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Structural Reliability Considerations for Lunar Base Design

Structural Reliability Considerations for Lunar Base Design. Florian RUESS & Benjamin BRAUN. Rutgers Symposium on Lunar Settlements 3-8 June 2007 New Brunswick, NJ. HE 2 Habitats for Extreme Environments www.he-squared.com. Contents.

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Structural Reliability Considerations for Lunar Base Design

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  1. Structural Reliability Considerationsfor Lunar Base Design Florian RUESS & Benjamin BRAUN Rutgers Symposium onLunar Settlements3-8 June 2007New Brunswick, NJ HE2 Habitats for Extreme Environments www.he-squared.com

  2. Contents Ruess / Braun - Structural Reliability Considerations for Lunar Base Design • Motivation • Structural Concepts • Structural Reliability • Example • V. Conclusions www.he-squared.com

  3. I. Motivation Ruess / Braun - Structural Reliability Considerations for Lunar Base Design I. Motivation – II. Structural Concepts – III.Structural Reliability – IV. Example – V. Conclusions

  4. NASA Constellation Program Ruess / Braun - Structural Reliability Considerations for Lunar Base Design The Vision for Space Exploration Photo: NASA Goals on the Moon: Science, Exploration Preparation, Eventual Settlement… I. Motivation – II. Structural Concepts – III.Structural Reliability – IV. Example – V. Conclusions

  5. Everybody wants to go to the Moon Ruess / Braun - Structural Reliability Considerations for Lunar Base Design The European Aurora program intends to sends humans to the Moon by 2024 China’s Chang’e program plans human missions to the Moon after 2020 Russia, India, Japan and many others also have lunar ambitions Photo: ESA I. Motivation – II. Structural Concepts – III.Structural Reliability – IV. Example – V. Conclusions

  6. II. Structural Concepts Ruess / Braun - Structural Reliability Considerations for Lunar Base Design I. Motivation – II. Structural Concepts – III.Structural Reliability – IV. Example – V. Conclusions

  7. Structure Classification Ruess / Braun - Structural Reliability Considerations for Lunar Base Design first generation: pre-fabricated and pre-outfitted modules like the ones for the ISS second generation: locally assembled structures after a certain presence on the Moon as been established third generation: structures exclusively made from local materials I. Motivation – II. Structural Concepts – III.Structural Reliability – IV. Example – V. Conclusions

  8. Structural Concepts Ruess / Braun - Structural Reliability Considerations for Lunar Base Design Focusing on second generation habitats, most proposed concepts can be divided into: • inflatable structures • cable structures • rigid structures Photo: NASA I. Motivation – II. Structural Concepts – III.Structural Reliability – IV. Example – V. Conclusions

  9. Rigid Structures Ruess / Braun - Structural Reliability Considerations for Lunar Base Design Advantages: • experience • robustness • all-in-one concept possible Disadvantage: Photo and concept: Schroeder et al. • relatively large volume + mass I. Motivation – II. Structural Concepts – III.Structural Reliability – IV. Example – V. Conclusions

  10. A Tied-Arch Shell Structure Ruess / Braun - Structural Reliability Considerations for Lunar Base Design Concept by HE2 and H. Benaroya I. Motivation – II. Structural Concepts – III.Structural Reliability – IV. Example – V. Conclusions

  11. Structural Design on the Moon Reliability-based concept • complex to use • efficient • quantitive measure of safety Ruess / Braun - Structural Reliability Considerations for Lunar Base Design Scope of existing design standards exceeded Many more uncertainties exist ► resistances, e.g. new materials ► loads, e.g. micrometeoroid impacts Global safety factor concept • easy to apply • uneconomic • actual reliability unknown I. Motivation – II. Structural Concepts – III. Structural Reliability – IV. Example – V. Conclusions

  12. III. Structural Reliability Ruess / Braun - Structural Reliability Considerations for Lunar Base Design I. Motivation – II. Structural Concepts – III. Structural Reliability – IV. Example – V. Conclusions

  13. Classical vs. Structural Reliability • Technical components • large numbers, same type • single failure mode • relative failure frequencies • Structural systems • unique components • different failure modes • rare failures • Characteristics of the reliability analysis • failure due to ageing • estimation of life-time • failure due to extreme events • measure of safety © KMJ probabilistic modeling of time until failure probabilistic modeling of resistances and loads ► failure rate ► reliability index b Ruess / Braun - Structural Reliability Considerations for Lunar Base Design 1000 hours / life I. Motivation – II. Structural Concepts – III. Structural Reliability – IV. Example – V. Conclusions

  14. How to picture the reliability index ? fM (x) probability density function of the safety margin M failure safe M x b bM Ruess / Braun - Structural Reliability Considerations for Lunar Base Design Probabilistic models for the uncertain►resistance R►load S Probability of failure: In case of two N-distributed variables: I. Motivation – II. Structural Concepts – III. Structural Reliability – IV. Example – V. Conclusions

  15. Limit state functions Ruess / Braun - Structural Reliability Considerations for Lunar Base Design In the general case: functions of several random variables x u2 safeg(u) > 0 R – S = fR(x) – fS(x) = g(x) Limit state function g(x) can be u1 ►linear failureg(u) < 0 ►nonlinear Normalisation of therandom variables x: g(x)→ g(u) g(u) = 0 I. Motivation – II. Structural Concepts – III. Structural Reliability – IV. Example – V. Conclusions

  16. Limit state functions g (u) = 0 b a - vector Ruess / Braun - Structural Reliability Considerations for Lunar Base Design In the general case: functions of several random variables x u2 safeg(u) > 0 R – S = fR(x) – fS(x) = g(x) Limit state function g(x) can be u1 ►linear failureg(u) < 0 ►nonlinear Normalisation of therandom variables x: g(x)→ g(u) g(u) = 0 I. Motivation – II. Structural Concepts – III. Structural Reliability – IV. Example – V. Conclusions

  17. How safe is safe enough ? 2.33 10-2 3.09 10-3 3.72 10-4 4.27 10-5 Target reliabilities on the Moon ? 4.77 10-6 Ruess / Braun - Structural Reliability Considerations for Lunar Base Design b Pf • Level of safety depends on • Societal acceptance • Costs • Failure consequences • injuries • loss of life • economic loss Structural codes on Earth I. Motivation – II. Structural Concepts – III. Structural Reliability – IV. Example – V. Conclusions

  18. IV. Example Ruess / Braun - Structural Reliability Considerations for Lunar Base Design I. Motivation – II. Structural Concepts – III.Structural Reliability – IV. Example – V. Conclusions

  19. Example Calculation Ruess / Braun - Structural Reliability Considerations for Lunar Base Design Internal pressure I. Motivation – II. Structural Concepts – III.Structural Reliability – IV. Example – V. Conclusions

  20. Example Calculation Ruess / Braun - Structural Reliability Considerations for Lunar Base Design Regolith cover I. Motivation – II. Structural Concepts – III.Structural Reliability – IV. Example – V. Conclusions

  21. Assumptions for random variables Limit state function g(x) Ruess / Braun - Structural Reliability Considerations for Lunar Base Design Coefficient of variation (COV) 0.07 0.30 0.12 0.03 0.04 Random variable Yield strength fy (aluminium fy,nom = 50 kPa) Internal pressure sint Regolith cover sreg Cross section A Section modulus W Mean value 54.1 kPa 69.0 kPa 8.3 kPa nominal value nominal value I. Motivation – II. Structural Concepts – III.Structural Reliability – IV. Example – V. Conclusions

  22. Calculation results u2 safe g (u) = 0 afy asint asreg aA aW - 0.797 0.382 0.280 - 0.212 - 0.308 u1 b failure a- vector g(u) = 0 Ruess / Braun - Structural Reliability Considerations for Lunar Base Design • Target reliability b = 4.77 • Iteration result for a - values: ►Determination of required cross - sectional properties I. Motivation – II. Structural Concepts – III.Structural Reliability – IV. Example – V. Conclusions

  23. Savings in Structural Mass Ruess / Braun - Structural Reliability Considerations for Lunar Base Design on Earth 100 % 73 % 40 % 30 % Global safety factor Reliability-based LRFD gglob = 5.0 gglob = 4.0 Pf = 10-6, gglob 2.6 Pf = 10-4, gglob 2.1 I. Motivation – II. Structural Concepts – III.Structural Reliability – IV. Example – V. Conclusions

  24. V. Conclusions Ruess / Braun - Structural Reliability Considerations for Lunar Base Design I. Motivation – II. Structural Concepts – III.Structural Reliability – IV. Example – V. Conclusions

  25. Conclusions Ruess / Braun - Structural Reliability Considerations for Lunar Base Design • Reliability-based framework most appropriate • Agreement on target reliabilities necessary • Further steps should include … • Influence of system redundancy • Consideration of maintenance strategies • Collection and statistical evaluation of data I. Motivation – II. Structural Concepts – III.Structural Reliability – IV. Example – V. Conclusions

  26. Thank you for your attention Ruess / Braun - Structural Reliability Considerations for Lunar Base Design www.he-squared.com

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