rigidBodyCOMtest.py

You can view and download this file on Github: rigidBodyCOMtest.py

  1#+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
  2# This is an EXUDYN example
  3#
  4# Details:  Test rigid body formulation for different center of mass (COM)
  5#
  6# Author:   Johannes Gerstmayr
  7# Date:     2020-04-22
  8#
  9# 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.
 10#
 11#+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 12
 13import exudyn as exu
 14from exudyn.utilities import *
 15from exudyn.FEM import *
 16
 17import numpy as np
 18
 19useGraphics = True #without test
 20#+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 21#you can erase the following lines and all exudynTestGlobals related operations if this is not intended to be used as TestModel:
 22try: #only if called from test suite
 23    from modelUnitTests import exudynTestGlobals #for globally storing test results
 24    useGraphics = exudynTestGlobals.useGraphics
 25except:
 26    class ExudynTestGlobals:
 27        pass
 28    exudynTestGlobals = ExudynTestGlobals()
 29#+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 30
 31SC = exu.SystemContainer()
 32mbs = SC.AddSystem()
 33
 34nBodies = 2
 35color = [0.1,0.1,0.8,1]
 36s = 0.1 #width of cube
 37sx = 3*s #length of cube/body
 38cPosZ = 0. #offset of constraint in z-direction
 39zz = sx * (nBodies+1)*2 #max size of background
 40
 41background0 = GraphicsDataRectangle(-zz,-zz,zz,2.5*sx,color)
 42oGround=mbs.AddObject(ObjectGround(referencePosition= [0,0,0],
 43                                   visualization=VObjectGround(graphicsData= [background0])))
 44
 45m=25
 46inertia=np.array([[10,1,2],
 47                  [ 1,7,3],
 48                  [ 2,3,6]])
 49
 50nodeList=[]
 51objectList=[]
 52for case in range(2):
 53    nRB=-1
 54    if case == 0:
 55        com=[0,0,0]
 56    else:
 57        #com=[0.4,0.6,1.3]
 58        com=[0.4,0.22,-0.35]
 59    zOff = 0.5*case*0
 60
 61    RBinertia = RigidBodyInertia(mass=m, inertiaTensor=inertia)
 62    #exu.Print("RBinertia orig =", RBinertia)
 63    RBinertia = RBinertia.Translated(com) #this includes the correct terms in inertia
 64
 65    if NormL2(RBinertia.com) != 0 and i==1:
 66        exu.Print("AddRigidBody COM=", RBinertia.com)
 67        exu.Print("inertia6D=", RBinertia.GetInertia6D())
 68    #exu.Print("RBinertia trans=", RBinertia)
 69    #exu.Print("inertia6D=", RBinertia.GetInertia6D())
 70    #exu.Print("inertia.com=", RBinertia.com)
 71    oRBlast = oGround
 72
 73    #create a chain of bodies:
 74    for i in range(nBodies):
 75        omega0 = [0,0,0] #arbitrary initial angular velocity
 76
 77        #Rotxyz:
 78        #ep0 = [0,0,0]
 79        #ep_t0 = [0,0,0]
 80
 81        p0 = VSub([i*2*sx+sx,0.,zOff],com) #reference position
 82        v0 = [0.,0.,0.] #initial translational velocity
 83
 84        color=[0.8,0.1,0.1,1]
 85        if case==0:
 86            color=[0.1,0.1,0.8,1]
 87
 88        oGraphics = GraphicsDataOrthoCubeLines(-sx+com[0],-s+com[1],-s+com[2], sx+com[0],s+com[1],s+com[2], color)
 89        d=0.02
 90        oGraphicsCOM = GraphicsDataOrthoCubeLines(-d+com[0],-d+com[1],-d+com[2], d+com[0],d+com[1],d+com[2], [0.1,0.8,0.1,1])
 91
 92        rDict = mbs.CreateRigidBody(inertia=RBinertia,
 93                                  referencePosition=p0,
 94                                  initialVelocity=v0,initialAngularVelocity=omega0,
 95                                  gravity=[0.,-9.81,0.],
 96                                  graphicsDataList=[oGraphics,oGraphicsCOM],returnDict=True)
 97        oRB = rDict['bodyNumber']
 98        nRB = rDict['nodeNumber']
 99
100        val=0
101        if i==0: val=1
102        mbs.CreateGenericJoint(bodyNumbers=[oRB, oRBlast], position=VAdd([-sx,0.,0],com),
103                               constrainedAxes=[1,1,1, val,val,0], useGlobalFrame=False)
104
105        #for next chain body
106        oRBlast = oRB
107
108    sCoords=mbs.AddSensor(SensorNode(nodeNumber=nRB, storeInternal=True,#fileName="solution/sensor"+str(case)+".txt",
109                             outputVariableType=exu.OutputVariableType.Coordinates))
110    nodeList += [nRB]
111    objectList += [oRB]
112
113mbs.Assemble()
114#exu.Print(mbs)
115
116simulationSettings = exu.SimulationSettings() #takes currently set values or default values
117
118fact = 100
119simulationSettings.timeIntegration.numberOfSteps = 1*fact
120simulationSettings.timeIntegration.endTime = 0.01*fact
121simulationSettings.solutionSettings.solutionWritePeriod = simulationSettings.timeIntegration.endTime/1000
122simulationSettings.timeIntegration.verboseMode = 1
123simulationSettings.solutionSettings.writeSolutionToFile = False
124
125simulationSettings.timeIntegration.newton.useModifiedNewton = True
126simulationSettings.timeIntegration.generalizedAlpha.useIndex2Constraints = True
127simulationSettings.timeIntegration.generalizedAlpha.useNewmark = True
128simulationSettings.timeIntegration.generalizedAlpha.spectralRadius = 0.6 #0.6 works well
129
130simulationSettings.solutionSettings.solutionInformation = "rigid body tests"
131SC.visualizationSettings.nodes.defaultSize = 0.025
132SC.visualizationSettings.nodes.drawNodesAsPoint = False
133SC.visualizationSettings.nodes.showBasis = True
134
135#simulationSettings.displayComputationTime = True
136#simulationSettings.displayStatistics = True
137
138
139if useGraphics:
140    exu.StartRenderer()
141    mbs.WaitForUserToContinue()
142
143mbs.SolveDynamic(simulationSettings)
144
145
146
147p0=mbs.GetObjectOutputBody(objectList[0], exu.OutputVariableType.Displacement, mbs.GetObject(objectList[0])['physicsCenterOfMass'])
148#exu.Print("p0=", p0)
149p1=mbs.GetObjectOutputBody(objectList[1], exu.OutputVariableType.Displacement, mbs.GetObject(objectList[1])['physicsCenterOfMass'])
150#exu.Print("p1=", p1)
151
152#exu.Print("p0-p1=", p0-p1)
153#convergence of two formulations (difference due to time integration):
154#h=0.001:  p0-p1= [ 2.89037808e-06 -4.38559926e-07  4.83240595e-07] #similar results for Rxyz parameterization
155#h=0.0001: p0-p1= [ 2.88781241e-08 -4.40013365e-09  5.24721844e-09]
156#h=0.00001:p0-p1= [ 2.64592348e-10 -5.90557048e-11  4.66975986e-10]
157
158#+++++++++++++++++++++++++++++++++++++++++++++
159u=NormL2(p0) + NormL2(p1)
160exu.Print('solution of rigidBodyCOMtest=',u)
161
162exudynTestGlobals.testError = u - (3.409431467726293) #2020-04-22: 3.409431467726293
163exudynTestGlobals.testResult = u
164
165
166if useGraphics:
167    SC.WaitForRenderEngineStopFlag()
168    exu.StopRenderer() #safely close rendering window!