Including the Effect of a Future Test and Redesign in Reliability Calculations

Villanueva, Diane; Haftka, Raphael T.; Sankar, Bhavani V.

doi:10.2514/1.j051150

Cited by 19 publications

(9 citation statements)

References 9 publications

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“…(3), its risk of redesign after a certification test is evaluated. Taking an advantage of the capability of probabilistic design, our earlier work proposed a method to simulate multiple possible future outcomes out of post-design processes, including test observation, error calibration, redesign decision, and redesign [5,24]. The method deploys uncertainty propagation throughout the future processes and allows us to calculate the probability of redesign and the expected mass after redesign if needed for any given design candidate.…”

Section: American Institute Of Aeronautics and Astronauticsmentioning

confidence: 99%

Conservativeness in Failure Probability Estimate: Redesign Risk vs. Performance

Matsumura

Haftka

Kim

2013

54th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference

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Being conservative is in the nature of engineering design in order to compensate for uncertainty. Traditionally in the deterministic design approach, the level of conservativeness has not been a major concern for manufacturers in aerospace since it is defined and strictly required by the regulators as factors of safety. However, once a probabilistic design approach comes into play, the selection of conservativeness of probability of failure estimate considering epistemic uncertainty is an inevitable issue because conservativeness penalizes system performance. This paper investigates the tradeoff between performance and risk in development (redesign after certification test), to which regulators do not pay much attention. We conduct the study in the context of risk aversion of expected utility theory. With a practical design problem, a thermal protection system, it is shown that the level of risk aversion of the decision maker is not the key driver of the conservativeness selection, but the severity of redesign cost is. On top of that, the study reveals that expected utility theory may give unreasonable solutions if the level of risk aversion is set too high.

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Section: American Institute Of Aeronautics and Astronauticsmentioning

confidence: 99%

Conservativeness in Failure Probability Estimate: Redesign Risk vs. Performance

Matsumura

Haftka

Kim

2013

54th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference

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“…Use relationships for the elastic constants in terms of volume fraction from mixture rule, the correlation between material properties are calculated. Variabilities of material properties are given in table 9. We assume that the nominal material properties in table 7 have variabilities in table 9 Uniform distribution Imperfection mode is randomly selected among mode 1, 2, 3, and 4 Load CV=10% for P Normal distribution…”

Section: Uncertainty Modeling Of Curved Composite Panelmentioning

confidence: 99%

Estimating Probability of Failure of Composite Laminated Panel with Multiple Failure Modes

Park¹,

Kim²,

Haftka³

2012

53rd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference

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As composite structures play a key role in aircraft structure design, assessing probability of failure (PF) of the composite structures has become important to ensuring safety of the aircraft design. To assess the PF of the design, computational models are frequently used to estimate probability of the composite structures but the computational models have uncertainty in predicting failures due to lacking knowledge of composite structure failures. Structural tests can provide additional knowledge of the failures to effectively reduce the uncertainty in the computational model. The presence of multiple failure modes due to variabilities is the other concern because correlated failure modes causes difficulty to estimate PF and it brings significant error for use of the effective reliability analysis methods, such as FORM or SORM. Undetected failure mode is the other issue relevant to the multiple failure modes. A single test can detect one failure mode, each failure modes has different probability of occurrence. Hence, a existing failure mode may not be detected and neglected. Possibly we have significantly under estimated PF. In the study, we make an uncertainty quantification model to estimate PF for correlated failure modes. Also the probability of failure occurrence of each failure modes is also estimated with the model. The model is demonstrated through a simple example and PF estimation of a curved composite panel with a hole is made. From the numerical study, it is observed that performing a single failure test can significantly reduce conservativeness on estimating PF. Test for a given probability of failure allows lighter design.

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“…Redesigning one component may trigger the propagation of changes throughout the system; however, this subsequent change propagation is not directly addressed in this study. Villanueva et al simulated the effects of future tests and redesign on an integrated thermal protection system (ITPS) considering the effect of redesign on the uncertainty in the probability of failure [13]. Matsumura et al compared reliability-based design optimization (RBDO) considering future redesign to traditional RBDO [14].…”

Section: Introductionmentioning
confidence: 99%

“…Price et al compared designer versus company perspectives on starting with a higher margin and possibly redesigning to improve performance to starting with a lower margin and possibly redesigning to improve safety [16]. This study develops a generalized formulation of the previously application-specific formulations [13,15,16] and explores how the degree of conservativeness in the initial design relates to the expected design performance after possible redesign. In related work, Price et al introduced a Kriging surrogate to represent epistemic model uncertainty in order to consider spatial variations in model uncertainty in the context of simulating the effects of future tests and redesign [17].…”

Section: Introductionmentioning
confidence: 99%

Deciding Degree of Conservativeness in Initial Design Considering Risk of Future Redesign
Price
¹
,
Kim
²
,
Haftka
³

et al. 2016
Journal of Mechanical Design
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International audienceEarly in the design process, there is often mixed epistemic model uncertainty and aleatory parameter uncertainty. Later in the design process, the results of high-fidelity simulations or experiments will reduce epistemic model uncertainty and may trigger a redesign process. Redesign is undesirable because it is associated with costs and delays; however, it is also an opportunity to correct a dangerous design or possibly improve design performance. In this study, we propose a margin-based design/redesign method where the design is optimized deterministically, but the margins are selected probabilistically. The final design is an epistemic random variable (i.e., it is unknown at the initial design stage) and the margins are optimized to control the epistemic uncertainty in the final design, design performance, and probability of failure. The method allows for the tradeoff between expected final design performance and probability of redesign while ensuring reliability with respect to mixed uncertainties. The method is demonstrated on a simple bar problem and then on an engine design problem. The examples are used to investigate the dilemma of whether to start with a higher margin and redesign if the test later in the design process reveals the design to be too conservative, or to start with a lower margin and redesign if the test reveals the design to be unsafe. In the examples in this study, it is found that this decision is related to the variance of the uncertainty in the high-fidelity model relative to the variance of the uncertainty in the low-fidelity model

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Including the Effect of a Future Test and Redesign in Reliability Calculations

Cited by 19 publications

References 9 publications

Conservativeness in Failure Probability Estimate: Redesign Risk vs. Performance

Conservativeness in Failure Probability Estimate: Redesign Risk vs. Performance

Estimating Probability of Failure of Composite Laminated Panel with Multiple Failure Modes

Deciding Degree of Conservativeness in Initial Design Considering Risk of Future Redesign

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