Cable bending stiffness capabilities have been added to the lumped-mass mooring dynamics model MoorDyn to enable modeling of dynamic power cables. The large degree of motion seen by floating wind turbines and wave energy converters poses a challenge to power cables due to the propensity for large and rapid changes in cable profile. Power cables, with complex internal construction and significant stiffness, are sensitive to bending deformations for both extreme and fatigue limits. Furthermore, their behavior and associated design considerations in highly dynamic situations are still relatively underexplored. As such, improving modeling tools for dynamic power cables, particularly in coupled scenarios, is of high relevance to the floating wind and wave energy industries.MoorDyn is an open-source lumped-mass mooring dynamics model used for floating wind energy simulation (often coupled with OpenFAST) and floating wave energy converter simulation (often coupled with WEC-Sim). Thus far, it has considered only axial stiffness of line elements, making it suitable for mooring line simulation but not for power cables where bending stiffness is a design-driving phenomenon. To address this limitation, a cable bending stiffness model has been added to MoorDyn’s lumped-mass formulation. The model approximates cable curvature based on the difference in tangent vectors of adjacent line elements, then applies forces on each set of three associated nodes to exert the equivalent bending reaction moment while leaving the net forces unaffected. This creates a first-order bending stiffness behavior that can be turned on and off without changing the underlying lumped-mass formulation and with minimal impact to overall computational efficiency.The bending stiffness implementation is verified in static conditions against analytical solutions and then in realistic dynamic power cable scenarios by comparing with results from the commercial modeling tool OrcaFlex. Comparison across several representative dynamic cable cases with applicability to both floating wind turbine and wave energy converter designs shows that the new capability is suitable for modelling dynamic power cables under typical conditions.

Implementation and Verification of Cable Bending Stiffness in MoorDyn

Paper Proceedings: https://asmedigitalcollection.asme.org/OMAE/IOWTC2021/volume/84768

ASME 2021 International Offshore Wind Technical Conference (IOWTC2021)

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