Getting Started
Prerequisites
Python 3
The following Python packages: NumPy, MatPlotLib, yaml, scipy
Installation
Clone the MoorPy GitHub repository.
To install for development use:
run `python setup.py develop` or `pip install -e .` from the command line in the main MoorPy directory.
To install for non-development use:
run `python setup.py` or `pip install .` from the command line in the main MoorPy directory.
Examples
The MoorPy repository has an examples folder containing two example scripts:
manual_system.py constructs a mooring system from scratch using functions for creating each line and attachment point.
imported_system.py creates a mooring system by reading an included MoorDyn-style input file.
Running either of these scripts will produce a basic mooring system model that can be used in further analysis.
Creating a MoorPy System Manually
MoorPy has internal functions to facilitate the orderly creation of a mooring system. The following gives an example of how they work (from manual_system.py).
# ----- choose some system geometry parameters -----
depth = 600 # water depth [m]
angles = np.radians([60, 180, 300]) # line headings list [rad]
rAnchor = 1600 # anchor radius/spacing [m]
zFair = -21 # fairlead z elevation [m]
rFair = 20 # fairlead radius [m]
lineLength= 1800 # line unstretched length [m]
typeName = "chain1" # identifier string for the line type
# ----- set up the mooring system and floating body -----
# Create new MoorPy System and set its depth
ms = mp.System(depth=depth)
# add a line type
ms.setLineType(dnommm=120, material='chain', name=typeName) # this would be 120 mm chain
# Add a free, body at [0,0,0] to the system (including some properties to make it hydrostatically stiff)
ms.addBody(0, np.zeros(6), m=1e6, v=1e3, rM=100, AWP=1e3)
# For each line heading, set the anchor point, the fairlead point, and the line itself
for i, angle in enumerate(angles):
# create end Points for the line
ms.addPoint(1, [rAnchor*np.cos(angle), rAnchor*np.sin(angle), -depth]) # create anchor point (type 0, fixed)
ms.addPoint(1, [ rFair*np.cos(angle), rFair*np.sin(angle), zFair]) # create fairlead point (type 0, fixed)
# attach the fairlead Point to the Body (so it's fixed to the Body rather than the ground)
ms.bodyList[0].attachPoint(2*i+2, [rFair*np.cos(angle), rFair*np.sin(angle), zFair])
# add a Line going between the anchor and fairlead Points
ms.addLine(lineLength, typeName, pointA=2*i+1, pointB=2*i+2)
Note that both the fairlead and anchor points are set to type 1 (fixed). See the The API Page for more information about the methods used above.
Creating a MoorPy System from a MoorDyn Input File
A MoorPy System can be initialized by reading in a MoorDyn-style input file. This is simply done by passing the input file name when creating the System object (from imported_system.py):
ms = mp.System(file='the MoorDyn-style input file.txt')
The format of the input file is expected to follow the MoorDyn v2 format, an example of which is shown below:
MoorDyn v2 Input File
Sample for input to MoorPy
---------------------- LINE TYPES --------------------------------------------------
TypeName Diam Mass/m EA BA/-zeta EI Cd Ca CdAx CaAx
(name) (m) (kg/m) (N) (N-s/-) (N-m^2) (-) (-) (-) (-)
chain 0.2160 286.56 1.23e9 -1.0 0.00 1.00 1.00 0.00 0.00
----------------------- BODIES ------------------------------------------------------
ID Attachment X0 Y0 Z0 r0 p0 y0 Mass CG* I* Volume CdA* Ca*
(#) (-) (m) (m) (m) (deg) (deg) (deg) (kg) (m) (kg-m^2) (m^3) (m^2) (-)
1 coupled 0.00 0.00 -0.75 0.00 0.00 0.00 1.0e6 0.00 0.00 1.0e3 0.00 0.00
---------------------- POINTS -------------------------------------------------------
ID Attachment X Y Z Mass Volume CdA Ca
(#) (-) (m) (m) (m) (kg) (mˆ3) (m^2) (-)
1 Fixed 800.00 1385.64 -600.00 0.00 0.00 0.00 0.00
2 Body1 10.00 17.32 -21.00 0.00 0.00 0.00 0.00
3 Fixed -1600.00 0.00 -600.00 0.00 0.00 0.00 0.00
4 Body1 -20.00 0.00 -21.00 0.00 0.00 0.00 0.00
5 Fixed 800.00 -1385.64 -600.00 0.00 0.00 0.00 0.00
6 Body1 10.00 -17.32 -21.00 0.00 0.00 0.00 0.00
---------------------- LINES --------------------------------------------------------
ID LineType AttachA AttachB UnstrLen NumSegs LineOutputs
(#) (name) (#) (#) (m) (-) (-)
1 chain 1 2 1800.000 40 p
2 chain 3 4 1800.000 40 p
3 chain 5 6 1800.000 40 p
---------------------- OPTIONS ------------------------------------------------------
600.0 depth
--------------------- need this line ------------------------------------------------
Note that some parameters are only applicable to a dynamic model like MoorDyn, and are not used by MoorPy. Conversely, some Body parameters used by MoorPy for hydrostatics are not captured in a MoorDyn-style file and would need to be added as a second step after reading in the input file.
Running the MoorPy Model
Once the MoorPy System is set up, it can be analyzed, viewed, and manipulated using a handful of main functions, as well as a variety of additional helper functions for more specialized tasks.
Here is an example showing one of the possible functions to analyze a mooring system:
ms.initialize() # make sure everything's connected
ms.solveEquilibrium() # equilibrate
fig, ax = ms.plot() # plot the system in original configuration
ms.unload("sample.txt") # export to MD input file
ms.bodyList[0].f6Ext = np.array([3e6, 0, 0, 0, 0, 0]) # apply an external force on the body
ms.solveEquilibrium() # equilibrate
fig, ax = ms.plot(ax=ax, color='red') # plot the system in displaced configuration (on the same plot, in red)
Documentation Overview
An overview of how a mooring system is represented in MoorPy can be found in The Model Structure page.
More documentation and examples of other functions that can be applied to a MoorPy mooring system can be found in The Usage page.
Links to papers that cover MoorPy theory can be found in The Theory Page.
Descriptions of the MoorPy System class methods, the main way to interact with MoorPy programmatically, can be found in The API Page.