MAP++ linear spring approach improvement #1752
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Small modification for the linear spring approach in MAP++. This modification allows to study conventional catenary systems as well as lines that have the anchor point above the fairlead connection.
Feature or improvement description
The default MAP++ version can only apply vertical forces in the downward direction. This is the force that we would expect in a conventional mooring line system. However, there are some conditions when the force should be applied in the upward direction (e.g., when then anchor location is above the fairlead connection).
The proposed modifications allows MAP++ to apply positive or negative forces in the vertical direction when using the linear spring approach.
For reference MAP++ can solve a mathematical problem by means of a catenary formulation or a linear spring formulation. The modifications presented here, only impact the linear spring formulation.
Related issue, if one exists
This modification solves the problems for the linear spring approach in MAP++ reported here: #1750
Impacted areas of the software
The modifications only affect MAP++ when the
linear_spring
flag is selected in the line properties section.Additional supporting information
Sometimes, when performing scale tests of floating offshore wind turbines in a wave tank, horizontal mooring lines are used. Usually monofilament fishing lines connected in series to a spring are used to reproduce a similar elastic restoring force as the corresponding catenary line. See for reference section 2.4 of the paper: https://doi.org/10.3390/machines11090865. For this kind of applications, the linear spring approach from MAP++ is a convenient approach to simulate the system.
Test results, if applicable
Several tests cases have been performed with satisfactory results. The outputs from the modified code (MAP++) has been also compared against MoorDyn v2. See for reference: #1750