def _barrowmanAeroFunc(self,
rocketState,
time,
environment,
precomputedData,
CG=Vector(0, 0, 0),
finDeflectionAngle=None):
'''
Precomputed Data is a named tuple (PreComputedFinAeroData) which contains data/results from the parts of the fin aerodynamics calculation
that are common to all fins in a FinSet (drag calculations mostly). These calculations are performed at the FinSet level.
Only the parts of the Fin Aero Computation that change from fin to fin (normal force mostly, since different fins can have different angles of attack) are computed here
'''
Mach = AeroParameters.getMachNumber(rocketState, environment)
dynamicPressure = AeroParameters.getDynamicPressure(
rocketState, environment)
if finDeflectionAngle == None:
finDeflectionAngle = self.finAngle # Adjusted by parent finset during each timestep, when the FinSet is controlled
# Unpack precomputedData
airVelRelativeToFin, CPXPos, totalDragCoefficient = precomputedData
#### Compute normal force-----------------------------------------------------------------------------------------------------------------
# Find fin normal vector after fin deflection
finDeflectionRotation = Quaternion(
axisOfRotation=self.spanwiseDirection,
angle=radians(finDeflectionAngle))
finNormal = finDeflectionRotation.rotate(self.undeflectedFinNormal)
# Get the tangential velocity component vector, per unit radial distance from the rocket centerline
rollAngVel = AngularVelocity(0, 0, rocketState.angularVelocity.Z)
unitSpanTangentialAirVelocity = rollAngVel.crossProduct(
self.spanwiseDirection) * (-1)
def subsonicNormalForce(Mach): # Subsonic linear method
tempBeta = AeroParameters.getBeta(Mach)
CnAlpha = getFinCnAlpha_Subsonic_Barrowman(self.span,
self.planformArea,
tempBeta,
self.midChordSweep)
return getSubsonicFinNormalForce(airVelRelativeToFin,
unitSpanTangentialAirVelocity,
finNormal, self.spanwiseDirection,
self.CPSpanWisePosition.length(),
CnAlpha, self)
def supersonicNormalForce(Mach): # Supersonic Busemann method
gamma = AeroFunctions.getGamma()
tempBeta = AeroParameters.getBeta(Mach)
K1, K2, K3, Kstar = getBusemannCoefficients(Mach, tempBeta, gamma)
# Mach Cone coords
machAngle = asin(1 / Mach)
machCone_negZPerRadius = 1 / tan(machAngle)
machConeEdgeZPos = []
outerRadius = self.spanSliceRadii[-1]
for i in range(len(self.spanSliceRadii)):
machConeAtCurrentRadius = (
outerRadius - self.spanSliceRadii[i]
) * machCone_negZPerRadius + self.tipPosition
machConeEdgeZPos.append(machConeAtCurrentRadius)
return getSupersonicFinNormalForce(
airVelRelativeToFin, unitSpanTangentialAirVelocity, finNormal,
machConeEdgeZPos, self.spanwiseDirection,
self.CPSpanWisePosition.length(), K1, K2, K3, Kstar, self)
if Mach <= 0.8:
normalForceMagnitude, finMoment = subsonicNormalForce(Mach)
elif Mach < 1.4:
# Interpolate in transonic region
# TODO: Do this with less function evaluations? Perhaps precompute AOA and Mach combinations and simply interpolate? Lazy precompute? Cython?
x1, x2 = 0.8, 1.4 # Start, end pts of interpolated region
dx = 0.001
# Find normal force and derivative at start of interpolation interval
f_x1, m_x1 = subsonicNormalForce(x1)
f_x12, m_x12 = subsonicNormalForce(x1 + dx)
# Find normal force and derivative at end of interpolation interval
f_x2, m_x2 = supersonicNormalForce(x2)
f_x22, m_x22 = supersonicNormalForce(x2 + dx)
normalForceMagnitude = Interpolation.cubicInterp(
Mach, x1, x2, f_x1, f_x2, f_x12, f_x22, dx)
finMoment = Interpolation.cubicInterp(Mach, x1, x2, m_x1, m_x2,
m_x12, m_x22, dx)
else:
normalForceMagnitude, finMoment = supersonicNormalForce(Mach)
# Complete redimensionalization of normal force coefficients by multiplying by dynamic pressure
# Direct the normal force along the fin's normal direction
normalForce = normalForceMagnitude * dynamicPressure * finNormal
finMoment *= dynamicPressure
#### Get axial force-----------------------------------------------------------------------------------------------------------------------
avgAOA = getFinSliceAngleOfAttack(
self.spanSliceRadii[round(len(self.spanSliceAreas) / 2)],
airVelRelativeToFin, unitSpanTangentialAirVelocity, finNormal,
self.spanwiseDirection,
self.stallAngle) # Approximate average fin AOA
totalAxialForceCoefficient = AeroFunctions.getDragToAxialForceFactor(
avgAOA) * totalDragCoefficient
axialForceMagnitude = totalAxialForceCoefficient * self.rocket.Aref * dynamicPressure
axialForceDirection = self.spanwiseDirection.crossProduct(finNormal)
axialForce = axialForceDirection * axialForceMagnitude
#### Get CP Location ----------------------------------------------------------------------------------------------------------------------
CPChordWisePosition = self.position - Vector(
0, 0, CPXPos
) # Ignoring the change in CP position due to fin deflection for now
globalCP = self.CPSpanWisePosition + CPChordWisePosition
#### Assemble total force moment system objects--------------------------------------------------------------------------------------------
totalForce = normalForce + axialForce
return ForceMomentSystem(totalForce,
globalCP,
moment=Vector(0, 0, finMoment)), globalCP
def getVelocity(self, time):
pos = self.getPosition(time)
angVel = AngularVelocity(0, 0, self.earthAngVel)
return angVel.crossProduct(pos)
