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

This is a bug in 2021R1 (DPF). The workaround to this is using the displacement operator
UX
and do a double derivative ofUX
to get acceleration usingcplx_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)
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ACEL is not in the RST for harmonic response. You can calculate it by scaling displacement by (2pi()FREQ)^2
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