60d7073794
From https://github.com/Juanvvc/c172p-detailed.git Commit df6b2c5f4f75d000c5f5ef9c6cc4446784348f20
71 lines
3.3 KiB
Text
71 lines
3.3 KiB
Text
Setup for computing buoyancy forces and moments of a 3d shape using the
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Gerris Flow Solver, http://gfs.sourceforge.net/wiki/index.php/Main_Page
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1. The hull of the vessel needs to be described by a 3d model.
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The hull model must be a manifold
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It is preferable if the origin of the 3d model is the same as the
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origin of the FDM structural frame.
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2. Convert the hull 3d model to GTS format for use with Gerris.
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Example with the model originally in blender:
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1. Export the model in STL format.
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2. Convert the STL model to GTS format with the stl2gts tool (from the gts
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library). For unknown reasons the normals have to be reverted in this
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step.
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% gts2stl --revert < floats.stl > floats.gts.base
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3. Check the model with gtscheck
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% gtscheck -v < floats.gts.base
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If there are any problems, such as incompatible faces or non-manifold
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edges, the model is very likely not to work in the latter stages.
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Make a cleaned up version for the buoyancy computation.
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The model.gts.base will be the original for the various cases/configurations
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described below.
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3. Edit the reference length and solid model scaling in the buoyancy3D.gfs
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file.
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4. Prepare the cases/configurations of interest. A case/configuration is one
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position and orientation of the 3d model with respect to the water surface.
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Each case becomes a separate gerris3D run.
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The create_experiment.sh script can be used to create a set of cases.
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The script needs to be edited to set the location of the hydrodynamic
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reference point, HRP, (which should be close to the CG), the desired set
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of data points in roll and pitch, and finally the distance between the HRP
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and the water surface. The last parameter currently has to be manually
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entered in the script file for each set of cases.
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Example:
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(Uncomment the distance line "HAGL=1.2192 # 4ft")
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% ./create_experiment.sh 20150529 p4ft
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(Uncomment the distance line "HAGL=HAGL=1.524 # 5ft")
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% ./create_experiment.sh 20150529 p5ft
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...
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This creates a base directory 20150529 with a multitude of p4ft_* and
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p5ft_* etc. subdirectories, each one being a case.
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5. Run the cases.
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% ./run_experiment.sh <base dir> <name base>
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Example:
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% ./run_experiment.sh 20150529 p4ft
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You can also leave out the second argument to run all cases in 20150529.
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Do consider running a suitable number of cases in parallel
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./run_experiment.sh calls to speed up this step. E.g. as many as you have
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CPU cores if you don't run out of memory.
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6. Summarize the case results into tables that can be copied into a JSBSim
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hydrodynamics configuration.
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% ./summarize_experiment.sh <base dir>/<name base>
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Will summarize the cases (roll and pitch) for one distance between the
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HRP and the water surface.
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This script must be edited to set the roll and pitch range and the
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scaling factors used.
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The resulting "coefficients" are scaled for imperial units and expressed
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as F/(Rho*G) and M/(Rho*G).
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Example:
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% ./summarize_experiment.sh 20150529/p4ft
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See Systems/c172p-hydrodynamics.xml to see where the tables for buoyancy
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lift force and pitch and roll moment "coefficients" go and how the
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"coefficients" are transformed back into forces and moments.
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(Search for 'breakPoint="4.0"'.)
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