NEMOH |
 
|
NEMOH |
|
This section outlines how the relevant data is obtained from NEMOH and converted into Flexcom.
NEMOH is slightly different from both WAMIT and AQWA in that not all the relevant information is contained in one single formatted output file. This requires the NEMOH output file and folder structure to be intact and as follows:
• Nemoh Directory
o'Nemoh.cal' : Output file
o'mesh' : Directory
↳ 'KH.dat' : Hydrostatic stiffness data
o'results' : Directory
↳ 'ExicationForce.tec' : Force RAO data
↳ 'RadiationCoefficients.tec' : Added mass and radiation damping coefficients
The Nemoh.cal file is the main input file to the Hydrodynamic Data Importer. This is parsed first and the 'Description of floating bodies' section is read for the number of degrees of freedom and number of resulting generalised forces.
Nemoh.cal
--- Environment -------------------------------------------------------------------------
1025.0 ! RHO ! KG/M**3 ! Sea water density
9.81 ! G ! M/S**2 ! Gravity
0. ! DEPTH ! M ! Water depth (0 for deep water)
0. 0. ! XEFF YEFF ! M ! Wave measurement point
--- Description of floating bodies ------------------------------------------------------
1 ! Number of bodies
--- Body 1 ------------------------------------------------------------------------------
Meshes\Cylinder.dat ! Name of mesh file
500 280 ! Number of points and number of panels
6 ! Number of degrees of freedom
1 1. 0. 0. 0. 0. 0. ! 1 for translation, 2 for rotation followed by direction vector and axis for rotation. In this example, it is surge
1 0. 1. 0. 0. 0. 0. ! Sway
1 0. 0. 1. 0. 0. 0. ! Heave
2 1. 0. 0. 0. 0. -7.5 ! Roll about gravity centre
2 0. 1. 0. 0. 0. -7.5 ! Pitch about gravity centre
2 0. 0. 1. 0. 0. -7.5 ! Pitch about gravity centre
6 ! Number of resulting generalised forces
1 1. 0. 0. 0. 0. 0. ! Force along x axis
1 0. 1. 0. 0. 0. 0. ! Force along y axis
1 0. 0. 1. 0. 0. 0. ! Force along z axis
2 1. 0. 0. 0. 0. -7.5 ! Moment force along x axis about gravity centre
2 0. 1. 0. 0. 0. -7.5 ! Moment force along y axis about gravity centre
2 0. 0. 1. 0. 0. -7.5 ! Moment force along z axis about gravity centre
0 ! Number of lines of additional information
The relevant Hydrodynamic Stiffness data is located in the 'KH.dat' file in the 'mesh' directory. The relevant data is parsed from lines 3, 4 & 5:
0.0000000E+00 0.0000000E+00 0.0000000E+00 0.0000000E+00 0.0000000E+00 0.0000000E+00
0.0000000E+00 0.0000000E+00 0.0000000E+00 0.0000000E+00 0.0000000E+00 0.0000000E+00
0.0000000E+00 0.0000000E+00 -0.1093750E+00 0.0000000E+00 0.3255625E+03 0.0000000E+00
0.0000000E+00 0.0000000E+00 0.0000000E+00 -0.8896512E+08 0.0000000E+00 0.0000000E+00
0.0000000E+00 0.0000000E+00 0.3255625E+03 0.0000000E+00 -0.8921333E+08 0.0000000E+00
0.0000000E+00 0.0000000E+00 0.0000000E+00 0.0000000E+00 0.0000000E+00 0.0000000E+00
The relevant Added Mass and Radiation Damping data is located in the 'RadiationCoefficients.tec' file in the 'results' directory. The relevant data is parsed from each line according to the degrees of freedom requested in the Nemoh.cal file.
VARIABLES="w (rad/s)"
"A 1 1" "B 1 1"
"A 1 2" "B 1 2"
"A 1 3" "B 1 3"
Zone t="Motion of body 1 in DoF 1",I= 20,F=POINT
0.3000000E-01 0.6992227E+06 0.5643575E+01 -0.2606135E+03 -0.5823575E-02 -0.4416792E+07 -0.3034381E+02
0.3442105E+00 0.7568660E+06 0.1010863E+05 -0.3684811E+03 -0.1307687E+02 -0.4841597E+07 -0.5831523E+05
0.6584210E+00 0.8639779E+06 0.1124563E+06 -0.1008213E+04 -0.4749821E+03 -0.6265692E+07 -0.8083449E+06
0.9726315E+00 0.7227339E+06 0.6939101E+06 0.2187267E+04 -0.7428232E+03 -0.6771008E+07 -0.7490646E+07
0.1286842E+01 0.1599056E+05 0.1923467E+06 0.5095169E+02 0.1706791E+04 0.4906552E+07 -0.5231804E+07
The relevant Force RAO data is located in the 'ExicationForce.tec' file in the 'results' directory. The relevant data is parsed from each line according to the degrees of freedom requested in the Nemoh.cal file.
VARIABLES="w (rad/s)"
"abs(F 1 1)" "angle(F 1 1)"
"abs(F 1 2)" "angle(F 1 2)"
"abs(F 1 3)" "angle(F 1 3)"
Zone t="Diffraction force - beta = 0.000 deg",I= 20,F=POINT
0.3000000E-01 0.5227926E+05 -0.1570717E+01 0.4654428E+04 0.3140393E+01 0.2810593E+06 0.1570906E+01
0.3442105E+00 0.6040670E+06 -0.1559181E+01 0.6800956E+06 -0.3135197E+01 0.3484404E+07 0.1582813E+01
0.6584210E+00 0.1166256E+07 -0.1502177E+01 0.3596944E+07 -0.2886035E+01 0.8370106E+07 0.1640625E+01
0.9726315E+00 0.1698730E+07 -0.1172833E+01 0.3424150E+07 -0.1516424E+01 0.1827553E+08 0.1969514E+01
0.1286842E+01 0.5728897E+06 -0.2830505E+00 0.1075440E+07 -0.1654646E+01 0.1513591E+08 0.2858327E+01
•The order of translational RAOs is changed from NEMOH format (Surge, Sway, Heave) to Flexcom format (Heave, Surge, Sway).
•The order of rotational RAOs is changed from NEMOH format (Roll, Pitch, Yaw) to Flexcom format (Yaw, Roll, Pitch).
•The definition of wave heading is transformed such that a zero degree heading, which is incident on the stern in the NEMOH format, is incident on the bow in the Flexcom format.
•The units of wave frequency are changed from radians/sec (NEMOH format) to Hertz (Flexcom format).
•Full details regarding NEMOH's modelling capabilities and its underlying theory are available from the NEMOH website.
•Refer to Installing and Running NEMOH if you would like to install and run the software on your own computer.