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Merge pull request #153 from hivanov-nrel/mooring
Mooring module
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‎changelog.md‎

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# Current development
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## PR 153 - Mooring Module
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- Author: @hivanov-nrel
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- Addition of the mooring module, which includes
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- Read in MoorDyn files into MATLAB
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- Function to calculate mooring line lay length
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- Functions to visualize mooring line dynamics in 2D or 3D.
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- Example LiveScript demonstrating the functionality of the mooring module
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## PR 170 - WDRT leftovers
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- Author: @hivanov-nrel

‎examples/data/mooring/Test.MD.out‎

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‎examples/data/mooring/TestInput.MD.dat‎

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--------------------- MoorDyn Input File ------------------------------------
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Mooring system for OC4-DeepCwind Semi
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FALSE Echo - echo the input file data (flag)
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----------------------- LINE TYPES ------------------------------------------
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Name Diam MassDen EA BA/-zeta EI Cd Ca CdAx CaAx
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(-) (m) (kg/m) (N) (N-s/-) (-) (-) (-) (-) (-)
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main 0.0766 113.35 7.536E8 -1.0 0 2.0 0.8 0.4 0.25
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---------------------- POINTS --------------------------------
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ID Attachment X Y Z M V CdA CA
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(-) (-) (m) (m) (m) (kg) (m^3) (m^2) (-)
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1 Fixed 418.8 725.383 -200.0 0 0 0 0
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2 Fixed -837.6 0.0 -200.0 0 0 0 0
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3 Fixed 418.8 -725.383 -200.0 0 0 0 0
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4 Vessel 20.434 35.393 -14.0 0 0 0 0
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5 Vessel -40.868 0.0 -14.0 0 0 0 0
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6 Vessel 20.434 -35.393 -14.0 0 0 0 0
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---------------------- LINES --------------------------------------
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ID LineType AttachA AttachB UnstrLen NumSegs Outputs
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(-) (-) (-) (-) (m) (-) (-)
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1 main 1 4 835.35 20 -
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2 main 2 5 835.35 20 -
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3 main 3 6 835.35 20 -
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---------------------- SOLVER OPTIONS ---------------------------------------
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0.001 dtM - time step to use in mooring integration (s)
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3.0e6 kbot - bottom stiffness (Pa/m)
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3.0e5 cbot - bottom damping (Pa-s/m)
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2.0 dtIC - time interval for analyzing convergence during IC gen (s)
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60.0 TmaxIC - max time for ic gen (s)
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4.0 CdScaleIC - factor by which to scale drag coefficients during dynamic relaxation (-)
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0.01 threshIC - threshold for IC convergence (-)
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------------------------ OUTPUTS --------------------------------------------
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FairTen1
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FairTen2
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FairTen3
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AnchTen1
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AnchTen2
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AnchTen3
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END
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------------------------- need this line --------------------------------------

‎examples/data/mooring/line1_test.out‎

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‎examples/mooring_example.html‎

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‎examples/mooring_example.m‎

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%% Mooring Module Example
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% In this example, we'll explore the functionalities of the Mooring module of
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% the Marine and Hydrokinetic Toolkit (MHKiT). As of now, this module primarily
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% supports output from MoorDyn, an innovative tool for simulating the complex
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% dynamics of mooring lines used in marine applications.
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%
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% The objective will be to analyze the MoorDyn output data of a single mooring
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% line. The steps are:
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%%
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% # *Import Data* - Import the MoorDyn output
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% # *Lay Length* - Calculate the lay length parameter
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% # *Visualize* - Create graphical animations
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% Importing Data
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% The first step is to import the MoorDyn output file. This file contains the
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% key data that we'll be analyzing throughout this notebook. If support for other
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% types of output is desired, please raise an issue or reach out to the MHKiT
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% team!
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%
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% The code below provides paths to two files:
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%%
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% * |fpath| = MoorDyn output file of a single mooring line containing node positions
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% and segment tensions
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% * |inputfile| = Path to MoorDyn input file that corresponds to the output.
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% This is an optional argument which parses the input parameters and writes them
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% a struct for reference. Note: the input file provided here does not match the
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% output and is only meant for demonstration purposes.
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% define the paths
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fpath = "./examples/data/mooring/line1_test.out";
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inputfile = "./examples/data/mooring/TestInput.MD.dat";
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% load in data
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[data, input] = read_moordyn(fpath, inputfile)
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% Calculating the Lay Length with MoorDyn Data
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% Next, we turn our focus to calculating the 'lay length'. Lay length is the
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% measure of how much of the mooring line is in contact with the seabed.
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%
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% To calculate the lay length, we'll use the MoorDyn output data we imported
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% in the previous step. We also need to define two key parameters:
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%%
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% * The |depth| of the seabed, which we've set as -56m for this example. Please
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% note that the seabed depth is considered negative as we're measuring downwards
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% from the sea level.
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% * The |tolerance|, or the threshold, for determining when a node is deemed
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% to be in contact with the seabed. For this exercise, we'll use a tolerance of
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% 0.25m. The selection of a suitable tolerance value depends on various factors
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% including the resolution of your data and the specifics of your application.
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%%
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% We use the |lay_length| function for this calculation, which will yield an
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% array representing the lay length of the mooring line at each time step. Let's
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% execute the function:
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depth = -56; % meters
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tolerance = 0.25; % meters
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laylength = lay_length(data, -56, 0.25)
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%%
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% Additionally we can use this information to get an average lay length for
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% the whole time period.
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fprintf('The average lay length of the mooring line is: %.1f meters', mean(laylength))
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% Visualizing Mooring Line Dynamics with Graphics
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% After calculating the lay length, let's progress to the final step of our
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% journey: visualization. The mooring module within MHKiT provides tools to create
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% interactive, informative graphics that can help us visualize and better understand
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% the behavior of the mooring line.
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%
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% However, to keep things performance-friendly, we will first slice our initial
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% data down to a 10-second window. This reduces computational demand while still
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% providing a useful snapshot of our mooring line's dynamics.
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%
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% With our data subset ready, we can create a 3D animation of the mooring line
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% using the |plot_mooring_animate|.
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plot_mooring_animate(data(data.Time<10, :), '3D', 0.05, ...
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'xlabel','X-axis','ylabel','Y-axis','zlabel','depth','title','3D example')
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%%
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% In this simplified example, the mooring line is constrained from moving along
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% the y-axis. Since there is no motion along the y-axis, it would actually be
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% easier to view the animation in 2D instead. This can be accomplished with the
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% |plot_mooring_animate| function specifying dimension=|'2D'|.
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plot_mooring_animate(data(data.Time<10, :), '2D', 0.05, ...
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'xlabel','X-axis','ylabel','depth [m]','title','2D example')
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%%
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% Through these graphical representations, we can gain a more intuitive understanding
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% of how the mooring line interacts with the surrounding marine environment over
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% time.
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% Summary and Conclusion
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% In this notebook, we walked through the MHKiT Mooring module learning how
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% to utilize MHKiT in conjunction with MoorDyn output to analyze the dynamics
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% of a single mooring line.
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%
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% We used the |read_moordyn| function to bring this data into Matlab, preparing
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% it for further analysis. Next, we calculated the 'lay length' of our mooring
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% line using the |lay_length| function, obtaining an array representing the lay
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% length at each time step. Finally, we visualized 2D and 3D animations of the
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% mooring line's behavior over a 10-second period using the |plot_mooring_animate|
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% function.
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%
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% We hope that this example serves as a valuable guide to employing the MHKiT
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% Mooring module and MoorDyn analyses.
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%
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% Thank you for your interest in MHKiT! We encourage you to continue to open
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% an issue or pull request if you have any feedback or expansions which would
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% help you improve your mooring data analysis.

‎examples/mooring_example.mlx‎

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‎mhkit/mooring/lay_length.m‎

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function line_lay_length = lay_length(data, depth, tolerance)
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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% Calculate the lay length of a mooring line over time.
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%
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% Lay length is the measure of how much of the mooring line is in contact
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% with the seabed. This function requires MoorDyn line output data containing
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% individual node positions NodeNpx, NodeNpy, NodeNpz.
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%
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% Parameters
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% ----------
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% data: table
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% MoorDyn line output data table containing Time column and node
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% position data (NodeNpx, NodeNpy, NodeNpz) where N is the node number.
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% Data should be obtained using mhkit.mooring.read_moordyn() with a
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% MoorDyn line output file (*.Line*.out).
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% depth: double
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% Depth of seabed (m). Should be negative for depths below sea level.
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% tolerance: double, optional
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% Tolerance to detect first lift point from seabed, by default 0.25
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% meters. Nodes with z-position > depth + abs(tolerance) are
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% considered lifted from seabed.
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%
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% Returns
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% -------
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% line_lay_length: double array
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% Array containing the lay length at each time step (m)
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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arguments
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data table
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depth {mustBeNumeric}
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tolerance {mustBeNumeric} = 0.25
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end
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%channel names
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chans = data.Properties.VariableNames;
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% get node names
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idx = strfind(chans, 'x');
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idx = cell2mat(cellfun(@(x)any(~isempty(x)),idx,'UniformOutput',false));
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nodes_x = {chans{idx}};
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idy = strfind(chans, 'y');
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idy = cell2mat(cellfun(@(x)any(~isempty(x)),idy,'UniformOutput',false));
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nodes_y = {chans{idy}};
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idz = strfind(chans, 'z');
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idz = cell2mat(cellfun(@(x)any(~isempty(x)),idz,'UniformOutput',false));
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nodes_z = {chans{idz}};
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% check if data contains the necessary nodes
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if isempty(nodes_x) || isempty(nodes_y) || isempty(nodes_z)
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error("The data must contain x, y, and z node data!")
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end
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if length(nodes_z) < 3
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error("This function requires at least 3 nodes to calculate lay length")
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end
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% find name of first z point where tolerance is exceeded
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zdata = table2array(data(:,nodes_z)); % Convert table to array
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laypoint_mask = zdata > (depth + abs(tolerance));
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laypoint = nodes_z(any(laypoint_mask));
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% get previous z-point
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lay_indx = find(cellfun(@(x) strcmp(x, laypoint), nodes_z)) - 1;
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lay_z = nodes_z(lay_indx);
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% get corresponding x-point and y-point node names
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lay_x = strcat(lay_z{:}(1:end-1), "x");
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lay_y = strcat(lay_z{:}(1:end-1), "y");
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lay_0x = nodes_x{1};
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lay_0y = nodes_y{1};
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% find distance between initial point and lay point
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laylength_x = data.(lay_x) - data.(lay_0x);
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laylength_y = data.(lay_y) - data.(lay_0y);
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line_lay_length = (laylength_x.^2 + laylength_y.^2) .^ 0.5;
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end
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‎mhkit/mooring/plot_mooring_animate.m‎

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function plot_mooring_animate(data, dimension, step, varargin)
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%Graphics function that creates a 2D or 3D animation of the node
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% positions of a mooring line over time.
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% Detailed explanation goes here
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arguments (Input)
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data
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dimension {mustBeTextScalar} = '2D'
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step {mustBeNumeric} = 0.05
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end
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arguments (Repeating)
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varargin
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end
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%channel names
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chans = data.Properties.VariableNames;
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% get node names
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idx = strfind(chans, 'x');
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idx = cell2mat(cellfun(@(x)any(~isempty(x)),idx,'UniformOutput',false));
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nodes_x = {chans{idx}};
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idy = strfind(chans, 'y');
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idy = cell2mat(cellfun(@(x)any(~isempty(x)),idy,'UniformOutput',false));
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nodes_y = {chans{idy}};
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idz = strfind(chans, 'z');
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idz = cell2mat(cellfun(@(x)any(~isempty(x)),idz,'UniformOutput',false));
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nodes_z = {chans{idz}};
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figure;
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% allow for axis labels
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for k = 1:2:length(varargin)
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labelType = varargin{k};
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labelText = varargin{k+1};
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switch lower(labelType)
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case 'title'
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title(labelText);
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case 'xlabel'
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xlabel(labelText);
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case 'ylabel'
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ylabel(labelText);
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case 'zlabel'
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zlabel(labelText);
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otherwise
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warning('Unknown label type: %s', labelType);
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end
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end
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% 2D animate
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if strcmp(dimension,'2D')
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h = animatedline('Marker','o');
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grid on
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clearpoints(h);
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for k=1:size(data,2)
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clearpoints(h);
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x = table2array(data(k, nodes_x));
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z = table2array(data(k, nodes_z));
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addpoints(h,x,z)
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drawnow
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pause(step)
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end
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% 3D animate
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elseif strcmp(dimension,'3D')
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view(3);
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h = animatedline('Marker','o');
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grid on
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clearpoints(h);
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for k=1:size(data,2)
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clearpoints(h);
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x = table2array(data(k, nodes_x));
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y = table2array(data(k, nodes_y));
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z = table2array(data(k, nodes_z));
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addpoints(h,x,y,z)
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drawnow
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pause(step)
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end
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else
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error('Please make sure to specify the correct dimension!')
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end
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end
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