How to retrieve nodal acceleration for all frequencies of different RPM sets in Harmonic Analysis us

Ayush Kumar

While trying to retrieve nodal acceleration for all frequencies of different RPM sets in Harmonic Analysis using DPF operator "AX", I get the following error:

Ayush Kumar

This is a bug in 2021R1 (DPF). The workaround to this is using the displacement operator UX and do a double derivative of UX to get acceleration using cplx_derive operator.

I have this example code which retrieves Nodal acceleration for a defined Named selection "node" (containing 1 node) in Mechanical and prints out the acceleration amplitude for that node in X for each frequency and rpm set in a Harmonic Analysis.

Assumption: Each RPM set has same number of solution intervals. In case of different solution intervals, please adjust the code to get the correct rpm set number.

import math
import mech_dpf
mech_dpf.setExtAPI(ExtAPI)
import Ans.DataProcessing as dpf
from collections import defaultdict

# Data Source
ds = mech_dpf.GetDataSources(0)  # Adjust analysis system index
time_provider = dpf.operators.metadata.time_freq_provider()
time_provider.inputs.data_sources.Connect(ds)

# Number of frequencies
freqs = time_provider.outputs.time_freq_support.GetData()
numSets = freqs.NumberSets
ids = [index + 1 for index in range(numSets)]

# Get number of RPMs
analysis = Model.Analyses[0].AnalysisSettings  # Adjust analysis system index
n_rpms = analysis.NumberOfRPMs
n_freqs_per_rpm = int(len(ids) / n_rpms)

node_scoping = dpf.data.Scoping()
node_scoping.Ids = ExtAPI.DataModel.GetObjectsByName("node")[0].Ids

freq_scoping = dpf.data.Scoping()
freq_scoping.Ids = ids

# Displacement X
u_x = dpf.Operator("UX")
u_x.Connect(0, freq_scoping)
u_x.Connect(1, node_scoping)
u_x.Connect(4, ds)

# Velocity X - Single Derivative
u_d_x = dpf.Operator("cplx_derive")
u_d_x.Connect(0, u_x)

# Acceleration X - Double Derivative
u_d2_x = dpf.Operator("cplx_derive")
u_d2_x.Connect(0, u_d_x)

for freq_index in ids:
    real =  u_d2_x.GetOutputAsFieldsContainer(0).GetFieldByTimeId(freq_index).Data[0]
    imaginary = u_d2_x.GetOutputAsFieldsContainer(0).GetImaginaryField(freq_index).Data[0]

    amplitude = (real ** 2 + imaginary ** 2) ** 0.5

    rpm_set = math.ceil(freq_index / float(n_freqs_per_rpm))
    print "RPM Set - %s, Frequency - %s, Accleration X - %s" % (rpm_set, freq_index, amplitude)