@phdthesis{Jimenez-Roa2025,

title = {Reliability and Maintenance for Engineering Systems: Fault Trees, Degradation Modelling and Maintenance Optimisation},

author = {Lisandro Arturo Jimenez-Roa},

url = {https://primavera-project.com/wp-content/uploads/2024/12/manuscript-lisandro.pdf, Download the manuscript PDF},

isbn = {978-90-365-6407-6},

year  = {2025},

date = {2025-02-07},

urldate = {2025-02-07},

abstract = {Modern infrastructures, machines, and manufacturing processes require effective management through sustainable policies under constrained resources, where deter- mining when and how to intervene becomes crucial. The Prognostics and Health Management (PHM) paradigm provides a systematic framework for leveraging data collection and computational models, supporting the management of virtually any engineering component or system. This dissertation delves into three key aspects of PHM: Reliability Modelling, Markov Process-based Prognostics, and Maintenance Optimisation. Data-driven techniques are crucial in these areas, enhancing the automation of model development and deployment. Part I centres on Reliability Modelling, specifically the automatic inference of Fault Tree (FT) models. Traditionally, graph-based models like FTs are manually constructed through iterative collaboration between system experts and FT modellers. However, this manual approach is prone to human error and may result in incomplete models. With the increasing availability of data, methodologies that attempt to automate this process, discover patterns and reduce dependency on manual intervention have gained significant relevance. Thus, in Part I of this dissertation, we focus on how to obtain efficient and compact Fault Tree models from failure datasets in a robust and scalable manner. For this matter, we propose, for the first time, using Multi-Objective Evolutionary Algorithms (MOEAs) to automatically infer FT models and cast the optimisation as a multi-objective task. This resulted in the FT-MOEA algorithm (Chapter 2), focusing on three optimisation metrics, including FT size and accuracy-related metrics. FT-MOEA consistently produced compact FT structures, but faced scalability issues. To address this, we developed the SymLearn toolchain (Chapter 3), which uses a ‘divide-and-conquer’ approach by identifying modules and symmetries in the failure dataset, breaking the inference problem into smaller tasks. Additionally, to improve robustness and scalability, the FT-MOEA-CM extension (Chapter 4) includes additional metrics from the confusion matrix. Our approaches in Part I of this dissertation contribute to automating FT model construction, revealing compact structures. These consistent structures can help uncover relationships between basic and intermediate events, providing valuable insights for asset managers to improve reliability modelling. Part II focuses on Markov Process-based Prognostics, specifically the stochastic deterioration modelling of sewer mains. Sewer systems are critical to social welfare but pose significant challenges due to their extensive scale, slow degradation, and limited capacity to monitor the entire network. Accurate modelling of the deterioration profile is crucial for optimising inspections and maintenance, thereby enhancing the reliability and availability of the networks. Various deterioration models are discussed in the literature, ranging from physics-based to data-driven approaches, each with distinct advantages and limitations. In Part II of this dissertation, we address how and to what extent it is possible to accurately model Multi-State Deterioration with applications in sewer mains. For this, we focus on Markov chains, widely used to model stochastic sequences through states and transitions. Since the 1990s, they have been applied to represent damage severity levels in sewer mains using inspection data from Closed Circuit Television cameras. Nonetheless, further evaluation of their assumptions and properties is required. We present a case study of a Dutch sewer network (Chapter 5), starting with Discrete-Time Markov Chains for deterioration modelling and examining two Markov chain structures. Given challenges such as interval-censored data, advanced analysis was necessary. In Chapter 6, we use the Turnbull estimator for non-parametric analysis to establish a ground truth. Although both homogeneous and inhomogeneous-time Markov chains are employed for sewer mains deterioration, no prior studies have compared their performance on the same dataset. Chapter 6 addresses this by demonstrating that inhomogeneous-time Markov chains are more versatile at capturing non-linear stochastic behaviour, while also highlighting issues like overfitting that reduce predictive accuracy. Part II provides a real-world case study, emphasising the need to critically evaluate modelling assumptions to enhance deterioration modelling of sewer mains using Markov chains. Finally, Part III focuses on Maintenance Optimisation of sewer mains, where obtaining optimal maintenance policies for such large-scale systems is a complex task. This complexity arises, among others, from the system’s scale and simplifications in the deterioration model. Among the various techniques available, Reinforcement Learning (RL) approaches remain largely unexplored for devising strategic main- tenance actions in sewer mains. Thus, in Part III of this dissertation, we focus on how to devise optimal maintenance strategies for components with Multi-State Deterioration such as sewer mains using Deep Reinforcement Learning.In Chapter 7, we frame the sequential decision-making problem using Deep Reinforcement Learning (DRL) for component-level maintenance of sewer mains. This framework considers damage severity levels, testing different deterioration model assumptions and evaluating their impact on maintenance policy. Our results show that agent-based policies outperformed heuristics by learning optimal sequences of maintenance actions. Part III provides evidence that DRL-based techniques o!er a flexible framework with the potential to improve heuristics and support maintenance decision-making for sewer mains. However, training these models to achieve the desired behaviour remains a challenging task.

},

keywords = {Deep Reinforcement Learning, Degradation Modelling, Fault tree analysis, Maintenance optimization, Prognostics and Health Management},

pubstate = {published},

tppubtype = {phdthesis}

}

@phdthesis{Anbalagan2024,

title = {SPECTRUM: Towards Self-aware Industrial IoT Systems},

author = {Sabari Nathan Anbalagan},

doi = {https://doi.org/10.3990/1.9789036563352},

isbn = {978-90-365-6335-2},

year  = {2024},

date = {2024-12-03},

urldate = {2024-12-03},

abstract = {The Fourth Industrial Revolution (4IR) has sparked remarkable technological advancements, particularly in integrating the Internet of Things (IoT) into manufacturing industries, known as the Industrial Internet of Things (IIoT). This integration holds potential for revolutionizing industrial processes and boosting human progress through advanced applications within factory settings.



However, the diverse Quality of Service (QoS) requirements of 4IR applications, including data rate, latency, reliability, power efficiency, scalability, and mobility, present significant challenges. The IIoT network must support these diverse requirements while operating in harsh and dynamic industrial indoor environments characterized by metallic infrastructure, thick concrete pillars, and complex pipe networks. Additionally, environmental fluctuations like temperature and humidity, process dynamics such as spinning and smelting, and the mobility of operators and indoor vehicles contribute to the dynamic nature of these environments. Achieving the diverse QoS requirements in such challenging conditions necessitates intelligent and versatile solutions.



The latest telecommunications standard, 5G, holds promise as a solution to these challenges. This thesis addresses these challenges by focusing on the optimization of industrial use cases for 5G-based IIoT systems. It begins with an exploration of the significance and applications of 4IR in manufacturing industries, identifying the potential of 5G technology augmented by varying levels of Artificial Intelligence (AI) to meet the diverse demands of IIoT networks. The problem statement emphasizes the necessity for intelligent methodologies that adapt to the dynamic nature of industrial environments while supporting a wide range of industrial applications.

The thesis proposes a multifaceted approach to tackle these challenges, incorporating varying levels of context awareness within IIoT systems. Chapters delve into the evolution of IIoT systems, presenting a framework for assessing system maturity and providing practical guidance for implementation. The development of heuristics-based, coarse-grained, and fine-grained Channel Quality Prediction (CQP) techniques is explored, offering insights into optimizing wireless communication parameters for diverse 5G use cases. Simulations and analyses demonstrate the efficacy of these methodologies in enhancing throughput, resource utilization, and power efficiency across various industrial scenarios.



In conclusion, this thesis contributes to the advancement of wireless communication optimization in industrial settings, offering practical solutions and insights for realizing the potential of 4IR initiatives. By addressing a spectrum of challenges, requirements and use case scenarios, the research offers insights for future 5G and 6G releases.},

keywords = {Artificial Intelligence, Fourth Industrial Revolution, Internet of Things, Wireless Communication},

pubstate = {published},

tppubtype = {phdthesis}

}

@phdthesis{nokey,

title = {Advances in Asset Management: Maintenance Optimization under Incomplete Information and Sustainable Technology Selection},

author = {Ragnar Hans Eggertsson},

url = {https://research.tue.nl/files/342347796/20241122_Eggertsson_hf.pdf},

isbn = {978-90-386-6159-9},

year  = {2024},

date = {2024-11-22},

urldate = {2024-11-22},

keywords = {Inspection optimization, Maintenance optimization, Technology Selection},

pubstate = {published},

tppubtype = {phdthesis}

}

@phdthesis{nokey,

title = {Point taken: Translating the physical rail domain to cyber space using point clouds from mobile laser scanning},

author = {Bram Ton},

doi = {https://doi.org/10.3990/1.9789036561990},

isbn = {978-90-365-6199-0},

year  = {2024},

date = {2024-11-18},

abstract = {There is an active interest to digitise the rail infrastructure, because it is expected that the coming years rail transport will be an important key factor to combat climate change. Compared to other means of transport, such as air or road transportation, rail transport is viewed as being more environment-friendly. With the envisioned increase of passenger and freight rail traffic in the near future, there will be an increased burden on the railway infrastructure. To ensure continued reliability, availability, maintainability and safety of the railway network in an efficient way, it is vital to have an accurate and up-to-date digital representation of the railway environment. Often such a digital representation is also referred to as an `as-is' model or representation because it reflects the current state. These as-is representations can be used for various tasks, such as planning work, monitoring the infrastructural health, automated inventory assessment, robotised construction, and eventually predictive maintenance.



Automated creation of these as-is models is challenging because railway environments pose a complex scene structure and span several thousands of kilometres. Scenes contain discrete objects, such as signals, catenary arches, and relay cabinets on the one hand. On the other hand there are continuous objects, such as overhead catenary wires and rail tracks. Adding to the complexity, is the fact that the number of distinct objects around the track is large. Especially for countries with a dense rail network and a long history of rail transportation such as the Netherlands. These factors, combined with the large intra-class variance, make the digitalisation of the rail environment a challenging task.



To accomplish the task of digitising the rail environment, point cloud data is considered a viable data format. Point clouds are captured using Light Detection and Ranging (LiDAR) technology. This is done through laser scanning, which operates by emitting a usually non-visible laser light pulse and measuring its time-of-flight. This time is directly proportional to the distance of the object. This distance, combined with the known angles of direction of the laser are used to calculate the 3D position of the reflection occurrence relative to the sensor. Point clouds are able to capture the geometric surface structure of a scene with high accuracy, under varying illumination conditions, and produces an immediate representation.



This thesis focuses on digitising the rail environment using point cloud data. It takes a top-down approach, first objects are detected within the point cloud data with a low level of detail. Thereafter this thesis focuses on dissecting these large objects into smaller semantic meaningful pieces, providing a higher level of detail. These two steps conclude the translation from the physical world to cyber space. To complete the cycle, going from cyber space to the physical world again, this thesis also focuses on how information from cyber space can be visualised in an intuitive, immersive way using a head mounted display.



The thesis starts by looking at how large objects can be detected at large scale from point cloud data. To do so, existing models which have been successful in the domain of autonomous driving vehicles are evaluated for this task. A key insight from this evaluation is that the absolute positional accuracy required for `as-is' models cannot be obtained from these existing models. Another insight is that models do not generalise well to new scenarios, and that to combat this issue, transfer learning is very suitable to train new models using fewer labels.



To further scrutinise these large objects and thereby increase the level of detail of the digitisation process, semantic segmentation can be used. Semantic segmentation assigns a class to each point within the point cloud. This decomposition can then for instance be used to retrieve CAD models from a CAD library to create an accurate digital representation. This thesis looks at the semantic segmentation of catenary arches which are captured at high resolution. Catenary arches are decomposed into fourteen distinct classes and labelled accordingly. An overall mIoU of 71% was accomplished for this task.



Object detection and semantic segmentation conclude the process of translating the physical world to cyberspace. Once a representation is available in cyberspace, a wide range of applications become available. For instance, planning maintenance, robotised construction, predictive maintenance, and computerised clearance inspections. To complete the cycle, and go from cyberspace to the physical world again, this thesis explores immersive visualisation of point cloud data. A proof-of-concept for this immersive visualisation is presented in this thesis. It is based on a head-mounted display and enables the user to interact with the point cloud using hand gestures and voice commands.



To conclude, this thesis has explored the digitisation of the rail environment using point cloud data. It provides valuable insights and pointers to move this relatively new research area to the next level. One promising research direction to highlight is the use of self-supervised learning (SSL). By using SSL, models can learn some `common sense' about the data without external labels. This alleviates the expensive, and tedious task of labelling large amounts of data.},

keywords = {LiDAR, Point Cloud, Railway},

pubstate = {published},

tppubtype = {phdthesis}

}