connectorRigidBodySpringDamperTest.py

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#+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
# This is an EXUDYN example
#
# Details:  Test for RigidBodySpringDamper with springForceTorqueUserFunction;
#           the RigidBodySpringDamper can be used to model complicance effects in joints where 
#           one axis undergoes large rotations, and the other rotations are small
#
# Author:   Johannes Gerstmayr
# Date:     2021-01-07
#
# 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.
#
#+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

import sys
sys.path.append('../TestModels')            #for modelUnitTest as this example may be used also as a unit test

import exudyn as exu
from exudyn.utilities import * #includes itemInterface and rigidBodyUtilities
import exudyn.graphics as graphics
import numpy as np

testIsActive = exu.sys.get('testIsActive', False)

SC = exu.SystemContainer()
mbs = SC.AddSystem()

oGround=mbs.AddObject(ObjectGround(referencePosition= [0,0,0]))
nGround = mbs.AddNode(NodePointGround(referenceCoordinates=[0,0,0]))

#example with rigid body at [0,0,0], 1kg under initial velocity
graphicsBody = graphics.Brick(centerPoint=[0,0,0],size=[0.09,0.09,0.2], color=graphics.color.lightred)
nBody = mbs.AddNode(RigidRxyz(initialVelocities=[0,10,0, 2*pi*4,0,0]))
oBody = mbs.AddObject(RigidBody(mass=1, inertia=[1,1,1,0,0,0], nodeNumber=nBody, 
                                visualization=VRigidBody(graphicsData=[graphicsBody])))

mBody = mbs.AddMarker(MarkerNodeRigid(nodeNumber=nBody))
mGround = mbs.AddMarker(MarkerBodyRigid(bodyNumber=oGround, 
                                        localPosition = [0,0,0]))

def UFforce(mbs, t, itemIndex, displacement, rotation, velocity, angularVelocity, stiffness, damping, rotJ0, rotJ1, offset): 
    k = stiffness
    u = displacement
    v = velocity
    w = angularVelocity
    rot = rotation
    return [u[0]*k[0][0],u[1]*k[1][1]+v[1]*0.01*k[1][1],u[2]*k[2][2],
            rot[0]*k[0][0]+w[0]*0.001*k[0][0],rot[1]*k[0][0],rot[2]*k[0][0]]

#markerNumbers and parameters taken from mini example
k=5000
mbs.AddObject(RigidBodySpringDamper(markerNumbers = [mGround, mBody], 
                                    stiffness = np.diag([k,k,k, 0,0,0]), 
                                    damping = np.diag([0,k*0.01,0, 0,0,0]), 
                                    offset = [0,1,0, 0,0,0],
                                    springForceTorqueUserFunction = UFforce))

mbs.Assemble()

tEnd = 0.1
h=1e-3
if not testIsActive:
    tEnd = 1 #parameters sucht that we can see some motion
    h=1e-5


simulationSettings = exu.SimulationSettings()
simulationSettings.timeIntegration.newton.useModifiedNewton = False #Just for the test; modified Newton is usually faster
simulationSettings.timeIntegration.numberOfSteps = int(tEnd/h)
simulationSettings.timeIntegration.endTime = tEnd
simulationSettings.solution.file.write = False

simulationSettings.timeIntegration.generalizedAlpha.spectralRadius = 1 #no numerical damping

simulationSettings.show.statistics = True
simulationSettings.timeIntegration.verboseMode = 1

if not testIsActive:
    SC.renderer.Start()              #start graphics visualization
    SC.renderer.DoIdleTasks()    #wait for pressing SPACE bar to continue

#start solver:
mbs.SolveDynamic(simulationSettings)

if not testIsActive:
    SC.renderer.DoIdleTasks()#wait for pressing 'Q' to quit
    SC.renderer.Stop()               #safely close rendering window!

p0=mbs.GetObjectOutputBody(oBody, localPosition=[0.1,0.1,0.1], 
                           variableType = exu.OutputVariableType.Position)
result = p0[0]+p0[1]
exu.Print('solution of connectorRigidBodySpringDamperTest=',result) #use x-coordinate

exu.sys['testResult'] = result