Not applying Velocity Vector Field to model, features greyed out...

Submitted by timher on April 30, 2015 - 11:52

Problems

Hi,I'm trying to evaluate the Ceadium software for purchase but am having trouble applying a velocity vector field from the Results panel to my model. I've tried applying to all faces of the flow volume or just a single face.

What happens is that a panel comes up with choices for: Color Map, Arrows, Set Particles Target, and XY Plot but these choices are all "greyed out"... Is there something not turned on?

I downloaded and installed the latest version, 5.2.0 64 bit for Windows 7 and activated the Pro features for 30 days trial.

Thanks for your help

Try basic tutorials first

Submitted by symscape on April 30, 2015 - 12:15.

If you haven't already I suggest you try a couple of basic tutorials:

Geometry creation "Pipe into a Box"
RANS simulation "Incompressible Flow Through a Pipe into a Box"

You will need a closed volume representing the fluid around your model and you must assign a Substance to it before you can apply Results.

solved - had to select the whole volume instead

Submitted by timher on April 30, 2015 - 14:06.

Thank you. I was following the "Pipe into a Box" tutorial just fine and applying to my own custom model as I went along.

When it got to the step for assigning the velocity vector field, the tutorial said to "select the face"... so naturally I thought I had to select a face or just select all the faces. That didn't work. The Color Map, Arrows, etc. picks were greyed out as already described and no mesh was created.

I confirmed that I had properly assigned Air substance to the control volume, set the initial velocity, defined the walls and inlets and outlets. Everything up to that point appeared to be done exactly how the tutorial described.

So now, I tried selecting the whole volume when dragging the velocity vector field onto the model from the Results window. That worked! All the features became active and the program proceeded to create a mesh. It's still solving right now. Been about 30 min so far :)

Drag and drop results onto your model

Submitted by symscape on April 30, 2015 - 14:22.

There should not be any limitation on selecting a face instead of a volume. Having selected the face did the view window also have focus?

The easier approach is to drag and drop the Result onto the face in one operation, rather than pre-select the face.

I would encourage you to follow the tutorial with the original geometry then you can get a sense of how operations should proceed. Using your own geometry means you could face spurious problems caused by your geometry and un-related to the tutorial.

dragging and dropping wasn't the problem

Submitted by timher on April 30, 2015 - 14:45.

I'm not sure what you mean by Focus? A separate pop-up window?

I started by dragging the Result (velocity vector field) onto the model, not pre-selecting a face. After dragging and dropping onto an arbitrary face in the foreground, it pops up a small window that lists several possible faces, edges, all faces, whole volume, etc. This happens because the model is larger than a simple pipe into a box. So I had to select something in the pop-up.

When I tried selecting a face (or all faces) it doesn't work (features greyed out). When I tried selecting the whole volume, it worked (features active).

Since it's still running right now, I can't play with the original tutorial but I understand the step.

The geometry is only slightly more complicated than a pipe in a box. It's a donut shaped gas volume with 3 inlets on the bottom and 12 outlets on the top. All faces were defined as walls except the inlet and outlet faces.

After it's done running, I will send you screensnaps jpegs of the problem as well as results [Edit: removed email]

Thanks

Share your Caedium project file

Submitted by symscape on April 30, 2015 - 15:29.

It would be useful if you could share your Caedium project file (.sym) so I could try to diagnose the problem. I suggest you use a file sharing service, such as Dropbox.

project issue update

Submitted by timher on May 4, 2015 - 14:12.

I am unable to use Dropbox, due to my company's security policy. However, I uploaded the sym file to our ftp site. It will remain here for 5 days before automatic deletion. I also added a screensnap jpeg of the error message I get when I try to run the simulation. Apparently, there is some sort of geometry issue that I don't understand. I'm going to build a simpler flow volume inside the Caedium program and try that.

[Edit: removed login credentials]

The geometry for insert3.sym was imported as an IGES file which was created in PTC's Creo solids modeler (formerly known as Pro/E). This is the standard CAD package we use here and I can model things much faster in that.

There are no gaps or overlaps and no holes in the geometry, so I can't figure out why the RANS solver is hacking on it.

Thanks for your help

Model Diagnosis

Submitted by symscape on May 5, 2015 - 08:22.

Though there is nothing wrong with your geometry I suggest you use STEP (.stp) for geometry exchange. In my experience STEP is more accurate and more reliable than IGES. There is no requirement that you create your geometry in Caedium, that is why it supports geometry import. I can definitely understand that you will be more productive creating geometry in ProE.

A couple of surface meshes failed - there will be warnings in the File->Log. It is a good idea for non-trivial geometry (massive length scale variation as in your model) to first mesh the faces then the volume. If a face mesh fails then the volume mesh will also fail, which guarantees the solver will fail. For more details see the FAQ "How do I fix mesh and solver failures?"

I assigned the Accuracy tool to a couple of under-resolved edges (edge_154 and edge_3) which fixed the face mesh failures.

Also I switched the turbulence model back to k-omega SST, which is a relatively reliable model.

I did not see any problems assigning results using drag and drop. I did notice a lone face that was not part of your volume (face_70) which may have caused your selection issues. Also it appeared that you had successfully assigned Vector Fields->U as a color map to all your volume faces anyway.

If you'd like more help with your simulations then I suggest you purchase a Caedium Professional subscription.

thank you

Submitted by timher on May 5, 2015 - 09:59.

thank you very much for your help!

face_70 was added in an attempt to create a particles target, so I could see the velocity distribution inside the flow volume leading to each outlet. In the pipe in a box tutorial, it appears that an intermediate surface was added for this... Why not just pick the inlet and outlet surfaces?

Streamlines

Submitted by symscape on May 5, 2015 - 10:04.

You can use any surface, inlet or outlet. However, sometimes interesting streamlines are elsewhere and therefore need a different seed. Also, often you will want to control the number of streamlines independent of the simulation mesh. Experiment to see what happens.

weird velocity results

Submitted by timher on May 5, 2015 - 15:55.

So, is the seed surface typically defined as some arbitrary floating surface you add inside the flow volume? Does it have to be stitched to the flow volume?

I tried picking the bottom surface of my flow volume as a seed and some of the resulting streamlines go through the model into space... which I don't understand...

Also, when I ran the simulation, the Residuals Window showed convergence but 2 of the flow outlets of the flow volume look very strange with the velocity arrows going in instead of out. All other 10 outlets look pretty much the same in terms of flow arrows. Is there some way to query the result arrow at a certain location to see what it's actual value is? Maybe just slide the color scale from both sides? I'm just interested in how the velocity differs to each outlet.

I've uploaded jpegs at the same ftp site:
insert4_mesh.jpg = showing mesh on all faces of flow volume
insert4_vel_arrows.jpg = showing the initial Velocity arrows before running the sim
insert4_arrows2.jpg = showing the Velocity arrows after running, with the two strange outlets...
insert4_streamlines.jpg = showing the streamlines of the flow volume using the bottom face as a seed

thanks

Not converged, unrealistic velocity values

Submitted by symscape on May 6, 2015 - 06:42.

Having looked at the project file the simulation is not converged. Ideally you want to see all the residuals close to or below 1x10^-3, especially p/rho (pressure).

Also note that you are seeing unrealistic velocity values of 282 m/s (Mach = 0.8) another sign something is wrong, given your inlet velocity is only 38 m/s.

I set the Substance:Air->Properties->Phase:Single->Reference->omega:Turbulent Length Scale->Length Scale = 0.0025 m - more representative of your length scales and re-ran the simulation and it converged better (not ideal) and gave realistic velocity values.

I see no indication that you examined the surface (use Scalar Fields->E Ratio on surfaces) or volume (use Scalar Fields->Vol Ratio on the volume) mesh. This is a risky strategy given you then have no confidence that the mesh is reasonable.

With a paid subscription you not only gain access to the software but, more importantly, we provide the support to get you productive with our CFD offering.

velocities now make sense

Submitted by timher on May 6, 2015 - 17:09.

thanks for your support.

I have more questions, so I'll purchase a 1 month subscription, so I can complete my evaluation using this design problem. Basically, we're trying to calculate how much we should increase the inlet flow rate to ensure equal flow distribution to the outlets. The actual part has 120 outlet holes that are smaller in diameter. To keep things simple, I reduced to 12 holes of equivalent total flow area.

Can you explain why the streamlines are connected like a triangle across the inlets, outside the flow volume? I made a seed surface that is slightly raised off the bottom plane of the flow volume.

I don't know what criteria to use to determine if the E-ratio for a surface is reasonable.

Reduce Particles->Increment

Submitted by symscape on May 7, 2015 - 09:39.

There are no absolute values for E-Ratio and Vol-Ratio that indicate the solver will fail and therefore the mesh is bad. They are explained in the FAQ "How do I fix mesh and solver failures?" Also the tutorial "Flow Over a Double-Sided Membrane" shows how to visualize these metrics so you can see individual mesh elements.

Whenever the streamlines appear jagged it is an indication that the Particles->Increment is too large, so reduce it as described in "Particles or Streamlines"

I though we covered both of these issues earlier in the thread.

Can't view the mesh

Submitted by timher on May 7, 2015 - 10:04.

I'm trying to view the face mesh per the tutorial but can't. Also can't view the volume mesh. Do I have to reassign the substance even if the model already has it?

From the tutorial

Submitted by symscape on May 7, 2015 - 10:13.

No, keep the existing Substance.

From the section "Face Mesh" in the tutorial:

"To see individual surface mesh elements during the meshing process, right-click on the View Window background, double-click sim->Faces, and select Properties from the menu. In the Properties Panel, set Style to Flat."

From the section "Volume Mesh" in the tutorial:

"To see individual volume mesh elements after the volume meshing process is complete, right-click on any edge in the View Window, double-click flow-volume, and select Properties from the menu. In the Properties Panel, turn off the Transparent property and set Style to Flat."

This is also explained in the tip "View a Mesh."

yes, I followed the tip instructions

Submitted by timher on May 7, 2015 - 10:35.

But doing those steps does not show the mesh...

any other ideas?

Are arrows on?

Submitted by symscape on May 7, 2015 - 10:38.

Do you have arrows showing? If so you will need to delete them. Right click on the arrows icon in the View Legend and select Delete from the popup menu.

deleting view arrows worked

Submitted by timher on May 7, 2015 - 10:42.

thanks, deleting the arrows worked. I'll inspect the mesh now and look at E-ratio and Vol-ratio.

Create a new View

Submitted by symscape on May 7, 2015 - 10:45.

If you didn't want to change your original view with the arrows you can create a new view of the same simulation using New->View. This new view can then be configured to just examine the mesh.

Walls are a bad choice for streamlines

Submitted by symscape on May 5, 2015 - 16:33.

No, seeds do not need to be part of the flow volume - as in the tutorial you referenced the seed is a stand alone face.

Walls are a bad choice for streamline seeds - the velocity at a wall is close to zero, so the streamlines will not be interesting. Inlets, outlets, or standalone faces are usually the best choices for streamline seeds. You need to be careful you don't generate too many streamlines - they are compute and memory intensive. Often you'll need to reduce the Particles->Increment for the streamline to better resolve its path. For more on streamlines see the tip "Particles or Streamlines."

What makes you think the simulation is converged?

The simulation I ran here shows reasonable outflow on all the outlets. You could create a weighted area average for the velocity on each outlet and then monitor the value on each one.

I don't have the ftp login details anymore, please share it via email.

Got it

Submitted by symscape on May 4, 2015 - 14:21.

Thanks I'll take a look and get back to you.

Symscape