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Wing type data |
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Wing type data |
Both 6D buoys and wind turbines can use wing type data. 6D buoys can have wings attached, each with its own wing type, while turbine blades are made up of a number of segments, each of which has its own wing type.
Used to refer to the wing type.
The properties of each wing type are represented by a table of lift, drag and moment coefficients as a function of the incidence angle of the flow relative to the wing.
The graph button displays these coefficients graphically, so that you can easily check your data visually.
The incidence angle $\alpha$ is that which the relative flow vector makes with the wing surface. Linear interpolation is used to obtain coefficients for angles between the values given. You should take care with these data, as the precise interpretation of the incidence angle differs for wings attached to 6D buoys and those attached to turbines.
These steady coefficients of lift $(\C{l})$, drag $(\C{d})$, and moment $(\C{m})$ define the hydrodynamic and aerodynamic loads applied to the wing for each given incidence angle $\alpha$. See the separate topics for buoys and turbines for the details of the load equations in each case.
Data to control and parameterise the UA model for turbines.
If checked, unsteady aerofoil aerodynamics will be calculated for any turbine blade segments that use this wing type, if the turbine has a UA model selected.
The zero lift angle of attack in degrees.
The drag force coefficient at α0.
The pitching moment coefficient at α0.
Lagged components of the normal force coefficient at leading edge separation. Cn1 and Cn2 are the values for positive and negative angles of attack respectively. Damiani and Hayman suggest they can be calculated from the static values of the normal force coefficient at either the break in the pitching moment or the loss of chord force at the onset of stall. These values are aerofoil specific and must be provided.
Gradient of the normal force coefficient in the linear region, given per radian. To use this wing type with a UA model, a value greater than zero must be specified. If the gradient is zero, e.g. at a cylindrical root section of the blade, then unsteady aerodynamics are not appropriate and UA should not be enabled for this wing type.
Constants used to parameterise UA models. In most cases, the default values are appropriate. For information on usage and default values, see Damiani and Hayman.
Time constants used to parameterise UA models. For information on their definition and usage, see Damiani and Hayman. The default values are consistent with those used by AeroDyn; however, these values should be user specified if possible. They can be sensitive to Reynolds number, Mach number and aerofoil shape.
Strouhal’s shedding frequency.
UA cutout angle in degrees. If the magnitude of the angle of attack is within 5 degrees of the cutout angle, the steady and unsteady aerofoil models will be blended. If the magnitude of the angle of attack is above the cutout angle, the steady values are used.
Cutoff reduced frequency for the low pass filtering of the angle of attack and its first two derivatives, in the UA model. The filter cutoff frequency, in Hertz, is calculated from this reduced value by: \begin{equation} \frac{\textrm{filter cutoff} \times U }{\pi \times \textrm{chord}} \end{equation} where $U$ is the magnitude of the inflow velocity.
The drawing data apply only to wings attached to buoys. Turbines have their own drawing data. In the case of buoys, the wing type pen controls which pen is used to draw wings of this type. Use buoy pen means that the wing will be drawn with the pen of its parent 6D buoy. Use wing pen allows you to define a different pen for all wings of this type.
By default, for shaded 3D views, wings on 6D buoys are drawn as plates with the specified span and chord.
Alternatively the object can be represented by an imported 3D model by specifying the shaded drawing file. This can be one of the following formats:
If you use a relative path then the path will be taken as relative to the folder containing the OrcaFlex file.
Draw size (.x, .obj) allows you to scale the drawing. All directions are scaled equally such that the longest side in the drawing is drawn to the given draw size. This longest side is calculated by fitting the smallest possible cuboid around the vertices of the shaded drawing, aligned with the shaded drawing's local axes. The longest side is the length of the longest side of this cuboid.
Set draw size to '~' to display the drawing using the absolute coordinates as specified in the drawing file.
| Note: | If you use a value of '~' for draw size, then OrcaFlex uses the coordinates in the drawing file directly, taking them to be in the prevailing OrcaFlex units. If these coordinates use a different length unit from your OrcaFlex model, then you should define them in an auxiliary file called AdditionalInformation.txt. Examples of this can be found in the sample shaded drawings provided by Orcina. |
The culling mode (.x, .obj) option enables an optimisation that may provide a useful performance benefit. When enabled, only faces towards the viewer are drawn. The backward-facing faces are culled – they are not drawn. By culling these faces, less computation is required and performance is improved. In practice however, typical modern graphics cards are sufficiently powerful that you may not notice any benefit.
There are different conventions in common use regarding the specification of the outward facing direction, which we refer to as clockwise or anticlockwise. It is not always possible to detect programmatically which convention is in use, so we must pass the responsibility to you, the user, to do so. It is usually immediately apparent by trial and error which option is correct.
Culling requires that the faces defined in the drawing file have their outward-facing directions defined correctly. If this is not the case, then the object will not display correctly; typically, sections of the the object will be missing when it is drawn by OrcaFlex. This problem is usually resolved by disabling culling.
The mirror in plane (.x, .obj) option allows you to mirror the whole 3D model about the specified plane. Note that the axes refer to the 3D drawing axes rather than the OrcaFlex axes. This may be required if the original drawing axes convention does not match that assumed by OrcaFlex.
These assumptions may not be appropriate for your mesh file, so this option allows you to adjust the rendering so the model appears correctly. When you choose to mirror in a plane, this has the effect of switching from a left-handed axis convention to a right-handed axis convention, and vice versa.
A common sign that the coordinate convention needs switching is if asymmetric features, or text on the model, appear mirrored in the shaded view.
For panel mesh files you must specify the mesh length units and the mesh symmetry. OrcaFlex uses length units to scale the mesh panels to match the units system of the OrcaFlex model. Mesh symmetry can be one of the following values: none, xz plane, yz plane or xz and yz planes. This is used to generate the additional panels that are implied by the symmetry.
For panel mesh files that support multiple bodies or structures, you must specify the body number to be imported. If the panel mesh file format does not support multiple bodies then this value is ignored.
For panel mesh files that define panels above the waterline (dry panels), you must specify whether to import dry panels. If the panel mesh file format does not support dry panels then this value is ignored.
Shaded drawing origin is provided because the shaded drawing and the wing may have different origins. The shaded drawing origin defines the origin of the shaded drawing with respect to the wing's local axis system. Similarly shaded drawing orientation allows you to reorient the shaded drawing to match the wing's axis system.