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  • 1.
    Aronsson, Martin
    et al.
    SICS.
    Bohlin, Markus
    SICS.
    Doganay, Kivanc
    SICS.
    Holst, Anders
    SICS.
    An Integrated Adaptive Maintenance Concept2010Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, we present a novel maintenance concept based on condition monitoring and dynamic maintenance packaging, by showing how to connect the information flow from low-level sensors to high-level operations and planning under uncertainty. Today, condition-based maintenance systems are focused on data collection and custom-made rule based systems for data analysis. In many cases, the focus is on measuring "everything" without considering how to use the measurements. In addition, the measurements are often noisy and the future is unpredictable which adds a lot of uncertainty. As a consequence, maintenance is often planned in advance and not replanned when new condition data is available. This often reduces the benefits of condition monitoring. The concept is based on the combination of robust, dynamically adapted maintenance optimization and statistical data analysis where the uncertainty is considered. This approach ties together low-level data acquisition and high-level planning and optimization. The concept has been illustrated in a context of rail vehicle maintenance, where measurements of brake pad and pantograph contact strip wear is used to predict the near future condition, and plan the maintenance activities.

  • 2.
    Bohlin, Markus
    Mälardalens högskola, Akademin för innovation, design och teknik.
    A Study of Combinatorial Optimization Problems in Industrial Computer Systems2009Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    A combinatorial optimization problem is an optimization problem where the number of possible solutions are finite and grow combinatorially with the problem size. Combinatorial problems exist everywhere in industrial systems. This thesis focuses on solving three such problems which arise within two different areas where industrial computer systems are often used. Within embedded systems and real-time systems, we investigate the problems of allocating stack memory for an system where a shared stacks may be used, and of estimating the highest response time of a task in a system of industrial complexity. We propose a number of different algorithms to compute safe upper bounds on run-time stack usage whenever the system supports stack sharing. The algorithms have in common that they can exploit commonly-available information regarding timing behaviour of the tasks in the system. Given upper bounds on the individual stack usage of the tasks, it is possible to estimate the worst-case stack behaviour by analysing the possible and impossible preemption patterns. Using relations on offset and precedences, we form a preemption graph, which is further analysed to find safe upper-bounds on the maximal preemptions chain in the system. For the special case where all tasks exist in a single static schedule and share a single stack, we propose a polynomial algorithm to solve the problem. For generalizations of this problem, we propose an exact branch-and-bound algorithm for smaller problems and a polynomial heuristic algorithm for cases where the branch-and-bound algorithm fails to find a solution in reasonable time. All algorithms are evaluated in comprehensive experimental studies. The polynomial algorithm is implemented and shipped in the developer tool set for a commercial real-time operating system, Rubus OS. The second problem we study in the thesis is how to estimate the highest response time of a specified task in a complex industrial real-time system. The response-time analysis is done using a best-effort approach, where a detailed model of the system is simulated on input constructed using a local search procedure. In an evaluation on three different systems we can see that the new algorithm were able to produce higher response times much faster than what has previously been possible. Since the analysis is based on simulation and measurement, the results are not safe in the sense that they are always higher or equal to the true response time of the system. The value of the method lies instead in that it makes it possible to analyse complex industrial systems which cannot be analysed accurately using existing safe approaches. The third problem is in the area of maintenance planning, and focus on how to dynamically plan maintenance for industrial systems. Within this area we have focused on industrial gas turbines and rail vehicles.  We have developed algorithms and a planning tool which can be used to plan maintenance for gas turbines and other stationary machinery. In such problems, it is often the case that performing several maintenance actions at the same time is beneficial, since many of these jobs can be done in parallel, which reduces the total downtime of the unit. The core of the problem is therefore how to (or how not to) group maintenance activities so that a composite cost due to spare parts, labor and loss of production due to downtime is minimized. We allow each machine to have individual schedules for each component in the system. For rail vehicles, we have evaluated the effect of replanning maintenance in the case where the component maintenance deadline is set to reflect a maximum risk of breakdown in a Gaussian failure distribution. In such a model, we show by simulation that replanning of maintenance can reduce the number of maintenance stops when the variance and expected value of the distribution are increased.  For the gas turbine maintenance planning problem, we have evaluated the planning software on a real-world scenario from the oil and gas industry and compared it to the solutions obtained from a commercial integer programming solver. It is estimated that the availability increase from using our planning software is between 0.5 to 1.0 %, which is substantial considering that availability is currently already at 97-98 %.

  • 3.
    Bohlin, Markus
    Mälardalens högskola, Institutionen för Datavetenskap.
    Design and implementation of a graph-based constraint model for local search2004Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
  • 4.
    Bohlin, Markus
    et al.
    Swedish Institute of Computer Science, Sweden.
    Dahms, FlorianRWTH Aachen, Chair of Operations Research, Germany.Flier, HolgerETH Zürich, Institute of Theoretical Computer Science, Switzerland.Sara, GestreliusSwedish Institute of Computer Science, Sweden.
    Optimal Freight Train Classification using Column Generation2012Samlingsverk (redaktörskap) (Refereegranskat)
  • 5.
    Bohlin, Markus
    et al.
    Swedish Institute of Computer Science, SICS.
    Doganay, Kivanc
    Swedish Institute of Computer Science, SICS.
    Kreuger, P.
    Swedish Institute of Computer Science, SICS.
    Steinert, R.
    KTH.
    Wärja, Mathias
    Siemens Industrial Turbomachinery AB.
    Searching for Gas Turbine Maintenance Schedules2010Ingår i: The AI Magazine, ISSN 0738-4602, Vol. 31, nr 1, s. 21-36Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Preventive maintenance schedules occurring in industry are often suboptimal with regard to maintenance coal-location, loss-of-production costs and availability. We describe the implementation and deployment of a software decision support tool for the maintenance planning of gas turbines, with the goal of reducing the direct maintenance costs and the often costly production losses during maintenance downtime. The optimization problem is formally defined, and we argue that the feasibility version is NP-complete. We outline a heuristic algorithm that can quickly solve the problem for practical purposes and validate the approach on a real-world scenario based on an oil production facility. We also compare the performance of our algorithm with results from using integer programming, and discuss the deployment of the application. The experimental results indicate that downtime reductions up to 65% can be achieved, compared to traditional preventive maintenance. In addition, the use of our tool is expected to improve availability with up to 1% and reduce the number of planned maintenance days by 12%. Compared to a integer programming approach, our algorithm is not optimal, but is much faster and produces results which are useful in practice. Our test results and SIT AB’s estimates based< on operational use both indicate that significant savings can be achieved by using our software tool, compared to maintenance plans with fixed intervals.

  • 6.
    Bohlin, Markus
    et al.
    Swedish Institute of Computer Science, SICS.
    Doganay, Kivanc
    Swedish Institute of Computer Science, SICS.
    Kreuger, Per
    Swedish Institute of Computer Science, SICS.
    Steinert, Rebecca
    Swedish Institute of Computer Science, SICS.
    Wärja, Mathias
    Siemens Industrial Turbomachinery AB.
    A Tool for Gas Turbine Maintenance Scheduling2009Ingår i: Proceedings of the 21st Innovative Applications of Artificial Intelligence Conference, IAAI-09, 2009, s. 9-16Konferensbidrag (Refereegranskat)
    Abstract [en]

    We describe the implementation and deployment of a software decision support tool for the maintenance planning of gas turbines. The tool is used to plan the maintenance for turbines manufactured and maintained by Siemens Industrial Turbomachinery AB (SIT AB) with the goal to reduce the direct maintenance costs and the often very costly production losses during maintenance downtime. The optimization problem is formally defined, and we argue that feasibility in it is NP-complete. We outline a heuristic algorithm that can quickly solve the problem for practical purposes, and validate the approach on a real-world scenario based on an oil production facility. We also compare the performance of our algorithm with results from using mixed integer linear programming, and discuss the deployment of the application. The experimental results indicate that downtime reductions up to 65% can be achieved, compared to traditional preventive maintenance. In addition, using our tool is expected to improve availability with up to 1% and reduce the number of planned maintenance days with 12%. Compared to a mixed integer programming approach, our algorithm not optimal, but is orders of magnitude faster and produces results which are useful in practice. Our test results and SIT AB's estimates based on operational use both indicate that significant savings can be achieved by using our software tool, compared to maintenance plans with fixed intervals

  • 7. Bohlin, Markus
    et al.
    Flier, Holger
    Optimal Freight Train Classification using Column Generation2012Ingår i: 12th Workshop on Algorithmic Approaches for Transportation Modelling, Optimization, and Systems, September 13, 2012, Ljubljana, Slovenia, 2012, s. 10-22Konferensbidrag (Refereegranskat)
  • 8.
    Bohlin, Markus
    et al.
    Mälardalens högskola, Akademin för innovation, design och teknik. SICS, Sweden.
    Flier, Holger
    Mälardalens högskola, Akademin för innovation, design och teknik. ETH, Suisse.
    Maue, Jens
    ETH, Suisse.
    Mihalák, Matúš
    Mälardalens högskola, Akademin för innovation, design och teknik. ETH, Suisse.
    Hump Yard Track Allocation with Temporary Car Storage2011Ingår i: 4th International Seminar on Railway Operations Modelling and Analysis, 2011Konferensbidrag (Refereegranskat)
    Abstract [en]

    In rail freight operation, freight cars need to be separated and reformed into new trains at hump yards. The classification procedure is complex and hump yards constitute bottlenecks in the rail freight network, often causing outbound trains to be delayed. One of the problems is that planning for the allocation of tracks at hump yards is difficult, given that the planner has limited resources (tracks, shunting engines, etc.) and needs to foresee the future capacity requirements when planning for the current inbound trains. In this paper, we consider the problem of allocating classification tracks in a rail freight hump yard for arriving and departing trains with predetermined arrival and departure times. The core problem can be formulated as a special list coloring problem. We focus on an extension where individual cars can temporarily be stored on a special subset of the tracks. An extension where individual cars can temporarily be stored on a special subset of the tracks is also considered. We model the problem using mixed integer programming, and also propose several heuristics that can quickly give feasible track allocations. As a case study, we consider a real-world problem instance from the Hallsberg Rangerbangard hump yard in Sweden. Planning over horizons over two to four days, we obtain feasible solutions from both the exact and heuristic approaches that allow all outgoing trains to leave on time.

  • 9.
    Bohlin, Markus
    et al.
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Flier, Holger
    ETH Zürich, Institute of Theoretical Computer Science, Switzerland.
    Maue, Jens
    ETH Zürich, Institute of Theoretical Computer Science, Switzerland.
    Mihalák, Matúš
    ETH Zürich, Institute of Theoretical Computer Science, Switzerland.
    Track Allocation in Freight-Train Classification with Mixed Tracks2011Ingår i: OpenAccess Series in Informatics, Volume 20, 2011, 2011, s. 38-51Konferensbidrag (Refereegranskat)
    Abstract [en]

    We consider the process of forming outbound trains from cars of inbound trains at rail-freight hump yards. Given the arrival and departure times as well as the composition of the trains, we study the problem of allocating classification tracks to outbound trains such that every outbound train can be built on a separate classification track. We observe that the core problem can be formulated as a special list coloring problem in interval graphs, which is known to be NP-complete. We focus on an extension where individual cars of different trains can temporarily be stored on a special subset of the tracks. This problem induces several new variants of the list-coloring problem, in which the given intervals can be shortened by cutting off a prefix of the interval. We show that in case of uniform and sufficient track lengths, the corresponding coloring problem can be solved in polynomial time, if the goal is to minimize the total cost associated with cutting off prefixes of the intervals. Based on these results, we devise two heuristics as well as an integer program to tackle the problem. As a case study, we consider a real-world problem instance from the Hallsberg Rangerbangard hump yard in Sweden. Planning over horizons of seven days, we obtain feasible solutions from the integer program in all scenarios, and from the heuristics in most scenarios.

  • 10.
    Bohlin, Markus
    et al.
    SICS.
    Forsgren, Malin
    SICS.
    Holst, Anders
    SICS.
    Levin, Björn
    SICS.
    Aronsson, Martin
    SICS.
    Steinert, Rebecca
    SICS.
    Reducing vehicle maintenance using condition monitoring and dynamic planning2008Ingår i: In Proc. of the 4th IET Intl. Conf. on Railway Condition Monitoring (RCM’08), June 2008, 2008, Vol. 2216Konferensbidrag (Refereegranskat)
  • 11.
    Bohlin, Markus
    et al.
    SICS Swedish ICT AB, Sweden.
    Gestrelius, Sara
    SICS Swedish ICT AB, Sweden.
    Dahms, Florian
    RWTH Aachen University, Germany.
    Mihalák, Matúš
    ETH Zürich, Switzerland.
    Flier, Holger
    ETH Zürich, Switzerland.
    Optimization Methods for Multistage Freight Train Formation2015Ingår i: Transportation Science, ISSN 0041-1655, E-ISSN 1526-5447, Vol. 50, nr 3, s. 823-840Artikel i tidskrift (Refereegranskat)
  • 12.
    Bohlin, Markus
    et al.
    SICS Swedish ICT, Kista, Sweden.
    Gestrelius, Sara
    SICS Swedish ICT, Kista, Sweden.
    Fahimeh, Khoshniyat
    SICS Swedish ICT, Kista, Sweden.
    Simulation of planning strategies for track allocation at marshalling yards2013Ingår i: WIT Transactions on Modelling and Simulation, Volume 55, 2013, Ashurst, Southampton: WIT Press, 2013, Vol. 55, s. 465-475Konferensbidrag (Refereegranskat)
    Abstract [en]

    Planning the operational procedures in a railway marshalling yard is a complex problem. When a train arrives at a marshalling yard, it is uncoupled at an arrival yard and then its cars are rolled to a classification yard. All cars should eventually be rolled to the classification track that has been assigned to the train they're supposed to depart with. However, there is normally not enough capacity to compound all trains at once. In Sweden, cars arriving before a track has been assigned to their train can be stored on separate tracks called mixing tracks. All cars on mixing tracks will be pulled back to the arrival yard, and then rolled to the classification yard again to allow for reclassification. Today all procedures are planned by experienced dispatchers, but there are no documented strategies or guidelines for efficient manual planning. The aim of this paper is to examine operational planning strategies that could help dispatchers find a feasible marshalling schedule that minimizes unnecessary mixing. In order to achieve this goal, two different online planning strategies have been tested using deterministic and stochastic simulation. The Hallsberg marshalling yard was used as a case study, and was simulated for the time period between December 2010 and May 2011. The first tested strategy simply assigns tracks to trains on a first come-first served basis, while the second strategy uses time limits to determine when tracks should be assigned to departing trains. The online planning algorithms have been compared with an offline optimized track allocation. The results from both the deterministic and the stochastic simulation show that the optimized allocation is better than all online strategies and that the second strategy with a time limit of 32 hours is the best online method.

  • 13.
    Bohlin, Markus
    et al.
    Mälardalens högskola, Institutionen för datavetenskap och elektronik.
    Hänninen, Kaj
    Mälardalens högskola, Institutionen för datavetenskap och elektronik.
    Mäki-Turja, Jukka
    Mälardalens högskola, Institutionen för datavetenskap och elektronik.
    Shared Stack Analysis in Transaction-Based Systems2007Ingår i: Work in Progress Proceedings RTSS'07, Tucson, Arizona, USA, 2007, s. 37-40Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, we present our ongoing work on shared stack analysis for hybrid (static and dynamic) scheduled fixed priority systems. We present two methods that extend our previous work to support stack analysis for the general tasks model with offsets where several transactions can share a common run-time stack. The aim of this work is to support stack analysis of a wider range of systems. 

  • 14.
    Bohlin, Markus
    et al.
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Hänninen, Kaj
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Mäki-Turja, Jukka
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Carlson, Jan
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Nolin, Mikael
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Safe Shared Stack Bounds in Systems with Offsets and Precedences2008Rapport (Övrigt vetenskapligt)
    Abstract [en]

    The paper presents two novel methods to bound the stack memory used in preemptive, shared stack, real-time systems. The first method is based on branch-and-bound search for possible preemption patterns, and the second one approximates the first in polynomial time. The work extends previous methods by considering a more general taskmodel, in which all tasks can share the same stack. In addition, the new methods account for precedence and offset relations. Thus, the methods give tight bounds for a large set of realistic systems. The methods have been implemented and a comprehensive evaluation, comparing our new methods against each other and against existing methods, is presented. The evaluation shows that our exact method can significantly reduce the amount of stack memory needed. In our simulations, a decrease in the order of 40% was typical, with a runtime in the order of seconds. Our polynomial approximation consequently yields about 20% higher bound than the exact method. 

  • 15.
    Bohlin, Markus
    et al.
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Hänninen, Kaj
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Mäki-Turja, Jukka
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Carlson, Jan
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Sjödin, Mikael
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Bounding Shared-Stack Usage in Systems with Offsets and Precedences2008Ingår i: ECRTS 2008: PROCEEDINGS OF THE 20TH EUROMICRO CONFERENCE ON REAL-TIME SYSTEMS, 2008, s. 276-285Konferensbidrag (Refereegranskat)
    Abstract [en]

    The paper presents two novel methods to bound the stack memory used in preemptive, shared stack, real-time systems. The first method is based on branch-and-bound search for possible preemption patterns, and the second one approximates the first in polynomial time. The work extends previous methods by considering a more general task-model, in which all tasks can share the same stack. In addition, the new methods account for precedence and offset relations. Thus, the methods give tight bounds for a large set of realistic systems. The methods have been implemented and a comprehensive evaluation, comparing our new methods against each other and against existing methods, is presented. The evaluation shows that our exact method can significantly reduce the amount of stack memory needed.

  • 16.
    Bohlin, markus
    et al.
    SICS.
    Lu, Yue
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Kraft, Johan
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Kreuger, Per
    SICS, Sweden.
    Nolte, Thomas
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Best-Effort Simulation-Based Timing Analysis using Hill-Climbing with Random Restarts2009Ingår i: In Proc. of RTCSA, Aug. 2009., 2009Konferensbidrag (Refereegranskat)
  • 17.
    Bohlin, Markus
    et al.
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Lu, Yue
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Kraft, Johan
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Kreuger, Per
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Nolte, Thomas
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Simulation-Based Timing Analysis of Complex Real-Time Systems2009Ingår i: 2009 15TH IEEE INTERNATIONAL CONFERENCE ON EMBEDDED AND REAL-TIME COMPUTING SYSTEMS AND APPLICATIONS, PROCEEDINGS, 2009, s. 321-328Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents an efficient best-effort approach for simulation-based timing analysis of complex real- time systems. The method can handle in principle any software design that can be simulated, and is based on controlling simulation input using a simple yet novel hill- climbing algorithm. Unlike previous approaches, the new algorithm directly manipulates simulation parameters such as execution times, arrival jitter and input. An evaluation is presented using six different simulation models, and two other simulation methods as reference: Monte Carlo simulation and MABERA. The new method proposed in this paper was 4-11% more accurate while at the same time 42 times faster, on average, than the reference methods.

  • 18.
    Bohlin, Markus
    et al.
    Swedish Institute of Computer Science, Sweden.
    Wärja, Mathias
    Siemens Industrial Turbomachinery AB, Sweden.
    Maintenance optimization with duration-dependent costs2015Ingår i: Annals of Operations Research, ISSN 0254-5330, E-ISSN 1572-9338, Vol. 224, nr 1, s. 1-23Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    High levels of availability and reliability are essential in many industries where production is subject to high costs due to downtime. Examples include the mechanical drive in natural gas pipelines and power generation on oil platforms, where gas turbines are commonly used as a power source. To mitigate the effects of service outages and increase overall reliability, it is also possible to use one or more redundant units serving as cold standby backup units. In this paper, we consider preventive maintenance optimization for parallel k-out-of-n multi-unit systems, where production at a reduced level is possible when some of the units are still operational. In such systems, there are both positive and negative effects of grouping activities together. The positive effects come from parallel execution of maintenance activities and shared setup costs, while the negative effects come from the limited number of units which can be maintained at the same time. To show the possible economic effects, we evaluate the approach on models of two production environments under a no-fault assumption. We conclude that savings were substantial in our experiments on preventive maintenance, compared to a traditional preventive maintenance plan. For single-unit systems, costs were on average 39 % lower when using optimization. For multi-unit systems, average savings were 19 %. We also used the optimization models to evaluate the effects of re-planning at breakdown and effects due to modeling of inclusion relations. Breakdown re-planning saved between 0 and 11 % of the maintenance costs, depending on which component failed, while inclusion relation modeling resulted in an 7 % average cost reduction.

  • 19.
    Bohlin, Markus
    et al.
    SICS.
    Wärja, Mathias
    Siemens Industrial Turbomachinery AB.
    Holst, Anders
    SICS.
    Slottner, Pontus
    Siemens Industrial Turbomachinery AB.
    Doganay, Kivanc
    SICS.
    Optimization of condition-based maintenance for industrial gas turbines: Requirements and results2009Ingår i: Proceedings of the ASME Turbo Expo Volume 5, 2009, s. 455-464Konferensbidrag (Refereegranskat)
    Abstract [en]

    In oil and gas applications, the careful planning and execution of preventive maintenance is important due to the high costs associated with shutdown of critical equipment. Optimization and lifetime management for equipment such as gas turbines is therefore crucial in order to achieve high availability and reliability. In this paper, a novel condition-based gas turbine maintenance strategy is described and evaluated. Using custom-madegas turbine maintenance planning software, maintenance is repeatedly reoptimized to fit into the time intervals where production losses are least costly and result in the lowest possible impact. The strategy focuses on accurate online lifetime estimates for gas turbine components, where algorithms predicting future maintenance requirements are used to produce maintenance deadlines. This ensures that the gas turbines are maintained in accordance with the conditions on site. To show the feasibility and economic effects of a customer-adapted maintenance planning process, the maintenance plan for a gas turbine used in a real-world scenario is optimized using a combinatorial optimization algorithm and input from gas turbine operation data, maintenance schedules and operator requirements. The approach was validated through the inspection of a reference gas turbine after a predetermined time interval. It is shown that savings may be substantial compared to a traditional preventivemaintenance plan. In the evaluation, typical cost reductions range from 25 to 65 %. The calculated availability increase in practice is estimated to range from 0.5 to 1 %. In addition, down-time reductions of approximately 12 % are expected, due solely to improved planning. This indicates significant improvements.

  • 20.
    Doganay, Kivanc
    et al.
    Swedish Institute of Computer Science, SICS.
    Bohlin, Markus
    Swedish Institute of Computer Science, SICS.
    Maintenance plan optimization for a train fleet2010Ingår i: WIT Transactions on the Built Environment Volume 114, 2010, s. 349-358Konferensbidrag (Refereegranskat)
    Abstract [sv]

    Maintenance planning is an important problem for railways, as well as other application domains that employ machinerywith expensive replacements and high downtime costs. In a previous paper, we have developed methods for efficiently finding optimized maintenance schedules for a single unit, and proposed that the maintenance plan should be continuously re-optimized based on the condition of components. However, fleet-level resources, such as the availability of expensive spare parts, have largely been ignored. In this paper, we extend our previous approach by proposing a solution for the fleet level maintenance scheduling problem with spare parts optimization. The new solution is based on a mixed integer linear programming formulation of the problem. We demonstrate the merits of our approach by optimizing instances of maintenance schedules based on maintenancedata from railway companies operating in Sweden.

  • 21.
    Doganay, Kivanc
    et al.
    Swedish Institute of Computer Science, Kista Sweden.
    Bohlin, Markus
    Swedish Institute of Computer Science, Kista Sweden.
    Sellin, Ola
    Bombardier Transportation, Västeras.
    Search Based Testing of Embedded Systems Implemented in IEC 61131-3: An Industrial Case Study2013Ingår i: Proceedings - IEEE 6th International Conference on Software Testing, Verification and Validation Workshops, ICSTW 2013, 2013, s. 425-432Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents a case study of search-based test generation for embedded system software units developed using the Function Block Diagrams (FBDs), a graphical language in the IEC 61131-3 standard aimed at programmable logic controllers (PLCs). We consider 279 different components from the train control software developed by Bombardier Transportation, a major rail vehicle manufacturer. The software is compiled into C code with a particular structure. We use a modified hill climbing algorithm for generating test data to maximize MC/DC coverage for assignments with logical expressions in the C code, while retaining the semantics of the original FBD implementation. An experimental evaluation for comparing the effectiveness (coverage rate) and the efficiency (required number of executions) of hill climbing algorithm with random testing is presented. The results show that random testing performs well for most units under test, while around 30% of the artifacts significantly benefit from the hill climbing algorithm. Structural properties of the units that affect the performance of hill climbing and random testing are also discussed.

  • 22.
    Doganay, Kivanc
    et al.
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Eldh, Sigrid
    Ericsson AB, Kista, Sweden.
    Afzal, Wasif
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Bohlin, Markus
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Search-based Testing for Embedded Telecommunication Software with Complex Input Structures: An Industrial Case Study2014Rapport (Övrigt vetenskapligt)
    Abstract [en]

    In this paper, we discuss the application of search-based software test-ing techniques for unit level testing of a real-world telecommunication middleware at Ericsson. Input data for the system under test consists of nested data structures, and includes non-trivial variables such as unini-tialized pointers. Our current implementation analyzes the existing test cases to discover how to handle pointers, set global system parameters, and any other setup code that needs to run before the actual test case. Hill climbing (HC) and (1+1) evolutionary algorithm (EA) metaheuristic search algorithms are used to generate input data for branch coverage. We compare HC, (1+1)EA, and random search as a baseline of performance with respect to e˙ectiveness, measured as branch coverage, and eÿciency, measured as number of executions needed. Diÿculties arising from the specialized execution environment and the adaptations for handling these problems are also discussed.

  • 23.
    Enoiu, Eduard Paul
    et al.
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Doganay, Kivanc
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Bohlin, Markus
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Sundmark, Daniel
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Pettersson, Paul
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    MOS: An Integrated Model-based and Search-based Testing Tool for Function Block Diagrams2013Ingår i: 2013 1st International Workshop on Combining Modelling and Search-Based Software Engineering, CMSBSE 2013 - Proceedings, 2013, s. 55-60Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper we present a new testing tool for safety critical applications described in Function Block Diagram (FBD) language aimed to support both a model and a search-based approach. Many benefits emerge from this tool, including the ability to automatically generate test suites from an FBD program in order to comply to quality requirements such as component testing and specific coverage measurements. Search-based testing methods are used to generate test data based on executable code rather than the FBD program, alleviating any problems that may arise from the ambiguities that occur while creating FBD programs. Test cases generated by both approaches are executed and used as a way of cross validation. In the current work, we describe the architecture of the tool, its workflow process, and a case study in which the tool has been applied in a real industrial setting to test a train control management system.

  • 24.
    Gestrelius, Sara
    et al.
    SICS Swedish ICT AB, Sweden.
    Dahms, Florian
    RWTH Aachen, Germany.
    Bohlin, Markus
    SICS Swedish ICT AB, Sweden.
    Optimisation of simultaneous train formation and car sorting ar marshalling yards2013Ingår i: Proceedings of the 5th International Seminar on Railway Operations modelling and Analysis (RailCopenhagen), Monday 13 May 2013 - Wednesday 15 May 2013 Technical University of Denmark, 2013Konferensbidrag (Refereegranskat)
  • 25.
    Gestrelius, Sara
    et al.
    SICS Swedish ICT AB, Sweden.
    Dahms, Florian
    RWTH Aachen, Germany.
    Bohlin, Markus
    SICS Swedish ICT AB, Sweden.
    Optimisation of simultaneous train formation and car sorting at marshalling yards2013Ingår i: Proceedings of the 5th International Conference on Railway Operations Modelling and Analysis IAROR13, 2013Konferensbidrag (Refereegranskat)
    Abstract [en]

    Efficient and correct freight train marshalling is vital for high quality carload freight transportations. During marshalling, it is desirable that cars are sorted according to their individual drop-off locations in the outbound freight trains. Furthermore, practical limitations such as non-uniform and limited track lengths and the arrival and departure times of trains need to be considered. This paper presents a novel optimisation method for freight marshalling scheduling under these circumstances. The method is based on an integer programming formulation that is solved using column generation and branch and price. The approach minimises the number of extra shunting operations that have to be performed, and is evaluated on real-world data from the Hallsberg marshalling yard in Sweden.

  • 26.
    Ghaviha, Nima
    et al.
    Mälardalens högskola, Akademin för ekonomi, samhälle och teknik, Framtidens energi.
    Bohlin, Markus
    Mälardalens högskola, Akademin för ekonomi, samhälle och teknik, Framtidens energi.
    Dahlquist, Erik
    Mälardalens högskola, Akademin för ekonomi, samhälle och teknik, Framtidens energi.
    Speed profile optimization of an electric train with on-board energy storage and continuous tractive effort2016Ingår i: 2016 International Symposium on Power Electronics, Electrical Drives, Automation and Motion, SPEEDAM 2016, 2016Konferensbidrag (Refereegranskat)
    Abstract [en]

    Electric traction system is the most energy efficient traction system in railways. Nevertheless, not all railway networks are electrified, which is due to high maintenance and setup cost of overhead lines. One solution to the problem is battery-driven trains, which can make the best use of the electric traction system while avoiding the high costs of the catenary system. Due to the high power consumption of electric trains, energy management of battery trains are crucial in order to get the best use of batteries. This paper suggests a general algorithm for speed profile optimization of an electric train with an on-board energy storage device, during catenary-free operation on a given line section. The approach is based on discrete dynamic programming, where the train model and the objective function are based on equations of motion rather than electrical equations. This makes the model compatible with all sorts of energy storage devices. Unlike previous approaches which consider trains with throttle levels for tractive effort, the new approach considers trains in which there are no throttles and tractive effort is controlled with a controller (smooth gliding handle with no discrete levels). Furthermore, unlike previous approaches, the control variable is the velocity change instead of the applied tractive effort. The accuracy and performance of the discretized approach is evaluated in comparison to the formal movement equations in a simulated experimented using train data from the Bombardier Electrostar series and track data from the UK.

  • 27.
    Ghaviha, Nima
    et al.
    Mälardalens högskola, Akademin för ekonomi, samhälle och teknik, Framtidens energi.
    Bohlin, Markus
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Dahlquist, Erik
    Mälardalens högskola, Akademin för ekonomi, samhälle och teknik, Framtidens energi.
    Wallin, Fredrik
    Mälardalens högskola, Akademin för ekonomi, samhälle och teknik, Framtidens energi.
    Optimal Control of a Battery Train Using Dynamic Programming2015Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Electric propulsion system in trains has the highest efficiency compared to other propulsion systems (i.e. steam and diesel). Still, electric trains are not used on all the routes, due to the high setup and maintenance cost of the catenary system. Energy storage technologies and the battery driven trains however, make it possible to have the electric trains on the non-electrified routes as well. High energy consumption of the electric trains, makes the energy management of such trains crucial to get the best use of the energy storage device. This paper suggests an algorithm for the optimal control of the catenary free operation of an electric train equipped with an onboard energy storage device. The algorithm is based on the discrete dynamic programming and Bellman’s backward approach. The objective function is to minimize the energy consumption, i.e. having the maximum battery level left at the end of the trip. The constraints are the trip time, battery capacity, local speed limits and limitations on the traction motor. Time is the independent variable and distance, velocity and battery level are the state variables. All of the four variables are discretized which results in some inaccuracy in the calculations, which is discussed in the paper. The train model and the algorithm are based on the equations of motion which makes the model adjustable for all sorts of electric trains and energy storage devices. Moreover, any type of electrical constraints such as the ones regarding the voltage output of the energy storage device or the power output can be enforced easily, due to the nature of the dynamic programming. 

  • 28.
    Ghaviha, Nima
    et al.
    Mälardalens högskola, Akademin för ekonomi, samhälle och teknik, Framtidens energi. Mälardalen University.
    Bohlin, Markus
    Research Institutes of Sweden RISE SICS Västerås.
    Holmberg, Christer
    Bombardier Transportation.
    Dahlquist, Erik
    Mälardalens högskola, Akademin för ekonomi, samhälle och teknik, Framtidens energi.
    Speed Profile Optimization of Catenary-free Electric Trains with Lithium-ion BatteriesManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    Catenary-free operated electric trains, as one of the recent technologies in railwaytransportation, has opened a new field of research: speed profile optimization and energy optimaloperation of catenary-free operated electric trains. A well-formulated solution for this problem shouldconsider the characteristics of the energy storage device using a validated model and method. This paper,discusses the consideration of the battery behavior in the problem of speed profile optimization ofcatenary-free operated electric trains. We combine the single mass point train model with an electricalbattery model and apply a dynamic programming approach to minimize the charge taken from thebattery during the catenary-free operation. The models and the method are validated and evaluatedagainst experimental data gathered from the test runs of an actual battery driven train tested in Essex,UK. The results show a significant potential in energy saving. Moreover, we show that the optimumspeed profiles generated using our approach consume less charge from the battery compared to theprevious approaches.

  • 29.
    Ghaviha, Nima
    et al.
    Mälardalens högskola, Akademin för ekonomi, samhälle och teknik, Framtidens energi.
    Bohlin, Markus
    SICS - swedish institute of computer science, Sweden.
    Wallin, Fredrik
    Mälardalens högskola, Akademin för ekonomi, samhälle och teknik, Framtidens energi.
    Dahlquist, Erik
    Mälardalens högskola, Akademin för ekonomi, samhälle och teknik, Framtidens energi.
    AN ALGORITHM FOR OPTIMAL CONTROL OF AN ELECTRIC MULTIPLE UNIT2014Ingår i: Proceedings from The 55th Conference on Simulation and Modelling (SIMS 55),21-22 October, 2014. Aalborg, Denmark, Linköping: Linköping University Electronic Press, 2014Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper offers a solution for the optimal EMU train (Electric Multiple Unit) operation with the aim of minimizing the energy consumption. EMU is an electric train with traction motors in more than one carriage. The algorithm is based on dynamic programming and the Hamilton-Jacobi-Bellman equation. To model the train, real data has been used, which was provided by experts from Bombardier Transportation Västerås. To evaluate the model, some experiments have been done on the energy saving in exchange for the increase in the trip time. Moreover a simple accuracy factor is introduced to evaluate the accuracy of the model. The final goal is to use this approach as a base for a driver advisory system, therefore it is important to have the amount of calculations as minimum as possible. The paper also includes the studies done on the calculation time. The solution can be used for driverless trains as well as normal trains. It should be mentioned that this paper is a part of a research which is still in progress and the final model will also be used by Bombardier Transportation Västerås as an evaluation tool for the propulsions systems and trains.

  • 30.
    Ghaviha, Nima
    et al.
    Mälardalens högskola, Akademin för ekonomi, samhälle och teknik, Framtidens energi.
    Bohlin, Markus
    SICS Swedish ICT, Sweden.
    Wallin, Fredrik
    Mälardalens högskola, Akademin för ekonomi, samhälle och teknik, Framtidens energi.
    Dahlquist, Erik
    Mälardalens högskola, Akademin för ekonomi, samhälle och teknik, Framtidens energi.
    Optimal Control of an EMU Using Dynamic Programming2015Ingår i: Energy Procedia, ISSN 1876-6102, E-ISSN 1876-6102, Vol. 75, s. 1913-1919Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A model is developed for minimizing the energy consumption of an electric multiple unit through optimized driving style, based on Hamilton-Jacobi-Bellman equation and Bellman's backward approach. Included are the speed limits, track profile (elevations), different driving modes and the train load. This paper includes aspects like the power loss in the auxiliary systems, time management, validation of the model regarding energy calculations and a study on discretization and the accuracy of the model. The model will be used as a base for a new driver advisory system. 

  • 31.
    Ghaviha, Nima
    et al.
    Mälardalens högskola, Akademin för ekonomi, samhälle och teknik, Framtidens energi.
    Bohlin, Markus
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Wallin, Fredrik
    Mälardalens högskola, Akademin för ekonomi, samhälle och teknik, Framtidens energi.
    Dahlquist, Erik
    Mälardalens högskola, Akademin för ekonomi, samhälle och teknik, Framtidens energi.
    Optimal Control of an EMU Using Dynamic Programming and Tractive Effort as the Control Variable2015Ingår i: Proceedings of the 56th SIMS, Linköping University Electronic Press, Linköpings universitet, 2015, s. 377-382Konferensbidrag (Refereegranskat)
    Abstract [en]

    Problem of optimal train control with the aim of minimizing energy consumption is one of the old optimal control problems. During last decades different solutions have been suggested based on different optimization techniques, each including a certain number of constraints or different train configurations, one being the control on the tractive effort available from traction motor. The problem is previously solved using dynamic programming for trains with continuous tractive effort, in which velocity was assumed to be the control variable. The paper at hand presents a solution based on dynamic programming for solving the problem for trains with discrete tractive effort. In this approach, tractive effort is assumed to be the control variable. Moreover a short comparison is made between two approaches regarding accuracy and ease of application in a driver advisory system.

  • 32.
    Ghaviha, Nima
    et al.
    Mälardalens högskola, Akademin för ekonomi, samhälle och teknik, Framtidens energi.
    Campillo, Javier
    Mälardalens högskola, Akademin för ekonomi, samhälle och teknik, Framtidens energi.
    Bohlin, Markus
    Mälardalens högskola, Akademin för ekonomi, samhälle och teknik, Framtidens energi.
    Dahlquist, Erik
    Mälardalens högskola, Akademin för ekonomi, samhälle och teknik, Framtidens energi.
    Review of Application of Energy Storage Devices in Railway Transportation2017Ingår i: Energy Procedia, ISSN 1876-6102, E-ISSN 1876-6102, Vol. 105, s. 4561-4568Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Regenerative braking is one of the main reasons behind the high levels of energy efficiency achieved in railway electric traction systems. During regenerative braking, the traction motor acts as a generator and restores part of the kinetic energy into electrical energy. To use this energy, it should be either fed back to the power grid or stored on an energy storage system for later use. This paper reviews the application of energy storage devices used in railway systems for increasing the effectiveness of regenerative brakes. Three main storage devices are reviewed in this paper: batteries, supercapacitors and flywheels. Furthermore, two main challenges in application of energy storage systems are briefly discussed. 

  • 33.
    Helali Moghadam, Mahshid
    et al.
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Saadatmand, Mehrdad
    RISE SICS, Sweden.
    Bohlin, Markus
    RISE SICS, Sweden.
    Lisper, Björn
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Borg, Markus
    RISE SICS, Sweden.
    Adaptive Runtime Response Time Control in PLC-based Real-Time Systems using Reinforcement Learning2018Ingår i: ACM/IEEE 13th International Symposium on Software Engineering for Adaptive and Self-Managing Systems, SEAMS 2018, , co-located with International Conference on Software Engineering, ICSE 2018; Gothenburg; Sweden; 28 May 2018 through 29 May 2018; Code 138312, 2018, Vol. 28 May, s. 217-223Konferensbidrag (Refereegranskat)
    Abstract [en]

    Timing requirements such as constraints on response time are key characteristics of real-time systems and violations of these requirements might cause a total failure, particularly in hard real-time systems. Runtime monitoring of the system properties is of great importance to detect and mitigate such failures. Thus, a runtime control to preserve the system properties could improve the robustness of the system with respect to timing violations. Common control approaches may require a precise analytical model of the system which is difficult to be provided at design time. Reinforcement learning is a promising technique to provide adaptive model-free control when the environment is stochastic, and the control problem could be formulated as a Markov Decision Process. In this paper, we propose an adaptive runtime control using reinforcement learning for real-time programs based on Programmable Logic Controllers (PLCs), to meet the response time requirements. We demonstrate through multiple experiments that our approach could control the response time efficiently to satisfy the timing requirements.

  • 34.
    Helali Moghadam, Mahshid
    et al.
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system. RISE, SICS, Sweden.
    Saadatmand, Mehrdad
    RISE, SICS, Sweden.
    Borg, Markus
    RISE, SICS, Sweden.
    Bohlin, Markus
    Mälardalens högskola, Akademin för innovation, design och teknik. RISE, SICS, Sweden.
    Lisper, Björn
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Learning-based Response Time Analysis in Real-Time Embedded Systems: A Simulation-based Approach2018Ingår i: 1st International Workshop on Software Qualities and their Dependencies, located at the International Conference of Software Engineering (ICSE) 2018 SQUADE'18, 2018, s. 21-24Konferensbidrag (Refereegranskat)
    Abstract [en]

    Response time analysis is an essential task to verify the behavior of real-time systems. Several response time analysis methods have been proposed to address this challenge, particularly for real-time systems with different levels of complexity. Static analysis is a popular approach in this context, but its practical applicability is limited due to the high complexity of the industrial real-time systems, as well as many unpredictable runtime events in these systems. In this work-in-progress paper, we propose a simulationbased response time analysis approach using reinforcement learning to find the execution scenarios leading to the worst-case response time. The approach learns how to provide a practical estimation of the worst-case response time through simulating the program without performing static analysis. Our initial study suggests that the proposed approach could be applicable in the simulation environments of the industrial real-time control systems to provide a practical estimation of the execution scenarios leading to the worst-case response time.

  • 35.
    Helali Moghadam, Mahshid
    et al.
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system. RISE, SICS, Sweden.
    Saadatmand, Mehrdad
    RISE, SICS, Sweden.
    Borg, Markus
    RISE, SICS, Sweden.
    Bohlin, Markus
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Lisper, Björn
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Learning-Based Self-Adaptive Assurance of Timing Properties in a Real-Time Embedded System2018Ingår i: ICST Workshop on Testing Extra-Functional Properties and Quality Characteristics of Software Systems ITEQS'18, 2018, s. 77-80Konferensbidrag (Refereegranskat)
    Abstract [en]

    Providing an adaptive runtime assurance technique to meet the performance requirements of a real-time system without the need for a precise model could be a challenge. Adaptive performance assurance based on monitoring the status of timing properties can bring more robustness to the underlying platform. At the same time, the results or the achieved policy of this adaptive procedure could be used as feedback to update the initial model, and consequently for producing proper test cases. Reinforcement-learning has been considered as a promising adaptive technique for assuring the satisfaction of the performance properties of software-intensive systems in recent years. In this work-in-progress paper, we propose an adaptive runtime timing assurance procedure based on reinforcement learning to satisfy the performance requirements in terms of response time. The timing control problem is formulated as a Markov Decision Process and the details of applying the proposed learning-based timing assurance technique are described.

  • 36.
    Helali Moghadam, Mahshid
    et al.
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system. Research Institutes of Sweden (RISE) SICS, Sweden .
    Saadatmand, Mehrdad
    Research Institutes of Sweden (RISE) SICS, Sweden .
    Borg, Markus
    Research Institutes of Sweden (RISE) SICS, Sweden .
    Bohlin, Markus
    Research Institutes of Sweden (RISE) SICS, Sweden .
    Lisper, Björn
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Machine Learning to Guide Performance Testing: An Autonomous Test Framework2019Ingår i: ICST Workshop on Testing Extra-Functional Properties and Quality Characteristics of Software Systems ITEQS'19, 2019, s. 164-167Konferensbidrag (Refereegranskat)
    Abstract [en]

    Satisfying performance requirements is of great importance for performance-critical software systems. Performance analysis to provide an estimation of performance indices and ascertain whether the requirements are met is essential for achieving this target. Model-based analysis as a common approach might provide useful information but inferring a precise performance model is challenging, especially for complex systems. Performance testing is considered as a dynamic approach for doing performance analysis. In this work-in-progress paper, we propose a self-adaptive learning-based test framework which learns how to apply stress testing as one aspect of performance testing on various software systems to find the performance breaking point. It learns the optimal policy of generating stress test cases for different types of software systems, then replays the learned policy to generate the test cases with less required effort. Our study indicates that the proposed learning-based framework could be applied to different types of software systems and guides towards autonomous performance testing.

  • 37.
    Holst, A
    et al.
    Swedish Institute of Computer Science.
    Bohlin, Markus
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Ekman, J
    Swedish Institute of Computer Science.
    Sellin, O
    Bombardier Transportation.
    Lindström, B
    Addiva Consulting AB.
    Larsen, S
    Addiva Eduro AB.
    Statistical anomaly detection for train fleets2012Ingår i: Proceedings of the National Conference on Artificial Intelligence, vol. 3, 2012, 2012, s. 2217-2223Konferensbidrag (Refereegranskat)
    Abstract [en]

    We have developed a method for statistical anomaly detection which has been deployed in a tool for condition monitoring of train fleets. The tool is currently used by several railway operators over the world to inspect and visualize the occurrence of "event messages" generated on the trains. The anomaly detection component helps the operators to quickly find significant deviations from normal behavior and to detect early indications for possible problems. The savings in maintenance costs comes mainly from avoiding costly breakdowns, and have been estimated to several million Euros per year for the tool. In the long run, it is expected that maintenance costs can be reduced with between 5 and 10 % by using the tool.

  • 38.
    Hänninen, Kaj
    et al.
    Mälardalens högskola, Institutionen för datavetenskap och elektronik.
    Mäki-Turja, Jukka
    Mälardalens högskola, Institutionen för datavetenskap och elektronik.
    Bohlin, Markus
    Mälardalens högskola, Institutionen för datavetenskap och elektronik.
    Carlson, Jan
    Mälardalens högskola, Institutionen för datavetenskap och elektronik.
    Sjödin, Mikael
    Mälardalens högskola, Institutionen för datavetenskap och elektronik.
    Analysing Stack Usage in Preemptive Shared Stack Systems2006Rapport (Övrigt vetenskapligt)
    Abstract [en]

    This paper presents a novel method to determine the maximum stack memory used in preemptive, shared stack, real-time systems. We provide a general and exact problem formulation applicable for any preemptive system model based on dynamic (run-time) properties. We also show how to safely approximate the exact stack usage by using static (compile time) information about the system model and the underlying run-time system on a relevant and commercially available system model: A hybrid, statically and dynamically, scheduled system. Comprehensive evaluations show that our technique significantly reduces the amount of stack memory needed compared to existing analysis techniques. For typical task sets a decrease in the order of 70% is typical.

  • 39.
    Hänninen, Kaj
    et al.
    Mälardalens högskola, Institutionen för datavetenskap och elektronik. Arcticus Systems, Järfälla, Sweden.
    Mäki-Turja, Jukka
    Mälardalens högskola, Institutionen för datavetenskap och elektronik.
    Bohlin, Markus
    Mälardalens högskola, Institutionen för datavetenskap och elektronik. Swedish Institute of Computer Science, Kista, Sweden.
    Carlson, Jan
    Mälardalens högskola, Institutionen för datavetenskap och elektronik.
    Sjödin, Mikael
    Mälardalens högskola, Institutionen för datavetenskap och elektronik. CC Systems, Uppsala, Sweden .
    Determining Maximum Stack Usage in Preemptive Shared Stack Systems2007Ingår i: Proceedings of the 9th Real-Time in Sweden (RTiS'07), Västerås, Sweden, 2007, s. 118-126Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents a novel method to determine the

    maximum stack memory used in preemptive, shared stack,

    real-time systems. We provide a general and exact problem

    formulation applicable for any preemptive system model

    based on dynamic (run-time) properties.

    We also show how to safely approximate the exact stack

    usage by using static (compile time) information about the

    system model and the underlying run-time system on a relevant

    and commercially available system model: A hybrid,

    statically and dynamically, scheduled system.

    Comprehensive evaluations show that our technique significantly

    reduces the amount of stack memory needed compared

    to existing analysis techniques. For typical task sets

    a decrease in the order of 70% is typical.

  • 40.
    Hänninen, Kaj
    et al.
    Mälardalens högskola, Institutionen för datavetenskap och elektronik.
    Mäki-Turja, Jukka
    Mälardalens högskola, Institutionen för datavetenskap och elektronik.
    Bohlin, Markus
    Mälardalens högskola, Institutionen för datavetenskap och elektronik.
    Carlson, Jan
    Mälardalens högskola, Institutionen för datavetenskap och elektronik.
    Sjödin, Mikael
    Mälardalens högskola, Institutionen för datavetenskap och elektronik.
    Determining Maximum Stack Usage in Preemptive Shared Stack Systems2006Ingår i: Proceedings - Real-Time Systems Symposium, 2006, s. 445-453Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents a novel method to determine the maximum stack memory used in preemptive, shared stack, real-time systems. We provide a general and exact problem formulation applicable for any preemptive system model based on dynamic (run-time) properties. We also show how to safely approximate the exact stack usage by using static (compile time) information about the system model and the underlying run-time system on a relevant and commercially available system model: A hybrid, statically and dynamically, scheduled system.

    Comprehensive evaluations show that our technique significantly reduces the amount of stack memory needed compared to existing analysis techniques. For typical task sets a decrease in the order of 70% is typical.

  • 41.
    Lu, Yue
    et al.
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Bohlin, Markus
    Swedish Institute of Computer Science, Kista, Sweden).
    Kraft, Johan
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Kreuger, Per
    Swedish Institute of Computer Science, Kista, Sweden).
    Nolte, Thomas
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Norström, Christer
    Mälardalens högskola, Akademin för innovation, design och teknik.
    Approximate Timing Analysis of Complex Legacy Real-Time Systems using Simulation Optimization2008Ingår i: Proceedings of the Work-In-Progress (WIP) track of the 29th IEEE Real-Time Systems Symposium (RTSS), Barcelona, Spain, 2008Konferensbidrag (Refereegranskat)
  • 42.
    Tahvili, Sahar
    et al.
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system. RISE SICS Västerås, Sweden.
    Afzal, Wasif
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Saadatmand, Mehrdad
    RISE SICS Västerås, Sweden.
    Bohlin, Markus
    RISE SICS Västerås, Sweden.
    Hasan Ameerjan, Sharvathul
    ESPRET: A Tool for Execution Time Estimation of Manual Test Cases2018Ingår i: Journal of Systems and Software, ISSN 0164-1212, E-ISSN 1873-1228, Vol. 146, s. 26-41Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Manual testing is still a predominant and an important approach for validation of computer systems, particularly in certain domains such as safetycritical systems. Knowing the execution time of test cases is important to perform test scheduling, prioritization and progress monitoring. In this work, we present, apply and evaluate ESPRET (EStimation and PRediction of Execution Time) as our tool for estimating and predicting the execution time of manual test cases based on their test specifications. Our approach works by extracting timing information for various steps in manual test specifcation. This information is then used to estimate the maximum time for test steps that have not previously been executed, but for which textual specifications exist. As part of our approach, natural language parsing of the specifications is performed to identify word combinations to check whether existing timing information on various test steps is already available or not. Since executing test cases on the several machines may take different time, we predict the actual execution time for test cases by a set of regression models. Finally, an empirical evaluation of the approach and tool has been performed on a railway use case at Bombardier Transportation (BT) in Sweden.

  • 43.
    Tahvili, Sahar
    et al.
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Afzal, Wasif
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Saadatmand, Mehrdad
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Bohlin, Markus
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Sundmark, Daniel
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Larsson, Stig
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Towards Earlier Fault Detection by Value-Driven Prioritization of Test Cases Using Fuzzy TOPSIS2016Ingår i: Information Technology: New Generations, vol. 440, Las Vegas, United States, 2016, s. 745-759Konferensbidrag (Refereegranskat)
    Abstract [en]

    In industrial software testing, development projects typically set up and maintain test suites containing large numbers of test cases. Executing a large number of test cases can be expensive in terms of effort and wall-clock time. Moreover, indiscriminate execution of all available test cases typically lead to sub-optimal use of testing resources. On the other hand, selecting too few test cases for execution might leave a large number of faults undiscovered. Limiting factors such as allocated budget and time constraints for testing further emphasizes the importance of test case prioritization in order to identify test cases that enable earlier detection of faults while respecting such constraints. In this paper, we propose a multi-criteria decision making approach for prioritizing test cases in order to detect faults earlier. This is achieved by applying the TOPSIS (Technique for Order of Preference by Similarity to Ideal Solution) decision making technique combined with fuzzy principles. Our solution is based on important criteria such as fault detection probability, execution time, complexity, and other test case properties. By applying the approach on a train control management subsystem from Bombardier Transportation in Sweden, we demonstrate how it helps, in a systematic way, to identify test cases that can lead to early detection of faults while respecting various criteria.

  • 44.
    Tahvili, Sahar
    et al.
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Bohlin, Markus
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Test Case Prioritization Using Multi Criteria Decision Making Methods2016Ingår i: Orbit: medlemsblad for Dansk Selskab for Operationsanalyse og Svenska Op, ISSN 1601-8893, Vol. 26, s. 9-11Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    The lack of a systematic approach to decision making might leads to a non-optimal usage of resources. Nowadays, the real world decision making problems are multiple criteria, complex, large scale and generally consist of uncertainty and vagueness. Multiple-criteria decision making (MCDM) is a subset of operations research and is divided into Multi-Objective Decision Making (MODM) and Multi-Attribute Decision Making (MADM). The principal objective of the present article is proposing a systematic multi-criteria design making approach in the area of software testing that will be exemplified by an industrial example.

  • 45.
    Tahvili, Sahar
    et al.
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Bohlin, Markus
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Saadatmand, Mehrdad
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Larsson, Stig
    SICS, Sweden.
    Afzal, Wasif
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Sundmark, Daniel
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Cost-Benefit Analysis of Using Dependency Knowledge at Integration Testing2016Ingår i: Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics), 2016, Vol. 10027, s. 268-284Konferensbidrag (Refereegranskat)
    Abstract [en]

    In software system development, testing can take considerable time and resources, and there are numerous examples in the literature of how to improve the testing process. In particular, methods for selection and prioritization of test cases can play a critical role in efficient use of testing resources. This paper focuses on the problem of selection and ordering of integration-level test cases. Integration testing is performed to evaluate the correctness of several units in composition. Further, for reasons of both effectiveness and safety, many embedded systems are still tested manually. To this end, we propose a process, supported by an online decision support system, for ordering and selection of test cases based on the test result of previously executed test cases. To analyze the economic efficiency of such a system, a customized return on investment (ROI) metric tailored for system integration testing is introduced. Using data collected from the development process of a large-scale safety-critical embedded system, we perform Monte Carlo simulations to evaluate the expected ROI of three variants of the proposed new process. The results show that our proposed decision support system is beneficial in terms of ROI at system integration testing and thus qualifies as an important element in improving the integration testing process.

  • 46.
    Tahvili, Sahar
    et al.
    RISE SICS Västerås.
    Hatvani, Leo
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Felderer, Michael
    University of Innsbruck Innsbruck, Austria.
    Afzal, Wasif
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Bohlin, Markus
    RISE SICS Västerås AB , Västerås , Sweden.
    Automated Functional Dependency Detection Between Test Cases Using Text Semantic Similarity2019Ingår i: 2019 IEEE International Conference On Artificial Intelligence Testing (AITest), 2019, s. 19-26, artikel-id 8718215Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Knowing about dependencies and similarities between test cases is beneficial for prioritizing them for cost-effective test execution. This holds especially true for the time consuming, manual execution of integration test cases written in natural language. Test case dependencies are typically derived from requirements and design artifacts. However, such artifacts are not always available, and the derivation process can be very time-consuming. In this paper, we propose, apply and evaluate a novel approach that derives test cases' similarities and functional dependencies directly from the test specification documents written in natural language, without requiring any other data source. Our approach uses an implementation of Doc2Vec algorithm to detect text-semantic similarities between test cases and then groups them using two clustering algorithms HDBSCAN and FCM. The correlation between test case text-semantic similarities and their functional dependencies is evaluated in the context of an on-board train control system from Bombardier Transportation AB in Sweden. For this system, the dependencies between the test cases were previously derived and are compared to the results our approach. The results show that of the two evaluated clustering algorithms, HDBSCAN has better performance than FCM or a dummy classifier. The classification methods' results are of reasonable quality and especially useful from an industrial point of view. Finally, performing a random undersampling approach to correct the imbalanced data distribution results in an F1 Score of up to 75% when applying the HDBSCAN clustering algorithm.

  • 47.
    Tahvili, Sahar
    et al.
    RISE, SICS, Västerås, Sweden.
    Hatvani, Leo
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Felderer, Michael
    University of Innsbruck, Austria, Sweden.
    Afzal, Wasif
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Saadatmand, Mehrdad
    RISE, SICS, Västerås, Sweden.
    Bohlin, Markus
    RISE, SICS, Västerås, Sweden.
    Cluster-Based Test Scheduling Strategies Using Semantic Relationships between Test Specifications2018Ingår i: 5th International Workshop on Requirements Engineering and Testing RET'18, 2018, Vol. F137811, s. 1-4Konferensbidrag (Refereegranskat)
    Abstract [en]

    One of the challenging issues in improving the test efficiency is that of achieving a balance between testing goals and testing resources. Test execution scheduling is one way of saving time and budget, where a set of test cases are grouped and tested at the same time. To have an optimal test execution schedule, all related information of a test case (e.g. execution time, functionality to be tested, dependency and similarity with other test cases) need to be analyzed. Test scheduling problem becomes more complicated at high-level testing, such as integration testing and especially in manual testing procedure. Test specifications at high-level are generally written in natural text by humans and usually contain ambiguity and uncertainty. Therefore, analyzing a test specification demands a strong learning algorithm. In this position paper, we propose a natural language processing (NLP) based approach that, given test specifications at the integration level, allows automatic detection of test cases’ semantic dependencies. The proposed approach utilizes the Doc2Vec algorithm and converts each test case into a vector in n-dimensional space. These vectors are then grouped using the HDBSCAN clustering algorithm into semantic clusters. Finally, a set of cluster-based test scheduling strategies are proposed for execution. The proposed approach has been applied in a sub-system from the railway domain by analyzing an ongoing testing project at Bombardier Transportation AB, Sweden.

  • 48.
    Tahvili, Sahar
    et al.
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system. RISE SICS Västerås.
    Pimentel, Rita
    Afzal, Wasif
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Ahlberg, Marcus
    Fornander, Eric
    Bohlin, Markus
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system. Mälardalens högskola, Akademin för ekonomi, samhälle och teknik, Framtidens energi.
    sOrTES: A Supportive Tool forStochastic Scheduling of ManualIntegration Test CasesManuskript (preprint) (Övrigt vetenskapligt)
  • 49.
    Tahvili, Sahar
    et al.
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system. SICS Swedish ICT Västerås AB, Sweden.
    Saadatmand, Mehrdad
    SICS Swedish ICT Västerås AB, Sweden.
    Bohlin, Markus
    SICS Swedish ICT Västerås AB, Sweden.
    Multi-Criteria Test Case Prioritization Using Fuzzy Analytic Hierarchy Process2015Ingår i: ICSEA 2015: The Tenth International Conference on Software Engineering Advances, 2015, s. 290-296Konferensbidrag (Refereegranskat)
    Abstract [en]

    One of the key challenges in software testing today is prioritizing and evaluating test cases. The decision of which test cases to design, select and execute first is of great importance, in particular considering that testing is often done late in the implementation process, and therefore needs to be done within tight resource constraints on time and budget. In practice, prioritized selection of test cases requires the evaluation of different test case criteria, and therefore, test case prioritization can be formulated as a multi-criteria decision making problem. As the number of decision criteria grows, application of a systematic decision making solution becomes a necessity. In this paper we propose an approach for prioritized selection of test cases by using the Analytic Hierarchy Process (AHP) technique. To improve the practicality of the approach in real world scenarios, we apply AHP in fuzzy environment so that criteria values can be specified using fuzzy variables than requiring precise quantified values. One of the advantages of the decision making process it that the defined criteria with the biggest and most critical role in priority ranking of test cases is identified. We have applied our approach on an example case in which several test cases for testing non-functional requirements in a systems are defined.

  • 50.
    Tahvili, Sahar
    et al.
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Saadatmand, Mehrdad
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Bohlin, Markus
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Afzal, Wasif
    Mälardalens högskola, Akademin för innovation, design och teknik, Inbyggda system.
    Hasan Ameerjan, Sharvathul
    Towards Execution Time Prediction for Test Cases from Test Specification2017Ingår i: 2017 43RD EUROMICRO CONFERENCE ON SOFTWARE ENGINEERING AND ADVANCED APPLICATIONS (SEAA), Vienna, Austria, 2017, s. 421-425Konferensbidrag (Refereegranskat)
    Abstract [en]

    Knowing the execution time of test cases is important to perform test scheduling, prioritization and progress monitoring. This short paper presents a novel approach for predicting the execution time of test cases based on test specifications and available historical data on previously executed test cases. Our approach works by extracting timing information (measured and maximum execution time) for various steps in manual test cases. This information is then used to estimate the maximum time for test steps that have not previously been executed, but for which textual specifications exist. As part of our approach natural language parsing of the specifications is performed to identify word combinations to check whether existing timing information on various test activities already exists or not. Finally, linear regression is used to predict the actual execution time for test cases. A proof-of-concept use-case at Bombardier transportation serves to evaluate the proposed approach.

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