Use of GENOPT and BIGBOSOR4 to optimize weld lands in axially compressed stiffened cylindrical shells and evaluation of the optimized designs by STAGS

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Use of GENOPT and BIGBOSOR4 to optimize weld
lands in axially compressed stiffened cylindrical
shells and evaluation of the optimized designs by
STAGS

• David Bushnell, retired
• Robert P. Thornburgh
• U.S. Army Research Laboratory, Langley Research
  Center

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A cylindrical shell with embedded T-stiffened
weld lands
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SUMMARY OF TALK

• Purpose of the work
• What is a T-stiffened weld land?
• Decision variables for optimization
• The huge torus model of a shell of revolution
• About GENOPT and BIGBOSOR4
• Two-phase optimization problem
• Optimization of the acreage cylindrical shell
• Optimization of the T-stiffened weld land
• Evaluation of the optimized design by STAGS

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Purposes of the work

• A quick and dirty tool was needed to optimize
  T-stiffened weld lands embedded in cylindrical
  shells
• A paper was needed that provides enough detail so
  that the reader can use GENOPT/BIGBOSOR4 to
  optimize other shell structures.
• Examples are needed showing how to use a
  general-purpose finite element program such as
  STAGS to evaluate optimized designs produced by
  GENOPT/BIGBOSOR4

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What is a T-stiffened weld land?
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Decision variables for the optimization of a
T-stiffened weld land
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huge torus model of a cylindrical shell
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Huge torus model of 180 degrees of a
cylindrical shell with T-stiffened weld lands
every 120 degrees
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Huge torus model of 180 degrees of a
cylindrical shell with T-stiffened weld lands
every 120 degrees
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Cross section of huge torus model showing how
the shell segments in the BIGBOSOR4 model would
be numbered in an example that has T-stiffened
weld lands embedded in the acreage cylindrical
shell at 60-degree intervals
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About BIGBOSOR4 and GENOPT

• BIGBOSOR4 is essentially the same as BOSOR4
  except that it will handle many more shell
  segments than BOSOR4.
• GENOPT is described in the next several slides.

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PURPOSES OF GENOPT

• Convert an analysis into a user-friendly analysis
• Make the step into the world of automated
  optimization easy

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PROPERTIES OF GENOPT

• An analysis of a fixed design is automatically
  converted into an optimization of that design
  concept.
• GENOPT can be applied in any field. It is not
  limited to structural analysis.
• User-specified data names and one-line
  definitions appear throughout the output. Hence
  the input and output is in the jargon of the
  GENOPT-users field.
• GENOPT is a FORTRAN program that writes other
  FORTRAN programs.

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ARCHITECTURE OF GENOPT

• The program system generated by GENOPT has the
  BEGIN, DECIDE, MAINSETUP, OPTIMIZE,
  SUPEROPT, CHANGE, CHOOSEPLOT, CLEANUP
  architecture typical of other software written by
  the first author for specific applications
  (BOSOR4, BIGBOSOR4, BOSOR5, PANDA2)

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TWO TYPES OF USER

• GENOPT USER Uses GENOPT to create a
  user-friendly system of programs for optimizing a
  class of objects. In this paper the generic class
  is called weldland
• END USER Uses the user-friendly system of
  programs created by the GENOPT user to optimize
  objects in the class covered by the GENOPT USERs
  program system. In this paper the specific member
  of the weldland class is called wcold.

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ROLE OF THE GENOPT USER(1)

• Choose a generic class of problems for which a
  user-friendly analysis and/or optimization
  program is needed.
• Decide which phenomena (behaviors) may affect the
  design. These are called behavioral
  constraints. Examples stress, buckling, modal
  vibration, displacement, clearance.
• Establish the objective of the optimization.
  Examples minimum weight, minimum cost, minimum
  surface rms error, etc.

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ROLE OF THE GENOPT USER(2)

• Organize the input data. Simple constants?
  Arrays?, Tabular data?, Decision variables?
• For each input datum choose (a) a meaningful
  name, (b) a clear one-line definition, (c)
  supporting help paragraph(s).
• Write or borrow algorithms to predict various
  behaviors, such as buckling, modal vibration, and
  stress, that may affect the evolution of the
  design during optimization cycles.
• Test the new user-friendly program system.
• Interact with the END USER.

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ROLE OF THE END USER(1)

• Choose a specific problem that fits within the
  generic class established by the GENOPT USER.
• Choose an initial design with appropriate loads
  and an allowable and a factor of safety for each
  behavior.
• Choose appropriate decision variables with
  appropriate lower and upper bounds.
• Choose linked variables and linking expressions
  (equality constraints), if any. (These are chosen
  by the END USER in the processor called DECIDE).

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ROLE OF THE END USER(2)

• Choose inequality constraints, if any. (To be
  chosen by the END USER in DECIDE).
• During optimization use enough restarts,
  iterations, and CHANGE commands in the search
  for a global optimum design. (This is now done
  automatically by SUPEROPT).
• Interact with the GENOPT USER.
• Check the optimum design via general-purpose
  programs and/or tests.

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THE GENOPT MENU OF COMMANDS(1)
Command for the GENOPT USER and the END
USER GENOPTLOG (activates the GENOPT menu of
commands). Commands for the GENOPT USER GENTEXT
(GENOPT USER generates a prompt file with help
paragraphs. GENTEXT produces FORTRAN program
fragments, some complete FORTRAN programs, and
two skeletal FORTRAN subroutines to be fleshed
out later by the GENOPT user.) GENPROGRAMS
(GENOPT USER generates executable elements
BEGIN, DECIDE, MAINSETUP, OPTIMIZE, CHANGE,
STORE, CHOOSEPLOT, DIPLOT). INSERT (GENOPT USER
adds parameters, if necessary). CLEANGEN (GENOPT
user cleans up GENeric case files).
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THE GENOPT MENU OF COMMANDS(2)
Commands for the END USER BEGIN (END USER
provides initial design, material properties,
loads, allowables, and factors of safety). DECIDE
(END USER chooses decision variables, bounds,
linked variables, inequality constraints, and
escape variables). MAINSETUP (END USER sets up
strategy parameters for simple analysis of a
fixed design or optimization). OPTIMIZE (END USER
performs the analysis or optimization). SUPEROPT
(END USER tries to find a global
optimum). CHANGE (END USER changes some
variables).
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THE GENOPT MENU OF COMMANDS(3)
CHOOSEPLOT (END USER chooses which decision
variables to plot versus design
iterations). DIPLOT (END USER obtains postscript
plot files for margins and/or decision variables
and the objective versus design
iterations). CLEANSPEC (END USER cleans up
SPECific case files).
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SEVEN ROLES THAT VARIABLES PLAY
1. A possible decision variable for optimization,
typically a dimension of a structure. 2. A
constant parameter (cannot vary as the design
evolves), typically a control integer or material
property, but not a load, allowable, or factor of
safety, which are asked for later. 3. A parameter
characterizing the environment, such as a load
component or a temperature. 4. A quantity that
describes the response (behavior) of the
structure to its environment, (e.g. maximum
stress, buckling load, natural frequency, maximum
displacement). 5. An allowable, such as maximum
allowable stress. 6. A factor of safety. 7. The
objective, for example, weight.
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Glossary of variable names and one-line
definitions created by the GENOPT user for the
generic case called weldland
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Part of output from the specific case called
wcold. The variable names and one-line
definitions created by the GENOPT user show up in
the output seen by the end user.
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Part of the weldland.PRO file created
automatically by GENOPT for the generic case
called weldland
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GENPROGRAMS CREATES THESE EXECUTABLE FILES
BEGIN (end user supplies starting design, loads,
etc.) DECIDE (end user chooses decision
variables, bounds, equality and inequality
constraints, etc.) MAINSETUP (end user chooses
analysis type, which behaviors to process,
how many design iterations, etc.) CHANGE (end
user can change values of variables.) AUTOCHANGE
(automatic random change in decision
variables used by SUPEROPT.)
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GENPROGRAMS CREATES THESE EXECUTABLE FILES
(continued)
CHOOSEPLOT (end user chooses what variables to
plot v. design iterations.) OPTIMIZE
(end user launches the mainprocessor run,
either analysis of a fixed design or
optimization or design sensitivity
analysis.) STORE (variables, margins,
objective for all design iterations are
stored for display in the .OPP file.)
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A two-phase optimization is required

• First the acreage cylindrical shell must be
  optimized. This is a cylindrical shell with
  internal stringers and internal rings of
  rectangular cross section. The effect of
  cold-bending fabrication is included in the
  optimization loop.
• Next, a typical T-stiffened weld land to be
  embedded in the acreage must be optimized.
  During this second phase the acreage properties
  are held constant.

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Phase 1 optimization of nasacoldbend acreage
cylindrical shell by PANDA2
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Phase 2 Optimization of the T-stiffened weld
land by GENOPT/BIGBOSOR4
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Phase 2 T-stiffened weld land optimized by
GENOPT/BIGBOSOR4
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General buckling from wcold model
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Critical general buckling mode from STAGS
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A slightly higher general buckling mode from STAGS
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Critical general buckling mode from Thornburghs
STAGS model
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Critical general buckling mode from Thornburghs
STAGS model
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Local buckling from nasacoldbend/PANEL3 model
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Local buckling mode from Thornburghs STAGS model
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Weld land plate/T-stiffener buckling from wcold
model
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Weld land plate/T-stiffener buckling mode from
Thornburghs STAGS model
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T-stiffener crippling from nasacoldbend/PANEL3
model
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T-stiffener crippling from STAGS model
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T-stiffener rolling from nasacoldbend/PANEL3
model
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T-stiffener rolling from STAGS model
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Load-displacement curves from STAGS models
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Load-displacement curves from STAGS models for
the case in which T-stringer slenderness is
constrained.
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Conclusions

• The optimized T-stiffened weld lands are verified
  by various STAGS models.
• It is best to optimize including constraints on
  the slenderness of the T-stringers.
• The behavior is insensitive to the number of
  T-stiffened weld lands in the cylindrical shell.
• The long paper is detailed enough so that it can
  serve as a users manual for the use of
  GENOPT/BIGBOSOR4 in other contexts.