finite element based structural optimization by genesis · structural optimization in genesis. 8 2...
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Finite Element Based Structural Optimization
by GENESIS
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Outline
!Design approach!Numerical Optimization
"Advantages"Limitations
!Structural optimization in GENESIS!Examples
"Composite panel design optimization subject to crack propagation constraint
"High Speed Civil Transport Wing Problem
!Optimization Errors
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Design Approach
! Defined design goal" Minimum weight design: Given load, required strength
! Analyze proposed design, for acceptability ! Change one or more design variables to see if any
design improvement can be obtained.
! OK, when the design is a function of only a few variables
! More systematic approach needed: Numerical optimization
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Numerical OptimizationAdvantages (Vanderplaats)
! A major advantage is the reduction in design time –this is especially true when the same computer program can be applied to many design projects.
! Optimization provides a systematic design procedure.! We can deal with a wide variety of design variables
and constraints which are difficult to visualize using graphical or tabular methods.
! Optimization requires a minimal amount of human-machine interaction.
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! Computational time increases as the number of design variables increases. If one wishes to consider all possible design variables, the cost of automated design is often prohibitive.
! It can seldom be guaranteed that the optimization algorithm will obtain the global optimum design. Therefore, it may be desirable to restart the optimization process from several different points to provide reasonable assurance of obtaining the global optimum.
! Because many analysis programs were not written with automated design in mind, adaptation of these programs to an optimization code may require significant reprogramming of the analysis routines.
Numerical OptimizationLimitations (Vanderplaats)
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Structural Optimization in Genesis
! FEA for the initial proposed design! Design cycle starts
" Sensitivity analysis (gradient computations) for the responses included in the objective function and the constraints
" High quality approximation for the original problem and optimization of the approximated problem
" FEA for the new design" Convergence check, start new design cycle if necessary
! Improved Design/Optimum
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!DOBJ: defines objective function!DCONS: defines constraints!DOPT: defines optimization parameters!DEQUAT: to implement equations in
GENESIS!DTABLE: to assign values for parameters in
equations
Structural Optimization in Genesis
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2 ay
x
z
PyN
20"
20"
5"
0°
(45/-45/90/0)s
t45 t90 t0skinstiffener t45 t90 t0
Structural design variables
0.005 ≤≤≤≤ ≤≤≤≤ 0.025 in.
PyN
Composite panel design optimization subject to crack propagation constraint
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Low Fidelity (LF) Model
Stress intensity factor in the 0° ply
Far-field stress in the 0° ply
aK fLF πσ 00 =
LF Direct OptimizationImplemented in GENESIS via its equation utility0.10
0
≤Q
LF
KK
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LF optimization2a= 4.0 in., h= 2.5 in., Ny=2500 lb./in.
skint45
skint90
skint0
bladet45
bladet90
bladet0
0050.0 0050.0 0217.0
0050.0 0050.0 0250.0
0250.0 0250.0 0250.0
0250.0 0250.0 0250.0
W= 5.700 lb
K=64,642 psi√√√√in
W= 2.127 lb
K=99,986 psi√√√√in
0050.0 0050.0 0249.0
0050.0 0050.0 0050.0
W= 2.047 lb
K=105,927 psi√√√√in
0050.0 0050.0 0213.0
0050.0 0050.0 0250.0
W= 2.112 lb
K=101,000psi√√√√in
Cycle 0 Cycle 1
Cycle 2 Cycle 3
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a r
1 2 3 nb elements
yσσσσ
1yσσσσ
2yσσσσ 3yσσσσ
bynσσσσ
ar 125.r≈≈≈≈0.125 a
High Fidelity (HF) Model
rK
y πσ
2=
HF Direct OptimizationImplemented in GENESIS via its equation utility
0.10
0
≤Q
HF
KK
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HF optimization2a= 4.0 in., h= 2.5 in., Ny=2500 lb./in.
skint45
skint90
skint0
bladet45
bladet90
bladet0
0050.0 0050.0 0192.0
0050.0 0050.0 0250.0
0250.0 0250.0 0250.0
0250.0 0250.0 0250.0
W= 5.700 lb
K=61,935 psi√√√√in
W= 2.014 lb
K=99,982 psi√√√√in
0050.0 0050.0 0240.0
0050.0 0050.0 0050.0
W= 2.007 lb
K=104,643 psi√√√√in
0050.0 0050.0 0187.0
0050.0 0050.0 0250.0
W= 1.995 lb
K=101,440psi√√√√in
Cycle 0 Cycle 1
Cycle 2 Cycle 3
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! 250-passenger ! 5500 nmi. Range! Cruise Mach speed of 2.4
High Speed Civil Transport Wing Problem
cv4 +x
z
Location of maximumthickness (fixed)
Leading edge radius(fixed)
Outboard LE sweep (fixed)
xy
cv2
cv3
Wing semispan (fixed)
Nacelle locations(fixed)
cv1
! Root chord length! Tip chord length! In-board sweep angle! Thickness to chord ratio
Configuration variables
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Alternative to empirical weight equationsStructural Optimization
! Structural design variables" 26 skin panel thickness-plate" 12 spar cap areas-rod" 2 rib cap areas-rod
! Objective Function" Structural weight
! Constraints" Stress allowable" Buckling
Wing skin panel
Spar caps Rib capsShear webs
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DESIGN CYCLE HISTORY
! DESIGN OBJECTIVE MAXIMUM CONSTRAINT! CYCLE FUNCTION VIOLATION
! 0 79050 91.3%! 1 103380 0.0%! 2 100334 1.4%! 3 80670 32.0%! 4 106566 0.0%! 5 106414 0.0%
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Optimization Errors
! Modeling! Trapped in a local optimum
" Initial design" Round-off errors
! Convergence parameters
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Config. 2
PC WBMW (lb.)
70371
Alpha station WBMW (lb.)
90138
Config. 7
PC WBMW (lb.)
60286
Alpha station WBMW (lb.)
56808
Repairable Numerical Noise
70800 lbs.
Perturbed initial values
55835 lbs.
different optimization method
Optimization ErrorStructural Optimizations: GENESIS
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Optimization Errors
0.0001
0.001
0.01
0.1
1
10
100
0 5 10 15 20 25 30 35 40 45configuration
%(P
C-U
NIX
)/PC
objective functionWb
E PC
-UN
IX
0.0001
0.001
0.01
0.1
1
10
100
0 5 10 15 20 25 30 35 40 45configuration
%(P
C-U
NIX
)/PC
objective functionWb
E PC
-UN
IX