</li><li style="display: inline-block;"> [[Image:Mirage image.png ‎‎|thumb|left|200px|Complete model of Mirage aircraft.]]</li></ul></div>

===Planewave Source===Since we're computing a Radar Cross Section, we also need to add a planewave source. For this example, we will specify a TMz planewave with k = sqrt(2)/2 x - sqrt(2)/2 z, or theta &#952; = 135 degrees, phi &#966; = 0 degrees. , or:

[[Image:Large struct article mesh settings.png ‎‎|thumb|left|200px|Mesh settings used for the Mirage project.]]<math> \hat{k} = \frac{\sqrt{2}}{2} \hat{x} - \frac{\sqrt{2}}{2} \hat{z} </math>

[[Image:Large struct article ===Mesh Settings===For the mesh detail, we use the "Fast Run/Low Memory Settings" preset.png‎|thumb|left|200px|Mesh detail near This will set the cockpit region of minimum mesh rate at 15 cells per &#955;, and permits grid adaptation only where necessary. This preset provides slightly less accuracy than the aircraft"High Precision Mesh Settings" preset, but results in smaller meshes, and therefore shorter run times.]]

For the meshAt 850 MHz, we use the "Fast Run/Low Memory Settings" preset. This will set the minimum resulting FDTD mesh rate at 15 is about 270 million cells per lambda, and permits grid adaptation only where necessary. This preset provides slightly less accuracy than the "High Precision Mesh Settings" preset, but results With mesh-mode on in smaller meshes[[EM.Cube]], and therefore shorter run timeswe can visually inspect the mesh.

At 850 MHz, the resulting FDTD mesh is about 270 million cells. With mesh<div><ul> <li style="display: inline-mode on in block;"> [[EMImage:Large struct article mesh settings.png ‎‎|thumb|left|300px|Mesh settings used for the Mirage project.Cube]], we can visually inspect the </li><li style="display: inline-block;"> [[Image:Large struct article meshdetail. png‎|thumb|left|300px|Mesh detail near the cockpit region of the aircraft.]] </li></ul></div>

<br clear="all" />==Engine Settings===

After [[Image:Engine settings.png|thumb|left|300px|Engine settings used for Mirage project.]]For a given system, some experimentation may be needed to determine the sourcesbest number of threads to use. In many cases, observablesusing half of the available hardware concurrency works well. This comes as a result of there often being two cores per memory port on many modern processors. In other words, and mesh are set upfor many problems, the simulation can be runFDTD solver cannot load and store data from CPU memory quickly enough to use all available threads or hardware concurrency. For this exampleThe extra threads are idling waiting for data, we use the default engine settingsand a performance hit is incurred due to increased thread context switching.

[[EM.Cube]] will attempt use a version of the FDTD engine optimized for use with Intel's AVX instruction set, which provides a significant performance boost. If AVX is unavailable, a less optimal version of the engine will be used.

The complete simulationAfter the sources, including meshing, time-steppingobservables, and farfield calculation took 5 hoursmesh are set up, 50 minutes. The average performance of the timeloop was 330 MCells/s. The farfield computation requires a significant portion of the total simulation time. The farfield computation could have been reduced with larger theta and phi increments, but, typically, for electrically large structures, resolutions of 1 degree or less are requiredis ready to be run. After the simulation is complete, the nearfield visualization are available as seen below:<br clear="all" />

[[Image:Large struct article ScreenCapture3The complete simulation, including meshing, time-stepping, and farfield calculation took 5 hours, 50 minutes on the above-mentioned Amazon instance.png|thumb|left|500px|Figure 1: Geometry The average performance of the periodic unit cell timeloop was about 330 MCells/s. The farfield computation requires a significant portion of the dispersive water slab in EMtotal simulation time.Tempo The farfield computation could have been reduced with larger theta and phi increments, but, as mentioned previously, for electrically large structures, resolutions of 1 degree or less are required.]]

<div><ul> <li style="display: inline-block;"> [[Image:Large struct article ScreenCapture2ScreenCapture3.png|thumb|left|500px300px|Figure 1: Geometry RCS pattern of the periodic unit cell of the dispersive water slab Mirage model at 850 MHz in EM.TempodBsm.]] </li></ul></div>

[[ImageThe nearfield visualizations are also available as seen below:Large struct article ScreenCapture1.png|thumb|left|500px|Figure 1: Geometry of the periodic unit cell of the dispersive water slab in EM.Tempo.]]

<div><ul> <li style="display: inline-block;"> [[Image:RCS XY Polar.png||thumb|left|300px| XY Cut of RCS is dBsm]]</li><li style="display: inline-block;"> [[Image:RCS ZX Polar.png||thumb|left|300px| ZX Cut of RCS is dBsm]] </li><li style="display: inline-block;"> [[Image:Large struct article RCS YZPolar.png‎png||thumb|left|200px300px|YZ cut Cut of RCSis dBsm]]</li></ul></div>