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*ELEMENT SOLUTION

Purpose

To control aspects of the finite element solution.

Theory

Refer to Finite Element Formulation, and specifically Beam Finite Element Matrices, for further information.

Keyword Format

Optional line specifying the flexibility coefficients which are used in the scaling of axial and torque components in the finite element solution and help prevent ill-conditioning of the stiffness matrix. These values should rarely need to adjusted in practice, if ever.

[FLEXIBILITY PARAMETERS=Axial Flexibility Parameter, Torsional Flexibility Parameter]

The axial parameter (ρ1) and the torsional parameter (ρ2) default to 0.001 and 0.1, respectively.  

Line specifying if the additional penalty terms are to be included in the finite element solution.

SET=Set Name, PENALTY DOFs=Penalty Switch

By default, Flexcom uses a hybrid beam element, where axial force and torque are explicitly included in the finite element formulation, and solved for directly as solution variables, independently of the nodal displacement terms. You can disable the additional terms if you wish, reducing the solution to a more traditional beam element with 12 active degrees of freedom. Hence Penalty Switch can be ON or OFF, defaulting to ON.

However you should only disable the penalty terms if your model contains elements whose stiffness components in the axial, bending and torsional degrees of freedom have similar orders of magnitude. This might typically be the case for rigid structures, such as TTRs, SCRs, pipelines, jackets, etc. It is not recommended to disable the penalty terms for more flexible structures such as flexible risers, jumpers, mooring lines, electrical cables, etc. as these generally tend to have large disparities between the (relatively high) axial stiffness and (relatively low) bending and torsional stiffness.

By reducing the number of active DOFs, you may see some increase computational performance as a result. However any improvement in run time is likely to be limited by the fact that execution of the finite element solver is only component in the overall solution process. There are many other components, some of which are more time consuming than the solver itself, such as keyword processing, assembly of the global mass matrix and global load vector, seabed contact modelling, database writing, postprocessing etc.

FLEXIBILITY PARAMETERS

Purpose

To specify the flexibility coefficients which are used in the scaling of axial and torque components in the finite element solution and help prevent ill-conditioning of the stiffness matrix. These values should rarely need to adjusted in practice, if ever.

Table Input

PENALTY DOFs

Purpose

To specify if the additional penalty terms are to be included in the finite element solution.

Table Input

Notes

(a)By default, Flexcom uses a hybrid beam element, where axial force and torque are explicitly included in the finite element formulation, and solved for directly as solution variables, independently of the nodal displacement terms. You can disable the additional terms if you wish, reducing the solution to a more traditional beam element with 12 active degrees of freedom. However you should only disable the penalty terms if your model contains elements whose stiffness components in the axial, bending and torsional degrees of freedom have similar orders of magnitude. This might typically be the case for rigid structures, such as TTRs, SCRs, pipelines, jackets, etc. It is not recommended to disable the penalty terms for more flexible structures such as flexible risers, jumpers, mooring lines, electrical cables, etc. as these generally tend to have large disparities between the (relatively high) axial stiffness and (relatively low) bending and torsional stiffness. By reducing the number of active DOFs, you may see some increase computational performance as a result. However any improvement in run time is likely to be limited by the fact that execution of the finite element solver is only component in the overall solution process. There are many other components, some of which are more time consuming than the solver itself, such as keyword processing, assembly of the global mass matrix and global load vector, seabed contact modelling, database writing, postprocessing etc.