Extract Mass given a list of elements or properties

[Fabio Cunha]

Hi folks,

I am able to extract the mass of the whole model mesh through:

mesh.mass() or mesh.mass_properties()

Is it possible in a simple manner to extract the mass/mass_properties given a list of elements or properties?

Br,

Fábio.

[Steven Doyle]

The mass() method will be removed in the next version (to be released soon), so I recommend switching everything to mass_properties.

The calling signature & docstring for mass_properties is:

    def mass_properties(self, element_ids=None, reference_point=None,

                        sym_axis=None, num_cpus=1, scale=None):

        """

        Caclulates mass properties in the global system about the

        reference point.

        Parameters

        ---------------

        self : BDF

            The BDF object.

        element_ids : ndarray, optional

            An array of element ids.

        reference_point : ndarray, optional

            An array that defines the origin of the frame.

            default = <0,0,0>.

        sym_axis : str, optional

            The axis to which the model is symmetric. If AERO cards are used, this can be left blank

            allowed_values = 'x', 'y', 'z', 'xy', 'yz', 'xz', 'xyz'

        scale : float, optional

            The WTMASS scaling value.

            default=None -> PARAM, WTMASS is used

            float > 0.0

        Returns

        ----------

        mass : float

            The mass of the model.

        cg : ndarray

            The cg of the model as an array.

        I : ndarray

            Moment of inertia array([Ixx, Iyy, Izz, Ixy, Ixz, Iyz]).

Just call it with element_ids as a list/ndarray of the element ids.  You cannot explicitly get mass by property id.

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[Fabio Cunha]

Hi Steve,

Thanks for the very quick reply. I am still using version 0.6. I definitely need to update the code in the next few days...

In version 0.60 the signature is quite different:

mass_properties(self, reference_point=None) method of pyNastran.bdf.bdf.BDF instance

    Caclulates mass properties in the global system about the reference point.

    :param self: the BDF object
    :param reference_point: an array that defines the origin of the frame.
        default = <0,0,0>.
    :returns mass: the mass of the model
    :returns cg: the cg of the model as an array.
    :returns I: moment of inertia array([Ixx, Iyy, Izz, Ixy, Ixz, Iyz])
   
    I = mass * centroid * centroid
   
    .. math:: I_{xx} = m (dy^2 + dz^2)
   
    .. math:: I_{yz} = -m * dy * dz
   
    where:
    .. math:: dx = x_{element} - x_{ref}


Br,

Fábio,

[Steven Doyle]

v0.6 was released a longgg time ago.  That was pre-OP2 vectorization (which I'm now considering removing).

[Fabio Cunha]

Yes, I know... Sometime I am lazy to update packages.

I just updated and  tested the function. It worked perfectly!

Thanks a lot!