| 1. |
- Almgren, Torgny, 1962, et al.
(författare)
-
Optimization models for improving periodic maintenance schedules by utilizing opportunities
- 2012
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Ingår i: Proceedings of 4th Production and Operations Management World Conference, July 2012.
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Konferensbidrag (refereegranskat)abstract
- We present mathematical models for finding optimal opportunistic maintenance schedules for systems, in which components are assigned maximum replacement intervals. Our mod- els are applied to safety-critical components in an aircraft engine, for which maintenance opportunities naturally arise since entire modules are sent to the workshop when mainte- nance is required on one or more components. Case study results illustrate the advantage of the mathematical models over simpler policies, the benefit of coordinating the maintenance in economically dependent systems, and that our models can be utilized also for strategic investment decision support.
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| 2. |
- Almgren, Torgny, 1962, et al.
(författare)
-
Optimization of opportunistic replacement activities: A case study in the aircraft industry
- 2007
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- In the aircraft industry maximizing availability is essential. Maintenance schedules must therefore be opportunistic, incorporating preventive maintenance activities within the scheduled as well as the unplanned ones. At the same time, the maintenance contractor should utilize opportunistic maintenance to enable the minimization of the total expected cost to have a functional aircraft engine and thus to provide attractive service contracts. This paper provides an opportunistic maintenance optimization model which has been constructed and tested together with Volvo Aero Corporation in Trollhättan, Sweden for the maintenance of the RM12 engine. The model incorporates components with deterministic as well as with stochastic lives. The replacement model is shown to have favourable properties; in particular, when the maintenance occasions are fixed the remaining problem has the integrality property, the replacement polytope corresponding to the convex hull of feasible solutions is full-dimensional, and all the necessary constraints for its definition are facet-inducing. We present an empirical crack growth model that estimates the remaining life and also a case study that indicates that a non-stationary renewal process with Weibull distributed lives is a good model for the recurring maintenance occasions. Using one point of support for the distribution yields a deterministic replacement model; it is evaluated against classic maintenance policies from the literature through stochastic simulations. The deterministic model provides maintenance schedules over a finite time period that induce fewer maintenance occasions as well as fewer components replaced.
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| 3. |
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| 4. |
- Almgren, Torgny, 1962, et al.
(författare)
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The opportunistic replacement problem: analysis and case studies
- 2011
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We consider an optimization model for determining optimal opportunistic maintenance (that is, component replacement) schedules when data is deterministic. This problem generalizes that of Dickman, Epstein, and Wilamowsky [21] and is a natural starting point for the modelling of replacement schedules when component lives are non-deterministic. We show that this basic opportunistic replacement problem is NP-hard. We show that the convex hull of the set of feasible replacement schedules is full-dimensional, and that all the necessary inequalities also are facet-inducing. We show that when maintenance occasions are fixed, the remaining problem can be stated as a linear program; when maintenance costs are monotone with time, the latter is solvable through a greedy procedure. Results from a series of case studies performed in the areas of aircraft engine and wind turbine maintenance are also reported. These illustrate the advantages of utilizing opportunistic maintenance activities based on a complete optimization model, as compared to simpler policies.
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| 5. |
- Almgren, Torgny, 1962, et al.
(författare)
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The opportunistic replacement problem: theoretical analyses and numerical tests
- 2012
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Ingår i: Mathematical Methods of Operations Research. - : Springer Science and Business Media LLC. - 1432-2994 .- 1432-5217. ; 76:3, s. 289-319
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Tidskriftsartikel (refereegranskat)abstract
- We consider a model for determining optimal opportunistic maintenance schedules with respect to a maximum replacement interval. This problem generalizes that of Dickman et al. (J Oper Res Soc India 28:165–175, 1991) and is a natural starting point for modelling replacement schedules of more complex systems. We show that this basic opportunistic replacement problem is NP-hard, that the convex hull of the set of feasible replacement schedules is full-dimensional, that all the inequalities of the model are facet-inducing, and present a new class of facets obtained through a {0,1/2}-Chvátal–Gomory rounding. For costs monotone with time, a class of elimination constraints is introduced to reduce the computation time; it allows maintenance only when the replacement of at least one component is necessary. For costs decreasing with time, these constraints eliminate non-optimal solutions. When maintenance occasions are fixed, the remaining problem is stated as a linear program and solved by a greedy procedure. Results from a case study on aircraft engine maintenance illustrate the advantage of the optimization model over simpler policies. We include the new class of facets in a branch-and-cut framework and note a decrease in the number of branch-and-bound nodes and simplex iterations for most instance classes with time dependent costs. For instance classes with time independent costs and few components the elimination constraints are used favorably. For fixed maintenance occasions the greedy procedure reduces the computation time as compared with linear programming techniques for all instances tested.
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| 6. |
- Almgren, Torgny, 1962, et al.
(författare)
-
The replacement problem: A polyhedral and complexity analysis. The complete version
- 2009
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We consider an optimization model for determining optimal opportunistic maintenance (that is, component replacement) schedules when data is deterministic. This problem, which generalizes that of Dickman et al., is a natural starting point for the modelling of replacement schedules when component lives are non-deterministic, whence a mathematical study of the model is of large interest. We show that the convex hull of the set of feasible replacement schedules is full-dimensional, and that all the necessary inequalities are facet-inducing. Additional facets are then provided through Chvatal-Gomory rounding. We show that when maintenance occasions are fixed, the remaining problem reduces to a linear program; in some cases the latter is solvable through a greedy procedure. We further show that this basic replacement problem is NP-hard.
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| 7. |
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| 8. |
- Besnard, Francois, 1983, et al.
(författare)
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A stochastic model for opportunistic maintenance planning of offshore wind farms
- 2011
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Ingår i: 2011 IEEE PES Trondheim PowerTech: The Power of Technology for a Sustainable Society, POWERTECH 2011; Trondheim; 19 June 2011 through 23 June 2011. - 9781424484195
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Konferensbidrag (refereegranskat)abstract
- A sound maintenance planning is of crucial importance for wind power farms, and especially for offshore locations. This paper presents a stochastic optimization model for opportunistic service maintenance of offshore wind farms. The model takes advantage of 7 days wind production ensemble forecast and opportunities at corrective maintenance activities in order to perform the service maintenance tasks at the lowest cost. The model is based on a rolling horizon, i.e. the optimization is performed on a daily basis to update the maintenance planning based on the updated production and weather forecasts. An example based on real wind data is used to demonstrate the value of the proposed approach. In this example, it is shown that 32% of the cost for production losses and transportation could be saved. © 2011 IEEE.
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| 9. |
- Besnard, Francois, et al.
(författare)
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An Optimization Framework for Opportunistic Maintenance of Offshore Wind Power System
- 2009
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Ingår i: 2009 IEEE BUCHAREST POWERTECH, VOLS 1-5. - NEW YORK : IEEE. - 9781424422340 ; , s. 2970-2976
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Konferensbidrag (refereegranskat)abstract
- A sound maintenance planning is of crucial importance for wind power farms, and especially for offshore locations. There is a large potential in cost savings by maintenance optimization to make the projects more cost-efficient. This paper presents an opportunistic maintenance optimization model for offshore wind power system. The model takes advantage of wind forecasts and corrective maintenance activities in order to perform preventive maintenance tasks at low costs. The approach is illustrated with an example to demonstrate the value of the optimization. In this example 43% of the cost to perform preventive maintenance could be saved using the proposed method.
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| 10. |
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| 11. |
- Eriksson Barman, Sandra, 1985, et al.
(författare)
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Modeling and solving vehicle routing problems with many available vehicle types
- 2015
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Ingår i: Springer Proceedings in Mathematics & Statistics. - Cham : Springer International Publishing. - 2194-1009 .- 2194-1017. - 9783319185668
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Konferensbidrag (refereegranskat)abstract
- Vehicle routing problems (VRP) involving the selection of vehicles from a large set of vehicle types are hitherto not well-studied in the literature. Such problems arise at Volvo Group Trucks Technology, who faces an immense set of possible vehicle configurations, of which an optimal set needs to be chosen for each specific combination of transport missions. Another property of real-world VRP’s that is often neglected in the literature is that the fuel resources required to drive a vehicle along a route is highly dependent on the actual load of the vehicle. We define the fleet size and mix VRP with many available vehicle types, called many-FSMVRP, and suggest an extended set-partitioning model of this computationally demanding combinatorial optimization problem. To solve the extended model, we have developed a method based on Benders’ decomposition, the subproblems of which are solved using column generation, and the column generation subproblems being solved using dynamic programming; the method is implemented with a so-called projection-of-routes procedure. The resulting method is compared with a column generation approach for the standard set-partitioning model. Our method for the extended model performs on par with column generation applied to the standard model for instances such that the two models are equivalent. In addition, the utility of the extended model for instances with very many available vehicle types is demonstrated. Our method is also shown to efficiently handle cases in which the costs are dependent on the load of the vehicle. Computational tests on a set of extended standard test instances show that our method, based on Benders’ algorithm, is able to determine combinations of vehicles and routes that are optimal to a relaxation (w.r.t. the route decision variables) of the extended model. Our exact implementation of Benders’ algorithm appears, however, too slow when the number of customers grows. To improve its performance, we suggest that relaxed versions of the column generation subproblems are solved, and that the set-partitioning model is replaced by a set-covering model.
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| 12. |
- Fotedar, Sunney, 1989, et al.
(författare)
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A criterion space decomposition approach to generalized tri-objective tactical resource allocation
- 2023
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Ingår i: Computational Management Science. - : Springer Science and Business Media LLC. - 1619-697X .- 1619-6988. ; 20:1
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Tidskriftsartikel (refereegranskat)abstract
- We present a tri-objective mixed-integer linear programming model of the tactical resource allocation problem with inventories, called the generalized tactical resource allocation problem (GTRAP). We propose a specialized criterion space decomposition strategy, in which the projected two-dimensional criterion space is partitioned and the corresponding sub-problems are solved in parallel by application of the quadrant shrinking method (QSM) (Boland in Eur J Oper Res 260(3):873–885, 2017) for identifying non-dominated points. To obtain an efficient implementation of the parallel variant of the QSM we suggest some modifications to reduce redundancies. Our approach is tailored for the GTRAP and is shown to have superior computational performance as compared to using the QSM without parallelization when applied to industrial instances.
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| 13. |
- Fotedar, Sunney, 1989, et al.
(författare)
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A decision-making tool to identify routings for an efficient utilization of machining resources: the decision makers’ perspective
- 2020
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Ingår i: PLANs forsknings-och tillämpningskonferens.
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Konferensbidrag (refereegranskat)abstract
- In the aerospace industry, efficient management of machining capacity is crucial to meet the required service levels to customers (which includes, measures of quality and lead-times ) and keeps the tied-up working capital in check. The proposed decision-making tool, described in this paper, aims to combine information and knowledge of manufacturing and logistics experts in a company to improve flow of materials through the factory. The material flow situation is different for a large aerospace tier-1 supplier as opposed to flow-based manufacturing company; when there is no pandemic or natural calamity, having relatively stable demand due to long-term contract is common, but there exists short-term demand variability. There is a complex flow of products at GKN Aerospace, as the products share machining resources, thus, resulting in uneven loads at machines and sometimes excess loading at certain machines. This along with short-term demand variability results in long queues in-front of machines which contributes with the biggest share of the total lead-time. Thus, long waiting times at one/many machine/s is common and may lead to bottlenecks in many places in the production pipeline. So, there is potential benefit in having rerouting-flexibility for products which can help in reducing queuing. However, qualifying a product for a new machine is time-consuming activity, and thus, should be done few years in advance. We propose a mathematical model aimed at improving some of these deficiencies of commonly used methods by facilitating balanced resource loading levels, i.e. to provide more degrees of freedom to the planner to absorb demand variations. The output provided by the model includes production routings in each time period (quarter) for the next 4–5 years; new qualifications to be done by technical staff for allocation of part types/products to machines which are not yet qualified/used for a given product. We keep the resource loading levels that are above a given threshold as low as possible and reduce the time/money spent for qualifying new allocations.
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| 14. |
- Fotedar, Sunney, et al.
(författare)
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Bi-objective optimization of the tactical allocation of job types to machines: mathematical modeling, theoretical analysis, and numerical tests
- 2022
-
Ingår i: International Transactions in Operational Research. - : Wiley. - 0969-6016 .- 1475-3995.
-
Tidskriftsartikel (refereegranskat)abstract
- We introduce a tactical resource allocation model for a large aerospace engine system manufacturer aimed at long-term production planning. Our model identifies the routings a product takes through the factory, and which machines should be qualified for a balanced resource loading, to reduce product lead times. We prove some important mathematical properties of the model that are used to develop a heuristic providing a good initial feasible solution. We propose a tailored approach for our class of problems combining two well-known criterion space search algorithms, the bi-directional epsilon-constraint method and the augmented weighted Tchebycheff method. A computational investigation comparing solution times for several solution methods is presented for 60 numerical instances.
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| 15. |
- Fotedar, Sunney, 1989, et al.
(författare)
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Mathematical optimization of the tactical allocation of machining resources for an efficient capacity utilization in aerospace component manufacturing
- 2019
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Ingår i: Proceedings of the 10th Aerospace Technology Congress. - : Linköping University Electronic Press. - 1650-3686 .- 1650-3740. - 9789175190068 ; , s. 183-188
-
Konferensbidrag (refereegranskat)abstract
- In the aerospace industry, with low volumes and many products, there is a critical need to efficiently use available manufacturing resources. Currently, at GKN Aerospace, resource allocation decisions that in many cases will last for several years are to some extent made with a short-term focus so as to minimize machining time, which results in a too high load on the most capable machines, and too low load on the less capable ones. This creates an imbalance in capacity utilization that leads to unnecessary queuing at some machines, resulting in long lead times and in an increase in tied-up capital. Tactical resource allocation on the medium to long-range planning horizon (six months to several years) aims to address this issue by allocating resources to meet the predicted future demand as effectively as possible, in order to ensure long range profitability. Our intent is to use mathematical optimization to find the best possible allocations.
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| 16. |
- Fotedar, Sunney, et al.
(författare)
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Robust optimization of a bi-objective tactical resource allocation problem with uncertain qualification costs
- 2022
-
Ingår i: Autonomous Agents and Multi-Agent Systems. - : Springer Science and Business Media LLC. - 1387-2532 .- 1573-7454. ; 36:2
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Tidskriftsartikel (refereegranskat)abstract
- In the presence of uncertainties in the parameters of a mathematical model, optimal solutions using nominal or expected parameter values can be misleading. In practice, robust solutions to an optimization problem are desired. Although robustness is a key research topic within single-objective optimization, little attention is received within multi-objective optimization, i.e. robust multi-objective optimization.This work builds on recent work within robust multi-objective optimization and presents a new robust efficiency concept for bi-objective optimization problems with one uncertain objective. Our proposed concept and algorithmic contribution are tested on a real-world multi-item capacitated resource planning problem, appearing at a large aerospace company manufacturing high precision engine parts. Our algorithm finds all the robust efficient solutions required by the decision-makers in significantly less time than the approach of Kuhn et al. (Eur J Oper Res 252(2):418-431, 2016) on 28 of the 30 industrial instances.
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| 17. |
- Fröidh, Oskar, et al.
(författare)
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Färdplan för ökad forskning och innovation inom underhåll av järnvägsfordon
- 2015
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- KTH, Chalmers och Handelshögskolan vid Göteborgs universitet har av Trafikverket fått uppdraget att ta fram ett dokument om forskningen inom underhåll av järnvägsfordon. Det är föreliggande färdplan som ingår i Trafikverkets satsning Morgondagens depåer. Färdplanen ska ligga till grund för en strategi och förslag på utveckling för kostnadseffektivt fordonsunderhåll med de förutsättningar som råder i Sverige, med avreglering och många aktörer i branschen likväl som speciella klimatförutsättningar. Trafikverket har uppmärksammat att frågor om depåer och fordonsunderhåll inte alltid hanteras på ett bra sätt för att utveckla järnvägssystemet. Tidigare hade Banverket ett sektorsansvar men det avskaffades i och med att Trafikverket bildades. Det behövs dock ett övergripande systemansvar och incitament för att leda processen framåt mot en stabil utveckling genom forskning, utveckling och innovation i den fortsatta omreglering som sker av den svenska järnvägssektorn. Hur kan en effektiv samverkan mellan universitet, näringsliv och offentlig sektor utformas för att bidra till en säker och pålitlig tågtrafik i Sverige? En litteraturgenomgång har genomförts för att visa var den internationella forskningsfronten står. Det tycks dock som att det samlade greppet inom underhåll av järnvägsfordon inte är ett genomarbetat forskningsområde, utan det kan bli ett svenskt ”pionjärområde” där universitet, högskolor och institut i samarbete med branschen kan skapa forskningsresultat och kunskapsutveckling. Denna färdplan föreslår ett antal olika områden som skulle behöva ökad forskning för större kunskap och kompetens. Var ska depåer för person- respektive godsfordon mest effektivt lokaliseras, centralt eller perifert i jämförelse med trafiksystemet och respektive omlopp? Hur ska de utformas mest effektivt med tanke på fordonstyper, reservdelar och personalutnyttjande? Hur ska infrastrukturen till och internt i depåerna utformas för effektivt arbete? Detta ska ske i en avreglerad järnvägssektor med olika operatörer, vagnägare, depåägare samt underhållsleverantörer på olika långa kontrakt. Hur ska detta organiseras på ett stabilt sätt med långsiktig ekonomisk bärkraft för samtliga parter? Arbetet går att dela upp i avhjälpande och förebyggande underhåll; i depå eller mobilt, med säkerhets-, drifts- eller komfortrelaterat underhåll. På vilka olika sätt går det att utvärdera samt utveckla modeller för att prognostisera behovet av underhåll enligt ovan nämnda variabler? Målet är att ta fram vetenskapliga metoder för att effektivisera fordonsunderhåll för järnvägstrafiken på ett optimalt sätt. I färdplanen rekommenderas en strategi för fordonsunderhåll: Trafikverket ska verka för att efterfrågad funktion i det svenska järnvägssystemet uppnås, inkluderande kostnadseffektivt underhåll av både infrastruktur och fordon. Hög driftsäkerhet är attraktivt för resenärer och godskunder och har ett värde och motiverar ett samhällsekonomiskt synsätt på underhåll av järnvägsfordon. Tillståndsövervakning och relaterad prediktering ges en viktigare roll för förebyggande underhåll. Öka synergin mellan infrastruktur- och fordonsbaserad tillståndsövervakning, inte minst av den dynamiska samverkan mellan infrastruktur och fordon. Utred hur ”intelligensen” hos infrastruktur och fordon bäst fördelas och utvecklas för ett mera kostnadseffektivt underhåll av järnvägssystemet. Detta innefattar att man vet vad man skall mäta och att uppmätta storheter kan länkas till framtida nedbrytning av fordon och infrastruktur. Utred flödet och ”flaskhalsar” i dagens system av fordonsunderhåll (kritiska aspekter). Utveckla distinktionen av säkerhetsnödvändigt underhåll och komfortrelaterat underhåll. Verka för tydliga och rimliga ”spelregler” för aktörer inom fordonsunderhåll. Förbättra nätverket bland dessa aktörer, inte minst kring tekniska frågor. Skapa ytterligare incitament för effektivt fordonsunderhåll genom att se över kostnader och intäkter i intressentkedjan mellan de primära kunderna och de som kan åtgärda problemen. Lyft fram goda exempel (best practice) på väl fungerande fordonsunderhåll. Låt universitet och högskolor få en viktig och neutral roll i den kunskapsbaserade utvecklingen. Detta bör ske genom att skapa ett forsknings- utvecklings- och demonstrations (FUD)-program inom området underhåll för järnvägsfordon. I denna färdplan föreslås även ett antal olika forskningsprojekt och -områden som skulle kunna utvecklas i ett sammanhållet forskningsprogram.
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| 18. |
- Fröidh, Oskar, et al.
(författare)
-
Färdplan för ökad forskning och innovation inom underhåll av järnvägsfordon
- 2015
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- KTH, Chalmers och Handelshögskolan vid Göteborgs universitet har av Trafikverket fått uppdraget att ta fram ett dokument om forskningen inom underhåll av järnvägsfordon. Det är föreliggande färdplan som ingår i Trafikverkets satsning Morgondagens depåer. Färdplanen ska ligga till grund för en strategi och förslag på utveckling för kostnadseffektivt fordonsunderhåll med de förutsättningar som råder i Sverige, med avreglering och många aktörer i branschen likväl som speciella klimatförutsättningar.Trafikverket har uppmärksammat att frågor om depåer och fordonsunderhåll inte alltid hanteras på ett bra sätt för att utveckla järnvägssystemet. Tidigare hade Banverket ett sektorsansvar men det avskaffades i och med att Trafikverket bildades. Det behövs dock ett övergripande systemansvar och incitament för att leda processen framåt mot en stabil utveckling genom forskning, utveckling och innovation i den fortsatta omreglering som sker av den svenska järnvägssektorn. Hur kan en effektiv samverkan mellan universitet, näringsliv och offentlig sektor utformas för att bidra till en säker och pålitlig tågtrafik i Sverige?En litteraturgenomgång har genomförts för att visa var den internationella forskningsfronten står. Det tycks dock som att det samlade greppet inom underhåll av järnvägsfordon inte är ett genomarbetat forskningsområde, utan det kan bli ett svenskt ”pionjärområde” där universitet, högskolor och institut i samarbete med branschen kan skapa forskningsresultat och kunskapsutveckling.Denna färdplan föreslår ett antal olika områden som skulle behöva ökad forskning för större kunskap och kompetens. Var ska depåer för person- respektive godsfordon mest effektivt lokaliseras, centralt eller perifert i jämförelse med trafiksystemet och respektive omlopp? Hur ska de utformas mest effektivt med tanke på fordonstyper, reservdelar och personalutnyttjande? Hur ska infrastrukturen till och internt i depåerna utformas för effektivt arbete? Detta ska ske i en avreglerad järnvägssektor med olika operatörer, vagnägare, depåägare samt underhållsleverantörer på olika långa kontrakt. Hur ska detta organiseras på ett stabilt sätt med långsiktig ekonomisk bärkraft för samtliga parter? Arbetet går att dela upp i avhjälpande och förebyggande underhåll; i depå eller mobilt, med säkerhets-, drifts- eller komfortrelaterat underhåll. På vilka olika sätt går det att utvärdera samt utveckla modeller för att prognostisera behovet av underhåll enligt ovan nämnda variabler? Målet är att ta fram vetenskapliga metoder för att effektivisera fordonsunderhåll för järnvägstrafiken på ett optimalt sätt.I färdplanen rekommenderas en strategi för fordonsunderhåll:Trafikverket ska verka för att efterfrågad funktion i det svenska järnvägssystemet uppnås, inkluderande kostnadseffektivt underhåll av både infrastruktur och fordon.Hög driftsäkerhet är attraktivt för resenärer och godskunder och har ett värde och motiverar ett samhällsekonomiskt synsätt på underhåll av järnvägsfordon.Tillståndsövervakning och relaterad prediktering ges en viktigare roll för förebyggande underhåll.Öka synergin mellan infrastruktur- och fordonsbaserad tillståndsövervakning, inte minst av den dynamiska samverkan mellan infrastruktur och fordon.Utred hur ”intelligensen” hos infrastruktur och fordon bäst fördelas och utvecklas för ett mera kostnadseffektivt underhåll av järnvägssystemet. Detta innefattar att man vet vad man skall mäta och att uppmätta storheter kan länkas till framtida nedbrytning av fordon och infrastruktur.Utred flödet och ”flaskhalsar” i dagens system av fordonsunderhåll (kritiska aspekter).Utveckla distinktionen av säkerhetsnödvändigt underhåll och komfortrelaterat underhåll.Verka för tydliga och rimliga ”spelregler” för aktörer inom fordonsunderhåll.Förbättra nätverket bland dessa aktörer, inte minst kring tekniska frågor.Skapa ytterligare incitament för effektivt fordonsunderhåll genom att se över kostnader och intäkter i intressentkedjan mellan de primära kunderna och de som kan åtgärda problemen.Lyft fram goda exempel (best practice) på väl fungerande fordonsunderhåll.Låt universitet och högskolor få en viktig och neutral roll i den kunskapsbaserade utvecklingen.Detta bör ske genom att skapa ett forsknings- utvecklings- och demonstrations (FUD)-program inom området underhåll för järnvägsfordon. I denna färdplan föreslås även ett antal olika forskningsprojekt och -områden som skulle kunna utvecklas i ett sammanhållet forskningsprogram.
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| 19. |
- Granfeldt, Caroline, 1991, et al.
(författare)
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A Lagrangian relaxation approach to an electricity system investment model with a high temporal resolution
- 2023
-
Ingår i: OR Spectrum. - 1436-6304 .- 0171-6468. ; 45:4, s. 1263-1294
-
Tidskriftsartikel (refereegranskat)abstract
- The global production of electricity contributes significantly to the release of carbon dioxide emissions. Therefore, a transformation of the electricity system is of vital importance in order to restrict global warming. This paper proposes a modelling methodology for electricity systems with a large share of variable renewable electricity generation, such as wind and solar power. The model developed addresses the capacity expansion problem, i.e. identifying optimal long-term investments in the electricity system. Optimal investments are defined by minimum investment and production costs under electricity production constraints—having different spatial resolutions and technical detail—while meeting the electricity demand. Our model is able to capture a range of strategies to manage variations and to facilitate the integration of variable renewable electricity; it is very large due to the high temporal resolution required to capture the variations in wind and solar power production and the chronological time representation needed to model energy storage. Moreover, the model can be further extended—making it even larger—to capture a large geographical scope, accounting for the trade of electricity between regions with different conditions for wind and solar power. Models of this nature thus typically need to be solved using some decomposition method to reduce solution times. In this paper, we develop a decomposition method using so-called variable splitting and Lagrangian relaxation; the dual problem is solved by a deflected subgradient algorithm. Our decomposition regards the temporal resolution by defining 2-week periods throughout the year and relaxing the overlapping constraints. The method is tested and evaluated on some real-world cases containing regions with different energy mixes and conditions for wind power. Numerical results show shorter computation times as compared with the non-decomposed model, and capacity investment options similar to the optimal solution provided by the latter model.
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| 20. |
- Gustavsson, Emil, 1987, et al.
(författare)
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Preventive maintenance scheduling of multi-component systems with deterioration costs
- 2012
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We introduce the preventive maintenance scheduling problem with interval costs (PMSPIC), which is to schedule preventive maintenance of components of a system over a finite discretized time horizon, given a common set-up cost and component costs dependent on the lengths of the maintenance intervals. We present a 0-1 integer linear programming (0-1 ILP) model for the PMSPIC which was originally presented by Joneja (1990) to model the joint replenishment problem. We show that most of the integrality constraints can be relaxed and that the linear inequality constraints define facets of the convex hull of the feasible set. We present three applications demonstrating that the PMSPIC can be used to model several types of maintenance problems with deterioration costs. The first considers rail grinding. If the interval between the grinding occasions increases, then the sizes of the rail cracks increase, which implies that more grinding passes must be performed, generating a higher maintenance cost. We presume a deterministic model for crack growth and optimize the scheduling of the rail grinding on a set of track sections. Our second application concerns two approaches for the scheduling of component replacements in aircraft engines. In the first approach a bi-objective problem, simultaneously minimizing the cost for the scheduled preventive maintenance and the probability of unexpected stops, is formulated. The second approach considers the minimization of the sum of costs of preventive and expected corrective maintenance, without rescheduling. We also demonstrate that if rescheduling is allowed, then the 0-1 ILP model can be used as a policy by re-optimizing the schedule at a component failure, thus utilizing the opportunity for preventive maintenance. We evaluate the use of such a strategy in a simulation of the engine. The third approach considers components’ replacement in wind mills in a wind farm, extending the PMSPIC to consider several systems with a joint set-up cost. As for the aircraft engine application, we use the 0-1 ILP model as a policy for deciding upon replacement decisions allowing for rescheduling, and evaluate it by simulating the joint system. In each of the three applications, the use of the 0-1 ILP model is compared with age or constantinterval policies, resulting in a reduction of maintenance costs by up to 15% compared with the respective best simple policy.
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| 21. |
- Gustavsson, Emil, 1987, et al.
(författare)
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Preventive maintenance scheduling of multi-component systems with interval costs
- 2014
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Ingår i: Computers & industrial engineering. - : Elsevier BV. - 0360-8352. ; 76, s. 390-400
-
Tidskriftsartikel (refereegranskat)abstract
- We introduce the preventive maintenance scheduling problem with interval costs (PMSPIC), which is to schedule preventive maintenance (PM) of the components of a system over a finite and discretized time horizon, given a common set-up cost and component costs dependent on the lengths of the maintenance intervals. We present a 0–1 integer linear programming (0–1 ILP) model for the PMSPIC; the model is identical to that presented by Joneja (1990) for the joint replenishment problem within inventory management. We study this model from a polyhedral and exact solutions’ point of view, as opposed to previously studied heuristics (e.g. Boctor, Laporte, & Renaud, 2004; Federgruen & Tzur, 1994; Levi, Roundy, & Shmoys, 2006; Joneja, 1990).We show that most of the integrality constraints can be relaxed and that the linear inequality constraints define facets of the convex hull of the feasible set. We further relate the PMSPIC to the opportunistic replacement problem, for which detailed polyhedral studies were performed by Almgren et al. (2012a). The PMSPIC can be used as a building block to model several types of maintenance planning problems possessing deterioration costs. By a careful modeling of these costs, a polyhedrally sound 0–1 ILP model is used to find optimal solutions to realistic-sized multi-component maintenance planning problems. The PMSPIC is thus easily extended by side constraints or to multiple tiers, which is demonstrated through three applications; these are chosen to span several levels of unmodeled randomness requiring fundamentally different maintenance policies, which are all handled by variations of our basic model. Our first application considers rail grinding. Rail cracks increase with increasing intervals between grinding occasions, implying that more grinding passes must be performed—thus generating higher costs. We optimize the grinding schedule for a set of track sections presuming a deterministic model for crack growth; hence, no corrective maintenance (CM) will occur between the grinding occasions scheduled. The second application concerns two approaches for scheduling component replacements in aircraft engines. The first approach is bi-objective, simultaneously minimizing the cost for the scheduled PM and the probability of unexpected stops. In the second approach the sum of costs for PM and expected CM—without rescheduling—is minimized. When rescheduling is allowed, the 0–1 ILP model is used as a policy by re-optimizing the schedule at a component failure, which then constitutes an opportunity for PM. The policy manages the trade-off between costs for PM and unplanned CM and is evaluated in a simulation of the engine. The third application considers components’ replacement in wind mills in a wind farm, extending the PMSPIC to comprise multiple tiers with joint set-up costs. Due to the large number of components unexpected stops occur frequently, thus calling for a dynamic rescheduling, which is evaluated through a simulation of the system. In each of the three applications, the use of the 0-1 ILP model is compared with age or constant-interval policies; the maintenance costs are reduced by up to 16% as compared with the respective best simple policy. The results are strongest for the first two applications, possessing low levels of unmodeled randomness.
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| 22. |
- Gustavsson, Emil, 1987, et al.
(författare)
-
Primal convergence from dual subgradient methods for convex optimization
- 2012
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- When solving a convex optimization problem through a Lagrangian dual reformulation subgradient optimization methods are favourably utilized, since they often find near-optimal dual solutions quickly. However, an optimal primal solution is generally not obtained directly through such a subgradient approach. We construct a sequence of convex combinations of primal subproblem solutions, a so called ergodic sequence, which is shown to converge to an optimal primal solution when the convexity weights are appropriately chosen. We generalize previous convergence results from linear to convex optimization and present a new set of rules for constructing the convexity weights that define the ergodic sequence of primal solutions. In contrast to previously proposed rules, they exploit more information from later subproblem solutions than from earlier ones. We evaluate the proposed rules on a set of nonlinear multicommodity flow problems and demonstrate that they clearly outperform the ones previously proposed.
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| 23. |
- Gustavsson, Emil, 1987, et al.
(författare)
-
Primal convergence from dual subgradient methods for convex optimization
- 2015
-
Ingår i: Mathematical Programming. - : Springer Science and Business Media LLC. - 0025-5610 .- 1436-4646. ; 150:2, s. 365-390
-
Tidskriftsartikel (refereegranskat)abstract
- When solving a convex optimization problem through a Lagrangian dual reformulation subgradient optimization methods are favorably utilized, since they often find near-optimal dual solutions quickly. However, an optimal primal solution is generally not obtained directly through such a subgradient approach unless the Lagrangian dual function is differentiable at an optimal solution. We construct a sequence of convex combinations of primal subproblem solutions, a so called ergodic sequence, which is shown to converge to an optimal primal solution when the convexity weights are appropriately chosen. We generalize previous convergence results from linear to convex optimization and present a new set of rules for constructing the convexity weights that define the ergodic sequence of primal solutions. In contrast to previously proposed rules, they exploit more information from later subproblem solutions than from earlier ones. We evaluate the proposed rules on a set of nonlinear multicommodity flow problems and demonstrate that they clearly outperform the ones previously proposed.
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| 24. |
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| 25. |
- Göransson, Lisa, 1982, et al.
(författare)
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Management of Wind Power Variations in Electricity System Investment Models. A Parallel Computing Strategy
- 2021
-
Ingår i: Operations Research Forum. - : Springer Science and Business Media LLC. - 2662-2556. ; 2
-
Tidskriftsartikel (refereegranskat)abstract
- Accounting for variability in generation and load and strategies to tackle variability cost-efficiently are key components of investment models for modern electricity systems. This work presents and evaluates the Hours-to-Decades (H2D) model, which builds upon a novel approach to account for strategies to manage variations in the electricity system covering several days, the variation management which is of particular relevance to wind power integration. The model discretizes the time dimension of the capacity expansion problem into 2-week segments, thereby exploiting the parallel processing capabilities of modern computers. Information between these segments is then exchanged in a consensus loop. The method is evaluated with regard to its ability to account for the impacts of strategies to manage variations in generation and load, regional resources and trade, and inter-annual linkages. Compared to a method with fully connected time, the proposed method provides solutions with an increase in total system cost of no more than 1.12%, while reducing memory requirements to 1/26’th of those of the original problem. For capacity expansion problems concerning two regions or more, it is found that the H2D model requires 1–2% of the calculation time relative to a model with fully connected time when solved on a computer with parallel processing capability.
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| 26. |
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| 27. |
- Kans, Mirka, 1971-, et al.
(författare)
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Data Driven Maintenance : A Promising Way of Action for Future Industrial Services Management
- 2022
-
Ingår i: International Congress and Workshop on Industrial AI 2021. IAI 2021. - Cham : Springer. - 9783030936389 - 9783030936396 ; , s. 212-223, s. 212-223
-
Konferensbidrag (refereegranskat)abstract
- Maintenance and services of products as well as processes are pivotal for achieving high availability and avoiding catastrophic and costly failures. At the same time, maintenance is routinely performed more frequently than necessary, replacing possibly functional components, which has negative economic impact on the maintenance. New processes and products need to fulfil increased environmental demands, while customers put increasing demands on customization and coordination. Hence, improved maintenance processes possess very high potentials, economically as well as environmentally. The shifting demands on product development and production processes have led to the emergency of new digital solutions as well as new business models, such as integrated product-service offerings. Still, the general maintenance problem of how to perform the right service at the right time, taking available information and given limitations is valid.The project Future Industrial Services Management (FUSE) project was a step in a long-term effort for catalysing the evolution of maintenance and production in the current digital era. In this paper, several aspects of the general maintenance problem are discussed from a data driven perspective, spanning from technology solutions and organizational requirements to new business opportunities and how to create optimal maintenance plans. One of the main results of the project, in the form of a simulation tool for strategy selection, is also described.
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| 28. |
- Laksman, Efraim, 1983, et al.
(författare)
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The stochastic opportunistic replacement problem, part III: improved bounding procedures
- 2020
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Ingår i: Annals of Operations Research. - : Springer Science and Business Media LLC. - 1572-9338 .- 0254-5330. ; 292:2, s. 711-733
-
Tidskriftsartikel (refereegranskat)abstract
- We consider the problem to find a schedule for component replacement in a multi-component system, whose components possess stochastic lives and economic dependencies, such that the expected costs for maintenance during a pre-defined time period are minimized. The problem was considered in Patriksson et al. (Ann Oper Res 224:51–75, 2015), in which a two-stage approximation of the problem was optimized through decomposition (denoted the optimization policy). The current paper improves the effectiveness of the decomposition approach by establishing a tighter bound on the value of the recourse function (i.e., the second stage in the approximation). A general lower bound on the expected maintenance cost is also established. Numerical experiments with 100 simulation scenarios for each of four test instances show that the tighter bound yields a decomposition generating fewer optimality cuts. They also illustrate the quality of the lower bound. Contrary to results presented earlier, an age-based policy performs on par with the optimization policy, although most simple policies perform worse than the optimization policy.
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| 29. |
- Larsson, Torbjörn, et al.
(författare)
-
Ergodic convergence in subgradient optimization - with application to simplicial decomposition of convex programs
- 2012
-
Ingår i: Contemporary Mathematics. - Providence, Rhode Island : American Mathematical Society. - 0271-4132 .- 1098-3627. ; 568, s. 159-186
-
Tidskriftsartikel (refereegranskat)abstract
- When non-smooth, convex minimization problems are solved by subgradient optimization methods, the subgradients used will in general not accumulate to subgradients that verify the optimality of a solution obtained in the limit. It is therefore not a straightforward task to monitor the progress of subgradient methods in terms of the approximate fulfilment of optimality conditions. Further, certain supplementary information, such as convergent estimates of Lagrange multipliers and convergent lower bounds on the optimal objective value, is not directly available in subgradient schemes. As a means of overcoming these weaknesses in subgradient methods, we introduced in LPS96b, LPS96c, and LPS98 the computation of an ergodic (averaged) sequence of subgradients. Specifically, we considered a non-smooth, convex program solved by a conditional subgradient optimization scheme with divergent series step lengths, and showed that the elements of the ergodic sequence of subgradients in the limit fulfil the optimality conditions at the optimal solution, to which the sequence of iterates converges. This result has three important implications. The first is the finite identification of active constraints at the solution obtained in the limit. The second is the establishment of the convergence of ergodic sequences of Lagrange multipliers; this result enables sensitivity analyses for solutions obtained by subgradient methods. The third is the convergence of a lower bounding procedure based on an ergodic sequence of affine underestimates of the objective function; this procedure also provides a proper termination criterion for subgradient optimization methods. This article contributes first an overview of results and applications found in LPS96b, LPS96c, and LPS98 pertaining to the generation of ergodic sequences of subgradients generated within a subgradient scheme. It then presents an application of these results to that of the first instance of a simplicial decomposition algorithm for convex and non-smooth optimization problems.
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| 30. |
- Larsson, Torbjörn, et al.
(författare)
-
Ergodic results and bounds on the optimal value in subgradient optimization
- 1996
-
Ingår i: Operations Research Proceedings 1995. - 9783540608066 ; , s. 30-35
-
Konferensbidrag (refereegranskat)abstract
- Subgradient methods are popular tools for nonsmooth, convex minimization, especially in the context of Lagrangean relaxation; their simplicity has been a main contribution to their success. As a consequence of the nonsmoothness, it is not straightforward to monitor the progress of a subgradient method in terms of the approximate fulfilment of optimality conditions, since the subgradients used in the method will, in general, not accumulate to subgradients that verify optimality of a solution obtained in the limit. Further, certain supplementary information, such as convergent estimates of Lagrange multipliers, is not directly available in subgradient schemes. As a means for overcoming these weaknesses of subgradient optimization methods, we introduce the computation of an ergodic (averaged) sequence of subgradients. Specifically, we consider a nonsmooth, convex program solved by a conditional subgradient optimization scheme (of which the traditional sub gradient optimization method is a special case) with divergent series step lengths, which generates a sequence of iterates that converges to an optimal solution. We show that the elements of the ergodic sequence of subgradients in the limit fulfill the optimality conditions at this optimal solution. Further, we use the convergence properties of the ergodic sequence of subgradients to establish convergence of an ergodic sequence of Lagrange multipliers. Finally, some potential applications of these ergodic results are briefly discussed.
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| 31. |
- Larsson, Torbjörn, et al.
(författare)
-
Ergodic results in subgradient optimization
- 1996
-
Ingår i: Nonlinear Optimization and Applications. - 9780306453168 ; , s. 229-248
-
Konferensbidrag (refereegranskat)abstract
- Subgradient methods are popular tools for nonsmooth, convex minimization, especially in the context of Lagrangean relaxation; their simplicity has been a main contribution to their success. As a consequence of the nonsmoothness, it is not straightforward to monitor the progress of a subgradient method in terms of the approximate fulfilment of optimality conditions, since the subgradients used in the method will, in general, not accumulate to subgradients that verify optimality of a solution obtained in the limit. Further, certain supplementary information, such as convergent estimates of Lagrange multipliers, is not directly available in subgradient schemes. As a means for overcoming these weaknesses of subgradient optimization methods, we introduce the computation of an ergodic (averaged) sequence of subgradients. Specifically, we consider a nonsmooth, convex program solved by a conditional subgradient optimization scheme (of which the traditional subgradient optimization method is a special case) with divergent series step lengths, which generates a sequence of iterates that converges to an optimal solution. We show that the elements of the ergodic sequence of subgradients in the limit fulfill the optimality conditions at this optimal solution. Further, we use the convergence properties of the ergodic sequence of subgradients to establish convergence of an ergodic sequence of Lagrange multipliers. Finally, some potential applications of these ergodic results are briefly discussed.
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| 32. |
- Lindroth, Peter, 1979, et al.
(författare)
-
Approximating the Pareto Optimal Set using a Reduced Set of Objective Functions
- 2010
-
Ingår i: European Journal of Operational Research. - : Elsevier BV. - 0377-2217. ; 207:3, s. 1519-1534
-
Tidskriftsartikel (refereegranskat)abstract
- Real-world applications of multi-objective optimization often involve numerous objective functions. But while such problems are in general computationally intractable, it is seldom necessary to determine the Pareto optimal set exactly. A significantly smaller computational burden thus motivates the loss of precision if the size of the loss can be estimated. We describe a method for finding an optimal reduction of the set of objectives yielding a smaller problem whose Pareto optimal set w.r.t. a discrete subset of the decision space is as close as possible to that of the original set of objectives. Utilizing a new characterization of Pareto optimality and presuming a finite decision space, we derive a program whose solution represents an optimal reduction. We also propose an approximate, computationally less demanding formulation which utilizes correlations between the objectives and separates into two parts. Numerical results from an industrial instance concerning the configuration of heavy-duty trucks are also reported, demonstrating the usefulness of the method developed. The results show that multi-objective optimization problems can be significantly simplified with an induced error which can be measured.
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| 33. |
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| 34. |
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| 35. |
- Lindroth, Peter, 1979, et al.
(författare)
-
Optimizing truck tyres
- 2014
-
Ingår i: Orbit medlemsblad for Dansk Selskab for Operationsanalyse og Svenska OperationsAnalysFöreningen. - 1601-8893. ; :23, s. 12-14
-
Tidskriftsartikel (refereegranskat)
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| 36. |
- Nedelkova, Zuzana, 1987, et al.
(författare)
-
A splitting algorithm for simulation-based optimization problems with categorical variables
- 2019
-
Ingår i: Engineering Optimization. - 1029-0273 .- 0305-215X. ; 51:5, s. 815-831
-
Tidskriftsartikel (refereegranskat)abstract
- In the design of complex products, some product components can only be chosen from a finite set of options. Each option then corresponds to a multidimensional point representing the specifications of the chosen components. A splitting algorithm that explores the resulting discrete search space and is suitable for optimization problems with simulation-based objective functions is presented. The splitting rule is based on the representation of a convex relaxation of the search space in terms of a minimum spanning tree and adopts ideas from multilevel coordinate search. The objective function is underestimated on its domain by a convex quadratic function. The main motivation is the aim to find—for a vehicle and environment specification—a configuration of the tyres such that the energy losses caused by them are minimized. Numerical tests on a set of optimization problems are presented to compare the performance of the algorithm developed with that of other existing algorithms.
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| 37. |
- Nedelkova, Zuzana, 1987, et al.
(författare)
-
Efficient solution of many instances of a simulation-based optimization problem utilizing a partition of the decision space
- 2018
-
Ingår i: Annals of Operations Research. - : Springer Science and Business Media LLC. - 1572-9338 .- 0254-5330. ; 265:1, s. 93-118
-
Tidskriftsartikel (refereegranskat)abstract
- This paper concerns the solution of a class of mathematical optimization problems with simulation-based objective functions. The decision variables are partitioned into two groups, referred to as variables and parameters, respectively, such that the objective function value is influenced more by the variables than by the parameters. We aim to solve this optimization problem for a large number of parameter settings in a computationally efficient way. The algorithm developed uses surrogate models of the objective function for a selection of parameter settings, for each of which it computes an approximately optimal solution over the domain of the variables. Then, approximate optimal solutions for other parameter settings are computed through a weighting of the surrogate models without requiring additional expensive function evaluations. We have tested the algorithm's performance on a set of global optimization problems differing with respect to both mathematical properties and numbers of variables and parameters. Our results show that it outperforms a standard and often applied approach based on a surrogate model of the objective function over the complete space of variables and parameters.
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| 38. |
- Nedelkova, Zuzana, 1987, et al.
(författare)
-
Integration of expert knowledge into radial basis function surrogate models
- 2016
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Ingår i: Optimization and Engineering. - : Springer Science and Business Media LLC. - 1389-4420 .- 1573-2924. ; 17:3, s. 577-603
-
Tidskriftsartikel (refereegranskat)abstract
- A current application in a collaboration between Chalmers University of Technology and Volvo Group Trucks Technology concerns the global optimization of a complex simulation-based function describing the rolling resistance coefficient of a truck tyre. This function is crucial for the optimization of truck tyres selection considered. The need to explicitly describe and optimize this function provided the main motivation for the research presented in this article. Many optimization algorithms for simulation-based optimization problems use sample points to create a computationally simple surrogate model of the objective function. Typically, not all important characteristics of the complex function (as, e.g., non-negativity)—here referred to as expert knowledge—are automatically inherited by the surrogate model. We demonstrate the integration of several types of expert knowledge into a radial basis function interpolation. The methodology is first illustrated on a simple example function and then applied to a function describing the rolling resistance coefficient of truck tyres. Our numerical results indicate that expert knowledge can be advantageously incorporated and utilized when creating global approximations of unknown functions from sample points.
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| 39. |
- Nilsson, Julia, et al.
(författare)
-
An evaluation approach for opportunistic maintenance optimization models for nuclear power plants
- 2010
-
Ingår i: Power and Energy Society General Meeting, 2010 IEEE. - : IEEE. - 9781424483570
-
Konferensbidrag (refereegranskat)abstract
- Nuclear power constitutes one of the main electricity production sources in several countries, e.g. in Sweden, with about half of today's electricity production. Driving forces for cost-efficiency have pushed the development of new methods for maintenance planning and optimization forward. Reliability Centered Asset Management (RCAM) is one of these new approaches, and maintenance optimization is one way to perform quantitative analysis which is a feature of RCAM. This paper proposes a stochastic framework for evaluating opportunistic maintenance optimization models for the generation of replacement schedules for shaft seals in feed-water pump systems in nuclear power plants. Results show that the extended discounted model has a good overall performance, when compared to other strategies. Moreover, it is shown that it is the best strategy for high values of the constant cost for maintenance and the second best for lower values of the constant cost.
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| 40. |
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| 41. |
- Nilsson, Julia, et al.
(författare)
-
An Opportunistic Maintenance Optimization Model for Shaft Seals in Feed-Water Pump Systems in Nuclear Power Plants
- 2009
-
Ingår i: 2009 IEEE Bucharest PowerTech. - New York : IEEE. - 9781424422340 ; , s. 2962-2969
-
Konferensbidrag (refereegranskat)abstract
- Nuclear power is one of the main electricity production sources in Sweden today. Maintenance management is one tool for reducing the costs for operation of a power plant. Driving forces for cost-efficiency has pushed the development of new methods for maintenance planning and optimization forward. Reliability Centered Asset Management (RCAM) is one of these new approaches, and maintenance optimization is one way to perform quantitative analysis which is a feature of RCAM. This paper proposes a model for opportunistic maintenance optimization where replacement schedules for shaft seals in feed-water pump systems in nuclear power plants are constructed. The feed-water pump system is important for the availability of the entire nuclear power plant. Results show that the optimization model is dependent on e.g. the discount interest and a limit for when the optimal solution goes from non-opportunistic to opportunistic is calculated. The circumstances for which opportunistic maintenance could be used have been investigated given different values of discount rates and remaining life at start of the planning period.
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| 42. |
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| 43. |
- Obradovic, Gabrijela, 1994, et al.
(författare)
-
Scheduling the repair and replacement of individual components in operating systems: a bi-objective mathematical optimization model
- 2024
-
Ingår i: Journal of Scheduling. - 1099-1425 .- 1094-6136. ; 27:1, s. 87-101
-
Tidskriftsartikel (refereegranskat)abstract
- Preventive maintenance (PM) is performed so that failure is avoided while corrective maintenance is performed after a failure has occurred in order to restore the system back to an operational state. This research aims at scheduling PM activities for a multi-component system within a finite time horizon. We consider a setting with two stakeholders, being the system operator and themaintenanceworkshop, and two different contract types governing their joint activities, namely an availability contract and a turn-around time contract. Components in the systems that are to be maintained are sent to the maintenance workshop, which needs to schedule and perform all maintenance activities while at the same time satisfying the contract and not exceeding the workshop capacity. Our modelling is based on a mixed-binary linear optimization model of a PM scheduling problem with so-called interval costs over a finite and discretized time horizon.We enhance this scheduling model with the flow of individual components through the maintenance workshop, including stocks of spare components, both those components that need repair and the repaired ones. The resulting scheduling model is then utilized in the optimization of two main contracts, namely maximizing the availability of repaired (or new) components and minimizing the deviation from the contracted turn-around times for the components in the maintenance loop. Each of these objectives is combined with the objective to minimize the costs for maintenance of the operating system, leading to two bi-objective optimization problems. We analyse the two contracting forms between the stakeholders by studying and comparing the Pareto fronts resulting from different parameter settings, regarding minimum allowed stock levels and investments in repair capacity of the workshop. Our bi-objective mixed-binary linear optimization model is able to capture important properties of the results from the contracting forms as well as to show that, in our setting, an availability contract performs better than a turn-around time contract in terms of tractability.
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| 44. |
- Obradovic, Gabrijela, 1994, et al.
(författare)
-
Simultaneous scheduling of preventive system maintenance and of the maintenance workshop
- 2020
-
Ingår i: PLANs forsknings-och tillämpningskonferens.
-
Konferensbidrag (refereegranskat)abstract
- While a system operates, its components deteriorate and in order for the system to remain operational, maintenance of its components is required. Preventive maintenance (PM) is performed so that component failure is avoided. This research aims at scheduling PM activities for a multi-component system within a finite horizon. The system to be maintained possesses positive economic dependencies, meaning that each time any component maintenance activity is performed, a common set-up cost is generated. Each component PM activity generates a cost, including replacement, service, and spare parts costs. We start from a 0-1 mixed integer linear optimization model of the PM scheduling problem with interval costs, which is to schedule PM of the components of a system over a finite and discretized time horizon, given common set-up costs and component costs, of which the latter vary with the maintenance interval. We extend the PMSPIC model to incorporate the flow of components through the maintenance/repair workshop, including stocks of spare components, both the components that require repair and the repaired ones. Our resulting model is a tight integration of the PM and the maintenance workshop scheduling. We investigate two different contract types between stakeholders, present and analyze preliminary numerical results obtained.
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| 45. |
- Obradovic, Gabrijela, 1994, et al.
(författare)
-
Simultaneous scheduling of replacement and repair of common components in operating systems A multi-objective mathematical optimization model
- 2022
-
Ingår i: Annals of Operations Research. - : Springer Science and Business Media LLC. - 0254-5330 .- 1572-9338. ; 322, s. 147-65
-
Tidskriftsartikel (refereegranskat)abstract
- In order for a system to stay operational, its components need maintenance. We consider two stakeholders-a system operator and a maintenance workshop-and a contract governing their joint activities. Components in the operating systems that are to be maintained are sent to the maintenance workshop, which should perform all maintenance activities on time in order to satisfy the contract. The maintained components are then sent back to be used in the operating systems. Our modeling of this system-of-systems includes stocks of damaged and repaired components, the workshop scheduling, and the planning of preventive maintenance for the operating systems. Our modeling is based on a mixed-binary linear optimization (MBLP) model of a preventive maintenance scheduling problem with so-called interval costs over a finite and discretized time horizon. We generalize and extend this model with the flow of components through the workshop, including the stocks of spare components. The resulting scheduling model-a mixed-integer optimization (MILP) model-is then utilized to optimize the main contract in a bi-objective setting: maximizing the availability of repaired (or new) components and minimizing the costs of maintaining the operating systems over the time horizon. We analyze the main contract and briefly discuss a turn-around time contract. Our results concern the effect of our modeling on the levels of the stocks of components over time, in particular minimizing the risk for lack of spare components.
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| 46. |
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| 47. |
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| 48. |
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| 49. |
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| 50. |
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