Basic Geometry

OpenMDAO fully supports integrating geometry into a modeling process. Before we start working with geometry, let’s understand how OpenMDAO was designed to interact with geometry. The GeomComponent class, from openmdao.lib.components.api, allows you to plug in the parametric geometry engine of your choice and specify a particular geometry model to work with.

Note

We’re going to work this tutorial in the OpenMDAO GUI. When you’re working with geometry, it’s nice to be able to see what you’re building, and the GUI has a built-in viewer that makes this easy. If you don’t know how to use the GUI, check out the instructions in the GUI section to get started.

You could also build a script file that does the same thing we’re doing in the GUI. At the end of the tutorial, we’ll show you what that would look like, but you won’t be able to visualize the results in a viewer.

Start by creating a new clean project in the GUI. We’ll name it Geometry Tutorial. You’ll be greeted by a totally blank project page. First, you should create an instance of an assembly to work in. On the right-hand side, there is a Library tab with a text box at the top. In the box type “assemb” and hit enter. This will filter down the whole library so you can find things easier. Drag the Assembly and drop it into the workspace. Name it top.

../../_images/library_assembly.png

Creating the initial assembly

So now go back to the Library and change the filter text to “geom” and hit enter. Drag the GeomComponent instance and drop it into the top assembly. Name it geom when prompted. Whenever you want to work with geometry, you will always start with GeomComponent. No actual geometry has been loaded yet, so the geom instance is pretty boring. If you double-click on it, a component editor window will come up with nothing much in it.

Note

Depending on the plugins you have installed and the names of classes you’ve defined in your project (if any), what shows up when you filter the library might be slightly different from what we have here.

So now let’s add a very simple geometry model of a box. First, switch over to the Slots tab in the editor window for geom. Find BoxParametricGeometry in the Library pane and drag it into the parametric_geometry slot. When you’re done, it should look like this:

../../_images/box_geom.png

Dropping BoxParametricGeometry into the slot

Do you want to see what your newly added geometry model of a box looks like? Click on the Outputs tab of the editor window and then click the View Geom button next to the geom_out variable. This will bring up the 3D viewer in a separate window.

../../_images/box_viewer_1.png

Initial box geometry

This VERY simple model lets you control the height of the box, which is its only parameter. So switch to the Inputs tab in the editor window and you should see the height variable. Set it to a new value, such as 10. Now, go back to the 3D editor window. Nothing changed! GeomComponent is just like any other OpenMDAO Component; it needs to be run before the new outputs can be calculated with the new input values. So right-click on geom and select run. Now the viewer will update with the new geometry, and you can see how it got much taller.

../../_images/box_viewer_2.png

Box with height=10

Auto Run

Sometimes when you’re working with geometry, the extra step of calling run will be a bit tedious. On the Inputs tab is an input called auto_run, which you can set to True. When the value is set to True, the component will run itself whenever a new value is set for one of its parameters. The viewer will update automatically as well. This makes it nice for playing with parameters and seeing the results quickly; but for any kind of actual optimization, this can cause a lot of extra executions of your geometry component as different variables are set at different times. So make sure that you set auto_run to False before you do any kind of DOE or optimization work.

Working with a Script

Below you can see how you would set up this tutorial in a script. It’s pretty straight forward, but as we said before, you won’t be able to render the geometry in the viewer this way.

from openmdao.main.api import Assembly
from openmdao.lib.components.api import GeomComponent
from openmdao.lib.geometry.box import BoxParametricGeometry

class GeomAsmb(Assembly):

    def configure(self):
        self.add('geom', GeomComponent())
        self.geom.add('parametric_geometry', BoxParametricGeometry())
        self.driver.workflow.add('geom')

if __name__ == "__main__":

    top = GeomAsmb()
    top.run()
    print "box volume: %3.2f"%top.geom.volume

    top.geom.height = 10
    top.run()
    print "new box volume: %3.2f"%top.geom.volume

Next Steps

That is pretty much it for the basics of working with geometry in OpenMDAO. Obviously for any real work, you’d want to use a more complex geometry model. Our next tutorial will cover working with a more substantial geometry model, but to do that we’ll have to install a plugin that has a more powerful geometry engine.

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