Johanna M. Leigh

Use of Petri Nets to Model the Maintenance of Wind Turbines

With large expansion plans for the offshore wind turbine industry, there has never been a greater need for effective operations and maintenance. The two main problems with the current operations and maintenance of an offshore wind turbine are the cost and availability. In this work, a simulation model has been produced of the maintenance process for a wind turbine with the aim of developing a procedure that can be used to optimise the process. This initial model considers three types of maintenance—periodic, conditional and corrective—and also considers the weather in order to determine the accessibility of the turbine. Petri nets have been designed to simulate each type of maintenance and weather conditions. It has been found that Petri nets are a very good method to model the maintenance process because of their dynamic modelling and adaptability and their ability to test optimisation techniques. Because of their versatility, Petri net models are developed for both system hardware and the maintenance processes, and these are combined in an efficient and concise manner. Copyright

Police Officer Dynamic Positioning for Incident Response and Community Presence - Using Maximum Demand Coverage and Kernel Density Estimation to Plan Patrols

Police Forces are under a constant struggle to provide the best service possible with limited and decreasing resources. One area where service cannot be compromised is incident response. Resources which are assigned to incident response must provide attendance to the scene of an incident in a timely manner to protect the public . To ensure the possible demand is met maximum coverage location planning can be used so response officers are located in the most effective position for incident response. This is not the only concern of response officer positioning. Location planning must also consider targeting high crime areas, hotspots, as an officer presence in these areas can reduce crime levels and hence reduce future demand on the response officers. In this work hotspots are found using quadratic kernel density estimation with historical crime data. These are then used to produce optimal dynamic patrol routes for response officers to follow. Dynamic patrol routes result in reduced response times and reduced crime levels in hotspot areas resulting in a lower demand on response officers.

Optimising police dispatch for incident response in real time

Abstract It is crucial that police forces operate in a cost efficient manner and, in the case of incident response, that the most efficient resources are allocated. The current procedure is that police response units are allocated manually by a dispatcher using a resource list and mapping software. The efficiency of this process can be improved by the use of integrated mathematical approaches embedded within an automatic framework, yielding the optimal selection framework developed in this paper. The framework combines mapping and routing algorithms, and a decision process to facilitate optimal officer selection for incident response. The decision process considers information such as quickest response time, predicted traffic conditions, driving qualifications, response unit availability and demand coverage. The selection framework has been tested and validated through simulation and has shown to increase the efficiency of response units through reduced response times, increased response unit availability, and greater demand coverage.

Modelling manufacturing processes using Markov chains

Optimizing manufacturing processes with inaccurate models of the process will lead to unre-liable results. This can be true when there is a strong human influence on the manufacturing process and many variable aspects. This study investigates modelling a manufacturing process influenced by human inter-action with very variable products being processed. To develop a more accurate process model for such pro-cesses radio frequency identification (RFID) tags can be used to track products through the process. The tags record information for each product and this data can be used to produce more accurate models of the manu-facturing process. The data produced has been used to create a Markov chain model. This model is used to predict future product paths for use in discrete event simulation. In this case an IT refurbishment company is used as a case study. RFID tags have been utilized to track the IT products moving through the refurbishment process and this information has been used to produce a Markov chain model.

Reliability modelling using Petri-Net simulation of polymer electrolyte membrane fuel cell degradation in automotive applications

Climate change concerns have increased in recent years, and technologies to reduce emissions from the transport industry have been put forward. Hydrogen fuel cells have the potential to mitigate emissions concerns as they only produce water vapor as an emission. However, their commercialization has been hindered due to reliability and lifetime concerns. They need to meet strict targets of 5000 hours of operation (equivalent to 150,000 miles), and currently struggle to do so. Reliability analysis of fuel cells can ascertain key information as to the reduction of current lifetimes due to degradation. Failure mode and effect analysis, and fault tree analysis was performed for a Polymer Electrolyte Membrane Fuel Cell (PEMFC) revealing interactions and relationships between failure modes which makes the use of FTA in this case unfeasible. Petri-Net simulation techniques have been pursued to alleviate these concerns and to develop an accurate degradation model of a PEMFC in an automotive context. The Petri-Net model is integrated into a PEMFC performance model for the purpose of incorporating key variables into each model. For example; membrane thickness is an input into the performance model, and this can be modified by the Petri-Net degradation model based upon failure modes such as radical attack of the membrane (which thins the membrane). Thus, outputs from the degradation relationships in the Petri-Net model directly feed into the running of the performance model. This work furthers the research in PEMFC reliability by providing an accurate degradation model of a PEMFC based upon Petri-Net simulation of interactions and relationships between failure modes. Integration of relationship concerns with a verified performance model of a PEMFC is invaluable to increase the accuracy of PEMFC degradation research. Future work will include PEMFC stack experimentation to fill holes in the literature regarding failure mode failure rates that are fed into the model.

Police Response Officer Selection - Development of Tool to Aid the Dispatch of Police Response Officers

It’s essential the Police force use their resources to the highest possible efficiency to ensure adequate service in the face of major funding cuts. Automation of the response officer selection process can improve efficiency by assisting in selecting the most appropriate response officer to attend an incident. Currently dispatchers are tasked with selecting the appropriate response officers to send to incidents. Often these dispatchers ask response officers who can attend rather than making an informed decision. This may not result in the most efficient officer being selected to attend an incident. Providing a software tool to assist in the decision making process will decrease uncertainty in the decision and hence increase the likelihood of the most efficient officer being selected to attend an incident. The selection considers response time, availability, area coverage, driving standard and traffic conditions. The tool incorporates mapping, routing and decision making.