CHAFF 6.2.11

15.1. Example 1

In this example, we will calculate the monostatic RCS Far Field for a spherical chaff usign the Method of Moments Solver. We will compare the results gathered when the ground plane is disabled and when a ground plane has been enabled.

Step 1

Create a new Chaff Project. Select “File → New” (or alternatively, press Ctrl+N), and select Chaff from the list of modules by clicking in the following button:

Chaff module button

Step 2

Add a Spherical Chaff. Select “Chaff → Spherical Chaff”. We will use the default parameters in this example, so click on OK on parameters tab to generate the chaff:

Spherical Cloud → Dipole Menu option

Chaff parameters tab

Step 3

Change the Simulation parameters for this project. Select “Simulation → Parameters”, change the frequency to 2.0 GHz as shown in the figure and press the “Save” button.

Simulation → Parameters Menu option

Simulation parameters

Step 4

Set the solver parameters for this project. Select “Solver → Parameters”. For the purpose of this training case, we will use the values presented in the figure:

  • Method: Method of Moments (MoM).
  • Conductor Losses: 0.0 Ω/m.
  • Relative Error: 0.01
  • Maximum iterations: 5000

Press the “Save” button.

Solver → Parameters Menu option

Solver parameters

Step 5

We will set the RCS type. Select “RCS → Parameters”. Then select “Monostatic RCS”. The values can be left as they are. Press Save to set the RCS.

RCS → Parameters Menu option

RCS parameters

Step 6

Select “Output → Observation Directions” and introduce the following far field observations using phi cuts:

  • Phi Cut: 0.0º
  • Initial Theta: 0.0º
  • Increment: 10º
  • Samples: 19

Final frequency should be 180º. This is described in the figure. Press the “Save” button.

Output → Observation Directions Menu option

Far Field Observation Directions

Step 7

Before being able to calculate, the project has to be meshed. Select “Meshing → Create Mesh”.

Meshing → Create Mesh Menu option

Step 8

Select 10 divisions in both planar and curved surfaces and the default frequency value. Since this is a very simple example, one processor should be enough for the meshing process. Press the “Mesh” button.

Meshing parameters

Step 9

Select “Calculate → Execute”, choose the number of processors used to run the simulation and press the “Execute” button.

Selection of number of processors

Step 10

When the simulation has finished (i.e. the text in the progress bar in the bottom-right corner of the window is “Done.”) we can see the results. Select “Show Results → Far Field → View Cuts” to show the Chaff graphic:

Show Results → Far Field → View Cuts Menu option

RCS graph

Step 11

Export the series to your hard drive, so that we can load it later to compare it with the ground plane results. Press the Export Series button and save it to a location of your choice.

Step 12

Let's inspect the numerical results before continuing the simulation. Select “Show Results → Far Field → View Text Files”.

Show Results → Far Field → View Text Files Menu option

Select Step 1 and the frequency “2.0E9 Hz” and press the OK button to show the text files.

Far Field File Text options

Text file visualization

Step 13

Now, we are going to add a ground plane to the simulation and see the difference of the computed RCS values in the result. To add a ground plane, select “Simulation → Parameters” and check the “Enable ground plane” checkbox. Then press the “Parameters” button next to it. Leave the default parameters (conductor material) and press the “Save” button.

Ground Plane parameters

Close the "Ground Plane" tab to go back to the "Simulation" tab. Press the “Save” button to save the changes to the ground plane configuration.

Step 14

Re-mesh the geometry by selecting the “Meshing → Create Mesh” option. Leave the same parameters as the previous time and press the “Mesh” button (similar to steps 8 and 9).

Step 15

Select “Calculate → Execute”, select the number of processors to run the simulation and press the “Execute” button (similar to step 10).

Step 16

When the simulation is done, select “Show Results → Far Field → View Cuts” to show the Far Field Diagram.

RCS graph

Step 17

Select “Show Results → Far Field → View Text Files”. Select the “2.0E9 Hz” frequency and the first (and only) step. Press the “OK” button.

Viewing results in text format

Step 18

Now, we are going to compare the Far Field Values of the simulation without ground plane and the current simulation. Select “Show Results → Far Field → View Cuts” to show the Far Field Diagram for the current simulation.

RCS plot for the simulation with ground plane.

Import the series from the first simulation -the one without ground plane we did before. To do this, press the “Import Series” button and select the file saved earlier. Doing this will add a new (blue) line in the graph area, allowing the user to compare the results from both simulations.

Visualizing the graphs of both simulations

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