The BFLEX program system is a special purpose FEM tool developed for analysis of flexible pipes, umbilicals and power cables during load-out, installation and under in-service load conditions. As a special purpose tool, it is much more efficient than other more general purpose tools in terms of analysis time. The modelling approach is also tailored towards beam/pipe objects and helical components, simplifying the modeling effort.

The BFLEX development started in the early 90s, and the first generation of BFLEX was focused towards obtaining the global properties of non bonded flexible pipes, as well as the fatigue life of the tensile armour wires. The target load conditions were for the North Sea with fairly constant tension levels corresponding to water depths of a few hundred meters. The effort started based on the PhD work by Svein Sævik, and has since then been further developed in a continous process supported by the oil industry through several industry and joint industry projects.

The original modelling approach included both the moment-curvature and the individual helix sandwich beam model approach. In both cases, the axisymmetric stresses and layer contact pressures are found by applying the CAFLEX model which was developed as a cooperation between SINTEF and IFP. The caflex model assumes concentric layers and Lagrange multipliers to resolve layer contact pressures.

With increasing depths and pressure levels, the need for detailed stress results on the pressure spirals became more important, as a basis for fatigue life calculations. This lead to the development of the PFLEX, BOUNDARY and LIFETIME modules that could extend the level of detail to include stresses and strains in these components. This was developed through a sub-modelling concept, selecting a hot-spot along the riser. A limited number of pressure spirals were included at this location, to be studied in detail capturing the longitudinal and transverse bending moment. In addition a boundary procedure are able to capture stress concentrations at for example corners as well as contact stresses relevant for fretting fatigue. The modules operates seamlessly with BFLEX.

A major development effort to increase the flexibility was undertaken around 2010, which resulted in the new BFLEX2010 framework. This replaced the original BLEX. From that time on, access to the old format required by the PFLEX, BOUNDARY and LIFETIME modules must be established through a post processing step using the BFLEX2010POST postprocessor.

With the new develpment, several options for helical layers were introduced, applying detaled single helix elements or helix layer models. Bi-derectional slip and lateral contact can now be accounted for. The effect of tension variation on the stick-slip transition of the helices during the bending process can be captured. The new functionality enables a wide range of specialist analysis such as lateral buckling of armour wires under compression, broken or missing single wires, spooling operations etc.

From early 2020s, the modelling capabilities of USAP were merged into BLFEX2010. This includes modelling of long pitch length tubular components with limited interaction between helices.

The most recent and on-going developments are mainly related to proper modelling and analysis of power cables.

The input to BFLEX and its different modules are based on text files, and can hence easily be batch processed by scripting and parameter substitution.

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