def process_sref(compound):
"""
Process a wing reference surface. The compound should contain a single
face. The underlying surface of this faces will be used to generate a
new NurbsSurface. Since the OpenVSP surface uses uniform
parametrization, a chord line is extracted at each unique knot in the
v-direction. Then a linear surface is lofted through these lines to
form a bilinear surface where the u-direction is chordwise and the
v-direction is spanwise.
:param afem.topology.entities.Compound compound: The compound.
:return: The reference surface.
:rtype: afem.geometry.entities.NurbsSurface
"""
# Get underlying surface
srf = compound.faces[0].surface
# Loft new surface
vknots = srf.vknots
crvs = []
for vi in vknots:
c = srf.v_iso(vi)
crvs.append(c)
srf = NurbsSurfaceByInterp(crvs, 1).surface
return srf
def _reloft_wing_surface(srf, tol):
"""
Attempt to reloft an OpenVSP wing surface which was not split to achieve
higher continuity.
"""
logger.info('\tAttempting to reloft the surface...')
# Gather isocurves at each section, tessellate, and approximate
crvs = []
for u in srf.uknots:
c0 = srf.u_iso(u)
adp_crv = AdaptorCurve.to_adaptor(c0)
tool = GCPnts_QuasiUniformDeflection(adp_crv.object, tol)
if not tool.IsDone():
logger.info('\tTessellation failed. Using original surface.')
return srf
pnts = [c0.eval(tool.Parameter(i)) for i in
range(1, tool.NbPoints() + 1)]
c = NurbsCurveByApprox(pnts, tol=tol, continuity=Geometry.C1).curve
crvs.append(c)
return NurbsSurfaceByInterp(crvs, 1).surface
def rebuild_wing_sref(srf):
"""
Attempt to rebuild a wing reference surface using the given OML
surface. This method is intended to operate on OpenVSP surfaces that
define the OML of a wing component and/or have similar parametrization.
:param afem.geometry.entities.NurbsSurface srf: The surface.
:return: The reference surface.
:rtype: afem.geometry.entities.NurbsSurface
"""
# For VSP, wing surfaces are degree=1 in the spanwise direction, so
# each knot vector usually represents where a wing cross section is
# located. For each knot vector in spanwise direction, generate a
# straight line segment between the LE and TE (i.e., the chord line).
# These chords will serve as the wing reference surface. This assumes
# that the LE is at v=0.5 in the local parametric domain.
uknots = srf.uknots
le_param = srf.local_to_global_param('v', 0.5)
te_param = srf.local_to_global_param('v', 0.)
chords = []
for u in uknots:
le = srf.eval(u, le_param)
te = srf.eval(u, te_param)
c = NurbsCurveByPoints([le, te]).curve
chords.append(c)
# VSP wing components wrap around the ends and there may be duplicate
# chord lines at the root and tip. Retain only unique lines based on LE
# point.
unique_chords = [chords[0]]
for i in range(1, len(chords)):
c0 = unique_chords[-1]
ci = chords[i]
if not ci.eval(0.).is_equal(c0.eval(0.)):
unique_chords.append(ci)
# Create degree=1 reference surface by skinning chord lines
sref = NurbsSurfaceByInterp(unique_chords, 1).surface
# Set domains to be 0 to 1.
sref.set_udomain(0., 1.)
sref.set_vdomain(0., 1.)
return sref
