mass_properties Module

Defines:
  • mass_poperties

    get the mass & moment of inertia of the model

pyNastran.bdf.mesh_utils.mass_properties.get_sub_eids(all_eids: ndarray, eids: list[int], etype: str) → ndarray[source]

supports limiting the element/mass ids

pyNastran.bdf.mesh_utils.mass_properties.hstack_dict_values(adict: dict[Any, list[int]]) → ndarray[source]
pyNastran.bdf.mesh_utils.mass_properties.increment_inertia(centroidi: ndarray, reference_xyz: ndarray, massi: float, mass: float, mass_cg: ndarray, inertia: ndarray, mass_list: list[float], cg_list: list[ndarray], inertia_list: list[ndarray]) → float[source]

helper method

centroidi: (3,) float np.ndarray

delta value

reference_xyz(3,) float np.ndarray

origin

massifloat

delta value

massfloat

total value

mass_cg: (3,) float np.ndarray

total value

inertia: (6,) float np.ndarray

total value; [Ixx, Iyy, Izz, Ixy, Ixz, Iyz]

pyNastran.bdf.mesh_utils.mass_properties.mass_properties(model: BDF, element_ids: list[int] | None = None, mass_ids: list[int] | None = None, reference_point: np.ndarray | None = None, sym_axis: str = '', scale: float | None = None, inertia_reference: str = 'cg')[source]

Calculates mass properties in the global system about the reference point, while considering WTMASS.

Parameters:
modelBDF()

a BDF object

element_idslist[int]; ndarray

the element ids to consider

mass_idslist[int]; ndarray

the mass ids to consider

reference_point(3, ) ndarray; default = <0,0,0>.

an array that defines the origin of the frame.

inertia_referencestr; default=’cg’

‘cg’ : inertia is taken about the cg ‘ref’ : inertia is about the reference point

sym_axisstr; default=’’

‘yz’, ‘xz’, ‘xy’

scalefloat; default=WTMASS

scales weight to mass (1/g) overwrites PARAM,WTMASS

Returns:
massfloat

the mass of the model; wtmass is considered

cg(3, ) float ndarray

the cg of the model as an array.

I(6, ) float ndarray

moment of inertia array([Ixx, Iyy, Izz, Ixy, Ixz, Iyz]); wtmass is considered

See also

model.mass_properties ..

pyNastran.bdf.mesh_utils.mass_properties.mass_properties_breakdown(model: BDF, element_ids=None, mass_ids=None, nsm_id=None, reference_point=None, sym_axis: str | None = None, scale: float | None = None, inertia_reference: str = 'cg', debug: bool = False)[source]

Gets an incomplete breakdown the mass properties on a per element basis

pyNastran.bdf.mesh_utils.mass_properties.mass_properties_no_xref(model, element_ids=None, mass_ids=None, reference_point=None, sym_axis: str = '', scale=None, inertia_reference='cg')[source]

Calculates mass properties without cross-referencing the model.

pyNastran.bdf.mesh_utils.mass_properties.mass_properties_nsm(model: BDF, element_ids: list[int] | None = None, mass_ids: list[int] | None = None, nsm_id: int | None = None, reference_point: np.ndarray | None = None, sym_axis: str = '', scale: float | None = None, inertia_reference: str = 'cg', xyz_cid0_dict=None, debug: bool = False) → tuple[float, np.ndarray, np.ndarray][source]

Calculates mass properties in the global system about the reference point. Considers NSM, NSM1, NSML, NSML1, and WTMASS.

Parameters:
modelBDF()

a BDF object

element_idslist[int]; (n, ) ndarray, optional

An array of element ids.

mass_idslist[int]; (n, ) ndarray, optional

An array of mass ids.

nsm_idint

the NSM id to consider

reference_pointndarray/int, optional
typendarray

An array that defines the origin of the frame. default = <0,0,0>.

typeint

the node id

sym_axisstr; default=’’

The axis to which the model is symmetric. If AERO cards are used, this can be left blank. allowed_values = ‘no’, x’, ‘y’, ‘z’, ‘xy’, ‘yz’, ‘xz’, ‘xyz’

scalefloat; default=wtmass

The WTMASS scaling value. default=None -> PARAM, WTMASS is used float > 0.0

inertia_referencestr; default=’cg’

‘cg’ : inertia is taken about the cg ‘ref’ : inertia is about the reference point

xyz_cid0_dictdict[nid]xyz; default=None -> auto-calculate

mapping of the node id to the global position

debugbool; default=False

developer debug; may be removed in the future

Returns:
massfloat

The mass of the model; wtmass is considered

cg(3,) float ndarray

The cg of the model

inertia(6,) float ndarray

Moment of inertia array([Ixx, Iyy, Izz, Ixy, Ixz, Iyz]); wtmass is considered

inertia = mass * centroid * centroid
\[I_{xx} = m (dy^2 + dz^2) ..\]
\[I_{yz} = -m * dy * dz ..\]
where:
\[dx = x_{element} - x_{ref} ..\]

See also

https://en.wikipedia.org/wiki/Moment_of_inertia#Moment_of_inertia_tensor ..

Note

This doesn’t use the mass matrix formulation like Nastran. It assumes m*r^2 is the dominant term. If you’re trying to get the mass of a single element, it will be wrong, but for real models will be correct.

Warning

  • If eids are requested, but don’t exist, no warning is thrown. Decide if this is the desired behavior.

  • If the NSMx ALL option is used, the mass from all elements will be considered, even if not included in the element set

Examples

mass properties of entire structure

>>> mass, cg, inertia = mass_properties(model)
>>> Ixx, Iyy, Izz, Ixy, Ixz, Iyz = inertia

mass properties of model based on Property ID >>> pids = list(model.properties.keys()) >>> pid_eids = model.get_element_ids_dict_with_pids(pids) >>> for pid, eids in sorted(pid_eids.items()): >>> mass, cg, inertia = mass_properties(model, element_ids=eids)

pyNastran.bdf.mesh_utils.mass_properties.plot_inertia(total_mass: ndarray, cg: ndarray, inertia: ndarray) → None[source]
pyNastran.bdf.mesh_utils.mass_properties.transform_inertia(mass: float, xyz_cg: np.ndarray, xyz_ref1: np.ndarray, xyz_ref2: np.ndarray, inertia_ref1: np.ndarray, coord_cg=None, coord_ref1=None, coord_ref2=None, coord1: CORD2R | None = None, coord2: CORD2R | None = None, debug: bool = False) → np.ndarray[source]

Transforms mass moment of inertia using parallel-axis theorem.

Parameters:
massfloat

the mass

xyz_cg(3, ) float ndarray

the CG location in coord1

xyz_ref1(3, ) float ndarray

the original reference location in coord1

xyz_ref2(3, ) float ndarray

the new reference location in coord2

coord_cg: CORD2R | None; default=None -> cid=0

the coordinate system for xyz_cg

coord_ref1: CORD2R | None; default=None -> cid=0

the coordinate system for xyz_ref1

coord_ref2: CORD2R | None; default=None -> cid=0

the coordinate system for xyz_ref2

inertia_ref1(6, ) float ndarray

the mass moment of inertias about the original reference point [Ixx, Iyy, Izz, Ixy, Ixz, Iyz] in coord1

coord1: CORD2R | None

the coordinate system for inertia_ref1 None: cid=0 (basic frame) not supported yet

coord2: CORD2R | None

the coordinate system for inertia_ref2 None: cid=0 (basic frame) not validated yet

Returns:
inertia_new(6, ) float ndarray

the mass moment of inertias about the new reference point [Ixx, Iyy, Izz, Ixy, Ixz, Iyz]