Geometries¶
You can include geometries in text-based simulations, either by importing existing geometries or creating them in your prefile.
Creating Geometries¶
One can create primitives and perform operations on them, just as in the
visual setup. By importing the geometry
macro as detailed above,
one gets a number of predefined primitives, as well as functions that
can be used to perform operations on these primitives, or to create
custom shapes.
Along with the creation of primitives and/or functionally-defined shapes, the following operations will be detailed herein:
Moving and rotating shapes
Advanced filling and voiding
Making your own primitives
Primitives¶
The geometry
macro includes a number of primitives, including some
that are available in visual setup as well as ones that are unique to
the macro. Primitives that are also found in visual setup are as
follows:
geoBoxP
geoCylinderXP
geoPipeXP
geoConeXP
geoSphereXP
geoTorusX
The primitives that are unique to the macro are below.
geoQuadrilateralSlabXP
geoHemiSphereXP
geoBiParabolicSlabXP
geoTriangleSlabXP
geoRndCylinderXP
geoRndRectangleSlabXP
geoEllipsoid
geoHemiEllipsoidXP
geoEllipticalCylinderXP
geoEllipticalConeXP
To use these primitive functions, one must assign a geometry name to
appear on the first in the parentheses, followed by the primitive
function and values you’ve entered for the parameters. Below is an
example showing the creation of a hollow cylinder with the
geoCylinderXP
function, using the described syntax.
fillGeoExpression(hollowCylinder, geoPipeXP(x,y,z,INNER_RADIUS,RADIUS,LXO))
The parameters used above are as follows, though one could also just input numerical values rather than parameters or constants:
x
y
z
- INNER_RADIUS
Inner radius of the cylinder.
- RADIUS
Outer radius of the cylinder.
- LXO
Length of cylinder in the axial direction (x).
The parameters required for each of the primitive functions in the macro are detailed fully in the section on the macro file in VSim Reference.
Moving and Rotating Shapes¶
The above shapes are defined around points of symmetry; cylinders and spheres are centered around the origin, and rectilinear shapes begin at the origin and extend out in the x-direction.
However, one can provide offsets in any direction–x, y, or z–by subtracting the desired offset from the respective variable parameter. For instance,
fillGeoExpression(hollowCylinder, geoPipeXP(x-0.03,y+0.04,z,INNER_RADIUS,RADIUS,.1))
would result in our cylinder being offset from the origin by 3 centimeters in the x-direction and 4 centimeters in the y-direction. Its length in the z-direction would be 10 centimeters.
One can also rotate the shape so that it is centered about a different axis. For example, if the cylinder needed to be centered about the z-axis, the .pre file input would be:
fillGeoExpression(hollowCylinder, geoPipe(z,x,y,INNER_RADIUS,RADIUS,.1))
Notice that the x, y, and z entries from before have changed so that they now are z, x, and y. The first entry is the axial direction.
You can mimic the Boolean operations that are available with visual setup by using the
voidGeoExpression
fillGeoExpression
functions with the primitives you have already defined in your
simulation. The first example below walks through joining two
primitives, one being a box named box1
and the other being our
hollowCylinder
.
fillGeoExpression(box1, hollowCylinder)
Advanced Filling and Voiding¶
There are two main methods of creating custom shapes, function-defined and primitive-based.
The function-based way of creating shapes involves first creating
functions that describe your desired shapes, which can be done through
implementation of Heaviside functions. You can then use these functions
as input for either the fillGeoExpression
or voidGeoExpression
functions. We can use this process as an alternate means of building
our hollow cylinder from before, beginning with the function definition:
<function cylinderFunc>
H(-INNER_RADIUS^2 + x^2 + y^2)*H(RADIUS^2-x^2-y^2)
</function>
where the INNER_RADIUS and RADIUS parameters are the same as those used in the hollowCylinder primitive above.
The geometry itself can then be defined by simply determining a name as the first parameter–here, we have chosen hollowCylinder again–and then invoking the function defined above.
fillGeoExpression(hollowCylinder, cylinderFunc(x,y,z))
The voidGeoExpression
function, on the other hand, designates a
certain volume of space to be removed from another. For example, this
can be applied to a box, which can then be “subtracted” from a larger
box. These operations are implemented in a macro, whose name is that of
the overall geometry.
<macro boxes>
voidGeoExpression(smallBox, geoBoxP(x,y,z,0.05,0.05,0.05))
fillGeoExpression(bigBox, geoBoxP(x,y,z,0.1,0.1,0.1))
</macro>
Making Your Own Primitives¶
If you want to make your own primitive that can then be used repeatedly in your simulation, you can define your geometry in the macro format and then call the macro from multiple places in your .pre file. For example, we can define our hollowCylinder as below:
<macro hollowCylinder>
H(-INNER_RADIUS^2 + x^2 + y^2)*H(RADIUS^2-x^2-y^2)
</macro>
Importing Geometries¶
One can import both .stl and Python-defined shapes. CAD geometries can be used in conjunction with CSG primitives built in VSim.
CAD (.stl) Shapes¶
You can import existing shapes whose files end with the .stl extension
by using the (slightly different) functions fillGeoCad
and
voidGeoCad
. There also exists the optional function
fillGeoFastCAD
.
These functions’ parameters are detailed in full in the geometry
macro file section, but a basic example of fillGeoCad
being used to
import an .stl file is given below:
fillGeoCad(hollowCylinder, hollowCylinder.stl, False, 1.0,[0 0 0])
where “hollowCylinder” is the name of the object in VSim and “hollowCylinder.stl” is the .stl file being imported. The last three entries, “False,” “1.0,” and “[0 0 0],” are default values, and as such the hollowCylinder object has imported with 1-1 scaling and no translations.
Importing a Python File¶
To import a Python-defined geometry, one can use the functions
fillGeoPython
and voidGeoPython
in conjunction with a Python
function that is defined in a .py file.
fillGeoPython(hollowCylinder, makeHollowCylinder)
The Python file must have the same name as the input file name and contain the function you wish you use. The function should be equal to 1 inside the geometry object and to 0 outside.