This paper presents an efficient and accurate analytical model for the radio interface of the general packet radio service (GPRS) in a GSM network. The model is utilized for investigating how many packet data channels should be allocated for GPRS under a given amount of traffic in order to guarantee appropriate quality of service. The presented model constitutes a continuous-time Markov chain. The Markov model represents the sharing of radio channels by circuit switched GSM connections and packet switched GPRS sessions under a dynamic channel allocation scheme. In contrast to previous work, the Markov model explicitly represents the mobility of users by taking into account arrivals of new GSM and GPRS users as well as handovers from neighboring cells. Furthermore, we take into account TCP flow control for the GPRS data packets. To validate the simplifications necessary for making the Markov model amenable to numerical solution, we provide a comparison of the results of the Markov model with a detailed simulator on the network level.

Behovet av akut vård har ökat under de senaste åren och satt ökad press på ambulanssektorn i stort. Hur man kan förbättra och effektivisera olika delar av vårdkedjan är en fråga som beslutsfattare inom denna sektor ständigt behöver ha i åtanke för att kunna möta detta behov. Det finns visioner om en likvärdig vård för alla människor i vårt samhälle, som tyvärr kan vara svåra att nå i praktiken. Människor som bor i glesbefolkade områden behöver i regel vänta längre på en ambulans än personer som bor i urbana områden, och transporttiden för dessa ambulansutryckningar blir längre eftersom det ofta är långt till närmaste akutmottagning. För ambulanspersonalen kan det dessutom i vissa fall vara svårt att göra en korrekt bedömning om huruvida en mindre akut patient behöver transporteras till en akutmottagning eller inte. En tänkbar förändring i vårdkedjan kan vara att transportera mindre akuta patienter till en närliggande vårdcentral istället för en akutmottagning - en så kallad alternativ vårdväg. Detta hade både kunnat resultera i kortare transporttider på glesbyggden (vilket i sin tur kan ha en påverkan på ambulansens tillgänglighet) och ge ambulanspersonal möjlighet att välja ett mellansteg mellan att lämna kvar en patient i hemmet och att transportera den till en akutmottagning.  För att undersöka vilken påverkan en alternativ vårdväg kan ha på ambulanser sett till både tid och tillgänglighet, har en diskret händelsestyrd simuleringsmodell utvecklats. Denna modell har använts i en scenariostudie för att undersöka hur en alternativ vårdväg kan påverka ambulans och patienter på glesbygden. Data från SOS Alarm och Region Skåne har möjliggjort en generering av indata som bättre överensstämmer med verkligheten. Resultatet av scenariostudien tyder på att en alternativ vårdväg kan förbättra tillgängligheten för en ambulans på glesbygden genom att förkorta transporttiden till mottagande vårdinstans. / The need for emergency care has increased in recent years and has put increased pressure on the ambulance sector in general. How to improve and streamline different parts of the care chain is an issue that decision-makers in this sector constantly need to keep in mind in order to meet this need. There are visions of equal care for all people in our society, which unfortunately can be difficult to achieve in practice. People who live in sparsely populated areas usually experience longer waiting times to receive an ambulance than people in urban areas, and the transport time for these ambulance calls is longer because of the (usually) longer distance to the nearest emergency room. In addition, for ambulance personnel, it can in some cases be difficult to make a correct assessment of whether a less acute patient needs to be transported to an emergency department. A possible change in the care chain could be to transport less acute patients to a nearby health center instead of an emergency room - a so-called alternate route of care. This could result in both shorter transport times in sparsely populated areas (which in turn can have an impact on the availability of the ambulance) and give ambulance staff the opportunity to choose an intermediate step between leaving a patient at home and transporting it to an emergency department. To investigate the impact that an alternate route of care can have on the aspects of time and accessibility for ambulances, a discrete event-driven simulation model was developed. This model has been used in a scenario study to investigate how an alternate route of care can affect ambulances and patients in sparsely populated areas. Data from SOS Alarm and Region Skåne have made it possible to generate input data that better corresponds to reality. The results of the scenario study indicate that an alternate route of care can improve the accessibility of an ambulance in sparsely populated areas by shortening the transport times to the receiving care institution.

Studien presenterar hur Södra Wood kan applicera diskret händelsestyrd simulering (DES) genom modeller på sågverk för att bland annat öka produktionsvolym, förkorta ledtider och minska lagernivåer. Med hjälp av digitala verktyg som FACTS Analyzer simulerades önskade förändringar på produktionsflödet och även andra organisationella förändringar. Utfallet av de simulerade förändringarna resulterade i flertalet positiva slutsatser som kunde presenteras och även visualiseras. Bevisligen kan simuleringar användas som grund till diverse besulttaganden och vidare även till Proof-Of-Concept trots att aggregerade modeller används. Det finns dock mycket utrymme kvar till vidareutveckling av denna typ av arbeten där värdeflödet i industrier av denna domän kan gynnas väsentligt.

The optimization of production has come a long way in the last few years. From having to implement new production philosophies directly into the production, today you can simply build a simulation on the computer that can be used to test new solutions. This makes it cheaper and less time-consuming to improve production. This report will describe the thesis work made by two students from Lulea University of Technology studying mechanical engineering with orientation production technology. The thesis work was made at Boliden MineralsAB during the spring term of 2021. This master thesis aim is to look at the potential of using discrete-event simulation as a tool to test different production philosophies. To do this, a simulation model is built to represent Boliden’s mining operation. The focus will be on the Cut and fill process, and how vehicles and operators are dispatched. From interviews, videos and information gave by Boliden a current state analysis was done to get a good understanding of the situation and how the process works. This combined with a litterateur study a good foundation was made to start building the simulation. Since this is the first time Boliden uses simulation on the cut and fill process in this manner, there’s been close contact with Boliden to validate and verify the models. The different production scenarios that were simulated were selected with the guidance of Boliden to look at the most relevant areas for them. Firstly, a base model was constructed, this model had a number of restrictions compared to the real-life process. With data from previous work that Boliden had with simulation models, the base model could be controlled that it worked properly. From this model others, models could be build-up, with the difference of using another production control philosophy for the simulation. By using these philosophies there could be determined an increase by 1% in productivity when prioritizing operators to the bottleneck of the process to maximize utilization.

Vor dem Hintergrund demographischer Entwicklungen, der zunehmenden Nutzung von Informationstechnologien in unserem Alltag (Stichwort „Digitales Leben“) und einem begrenzten Maß natürlicher Ressourcen ist die Wissenschaft zunehmend gefordert, das Verhältnis aus Informationstechnologie, menschlichem Verhalten und unserer Umwelt neu zu hinterfragen. Gegenstand des Dissertationsvorhabens ist daher die Untersuchung von Informationssystemen im Hinblick auf deren ökologische Nachhaltigkeit. Dabei zeigt sich auf der einen Seite, dass Informationssysteme aufgrund der genutzten physischen IT-Infrastruktur (PCs, Server, Mobiltelefone etc.) als Ursache von Umweltproblematiken in Erscheinung treten können. Neben dem Stromverbrauch bei der Nutzung von IT steht dabei vor allem der Verbrauch seltener Metalle wie Gold, Palladium und Tantal sowie das Problem der Entsorgung von Altgeräten im Fokus. Auf der anderen Seite werden Informationssysteme zunehmend auch als Mittel zur Lösung von Umweltproblematiken gesehen. So können Informationssysteme dazu beitragen, Geschäftsprozesse effizienter und damit umweltfreundlicher zu gestalten, Konsumenten von Produkten und Dienstleistungen sowie Entscheider im Unternehmen für Umweltprobleme zu sensibilisieren oder neue umweltfreundliche Produktinnovationen zu unterstützen. Zur Untersuchung des Themenkomplexes werden etablierte Ansätze zur Untersuchung physischer Systeme auf Informationssysteme übertragen. Zum einen werden Methoden und Softwaretools aus dem Bereich ereignisdiskreter Simulationen (Materialflusssimulationen, Simulation von Supply Chains, Produktionsabläufen etc.) genutzt. Ereignisdiskrete Simulationen erlauben es, die Auswirkungen von Informationssystemen auf ein physisches System (z. B. eine Fabrik oder ein öffentliches Transportsystem) realitätsnah in einem Simulationsmodell abzubilden. Hierdurch ist es möglich eine Verbindung zwischen virtuellen Informationen und physischen Prozessen (z. B. Entstehung von CO2-Emission) herzustellen. Zum anderen werden Methoden und Softwaretools aus dem Bereich Ökobilanzierung (engl. Life Cycle Assessment) eingesetzt, um die ökologischen Auswirkungen von Informationssystemen messbar zu machen. Dabei wird der Einfluss physischer Prozesse, die durch Informationssysteme beeinflusst werden, auf ein ökologisches System (z. B. das Klima) abgeschätzt.

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This master thesis is the last part of the master program Production Engineering and Management at the Royal Institute of Technology, KTH, in Stockholm. The thesis is conducted at Exeger Operations AB, in short Exeger. The company is in an expansion phase and wants to prepare for future production expansion. Thus, a simulation capability to test future production scenarios was desirable. The problem definition was defined by the company together with the authors and led to a literature study within simulation, TPS and Lean manufacturing. Following the literature study, a current state map was produced to achieve sufficient understanding of the production flow at the company. A simulation model was then built. The model was used to test three different ”what-if” scenarios. Buy or Optimize, Future ratio 3:1:1 and Buy or SMED. The authors’ findings in the Buy or Optimize scenario suggest that optimizing the process time in the printers is far better, from multiple perspectives, than investing in new machinery. A 3:1:1 ratio of printers, sinter 1 and assembly station was developed using the simulation model to achieve leveled production flow of these specific processes. Lastly, conducting a SMED on the sinter 1 machine, the setup-,and wait-times achieved a theoretical reduction up to 75 % by altering the SOP and allocating additional preparatory space, in accordance with Lean philosophy. This change would offer the same improvement to a full-scale production as investing in a new sinter 1 according to the simulation model. Future work may consist of Layout Planning and adopting the simulation model to new prerequisites.

The case study has been carried out at SSAB Oxelösund, where a major project is on the way to improve the system support for substance planning, to ensure that the right products are actually produced. Purpose: The purpose of this thesis is to analyze inventory control in intermediate storage within steel industry with data-driven methods and simulation. Where the thesis aims to identify the causes and improvement opportunities of the missing products at the intermediate storage. Method: This study consisted of quantitative research with a deductive approach. Which was done by analyzing the forecast accuracy and erroneous product at rolling, and study how changes in safety stock and batch sizes affect the production with help of discrete event simulation. All analysis was done on secondary data provided by SSAB. Results: Few product groups had high percentual error and absolute error. About one percent of products at rolling had wrong product type. Lastly, the study found that larger batches resulted in less orders being missed. The changes of safety stocks did not have any significant impact on the simulation, due to possible errors under simulation modeling.  Conclusion: Depending on the actual production in other steel industries, the contribution of this thesis only applies to similar production. Suggestions for future research should be to improve the simulation and apply other inventory control methods. In addition, to try other forecasting methods to improve the demand forecasts and try to find a root of the problem for wrong production.

[pt] O presente estudo tem como objetivo o uso de simulação de eventos discretos para avaliar cenários e propor melhorias no processo de formação de carga para embarque marítimo de um derivado de petróleo. Foram simulados cenários com alterações em três variáveis, de modo a observar o impacto na produção anual: capacidade de armazenamento da refinaria, vazão de produção e tamanho do lote de embarque. A criticidade do processo está relacionada à produção ser interrompida por falta de espaço para armazenamento do produto, ao transporte intermodal nos elos da cadeia, à janela de carregamento rodoviário e à existência de incertezas e restrições inerentes às operações de produção, manuseio, armazenamento e transporte. Uma importante conclusão do estudo é que trabalhar com menor lote para embarque marítimo resulta em maior produção anual do derivado, ou seja, tem-se uma estratégia que não envolve nenhuma alteração nos processos ou na infraestrutura. Outros fatores que contribuíram para o aumento da produção anual foram a adição de um tanque na refinaria e o aumento da vazão de produção. As análises conduzidas no estudo são importantes insumos para a tomada de decisão referente ao gerenciamento dos estoques da refinaria e da cadeia de suprimentos. A técnica da simulação permitiu analisar diversos cenários sem a necessidade de implementá-los, mostrando-se, portanto, uma ferramenta eficaz com grande adição de valor ao estudo e à prática da organização. / [en] The present study aims to use discrete event simulation to evaluate scenarios and propose improvements in the batch formation process for the marine shipment of an oil product. Scenarios with changes in three variables will be simulated in order to observe the impact on annual production: storage capacity of the refinery, production flow rate and size of the shipment batch. The process is critical because of the fact that production is interrupted due to the lack of space for product storage, the intermodal transportation through the echelons in the chain, the loading window for the road modal and the existence of uncertainties and restrictions inherent to production, handling, storage and transportation operations. The study led to the conclusion that shipping a smaller batch results in a higher annual production, which is a strategy that does not involve any changes in processes or infrastructure. Other factors that contributed to the increase in annual production were the addition of a tank at the refinery and the increase in production flow rate. The analyzes conducted in the study are important inputs for decision making regarding the management of refinery and supply chain inventory. The simulation technique allowed the analysis of several scenarios without the need to implement them and is, therefore, an effective tool with great added value to the study and practice of the organization

Parallelizing the development cycles of hardware and software is becoming the industry’s norm for reducing time to market for electronic devices. In the absence of hardware, software development is based on a virtual platform; a fully functional software model of a system under development, able to execute unmodified code. A Transaction Level Model, expressed with the SystemC TLM 2.0 language, is one of the many possible ways for constructing a virtual platform. Under SystemC’s simulation engine, hardware and software is being co-simulated. However, the sequential nature of the reference implementation of the SystemC’s simulation kernel, is a limiting factor. Poor simulation performance often constrains the scope and depth of the design decisions that can be evaluated. It is the main objective of this thesis’ project to demonstrate the feasibility of parallelizing the co-simulation of hardware and software using Transaction Level Models, outside SystemC’s reference simulation environment. The major obstacle identified is the preservation of causal relations between simulation events. The solution is obtained by using the process synchronization mechanism known as the Chandy/Misra/Bryantt algorithm. To demonstrate our approach and evaluate under which conditions a speedup can be achieved, we use the model of a cache-coherent, symmetric multiprocessor executing a synthetic application. Two versions of the model are used for the comparison; the parallel version, based on the Message Passing Interface 3.0, which incorporates the synchronization algorithm and an equivalent sequential model based on SystemC TLM 2.0. Our results indicate that by adjusting the parameters of the synthetic application, a certain threshold is reached, above which a significant speedup against the sequential SystemC simulation is observed. Although performed manually, the transformation of a SystemC TLM 2.0 model into a parallel MPI application is deemed feasible.