How to compute time dependent results difference between two nodes and display the results?

Pierre Thieffry

After a nonlinear or transient run, I want to plot a graph that shows (uy@node1 - uy@node2)-(uy@node1 - uy@node2)@reftime. How can I achieve this in Mechanical?

Pierre Thieffry

There are two answers to this question - one in APDL, one with DPF and a Python result.

While the code looks more complex for an APDL user, the Python results has several benefits:

• Scoping could be added to select nodes to compare

• Graph is a native Mechanical object

• Results are unit dependent

• Table can be easily copied

APDL:

set,last

sho,png /post26 nsol,2,359,u,y,UY_OD ! Retrieve UY at node 359 
nsol,3,360,u,y,UY_ID ! Retrieve UY at node 360 
add,4,2,3,,UY(OD-ID),,,1,-1 ! Compute UY_OD-UY_ID

*get,y_assem,vari,4,real,1.0 ! Get refvalue of above difference at time = 1.0 
filldata,5,,,,y_assem ! Create vector with above refvalue

add,6,4,5,,DELTA,,,1,-1 ! Compute (UY_OD-UY_ID)-refvalue

prvar,2,3,4,5,6 ! Print all variables

/xrange,1,30 ! Limit plot range to time from 1. to 30.s 
plvar,6 ! Plot variable 6

DPF/Python Result

node1=359
node2=360
reftime=1.0

model=dpf.Model(dataSource)
all_times=model.TimeFreqSupport.TimeFreqs.Data # Retrieve all time values

refIndex=all_times.IndexOf(reftime)+1 # Index of reftime

timeIds=range(refIndex,len(all_times)+1) # List of time steps for time scoping

nodeSc1=dpf.Scoping([node1],'Nodal') # scoping for uy at node 1
nodeSc2=dpf.Scoping([node2],'Nodal') # scoping for uy at node 2

uy1 = dpf.operators.result.displacement_Y(data_sources=dataSource,time_scoping=timeIds,mesh_scoping=nodeSc1) # operator for node 1 
uydiff = dpf.operators.result.displacement_Y(data_sources=dataSource,time_scoping=timeIds,mesh_scoping=nodeSc1) # operator for end result 
uy2 = dpf.operators.result.displacement_Y(data_sources=dataSource,time_scoping=timeIds,mesh_scoping=nodeSc2) # operator for node 1

for time in timeIds: # Compute uy1-uy2 and store in uydiff    
    v1=uy1.outputs.getfields_container().GetFieldByTimeId(time).Data[0]
    v2=uy2.outputs.getfields_container().GetFieldByTimeId(time).Data[0]
    uydiff.outputs.getfields_container().GetFieldByTimeId(time).Data=[v1-v2]

refval=uydiff.outputs.getfields_container().GetFieldByTimeId(all_times.IndexOf(reftime)+1).Data[0] # Retrieve refvalue at reftime

uydiff=uydiff-refval # substract from previous results

with open(r'd:\temp\udiff.txt','w') as f: # write results to text file 
for time in timeIds:
    v1=uy1.outputs.getfields_container().GetFieldByTimeId(time).Data[0] 
    v2=uy2.outputs.getfields_container().GetFieldByTimeId(time).Data[0] 
    vdiff=uydiff.outputs.getfields_container().GetFieldByTimeId(time).Data[0] 
    f.write("{:16.9f}{:16.9f}{:16.9f}{:16.9f}{:16.9f}{:16.9f}\n".format(all_times[time-1],v1,v2,v1-v2,refval,vdiff))

#Display in Mechanical
dpf_workflow = dpf.Workflow()
dpf_workflow.Add(uydiff)
dpf_workflow.SetOutputContour(uydiff) 
dpf_workflow.Record('wf_id', True) 
this.WorkflowId = dpf_workflow.GetRecordedId()