Tagged: mesh, meshnodes, nodeselection, structural


July 1, 2021 at 2:38 pmamit.pandeySubscriber
Hello,
I am trying to remodel a deformed lens by the following steps:
Extracting the deformed .STL file
Reading the file in MATLAB
Fitting a surface to the deformed lens surfaces.
Extracting the polynomial equation of the surface and using the equation to remodel the lens in the Optical simulation software and evaluating the change in performance.
For this, I am interested on the surface nodes because the optical simulation is only calculating the ray paths based on surface interactions. So it is enough to have two surfaces and the distance between these surfaces.
Is there a way to select nodes only on one or maybe nodes on selected surface(s)?
Any lead is appreciated.
With best regards,
Amit

July 1, 2021 at 10:49 pmpeteroznewmanSubscriberHello Amit Optical surface deformation is usually measured in nm so you do not want to export an STL file because you will lose a lot of precision in that operation.
It is much better to export the deformations directly to a text file.
You can make a Named Selection of all the nodes on the the front surface and another Names Selection of all the nodes on the back surface.
It is important to create a Coordinate System at the vertex of each surface with the Z axis normal to the surface.
You should write out the coordinates of the undeformed nodes of each surface in its coordinate frame to check that the nodes exactly match the formula for each surface.
Then you can write out the deformation of each node in those same coordinate frames.
You should use Zernike polynomials to fit the surface. The coefficients of those are directly usable in most Optical simulation software such as Zemax or CodeV.
If you don't want to write the matlab code to fit the deformations with Zernike polynomials, you can try out software written to do this called Sigfit by Sigmadyne.
https://www.sigmadyne.com/sigweb/downloads/MSCUC2011Genberg.pdf

July 2, 2021 at 8:00 amamit.pandeySubscriberHello Peter Thank you for the response.
The idea of developing this method was not to use a commercially available software like Sigfit or ZEMAX STAR. (Honestly, I am just pushing myself to take the longer and more complex route :) )
"You can make a Named Selection of all the nodes on the the front surface and another Names Selection of all the nodes on the back surface." when generating a named selection, how do I filter out the nodes on one surface? I see the following options in the selection worksheet but I do not see a combination of the various options to have a filter that gives me nodes only on the surface.
To select the nodes on the convex surface, what I am trying to do is, first select all nodes in the Add step. Then remove the nodes on the faces grouped into a named selection one by one. There are three faces which needs to be removed (two highlighted green faces and one flat face at the bottom). However the generate button does only what is expected of the ADD step and nothing else. Is it because there are shared nodes between the convex faces and the highlighted faces that ANSYS is not able to remove the nodes?

July 2, 2021 at 9:47 am

July 2, 2021 at 11:30 amamit.pandeySubscriberHi Peter
Could you please elaborate a little: You should write out the coordinates of the undeformed nodes of each surface in its coordinate frame to check that the nodes exactly match the formula for each surface?
What formula are we talking about here?
And after adding the respective new coordinate systems, how do I extract the position of nodes on the surfaces with respect to the new coordinate systems?

July 2, 2021 at 5:57 pmpeteroznewmanSubscriberHello Amit Nodal Named Selections are tricky, glad to see you figured it out.
Optical surfaces are typically defined using a Sag equation.
A spherical surface is defined by the Radius of Curvature R and the Diameter D. I would replace D/2 with r in the equation below because if you have the X,Y coordinates of a node in the coordinate frame as I described above, then the value of r is simply the square root of the sum of the squares, and the Z coordinate is the SAG.
CAD systems can create a perfect spherical surface, so it is likely that the nodes in the model lie exactly on the surface defined by this equation.
Many optics use an aspheric surface https://en.wikipedia.org/wiki/Sagitta_(optics)
The optical design engineer would provide the coefficients in that equation to the mechanical design engineer/analyst who can recreate the surface precisely.
The CAD geometry you have may not precisely match this sag equation if it is an aspheric surface. It is a good idea to check the deviation of the sag of each node location from the sag value calculated from the equation and provided coefficients. The error should be less than a small fraction of a nanometer.
I don't know how to export nodal coordinates in a local coordinate frame in ANSYS (I know how to do it in Nastran). I expect there is a way. That might be a good question for a new Discussion and perhaps an ANSYS staff member will reply. It would make sense if you only have two surfaces, to align them so the global coordinate frame is on the vertex of one of the surfaces with the Z coordinate pointing to the other vertex, then the local coordinates of the other surface is easily obtained by subtracting the lens thickness from the z coordinate of the second surface.
I tested a Directional Deformation result and you get to specify the local coordinate system in which to measure the deformation, which is good. However, when you export the data, the nodal location is given in Global coordinates, which seems silly. What is worse, the text file doesn't even name the coordinate system in which the deformation is measured, so you need to do careful bookkeeping.

July 5, 2021 at 6:04 amamit.pandeySubscriberDear Peter
Thank you for the detailed explanation.
I will create a new discussion for the extraction o nodal data in terms of custom coordinate systems.
Bets regards Amit

 You must be logged in to reply to this topic.
Simulation World 2022
Check out more than 70 different sessions now available on demand. Get inspired as you hear from visionary companies, leading researchers and educators from around the globe on a variety of topics from lifesaving improvements in healthcare, to bold new realities of space travel. Take a leap of certainty and check out a session today here.
Earth Rescue – An Ansys Online Series
The climate crisis is here. But so is the human ingenuity to fight it. Earth Rescue reveals what visionary companies are doing today to engineer radical new ideas in the fight against climate change. Click here to watch the first episode.
Ansys Blog
Subscribe to the Ansys Blog to get great new content about the power of simulation delivered right to your email on a weekly basis. With content from Ansys experts, partners and customers you will learn about product development advances, thought leadership and trends and tips to better use Ansys tools. Sign up here.
 How to calculate the residual stress on a coating by Vickers indentation?
 Saving & sharing of Working project files in .wbpz format
 An Unknown error occurred during solution. Check the Solver Output…..
 Solver Pivot Warning in Beam Element Model
 Understanding Force Convergence Solution Output
 Colors and Mesh Display
 whether have the difference between using contact and target bodies
 The solver engine was unable to converge on a solution for the nonlinear problem as constrained.
 What is the difference between bonded contact region and fixed joint
 Massive amount of memory (RAM) required for solve

2072

1734

969

754

423
© 2022 Copyright ANSYS, Inc. All rights reserved.