This paper shows that, provided circuits contain no zero-delay loops, a tight relationship, full abstraction, exists between a natural event-based operational semantics for circuits and a natural denotational semantics for circuits based on causal functions on value timelines. The paper also discusses what goes wrong if zero-delay loops are allowed, and illustrates the application of this semantic relationship to modeling questions.

Due to the increasing size and complexity of software systems, software architectures have become a crucial part in development projects. A lot of effort has been put into defining formal ways for describing architecture specifications using Architecture Description Languages (ADLs). Since no common ADL today offers tools for evaluating the performance, an attempt to develop such a tool based on an event-based simulation engine has been made. Common ADLs were investigated and the work was based on the fundamentals within the field of software architectures. The tool was evaluated both in terms of correctness in predictions as well as usability to show that it actually is possible to evaluate the performance using high-level architectures as models.

Pedestrian crowd simulation explores crowd behaviors in virtual environments. It is extensively studied in many areas, such as safety and civil engineering, transportation, social science, entertainment industry and so on. As a common phenomenon in pedestrian crowds, grouping can play important roles in crowd behaviors. To achieve more realistic simulations, it is important to support group modeling in crowd behaviors. Nevertheless, group modeling is still an open and challenging problem. The influence of groups on the dynamics of crowd movement has not been incorporated into most existing crowd models because of the complexity nature of social groups. This research develops a framework for group modeling in agent-based pedestrian crowd simulations. The framework includes multiple layers that support a systematic approach for modeling social groups in pedestrian crowd simulations. These layers include a simulation engine layer that provides efficient simulation engines to simulate the crowd model; a behavior-based agent modeling layers that supports developing agent models using the developed BehaviorSim simulation software; a group modeling layer that provides a well-defined way to model inter-group relationships and intra-group connections among pedestrian agents in a crowd; and finally a context modeling layer that allows users to incorporate various social and psychological models into the study of social groups in pedestrian crowd. Each layer utilizes the layer below it to fulfill its functionality, and together these layers provide an integrated framework for supporting group modeling in pedestrian crowd simulations. To our knowledge this work is the first one to focus on a systematic group modeling approach for pedestrian crowd simulations. This systematic modeling approach allows users to create social group simulation models in a well-defined way for studying the effect of social and psychological factors on crowd’s grouping behavior. To demonstrate the capability of the group modeling framework, we developed an application of dynamic grouping for pedestrian crowd simulations.

Traffic simulation is a safe and efficient tool to investigate infrastructural changes as well as traffic conditions. This master thesis aims to analyse a microscopic traffic simulation method for evaluation of bus terminal capacity. The evaluation is performed by investigating a case study of the bus terminal at Norrköping travel centre. The analysed method, referred to as terminal logic in the thesis, uses a combination of time based and event based simulation. Through the combination of time and event, it is possible to capture all movements within the terminal for individual vehicles. The simulation model is built in the software Vissim. A new travel centre for Norrköping is under development. Among the reasons for a new travel centre is the railway project Ostlänken in the eastern part of Sweden. An evaluation of the bus terminal is interesting due to a suspicion of overcapacity and the opportunity of redesigning. To investigate both the terminal capacity and the terminal logic, three scenarios were implemented. Scenario 1: Current design and frequency Scenario 2: Current design with higher frequency Scenario 3: Decreased number of bus stops with current frequency The results from the scenarios confirm the assumption of overcapacity. The capacity was evaluated based on several different measures, all indicating a low utilization. Even so, the utilization was uneven over time and congestion could still occur when several buses departed at the same time. This was also seen when studying the simulation, which showed congestions when several buses departed at the same time. The case study established the terminal logic to be useful when evaluating capacity at bus terminals. It provides a good understanding of how the terminal operates and captures the movements. However, it was time-consuming to adjust the logic to the studied terminal. This is a disadvantage when investigating more than one alternative. The thesis resulted in two main conclusions. Firstly, a more optimised planning of the buses at Norrköping bus terminal would probably be achievable and lead to less congestions at the exits. Secondly, the terminal logic is a good method to use when evaluating bus terminals but it is not straight forward to implement.

Different paths for trains throughout a railway system are more or less convenient, where intersecting train paths require a safety margin in time between different trains to reduce the risks of accidents. Intersecting train paths are just as much of a challenge on a railway station, especially when multiple trains are entering the station close in time. Some trains might have to wait before entering the station area, which as a result create delays that can affect other trains and passengers. One method of reducing the delay is by allocating trains efficiently to different platforms on the station, which makes it possible for more trains to be at the station at the same time. The purpose of this report was to investigate the effect of different platform allocation strategies in regard to the punctuality of trains, passengers’ convenience, travel time in the system as well as the delay compared to arrival and departure times. Three research questions were formulated to answer to the purpose, which included how a reduction in platforms affect the railway system, how different strategies affect walking time for passengers and whether it was possible to prioritize different train types to different platforms. To investigate how different platform allocation strategies affect the railway system, simulation as a method was used. With simulation, a model could be constructed similar to the real system, which made it possible to perform different experiments quickly without any impact on the real system. Linköping Central Station was chosen as a test case as it was both reasonably large and geographically close for observations. Four experiments were constructed, with four separate platform allocation strategies, all aimed to answer some part of the purpose. Before conducting the experiments, a base scenario was tested that attempted to mimic the current platforming strategy as much as possible and was used to compare the different experiments to. This thesis demonstrates that several different platform allocation strategies are possible to be used in the test case, where a risk of train delays were present when the number of tracks used were decreased. With the help of the experiments, the three research questions and therefore the purpose of the study have been answered. / <p>Examensarbetet är utfört vid Institutionen för teknik och naturvetenskap (ITN) vid Tekniska fakulteten, Linköpings universitet</p>