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TestExternalReactions.py
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# TestExternalReactions.py
#
# Regression test to check that external reactions are working correctly.
#
# Copyright (c) 2017 Bertrand Coconnier
#
# This program is free software; you can redistribute it and/or modify it under
# the terms of the GNU General Public License as published by the Free Software
# Foundation; either version 3 of the License, or (at your option) any later
# version.
#
# This program is distributed in the hope that it will be useful, but WITHOUT
# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
# FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
# details.
#
# You should have received a copy of the GNU General Public License along with
# this program; if not, see <http://www.gnu.org/licenses/>
#
import numpy as np
import xml.etree.ElementTree as et
from JSBSim_utils import JSBSimTestCase, CreateFDM, RunTest, CopyAircraftDef
def getParachuteArea(tree):
parachute_area = 1.0
for value in tree.getroot().findall('external_reactions/force/function/product/value'):
parachute_area *= float(value.text)
return parachute_area
class TestExternalReactions(JSBSimTestCase):
def getLeverArm(self, fdm, name):
lax = (fdm['external_reactions/'+name+'/location-x-in']
- fdm['inertia/cg-x-in'])
lay = (fdm['external_reactions/'+name+'/location-y-in']
- fdm['inertia/cg-y-in'])
laz = (fdm['external_reactions/'+name+'/location-z-in']
- fdm['inertia/cg-z-in'])
# Convert from inches in the structural frame to feet in the body frame.
return np.array([-lax, lay, -laz])/12
def test_wind_frame(self):
script_path = self.sandbox.path_to_jsbsim_file('scripts',
'ball_chute.xml')
fdm = CreateFDM(self.sandbox)
fdm.load_script(script_path)
fdm.run_ic()
self.assertAlmostEqual(fdm['external_reactions/parachute/location-x-in'],
12.0)
self.assertAlmostEqual(fdm['external_reactions/parachute/location-y-in'],
0.0)
self.assertAlmostEqual(fdm['external_reactions/parachute/location-z-in'],
0.0)
self.assertAlmostEqual(fdm['external_reactions/parachute/x'], -1.0)
self.assertAlmostEqual(fdm['external_reactions/parachute/y'], 0.0)
self.assertAlmostEqual(fdm['external_reactions/parachute/z'], 0.0)
tree, _, _ = CopyAircraftDef(script_path, self.sandbox)
parachute_area = getParachuteArea(tree)
while fdm.run():
Tw2b = fdm.get_auxiliary().get_Tw2b()
mag = fdm['aero/qbar-psf'] * fdm['fcs/parachute_reef_pos_norm']*parachute_area
f = Tw2b * np.matrix([-1.0, 0.0, 0.0]).T * mag
self.assertAlmostEqual(fdm['forces/fbx-external-lbs'], f[0, 0])
self.assertAlmostEqual(fdm['forces/fby-external-lbs'], f[1, 0])
self.assertAlmostEqual(fdm['forces/fbz-external-lbs'], f[2, 0])
m = np.cross(self.getLeverArm(fdm,'parachute'),
np.array([f[0,0], f[1,0], f[2, 0]]))
self.assertAlmostEqual(fdm['moments/l-external-lbsft'], m[0])
self.assertAlmostEqual(fdm['moments/m-external-lbsft'], m[1])
self.assertAlmostEqual(fdm['moments/n-external-lbsft'], m[2])
def test_body_frame(self):
fdm = CreateFDM(self.sandbox)
fdm.load_model('f16')
fdm.load_ic('reset00.xml', True)
fdm.run_ic()
self.assertAlmostEqual(fdm['external_reactions/pushback/location-x-in'],
-2.98081)
self.assertAlmostEqual(fdm['external_reactions/pushback/location-y-in'],
0.0)
self.assertAlmostEqual(fdm['external_reactions/pushback/location-z-in'],
-1.9683)
self.assertAlmostEqual(fdm['external_reactions/pushback/x'], 1.0)
self.assertAlmostEqual(fdm['external_reactions/pushback/y'], 0.0)
self.assertAlmostEqual(fdm['external_reactions/pushback/z'], 0.0)
self.assertAlmostEqual(fdm['external_reactions/pushback/magnitude'],
0.0)
self.assertAlmostEqual(fdm['external_reactions/hook/location-x-in'],
100.669)
self.assertAlmostEqual(fdm['external_reactions/hook/location-y-in'],
0.0)
self.assertAlmostEqual(fdm['external_reactions/hook/location-z-in'],
-28.818)
dx = -0.9995
dz = 0.01
fhook = np.array([dx, 0.0, dz])
fhook /= np.linalg.norm(fhook)
self.assertAlmostEqual(fdm['external_reactions/hook/x'], fhook[0])
self.assertAlmostEqual(fdm['external_reactions/hook/y'], fhook[1])
self.assertAlmostEqual(fdm['external_reactions/hook/z'], fhook[2])
self.assertAlmostEqual(fdm['external_reactions/hook/magnitude'], 0.0)
self.assertAlmostEqual(fdm['forces/fbx-external-lbs'], 0.0)
self.assertAlmostEqual(fdm['forces/fby-external-lbs'], 0.0)
self.assertAlmostEqual(fdm['forces/fbz-external-lbs'], 0.0)
self.assertAlmostEqual(fdm['moments/l-external-lbsft'], 0.0)
self.assertAlmostEqual(fdm['moments/m-external-lbsft'], 0.0)
self.assertAlmostEqual(fdm['moments/n-external-lbsft'], 0.0)
# Check the 'pushback' external force alone
fdm['/sim/model/pushback/position-norm'] = 1.0
fdm['/sim/model/pushback/target-speed-fps'] = 1.0
fdm['/sim/model/pushback/kp'] = 0.05
fdm.run()
fpb = np.array([1.0, 0.0, 0.0]) * 0.05
self.assertAlmostEqual(fdm['external_reactions/pushback/magnitude'],
0.05)
self.assertAlmostEqual(fdm['forces/fbx-external-lbs'], fpb[0])
self.assertAlmostEqual(fdm['forces/fby-external-lbs'], fpb[1])
self.assertAlmostEqual(fdm['forces/fbz-external-lbs'], fpb[2])
m = np.cross(self.getLeverArm(fdm, 'pushback'), fpb)
self.assertAlmostEqual(fdm['moments/l-external-lbsft'], m[0])
self.assertAlmostEqual(fdm['moments/m-external-lbsft'], m[1])
self.assertAlmostEqual(fdm['moments/n-external-lbsft'], m[2])
# Reset the 'pushback' external force to zero
fdm['/sim/model/pushback/position-norm'] = 0.0
fdm.run()
self.assertAlmostEqual(fdm['external_reactions/pushback/magnitude'], 0.0)
self.assertAlmostEqual(fdm['forces/fbx-external-lbs'], 0.0)
self.assertAlmostEqual(fdm['forces/fby-external-lbs'], 0.0)
self.assertAlmostEqual(fdm['forces/fbz-external-lbs'], 0.0)
self.assertAlmostEqual(fdm['moments/l-external-lbsft'], 0.0)
self.assertAlmostEqual(fdm['moments/m-external-lbsft'], 0.0)
self.assertAlmostEqual(fdm['moments/n-external-lbsft'], 0.0)
# Check the 'hook' external force alone
fdm['external_reactions/hook/magnitude'] = 10.0
fhook *= 10.0
fdm.run()
self.assertAlmostEqual(fdm['forces/fbx-external-lbs'], fhook[0])
self.assertAlmostEqual(fdm['forces/fby-external-lbs'], fhook[1])
self.assertAlmostEqual(fdm['forces/fbz-external-lbs'], fhook[2])
m = np.cross(self.getLeverArm(fdm, 'hook'), fhook)
self.assertAlmostEqual(fdm['moments/l-external-lbsft'], m[0])
self.assertAlmostEqual(fdm['moments/m-external-lbsft'], m[1])
self.assertAlmostEqual(fdm['moments/n-external-lbsft'], m[2])
# Add the 'pushback' force to the hook force and check that the global
# external forces is the sum of the push back force and the hook force.
fdm['/sim/model/pushback/position-norm'] = 1.0
fdm.run()
fp = fdm['systems/pushback/force']
fpb = np.array([1.0, 0.0, 0.0]) * fp
f = fhook + fpb
self.assertAlmostEqual(fdm['external_reactions/pushback/magnitude'], fp)
self.assertAlmostEqual(fdm['forces/fbx-external-lbs'], f[0])
self.assertAlmostEqual(fdm['forces/fby-external-lbs'], f[1])
self.assertAlmostEqual(fdm['forces/fbz-external-lbs'], f[2])
# Modify the push back force direction and check that the global external
# force is modified accordingly.
fdm['external_reactions/pushback/x'] = 1.5
fdm['external_reactions/pushback/y'] = 0.1
fdm.run()
fp = fdm['systems/pushback/force']
fpb = np.array([1.5, 0.1, 0.0]) * fp
f = fhook + fpb
self.assertAlmostEqual(fdm['external_reactions/pushback/magnitude'], fp)
self.assertAlmostEqual(fdm['forces/fbx-external-lbs'], f[0])
self.assertAlmostEqual(fdm['forces/fby-external-lbs'], f[1])
self.assertAlmostEqual(fdm['forces/fbz-external-lbs'], f[2])
m = (np.cross(self.getLeverArm(fdm, 'pushback'), fpb)
+ np.cross(self.getLeverArm(fdm, 'hook'), fhook))
self.assertAlmostEqual(fdm['moments/l-external-lbsft'], m[0])
self.assertAlmostEqual(fdm['moments/m-external-lbsft'], m[1])
self.assertAlmostEqual(fdm['moments/n-external-lbsft'], m[2])
fdm['external_reactions/hook/location-y-in'] = 50.0
fdm.run()
fp = fdm['systems/pushback/force']
fpb = np.array([1.5, 0.1, 0.0]) * fp
f = fhook + fpb
self.assertAlmostEqual(fdm['external_reactions/pushback/magnitude'], fp)
self.assertAlmostEqual(fdm['forces/fbx-external-lbs'], f[0])
self.assertAlmostEqual(fdm['forces/fby-external-lbs'], f[1])
self.assertAlmostEqual(fdm['forces/fbz-external-lbs'], f[2])
m = (np.cross(self.getLeverArm(fdm, 'pushback'), fpb)
+ np.cross(self.getLeverArm(fdm, 'hook'), fhook))
self.assertAlmostEqual(fdm['moments/l-external-lbsft'], m[0])
self.assertAlmostEqual(fdm['moments/m-external-lbsft'], m[1])
self.assertAlmostEqual(fdm['moments/n-external-lbsft'], m[2])
def test_moment(self):
script_path = self.sandbox.path_to_jsbsim_file('scripts',
'ball_chute.xml')
tree, aircraft_name, _ = CopyAircraftDef(script_path, self.sandbox)
extReact_element = tree.getroot().find('external_reactions')
moment_element = et.SubElement(extReact_element, 'moment')
moment_element.attrib['name'] = 'parachute'
moment_element.attrib['frame'] = 'WIND'
direction_element = et.SubElement(moment_element, 'direction')
x_element = et.SubElement(direction_element, 'x')
x_element.text = '0.2'
y_element = et.SubElement(direction_element, 'y')
y_element.text = '0.0'
z_element = et.SubElement(direction_element, 'z')
z_element.text = '-1.5'
tree.write(self.sandbox('aircraft', aircraft_name,
aircraft_name+'.xml'))
fdm = CreateFDM(self.sandbox)
fdm.set_aircraft_path('aircraft')
fdm.load_script(script_path)
fdm.run_ic()
mDir = np.array([0.2, 0.0, -1.5])
mDir /= np.linalg.norm(mDir)
self.assertAlmostEqual(fdm['external_reactions/parachute/l'], mDir[0])
self.assertAlmostEqual(fdm['external_reactions/parachute/m'], mDir[1])
self.assertAlmostEqual(fdm['external_reactions/parachute/n'], mDir[2])
fdm['external_reactions/parachute/magnitude-lbsft'] = -3.5
parachute_area = getParachuteArea(tree)
while fdm.run():
Tw2b = fdm.get_auxiliary().get_Tw2b()
mag = fdm['aero/qbar-psf'] * fdm['fcs/parachute_reef_pos_norm']*parachute_area
f = Tw2b * np.matrix([-1.0, 0.0, 0.0]).T * mag
self.assertAlmostEqual(fdm['forces/fbx-external-lbs'], f[0, 0])
self.assertAlmostEqual(fdm['forces/fby-external-lbs'], f[1, 0])
self.assertAlmostEqual(fdm['forces/fbz-external-lbs'], f[2, 0])
m = -3.5 * Tw2b * np.matrix(mDir).T
fm = np.cross(self.getLeverArm(fdm,'parachute'),
np.array([f[0,0], f[1,0], f[2, 0]]))
self.assertAlmostEqual(fdm['moments/l-external-lbsft'], m[0, 0] + fm[0])
self.assertAlmostEqual(fdm['moments/m-external-lbsft'], m[1, 0] + fm[1])
self.assertAlmostEqual(fdm['moments/n-external-lbsft'], m[2, 0] + fm[2])
RunTest(TestExternalReactions)