Tubular tower

A single tubular tower is the dominating kind of support structure for onshore wind turbines. For bottom-fixed offshore wind turbines, a tubular tower on top of a monopile is the dominating support structure configuration. A tubular tower can be defined from parameters or imported from a text file. If a text file is imported, it is possible to have any kind of configuration (i.e. it does not have to be a tubular tower anymore). However, we suggest that if a support section that is not actually a tubular tower is to be used, then the Truss tower support section is used to avoid unnecessary confusion. 

The icons highlighted in the figure below correspond to the different Part actions available for Tubular towers, and are explained from left to right.



  •  import a text file. The format of the text file is explained in the Support section files section
  •  export the text file corresponding to the current tubular tower
  •  import a file containing a load history. The format of the file is explained in the Load history file section
  •  applied loads calculated with a python script. More details are given in Section 2 of the Support structure document
  •  import a Craig-Bampton superelement
  •  export the mass, damping and stiffness matrices

The following parameters are available for a Tubular Tower support section

General

Input file

The file to be imported to generate the support section. Import (in batch) by pressing the 'Import a support section from file' button in the action button collection to the right. This parameter (and this text) can only be visible in the batch (and not anywhere in the Time simulation window).

To import a support section in the Time simulation window, the 'Import a support section from file' action button must be used. Correspondingly, a support section can be exported to file in the time simulation window by using the 'Export the support section to file' action button. In batch the same buttons are placed to the right of the 'normal' parameters.


If the file is changed, moved, or removed after the import this will not affect the support section. For a change in the file to be effective the file must be imported again.

  • Default value:
  • Unit:

Scaling scheme

Scheme for scaling of this support section only (i.e. not the complete support structure - the complete support structure can be scaled on the Support structure part).

This parameter is only shown if the Wind turbine's 'Scaling scheme' parameter is set to 'Local scaling'.


A support section imported from file cannot be scaled. Thus, this parameter is never shown if the support section is imported from file.


Options:

Parent (default):

The scaling factor is set equal to the scaling factor for the whole Support structure.

Override:

A scale factor (set by you) for this section only (i.e. the scale factor set for the support structure is overridden).

Scaling factor

The geometry of this section of the support structure defined by parameters and/or files will be scaled by this factor.


  • Default value: 1
  • Unit:
  • Range: 0.001 — 1000

Height

The height of this section of the support structure. The height also takes into consideration any part below the seabed/ground, e.g. the piles on a truss tower.

If the height is set so low that the top of the section is below the sea surface, the set height is overruled and increased automatically so that the top is at the surface.

  • Default value: 100
  • Unit: $\text{m}$
  • Range: 1 — 1000

Material

The material used for this sub section of the support structure.

  • Default value: Steel
  • Unit:

Maximum element length

The maximum length a generated frame element can have, i.e. the elements will have this length or shorter.


  • Default value: 5
  • Unit: $\text{m}$
  • Range: 0.01 — 1000

Load histories file

The file adds load (time) histories to one or more nodes of the support section. The node names in the file must be found in the support section. The history can either be a force or moment history. If it is a moment history, the node name must be followed by any other string than 0 (i.e. the line contains two strings). An example of a load histories file can be found in the Examples folder. Open it from the menu: Help | Open examples folder. Make a copy of this file and then adapt it to the support section.

Note: A load histories file can only be used when the support section has been imported from file. You can right-click the support section and select Export to file to create a file that you can import again (by right-clicking the support section).


  • Default value:
  • Unit:

Geometry

Top diameter

The outer diameter of the tubular tower at the top.


  • Default value: 3.87
  • Unit: $\text{m}$
  • Range: 0.01 — 100

Top thickness

The thickness at the top of the tubular tower. If the thickness is set to greater than half the diameter it is reduced to half the diameter.


  • Default value: 0.025
  • Unit: $\text{m}$
  • Range: 0.001 — 10

Base diameter

The outer diameter of the tubular tower at the bottom.


  • Default value: 6
  • Unit: $\text{m}$
  • Range: 0.01 — 100

Base thickness

The thickness of the tubular tower at the base (thickness of the circular hollow cross section). The thickness of the tubular tower between the base and the top is interpolated. If the thickness is set to greater than half the diameter it is reduced to half the diameter.


  • Default value: 0.035
  • Unit: $\text{m}$
  • Range: 0.001 — 1

Transition piece

Has transition piece

If checked, the bottom part of the tubular tower is made into a transition piece. The transition piece is circular with constant diameter and thickness.

A tubular tower can have a transition piece (TP) at its lower part. However, onshore WTs typically don't have a TP - this design choice is more common for offshore bottom-fixed WTs. If you want to model a TP with different geometry and/or stiffness/mass properties than allowed by the parameters here (i.e. circular hollow), then it must be modelled in a text file and imported.


Note: A parameterized truss tower also has a transition piece connecting the upper point of its legs to the start point of a tubular tower or an RNA on top of the truss tower.

  • Default value: False
  • Unit:

Mass

Mass added to the upper node of the transition piece, i.e. the node connecting the transition piece to the tubular tower above it. The total mass of the transition piece is thus its structural mass plus this mass.


  • Default value: 66600
  • Unit: $\text{kg}$
  • Range: 0 — 100000

Height

The height of the transition piece (TP). This height is NOT added to the height of the the tubular tower itself. The height can be max 70% of the (total) height of tubular tower. If it is set to a greater value it is auto-corrected to 70%.


  • Default value: 4
  • Unit: $\text{m}$
  • Range: 0.1 — 100

Diameter

The cross-sectional outer diameter of the hollow circular member making up the transition piece (TP) of the tubular tower.


  • Default value: 7
  • Unit: $\text{m}$
  • Range: 0.01 — 10

Thickness

The cross-sectional thickness of the hollow circular member making up the transition piece(TP).

The thickness cannot be greater than the half of the outer diameter. If it is set to a greater value, then it is auto-corrected to half.

  • Default value: 0.4
  • Unit: $\text{m}$
  • Range: 0.001 — 1

Loads

Can have hydro loading

If this is not checked, the tubular tower cannot have hydrodynamic loading (not even with 0 value), no matter what settings on other parameters.

  • Default value: False
  • Unit:

Potential flow

WAMIT .1 table

The WAMIT .1 table defined in the .1 file. Note that Ashes assumes each column has a column title on the first row, modify your files so they have column titles.


  • Default value:
  • Unit:

WAMIT .1 table file path

The file path to the WAMIT .1 table. Only used in batch. If set, the WAMIT .1 table is imported from this file.


  • Default value:
  • Unit:

WAMIT .3 table

The WAMIT .3 table defined in the .3 file. Note that Ashes assumes each column has a column title on the first row, modify your files so they have column titles.


  • Default value:
  • Unit:

WAMIT .3 table file path

The WAMIT .3 table file path. Only used in batch. If set, the WAMIT .3 table is imported from this file.


  • Default value:
  • Unit:

WAMIT .12D table

The WAMIT 12D table defined in the .12D file. Note that Ashes assumes each column has a column title on the first row, modify your files so they have column titles.


  • Default value:
  • Unit:

WAMIT .12D table file path

The WAMIT .12D table file path. Only used in batch. If set, the WAMIT .12D table is imported from this file.


  • Default value:
  • Unit:

Characteristic length

The characteristic length used to compute potential flow loads.


  • Default value: 1
  • Unit:
  • Range: 0 — 1e+08

Apply to node option

Specifies if the potential flow loads should be applied to the node closes to center-of-mass, or if the node is specified by the user.


Options:

Node closest to center-of-mass (default):

The loads will be applied to the node closest to the center-of-mass.

User-defined:

The node is specified by the user.

Node name

The name of the node where potential flow loads are to be applied. The name does not include the word "Node", but rather the string after "Node" (which can be a number but also just text). You can find a node's name by right-clicking the structure.


  • Default value:
  • Unit: