loads Module

Defines:

• sum_forces_moments

  find the net force/moment on the model

• sum_forces_moments_elements

  find the net force/moment on the model for a subset of elements

pyNastran.bdf.mesh_utils.loads.get_ndof(model: BDF, subcase: Subcase) → tuple[int, int, int]

gets the size of the DOFs

pyNastran.bdf.mesh_utils.loads.get_static_force_vector_from_subcase_id(model: BDF, subcase_id: int) → np.ndarray

solves for F in:

[K]{x} = {F}

pyNastran.bdf.mesh_utils.loads.isnan(value: float | None) → bool

pyNastran.bdf.mesh_utils.loads.sum_forces_moments(model: BDF, p0: int | np.ndarray, loadcase_id: int, cid: int = 0, include_grav: bool = False, xyz_cid0: dict[int, NDArray3float] | None = None) → tuple[NDArray3float, NDArray3float]

Sums applied forces & moments about a reference point p0 for all load cases.

Considers:

• FORCE, FORCE1, FORCE2

• MOMENT, MOMENT1, MOMENT2

• PLOAD, PLOAD2, PLOAD4

• LOAD

Parameters:

modelBDF()

a BDF object

p0NUMPY.NDARRAY shape=(3,) or integer (node ID)

the reference point

loadcase_idint

the LOAD=ID to analyze

cidint; default=0

the coordinate system for the summation

include_gravbool; default=False

includes gravity in the summation (not supported)

xyz_cid0None / dict[int] = (3, ) ndarray

the nodes in the global coordinate system

Returns:

forcesNUMPY.NDARRAY shape=(3,)

the forces

momentsNUMPY.NDARRAY shape=(3,)

the moments

Warning

not full validated ..

Todo

It’s super slow for cid != 0. We can speed this up a lot if we calculate the normal, area, centroid based on precomputed node locations.

Pressure acts in the normal direction per model/real/loads.bdf and loads.f06

pyNastran.bdf.mesh_utils.loads.sum_forces_moments_elements(model: BDF, p0: int | np.ndarray, loadcase_id: int, eids: list[int] | None, nids: list[int] | None, cid: int = 0, include_grav: bool = False, xyz_cid0: dict[int, NDArray3float] | None = None) → tuple[NDArray3float, NDArray3float]

Sum the forces/moments based on a list of nodes and elements.

Parameters:

modelBDF()

a BDF object

eidslist[int]

the list of elements to include (e.g. the loads due to a PLOAD4)

nidslist[int]

the list of nodes to include (e.g. the loads due to a FORCE card)

p0int; (3,) ndarray

the point to sum moments about type = int

sum moments about the specified grid point

type = (3, ) ndarray/list (e.g. [10., 20., 30]):

the x, y, z location in the global frame

loadcase_idint

the LOAD=ID to analyze

include_gravbool; default=False

includes gravity in the summation (not supported)

xyz_cid0None / dict[int] = (3, ) ndarray

the nodes in the global coordinate system

Returns:

forcesNUMPY.NDARRAY shape=(3,)

the forces

momentsNUMPY.NDARRAY shape=(3,)

the moments

Nodal TypesFORCE, FORCE1, FORCE2,

MOMENT, MOMENT1, MOMENT2, PLOAD

Element Types: PLOAD1, PLOAD2, PLOAD4, GRAV

If you have a CQUAD4 (eid=3) with a PLOAD4 (sid=3) and a FORCE

card (nid=5) acting on it, you can include the PLOAD4, but

not the FORCE card by using:

For just pressure:

For just force:

or both:

Note

If you split the model into sections and sum the loads on each section, you may not get the same result as if you summed the loads on the total model. This is due to the fact that nodal loads on the boundary are double/triple/etc. counted depending on how many breaks you have.

Todo

not done… ..