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-   -   Lattice Structure Wind Load STAR-CCM+ (https://www.cfd-online.com/Forums/star-ccm/227064-lattice-structure-wind-load-star-ccm.html)

Fluidy May 15, 2020 22:19

Lattice Structure Wind Load STAR-CCM+
 
For my final year bachelor project, I need to make a CFD-model to calculate the wind load on a lattice structure/crane arm. As comparison material, I have the real wind tunnel measurements with a net force of around 4.05 N. I made the lattice structure in SW, saved it as Parasolid, imported it through 3D-CAD Models, and then made a new geometry part from it. Also, the model is made with part-based meshing. For the calculation of the number of prism layers and the prism layer thickness. The results after 1000 iterations are around 4.14 N which is great, however I am unsure if this is accurate or just pure luck because the mesh does not look great. I currently have a few problems/questions that I would like to have your insights on, thank you in advance!

Parts:
Lattice Structure (only half with a symmetry plane)
Wind tunnel
Volume of Refinement Wind Tunnel
Volume of Refinement Wake
Volume of Refinement Offset of Lattice Structure

Models:
All y+ Wall Treatment
Constant Density
Gas (Air)
Gradients
K-Omega Turbulence (SST)
RANS
Segregated Flow
Solution Interpolation
Steady
Three Dimensional
Turbulent
Wall Distance

Settings:
https://imgur.com/bWuKP2q

Volume Mesh Inside:
https://imgur.com/7M4ug1u

Volume Mesh Outside:
https://imgur.com/2GQomkd


Questions:
1. There are weird lines on the tubes of my mesh because of the prism layers. How can I solve this?
https://imgur.com/Uv5alm0


2. I made an Excel table/calculation for the prism layer thickness and amount of prism layers and it works because if I measure the last prism layer it is exactly 1.3X smaller than the base size of the smallest volume of refinement (Offset). However, there is a smaller transition mesh between the last boundary layer and the volume of refinement mesh, how do I get rid of this?
https://imgur.com/nSO67do


3. After reading online that for a trimmed mesh you need to have custom sizes that are n * 0.5 * base size, I changed the following controls, but it made the boundary layers have a weird cone-like shape. I expected the mesh to improve after this change, so I am wondering what I did do wrong?
Old: https://imgur.com/LroApty
New: https://imgur.com/W524HqY
Base size: 0.1
Minimum Surface Size: 0.0002 -> 0.0001953125
VoR - Offset: 0.001 -> 0.0015625
VoR - Wake: 0.005 -> 0.00625
VoR - Windtunnel: 0.01 -> 0.0125
Number of Prism Layers: 17 -> 19
Prism Layer Total Thickness: 4.41E-3 -> 7.49E-3


4.The y+ calculation is based on a reference length of 4mm, which is the diameter of the diagonal V-tubes on the side of the lattice structure. I used 4 mm because that is the diameter of the diagonal V-tubes in the lattice structure that are the most common and therefore probably the most critical. Is this method acceptable or do I need to calculate the reference length by calculating Total Volume/Effective Area?
https://imgur.com/RockrMO

mazhar16823 May 17, 2020 14:33

Quote:

Originally Posted by Fluidy (Post 770727)
For my final year bachelor project, I need to make a CFD-model to calculate the wind load on a lattice structure/crane arm. As comparison material, I have the real wind tunnel measurements with a net force of around 4.05 N. I made the lattice structure in SW, saved it as Parasolid, imported it through 3D-CAD Models, and then made a new geometry part from it. Also, the model is made with part-based meshing. For the calculation of the number of prism layers and the prism layer thickness. The results after 1000 iterations are around 4.14 N which is great, however I am unsure if this is accurate or just pure luck because the mesh does not look great. I currently have a few problems/questions that I would like to have your insights on, thank you in advance!

Parts:
Lattice Structure (only half with a symmetry plane)
Wind tunnel
Volume of Refinement Wind Tunnel
Volume of Refinement Wake
Volume of Refinement Offset of Lattice Structure

Models:
All y+ Wall Treatment
Constant Density
Gas (Air)
Gradients
K-Omega Turbulence (SST)
RANS
Segregated Flow
Solution Interpolation
Steady
Three Dimensional
Turbulent
Wall Distance

Settings:
https://imgur.com/bWuKP2q

Volume Mesh Inside:
https://imgur.com/7M4ug1u

Volume Mesh Outside:
https://imgur.com/2GQomkd


Questions:
1. There are weird lines on the tubes of my mesh because of the prism layers. How can I solve this?
https://imgur.com/Uv5alm0


2. I made an Excel table/calculation for the prism layer thickness and amount of prism layers and it works because if I measure the last prism layer it is exactly 1.3X smaller than the base size of the smallest volume of refinement (Offset). However, there is a smaller transition mesh between the last boundary layer and the volume of refinement mesh, how do I get rid of this?
https://imgur.com/nSO67do


3. After reading online that for a trimmed mesh you need to have custom sizes that are n * 0.5 * base size, I changed the following controls, but it made the boundary layers have a weird cone-like shape. I expected the mesh to improve after this change, so I am wondering what I did do wrong?
Old: https://imgur.com/LroApty
New: https://imgur.com/W524HqY
Base size: 0.1
Minimum Surface Size: 0.0002 -> 0.0001953125
VoR - Offset: 0.001 -> 0.0015625
VoR - Wake: 0.005 -> 0.00625
VoR - Windtunnel: 0.01 -> 0.0125
Number of Prism Layers: 17 -> 19
Prism Layer Total Thickness: 4.41E-3 -> 7.49E-3


4.The y+ calculation is based on a reference length of 4mm, which is the diameter of the diagonal V-tubes on the side of the lattice structure. I used 4 mm because that is the diameter of the diagonal V-tubes in the lattice structure that are the most common and therefore probably the most critical. Is this method acceptable or do I need to calculate the reference length by calculating Total Volume/Effective Area?
https://imgur.com/RockrMO


What is the max. skewness angle, face validity and min. face quality for your mesh? Also, have you checked your imported geometry for errors before creating mesh?


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