789
edits
Howto:Modelling hydrodynamics in JSBSim: Difference between revisions
Jump to navigation
Jump to search
Howto:Modelling hydrodynamics in JSBSim (view source)
Revision as of 14:02, 12 March 2017
, 12 March 2017→Modelling hydrodynamic coefficients: A bit more on planing drag.
(→Modelling hydrodynamic coefficients: Added a visualization of the planing model configuration.) |
(→Modelling hydrodynamic coefficients: A bit more on planing drag.) |
||
| Line 304: | Line 304: | ||
The system outputs lift, drag (Fbx) and side (Fby) forces as well as pitch and roll moments (yaw is missing presently) that need to be added into the corresponding channels of the craft specific hydrodynamics configuration. A visualization of the configuration is shown in the image below. | The system outputs lift, drag (Fbx) and side (Fby) forces as well as pitch and roll moments (yaw is missing presently) that need to be added into the corresponding channels of the craft specific hydrodynamics configuration. A visualization of the configuration is shown in the image below. | ||
[[File:Swedish Navy T21 class MTB-planing-surfaces.jpg|thumb|600px|center|The [[Swedish Navy T21 class MTB]] with the planing surfaces for the hydrodynamic-planing system marked yellow. The marker is placed at the hydrodynamic, hydro RP, reference point. Note that the system only supports flat planing surfaces but at planing speeds only the rearmost part of each surface will be in contact with water.]] | [[File:Swedish Navy T21 class MTB-planing-surfaces.jpg|thumb|600px|center|The [[Swedish Navy T21 class MTB]] with the planing surfaces for the hydrodynamic-planing system marked yellow. The marker is placed at the hydrodynamic, hydro RP, reference point. Note that the system only supports flat planing surfaces but at planing speeds only the rearmost part of each surface will be in contact with water, anyway.]] | ||
The integration of the planing drag into the craft specific hydrodynamics configuration is shown below. First the drag from the various surfaces is combined. | |||
<syntaxhighlight lang="xml"> | |||
<fcs_function name="hydro/planing-drag-lbs"> | |||
<function> | |||
<description>Drag due to planing.</description> | |||
<sum> | |||
<property>hydro/planing/forebody-induced-fbx-force-lbs</property> | |||
<property>hydro/planing/middlebody-induced-fbx-force-lbs</property> | |||
<property>hydro/planing/afterbody-induced-fbx-force-lbs</property> | |||
<property>hydro/planing/forebody-friction-fbx-force-lbs</property> | |||
<property>hydro/planing/middlebody-friction-fbx-force-lbs</property> | |||
<property>hydro/planing/afterbody-friction-fbx-force-lbs</property> | |||
</sum> | |||
</function> | |||
</fcs_function> | |||
</syntaxhighlight> | |||
Then it is included in the Body-X or drag channel total. Due to a potential implementation problem in hydrodynamics.xml (probably the coordinate frames issues as mentioned far above) the drag was included in the drag channel rather than in the Body-X channel. When included there it should always be positive (while in the Body-X channel it would almost always be negative), hence the added <abs>-element here. | |||
<syntaxhighlight lang="xml"> | |||
<fcs_function name="hydro/fdrag-lbs"> | |||
<function> | |||
<product> | |||
<property>hydro/active-norm</property> | |||
<sum> | |||
<property>hydro/displacement-drag-lbs</property> | |||
<property>hydro/rudder-drag-lbs</property> | |||
<abs> | |||
<property>hydro/planing-drag-lbs</property> | |||
</abs> | |||
</sum> | |||
</product> | |||
</function> | |||
</fcs_function> | |||
</syntaxhighlight> | |||
''''To be continued... '''' | ''''To be continued... '''' | ||