Comments (6)
Hi, have you considered just transforming the existing WAMIT data files that are provided in the repo? If I'm thinking about this correctly, the math to convert the data from the current reference point at z=0 to a reference point with z=-14.4 could be implemented in a script -- probably much more quickly than it would take to recompute all the data files with WAMIT. The entries that would need to be adjusted would be the roll and pitch DOFs, and any cross-coupling (off-diagonal) entries involving those DOFs.
from iea-15-240-rwt.
Hi @hachikoi1
I agree with @mattEhall that it's probably better to transform the existing WAMIT data about z=0 to about z=-14.4 m. Make sure you account for the fact that both the moments and the rotation (roll and pitch) are about a new reference point.
Also, it is necessary to approximate the first-order motion response of the whole system when computing the second-order wave excitation. That's why XCG=0,0,-2.32m in the second-order input file. This XCG is that of the whole system including the tower and the turbine, not just the platform.
from iea-15-240-rwt.
Dear mattEhall and luwang00
Thank you very much for your suggestion. I will try the conversion method you described.
Best regards,
from iea-15-240-rwt.
Dear mattEhall and luwang00
Thank you very much for your advice. If I understand correctly, you mean that the hydrodynamic coefficients at COG (0 0 -14.4) can be evaluated based on those at PRP (0 0 0) using coordinate conversion, similar to the method mentioned in WEC-Sim/WEC-Sim#1051.
Take added mass term as an example. Theoretically, we can get added mass load and velocity at COG based on the added mass load, displacement and velocity at PRP. With the constraint conditions of Add_{COG}(1,1) = Add_{PRP}(1,1), Add_{COG}(2,2) = Add_{PRP}(2,2), Add_{COG}(3,3) = Add_{PRP}(3,3), Add_{COG}(6,6) = Add_{PRP}(6,6) and Add_{COG}(4,4) = Add_{COG}(5,5), we can ontain added mass matrix at COG, by solving the equation system of F_{addCOG} = -Add_{COG}*a_Cog at each time step, totalling 31 quantities. And multiple time steps must be introduced into the system of equations to solve them simultaneously
However, the method may give rise to unstable results for radiation and wave excitation terms, i.e. the results of the conversion vary considerably at each time step.
Or you mean that the conversion of the reference point of hydrodynamic coefficients can be achieved by multiplying the hydrodynamic coefficient matrix by conversion matrix?
Best regards,
from iea-15-240-rwt.
A coordinate conversion is what I had in mind. I'm not quickly grasping what you wrote or what is in the WEC-Sim link. That said, the link looked to be about transforming the quadratic drag matrix. For what it's worth, that would be very difficult because that matrix is for nonlinear terms, so I don't think it would be possible to accurately shift its reference point.
I'm also not sure what you mean by "the method may give rise to unstable results for radiation and wave excitation terms". As far as I know, its a transformation of linear matrices and the results should be exact; there shouldn't be any effect on stability.
This function here is an example of the sort of transformation I was thinking of (for matrices): https://github.com/WISDEM/RAFT/blob/8c0445086969f480e76b9409087cbd56dce19437/raft/helpers.py#L321
https://github.com/WISDEM/RAFT/blob/8c0445086969f480e76b9409087cbd56dce19437/raft/helpers.py#L321
It is simpler for excitation because you just adjust the pitch and roll moments by adding the surge or sway forces multiplied by the z shift in the reference point.
Matt
from iea-15-240-rwt.
Dear mattEhall
Many thanks for your sharing.
Best regards,
Tianyuan
from iea-15-240-rwt.
Related Issues (20)
- Unexpected difference in platform motions(IEA 15MW Semi-sub) with and without a cable (Steep wave) HOT 1
- CAD models all show anti clockwise rotation HOT 1
- Running problem with IEA-15-240-RWT-UMaineSemi Openfast model HOT 1
- IEA-15-240-RWT-Umainesemi encountered bad real number HOT 4
- Why have I replaced the latest DISCON.IN, or is there an error HOT 1
- The VTK file can't be created when considering the difference-frequency 2nd-order wave kinematics? HOT 3
- When I run the IEA-15MW model, I am prompted with an error DISCON error.
- The ServoDyn module seems doesn't work HOT 3
- zsh: segmentation fault openfast IEA-15-240-RWT-Monopile.fst HOT 3
- A problem about some data of CarbonUD is 0 in lines 817, 818, and 819 of the IEA-15-240-RWT.yaml file HOT 5
- Confirmation of Mooring Line Diameter for the UMaineSemi Model HOT 4
- starting simulation of IEA-15MW RWT UMaineSemi HOT 3
- controller does not works in SIMA software HOT 1
- simulation error 15MW monopile with comphydro deactivated HOT 2
- BModes .bmi and _tower_secs.dat files for the tower of the UMaine SS HOT 9
- Damping ratios UMaine VoluturnUS-S FOWT HOT 3
- IEA-15-240-RWT-UMaineSemi Operational issues HOT 5
- QTF of UMaine VolturnUS-S platform calculated by Nemoh is inconsistent with the results given by WAMIT. HOT 5
- Time histories of free decay tests for each DoF HOT 2
- Deviations between the 6*6 stiffness through SONATA results and the origin BeamDyn blade data HOT 11
Recommend Projects
-
React
A declarative, efficient, and flexible JavaScript library for building user interfaces.
-
Vue.js
🖖 Vue.js is a progressive, incrementally-adoptable JavaScript framework for building UI on the web.
-
Typescript
TypeScript is a superset of JavaScript that compiles to clean JavaScript output.
-
TensorFlow
An Open Source Machine Learning Framework for Everyone
-
Django
The Web framework for perfectionists with deadlines.
-
Laravel
A PHP framework for web artisans
-
D3
Bring data to life with SVG, Canvas and HTML. 📊📈🎉
-
Recommend Topics
-
javascript
JavaScript (JS) is a lightweight interpreted programming language with first-class functions.
-
web
Some thing interesting about web. New door for the world.
-
server
A server is a program made to process requests and deliver data to clients.
-
Machine learning
Machine learning is a way of modeling and interpreting data that allows a piece of software to respond intelligently.
-
Visualization
Some thing interesting about visualization, use data art
-
Game
Some thing interesting about game, make everyone happy.
Recommend Org
-
Facebook
We are working to build community through open source technology. NB: members must have two-factor auth.
-
Microsoft
Open source projects and samples from Microsoft.
-
Google
Google ❤️ Open Source for everyone.
-
Alibaba
Alibaba Open Source for everyone
-
D3
Data-Driven Documents codes.
-
Tencent
China tencent open source team.
from iea-15-240-rwt.