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*Stiffener

Purpose

To define the properties of a conical bend stiffener positioned on a flexible riser or pipe.

Theory

Refer to Bend Stiffeners for further information on this feature.

Keyword Format

A block of two lines to define a bend stiffener repeated as often as necessary.

SET=Set Name [, E=Curve Name] [, SYMMETRY=Symmetry]

Dfree, Dfix, [E], m, Dint[, Mass & Buoyancy Flag]

 

Mass & Buoyancy Flag defaults to 0, meaning the stiffener mass and buoyancy are not included in the analysis. For a non-linear stiffener the value of E should be omitted. Symmetry can be AUTOMATIC (the default), SYMMETRIC or ASYMMETRIC. You must use the *NONLINEAR STIFFENER keyword to define non-linear stiffener material properties if you specify a non-linear stiffener here.

Table Input

Notes

(a)The procedure when using this option to define the properties of a conical bend stiffener is as follows. You first define the properties of the riser or pipe in the usual way using the *GEOMETRIC SETS keyword. You then define an element set for the section over which the bend stiffener is to be positioned, and then complete the specification by inputting the actual stiffener properties and dimensions here.

(b)This means that the properties assigned to elements using this menu are additional to the properties defined using the *GEOMETRIC SETS keyword. Flexcom automatically increases the bending stiffness of the elements where the bend stiffener is positioned, using the data you specify here.

(c)The order in which the elements are specified in defining the bend stiffener element set is very important. The first element specified is assumed to be at the free end of the bend stiffener and the last element is assumed to be at the fixed end. Intermediate elements must be specified in order from the free end to the fixed end. Note that the elements in an element set can be specified in any order, including reverse (descending) order, for this reason. Elements can be added to an element set in reverse order by using an Element Increment of -1 under *ELEMENT SETS

(d)The free end diameter must be less than the fixed end diameter.

(e)If a non-linear material curve name is specified for Young’s Modulus, then the non-linear material curve must be defined using the the *NONLINEAR STIFFENER keyword.

(f)The specification of an internal diameter for the bend stiffener is optional. If omitted, the internal diameter defaults to the drag diameter of the first element of the stiffener set.

(g)Refer to Bend Stiffeners for a discussion on how bend stiffeners are handled in this program release and earlier versions. Specifically, the mass (inertia), weight and buoyancy of the stiffener are not by default included in an analysis. You do though have the option to instruct Flexcom to include them, which you do using the Mass/Buoyancy list.

(h)Refer to the Non-Linear Elastic section for a discussion on nonlinear bending symmetry models. If the bending symmetry of a nonlinear bend stiffener is to be automatically set by Flexcom then the symmetry chosen will depend on the material of the element to which the stiffener is attached. The stiffener bending symmetry will be asymmetric only if the element material is specified using the Flexible Riser Format and is (i) nonlinear asymmetric, i.e. EIyy and EIzz are defined by nonlinear stress/strain curves, or (ii) linear with unequal values of EIyy and EIzz. In all other cases the stiffener bending symmetry will be symmetric.