adaptable structures for space exploration · adaptable structures for space exploration ... there...

ÉCOLE POLYTEC HNIQUEFÉDÉRALE DE LAUSANNE

Slide 1/41Lausanne, December 2006

Adaptable Structures for Space ExplorationIan F.C. Smith

Applied Computing and Mechanics LaboratoryEPFL, Lausanne, Switzerland



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



Control system setup

Inductive standard displacement transducer

Transducer displacement data acquisition unit

Sensors

Control computer

Actuators

Modular inverter

CAN-busCAN-bus



Linear analysisNon-linear analysis

Structural Response, mm

0

4

8

12

4 8 12 15

Number of active bars

8 12

Tests



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?



Computationalcontrol

Actuators Structure Sensors

Active structural control

Time required to test all sets of possiblestrut movements is 3.6 E+22 years!

Perturbation



Advantages of adapting cases

Control task 1.1-776 (CB III)

0

2

4

6

8

10

12

14

0 500 1000Number of iterations

CostSearch alone (PGSL)

CBR (PGSL)

CBR (SA)

CBR (DH)

CBR (GA)



0.1

1

10

100

1000

0 1000Iterations

Best Cost

PGSLCase based reasoning + PGSLThreshold

~one hour1.5 minutes



Casebases

Cases were made from 280 loading situations

Five case bases are studied

210IV

2801438030Number of casesVIIIIIICasebase



Performance enhancement over time

0

50

100

150

200

250

300

350

400

PureOptimization

I II III IV V

Number of cases

Iterations

Control-task 900_26



Self diagnosis

DefinitionLoad identificationDamage location

MotivationControl in cases of partially known eventsAvoid direct measurements

MethodologyAnalyze structural response to the event and to perturbations



Damaged structure



Damage location

Case study : a cable is broken

48

2650

32

43

37 41 45



Self-repair : stiffness



Self-repairing : stress



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



Conflicting Objectives

Slope Stroke

Stress Stiffness



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.



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

1

2

3 45 6

1

2

3 4 56

Buckling of strut



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

ÉCOLE POLYTECHNIQUEFÉDÉRALE DE LAUSANNE

Autonomous Architecture

Greenland Summit Station


Architectural and engineering conceptual proposal for the Summit Station in Greenland


• 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


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


Concept

Triangular platform with 3 upper floors and 3 jacking columnsSelf-climbing structure that can be adjustedAdjustable edge skirt (not shown)


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


Wind Tunnel Studies at EPFL


Scale Model


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


0°

180°

Column A

Column C

Column B

Wind Direction

Particle Transport


Section A - A) α

A A

SkirtSkirt

Active Structure


Section A - A) α

Skirt (completesurface)

Skirt (reducedsurface)

A A

Active Structure – Reduced surface


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)


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



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)

adaptable structures for space exploration · adaptable structures for space exploration ... there...

Documents