The simulation of power system behavior, especially transient behavior, helps us in the analysis and planning of various power systems. However, power systems are usually highly complex and geographically distributed. Therefore system partitioning can be used to allow for sharing resources in simulation. In this work, distributed simulations of power system models have been developed using an electromagnetic transient simulator, namely Real Time Digital Simulator (RTDS). The goal is to demonstrate and assess the feasibility of both non-real-time and real-time simulations using the RTDS in a geographically distributed scenario. Different protocols and options used in the communication between power systems have been studied and analyzed. In this work, a test bed has been developed for data transfer between a power system simulated in RTDS at Mississippi State University and the power system simulated in RTDS at Texas A&M University. Different protocols, available for the interface and communication in the RTDS, have been studied and applied in this work. Finally, a locally distributed wide area control test bed was developed and simulated.

Simulation provides the ability to obtain results from, and analyse, a system without physically building the system. These results can be used to inform the actual construction of the physical system, how best to use a system, how best to integrate a system with another system, and so on. A simulation can also be used to train and educate the end-users of a system either before the system is actually produced or when the availability of the actual system is limited. Most end systems are in some way composed of subsystems. The subsystems themselves may be composed of subsystems. This type of architecture is generically referred to as a system of systems. For example, a ship is composed of a hull, engines, sensors, etc. The engine system may be composed of the fuel and cooling subsystems, for example. Systems constructed this way have numerous benefits including allowing subsystems to be built independently of each other (after creating well defined interfaces), and allowing for subsystems to be replaced without affecting other subsystems. These same benefits are desirable in the construction of a simulation of a system. One simulation framework that supports these ideals is the High Level Architecture (HLA). The HLA is an international modelling and simulation framework that specifically provides for distributed simulation. The HLA uses the term federate for component simulations that are then brought together in a distributed computing environment to form a federation. The HLA defines a data model for documenting the data interfaces of the federates and the application programming interface used by the federates to communicate data. A simulation of a systems of systems architecture can be implemented in the HLA by creating federates for each subsystem and defining the data communicated between subsystems in terms of HLA’s data model. HLA’s default communication model defines publishers and subscribers of data classes. The HLA provides class based filtering, i.e., a federate only receives data for a data class to which it has subscribed. However, HLA’s default communication model has no notion of direct ‘wiring’ between federates. Thus, it is not possible to have data sent to a specific federate. This creates a problem if multiple instances of a system of systems are simulated concurrently, which may be desirable so as to observe the interactions between systems. In this case, the data sent within one system is exposed to all other systems in the simulation. This thesis explores this problem of simulating multiple systems of systems using the HLA. The problem is stated formally by introducing the concept of a message path and showing that a federation containing multiple systems of systems contains incorrect message paths which communicate intra-system data between systems. Three methods are presented and shown to solve the problem by either eliminating the incorrect message paths or allowing a receiving federate to determine whether intra-system data was delivered via an incorrect message path. The three solutions are Local Data Filtering (LDF), Data Distribution Management (DDM), and Federation Communities (FC). The LDF solution marks all intra-system data with a system identifier, allowing receivers to distinguish whether they should process it. The DDM method uses a service defined by the HLA that essentially provides an automated version of the LDF solution. The FC method restricts one federation to simulating one system and requires a multiple system simulation to enable inter-federation communication, something that is not defined in the HLA. These three methods are analysed both quantitatively and qualitatively. The quantitative analysis looks at performance overhead imposed by each method and how well each method reduces the number of incorrect intra-system messages communicated. The qualitative analysis is presented in terms of identifying the complexity of implementing each method for a specific systems of systems federation: the election process for the Australian federal government. The thesis concludes that the LDF method is simple to understand but potentially finicky to implement and is wasteful of network resources. The DDMmethod is advantageous in that it is a service defined by the HLA standard. However, the implementation of the DDM services by a Runtime Infrastructure (RTI) is not defined by the HLA. Thus, the performance of the DDMmethod is coupled to a specific RTI and its configurability. The FC method achieves an ideal of replicating the simulation of a single system without modification to achieve a multisystem simulation. However, it requires and inter-federation communicationmechanism that is not defined by the HLA. The FC method introduces extra latency and reduced throughput to inter-system messages in a Local Area Network (LAN) environment. / Thesis (Ph.D.) -- University of Adelaide, School of Computer Science, 2009

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This dissertation investigates the High Level Architecture (HLA) as a possible distributed simulation framework for transportation systems. The HLA is an object-oriented approach to distributed simulations developed by the Department of Defense (DoD) to handle the issues of reuse and interoperability of simulations. The research objectives are as follows: (1) determine the feasibility of making existing traffic management simulation environments HLA compliant; (2) evaluate the usability of existing HLA support software in the transportation arena; (3) determine the usability of methods developed by the military to test for HLA compliance on traffic simulation models; and (4) examine the possibility of using the HLA to create Internet-based virtual environments for transportation research. These objectives were achieved in part via the development of a distributed simulation environment using the HLA. Two independent traffic simulation models (federates) comprised the environment (federation). A CORSIM federate models a freeway feeder road with an on-ramp while an Arena federate models a tollbooth exchange.

Simulation enables preliminary testing of products that may otherwise be dicult, ex-pensive, or dangerous to test physically. Unfortunately, intellectual property concernscan make it dicult or impossible to share the human-readable simulation models toend-users. In fact, there can even be diculties with sharing executables because ofthe possibility for reverse-engineering. This presents a problem when simulating if themodel relies on components for which the source code or executable is not available,such as proprietary components developed by another party. This thesis investigateswhether it is possible to enable a set of networked peers to all take part in computingthe same simulation without any of them having access to the entire model. One way tosolve this problem is to let each system that holds a model of a component to computeits part of the simulation for a single timestep and to share the new state through peer-to-peer connections with the other systems, once a response has been received fromall other peers, the local simulation can advance one timestep and the process can berepeated. But running a simulation over a network can make it signicantly slower,since local operations on the CPU and memory are much faster than operations overa network, and the peers will be spending most of their time waiting for each other asa result. To avoid such delays, each peer maintains expected values for variables thatare not in the local model, and updates are sent only when a local variable changes.These updates are stamped with the local simulation-time, thus allowing the recipientpeers to know when the update is required in the simulations future, or to when itshould be retroactively applied in the simulations past. Using this technique, the peerscan compute their respective local models under the assumption that the variablesthat the other peers control are unchanged. Thus the peers can advance any numberof timesteps without needing to stop and wait for other peers. These techniques willlikely result in wasted work if one or more peers are advancing their simulation timeslower than the others, when this happens, the peers have the ability to re-distributethe workload on the y by transferring control over models. This also makes it possibleto accommodate for systems joining or leaving the simulation while it is running.In this thesis we show that co-simulating in this fashion is a workable option to tra-ditional simulation when the local models are incomplete, but that the performanceis very dependent on the models being simulated. Especially the relation between thefrequency of required synchronizations, and the time to compute a timestep. In ourexperiments with fairly basic models, the performance ratio, compared to traditionalsimulation, ranged between less than one percent of that of traditional simulation, upto roughly 70%. But with slower models always having a better ratio.

This dissertation investigates the High Level Architecture (HLA) as a possible distributed simulation framework for transportation systems. The HLA is an object-oriented approach to distributed simulations developed by the Department of Defense (DoD) to handle the issues of reuse and interoperability of simulations. The research objectives are as follows: (1) determine the feasibility of making existing traffic management simulation environments HLA compliant; (2) evaluate the usability of existing HLA support software in the transportation arena; (3) determine the usability of methods developed by the military to test for HLA compliance on traffic simulation models; and (4) examine the possibility of using the HLA to create Internet-based virtual environments for transportation research. These objectives were achieved in part via the development of a distributed simulation environment using the HLA. Two independent traffic simulation models (federates) comprised the environment (federation). A CORSIM federate models a freeway feeder road with an on-ramp while an Arena federate models a tollbooth exchange.

Simulation of power system behavior is a highly useful tool for planning, analysis of stability, and operator training. Traditionally, small power system studies are dominated by the time taken to solve the machine dynamics equations, while larger studies are dominated by the time taken to solve the network equations. With the trend towards more sophisticated and realistic modeling, the size and complexity of simulations of a power system grow tremendously. The ever-increasing need for computational power can be satisfied by the application of distributed simulation. Also power systems are distributed in nature. The terrestrial power systems are divided into groups and controlled by different Regional Transmission Organization (RTO). Each RTO owns the detailed parameter for the area under control, but only limited data and boundary measurement of the external network. Thus, performing power system analysis in such case is a challenge. Also, simulating a large-scale power system with detailed modeling of the components causes a heavy computational burden. One possible way of relieving this problem is to decouple the network into subsystems and solve the subsystem respectively, and then combine the results of the subsystems to get the solution. The way to decouple a network and represent the missing part will affect the result greatly. Also, due to information distribution in the dispatch centers, a problem of doing power system analysis with limited data available arises. The equivalents for other networks need to be constructed to analyze power system. In this research work, a distributed simulation algorithm is proposed to handle the issues above. A history of distributed simulation is briefly introduced. A generalized coupling method dealing with natural coupling is proposed. Distributed simulation models are developed and demonstrated in Virtual Test Bed (VTB). The models are tested with different network configurations. The test results are presented and analyzed. The performance of the distributed simulation is compared with the steady state result and time domain simulation result. Satisfactory results are achieved.

The traditions of real-time and embedded system engineering have evolved into a new field of cyber-physical systems (CPSs). The increase in complexity of CPS components and the multi-domain engineering composition of CPSs challenge the current best practices in design and simulation. To address the challenges of CPS simulation, this work introduces a simulator coordination method drawing from strengths of the field of parallel and distributed simulation (PADS), yet offering benefits aimed towards the challenges of coordinating CPS engineering design simulators. The method offers the novel concept of Interpolated Event data types applied to Kahn Process Networks in order to provide simulator coordination. This can enable conservative and optimistic coordination of multiple heterogeneous and homogeneous simulators, but provide important benefits for CPS simulation, such as the opportunity to reduce functional requirements for simulator interfacing compared to existing solutions. The method is analyzed in theoretical properties and instantiated in software tools SimConnect and SimTalk. Finally, an experimental study applies the method and tools to accelerate Spice circuit simulation with tradeoffs in speed versus accuracy, and demonstrates the coordination of three heterogeneous simulators for a CPS simulation with increasing component model refinement and realism. / text

Distributed simulation over Cloud environment is still a new subject. Cloud computing is expected to bring new benefits to conventional distributed simulation, including elasticity on computation resource, cost saving on investment and convenience on service accessibility. A few researches have been done on applying Cloud computing on distributed simulation. However, there are various drawbacks and limitations on those works. Lack of interoperability across Cloud platforms is one of critical drawbacks among them. It can greatly limit the usability and flexibility of distributed simulation over Cloud environment. Based on the investigation on Cloud computing and existing distributed simulation systems over Cloud environment, a novel interoperable HLA-based (High Level Architecture) simulation system over a Cloud environment, ISSC (Interoperable Simulation System over a Cloud Environment), is proposed in this thesis. ISSC aims to address the interoperability issue of simulation system across various Cloud platforms. It employs OCCI and a set of technologies, including Ruby on Rails, OpenVPN and RESTful web services, to build the interoperability across Cloud platforms. It adopts a distributed architecture to construct flexibility and expansibility of the system. The prototype and related experiments performed provides an excellent demonstration that ISSC is a reliable and effective solution on interoperable simulation system over a diverse Cloud environment.

The domain of distributed simulation is growing rapidly. This growth leads to larger and more complex supporting network architectures with high requirements on availability and reliability. For this purpose, efficient fault-monitoring is required. This work is an attempt to evaluate the viability of an Active probing approach in a distributed simulation system in a wide area network setting. In addition, some effort was directed towards building the probing-software with future extensions in mind. The Active probing approach was implemented and tested against certain performance requirements in a simulated environment. It was concluded that the approach is viable for detecting the health of the network components. However, additional research is required to draw a conclusion about the viability in more complicated scenarios that depend on more than the responsiveness of the nodes. The extensibility of the implemented software was evaluated with the QMOOD-metric and not deemed particularly extensible.