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Regarding Connector Nodes and Cables

#1 · 19. February 2023, 05:35

Hello,

I had a couple of structural questions for VAWT simulation that I have been stumped on for a while. I have listed them below:

1.) While the blades have nodes that are specifically designated to attach them to the tower, the guy cables have no such thing. In the code, how is the effect of the guy cables translated to the main VAWT structure?

2.) Are the connector nodes essentially just structural nodes that serve the additional purpose of acting as connectors, or do they strictly translate information obtained via interpolation from the structural nodes above and below said connector node.

3.) When viewing the Sandia VAWT example, there are 34 different blade sections in the “VAWT Rotorblade Design” module. However, there are 38 rows in the blade structure input file. I assume that the 34 blade sections, paired with the top and bottom connector nodes make up 36 of the 38 rows of data, but I cannot figure out what part of the blades the remaining two rows represent. I wondering if someone would be willing to help me understand this better?

4.) In the blade structure file, the number of evenly spaced nodes is set to 21. In the “Turbine Definition” module, as long as the connector nodes are not counted, each blade does indeed have 21 evenly spaced nodes. However, I am a bit confused as to why the geometric and material properties at 38 locations on the blade are needed when only 21 nodes are being used. More specifically, why aren’t users required to input the geometric and material data at each node?

(I have included a screenshot of the blade from the rotorblade design module and an image of the turbine from the turbine definition module in case it helps with answering the questions). Thank you for taking the time to read my forum post. I greatly appreciate any input.

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#2 · 20. February 2023, 17:01

Quote from David on 20. February 2023, 17:01
Hi Ryan,
let my try to answer your questions:
1.) While the blades have nodes that are specifically designated to attach them to the tower, the guy cables have no such thing. In the code, how is the effect of the guy cables translated to the main VAWT structure?
Have alook at this part of the documentation: https://docs.qblade.org/src/user/turbine/structure.html#cable-elements-ground-fixing-and-station-keeping-parameters. Mooring lines can either be connected to the ground, the floater (in which case it is rigidly constrained with the transition piece) or to any joint of the model. By connecting with a joint you can connect the mooring lines to any part of the structure.
2.) Are the connector nodes essentially just structural nodes that serve the additional purpose of acting as connectors, or do they strictly translate information obtained via interpolation from the structural nodes above and below said connector node.
When the structural model is setup connector nodes are automatically placed at certain parts of the structure to connect them. For instance when a strut connects to a blade, a node is placed at the exact location where the strut intersects with the blade if no node exists at this location already. The structural loads at these locations are automatically presented in the structural time graphs.
3.) When viewing the Sandia VAWT example, there are 34 different blade sections in the “VAWT Rotorblade Design” module. However, there are 38 rows in the blade structure input file. I assume that the 34 blade sections, paired with the top and bottom connector nodes make up 36 of the 38 rows of data, but I cannot figure out what part of the blades the remaining two rows represent. I wondering if someone would be willing to help me understand this better?
The aerodynamic discretization and the structural discretization are completely independent. Also, it is not necessary to assign a structural table with a number of rows that is equal to the number of structural nodes. During the model is setup in QBlade, the data from the structural tables is automatically interpolated linearly onto the structural elements. This interpolation is carried out based on the normalized length at which the element is located and the normalized length that is defined in the first row of the structural data table. During the simulations the aerodynamic loads are also linearly interpolated from the aerodynamic panels onto the structural elements.
4.) In the blade structure file, the number of evenly spaced nodes is set to 21. In the “Turbine Definition” module, as long as the connector nodes are not counted, each blade does indeed have 21 evenly spaced nodes. However, I am a bit confused as to why the geometric and material properties at 38 locations on the blade are needed when only 21 nodes are being used. More specifically, why aren’t users required to input the geometric and material data at each node?
I think the answer above also answers this question.
I hope these answers help to clarify things a bit!
Cheers,
David

Hi Ryan,

let my try to answer your questions:

1.) While the blades have nodes that are specifically designated to attach them to the tower, the guy cables have no such thing. In the code, how is the effect of the guy cables translated to the main VAWT structure?

Have alook at this part of the documentation: https://docs.qblade.org/src/user/turbine/structure.html#cable-elements-ground-fixing-and-station-keeping-parameters. Mooring lines can either be connected to the ground, the floater (in which case it is rigidly constrained with the transition piece) or to any joint of the model. By connecting with a joint you can connect the mooring lines to any part of the structure.

2.) Are the connector nodes essentially just structural nodes that serve the additional purpose of acting as connectors, or do they strictly translate information obtained via interpolation from the structural nodes above and below said connector node.

When the structural model is setup connector nodes are automatically placed at certain parts of the structure to connect them. For instance when a strut connects to a blade, a node is placed at the exact location where the strut intersects with the blade if no node exists at this location already. The structural loads at these locations are automatically presented in the structural time graphs.

3.) When viewing the Sandia VAWT example, there are 34 different blade sections in the “VAWT Rotorblade Design” module. However, there are 38 rows in the blade structure input file. I assume that the 34 blade sections, paired with the top and bottom connector nodes make up 36 of the 38 rows of data, but I cannot figure out what part of the blades the remaining two rows represent. I wondering if someone would be willing to help me understand this better?

The aerodynamic discretization and the structural discretization are completely independent. Also, it is not necessary to assign a structural table with a number of rows that is equal to the number of structural nodes. During the model is setup in QBlade, the data from the structural tables is automatically interpolated linearly onto the structural elements. This interpolation is carried out based on the normalized length at which the element is located and the normalized length that is defined in the first row of the structural data table. During the simulations the aerodynamic loads are also linearly interpolated from the aerodynamic panels onto the structural elements.

4.) In the blade structure file, the number of evenly spaced nodes is set to 21. In the “Turbine Definition” module, as long as the connector nodes are not counted, each blade does indeed have 21 evenly spaced nodes. However, I am a bit confused as to why the geometric and material properties at 38 locations on the blade are needed when only 21 nodes are being used. More specifically, why aren’t users required to input the geometric and material data at each node?

I think the answer above also answers this question.

I hope these answers help to clarify things a bit!

Cheers,

David

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