This study presents a novel risk-based robust mixed-integer linear programming model for configuring a complex cement supply chain network under carbon emission policies (CEPs). In addition to the non-deterministic mo...
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This study presents a novel risk-based robust mixed-integer linear programming model for configuring a complex cement supply chain network under carbon emission policies (CEPs). In addition to the non-deterministic model solved with the robust approach, its corresponding deterministic model is also solved and the results are compared. In the models, critical dimensions of the cement industry, including inventory and shortages, are mathematically examined. Other important features of the industry, including the large number of suppliers of different materials, the production of diverse products with different processing flows, and diverse transportation methods appropriate to different types of cement and market climates, are also considered in the models. A scenario-based conditional value-at-risk approach is used to deal with the inherent uncertainty of cement demand in the uncertain counterpart of the model. The results demonstrate the effectiveness of the robust approach for the optimal configuration of the integrated cement inventory-production system and its inbound-outbound logistics. Analyzing the results establishes widespread trade-offs between the parameters. In particular, the model suggests the highest level of risk-taking for a profit-sensitive DM to maximize her/his profit. It may push the robustness-sensitive DM toward more conservatism by accepting lower profits. Besides, an emission-sensitive DM is recommended to implement both the carbon-cap-and-trade and carbon tax under carbon cap-and-trade regulation policies.
Supply and manufacturing networks in the chemical industry involve diverse processing steps across different locations, rendering their operation vulnerable to disruptions from unplanned events. Optimal responses shou...
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Supply and manufacturing networks in the chemical industry involve diverse processing steps across different locations, rendering their operation vulnerable to disruptions from unplanned events. Optimal responses should consider factors such as product allocation, delayed shipments, and price renegotiation, among other factors. In such context, we propose a multiperiod mixed-integer linear programming model that integrates production, scheduling, shipping, and order management to minimize the financial impact of such disruptions. The model accommodates arbitrary supply chain topologies and incorporates various disruption scenarios, offering adaptability to real-world complexities. A case study from the chemical industry demonstrates the scalability of the model under finer time discretization and explores the influence of disruption types and order management costs on optimal schedules. This approach provides a tractable, adaptable framework for developing responsive operational plans in supply chain and manufacturing networks under uncertainty.
Urban air mobility (UAM) is an emerging air transportation mode to alleviate the ground traffic burden and achieve zero direct aviation emissions. Due to the potential economic scaling effects, the UAM traffic flow is...
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Urban air mobility (UAM) is an emerging air transportation mode to alleviate the ground traffic burden and achieve zero direct aviation emissions. Due to the potential economic scaling effects, the UAM traffic flow is expected to increase dramatically once implemented, and its market can be substantially large. To be prepared for the era of UAM, we study the fair and risk-averse urban air mobility resource allocation model (FairUAM) under passenger demand and airspace capacity uncertainties for fair, safe, and efficient aircraft operations. FairUAM is a two-stage model, where the first stage is the aircraft resource allocation, and the second stage is to fairly and efficiently assign the ground and airspace delays to each aircraft provided the realization of random airspace capacities and passenger demand. We show that FairUAM is NP-hard even when there is no delay assignment decision or no aircraft allocation decision. Thus, we recast FairUAM as a mixed-integerlinear program (MILP) and explore model properties and strengthen the model formulation by developing multiple families of valid inequalities. The stronger formulation allows us to develop a customized exact decomposition algorithm with both benders and L-shaped cuts, which significantly outperforms the off-the-shelf solvers. Finally, we numerically demonstrate the effectiveness of the proposed method and draw managerial insights when applying FairUAM to a real-world network.
The food-energy-water nexus (FEWN) postulates that sustainable decision-making regarding the interconnected resources food, energy and water must consider all involved resources holistically. Due to its multi-scale co...
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The food-energy-water nexus (FEWN) postulates that sustainable decision-making regarding the interconnected resources food, energy and water must consider all involved resources holistically. Due to its multi-scale complexity, modeling challenges and computational intractability regarding the interconnected FEWN optimization remain. To overcome these challenges, this work proposes employing surrogate models based on data-driven and model optimization techniques, while quantifying the introduced errors due to both the selected approximation and optimization methods. In turn, we derive a mixed-integerlinear FEWN planning and scheduling optimization model based on a greenhouse farming, a renewable energy and a reverse osmosis desalination water supply system, which is initially computationally intractable. This computational complexity is first discussed and overcome for the energy-water nexus supply system, before solving the complete FEWN supply system by utilizing strategies such as relaxation, modularization and convex hull reformulation.
Unit commitment (UC) is a critical challenge in power system optimization, typically formulated as a high-dimensional mixed-integer linear programming (MILP) problem with non-deterministic polynomial-time hard (NP-har...
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Unit commitment (UC) is a critical challenge in power system optimization, typically formulated as a high-dimensional mixed-integer linear programming (MILP) problem with non-deterministic polynomial-time hard (NP-hard) complexity. While the branch-and-bound (B&B) algorithm can determine optimal solutions, its computational cost increases exponentially with the number of units, which limits the practical application of UC. Machine learning (ML) has recently emerged as a promising tool for addressing UC, but its effectiveness relies on substantial training samples. Moreover, ML models suffer significant performance degradation when the number of units changes, a phenomenon known as the task mismatch problem. This paper introduces a novel method for Branching Acceleration for UC, aiming to reduce the computational complexity of the B&B algorithm while achieving near-optimal solutions. The method leverages invariant branching tree-related features and UC domain-specific features, employing imitation learning to develop an enhanced pruning policy for more precise node pruning. Numerical studies on both standard and practical testing systems demonstrate that the method significantly accelerates computation with few training samples and negligible accuracy loss. Furthermore, it exhibits robust generalization capability for handling task mismatches and can be seamlessly integrated with other B&B acceleration techniques, providing a practical and efficient solution for UC problems.
This work presents a generic optimization framework using advanced mixed-integerprogramming techniques to integrate day-ahead and balancing markets with distributed energy resources such as storage, electric vehicles...
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This work presents a generic optimization framework using advanced mixed-integerprogramming techniques to integrate day-ahead and balancing markets with distributed energy resources such as storage, electric vehicles, demand response, and Transmission and Distribution System Operators' coordination schemes. The day-ahead model determines optimal initial energy scheduling, while the balancing model optimizes energy and reserve products for three market designs with varying Transmission and Distribution System Operators' coordination. The framework is applied to the interconnected Greek-Bulgarian-Romanian power system, considering 2030 installed capacities. The model outputs illustrate market coupling scenarios among Romania, Bulgaria, and Greece, highlighting clear price signals and distributed energy resources flexibility. Results reveal the significance of a diverse energy mix for energy security and show that Transmission and Distribution System Operators' coordination significantly influences ancillary service prices, with reductions of up to 80 % in certain scenarios. Net demand values determine electricity flow direction. Flexibility providers like storage can cover up to 100 % of the upward congestion management requirements and 11 % of upward balancing energy, helping smooth energy allocation from intermittent renewables. The impact of electric vehicle penetration on generation scheduling is minimal. The proposed model offers valuable insights for system operators, market participants, and policymakers, enabling them to provide accurate price signals and optimize resource allocation. The integrated day-ahead and balancing market models support efficient renewable energy integration, emissions reduction, enhanced grid stability, and investment in low-carbon technologies. This aligns with the United Nations Framework Convention on Climate Change goals, contributing to the development of sustainable and resilient energy systems.
Resilient inventory systems in every stage of a supply chain are becoming increasingly crucial to ensure its smooth functioning. In the context of production and manufacturing systems, flow time minimization plays a p...
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Resilient inventory systems in every stage of a supply chain are becoming increasingly crucial to ensure its smooth functioning. In the context of production and manufacturing systems, flow time minimization plays a pivotal role in enhancing the resilience of inventories. By minimizing flow times, firms decrease the amount of Work-In-Progress (WIP) inventory at any given moment, thereby reducing vulnerability to disruptions caused by the bullwhip effect, supply chain delays or market fluctuations. Optimizing flow time to control WIP is extremely important in flow shop environments, where the high production volume places a heavy premium on avoidable delays. In this work, the aim is to develop models and approaches for flow time minimization in Permutation Flow Shops that cleverly exploit problem characteristics to quickly provide optimal solutions or strong lower bounds. To this end, we first propose two polynomial-time algorithms-position-based lower bound algorithm (PBLBA) and Improved Position-Based Lower Bound Algorithm (IPBLBA)-to rapidly determine lower bounds on Total Flow Time. Then, we develop a novel, parameter-free Self-Tuning Lower Bound Algorithm (STLBA) that iteratively solves a mixed-integer linear programming model to strengthen the lower bounds identified by the PBLBA and the IPBLBA and provides upper bounds. This STLBA is then integrated with a Local Search procedure to further improve the upper bounds and get an implementable schedule. Finally, we test the developed approaches on 600 well-known benchmark instances to ascertain their strengths and gather valuable theoretical and practical insights.
Following the increasing relevance of Additive Manufacturing (AM) as Manufacturing-as-a-service (Maas), the AM scheduling (and related nesting) problem has been increasingly investigated. Due to their business nature,...
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Project scheduling is a vital management task in many organizations across various industries. A project typically consists of activities that require time and scarce resources for execution. In many projects, there a...
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Project scheduling is a vital management task in many organizations across various industries. A project typically consists of activities that require time and scarce resources for execution. In many projects, there are trade-offs between the resource requirements and the duration of activities. These trade-offs can be represented via multiple execution modes of activities, which are considered in the multi-mode resource-constrained project scheduling problem (MRCPSP). The MRCPSP comprises determining the activities' start times and execution modes to minimize the project completion time while respecting precedence relations and availabilities of renewable and nonrenewable resources. In this paper, we propose several discrete-time (DT) and one continuous-time (CT) mixed-integer linear programming (MILP) model for the MRCPSP based on models for the single-mode resource-constrained project scheduling problem (RCPSP). We first analyze the models' LP relaxations and show an equivalence between DT models. Then, we compare the computational performance of the models on benchmark instances. Our results indicate that the proposed CT model outperforms the state-of-the-art models on large problem instances and problem instances with relatively long activity durations, while it is competitive on smaller problem instances. A possible explanation for this outperformance is that the LP relaxations of the proposed CT model can be solved considerably faster than the LP relaxations of the state-of-the-art models.
This work presents a proactive distributed model for power system frequency stability. High-level penetration of renewable energy sources into the grid have introduced unforeseen and unmodeled system dynamics. Underfr...
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This work presents a proactive distributed model for power system frequency stability. High-level penetration of renewable energy sources into the grid have introduced unforeseen and unmodeled system dynamics. Underfrequency load shedding state-of-the-art solutions are reactive in design, with efficiency constrained by the modeling error. Being able to detect unstable conditions early makes it possible to generate optimized corrective actions. In this work, phasor measurement units are used to predict frequency values. When a disturbance is detected, the state of frequency is predicted a few seconds into the future via a particle filter algorithm. Corrective actions are modeled through a mixedintegerlinearprogramming algorithm within system areas established through spectral clustering. The solution is implemented on Matlab, considering IEEE test systems. The proactive design of the method combined with its multiple layers of optimization deliver results that outperform state-of-the-art solutions. Easy-to-implement model, without hard-to-derive parameters, highlights potential aspects towards real-life implementation.
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