Transcript Integration Frameworks - ISOGRID-SST

Habitat for Space and Lunar
Environments - Light Weight
Structure Concept
AIAA SPACE 2008
Conference & Exposition
Paul Slysh
PS Associates
John Carsten, Dr. Peter J. Rohl, Andrew Jabola
Advatech Pacific
September 9, 2008
Overview
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The Companies: PS Associates and Advatech Pacific
The Habitat Concept
Design Tool: Isogrid SST
CAD Model
Finite Element Analysis
Conclusions
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The Companies
PS Associates:
• Small business, started 1988
• Invented habitat concept presented here
• Developed SST design software
• Based in San Diego, CA
Advatech Pacific:
• Small business, ~90 employees, started in 1995
• Design, analysis and software solution provider
• HQ in Redlands, CA, with branch offices in Palmdale, San Diego,
Huntsville, AL and Tempe, AZ
• Developed CAD and CAE model for habitat concept
• Performed FE structural analysis
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The Habitat Concept
• Shown Deployed on the Lunar Surface
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The Habitat Concept
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Provides structural thermal and meteoroid protection
Spokes join interior and exterior structures
Consists of frustums and domes
Deployed by EVA and robotics
Stowed-to-deployed volume: 0.3 and lower
Lighter and better stowed than inflatable structures
Uses flanged isogrid
Provides pegboards for mounting equipment
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Stowed Configuration
• Nested Inner Structures Stowed Within the Nested Outer Structures
• Interior Volume Available for Cargo
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Layout of an Inner Section
• Isogrid on the Inside Serves as Pegboard for Mounting Equipment
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Flat Pattern of Isogrid Frustum
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Bolted Deployed Structure
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Structural Design Tool “SST”
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SST “Shell Structures Tools”
SST is a design and analysis tool for stiffened thin-walled structures
SST has been developed and validated over the past 40 years
SST facilitate rapid application to complex design objectives
Initial verification by Advatech successful
SST designs the following structure types:
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Isogrid
Waffle
Skin stringer
Honeycomb
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Chemically milled
Skin frame
Fluted core sandwich
Monocoque
Composites
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SST Input Categories
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Design Criteria
External Loads
Geometry
Interfaces
Material Selection
Structure Type
Mfg. Methods
Kick Ring Requirements
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Frame Locations
Analytical Models
Knockdown Factors
Mfg. Tolerances
Clearance Envelopes
Safety Factors
Cutout Requirements
Weight Bogie
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SST Capabilities
• Weight & Performance
Optimization
• Internal Loads
• Section Properties
• FEA Input
• Flat Patterns
• Performance Margins
• Trades
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Mass Properties
Mfg. Planning
NC Program
Rendering
Reports
Test Plans
Modal Response
Body Stiffness
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SST Top-Level Program Flow
Design Algorithm:
• Select initial design
• Compute weight-tolowest-margin ratio
• Increment features to
raise margin floor
• Only decrease weightto-lowest-margin ratio.
• Continue until margins
are positive
• Use SST to create final
design definition
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SST User Interface
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SST Output
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General instability
Mass properties
Skin buckling
Web, flange buckling
Bosses and cutouts
Kick rings
Frames
Shell intersection sizing
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Internal line loads
Bolted flanges
Dimensioned geometry
Modal response
Unique NC tool paths
High cycle fatigue
Crack initiation, growth
Margin summaries
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SST Summary Output
SST ISOGRID STRUCTURES
CASE
HABITAT LUNAR
DATE
4 May 2008
STRUCTURE
FLANGED STD. ISOGRID
MATERIAL
-423 F ALUM 2219-T851
ELEMENT
4 , 1 OPTION 1
UNITS
MODEL
ENGLISH UNITS
BODY, PRESSURE AND ACOUSTICALLY LOADED ISOGRID SHELL
GEOMETRY, WEIGHT
15.5 in.
SECTION LENGTH
TOTAL LENGTH
62 in.
FRAME SPACING
62 in.
SHELL MINIMUM RADIUS 40 in.
STIFFNESS
EI BENDING 1.25E+11 lb-in^2
AE AXIAL
1.18E+8 lbs
KAG SHEAR 2.21E+7 lbs
GJ TORSION 9.4E+10 lb-in^2
SHELL MAXIMUM RADIUS 47 in.
SECTION WEIGHT
18.2 lbs
TOTAL WEIGHT
77.5 lbs
UNIT AREA WEIGHT
.0045 lbs/sqin
WT. - EQUIV. THICKNESS .0441 in.
SECTIONS
NO. STATION RADIUS
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0 in.
40 in.
2
15.5 in.
41.75 in.
3
31 in.
43.5 in.
4
46.5 in.
45.25 in.
5
62 in.
47 in.
MATERIAL
ULTIMATE SRENGTH 81000 psi
YIELD SRENGTH
61000 psi
SHEAR SRENGTH
46200 psi
YOUNGS MODULUS
1.24E+7 psi
SHEAR MODULUS
4.65E+6 psi
DENSITY
.102 lbs/cuin
POISSON'S RATIO
.33
RAMBERG OSGOOD 15
FACTORS, MARGINS
FAILURE ULT. YLD. INSTA. SP8007 SKIN
FACTOR 1.5
1.32
MARGINS 15.7 13.3
1.5
1.5
1.5
20.4
60.7
.303
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Stiffener Detail Drawing
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SST and NX
• SST provides and excellent tool for designing ISOGRID
and similar structures
• We would like to combine SST with a state-of-the-art
CAD and CAE package for finite element analysis,
visualization, and manufacturing
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CAD Model
• Using the parameters from SST, a shell model and solid
model of the structure were created in Siemens NX6
Solid Model Full Structure
Shell Model Panel
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CAD Model
• The shell model consists of 2D sheets that represent the
skin and stiffener webs
Inner Frustum Shell Model
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CAD Model
• The solid model creates a single panel with full detail of
the structure, which was then instanced circumferentially
• Both the solid and shell models are associative to the
underlying parametric geometry
Outer Frustum Panel
Outer Frustum
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Solid Model Creation
• One of the issues with Siemens NX6 is rolling a flatpattern with varying thickness into a cylindrical shape
• Due to this difficulty, a 2D sketch of an instance of the
pattern was wrapped around the frustum
• Thicknesses were then applied to the 2D sketch to
create the skin, stiffener webs, and flanges
• Finally, the model was instanced, creating the full solidmodel structure
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Solid Model Creation
2D Sketch Before
Wrapping
2D Sketch Wrapped
Around Cone Frustum
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Finite Element Model (FEM)
• A FEM using the CAD Associative shell model was
created
• 2D linear shell elements represented the skin,
top/bottom flanges, and stiffener webs while 1D beam
elements represented the stiffener flanges
• Lower and higher resolution FEMs were created
Lower Resolution
Higher Resolution
Approx. DOF:
85680
Approx. DOF:
300600
Total number of elements:
21930
Total number of elements:
66360
Total number of nodes:
14430
Total number of nodes:
50100
Number of Beam elements:
7140
Number of Beam elements:
14280
Number of Quad4 elements:
14400
Number of Quad4 elements:
48840
Number of Tri3 elements:
390
Number of Tri3 elements:
3240
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Finite Element Model (FEM)
Full Finite Element
Model
Detail of Finite Element
Model
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Finite Element Analysis
• The FEM is solved using NX NASTRAN
• A modal analysis was performed on our FEM to test the
model
• Global stiffnesses of the FEM were calculated for
comparison against SST
Global Stiffness Comparison
Lower Res.
Higher Res.
SST
Axial
AE
1.0189E+08
1.0223E+08
1.1800E+08
Torsion
GJ
7.7000E+10
7.7549E+10
9.4000E+10
Shear
KAG
1.8000E+07
1.8010E+07
2.2100E+07
GJ
1.5376E+11
1.5651E+11
1.2500E+11
Bending
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Finite Element Analysis
Mode 5: 19.6 Hz
Von-Mises Stress Plot
Averaged
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Where We Are
• SST Provides an excellent tool for quickly and efficiently
designing a preliminary ISOGRID structure
• We have shown that we can develop both a CAD model
for visualization and an analysis model using NX6 and
parameters from SST
• Analyses performed show corroboration with SST results
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Next Steps
• Detailed stress analysis on a repeating sub-section cutout of the solid model will be performed using ESRD
StressCheck
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Next Steps
• Perform a deeper study into buckling and instability
using FEA methods.
Preliminary Linear Buckling Test
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Next Steps
• Model and analyze the full habitat structure
• Create a direct integration between SST and NX6 to
create a single, seamless tool
PS Associates SST
Siemens NX
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Conclusion
• SST provides a tool for quickly and efficiently developing an
ISOGRID Structure
• CAD and CAE methods provide a detailed analysis using finite
element methods along with providing models for CAE and
manufacturing
• ISOGRID structures provide an excellent concept for lunar habitats
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SST and NX
• SST provides and excellent tool for designing ISOGRID
and similar structures
• We would like to combine SST with a state-of-the-art
CAD and CAE package for finite element analysis,
visualization, and manufacturing
33
CAD Model
• Using the parameters from SST, a shell model and solid
model of the structure were created in Siemens NX6
Solid Model Full Structure
Shell Model Panel
34
CAD Model
• The shell model consists of 2D sheets that represent the
skin and stiffener webs
Inner Frustum Shell Model
35
CAD Model
• The solid model creates a single panel with full detail of
the structure, which was then instanced circumferentially
• Both the solid and shell models are associative to the
underlying parametric geometry
Outer Frustum Panel
Outer Frustum
36
Solid Model Creation
• One of the issues with Siemens NX6 is rolling a flatpattern with varying thickness into a cylindrical shape
• Due to this difficulty, a 2D sketch of an instance of the
pattern was wrapped around the frustum
• Thicknesses were then applied to the 2D sketch to
create the skin, stiffener webs, and flanges
• Finally, the model was instanced, creating the full solidmodel structure
37
Solid Model Creation
2D Sketch Before
Wrapping
2D Sketch Wrapped
Around Cone Frustum
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Finite Element Model (FEM)
• A FEM using the CAD Associative shell model was
created
• 2D linear shell elements represented the skin,
top/bottom flanges, and stiffener webs while 1D beam
elements represented the stiffener flanges
• Lower and higher resolution FEMs were created
Lower Resolution
Higher Resolution
Approx. DOF:
85680
Approx. DOF:
300600
Total number of elements:
21930
Total number of elements:
66360
Total number of nodes:
14430
Total number of nodes:
50100
Number of Beam elements:
7140
Number of Beam elements:
14280
Number of Quad4 elements:
14400
Number of Quad4 elements:
48840
Number of Tri3 elements:
390
Number of Tri3 elements:
3240
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Finite Element Model (FEM)
Full Finite Element
Model
Detail of Finite Element
Model
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Finite Element Analysis
• The FEM is solved using NX NASTRAN
• A modal analysis was performed on our FEM to test the
model
• Global stiffnesses of the FEM were calculated for
comparison against SST
Global Stiffness Comparison
Lower Res.
Higher Res.
SST
Axial
AE
1.0189E+08
1.0223E+08
1.1800E+08
Torsion
GJ
7.7000E+10
7.7549E+10
9.4000E+10
Shear
KAG
1.8000E+07
1.8010E+07
2.2100E+07
GJ
1.5376E+11
1.5651E+11
1.2500E+11
Bending
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Finite Element Analysis
Mode 5: 19.6 Hz
Von-Mises Stress Plot
Averaged
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Where We Are
• SST Provides an excellent tool for quickly and efficiently
designing a preliminary ISOGRID structure
• We have shown that we can develop both a CAD model
for visualization and an analysis model using NX6 and
parameters from SST
• Analyses performed show corroboration with SST results
43
Next Steps
• Detailed stress analysis on a repeating sub-section cutout of the solid model will be performed using ESRD
StressCheck
44
Next Steps
• Perform a deeper study into buckling and instability
using FEA methods.
Preliminary Linear Buckling Test
45
Next Steps
• Model and analyze the full habitat structure
• Create a direct integration between SST and NX6 to
create a single, seamless tool
PS Associates SST
Siemens NX
46
Conclusion
• SST provides a tool for quickly and efficiently developing an
ISOGRID Structure
• CAD and CAE methods provide a detailed analysis using finite
element methods along with providing models for CAE and
manufacturing
• ISOGRID structures provide an excellent concept for lunar habitats
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