How can I extract the rotational mass of a model using DPF?

Landon Mitchell Kanner

I would like to use pyDPF to extract the total Rotational mass from a modal analysis in Mechanical/APDL. This is necessary to check if a sufficient number of mode shapes have been extracted in the analysis.

I can get the total mass as:

data_sources = dpf.DataSources()
data_sources.add_file_path(Modefile)
mass_op = dpf.operators.result.total_mass(data_sources=data_sources)
model_total_mass = mass_op.outputs.mass()

Can I similarly read the rotational masses from the .mode or other (e.g. .rst) file?

Pierre Thieffry

Hi @Landon Mitchell Kanner I can't see a way to extract that information with DPF up to 25R1. Also looked at DPF Post without success...

Landon Mitchell Kanner

Thanks @Pierre Thieffry . Would this be reasonable enhancement request for DPF or is the issue that the data is not available in the .mode and/or .rst files?

Landon Mitchell Kanner

Here is a workaround that reads the .out file as seen in the question's screenshot:

def get_rotational_masses(Outfile):
    if not os.path.exists(Outfile):
        print("ERROR  File does not exist: " + Outfile)
        return None
    masses = [0,0,0,0,0,0]
    with open(Outfile) as f:
        line = f.readline()
        while line:
            if "Rotational mass (inertia)" in line:
                for i in range(3):
                    line = f.readline()
                    v = line.split()
                    masses[i+3] = float(v[i+1])
                line = f.readline()
                line = f.readline()
                v = line.split()
                for i in range(3):
                    masses[i] = float(v[3])
            line = f.readline()
    return masses

Pierre Thieffry

I don't see a way to get it with *get, so they are likely not stored. Your workaround is definitely a good one.

Mike Rife

Hi @Landon Mitchell Kanner
You can *get these right after a solution. Also you can *get the effective mass after the solve. The total mass and the first and second MoI are stored in the mode file if a PyDOF enhancement is a better solution for you.