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RANS shape optimization all gradients are zero

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Old   April 24, 2024, 09:52
Default RANS shape optimization all gradients are zero
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Hi everyone,

I am trying to minimize drag on a winglet using shape optimization. The flow conditions I am interested in are low subsonic (Mach 0.2). For this, I was using an RANS solver with a mesh including prism layers. However, when I run the optimization, it calculates the adjoint solution first, and when it calculates the gradients, they all result in zero for every control point.I have tried using Euler, and this works fine. However, the solution oscillates a lot, and since it is inviscid, I would prefer to use RANS.

Does anyone have any idea why this is happening with RANS? And why does Euler oscillate so much (lift coefficient in a range of 0.1 and drag coefficient in a range of 0.01)?

I have attached both configuration files.RANS-shapeOptimisation.txt EULER-shapeOptimisation.txt


Thanks for the help!!


This is the output I get for RANS:




Code:
----------------- FFD technique (parametric -> cartesian) ---------------
Checking FFD box dimension.
Checking FFD box intersections with the solid surfaces.
The FFD planes j=0, j=2, intersect solid surfaces.
SU2 is fixing the planes to maintain a continuous 2nd order derivative.
Update cartesian coord        | FFD box: WING. Max Diff: 7.5341e-14.

Design variable (FFD_CONTROL_POINT) number 0.
DRAG gradient : 0
-------------------------------------------------------------------------

Design variable (FFD_CONTROL_POINT) number 1.
DRAG gradient : 0
-------------------------------------------------------------------------

Design variable (FFD_CONTROL_POINT) number 2.
DRAG gradient : 0
-------------------------------------------------------------------------

Design variable (FFD_CONTROL_POINT) number 3.
DRAG gradient : 0
-------------------------------------------------------------------------

Design variable (FFD_CONTROL_POINT) number 4.
DRAG gradient : 0
-------------------------------------------------------------------------

Design variable (FFD_CONTROL_POINT) number 5.
DRAG gradient : 0
-------------------------------------------------------------------------

Design variable (FFD_CONTROL_POINT) number 6.
DRAG gradient : 0
-------------------------------------------------------------------------

Design variable (FFD_CONTROL_POINT) number 7.
DRAG gradient : 0
-------------------------------------------------------------------------

Design variable (FFD_CONTROL_POINT) number 8.
DRAG gradient : 0
-------------------------------------------------------------------------

Design variable (FFD_CONTROL_POINT) number 9.
DRAG gradient : 0
-------------------------------------------------------------------------

Design variable (FFD_CONTROL_POINT) number 10.
DRAG gradient : 0
-------------------------------------------------------------------------

Design variable (FFD_CONTROL_POINT) number 11.
DRAG gradient : 0
-------------------------------------------------------------------------

Design variable (FFD_CONTROL_POINT) number 12.
DRAG gradient : 0
-------------------------------------------------------------------------

Design variable (FFD_CONTROL_POINT) number 13.
DRAG gradient : 0
-------------------------------------------------------------------------

Design variable (FFD_CONTROL_POINT) number 14.
DRAG gradient : 0
-------------------------------------------------------------------------

Design variable (FFD_CONTROL_POINT) number 15.
DRAG gradient : 0
-------------------------------------------------------------------------

Design variable (FFD_CONTROL_POINT) number 16.
DRAG gradient : 0
-------------------------------------------------------------------------

Design variable (FFD_CONTROL_POINT) number 17.
DRAG gradient : 0
-------------------------------------------------------------------------

Design variable (FFD_CONTROL_POINT) number 18.
DRAG gradient : 0
-------------------------------------------------------------------------

Design variable (FFD_CONTROL_POINT) number 19.
DRAG gradient : 0
-------------------------------------------------------------------------

Design variable (FFD_CONTROL_POINT) number 20.
DRAG gradient : 0
-------------------------------------------------------------------------

Design variable (FFD_CONTROL_POINT) number 21.
DRAG gradient : 0
-------------------------------------------------------------------------

Design variable (FFD_CONTROL_POINT) number 22.
DRAG gradient : 0
-------------------------------------------------------------------------

Design variable (FFD_CONTROL_POINT) number 23.
DRAG gradient : 0
-------------------------------------------------------------------------

Design variable (FFD_CONTROL_POINT) number 24.
DRAG gradient : 0
-------------------------------------------------------------------------

Design variable (FFD_CONTROL_POINT) number 25.
DRAG gradient : 0
-------------------------------------------------------------------------

Design variable (FFD_CONTROL_POINT) number 26.
DRAG gradient : 0
-------------------------------------------------------------------------

Design variable (FFD_CONTROL_POINT) number 27.
DRAG gradient : 0
-------------------------------------------------------------------------

Design variable (FFD_CONTROL_POINT) number 28.
DRAG gradient : 0
-------------------------------------------------------------------------

Design variable (FFD_CONTROL_POINT) number 29.
DRAG gradient : 0
-------------------------------------------------------------------------

------------------------- Finalize Solver  -------------------------
Deleted CNumerics container.
Deleted CSolver container.
Deleted CGeometry container.
Deleted CSurfaceMovement class.
Deleted CVolumetricMovement class.
Deleted CConfig container.
Deleted COutput class.
Code:
Found: mesh.su2
New Project: ./
Sequential Least SQuares Programming (SLSQP) parameters:
Number of design variables: 30 ( 30 ) 
Objective function scaling factor: [1.0]
Maximum number of iterations: 100
Requested accuracy: 1e-15
Initial guess for the independent variable(s): [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]
Lower and upper bound for each independent variable: [(-10000.0, 10000.0), (-10000.0, 10000.0), (-10000.0, 10000.0), (-10000.0, 10000.0), (-10000.0, 10000.0), (-10000.0, 10000.0), (-10000.0, 10000.0), (-10000.0, 10000.0), (-10000.0, 10000.0), (-10000.0, 10000.0), (-10000.0, 10000.0), (-10000.0, 10000.0), (-10000.0, 10000.0), (-10000.0, 10000.0), (-10000.0, 10000.0), (-10000.0, 10000.0), (-10000.0, 10000.0), (-10000.0, 10000.0), (-10000.0, 10000.0), (-10000.0, 10000.0), (-10000.0, 10000.0), (-10000.0, 10000.0), (-10000.0, 10000.0), (-10000.0, 10000.0), (-10000.0, 10000.0), (-10000.0, 10000.0), (-10000.0, 10000.0), (-10000.0, 10000.0), (-10000.0, 10000.0), (-10000.0, 10000.0)]

  NIT    FC           OBJFUN            GNORM
    5     1     1.195152E-07     0.000000E+00
Positive directional derivative for linesearch    (Exit mode 8)
            Current function value: 1.1951518530000002e-07
            Iterations: 5
            Function evaluations: 1
            Gradient evaluations: 1
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