Shagun Agarwal* ([email protected]), Oriol Colomés ([email protected])
The next generation of offshore and nearshore structures will be focused towards expanding human activities into the ocean waters. These range from power generation using floating solar platforms, aquaculture farms and floating islands for use in farming, housing and production facilities. These structures are expected to have a large waterplane area and a structurally compliant design to enable them to survive the harsh offshore environment. Moreover, these platforms are also expected to require new mooring methods involving flexible synthetic mooring lines, especially for deployment in relatively shallow waters.
These problems require development of models capable of effectively capturing the geometric nonlinearity in the structural deformation associated with large deformations of flexible bodies. In these cases, the equilibrium is satisfied in the deformed configuration, while the problem is often formulated in the presently known undeformed configuration, resulting in a moving boundary problem. Moreover, modelling of structures like mooring lines involve dimensional reduction over curved manifolds, resulting in considerably more involved partial differential equations.
In this work we present a finite-element model for flexible mooring lines, capable of capturing the geometric nonlinearity associated with large deformations. We utilize the Tangential Different Calculus (TDC) method, devised in Fries (2020), for defining the geometric and differential quantities associated with finite strain (large deformation) analysis of mooring lines over curved manifolds. The technique can be applied on parametric and immersed manifolds, thus enabling the application to embedded flexible boundaries. However, this work will present the results only using the parametric manifold approach. The effect of the sea-floor is implemented using a damped spring bed, thus enabling large movement of the touch-down point of the mooring line. Additionally, the effect of the wave and current loading on the mooring line is implemented using Morison’s equation, with slender body approximation. The model is implemented using Gridap (Badia 2020), an advanced FEM library in Julia language. We utilize this model to study the variation in the tension at the fairlead and the anchor of a composite mooring line, comprised of chain and fiber sections, under wave and current loading. The work will highlight the influence of geometric nonlinearity on the tension and the excursion of the floater.
Aim:
Enable design of VLFS in near-shore conditions, through a unified modelling approach
Proposed Approach:
Use of Tangential Differential Calculus (TDC) (Fries 2020) for solving Partial Differential Equations on 1D and 2D manifolds
Advantages:
Geometric
Mechanical
Numerically versatile
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