B. Atasoy
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Electric Ground Support Equipment Operations at Airports
Fleetsizing under operational uncertainty: A KLM case study at Schiphol
Fleet sizing under operational uncertainty: A KLM case study at Schiphol
Electric Ground Support Equipment Operations at Airports
This thesis investigates how operational requirements, uncertainty, and charging affect the required fleet capacity and operational demand of eGSE in airport turnaround processes. A structured review of the GSE and eGSE modelling literature shows that existing studies provide important building blocks for routing, scheduling, energy management, and charging analysis. However, the joint integration of task execution, individual vehicle availability, charging behaviour, infrastructure constraints, and operational uncertainty remains limited. In particular, many models either simplify charging and vehicle-level states, treat fleet size as a fixed input, or do not represent uncertainty. This motivates the development of a simulation-based decision-support approach in which eGSE fleet sizing is evaluated as a dynamic vehicle-availability problem.
A rule-based Discrete Event Simulation (DES) framework is developed to represent daily eGSE operations. The model includes individual service tasks, vehicle-specific states, airport location groups, travel times, battery state of charge, charging sessions, charger capacity, refilling, dumping, depot-return behaviour, and service-specific operating rules. Vehicles are assigned to tasks based on task urgency, time-window feasibility, travel time, battery state, and operational resource constraints. Task-timing uncertainty and travel-time uncertainty are included to evaluate how stochastic operational variability affects service-window performance and fleet-size requirements.
The framework is applied in a case study at KLM Ground Services (KLMGS) at Apron Services (AAS). The validated case-study scope includes three vehicle groups: water vehicles, toilet vehicles, and loaders. These groups represent both depot-based resource-constrained operations and stand-side service operations. The model is verified using synthetic test cases and validated through operational data checks, expert judgement, service-demand validation, energy and charging behaviour, water-demand consistency, and uncertainty-representation checks. Simulation experiments are then used to assess baseline performance, deterministic fleet sizing, task-timing and travel-time uncertainty, combined uncertainty, demand-case robustness, idle forward staging, feasibility-aware task selection, and sensitivity to operational and charging parameters.
The results show that required fleet capacity depends strongly on the service-level interpretation. Under deterministic operating conditions, the smallest fleet sizes that achieve 100% on-time task completion are 12 water vehicles, 11 toilet vehicles, and 23 loaders. Under combined task-timing and travel-time uncertainty, the strict robust thresholds increase to 16 water vehicles, 15 toilet vehicles, and 25 loaders. These are the smallest tested configurations that achieve 100% on-time task completion across all 30 stochastic replications. However, if a very small number of short internal service-window violations is operationally acceptable, lower fleet sizes may also be defensible. Under this pragmatic interpretation, at least 11 water vehicles, 9 toilet vehicles, and 23 loaders achieve ≥99.90% on-time task completion. These results should be interpreted carefully, because the performance metric measures completion within internal service windows and does not directly measure aircraft departure delay.
The experiments also show that operational-control assumptions can materially affect fleet-size outcomes. Idle forward staging, where idle vehicles remain near the aircraft stand instead of returning immediately to the depot, reduces unnecessary deadheading and improves service performance for selected vehicle groups. For toilet vehicles, the deterministic strict requirement decreases from 11 to 9 vehicles. Under combined uncertainty, idle forward staging reduces the strict robust threshold from 16 to 14 vehicles for water vehicles and from 15 to 10 vehicles for toilet vehicles. For loaders, the fleet-size threshold remains unchanged, but driven distance and depot-return movements are substantially reduced. A feasibility-aware task-selection variant further shows that dispatching logic can reduce the number of late tasks under scarce-fleet conditions, although it may increase the lateness severity of tasks that are already infeasible.
The sensitivity analysis indicates that charging is not the main driver of late task completion within the tested configurations. Energy-related parameters mainly affect charging sessions, charger occupancy, and charging-infrastructure utilisation. Task punctuality is more strongly constrained by vehicle availability during demand peaks, travel-time assumptions, service-time assumptions, and operational positioning logic. Charging therefore remains important for infrastructure planning and vehicle availability, but it is not the dominant bottleneck in the tested case-study settings.
Overall, the study shows that explicitly simulating operational requirements, uncertainty, and charging changes the interpretation of eGSE fleet sizing from a static vehicle-count problem into a dynamic availability problem. Required fleet capacity depends not only on the number of tasks, but also on when and where vehicles are needed, how uncertainty clusters demand, how quickly vehicles can recover between tasks, and how charging and supporting infrastructure affect vehicle availability. A simulation-based approach therefore provides a useful decision-support method for assessing eGSE fleet capacity, operational robustness, and charging-related resource use in airport ground handling. The reported fleet sizes should be interpreted as operational fleet-capacity requirements under the tested service-level assumptions. Final implementation decisions should add a technical reserve for maintenance, failures, battery degradation, charger unavailability, and other sources of vehicle downtime. ...
This thesis investigates how operational requirements, uncertainty, and charging affect the required fleet capacity and operational demand of eGSE in airport turnaround processes. A structured review of the GSE and eGSE modelling literature shows that existing studies provide important building blocks for routing, scheduling, energy management, and charging analysis. However, the joint integration of task execution, individual vehicle availability, charging behaviour, infrastructure constraints, and operational uncertainty remains limited. In particular, many models either simplify charging and vehicle-level states, treat fleet size as a fixed input, or do not represent uncertainty. This motivates the development of a simulation-based decision-support approach in which eGSE fleet sizing is evaluated as a dynamic vehicle-availability problem.
A rule-based Discrete Event Simulation (DES) framework is developed to represent daily eGSE operations. The model includes individual service tasks, vehicle-specific states, airport location groups, travel times, battery state of charge, charging sessions, charger capacity, refilling, dumping, depot-return behaviour, and service-specific operating rules. Vehicles are assigned to tasks based on task urgency, time-window feasibility, travel time, battery state, and operational resource constraints. Task-timing uncertainty and travel-time uncertainty are included to evaluate how stochastic operational variability affects service-window performance and fleet-size requirements.
The framework is applied in a case study at KLM Ground Services (KLMGS) at Apron Services (AAS). The validated case-study scope includes three vehicle groups: water vehicles, toilet vehicles, and loaders. These groups represent both depot-based resource-constrained operations and stand-side service operations. The model is verified using synthetic test cases and validated through operational data checks, expert judgement, service-demand validation, energy and charging behaviour, water-demand consistency, and uncertainty-representation checks. Simulation experiments are then used to assess baseline performance, deterministic fleet sizing, task-timing and travel-time uncertainty, combined uncertainty, demand-case robustness, idle forward staging, feasibility-aware task selection, and sensitivity to operational and charging parameters.
The results show that required fleet capacity depends strongly on the service-level interpretation. Under deterministic operating conditions, the smallest fleet sizes that achieve 100% on-time task completion are 12 water vehicles, 11 toilet vehicles, and 23 loaders. Under combined task-timing and travel-time uncertainty, the strict robust thresholds increase to 16 water vehicles, 15 toilet vehicles, and 25 loaders. These are the smallest tested configurations that achieve 100% on-time task completion across all 30 stochastic replications. However, if a very small number of short internal service-window violations is operationally acceptable, lower fleet sizes may also be defensible. Under this pragmatic interpretation, at least 11 water vehicles, 9 toilet vehicles, and 23 loaders achieve ≥99.90% on-time task completion. These results should be interpreted carefully, because the performance metric measures completion within internal service windows and does not directly measure aircraft departure delay.
The experiments also show that operational-control assumptions can materially affect fleet-size outcomes. Idle forward staging, where idle vehicles remain near the aircraft stand instead of returning immediately to the depot, reduces unnecessary deadheading and improves service performance for selected vehicle groups. For toilet vehicles, the deterministic strict requirement decreases from 11 to 9 vehicles. Under combined uncertainty, idle forward staging reduces the strict robust threshold from 16 to 14 vehicles for water vehicles and from 15 to 10 vehicles for toilet vehicles. For loaders, the fleet-size threshold remains unchanged, but driven distance and depot-return movements are substantially reduced. A feasibility-aware task-selection variant further shows that dispatching logic can reduce the number of late tasks under scarce-fleet conditions, although it may increase the lateness severity of tasks that are already infeasible.
The sensitivity analysis indicates that charging is not the main driver of late task completion within the tested configurations. Energy-related parameters mainly affect charging sessions, charger occupancy, and charging-infrastructure utilisation. Task punctuality is more strongly constrained by vehicle availability during demand peaks, travel-time assumptions, service-time assumptions, and operational positioning logic. Charging therefore remains important for infrastructure planning and vehicle availability, but it is not the dominant bottleneck in the tested case-study settings.
Overall, the study shows that explicitly simulating operational requirements, uncertainty, and charging changes the interpretation of eGSE fleet sizing from a static vehicle-count problem into a dynamic availability problem. Required fleet capacity depends not only on the number of tasks, but also on when and where vehicles are needed, how uncertainty clusters demand, how quickly vehicles can recover between tasks, and how charging and supporting infrastructure affect vehicle availability. A simulation-based approach therefore provides a useful decision-support method for assessing eGSE fleet capacity, operational robustness, and charging-related resource use in airport ground handling. The reported fleet sizes should be interpreted as operational fleet-capacity requirements under the tested service-level assumptions. Final implementation decisions should add a technical reserve for maintenance, failures, battery degradation, charger unavailability, and other sources of vehicle downtime.
Improving Inland and Short-Sea Vessel Scheduling using Constraint Optimization
A Google OR-Tools Implementation for a Container Vessel Planning System
This thesis presents Orion, a constraint-based optimization solver built on the Google OR-Tools Routing Library, designed to automate and improve this vessel scheduling process. The problem is formulated using Constraint Programming, which allows complex business rules to be expressed as logical predicates rather than linearized inequalities. The solver pipeline includes a data preprocessing stage that aggregates individual container orders into compound orders, reducing problem size by approximately 90\% while preserving solution quality.
The evaluation follows a three-phase methodology. First, a feasibility analysis filters 14 construction heuristics down to two viable candidates: Local Cheapest Insertion and Parallel Cheapest Insertion. Second, a parameter tuning phase identifies Local Cheapest Insertion combined with Tabu Search as the best-performing configuration, achieving an Average Relative Percentage Deviation of 2.72\% across all scenarios. Third, a benchmarking phase compares Orion against human planners and the company's existing Simulated Annealing solver (Baseline SA) on six real-world scenarios from three distinct logistics operators.
The results show that Orion achieves travel cost reductions of 6.7\% to 32.8\% compared to human planners on five of six scenarios and outperforms Baseline SA's average result on five of six scenarios. A key structural advantage is determinism: Orion produces identical results across repeated runs, whereas Baseline SA exhibits variance of up to 37.5\% between its best and worst runs. Convergence analysis indicates that 96--99.97\% of objective improvement occurs within the first 30 seconds, making a 5-minute time budget sufficient for operational use.
The thesis concludes with recommendations for production deployment and identifies future research directions, including dynamic water level constraints, improved rolling-horizon replanning, custom fleet reduction operators, and hub-based consolidation strategies.
...
This thesis presents Orion, a constraint-based optimization solver built on the Google OR-Tools Routing Library, designed to automate and improve this vessel scheduling process. The problem is formulated using Constraint Programming, which allows complex business rules to be expressed as logical predicates rather than linearized inequalities. The solver pipeline includes a data preprocessing stage that aggregates individual container orders into compound orders, reducing problem size by approximately 90\% while preserving solution quality.
The evaluation follows a three-phase methodology. First, a feasibility analysis filters 14 construction heuristics down to two viable candidates: Local Cheapest Insertion and Parallel Cheapest Insertion. Second, a parameter tuning phase identifies Local Cheapest Insertion combined with Tabu Search as the best-performing configuration, achieving an Average Relative Percentage Deviation of 2.72\% across all scenarios. Third, a benchmarking phase compares Orion against human planners and the company's existing Simulated Annealing solver (Baseline SA) on six real-world scenarios from three distinct logistics operators.
The results show that Orion achieves travel cost reductions of 6.7\% to 32.8\% compared to human planners on five of six scenarios and outperforms Baseline SA's average result on five of six scenarios. A key structural advantage is determinism: Orion produces identical results across repeated runs, whereas Baseline SA exhibits variance of up to 37.5\% between its best and worst runs. Convergence analysis indicates that 96--99.97\% of objective improvement occurs within the first 30 seconds, making a 5-minute time budget sufficient for operational use.
The thesis concludes with recommendations for production deployment and identifies future research directions, including dynamic water level constraints, improved rolling-horizon replanning, custom fleet reduction operators, and hub-based consolidation strategies.
Predicting Freight Mode Choice with Machine Learning
A Case Study of the NEAC Model
Replanning Strategies for Synchromodal Resilience
A Deep Reinforcement Learning Approach to Real-Time Logistics Optimization
To this end, this study develops a comprehensive simulation framework that combines an advanced ride-pooling candidate generation algorithm (ExMAS) with an innovative two-stage vehicle assignment optimization process, and integrates a nested Logit model to quantify the competition structure with public transport. This framework is applied to 37 Dutch cities of varying scales to derive generalizable findings.
The study finds that population scale is a fundamental determinant of the required fleet size, exhibiting a strong linear relationship, especially in large cities. The key to enhancing operational efficiency, however, lies in more nuanced urban structure metrics. In large cities, longer commuting distances combined with more complex networks (higher node degrees) foster ride-pooling potential. In contrast, for small cities, the local compactness of the network (higher clustering coefficient) and demand density are critical for improving vehicle turnover efficiency. Furthermore, the research confirms that a uniform pricing strategies are unlikely to achieve best performance on pooling efficiency, highlighting the necessity of implementing differentiated pricing based on user preferences and city scale. In competition with public transport, the study's Public Transport Competitiveness Index reveals a non-monotonic relationship with travel distance. A state of competitive balance is observed for short-distance trips, while PT holds a distinct advantage in the medium-distance range. For long-distance trips, the inherent speed advantage of SAVs allows them to become the more competitive option. This external competition also structurally increases the internal pooling rate of the SAV system.
The findings of this study provide critical strategic insights for SAV operators and policymakers, emphasizing the critical importance of adjusting fleet management, service design, and pricing strategies according to specific urban characteristics and the competitive environment, thereby providing decision support for achieving an efficient and sustainable urban transportation system. ...
To this end, this study develops a comprehensive simulation framework that combines an advanced ride-pooling candidate generation algorithm (ExMAS) with an innovative two-stage vehicle assignment optimization process, and integrates a nested Logit model to quantify the competition structure with public transport. This framework is applied to 37 Dutch cities of varying scales to derive generalizable findings.
The study finds that population scale is a fundamental determinant of the required fleet size, exhibiting a strong linear relationship, especially in large cities. The key to enhancing operational efficiency, however, lies in more nuanced urban structure metrics. In large cities, longer commuting distances combined with more complex networks (higher node degrees) foster ride-pooling potential. In contrast, for small cities, the local compactness of the network (higher clustering coefficient) and demand density are critical for improving vehicle turnover efficiency. Furthermore, the research confirms that a uniform pricing strategies are unlikely to achieve best performance on pooling efficiency, highlighting the necessity of implementing differentiated pricing based on user preferences and city scale. In competition with public transport, the study's Public Transport Competitiveness Index reveals a non-monotonic relationship with travel distance. A state of competitive balance is observed for short-distance trips, while PT holds a distinct advantage in the medium-distance range. For long-distance trips, the inherent speed advantage of SAVs allows them to become the more competitive option. This external competition also structurally increases the internal pooling rate of the SAV system.
The findings of this study provide critical strategic insights for SAV operators and policymakers, emphasizing the critical importance of adjusting fleet management, service design, and pricing strategies according to specific urban characteristics and the competitive environment, thereby providing decision support for achieving an efficient and sustainable urban transportation system.
Dispatch Optimization with Inventory-Dependent Service Times using Approximate Dynamic Programming
A Case Study at Habesha Breweries S.C.
Damage-Aware Bin Packing for Online Grocery Delivery
Leveraging Customer Feedback Data to Improve Quality of Service
Therefore, we propose a novel two-part theoretical framework to process historical data of customer damage reports into quantifiable parameters that can be used by a bin packing model. In the first part, we formulate a predictive task and propose a classification machine learning model which provides a probability of damage for the bag, given a set of bag characteristics obtained from customer data. In the second part, we propose to integrate the machine learning component into a bin packing model as a weighted term in its objective function. This integrated model comprises our damage-aware bin packing model.
The proposed methodology was implemented and evaluated through a case study using real data from the daily operations of the online supermarket Picnic. As part of the experiments, we analysed over 60 million articles across 2.2 million deliveries. We started with a comprehensive data analysis to explore the relationships in the data and identify trends. We, then, developed and trained two machine learning variants, a logistic regression and an ensemble extreme gradient boost model (XGBoost) to fulfil the predicting task of bag-damage probability estimation. We applied random undersampling to the training dataset to mitigate the extreme class imbalance (0.41% damage rate). Then, we used the logistic regression model as the ML component and implemented a damage-aware bin packing model. We defined strategic empirical metrics to measure its performance and constructed an evaluation framework using counterfactual analysis on 6000 representative deliveries.
Our findings validate the technical feasibility of integrating customer feedback data into a bin packing algorithm. The damage-aware variant recorded a 14.1% relative reduction in the average probability of damage across all bags of the deliveries tested. On the other hand, extreme class imbalance severely limited the performance of the ML models trained (1% precision score in real operational conditions). As a result, a meaningful review of the economic impact of the model is not possible. The experiments illustrated sensible item movements across the bags tested, measured with some empirical key risk parameters, such as item categories, packaging types, and bag density. The implementation showed a tolerable computational overhead of around 18%, indicating that it is realistic to deploy an efficient model to real operations. ...
Therefore, we propose a novel two-part theoretical framework to process historical data of customer damage reports into quantifiable parameters that can be used by a bin packing model. In the first part, we formulate a predictive task and propose a classification machine learning model which provides a probability of damage for the bag, given a set of bag characteristics obtained from customer data. In the second part, we propose to integrate the machine learning component into a bin packing model as a weighted term in its objective function. This integrated model comprises our damage-aware bin packing model.
The proposed methodology was implemented and evaluated through a case study using real data from the daily operations of the online supermarket Picnic. As part of the experiments, we analysed over 60 million articles across 2.2 million deliveries. We started with a comprehensive data analysis to explore the relationships in the data and identify trends. We, then, developed and trained two machine learning variants, a logistic regression and an ensemble extreme gradient boost model (XGBoost) to fulfil the predicting task of bag-damage probability estimation. We applied random undersampling to the training dataset to mitigate the extreme class imbalance (0.41% damage rate). Then, we used the logistic regression model as the ML component and implemented a damage-aware bin packing model. We defined strategic empirical metrics to measure its performance and constructed an evaluation framework using counterfactual analysis on 6000 representative deliveries.
Our findings validate the technical feasibility of integrating customer feedback data into a bin packing algorithm. The damage-aware variant recorded a 14.1% relative reduction in the average probability of damage across all bags of the deliveries tested. On the other hand, extreme class imbalance severely limited the performance of the ML models trained (1% precision score in real operational conditions). As a result, a meaningful review of the economic impact of the model is not possible. The experiments illustrated sensible item movements across the bags tested, measured with some empirical key risk parameters, such as item categories, packaging types, and bag density. The implementation showed a tolerable computational overhead of around 18%, indicating that it is realistic to deploy an efficient model to real operations.
A literature review identified four prediction models to be investigated: Historical Average, Vector AutoRegression, Random Forest, and Long Short-Term Memory deep neural network. A case study involving six bus lines in Groningen was formulated, providing the necessary KoppelVlak 6 and GTFS schedule datasets to be used as inputs for the prediction models. During model development, patterns in historical travel time data were identified, and prediction accuracy was evaluated. The output from the most accurate prediction model was then utilised as input for the reachability analysis.
The analysis demonstrated that complex machine learning models, such as Random Forest and Long Short-Term Memory deep neural networks, yielded the most accurate predictions. The time of day when the journey occurs is particularly predictive of travel and dwell times. Integrating these predictions into a reachability analysis revealed instances of increased reachability, decreased reachability, and missed transfers compared to the original schedule.
The findings demonstrate that travel time prediction models can significantly enhance reachability analyses. This more accurate representation of reachability can be used to identify systemic issues in the design of the public transportation network, allowing for interventions to improve performance. ...
A literature review identified four prediction models to be investigated: Historical Average, Vector AutoRegression, Random Forest, and Long Short-Term Memory deep neural network. A case study involving six bus lines in Groningen was formulated, providing the necessary KoppelVlak 6 and GTFS schedule datasets to be used as inputs for the prediction models. During model development, patterns in historical travel time data were identified, and prediction accuracy was evaluated. The output from the most accurate prediction model was then utilised as input for the reachability analysis.
The analysis demonstrated that complex machine learning models, such as Random Forest and Long Short-Term Memory deep neural networks, yielded the most accurate predictions. The time of day when the journey occurs is particularly predictive of travel and dwell times. Integrating these predictions into a reachability analysis revealed instances of increased reachability, decreased reachability, and missed transfers compared to the original schedule.
The findings demonstrate that travel time prediction models can significantly enhance reachability analyses. This more accurate representation of reachability can be used to identify systemic issues in the design of the public transportation network, allowing for interventions to improve performance.
Consolidation of commercial waste collection
A case study of the urban area of the Municipality of Rotterdam
Google OR-tools to assess the potential benefits of collaboration in waste collection in Rotterdam. Four collaborative scenarios are simulated, three of them in a collaborative setting. Results show that collaboration can significantly reduce the distance traveled by vehicles and the costs for waste collectors, with smaller waste collectors benefiting the most. While full collaboration offers the greatest efficiency gains, even constrained partnerships improve operations. These findings highlight the potential for collaboration to enhance urban logistics and sustainability. ...
Google OR-tools to assess the potential benefits of collaboration in waste collection in Rotterdam. Four collaborative scenarios are simulated, three of them in a collaborative setting. Results show that collaboration can significantly reduce the distance traveled by vehicles and the costs for waste collectors, with smaller waste collectors benefiting the most. While full collaboration offers the greatest efficiency gains, even constrained partnerships improve operations. These findings highlight the potential for collaboration to enhance urban logistics and sustainability.
Data Based Traffic Capacity Estimation of Waterway Networks
A case study for the city of Amsterdam
The Impact of Autonomous Intra-Terminal Barge Concepts
A Case Study of the Port of Rotterdam
A port-wide discrete event simulation is developed with deep sea, feeder, conventional barge, and autonomous module services calling five terminals that share a dedicated module-crane pool. Current multi-stop barge operations are compared with scenarios in which barges detach short-calling modules under different barge–module mixes, sea-freight demand levels, module-crane inventories, and module capacities. Performance is assessed using throughput, turnaround and waiting times, berth occupancy, crane utilisation, and anchorage behaviour.
In the recommended 50-50 barge-module mix, modular splitting increases port-wide throughput by about 12% and reduces barge turnaround by more than half compared with current operations, while deep sea and feeder vessels remain largely unaffected. These gains arise from parallel module calls that use residual quay pockets more effectively. Hybrid fleets with around half of inland work carried by modules therefore provide the best compromise between higher throughput and manageable growth in vessel calls. Configuration experiments indicate that two dedicated module cranes per large terminal are sufficient under the tested loads and that medium-sized modules around 24 to 36 TEU perform robustly. Within the limits of the stylised simulation, the results indicate that modular intra-port services can improve inter-terminal operational performance, support port sustainability and modal-shift objectives, and provide guidance for the design of MAGPIE Demo 6. ...
A port-wide discrete event simulation is developed with deep sea, feeder, conventional barge, and autonomous module services calling five terminals that share a dedicated module-crane pool. Current multi-stop barge operations are compared with scenarios in which barges detach short-calling modules under different barge–module mixes, sea-freight demand levels, module-crane inventories, and module capacities. Performance is assessed using throughput, turnaround and waiting times, berth occupancy, crane utilisation, and anchorage behaviour.
In the recommended 50-50 barge-module mix, modular splitting increases port-wide throughput by about 12% and reduces barge turnaround by more than half compared with current operations, while deep sea and feeder vessels remain largely unaffected. These gains arise from parallel module calls that use residual quay pockets more effectively. Hybrid fleets with around half of inland work carried by modules therefore provide the best compromise between higher throughput and manageable growth in vessel calls. Configuration experiments indicate that two dedicated module cranes per large terminal are sufficient under the tested loads and that medium-sized modules around 24 to 36 TEU perform robustly. Within the limits of the stylised simulation, the results indicate that modular intra-port services can improve inter-terminal operational performance, support port sustainability and modal-shift objectives, and provide guidance for the design of MAGPIE Demo 6.
Synchronized Two-Echelon Routing Problems
Exact and Approximate Methods for Multimodal City Logistics