Adaptable Structures for Space Exploration · Adaptable Structures for Space Exploration ... There...
Transcript of Adaptable Structures for Space Exploration · Adaptable Structures for Space Exploration ... There...
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Adaptable Structures for Space ExplorationIan F.C. Smith
Applied Computing and Mechanics LaboratoryEPFL, Lausanne, Switzerland
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Serviceability controlObjective: Maintain top surface slope by modifying the self-stress state (telescopic strut length)
3 Compensated slope
4 Compensated slope
1 Initial slope
2 Altered slope
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Control system setup
Inductive standard displacement transducer
Transducer displacement data acquisition unit
Sensors
Control computer
Actuators
Modular inverter
CAN-busCAN-bus
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Linear analysisNon-linear analysis
Structural Response, mm
0
4
8
12
4 8 12 15
Number of active bars
8 12
Tests
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Methodology: Generate, analyse and test
Test for lowest RMS difference between required and provided slopes (we call this cost)
There is no closed form solution for strut movements
Required Slope Set of strut movements?
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Computationalcontrol
Actuators Structure Sensors
Active structural control
Time required to test all sets of possiblestrut movements is 3.6 E+22 years!
Perturbation
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Advantages of adapting cases
Control task 1.1-776 (CB III)
0
2
4
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0 500 1000Number of iterations
CostSearch alone (PGSL)
CBR (PGSL)
CBR (SA)
CBR (DH)
CBR (GA)
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0.1
1
10
100
1000
0 1000Iterations
Best Cost
PGSLCase based reasoning + PGSLThreshold
~one hour1.5 minutes
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Casebases
Cases were made from 280 loading situations
Five case bases are studied
210IV
2801438030Number of casesVIIIIIICasebase
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Performance enhancement over time
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100
150
200
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PureOptimization
I II III IV V
Number of cases
Iterations
Control-task 900_26
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Self diagnosis
DefinitionLoad identificationDamage location
MotivationControl in cases of partially known eventsAvoid direct measurements
MethodologyAnalyze structural response to the event and to perturbations
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Damaged structure
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Damage location
Case study : a cable is broken
48
2650
32
43
37 41 45
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Self-repair : stiffness
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Self-repairing : stress
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Multi-objective control command search
Multi-objective optimization rarely used for structural control (if ever)
Many solutions for slope compensation
Direct the search instead of taking the first solution
Criteria : Robustness of structure and control system
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Conflicting Objectives
Slope Stroke
Stress Stiffness
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Multi-objective optimization
Structure and Load Case
Control Command
Pareto Optimal SolutionsParetoPGSL
Slope Stroke Stress Stiffness
Hierarchical Selection1) Reject solutions with less than 95% of Slope compensation,
2) Reject the worst third for stroke,
3) Reject the worst third for stress,
4) Identify the best solution for stiffness.
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Multiple loading over service life
0 100 200 300 400 500 600 700-500
0
500Multi-objective control for multiple load application events
Step
Slo
pe
0 100 200 300 400 500 600 700-500
0
500Single objective (slope) control for multiple load application events
Step
Slo
pe
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2
3 45 6
1
2
3 4 56
Buckling of strut
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Results of TestsReuse of past experience improves performance
Learning : Increases in number of cases improves performance
Self Diagnosis : Evaluation of behavior during small actuator movements helps detect damaged structures
Repair : Lower stress and increased stiffness is possible
Multi-Objective Control : Increases robustness of both structure and active control system
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Autonomous Architecture
Greenland Summit Station
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Architectural and engineering conceptual proposal for the Summit Station in Greenland
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• Concepts for autonomously adjustableelements of structures + systems in extreme environments
• Improve understanding through design and research
• Test-bed capabilities for Moon and Mars missions
• Perform a study for future station expansion in Greenland.
Purpose of the Project
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Current Problems
• Station too small• Polluting power
generation• Snow drifting
• Not enough lab space• Lack of year round office
space• Multiple structures are
scattered on the site
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Concept
Triangular platform with 3 upper floors and 3 jacking columnsSelf-climbing structure that can be adjustedAdjustable edge skirt (not shown)
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Design objectives
• Minimize impact on environment during and after construction
• Accommodate differential settlement
• Incorporate an active structure into platform to minimize snow drifting around and under the building
• Versatile expansion and reconfiguration
• Possible temporary shut downs
• Elements to fit into payload of ski equipped LC-130 airplane
• Avoid need for heavy equipment
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Wind Tunnel Studies at EPFL
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Scale Model
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Test details
Over 50 different combinations of wind speed, wind direction, platform height and skirt designs
Wind velocity 3 - 5.5 m/s
17 equivalent hours per test
1.5 – 2.5 kg of heated glass spheres to simulate snow
Spheres weighed before and after
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0°
180°
Column A
Column C
Column B
Wind Direction
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Particle Transport
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Section A - A) α
A A
SkirtSkirt
Active Structure
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Section A - A) α
Skirt (completesurface)
Skirt (reducedsurface)
A A
Active Structure – Reduced surface
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Summary of test results
• Wind direction of 180° creates most snow transport• Elevations of less that 4.6 m above glacier risk being buried• Elevations greater than 4.6 m above glacier risk uneven
accumulation• Near rectangular shapes better than triangular shapes• Positive angles of approx 10° good for ensuring transport• Skirt size can be reduced to 75% of original size
More quantitative results not possible (modeling inaccuracies)
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This new design has the following benefits
• Use of renewable energy to minimize operational costs and environmental impact
• Adjustable support structure maintains necessary clearancebetween structure and snow surface
• Active structures along edges of buildings may reduce snow drifting, thereby reducing energy needs for snow removal
• Experience gained during construction and operation of the station will be valuable for future planetary exploration missions
General Results
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Conclusions
Adaptable structures have much potential for space exploration
Capacity for learning, self diagnosis, self repair and multi-objective control increases robustness when environment is not fully known
Such potential is currently being studied in an “analogue”environment in Greenland (with NSF, NASA, SICSA and RWDI)