Date of Award

Winter 12-2015

Embargo Period

7-28-2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil and Environmental Engineering

Advisor(s)

Matteo Pozzi

Abstract

Many infrastructure systems in the US such as road networks, bridges, water and wastewater pipelines, and wind farms are aging and their condition are deteriorating. Accurate risk analysis is crucial to extend the life span of these systems, and to guide decision making towards a sustainable use of resources. These systems are subjected to fatigue-induced degradation and need periodic inspections and repairs, which are usually performed through semi-annual, annual, or bi-annual scheduled maintenance. However, better maintenance can be achieved by flexible policies based on prior knowledge of the degradation process and on data collected in the field by sensors and visual inspections. Traditional methods to model the operation and maintenance (O&M) process, such as Markov decision processes (MDP) and partially observable MDP (POMDP) have limitations that do not allow the model to properly include the knowledge available and that may result in nonoptimal strategies for management of infrastructure systems. Specifically, the conditional probabilities for modeling the degradation process and the precision of the observations are usually affected by epistemic uncertainty: this cannot be captured by traditional methods. The goal of this dissertation is to propose a computational framework for adaptive monitoring and control of infrastructures at the system-level and to connect different aspects of the management process together. The first research question we address is how to take optimal sequential decisions under model uncertainty. Second, we propose how to combine decision optimization with learning of the degradation of components and the precision of monitoring system. Specifically, we address the issue of systems made by similar components, where iv transfer of knowledge across components is relevant. Finally, we propose how to assess the value of information in sequential decision making and whether it can be used as a heuristic for system-level inspection scheduling. In this dissertation, first a novel learning and planning method is proposed, called “Planning and Learning for Uncertain dynamic Systems” (PLUS), that can learn from the environment, update the distributions of parameters, and select the optimal strategy considering the uncertainty related to the model. Validating with synthetic data, the total management cost of operating a wind farm using PLUS is shown to be significantly less than costs achieved by a fixed policy or though the POMDP framework. Moreover, when the system is made up by similar components, data collected on one is also relevant in the management of others. This is typically the case of wind farms, which are made up by similar turbines. PLUS models the components as independent or identical and eithers learn the model for each component independently or learn a global model for all components. We extend that formulation, allowing for a weaker similarity among components. The proposed approach, called “Multiple Uncertain POMDP” (MU-POMDP), models the components as POMDPs, and assumes the corresponding model parameters as dependent random variables. By using this framework, we can calibrate specific degradation and emission models for each component while, at the same time, processing observations at the level of the entire system. We evaluate the performance of MU-POMDP compared to PLUS and discuss its potentials and computational complexity. Lastly, operation and maintenance of an infrastructure system rely on information collected on its components, which can provide the decision maker with an accurate assessment of their condition states. However, resources to be invested in data gathering are usually limited and v observations should be collected based on their value of information (VoI). VoI is a key concept for directing explorative actions, and in the context of infrastructure operation and maintenance, it has application to decisions about inspecting and monitoring the condition states of the components. Assessing the VoI is computationally intractable for most applications involving sequential decisions, such as long-term infrastructure maintenance. The component-level VoI can be used as a heuristic for assigning priorities to system-level inspection scheduling. In this research, we propose two alternative models for integrating adaptive maintenance planning based on POMDP and inspection scheduling based on a tractable approximation of VoI: the stochastic allocation model (and its two limiting scenarios called pessimistic and optimistic) that assumes observations are collected with a given probability, and the fee-based allocation model that assumes observations are available at a given cost. We illustrate how these models can be used at component-level and for system-level inspection scheduling. Furthermore, we evaluate the quality of solution provided by pessimistic and optimistic approaches. Finally, we introduce analytical formulas based on the stochastic and fee-based allocation models to predict the impact of a monitoring system (or a piece of information) on the operation and maintenance cost of infrastructure systems.

Available for download on Saturday, July 28, 2018

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