FFD + bdf

[Gittwell]

Good afternoon!

Could you please tell me if there are any examples of how I can link an FFD and a BDF file to manipulate the geometry and save the modified BDF file? Without including optimization, just like it's done in the tutorial: https://mdolab-pygeo.readthedocs-hosted.com/en/latest/advanced_ffd.html.

[Gittwell]

In general, using some workaround methods, I managed to do it through TACS. Non-obvious aspects of this approach:

You must definitely define a problem, otherwise you cannot use the writeBDF method.

FFD addPointSet accepts data in the format [[x,y,z],...,[x,y,z]], while Xpts0 is stored in the format [x,y,z,x,y,z,...,x,y,z]. Because of this, you need to perform list transformations for the input to addPointSet and for the input to SetNodes.

You can override the grid node coordinates through the setNodes method of the problem object. Unfortunately, I couldn't find a similar method in the pyTacs class (apparently it doesn't exist).

In general, for setting up FFD + bdf tasks, I'm attaching my resulting code. I'd be interested to learn about other approaches. Does anyone have any ideas?

import numpy as np
from pygeo import DVGeometry
from tacs import pyTACS, elements, constitutive, functions

rho = 2500.0  # density, kg/m^3
E = 70e9  # elastic modulus, Pa
nu = 0.3  # poisson's ratio
ys = 350e6  # yield stress, Pa
min_thickness = 0.002
max_thickness = 0.20
thickness = 0.02
bdf_name = 'wing3.bdf'

def elemCallBack(
        dvNum, compID, compDescript, elemDescripts, globalDVs, **kwargs
):
    prop = constitutive.MaterialProperties(rho=rho, E=E, nu=nu, ys=ys)
    con = constitutive.IsoShellConstitutive(
        prop, t=thickness, tNum=dvNum, tlb=min_thickness, tub=max_thickness
    )
    transform = None
    elem = elements.Quad4Shell(transform, con)
    return elem

fea_assembler = pyTACS(bdf_name)
fea_assembler.initialize(elemCallBack)
static_problem = fea_assembler.createStaticProblem("uniform_z_load")
fea_assembler.writeBDF('wing3_new.bdf', static_problem)

X_0 = [fea_assembler.Xpts0.getArray()[i:i+3] for i in range(0, len(fea_assembler.Xpts0.getArray()), 3)]

def create_fresh_dvgeo():
    FFDfile = "ffdbox3.xyz"
    DVGeo = DVGeometry(FFDfile)
    DVGeo.addPointSet(X_0, "mesh")
    return DVGeo

DVGeo = create_fresh_dvgeo()

DVGeo.addLocalDV("shape_z", lower=-0.5, upper=0.5, axis="z", scale=1.0)
dvdict = DVGeo.getValues()

for i in range(19):
    dvdict["shape_z"][DVGeo.getLocalIndex(0)[i, 0, -1]] += 200
    dvdict["shape_z"][DVGeo.getLocalIndex(0)[i, 1, -1]] += 200

DVGeo.setDesignVars(dvdict)
new_nodes = DVGeo.update("mesh")

X_pt = []
for sublist in new_nodes:
    for item in sublist:
        X_pt.append(item)

static_problem.setNodes(np.array(X_pt))
fea_assembler.writeBDF('wing3_new.bdf', static_problem)