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QBlade ForumQBlade: Structural DynamicsStructural Input File for VAWT Mo …

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Structural Input File for VAWT Mode

#1 · 24. August 2022, 09:59

Quote from selvarajooSR on 24. August 2022, 09:59
Hi Dr. Marten,
Since simulating self-starting rotors requires a structural input file, based on the documentation I have edited the following files as attached. I managed to get the NREL 5MW example file to self-start, but I have two questions regarding the setup on a VAWT. Firstly, what is the keyword GLBGEOEPS in the fourth line of the turbine structural file and how does it affect the simulation? I am assuming it has something to do with the structural analysis?
Secondly, when I attempt to import the structural file, I receive the following error: Keyword: TRQTBFILE not found!
I’ve looked through the documentation but the closest keyword I can find is TRQ_X. However, I’m unsure of how it is relevant to to my simulation. Even copying the turbine structural file from the documentation results in the same error.
By the way, once I’m done with this work I would like to provide all these input files as an example for the community to run their own simulations, thus the level of detail in my posts. Thus, the following details are additional information
—————————————————————————————————————————————————————————
I have deleted the unnecessary portions of the structural model file, thus it is rather empty. I intend to model the Rainbird rotor [1] where not much data is available regarding the mechanical properties, except for the rotational inertia*. In the structural model file, the rotational inertia is set to zero as the applied value is implemented in the blade properties file. Additionally, the drive train parasitic torque is set to zero because of the use of an axial-flux generator which provides no resistance unless electrically loaded [2].
Regarding the blade properties file, MASSD, XCM, YCM, XCS, YCS have been adjusted to 0.128kg/m, 0.25 , zero, 0.25, and 0.25 respectively. The MASSD was calculated based on the formula: I = mR^2. XCM, YCM, XCS, YCS were set to the above values to be equal to the quarter chord location. Lastly, the blade properties file is kept in the same folder as the simulation project file (.qpr) and structural input file.
*Contrary values of 0.018 kg.m^22 [3] and 0.3kg.m^2 [4] are obtained by the works of Torabi et al., and Celik et al. respectively. Applying 0.3kg.m^2 blows up the computational time, thus 0.018 kg.m^2 is used despite being less realistic. However, the issue of the applied value being less realistic is overcome by normalizing the time via the T* method [3].
[1] The Aerodynamic Development of a Vertical Axis Wind Turbine (Rainbird, MSc Thesis, University of Durham, 2007)
[2] Darrieus turbines: the physics of self-starting (Hill et al., Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, 2008)
[3] Study on Start-up Characteristics of H-Darrieus Vertical Axis Wind Turbines Comprising NACA 4-Digit Series Blade Airfoils (Torabi et al., Energy, 2016)
[4] Aerodynamic investigation of the start-up process of H-type vertical axis wind turbines using CFD (Celik et al., Journal of Wind Engineering and Industrial Aerodynamics, 2020)

Hi Dr. Marten,

Since simulating self-starting rotors requires a structural input file, based on the documentation I have edited the following files as attached. I managed to get the NREL 5MW example file to self-start, but I have two questions regarding the setup on a VAWT. Firstly, what is the keyword GLBGEOEPS in the fourth line of the turbine structural file and how does it affect the simulation? I am assuming it has something to do with the structural analysis?

Secondly, when I attempt to import the structural file, I receive the following error: Keyword: TRQTBFILE not found!

I’ve looked through the documentation but the closest keyword I can find is TRQ_X. However, I’m unsure of how it is relevant to to my simulation. Even copying the turbine structural file from the documentation results in the same error.

By the way, once I’m done with this work I would like to provide all these input files as an example for the community to run their own simulations, thus the level of detail in my posts. Thus, the following details are additional information
—————————————————————————————————————————————————————————

I have deleted the unnecessary portions of the structural model file, thus it is rather empty. I intend to model the Rainbird rotor [1] where not much data is available regarding the mechanical properties, except for the rotational inertia*. In the structural model file, the rotational inertia is set to zero as the applied value is implemented in the blade properties file. Additionally, the drive train parasitic torque is set to zero because of the use of an axial-flux generator which provides no resistance unless electrically loaded [2].

Regarding the blade properties file, MASSD, XCM, YCM, XCS, YCS have been adjusted to 0.128kg/m, 0.25 , zero, 0.25, and 0.25 respectively. The MASSD was calculated based on the formula: I = mR^2. XCM, YCM, XCS, YCS were set to the above values to be equal to the quarter chord location. Lastly, the blade properties file is kept in the same folder as the simulation project file (.qpr) and structural input file.

*Contrary values of 0.018 kg.m^22 [3] and 0.3kg.m^2 [4] are obtained by the works of Torabi et al., and Celik et al. respectively. Applying 0.3kg.m^2 blows up the computational time, thus 0.018 kg.m^2 is used despite being less realistic. However, the issue of the applied value being less realistic is overcome by normalizing the time via the T* method [3].

[1] The Aerodynamic Development of a Vertical Axis Wind Turbine (Rainbird, MSc Thesis, University of Durham, 2007)
[2] Darrieus turbines: the physics of self-starting (Hill et al., Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, 2008)
[3] Study on Start-up Characteristics of H-Darrieus Vertical Axis Wind Turbines Comprising NACA 4-Digit Series Blade Airfoils (Torabi et al., Energy, 2016)
[4] Aerodynamic investigation of the start-up process of H-type vertical axis wind turbines using CFD (Celik et al., Journal of Wind Engineering and Industrial Aerodynamics, 2020)

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#2 · 24. August 2022, 17:48

Hi,

in general the structural VAWT files are a bit different when compared to the structural files for HAWT. For instance a torquetube file (TRQTBFILE) is required in addition to the tower file. I agree that this is not yet very well documented in the online documentation.

For the time being I suggest that you use the SANDIA 34m VAVT as a template (found in the download section) instead of the NREL 5MW template. You can use the scetch below as a reference for some of the terms and keywords in the main structural VAWT input file.

Regarding the GLBGEOEPS parameter: this parameter controls the creation of new nodes during the connection of different structural bodies (blades and struts for example). Only if the distance of an interconnection point on a body from an already existing structural node on the same body is above this parameter multiplied with the local structural element length – then a new node is created, otherwise an already existing node is used instead. Thus, this parameter allows to somewhat prevent a too close node spacing on structural elements that can lead to divergence of the structural solver. But in short: this does not relate to the problem that you have observed.

Best,

David

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