Flexcom was originally developed by a small start-up company, Marine Computation Services, founded at University College Galway in 1983. Nowadays it is managed by John Wood Group plc. The name derives from its origins as a computational software initially geared towards the analysis of flexible risers, befitting the emerging riser technology of the North Sea in the early 1980s. Although originally a time domain analysis tool only, it also incorporates frequency domain and modal analysis capabilities. The first version was released circa 1985, and a continuous update program has been maintained since then.
Subsea mid-water arch modelled by FlexcomDropped riser modelled by FlexcomStiesdal TetraSpar modelled by Flexcom
Flexcom uses a specialised finite element formulation, incorporating a hybrid Euler–Bernoulli beam-column element with fully coupled axial, bending and torque forces, well suited to the modelling of slender offshore structures such as mooring lines. Up to 10 integration points are used within each finite element to ensure a precise distribution of applied forces. Third order shape functions are used to predict solution variable (e.g. moment, curvature) variations within each element. Flexcom uses a consistent mass formulation which integrates the mass along the length of each finite element, consistent with the fundamental principles of the finite element method, stiffness matrix assembly and shape functions. This results in a fully populated mass matrix with off-diagonal terms that include coupling terms between different degrees of freedom and different nodes, and represents a complete numerical definition of the structural mass in reality. A consistent mass definition is important for implicit time domain solvers which simulate dynamic structures, and is particularly important in accurately capturing rotational inertia effects.
Flexcom Beam-Column Element
For a numerical solver to be capable of analysing both flexible materials (such as mooring wires, power cables etc.), and inflexible structures (such as the rigid columns and pontoons of a floating platform), a solution scheme is required which caters for bending stiffness values which are much lower than corresponding axial stiffness values. To achieve this effect, axial force is explicitly included as a solution variable, which is solved for independently of the axial strain. The stress-strain compatibility relationship is applied outside of the virtual work statement by means of a Lagrangian constraint.[1] Torque is handled in a similar manner, which leads to a fourteen degree of freedom hybrid finite element with two end nodes, where the axial force and torque are added to the usual form of a three-dimensional beam-column element.
Floating bodies typically undergo significant rigid body motions when subjected to ocean waves, so the numerical solver must also cater for arbitrarily large and non-linear displacements and rotations in three dimensions. This is a key aspect of the structural model which is necessary to ensure accurate modelling of the restoring forces such as effective tension and bending moment. The solver uses a convected coordinate technique to cater for large three-dimensional displacements and rotations.[2] Each element of the finite element discretisation has a local axis system associated with it, which moves with the element as it moves in space and time. The internal and external virtual work statements are written in the convected system, and deformations along the element relative to this system are assumed to be moderate.
Truss element
Flexcom Truss Element
A truss element was added in 2022. It is designed specifically for modelling structures which have very low levels of structural bending stiffness (such as mooring chains) and is essentially a simplified version of the beam element. Code-to-code comparisons have shown the truss element to be numerically accurate, dynamically robust and computational efficient.[3]
Hydrodynamic model
Hydrodynamic loading on the beam elements is based on Morison's equation. Morison's equation is widely established in marine engineering for modelling wave forces on slender offshore structures such as oil and gas export lines and mooring lines. In situations where the body size becomes significant with respect to wavelength, the underlying assumptions become invalid, and the effects of radiation and diffraction must also be considered.
Hydrodynamic loading on larger bodies is based on the application of potential theory. Dedicated hydrodynamic modelling packages such as WAMIT solve the velocity potential using a boundary integral equation method, and provide hydrodynamic coefficients which may be subsequently used as inputs by Flexcom. This provides a more detailed model than Morison's equation, and includes wave excitation forces (due to the pressure acting on a still vessel), diffraction forces (caused by disturbances of the wave field due to the presence of the vessel), and radiation damping forces (representing waves caused by oscillations of the vessel itself). Flexcom uses a convolution technique to integrate frequency-dependent added mass and radiation damping terms into the time domain simulation.
Flexcom has been validated over many years via comparisons with other software, analytical solutions and other published work. Sample publications are listed below.
Turret disconnect modelled by FlexcomColliding object modelled by FlexcomTower crane modelled by Flexcom
↑ O'Brien, P.J.; McNamara, J.F. (1988), "Analysis of Flexible Riser Systems Subject to Three-Dimensional Seastate Loading", Proceedings of the International Conference on Behaviour of Offshore Structures, vol.3, pp.1373–1388
↑ O'Brien, P.J.; McNamara, J.F. (2002), "Improvements to the convected co-ordinates method for predicting large deflection extreme riser response", In 21st International Conference on Offshore Mechanics and Arctic Engineering (OMAE), ASME, pp.481–488, doi:10.1115/OMAE2002-28237
1 2 Connolly, A.; Lang, D.; Conway, O. (2025), "Validation of a Truss Finite Element for Mooring Applications via Code-To-Code Comparisons", In International Conference on Offshore Mechanics and Arctic Engineering, American Society of Mechanical Engineers
↑ Smith, R.; Carr, T.; Lane, M. (2007), "Computational tool for the dynamic analysis of flexible risers incorporating bending hysteresis", In International Conference on Offshore Mechanics and Arctic Engineering, American Society of Mechanical Engineers, doi:10.1115/OMAE2007-29276
↑ Grealish, F.; Kavanagh, K.; Connaire, A.; Batty, P. (2007), "Advanced Nonlinear Analysis Methodologies for SCRs", In Offshore Technology Conference, Offshore Technology Conference, doi:10.4043/18922-MS
↑ Connaire, A.; Lang, D.; Galvin, C. (2003), "Closely-Moored Floating Bodies in a Production and Offloading Facility - Requirement for and Application of a Coupled Analysis Capability", In Offshore Technology Conference, Offshore Technology Conference, doi:10.4043/15378-MS
↑ Kavanagh, K.; Connaire, A.; Payne, J.; Connolly, A.; McLoughlin, J. (2013), "Slug Response in Subsea Piping: Advancements in Analytical Methods", In Offshore Technology Conference, Offshore Technology Conference, doi:10.4043/24134-MS
↑ Grealish, F.; Lang, D.; Connolly, A.; Lane, M. (2005), "Advances in contact modelling for simulation of deep water pipeline installation", In Rio pipeline 2005 conference and exposition, U.S. Department of Energy, Office of Scientific and Technical Information, doi:10.4043/24134-MS
↑ Connolly, A.J.; O'Mahony, G.T. (2021), "Validation of a Novel Floating Wind Turbine Simulation Tool via Benchmarking: Case Study of Jacket Structure", In The 31st International Ocean and Polar Engineering Conference (ISOPE), OnePetro
↑ Connolly, A.J.; O'Mahony, G.T. (2021), "Validation of a Novel Floating Wind Turbine Simulation Tool via Benchmarking: Case Study of a Semi-Submersible Platform", In SPE Offshore Europe Conference & Exhibition, OnePetro, doi:10.2118/205415-MS
↑ Bergua, R. (2023), "OC6 Project Phase IV: Validation of Numerical Models for Novel Floating Offshore Wind Support Structures", In Wind Energy Science, European Academy of Wind Energy, doi:10.5194/wes-2023-103, hdl:11250/3130224
↑ Conway, O.; Connolly, A.; Leen, S. (2024), "Numerical Modelling of Novel Floating Offshore Wind Turbine Concept", In International Conference on Offshore Mechanics and Arctic Engineering, American Society of Mechanical Engineers, doi:10.1115/OMAE2024-126681
↑ Britton, B.; Connolly, A.; Conway, O.; Leen, S. (2024), "Aerodynamic Code-To-Code Comparison via IEA 22 MW Reference Turbine", In International Offshore Wind Technical Conference, American Society of Mechanical Engineers
↑ Connolly, A.; Brewster, P. (2017), "Application of Coupled Numerical Simulation to Design Wave Energy Converters", In International Ocean and Polar Engineering Conference, International Society of Offshore and Polar Engineers, ISBN978-1-880653-97-5
↑ Connolly, A.; O'Connor, A.; O'Mahony, G. (2018), "Computationally Efficient Simulation of Floating DualBody Point Absorber", In International Conference on Ocean Energy, IEA Ocean Energy Systems
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