Units and Dimensions of Salome Geometry

[annier]

Hi,

• 1. If we are constructing the geometry within Salome, it can be quite practical when we assume that Salome just uses the length values and not the units . the consideration of units will be helpful to us for the context when we construct/draw geometry outside Salome i.e. in another CAD software and import it by Salome.

• 2. I am not sure about what units do Salome versions V5.1.1 and V5.1.2 use (I herein assume that they also use SI units).

A. For Salome Versions V2.2.8, V3.2.1,V3.2.6,V4.1.4,V4.1.5
This is the thing which i find worth taking care of considering the topic of dimensions/units while exporting Salome Geometry and Mesh into Elmer .

• -> Earlier versions of Salome (those earlier than V5) use the "mm" unit but do not retain unit in exported files (.unv files). i guess it only exports numbers.

• -> I guess Elmer uses SI units.

Let me give the illustrations.
Method 1

• When we need to simulate a cube of 1 m *1 m* 1m.

• We can draw a cube 1*1*1 in Salome (it is in mm there) and export it into Elmer.

• Elmer reads it as (1 m * 1 m* 1m).

• We are using the property of Salome that it does not retain the unit in the exported geometry and mesh.

Method 2

• When we need to simulate a cube of 1 mm*1 mm* 1 mm

• We can draw a cube 1*1*1 in Salome (it is in mm there) and export it into Elmer.

• Elmer will read it as (1 m * 1 m* 1m) if coordinate scaling is not done.

• In the simulation section of Solver Input File (SIF) of Elmer, we add

  Code: Select all

  Coordinate Scaling = 0.001

  and the cube is read as 0.001 m* 0.001 m *0.001 m by Elmer Solver.

B. For Salome Version V5.1.3 and Later Versions
This is the thing which i find worth taking care of considering the topic of dimensions/units while exporting Salome Geometry and Mesh into Elmer .

• -> Later versions of Salome (those later than V5) use the "m" SI unit but do not retain unit in exported files (.unv files). i guess it only exports numbers.

• -> I guess Elmer uses SI units.

Let me give the illustrations.
Method 1

• When we need to simulate a cube of 1 m *1 m* 1m.

• We can draw a cube 1*1*1 in Salome (it is in m there) and export it into Elmer.

• Elmer reads it as (1 m * 1 m* 1m).

• We are using the property of Salome that it does not retain the unit in the exported geometry and mesh.

Method 2-a

• When we need to simulate a cube of 1 mm*1 mm* 1 mm

• We can draw a cube 1*1*1 in Salome (it is in m there) and export it into Elmer.

• Elmer will read it as (1 m * 1 m* 1m) if coordinate scaling is not done.

• In the simulation section of Solver Input File (SIF) of Elmer, we add

  Code: Select all

  Coordinate Scaling = 0.001

  and the cube is read as 0.001 m* 0.001 m *0.001 m by Elmer Solver.

Method 2-b

• When we need to simulate a cube of 1 mm*1 mm* 1 mm

• We can draw a cube 0.001*0.001*0.001 in Salome (it is in m there) and export it into Elmer.

• Elmer will read it as (0.001 m *0.001 m* 0.001m).

[Franz Pichler]

Hello,
I don't think that salome actually has any length unit associated with the dimensions.

As you explained you make a cube of 1*1*1 in saalome and the rest is interpretation. If you want to have 0.001 in elmer directly without usenig the elmer internal scaling. Just make the length 0.001 in Salome.

best regards
Franz

[annier]

Hi Franz,
Thank you for your reply and valuable remarks.i have already updated the above post (Method 2-b).
In the condition that we draw the geometry in Salome and export it into the Elmer (or another software), it is quite practical to say that Salome doesn't use "units " since Salome doesn't retain units when exporting .unv files.
Sometimes, there may be the situation where Salome is used for importing the geometry created in another CAD software and creating mesh for the geometry. In the context of importing geometry files from other CAD softwares (where the length dimensions are in unit, let's say "mm"), due consideration should be made to how Salome reads those files. So, in this context I have tried to express that earlier versions of Salome (those earlier than Salome V5) read dimensions in "mm" and the later versions of Salome(later than V5) read dimensions in "m" (Please correct me here if i am wrong).
So rather than just saying that Salome doesn't use units but only uses "length values" it might be more contextual if we say like this

Salome uses "mm" scale in Earlier Versions (earlier than V5) whereas uses "m" scale in later versions. However, it doesn't retain units when exporting .unv files. If we are drawing geometry in Salome, we can act like we are just dealing with length values. When we are drawing geometry in another CAD software, meshing it with Salome and exporting it to another software, the interface between the CAD software and Salome requires us to be careful in the scales of units.

Some useful references are as following:
http://www.salome-platform.org/forum/forum_10/736733668
http://www.caelinux.com/CMS/index.php?o ... mid=300025
http://www.cfd-online.com/Forums/openfo ... alome.html
yours
annier