303 lines
9.2 KiB
XML
303 lines
9.2 KiB
XML
<!--
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Airship added/virtual mass model for JSBSim.
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Copyright (C) 2008 - 2018 Anders Gidenstam (anders(at)gidenstam.org)
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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-->
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<system name="added-mass">
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<documentation>
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This system computes forces and moments due to added/virtual mass.
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The model is based on
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[Max M. Munk, "Aerodynamic forces on airship hulls", NACA report 184, 1924]
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and the introduction in
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[Christopher J. Atkinson, Robert G. Urso, "Modeling of Apparent Mass Effects
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for the Real-Time Simulation of a Hybrid Airship", AIAA Modeling and
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Simulation Technologies Conference, Aug 2006].
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Usage:
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Define the following properties:
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aero/constants/volume-ft3
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aero/constants/length-diameter-ft2 (length^2 + diameter^2)
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aero/constants/added-mass/k-axial (all three are positive but
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aero/constants/added-mass/k-transverse can be entered as negative
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aero/constants/added-mass/k-rotational for backwards compatibility)
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aero/constants/added-mass/tweak-factor (1.0 is the standard value)
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aero/constants/added-mass/k-traverse (old misspelling, can be given
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to work with older FlightGear)
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Define the following external forces and moments:
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<force name="added-mass-bx" frame="BODY">
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<location unit="">
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{ AERORP }
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</location>
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<direction>
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<x> 1.0 </x>
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<y> 0.0 </y>
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<z> 0.0 </z>
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</direction>
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</force>
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<force name="added-mass-by" frame="BODY">
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<location unit="">
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{ AERORP }
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</location>
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<direction>
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<x> 0.0 </x>
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<y> 1.0 </y>
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<z> 0.0 </z>
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</direction>
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</force>
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<force name="added-mass-bz" frame="BODY">
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<location unit="">
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{ AERORP }
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</location>
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<direction>
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<x> 0.0 </x>
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<y> 0.0 </y>
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<z> 1.0 </z>
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</direction>
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</force>
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<moment name="added-mass-pitch" frame="BODY" unit="LBSFT">
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<direction>
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<x> 0.0 </x>
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<y> 1.0 </y>
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<z> 0.0 </z>
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</direction>
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</moment>
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<moment name="added-mass-roll" frame="BODY" unit="LBSFT">
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<direction>
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<x> 1.0 </x>
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<y> 0.0 </y>
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<z> 0.0 </z>
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</direction>
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</moment>
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<moment name="added-mass-yaw" frame="BODY" unit="LBSFT">
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<direction>
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<x> 0.0 </x>
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<y> 0.0 </y>
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<z> 1.0 </z>
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</direction>
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</moment>
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The old deprecated force based external moment implementation below is still
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supported.
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<force name="added-mass-pitch[0]" frame="BODY">
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<location unit="">
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<x> AERORP X </x>
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<y> AERORP Y </y>
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<z> AERORP Z - 0.3048 </z>
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</location>
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<direction>
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<x> 1.0 </x>
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<y> 0.0 </y>
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<z> 0.0 </z>
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</direction>
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</force>
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<force name="added-mass-pitch[1]" frame="BODY">
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<location unit="M">
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<x> AERORP X </x>
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<y> AERORP Y </y>
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<z> AERORP Z + 0.3048 </z>
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</location>
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<direction>
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<x> 1.0 </x>
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<y> 0.0 </y>
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<z> 0.0 </z>
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</direction>
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</force>
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<force name="added-mass-yaw[0]" frame="BODY">
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<location unit="M">
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<x> AERORP X </x>
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<y> AERORP Y - 0.3048 </y>
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<z> 0.0 </z>
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</location>
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<direction>
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<x> 1.0 </x>
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<y> 0.0 </y>
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<z> 0.0 </z>
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</direction>
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</force>
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<force name="added-mass-yaw[1]" frame="BODY">
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<location unit="M">
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<x> AERORP X </x>
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<y> AERORP Y + 0.3048 </y>
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<z> 0.0 </z>
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</location>
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<direction>
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<x> 1.0 </x>
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<y> 0.0 </y>
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<z> 0.0 </z>
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</direction>
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</force>
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</documentation>
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<channel name="startup">
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<!-- Allow the vehicle state to stabilize. -->
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<fcs_function name="aero/added-mass/active">
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<function>
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<min>
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<property> aero/constants/added-mass/tweak-factor </property>
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<max>
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<value> 0.0 </value>
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<difference>
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<property> simulation/sim-time-sec </property>
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<value> 2.0 </value>
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</difference>
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</max>
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</min>
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</function>
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</fcs_function>
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</channel>
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<property>aero/constants/added-mass/k-transverse</property>
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<property>aero/constants/added-mass/k-traverse</property>
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<channel name="backward-compatibility">
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<!-- Allow vehicles still using the old misspelled k-traverse coefficient. -->
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<switch name="aero/constants/added-mass/k-transverse-final">
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<default value="aero/constants/added-mass/k-transverse"/>
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<test logic="AND" value="aero/constants/added-mass/k-transverse">
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aero/constants/added-mass/k-transverse NE 0.0
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</test>
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<test logic="AND" value="aero/constants/added-mass/k-traverse">
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aero/constants/added-mass/k-traverse NE 0.0
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</test>
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</switch>
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</channel>
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<channel name="translational">
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<fcs_function name="aero/added-mass/force-bx-lbs">
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<function>
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<product>
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<value>-1.0</value>
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<property> aero/added-mass/active </property>
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<property> atmosphere/rho-slugs_ft3 </property>
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<abs><property> aero/constants/added-mass/k-axial </property></abs>
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<property> aero/constants/volume-ft3 </property>
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<property> accelerations/udot-ft_sec2 </property>
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</product>
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</function>
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<output> external_reactions/added-mass-bx/magnitude </output>
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</fcs_function>
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<fcs_function name="aero/added-mass/force-by-lbs">
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<function>
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<product>
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<value>-1.0</value>
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<property> aero/added-mass/active </property>
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<property> atmosphere/rho-slugs_ft3 </property>
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<abs><property> aero/constants/added-mass/k-transverse-final </property></abs>
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<property> aero/constants/volume-ft3 </property>
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<property> accelerations/vdot-ft_sec2 </property>
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</product>
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</function>
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<output> external_reactions/added-mass-by/magnitude </output>
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</fcs_function>
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<fcs_function name="aero/added-mass/force-bz-lbs">
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<function>
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<product>
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<value>-1.0</value>
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<property> aero/added-mass/active </property>
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<property> atmosphere/rho-slugs_ft3 </property>
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<abs><property> aero/constants/added-mass/k-transverse-final </property></abs>
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<property> aero/constants/volume-ft3 </property>
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<property> accelerations/wdot-ft_sec2 </property>
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</product>
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</function>
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<output> external_reactions/added-mass-bz/magnitude </output>
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</fcs_function>
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</channel>
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<channel name="rotational">
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<fcs_function name="aero/added-mass/pitch-moment-lbsft">
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<function>
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<product>
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<property> aero/added-mass/active </property>
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<value>-0.05 </value>
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<property> atmosphere/rho-slugs_ft3 </property>
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<abs><property> aero/constants/added-mass/k-rotational </property></abs>
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<property> aero/constants/volume-ft3 </property>
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<property> aero/constants/length-diameter-ft2 </property>
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<property> accelerations/qdot-rad_sec2 </property>
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</product>
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</function>
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</fcs_function>
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<fcs_function name="aero/added-mass/yaw-moment-lbsft">
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<function>
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<product>
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<property> aero/added-mass/active </property>
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<value>-0.05 </value>
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<property> atmosphere/rho-slugs_ft3 </property>
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<abs><property> aero/constants/added-mass/k-rotational </property></abs>
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<property> aero/constants/volume-ft3 </property>
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<property> aero/constants/length-diameter-ft2 </property>
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<property> accelerations/rdot-rad_sec2 </property>
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</product>
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</function>
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</fcs_function>
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<pure_gain name="aero/added-mass/pitch-moment/moment-lbsft">
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<input>aero/added-mass/pitch-moment-lbsft</input>
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<gain>1.0</gain>
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<output>external_reactions/added-mass-pitch/magnitude-lbsft</output>
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</pure_gain>
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<pure_gain name="aero/added-mass/pitch-moment/force-lbs[0]">
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<input> aero/added-mass/pitch-moment-lbsft </input>
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<gain>-0.5</gain>
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<output> external_reactions/added-mass-pitch[0]/magnitude </output>
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</pure_gain>
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<pure_gain name="aero/added-mass/pitch-moment/force-lbs[1]">
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<input> aero/added-mass/pitch-moment-lbsft </input>
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<gain>0.5</gain>
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<output> external_reactions/added-mass-pitch[1]/magnitude </output>
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</pure_gain>
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<pure_gain name="aero/added-mass/yaw-moment/moment-lbsft">
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<input>aero/added-mass/yaw-moment-lbsft</input>
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<gain>1.0</gain>
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<output>external_reactions/added-mass-yaw/magnitude-lbsft</output>
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</pure_gain>
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<pure_gain name="aero/added-mass/yaw-moment/force-lbs[0]">
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<input> aero/added-mass/yaw-moment-lbsft </input>
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<gain>-0.5</gain>
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<output> external_reactions/added-mass-yaw[0]/magnitude </output>
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</pure_gain>
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<pure_gain name="aero/added-mass/yaw-moment/force-lbs[1]">
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<input> aero/added-mass/yaw-moment-lbsft </input>
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<gain>0.5</gain>
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<output> external_reactions/added-mass-yaw[1]/magnitude </output>
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</pure_gain>
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</channel>
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</system>
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