sphericalJointTest.py

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  1#+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
  2# This is an EXUDYN example
  3#
  4# Details:  Simulate Chain with 3D rigid bodies and SphericalJoint;
  5#           Also test MarkerNodePosition
  6#
  7# Author:   Johannes Gerstmayr
  8# Date:     2020-04-09
  9#
 10# Copyright:This file is part of Exudyn. Exudyn is free software. You can redistribute it and/or modify it under the terms of the Exudyn license. See 'LICENSE.txt' for more details.
 11#
 12#+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 13
 14import exudyn as exu
 15from exudyn.utilities import *
 16
 17useGraphics = True #without test
 18#+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 19#you can erase the following lines and all exudynTestGlobals related operations if this is not intended to be used as TestModel:
 20try: #only if called from test suite
 21    from modelUnitTests import exudynTestGlobals #for globally storing test results
 22    useGraphics = exudynTestGlobals.useGraphics
 23except:
 24    class ExudynTestGlobals:
 25        pass
 26    exudynTestGlobals = ExudynTestGlobals()
 27#+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 28
 29SC = exu.SystemContainer()
 30mbs = SC.AddSystem()
 31
 32nBodies = 4
 33color = [0.1,0.1,0.8,1]
 34s = 0.1 #width of cube
 35sx = 3*s #lengt of cube/body
 36cPosZ = 0.1 #offset of constraint in z-direction
 37zz = sx * (nBodies+1)*2 #max size of background
 38
 39background0 = GraphicsDataRectangle(-zz,-zz,zz,sx,color)
 40oGround=mbs.AddObject(ObjectGround(referencePosition= [0,0,0],
 41                                   visualization=VObjectGround(graphicsData= [background0])))
 42mPosLast = mbs.AddMarker(MarkerBodyPosition(bodyNumber = oGround,
 43                                            localPosition=[-sx,0,cPosZ*0]))
 44
 45#create a chain of bodies:
 46for i in range(nBodies):
 47    f = 0 #factor for initial velocities
 48    omega0 = [0,50.*f,20*f] #arbitrary initial angular velocity
 49    ep0 = eulerParameters0 #no rotation
 50    ep_t0 = AngularVelocity2EulerParameters_t(omega0, ep0)
 51
 52    p0 = [-sx+i*2*sx,0.,0] #reference position
 53    v0 = [0.2*f,0.,0.] #initial translational velocity
 54
 55    nRB = mbs.AddNode(NodeRigidBodyEP(referenceCoordinates=p0+ep0,
 56                                      initialVelocities=v0+list(ep_t0)))
 57    #nRB = mbs.AddNode(NodeRigidBodyEP(referenceCoordinates=[0,0,0,1,0,0,0], initialVelocities=[0,0,0,0,0,0,0]))
 58    oGraphics = GraphicsDataOrthoCubeLines(-sx,-s,-s, sx,s,s, [0.8,0.1,0.1,1])
 59    oRB = mbs.AddObject(ObjectRigidBody(physicsMass=2,
 60                                        physicsInertia=[6,1,6,0,0,0],
 61                                        nodeNumber=nRB,
 62                                        visualization=VObjectRigidBody(graphicsData=[oGraphics])))
 63
 64    mMassRB = mbs.AddMarker(MarkerBodyMass(bodyNumber = oRB))
 65    mbs.AddLoad(Gravity(markerNumber = mMassRB, loadVector=[0.,-9.81,0.])) #gravity in negative z-direction
 66
 67    if i==0:
 68        #mPos = mbs.AddMarker(MarkerBodyPosition(bodyNumber = oRB, localPosition = [-sx*0,0.,cPosZ*0]))
 69        mPos = mbs.AddMarker(MarkerNodePosition(nodeNumber=nRB))
 70    else:
 71        mPos = mbs.AddMarker(MarkerBodyPosition(bodyNumber = oRB, localPosition = [-sx,0.,cPosZ]))
 72
 73    #alternative with spring-damper:
 74    #mbs.AddObject(ObjectConnectorCartesianSpringDamper(markerNumbers = [mPosLast, mPos],
 75    #                                                   stiffness=[k,k,k], damping=[d,d,d])) #gravity in negative z-direction
 76    axes = [1,1,1]
 77    if (i==0):
 78        axes = [0,1,1]
 79
 80    mbs.AddObject(SphericalJoint(markerNumbers = [mPosLast, mPos], constrainedAxes=axes))
 81
 82    #marker for next chain body
 83    mPosLast = mbs.AddMarker(MarkerBodyPosition(bodyNumber = oRB, localPosition = [sx,0.,cPosZ]))
 84
 85
 86mbs.Assemble()
 87#exu.Print(mbs)
 88
 89simulationSettings = exu.SimulationSettings() #takes currently set values or default values
 90
 91fact = 1000
 92simulationSettings.timeIntegration.numberOfSteps = 1*fact
 93simulationSettings.timeIntegration.endTime = 0.001*fact
 94simulationSettings.solutionSettings.solutionWritePeriod = simulationSettings.timeIntegration.endTime/fact*10
 95simulationSettings.timeIntegration.verboseMode = 1
 96
 97simulationSettings.timeIntegration.newton.useModifiedNewton = True
 98simulationSettings.timeIntegration.generalizedAlpha.useIndex2Constraints = False
 99simulationSettings.timeIntegration.generalizedAlpha.useNewmark = False
100simulationSettings.timeIntegration.generalizedAlpha.spectralRadius = 0.6 #0.6 works well
101
102simulationSettings.solutionSettings.solutionInformation = "rigid body tests"
103SC.visualizationSettings.nodes.defaultSize = 0.05
104#simulationSettings.displayComputationTime = True
105#simulationSettings.displayStatistics = True
106
107if useGraphics:
108    exu.StartRenderer()
109    mbs.WaitForUserToContinue()
110
111mbs.SolveDynamic(simulationSettings)
112
113#+++++++++++++++++++++++++++++++++++++++++++++
114sol = mbs.systemData.GetODE2Coordinates();
115solref = mbs.systemData.GetODE2Coordinates(configuration=exu.ConfigurationType.Reference);
116#exu.Print('sol=',sol)
117u = 0
118for i in range(14): #take coordinates of first two bodies
119    u += abs(sol[i]+solref[i])
120
121exu.Print('solution of sphericalJointTest=',u)
122
123exudynTestGlobals.testError = u - (4.409080446574593) #up to 2021-06-28: 4.409080446580333; 2020-04-04: 4.409004179180698
124exudynTestGlobals.testResult = u
125
126
127if useGraphics:
128    #SC.WaitForRenderEngineStopFlag()
129    exu.StopRenderer() #safely close rendering window!