Aerostructural FFD

In additional to OpenAeroStruct’s internal geometry manipulation group, you can also use pyGeo to perform free-form deformation (FFD) manipulation on the mesh. This allows for more general design shape changes and helps sync up geometry changes between meshes from different levels of fidelity.


This example requires pyGeo, an external code developed by the MDO Lab. You can install it from here.

from openaerostruct.geometry.utils import generate_mesh, write_FFD_file

from openaerostruct.integration.aerostruct_groups import AerostructGeometry, AerostructPoint

import openmdao.api as om
from pygeo import DVGeometry

# Create a dictionary to store options about the surface
mesh_dict = {"num_y": 5, "num_x": 2, "wing_type": "CRM", "symmetry": True, "num_twist_cp": 5}

mesh, twist_cp = generate_mesh(mesh_dict)

surf_dict = {
    # Wing definition
    "name": "wing",  # name of the surface
    "symmetry": True,  # if true, model one half of wing
    # reflected across the plane y = 0
    "S_ref_type": "wetted",  # how we compute the wing area,
    # can be 'wetted' or 'projected'
    "fem_model_type": "tube",
    "thickness_cp": np.array([0.1, 0.2, 0.3]),
    "mesh": mesh,
    "geom_manipulator": "FFD",
    "mx": 2,
    "my": 3,
    # Aerodynamic performance of the lifting surface at
    # an angle of attack of 0 (alpha=0).
    # These CL0 and CD0 values are added to the CL and CD
    # obtained from aerodynamic analysis of the surface to get
    # the total CL and CD.
    # These CL0 and CD0 values do not vary wrt alpha.
    "CL0": 0.0,  # CL of the surface at alpha=0
    "CD0": 0.015,  # CD of the surface at alpha=0
    # Airfoil properties for viscous drag calculation
    "k_lam": 0.05,  # percentage of chord with laminar
    # flow, used for viscous drag
    "t_over_c_cp": np.array([0.15]),  # thickness over chord ratio (NACA0015)
    "c_max_t": 0.303,  # chordwise location of maximum (NACA0015)
    # thickness
    "with_viscous": True,
    "with_wave": False,  # if true, compute wave drag
    # Structural values are based on aluminum 7075
    "E": 70.0e9,  # [Pa] Young's modulus of the spar
    "G": 30.0e9,  # [Pa] shear modulus of the spar
    "yield": 500.0e6 / 2.5,  # [Pa] yield stress divided by 2.5 for limiting case
    "mrho": 3.0e3,  # [kg/m^3] material density
    "fem_origin": 0.35,  # normalized chordwise location of the spar
    "wing_weight_ratio": 2.0,
    "struct_weight_relief": False,  # True to add the weight of the structure to the loads on the structure
    "distributed_fuel_weight": False,
    # Constraints
    "exact_failure_constraint": False,  # if false, use KS function

surfaces = [surf_dict]

# Create the problem and assign the model group
prob = om.Problem()

# Add problem information as an independent variables component
indep_var_comp = om.IndepVarComp()
indep_var_comp.add_output("v", val=248.136, units="m/s")
indep_var_comp.add_output("alpha", val=5.0, units="deg")
indep_var_comp.add_output("Mach_number", val=0.84)
indep_var_comp.add_output("re", val=1.0e6, units="1/m")
indep_var_comp.add_output("rho", val=0.38, units="kg/m**3")
indep_var_comp.add_output("CT", val=grav_constant * 17.0e-6, units="1/s")
indep_var_comp.add_output("R", val=11.165e6, units="m")
indep_var_comp.add_output("W0", val=0.4 * 3e5, units="kg")
indep_var_comp.add_output("speed_of_sound", val=295.4, units="m/s")
indep_var_comp.add_output("load_factor", val=1.0)
indep_var_comp.add_output("empty_cg", val=np.zeros((3)), units="m")

prob.model.add_subsystem("prob_vars", indep_var_comp, promotes=["*"])

# Loop over each surface in the surfaces list
for surface in surfaces:

    # Get the surface name and create a group to contain components
    # only for this surface
    name = surface["name"]

    filename = write_FFD_file(surface, surface["mx"], surface["my"])
    DVGeo = DVGeometry(filename)
    aerostruct_group = AerostructGeometry(surface=surface, DVGeo=DVGeo)

    # Add tmp_group to the problem with the name of the surface.
    prob.model.add_subsystem(name, aerostruct_group)

# Loop through and add a certain number of aero points
for i in range(1):

    point_name = "AS_point_{}".format(i)
    # Connect the parameters within the model for each aero point

    # Create the aero point group and add it to the model
    AS_point = AerostructPoint(surfaces=surfaces)

    prob.model.add_subsystem(point_name, AS_point)

    # Connect flow properties to the analysis point
    prob.model.connect("v", point_name + ".v")
    prob.model.connect("alpha", point_name + ".alpha")
    prob.model.connect("Mach_number", point_name + ".Mach_number")
    prob.model.connect("re", point_name + ".re")
    prob.model.connect("rho", point_name + ".rho")
    prob.model.connect("CT", point_name + ".CT")
    prob.model.connect("R", point_name + ".R")
    prob.model.connect("W0", point_name + ".W0")
    prob.model.connect("speed_of_sound", point_name + ".speed_of_sound")
    prob.model.connect("empty_cg", point_name + ".empty_cg")
    prob.model.connect("load_factor", point_name + ".load_factor")

    for surface in surfaces:

        com_name = point_name + "." + name + "_perf"
            name + ".local_stiff_transformed", point_name + ".coupled." + name + ".local_stiff_transformed"
        prob.model.connect(name + ".nodes", point_name + ".coupled." + name + ".nodes")

        # Connect aerodyamic mesh to coupled group mesh
        prob.model.connect(name + ".mesh", point_name + ".coupled." + name + ".mesh")

        # Connect performance calculation variables
        prob.model.connect(name + ".radius", com_name + ".radius")
        prob.model.connect(name + ".thickness", com_name + ".thickness")
        prob.model.connect(name + ".nodes", com_name + ".nodes")
        prob.model.connect(name + ".cg_location", point_name + "." + "total_perf." + name + "_cg_location")
            name + ".structural_mass", point_name + "." + "total_perf." + name + "_structural_mass"
        prob.model.connect(name + ".t_over_c", com_name + ".t_over_c")

# Import the Scipy Optimizer and set the driver of the problem to use
# it, which defaults to an SLSQP optimization method
prob.driver = om.ScipyOptimizeDriver()

# Setup problem and add design variables, constraint, and objective
prob.model.add_design_var("wing.shape", lower=-3, upper=2)
prob.model.add_design_var("wing.thickness_cp", lower=0.01, upper=0.5, scaler=1e2)
prob.model.add_constraint("AS_point_0.wing_perf.failure", upper=0.0)
prob.model.add_constraint("AS_point_0.wing_perf.thickness_intersects", upper=0.0)

# Add design variables, constraisnt, and objective on the problem
prob.model.add_design_var("alpha", lower=-10.0, upper=10.0)
prob.model.add_constraint("AS_point_0.L_equals_W", equals=0.0)
prob.model.add_objective("AS_point_0.fuelburn", scaler=1e-5)

# Set up the problem

# prob.run_model()