Monopile Tower

Introduction

The tower is modelled by defining its characteristics at a number of stations from the tower base to the tower top. Tower properties must be defined for at least two tower stations (the tower base and tower top), although if tower vibrations are to be modelled, a minimum of 5 stations is recommended in order to achieve a reasonable degree of accuracy.

Defining a Tower Model

Check the Tower geometry check box to define the tower dimensions. These are used to calculate the tower shadow and windage loads.

Click the Add button to add a new tower station. Stations are automatically sorted by height. To highlight a station, click on the station number or a graph point. Click Delete to remove a highlighted station.

To enter or edit data, highlight the data item by clicking on it, or by moving to it using the arrow keys and then pressing the Return key. Press Escape to restore the previous value.

Highlight a block of cells by dragging the mouse. These cells may be copied to the clipboard, or the contents of the clipboard may be pasted in. In this way, data from a spreadsheet or a tab-delimited ASCII file may be directly pasted in. Click Undo to reverse a paste operation.

Enter the tower station height and tower diameter for each station. In the case of an onshore turbine the station heights are defined relative to ground level, whilst for an offshore turbine, station heights are defined relative to the mean water level. The user can select whether the turbine is onshore or offshore by selecting the relevant land or sea environment option.

If the first tower station is above the ground or seabed level, the tower is assumed to be mounted on a rigid pedestal, as indicated on the Tower Geometry diagram. If the height of the first tower station is below the ground or seabed level, the tower foundation is assumed to be buried as indicated, and no external forces are assumed to act on the buried portion of the tower.

For all cases, the height of the top tower station must correspond to the tower height defined on the Rotor screen.

The Show button controls the graphical display of tower properties. The graph is updated as soon as any new values are assigned, giving an instant indication if faulty values are entered. Controls are provided to print the graph or save it to a Metafile, which can subsequently be incorporated into a report.

Check the Mass check box to allow the mass per unit length to be entered at each tower station. This is necessary for correct calculation of the tower base loads, and also for modelling tower vibrations, in which case it is also necessary to check the Stiffness check box and supply bending stiffness values at each station. These are defined as the product of the Young's modulus and the second moment of area. Check the Shear flexibility check box to include effects of shear flexibility and to allow entering the shear stiffness at each station. These are defined as the product of the Shear modulus and the shear area that equals half of the cross-section area for a circular cross-section. Check the Torsional degree of freedom check box to allow the torsional stiffness and polar moment of inertia to be entered at each station.

Alternatively, for a tower of circular cross-section, the mass and stiffness distributions can be calculated automatically by entering the wall thickness at each station. Type the name of a material and enter its density and Young's modulus in the boxes provided. If the torsional degree of freedom or the shear flexibility is included, the Shear modulus should also be entered. A number of different materials may be entered if desired. Then select the appropriate material for each station. One such property computed by Bladed is the cross sectional shear stiffness. In this case it is assumed that the "effective shear area" is 0.5 x "cross-sectional area", which is the standard assumption for a thin walled pipe section. The cross sectional stiffness is then computed using "shear modulus" x "effective shear area".

If a discontinuity is to be defined, for example a step change in wall thickness or other property, simply enter two stations at exactly the same height to define the discontinuity. Do not enter very closely spaced stations.

Last updated 15-11-2024