2D Seabed Profile |
 
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2D Seabed Profile |
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In the context of elastic seabed contact, a 2D seabed contact surface is defined by a piecewise curve in the global XY plane horizontally extruded along the global Z axis. The global XY coordinates of the curve segment end points are specified by the user through the Seabed Utility application, which then pre-compiles the input data and generates a file that can be referenced by a Flexcom analysis. Intermediate locations are interpolated.
The 2D seabed file that is generated by the seabed utility is used for:
•Rendering the seabed in the Model View.
•Modeling contact with the seabed during analyses.
See the Seabed Utility section for further details on how to pre-compile a compatible 2D seabed file.
Once the seabed file has been generated it may be referenced in a keyword file under the *SEABED PROFILE keyword. The type of interpolation to be used is specified here also and can be linear, cubic spline or cubic bessel.
This is the default option and, if selected, the seabed profile is interpolated to lie on the straight line joining the input data points.
If this option is selected then a piecewise cubic polynomial which passes through all input points is used to interpolate the seabed profile. The global X elevation and slope at the global YZ interpolation point are taken to be the value and derivative, respectively, of the cubic Hermite spline defined by the curve segment endpoint values and slopes. The slopes at the extreme end points are assumed to be zero. Intermediate input point slopes are obtained by solving a symmetric positive-definite tri-diagonal linear system for the set of slopes associated with a Hermite cubic spline. This method of determining the slopes ensures that the curve has a continuous second derivative.
Also known as parabolic blending, this interpolation option is similar to the cubic spline option in that a cubic Hermite piecewise curve passes through each input data point and the slopes at the extreme end points are set to zero. It differs in the way that the intermediate data point slopes are calculated. The slope at each intermediate data point is determined from the slope of the parabola interpolating the data point and its two neighbouring data points. Because the nodal slopes depend only on adjacent node positions, the cubic Bessel interpolation gives a curve closer in shape to that of the linear interpolation than that of the cubic spline as shown in the figure below.
2D Seabed Profile Interpolation Options
The orientation of the 2D seabed profile about the global X axis may be specified also. By default, the profile lies in the global XY plane. The orientation can be changed so that the profile is rotated about the global X axis by a user specified amount in the same way that an elastic sloping profile may be rotated. Finally, the 2D seabed surface is assumed to be horizontal outside the range of the profile and to extend infinitely.
•*SEABED PROFILE is used to specify the seabed profile/bathymetry.
•*SEABED PROPERTIES is used to specify properties such as seabed type (i.e. rigid or elastic) and friction parameters.
If you would like to see an example of a 2D seabed profile, refer to F01 - As-Laid Span Analysis.