You can view and download this file on Github: fourBarMechanismTest.py
#+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
# This is an EXUDYN example
#
# Details: Test model for four bar mechanism
#
# Author: Johannes Gerstmayr
# Date: 2019-08-15
#
# 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 exudyn as exu
from exudyn.itemInterface import *
useGraphics = True #without test
#+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
#you can erase the following lines and all exudynTestGlobals related operations if this is not intended to be used as TestModel:
try: #only if called from test suite
from modelUnitTests import exudynTestGlobals #for globally storing test results
useGraphics = exudynTestGlobals.useGraphics
except:
class ExudynTestGlobals:
pass
exudynTestGlobals = ExudynTestGlobals()
#+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
SC = exu.SystemContainer()
mbs = SC.AddSystem()
nBodies = 4
mass = 3 #kg
g = 9.81 # m/s^2
omega0 = 2 #initial angular velocity of first link
#add nodes:
n0=mbs.AddNode(PointGround(referenceCoordinates=[0, 0, 0]))
n1=mbs.AddNode(Point(referenceCoordinates=[0, 2, 0], initialVelocities= [2*omega0,0,0]))
n2=mbs.AddNode(Point(referenceCoordinates = [4, 5, 0], initialVelocities= [5*omega0,0,0]))
n3=mbs.AddNode(Point(referenceCoordinates = [4, 0, 0]))
#nodetypes Point2DSlope1Slope2 Point2DSlope1 RigidBody RigidBody2D
L=4
Lo=0.
#add mass points and ground object:
rect = [-6,-6,6,6] #xmin,ymin,xmax,ymax
background = {'type':'Line', 'color':[0.1,0.1,0.8,1], 'data':[rect[0],rect[1],0, rect[2],rect[1],0, rect[2],rect[3],0, rect[0],rect[3],0, rect[0],rect[1],0]} #background
#oGround=mbs.AddObject(ObjectGround(referencePosition= [0,0,0], visualization=VObjectGround(graphicsData= [background])))
#graphics1 = {'type':'Line', 'color':[0.1,0.1,0.8,1], 'data':[-(L+Lo),-(L+Lo),0, (L+Lo),-(L+Lo),0, (L+Lo),Lo,0, -(L+Lo),Lo,0, -(L+Lo),-(L+Lo), 0]} #background
o0=mbs.AddObject(MassPoint(physicsMass=0,nodeNumber=n0,visualization=VObjectMassPoint(graphicsData= [background])))
o1=mbs.AddObject(MassPoint(physicsMass=mass,nodeNumber=n1))
o2=mbs.AddObject(MassPoint(physicsMass=mass,nodeNumber=n2))
o3=mbs.AddObject(MassPoint(physicsMass=mass,nodeNumber=n3))
#use NodePosition markers:
for i in range(nBodies):
mbs.AddMarker(MarkerNodePosition(nodeNumber = i))
#Coordinate Marker:
mc0 = mbs.AddMarker(MarkerNodeCoordinate(nodeNumber = n0, coordinate=0)) #Ground node ==> no action
mc1 = mbs.AddMarker(MarkerNodeCoordinate(nodeNumber = n3, coordinate=1))
mc2 = mbs.AddMarker(MarkerNodeCoordinate(nodeNumber = n3, coordinate=0))
mbs.AddObject(CoordinateConstraint(markerNumbers=[mc0,mc1]))
mbs.AddObject(CoordinateConstraint(markerNumbers=[mc0,mc2]))
useConstraint = True
if useConstraint:
#add distance:
mbs.AddObject(ObjectConnectorDistance(markerNumbers=[0,1], distance=2, visualization=VObjectConnectorDistance(drawSize=0.01)))
mbs.AddObject(ObjectConnectorDistance(markerNumbers=[1,2], distance=5, visualization=VObjectConnectorDistance(drawSize=0.01)))
mbs.AddObject(ObjectConnectorDistance(markerNumbers=[2,3], distance=5, visualization=VObjectConnectorDistance(drawSize=0.01)))
else:
#add spring-dampers:
k = 40000
d = 20
mbs.AddObject({'objectType': 'ConnectorSpringDamper', 'stiffness': k, 'damping': d, 'force': 0, 'referenceLength':2, 'markerNumbers': [0,1], 'VdrawSize': 0.01})
mbs.AddObject({'objectType': 'ConnectorSpringDamper', 'stiffness': k, 'damping': d, 'force': 0, 'referenceLength':5, 'markerNumbers': [1,2], 'VdrawSize': 0.01})
mbs.AddObject({'objectType': 'ConnectorSpringDamper', 'stiffness': k, 'damping': d, 'force': 0, 'referenceLength':5, 'markerNumbers': [2,3], 'VdrawSize': 0.01})
#add loads:
mbs.AddLoad(Force(markerNumber = 1, loadVector = [0, -mass*g, 0]))
mbs.AddLoad(Force(markerNumber = 2, loadVector = [0, -mass*g, 0]))
mbs.Assemble()
#exu.Print(mbs)
simulationSettings = exu.SimulationSettings() #takes currently set values or default values
f = 2000
simulationSettings.timeIntegration.numberOfSteps = 1*f
simulationSettings.timeIntegration.endTime = 0.001*f
simulationSettings.solutionSettings.writeSolutionToFile = True
simulationSettings.solutionSettings.solutionWritePeriod = simulationSettings.timeIntegration.endTime/500
simulationSettings.displayComputationTime = False
simulationSettings.displayStatistics = False
simulationSettings.timeIntegration.verboseMode = 1
simulationSettings.timeIntegration.newton.relativeTolerance = 1e-8*100 #10000
simulationSettings.timeIntegration.newton.absoluteTolerance = 1e-10
simulationSettings.timeIntegration.newton.useModifiedNewton = False
simulationSettings.timeIntegration.newton.maxModifiedNewtonIterations = 5
simulationSettings.timeIntegration.newton.numericalDifferentiation.minimumCoordinateSize = 1
simulationSettings.timeIntegration.newton.numericalDifferentiation.relativeEpsilon = 6.055454452393343e-06*10 #eps^(1/3)
simulationSettings.timeIntegration.generalizedAlpha.useIndex2Constraints = False
simulationSettings.timeIntegration.generalizedAlpha.useNewmark = False
simulationSettings.timeIntegration.generalizedAlpha.spectralRadius = 0.5
#SC.visualizationSettings.nodes.showNumbers = True
SC.visualizationSettings.bodies.showNumbers = True
#SC.visualizationSettings.connectors.showNumbers = True
SC.visualizationSettings.nodes.defaultSize = 0.05
simulationSettings.solutionSettings.solutionInformation = "Planar four-bar-mechanism with initial angular velocity and gravity"
#useGraphics = True #uncomment this line to visualize the example!
if useGraphics:
exu.StartRenderer()
#mbs.WaitForUserToContinue()
mbs.SolveDynamic(simulationSettings)
if useGraphics:
SC.WaitForRenderEngineStopFlag()
exu.StopRenderer() #safely close rendering window!
#compute error for test suite:
sol = mbs.systemData.GetODE2Coordinates();
u = sol[1]; #y-displacement of first node of four bar mechanism
exu.Print('solution of fourbar mechanism =',u)
exudynTestGlobals.testError = u - (-2.354666317492353) #2020-01-09: -2.354666317492353; 2019-12-15: (-2.3546596670554125); 2019-11-22:(-2.354659593986869); previous: (-2.354659593986899)
exudynTestGlobals.testResult = u