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Importing .STEP files

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Old   August 31, 2017, 00:13
Default Importing .STEP files
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Nilanka Ekanayake
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Hi,

I got a step file with a sphere inside a channel. But when I import as a database the following step file, the internal surfaces (sphere) won't import properly in Pointwise. Are there any properties that I should change when importing such file?
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Old   August 31, 2017, 21:22
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David Garlisch
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Quote:
Originally Posted by nilanka View Post
Hi,

I got a step file with a sphere inside a channel. But when I import as a database the following step file, the internal surfaces (sphere) won't import properly in Pointwise. Are there any properties that I should change when importing such file?
Can you attach the file?
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Old   August 31, 2017, 21:26
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Nilanka Ekanayake
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Sorry, the file is attached.
Attached Files
File Type: zip test3.step.zip (3.9 KB, 8 views)
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Old   September 1, 2017, 12:41
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David Garlisch
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I am fairly sure this STEP file is bad.

If you look at the appropriate section in the STEP file, you will see that the sphere (entity #352) is used as part of a face (entity #347).

Code:
#345 = ORIENTED_CLOSED_SHELL('',*,#346,.F.);
#346 = CLOSED_SHELL('',(#347));
#347 = ADVANCED_FACE('',(#348),#352,.T.);
#348 = FACE_BOUND('',#349,.T.);
#349 = VERTEX_LOOP('',#350);
#350 = VERTEX_POINT('',#351);
#351 = CARTESIAN_POINT('',(2.5,1.,0.9));
#352 = SPHERICAL_SURFACE('',#353,0.1);
#353 = AXIS2_PLACEMENT_3D('',#354,#355,#356);
#354 = CARTESIAN_POINT('',(2.5,1.,1.));
#355 = DIRECTION('',(0.,0.,1.));
#356 = DIRECTION('',(1.,0.,0.));
However, the face's trim loop (entity #349) is a single point (entity #350)! This results in a degenerate trimmed face with zero area.

This nonsensical entity is discarded during import.

The sphere is located at (2.5, 1, 1) with a radius of 0.1. I have attached several files with this sphere added back in.

The pw file was created with V18.0R3. If your Pointwise version is older and it can't read the pw file, import the NMB database file. If that won't work, import the IGES file.
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File Type: zip test3-fixed.zip (22.6 KB, 3 views)
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Old   September 1, 2017, 23:25
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Nilanka Ekanayake
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Many thanks.

I've been able to open the .pw ! Did you create the geo directly in pw using shapes? I had some trouble when placing the sphere in the correct location using the translation tool. I'll try point placement option.

The geometry I actually created is a channel flow, with a spherical portion removed from it (using a boolean operation). May be that would have been the issue.

Again thank.
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Old   September 5, 2017, 11:53
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Quote:
Did you create the geo directly in pw using shapes?
Yes, I used Create, Draw Shapes, Sphere... to create the sphere surface.
In the task panel:
  • In the Entity Type section, select Database
  • In the Point Placement section, set the sphere center point to 2.5 1 1
  • In the Shape Parameters section, set Radius to 0.1
  • Alter the various angle settings if you do not want a full sphere

By default, the sphere is aligned to the current view, if the alignment is important, you can change it using the various buttons in the Mode section.

Quote:
The geometry I actually created is a channel flow, with a spherical portion removed from it (using a boolean operation). May be that would have been the issue?
I don't think so. STEP and Pointwise are capable of handling closed solid bodies with internal holes (swiss cheese).
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Old   September 7, 2017, 04:34
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Nilanka Ekanayake
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Thank you.

Again, If I need to create a sphere with a 0.0001 radius (in m scale directly) how to do it since the minimum allowable length is 0.002. Anything to do with the tolerance?

Another problem related to boundary layer thickness adjustment in T-Rex. I would like to have different meshes with several boundary layers. But when I apply T-rex for the block, I am not sure which parameters that I should use to vary those. The Max. Layers/Full layers didn't help me much to specify the required boundary layer thickness.

Compressed .pw that I am working is exceeding the size, hence uploaded the STEP file that I am using.
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File Type: png boundary_layer.png (30.4 KB, 8 views)
Attached Files
File Type: zip 0_channel_halfsphere_new.step.zip (4.6 KB, 3 views)
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Old   September 7, 2017, 12:01
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As with all computer floating point calculations, there is a finite dynamic range that can be represented internally before numerical round off errors start to erode the integrity of calculations. For Pointwise, this range is around seven orders of magnitude. That is, to get meaningful calculations:
SmallestValue >= LargestValue / 10e7
Pointwise has a setting called Model Size that defaults to 1000 units. So the smallest value would be around 1000/10e7 == 0.0001. The Model Size drives the precision supported for all grid and database options.

However, it doesn't stop there. In a typical mesh, the grid entities are usually several orders of magnitude smaller than the database surfaces they are attached to! So, to help prevent unintended numerical problems, various values (such as sphere radius) are limited (in the GUI only) to ranges compatible with the Model Size. To be specific:
  • The minimum dimension/radius in draw shapes is 2x the fit tolerance
  • The fit tolerance is 10x the same point tolerance

For most applications the default works fine. However, if your grid is going to have "very small" details such as a sphere with a 0.0001m radius, or very small initial grid spacing, the Model Size will need to be adjusted to a smaller value.

The Model Size will need to be set to 10.0 or less to get the numerical precision necessary for a radius of 0.0001.

It will also help overall precision, if you keep all database and grid entities centered around the global origin as much as possible. Building a mesh centered at (10e3, 10e3, 10e3) will waste numerical precision.

The Model Size value should be set BEFORE any grid or database entities are created or imported using File, Properties....

Also, there are Model Size options available when CAD file is imported into an empty file. Please see the user manual or GUI help for details.

I hope this helps.

Last edited by dgarlisch; September 7, 2017 at 16:12.
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Old   September 7, 2017, 12:03
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As for your TRex questions, I will leave that to the grid experts on this forum. A club of which I am not a member.
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