We have a 3D Frame (imported geometry, not parameterized). A frame that consist
of round and square tubes. And we want to create a 1D mesh. So we need the
"skeleton" of the frame.
How do we create the easiest way the centerlines needed for the 1D mesh?
Although not flawless in all cases, there are some ways to swiftly extract/create the centerlines needed for the 1D mesh.
Best way is, when creating a fem, also create an idealized part.
In the idealized part. Select Wave (or promote) and select the imported model.
Make the ipart Display part, and go to the modelling application.
For Round tubes : Select "Extract virtual curve " (use the "command finder" to find this command)
Select the tubes. In case you have imported i.e. a step/iges file and the tubes consist of 2 half cylinders, just select one half and also the Centerline is created.
Once the centerlines are created, you can hide the Tubes, and only the "skeleton" lines are visible.
After this you can extend/trim the lines so they all end up at the same intersection point.
Do this by using the "Trim Curve" function, this function will both trim and extend curves. If you have a "simple" frame with nice angels, this option will work fine. If this is not the case you could work by creating "points" and connect them with lines. This is also explained using square beams.
For the Square tubes/beams :
This method will also work for other profiles. As long as you are able to define the Center-point of the profile section, this option will work.
For simple square tubes, do the following: Select "Point" (not from the sketch features, but from the Curve menu) --> Type: "Between two points" --> Select the Diagonal corners of the end profile of the beam. Now you have created a point in the center.
Do this for both sides of the beam. Hide the beam and connect the points with the "Line" feature from the Curve menu and select the 2 points.
After all lines of the frame are created, you can apply the 1D mesh on this model.
To make all a bit more clear, see the movie in which some examples are shown: