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[Aoxi Zhang <question701438@xxxxxxxxxxxxxxxxxxxxx>]

Question #701438 on Yade changed:
https://answers.launchpad.net/yade/+question/701438

Aoxi Zhang gave more information on the question:
Hi Jan,

Thanks for your comments.

>> it is not small enough to neglect the effect of its value.

I further tested on other smaller dt values, e.g. 1e-10, but it has the
same problem.

>> You are examining a few "random" particle's velocities in a
simulation with "many" particles. Such DEM simulation is "chaotic".

That is a good point. I updated phase2.py (attached below) by monitoring
a layer of sands, thereby more sands are monitored. But I still got this
problem.

#### updated phase2.py in which more sands are monitored###
from __future__ import division
from yade import pack, plot
import math
import numpy as np
import random
import pickle
from yade import ymport,export

utils.readParamsFromTable(dt=1e-7)
from yade.params import table


finalFricDegree=19

O.load('sample_generatedFromPhase1_afterRelax.yade.gz')

RunTimeLength=3e-4 # how long for the time of data recording
Odt=table.dt
O.dt=Odt

O.engines[3].dead=True## turn of GlobalStiffnessTimeStepper
# TimeStepper.dead=True## Note, use label cannot successfully close time stepper
StopRelaxation.dead=True## turn of StopRelaxation in previous phase
NewtonIntegrator.damping=0.0

# monitoredSand=[1000,2001,3002,4003,5004]
monitoredSand=[]
def getMonitoredSand():
	halfHeigh=aabbDim()[1]/2
	for i in O.bodies:
		if isinstance(i.shape, Sphere):
			if halfHeigh<i.state.pos[1]<halfHeigh+0.0015:
				i.shape.color=[1,0,0]
				monitoredSand.append(i.id)
			else:
				i.shape.color=[1,1,1]
	print ("number of monitoredSand is",len(monitoredSand))


getMonitoredSand()

def avgVel(idList):
	vel=0.0
	avg=0.0
	for i in idList:
			vel+=O.bodies[i].state.vel[1]
	avg=vel/len(idList)
	return avg

print("O.dt=",O.dt)
O.engines=O.engines+[PyRunner(command='outputData()', iterPeriod=1,label="outputData")]
O.engines=O.engines+[PyRunner(command='stopSimulation()', iterPeriod=1,label="stopSimu")]
# print("O.dt=",O.dt)
# NewtonIntegrator.damping=0

def stopSimulation():
	print ('Running, O.time,',O.time)
	if O.time > RunTimeLength:
		O.pause()
		print ('Running finished, O.realtime,',O.realtime)
		# plot.saveDataTxt('historyData_calmdownVel{}.txt'.format(calmDownVel)) # should revise the monitored data at history

 
def outputData():
	f = open("ResultsOfPhase2_dt{}.txt".format(Odt), "a+")
	f.write('{} {} {}\n'.format(O.time,O.dt,avgVel(monitoredSand)))
	f.close()
 

O.resetTime()
O.run()
utils.waitIfBatch()
#####
Do you have any ideas about this?

Thanks!
Aoxi

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