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Adaptive conflict resolution for multi-UAV 4D routes optimization using stochastic fractal search algorithm

TRANSPORTATION RESEARCH PART C-EMERGING TECHNOLOGIES 2022年 139卷

作者： Pang, Bizhao Low, Kin Huat Lv, Chen Nanyang Technol Univ Sch Mech & Aerosp Engn Singapore 639798 Singapore Nanyang Technol Univ Air Traff Management Res Inst Singapore 637460 Singapore

The increasing unmanned aircraft system (UAS) applications in urban environments pose challenges for safe and efficient low altitude air traffic management. As an essential enabler to meet these challenges, pre-flight 4D routes optimization is required to conduct conflict detection and resolution (CD&R) and to generate conflict-free flight routes before departure. Existing studies on strategic deconfliction cover several types of strategies such as scheduling or rerouting. However, a single type of strategy used to solve different types of conflicts may lead to an unsafe and inefficient way of conflict resolution. This paper proposes an adaptive decision-making framework to optimize the resolution strategies used for different types of conflicts with explainable mechanisms. The proposed framework is formulated as a double-layer optimization problem with the considerations of scheduling, speed adjustment, and rerouting strategies for conflict resolution. The first layer of the framework is established as a probabilistic selection model to make decisions on which strategy should be selected for what type of conflict. The second layer is developed as a mixed-integer nonlinear programming (MINLP) model to optimize the decision variables of the strategies selected by the first layer. To solve the proposed double-layer optimization problem, we introduce and improve a novel meta-heuristic stochastic fractal search (SFS) algorithm with two major improvements of a penalty-guided fitness function and an exploitation-exploration balancing scheme. Simulation results demonstrate that the proposed adaptive conflict resolution framework successfully optimizes the strategies used for each type of flight conflict, which subsequently optimizes the 4D routes with significant reductions in total operational cost, number of flight conflicts, and flight delays. The improved stochastic fractal search (ISFS) algorithm is also proved effective and reliable in solving the proposed optimizati

关键词： Unmanned aircraft system Conflict resolution mixed-integer nonlinear programming Third-party risk Urban environments

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Practical approximations and heuristic approaches for managing shiftable loads in the multi-period optimal power flow framework

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ELECTRIC POWER SYSTEMS RESEARCH 2021年 190卷

作者： Avramidis, Iason-Iraklis Capitanescu, Florin Deconinck, Geert Luxembourg Inst Sci & Technol LIST Environm Res & Innovat ERIN Dept 41 Rue Brill L-4422 Belvalux Luxembourg Katholieke Univ Leuven ESAT Electa Kasteelpk Arenberg 10 B-3001 Leuven Belgium

The presence of smart buildings (SBs) is expected to grow manifold in the next decade, leading to both challenges and opportunities in managing increasingly "active" distribution systems. SBs are host to a number of devices and technologies capable of providing residential flexibility in order to maintain acceptable operating conditions within the distribution system. A prevalent class of devices with significant potential for flexibility provision are shiftable loads (SLs), which represent a large amount of potential SB-provided flexibility. However, the accurate modelling of SLs within the multi-period optimal power flow (MP-OPF) framework results in complex non-convex mixed-integer nonlinear programming (MINLP) problems. For realistic feeders, MINLP problems are intractable and hence require some heuristic form of circumvention. This work evaluates the limitations of the MINLP formulation and proposes new practical alternatives, namely a flexible NLP approximation and a multi-faceted heuristic algorithm. The proposed approaches are generic and applicable for any problem size or type of SL, while they are shown to work efficiently, both speed-wise and solution-quality-wise, outperforming state-of-the-art MINLP solvers. A simple scoring and ranking scheme is also proposed in order to make a direct comparison between the different approaches.

关键词： mixed-integer nonlinear programming multi-period optimal power flow residential flexibility shiftable loads smart buildings

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Fair bandwidth allocation and end-to-end delay routing algorithms for wireless mesh networks

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IEICE TRANSACTIONS ON COMMUNICATIONS 2007年第5期E90B卷 1042-1051页

作者： Wen, Yean-Fu Lin, Yeong-Sung Frank Natl Taiwan Univ Dept Informat Management Taipei Taiwan

Quality-of-service (QoS) is essential for multimedia applications, such as video-conferencing and voice over IP (VoIP) services, in wireless mesh networks (WMNs). A consequence of many clients accessing the Internet via the same backhaul is that throughput depends on the number of hops from the backhaul. This spatial bias problem is formulated as a mixed-integer nonlinear programming problem that considers end-to-end delay in terms of gateway selection, least-hop and load-balanced routing, and link capacity constraints. In this paper, we propose a routing algorithm for the network layer and a bandwidth allocation scheme for the medium access control (MAC) layer. The latter achieves fairness in both throughput and end-to-end delay in orthogonal mesh backbone networks with a distributed scheme, thereby minimizing the objective function. Our experiment results show that the proposed algorithm achieves throughput fairness, reduces end-to-end delay, and outperforms other general schemes and algorithms by at least 10.19%.

关键词： delay fairness mixed-integer nonlinear programming performance wireless networks

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Planning of distributed ventilation systems for energy-efficient buildings by discrete optimisation

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JOURNAL OF BUILDING ENGINEERING 2023年 68卷

作者： Mueller, Tim M. Sachs, Marlene Breuer, Julius H. P. Pelz, Peter F. Tech Univ Darmstadt Fluid Syst Otto Berndt Str 2 D-64287 Darmstadt Germany

The EU's climate targets are increasingly affecting the building sector. Energy-efficient buildings should therefore be built as airtight as possible in order to meet these targets - ventilation systems are necessary to ensure a comfortable indoor climate. In the planning of ventilation systems, the placement, wiring and operation of the fans, among other things, must be considered. If, instead of the conventional planning for the maximum load case, the partial load scenarios are included, oversizing is reduced and energy efficiency is increased. In addition, there are new ventilation approaches that include distributed components in the central duct network and thus offer further opportunities to increase the energy efficiency of the systems. If one now considers multiple load cases and allows distributed components in the design, the number of combinations exceeds any human manageable amount and the human made design decision becomes far from optimal as a result. Therefore, in this paper a method is presented that uses mathematical optimisation techniques to control the complexity and support the design. The planning task is modeled techno-economically as a minimisation problem with respect to life-cycle costs (mixed-integer nonlinear Program) and solved with discrete optimisation methods. The approach is then tested on a case study, with which savings of 22% in life-cycle costs are achieved while reducing energy consumption by 28%. Furthermore, the embedding in the real planning process is considered and shown that the division into several planning phases has a negative impact on the efficiency of the ventilation system. These results show that increasing the complexity of the planning task and modelling and solving it using discrete optimisation methods allows for a huge increase in the efficiency of the ventilation system.

关键词： Distributed ventilation system Discrete optimisation Life -cycle cost optimisation mixed-integer nonlinear programming

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Computer-Aided Design of Ionic Liquids as Solvents for Extractive Desulfurization

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AICHE JOURNAL 2018年第3期64卷 1013-1025页

作者： Song, Zhen Zhang, Chenyue Qi, Zhiwen Zhou, Teng Sundmacher, Kai East China Univ Sci & Technol Sch Chem Engn State Key Lab Chem Engn Max Planck Partner Grp Shanghai 200237 Peoples R China Max Planck Inst Dynam Complex Tech Syst Proc Syst Engn Sandtorstr 1 D-39106 Magdeburg Germany Otto von Guericke Univ Proc Syst Engn Univ Pl 2 D-39106 Magdeburg Germany

Although ionic liquids (ILs) have been widely explored as solvents for extractive desulfurization (EDS) of fuel oils, systematic studying of the optimal design of ILs for this process is still scarce. The UNIFAC-IL model is extended first to describe the EDS system based on exhaustive experimental data. Then, based on the obtained UNIFAC-IL model and group contribution models for predicting the melting point and viscosity of ILs, a mixed-integer nonlinear programming (MINLP) problem is formulated for the purpose of computer-aided ionic liquid design (CAILD). The MINLP problem is solved to optimize the liquid-liquid extraction performance of ILs in a given multicomponent model EDS system, under consideration of constraints regarding the IL structure, thermodynamic and physical properties. The top five IL candidates preidentified from CAILD are further evaluated by means of process simulation using ASPEN Plus. Thereby, [C5MPy][C(CN)(3)] is identified as the most suitable solvent for EDS. (c) 2017 American Institute of Chemical Engineers

关键词： ionic liquid design extractive desulfurization UNIFAC-IL mixed-integer nonlinear programming process simulation

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Operational strategy and planning for raw natural gas refining complexes: Process modeling and global optimization

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AICHE JOURNAL 2017年第2期63卷 652-668页

作者： Zhang, Bing J. Chen, Qing L. Li, Jie Floudas, Christodoulos A. Sun Yat Sen Univ Sch Chem Engn & Technol Guangdong Engn Technol Res Ctr Petrochem Energy C Key Lab Low Carbon Chem & Energy Conservat Guangd 135 Xingang West Rd Guangzhou 510275 Guangdong Peoples R China Texas A&M Univ Artie McFerrin Dept Chem Engn 3122 TAMU College Stn TX 77843 USA Texas A&M Univ Texas A&M Energy Inst 3372 TAMU College Stn TX 77843 USA Univ Manchester Sch Chem Engn & Analyt Sci Manchester M13 9PL Lancs England

Optimal operational strategy and planning of a raw natural gas refining complex (RNGRC) is very challenging since it involves highly nonlinear processes, complex thermodynamics, blending, and utility systems. In this article, we first propose a superstructure integrating a utility system for the RNGRC, involving multiple gas feedstocks, and different product specifications. Then, we develop a large-scale nonconvex mixed-integer nonlinear programming (MINLP) optimization model. The model incorporates rigorous process models for input and output relations based on fundamentals of thermodynamics and unit operations and accurate models for utility systems. To reduce the noncovex items in the proposed MINLP model, equivalent reformulation techniques are introduced. Finally, the reformulated nonconvex MINLP model is solved to global optimality using state of the art deterministic global optimization approaches. The computational results demonstrate that a significant profit increase is achieved using the proposed approach compared to that from the real operation. (c) 2016 American Institute of Chemical Engineers AIChE J, 63: 652-668, 2017

关键词： natural gas operational planning mixed-integer nonlinear programming enterprise-wide optimization global optimization

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nonlinear topology optimization of District Heating Networks: A benchmark of a mixed-integer and a density-based approach

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ENERGY 2023年 278卷

作者： Wack, Yannick Serra, Sylvain Baelmans, Martine Reneaume, Jean-Michel Blommaert, Maarten Katholieke Univ Leuven Dept Mech Engn Celestijnenlaan 300 POB 2421 B-3001 Leuven Belgium Univ Pau & Pays Adour UPPA E2S LaTEP Pau France Flemish Inst Technol Res VITO Boeretang 200 B-2400 Mol Belgium EnergyVille Thor Pk 3600 Genk B-8310 Genk Belgium

The widespread use of optimization methods in the design phase of District Heating Networks is currently limited by the availability of scalable optimization approaches that accurately represent the network. In this paper, we benchmark two different approaches to nonlinear topology optimization of District Heating Networks in terms of computational cost and optimality gap. We compare a combinatorial approach, which directly solves a mixed-integer nonlinear program, against a density-based approach. This density-based approach relaxes the integer constraint on pipe placement and ensures near-discrete topologies through penalization. The benchmark shows subquadratic scaling of the computational cost for the density-based approach, making it tractable for large problems, while the combinatorial approach scales exponentially. The combinatorial approach took 29 h to optimize a network for a neighborhood of about 600 streets, compared to 35 min for the density-based method. Optimality gap analysis indicates that resolving the integer constraint on pipe placement does not necessarily lead to a superior design, while making the optimization of large practical problems intractable. In contrast, the scaling of the density-based approach remains tractable for large problems. Further study of the optimality gap highlights the importance of consciously choosing initialization strategies when deciding to solve the nonlinear topology optimization problem.

关键词： District Heating Networks Topology optimization mixed-integer nonlinear programming Benchmark

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Sustainable Design and Synthesis of Algae-Based Biorefinery for Simultaneous Hydrocarbon Biofuel Production and Carbon Sequestration

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AICHE JOURNAL 2013年第5期59卷 1599-1621页

作者： Gebreslassie, Berhane H. Waymire, Randall You, Fengqi Northwestern Univ Dept Chem & Biol Engn Evanston IL 60208 USA

The superstructure optimization of algae-based hydrocarbon biorefinery with sequestration of CO2 from power plant flue gas is proposed. The major processing steps include carbon capture, algae growth, dewatering, lipid extraction and power generation, and algal biorefinery. We propose a multiobjective mixed-integer nonlinear programming (MINLP) model that simultaneously maximizes the net present value (NPV) and minimizes the global warming potential (GWP) subject to technology selection constraints, mass balance constraints, energy balance constraints, technoeconomic analysis constraints, and environmental impact constraints. The model simultaneously determines the optimal decisions that include production capacity, size of each processing unit, mass flow rates at each stage of the process, utility consumption, economic, and environmental performances. We propose a two-stage heuristic solution algorithm to solve the non-convex MINLP model. Finally, the bicriteria optimization problem is solved with e-constraint method, and the resulting Pareto-optimal curve reveals the trade-off between the economic and environmental criteria. The results show that for maximum NPV, the optimal process design uses direct flue gas, a tubular photobioreactor for algae growth, a filtration dewatering unit, and a hydroprocessing pathway leading to 47.1 MM gallons of green diesel production per year at $6.33/gal corresponding to GWP of 108.7 kg CO2-eq per gallon. (C) 2013 American Institute of Chemical Engineers AIChE J, 59: 1599-1621, 2013

关键词： sustainability biorefinery mixed-integer nonlinear programming superstructure multiobjective

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Optimal sizing of renewables and battery systems for hybrid AC/DC microgrids based on variability management

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APPLIED ENERGY 2022年 321卷

作者： Xie, Peng Jia, Youwei Lyu, Cheng Wang, Han Shi, Mengge Chen, Hongkun Southern Univ Sci & Technol Dept Elect & Elect Engn Shenzhen Peoples R China Hong Kong Polytech Univ Dept Elect Engn Hong Kong Peoples R China Wuhan Univ Sch Elect Engn & Automat Wuhan Peoples R China

This paper proposes an explicit approach to optimal sizing of the integrated battery energy storage systems in hybrid renewable AC/DC islanded microgrids, where the economic impacts of variability management (in concerning operational volatility and uncertainty) are comprehensively investigated. To quantitatively measure the variability levels at different time scales, two indices (i.e. volatility management index and uncertainty management index) are firstly proposed from the perspectives of system planning and operation. Moreover, the probability boundaries of both indices are derived to facilitate the initial system design processes. In particular, the concerned problem is formulated as a bi-level mixed-integer nonlinear programming model to counterbalance the variability and its induced cost at both planning and operation stages. Finally, an original decomposition-coordination algorithm based on the dual decomposition and alternate iterative strategies is proposed to ensure the efficient convergence of the solution process for the constructed mathematical model. Numerical simulations are carried out by analyzing the impacts of various factors associated with optimal sizing solutions and comparing with state-of-the-art approaches. Results show that the proposed sizing technique can facilitate designers finding the optimal capacity combination of renewables and batteries under preset renewables penetration, capital cost, and system variability levels.

关键词： Hybrid AC/DC microgrid System variability Optimal sizing mixed-integer nonlinear programming Decomposition-coordination algorithm

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Heat-integrated distillation columns: Vapor recompression or internal heat integration?

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AICHE JOURNAL 2012年第12期58卷 3740-3750页

作者： Harwardt, Andreas Marquardt, Wolfgang Rhein Westfal TH Aachen D-52056 Aachen Germany

Internally, heat-integrated distillation columns (HIDiC) and vapor recompression (VRC) constitute alternative design options to provide sustainable distillation processes. However, the design is often based on heuristic rules or the experience of the designer, as no systematic methodology driven by economics has been established so far. The increased complexity of heat-integrated columns can hardly be dealt with using simulation studies but rather calls for a systematic design procedure. A new design methodology is presented here;it builds on a superstructure, mixed-integer minimization of total annualized cost of operation and rigorous thermodynamic modeling. Optimal VRC and HIDiC designs are identified for the separation of binary, multicomponent, and nonideal mixtures and benchmarked against conventional distillation column designs. A small number of intermediate heat exchangers is optimal for these HIDiC configurations, eventually reducing to a single heat exchanger similar to VRC. Therefore, VRC designs are often more cost efficient due to simpler equipment. (C) 2012 American Institute of Chemical Engineers AIChE J, 2012

关键词： heat-integrated distillation columns vapor recompression mixed-integer nonlinear programming rigorous optimization heat integration separation process synthesis

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