Structural and Hydronamic Properties |
 
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Structural and Hydronamic Properties |
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Flexcom provides two different formats for specifying structure geometric properties, although ultimately the information is the same and is used in the same way by the program. These are termed the Flexible Riser format and the Rigid Riser format. The Flexible Riser format is so called, naturally, because it is the format commonly used when defining flexible risers. Specifically, the data to be specified in this case comprises of bending stiffness about two axes, torsional stiffness, axial stiffness, mass per unit length etc. When you use the Rigid Riser format on the other hand, you input internal and external diameters, Young’s modulus, shear modulus, mass density etc. – data for the analysis of a Rigid Riser (whether a top tensioned riser or an SCR) would normally be available in this format. Refer to Geometric Properties in Flexible Riser Format for further information on this feature.
In this example the steep wave riser’s structural properties are specified in the Flexible Riser format, as shown below.
Structural Properties – Flexible riser
Refer to *GEOMETRIC SETS for further information on these data inputs.
The simplest hydrodynamic property specification in Flexcom is that of constant coefficients, which remain the same throughout an analysis. Five hydrodynamic coefficients are specified on an element set by set basis, to model drag, added mass and inertia loading. For simplicity, all elements in this example are assigned the same hydrodynamic coefficients as shown in the figure below. Refer to Constant Hydrodynamic Coefficients for further information on this feature.
Hydrodynamic Properties
Refer to *HYDRODYNAMIC SETS for further information on these data inputs.
Flexcom requires an effective outside diameter in order to compute stresses such as bending or Von Mises. For properties assigned using the Flexible Riser format, the default outer diameter is assumed equal to the drag diameter. In this example, the default value is suitable for the bare section, but is incorrect for the buoyant section. So the *PROPERTIES keyword is used to explicitly assign the correct outer diameter for the purposes of stress computations.
Buoyancy Properties