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Calibri 83ffff̙̙3f3fff3f3f33333f33333.LTU Delft Repositoryg z7uuidrepository linktitleauthorcontributorpublication yearabstract
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departmentresearch group programmeprojectcoordinates)uuid:1f228e88c7e7431d96afdf1abb195eddDhttp://resolver.tudelft.nl/uuid:1f228e88c7e7431d96afdf1abb195eddMaintenance Optimization of Tidal Energy Arrays: Design of a Probabilistic Decision Support Tool for Optimizing the Maintenance PolicyDe Nie, R.C.kWolfert, A.R.M. (mentor); Jarquin Laguna, A. (mentor); Leontaris, G. (mentor); Hoogendoorn, C.F.D. (mentor)The increasing demand for electricity offers many opportunities for renewable energy production, of which one alternative is tidal stream energy. Several feasibility studies have shown that the global tidal stream energy potential can contribute significantly to producing renewable energy. This tidal energy can mostly be produced at the 'tidal hotspots', where the kinetic energy density is very high due to fast flowing tidal currents. However, the tidal technology is not yet cost competitive in comparison with other renewables, such as photovoltaic and wind energy, which is why further cost reductions and efficiency improvements are to be achieved. Interviews with existing tidal system developers provided insight in the cost breakdown and showed that maintenance accounts for a significant share of the total project costs. This is due to the harsh environmental conditions that impose a large uncertainty, which increase the complexity of selecting an optimal maintenance policy. Damen Shipyards has shown interest in entering the tidal industry and is exploring the cost reduction possibilities by developing their own tidal system. This thesis contributes to Damen Shipyards' research by performing a time series analysis of a tidal hotspot to identify and model the multivariate dependence of the governing environmental phenomena. A probabilistic decision support tool is developed for selecting the optimal maintenance policy. The decision support tool primarily determines when and to what extent corrective maintenance should be performed. The corresponding overall maintenance costs are also calculated and secondary information regarding the activity duration is given. By means of the probabilistic approach, which captures the weather window uncertainty due to the environmental randomness, the results can be interpreted by the user based on the desired confidence level. In this research the weather window uncertainty is implemented by simulating a large number of random, but statistically identical environmental time series, which are based on available measurement data of the tidal field at EMEC, located at the Orkney Islands in the United Kingdom. The multivariate dependence between the significant wave height, wave peak period, wind velocity and current velocity is identified in the measurement set and fully represented in the generated time series by means of a paircopula construction simulation. The necessity for having time independence cannot be met in the original dataset, which is why a new simulation approach is developed. This method consists of a sequential simulation of paircopula constructions to include both the time dependence and multivariate dependence in the synthetic time series. Simulation of the set of synthetic time series showed to be more effective for describing uncertainty with respect to exclusively using the original dataset, due to the possibility of including more environmental realizations. The tidal array is represented as a semiMarkov decision process, which captures all costs and transition processes related to the deterioration and maintenance decisions. A policy optimization algorithm can then be used to find the optimal set of decisions and the corresponding maintenance cost rate which includes both the direct and indirect maintenance costs. The novel tidal system design of Damen Shipyards is then plugged into the decision support tool to determine the optimal m< aintenance policy and maintenance costs. The effect of different levels of detail for representing the tidal system have been compared and the benefits in terms of cost reductions of using this decision support tool with respect to less advanced approaches have been highlighted. Furthermore, multiple scenarios have been elaborated to identify the sensitivities in the cases of accounting for unreliability in the failure rates, varying the number of platforms in the array and including the economic fluctuations of the maintenance vessel day rates.probabilistic; tidal energy; maintenance policy; optimization; semiMarkov decision process; copula, multivariate dependence; decision support toolen
master thesis
20211216.Mechanical, Maritime and Materials EngineeringOffshore & Dredging Engineering)uuid:cc25fc3120ac46e09173b8e53ebef400Dhttp://resolver.tudelft.nl/uuid:cc25fc3120ac46e09173b8e53ebef400\Optimization of the operational use of entrance channels based on channel depth requirementsDobrochinski, J.P.H.CVellinga, T. (mentor); De Jong, M. (mentor); Groeneweg, J. (mentor)Y
Large capital and maintenance dredging operations are required to ensure the accessibility of many ports. The expenses associated with the dredging operations can have a significant impact on the finances of these ports. Therefore, considerable attention to the design of the width and depth aspects of access channels is justifiable. This study considered this topic within the framework of an Additional Master Thesis (3month internship). The objectives of the study are: i) to verify the influence of different processes and sources of uncertainties in the evaluation of minimum depth requirements; and ii) to investigate the advantages and drawbacks of different methods of depth requirement evaluation. The Port of Tubaro (Southeast Brazil) is used as a case study to verify processes and methods. Four different approaches were considered to evaluate depth requirements for the access channel of the Port. These methods are based on either deterministic and/or probabilistic methods, and on approaches without or including wave influences. The results for the case study indicate that ship motions due to waves have a minor influence on the required channel depth at that location during most of the time. However, in certain wave conditions (not only in terms of wave height, but also wave period and wave direction relative to the manoeuvring ship) vertical ship motions become the dominant issue regarding depth requirements; consequently waves should be included in a practical evaluation over time. In probabilistic approaches more knowledge can be incorporated in the analysis, however, this requires detailed information. The deterministic approach, on the other hand, is simpler to use and gives good insight about the main driving variables. Although, the main drawback of deterministic methods is that the reliability of the evaluation cannot be accessed, or that conservative assumptions need to be made. This may be uneconomical. The use of a probabilistic method for the case study led to a more optimized use of the channel in terms of accessibility in comparison to the results obtained with the deterministic method. Nevertheless, those results depend largely on the safety factors assumed in the deterministic computations relative to the probability distributions considered in the deterministic approach. Alternatively, the safety margins can be computed or calibrated for specific cases based on probabilistic calculations. In that case the results of deterministic and probabilistic methods can be similar, ensuring the required reliability of the practical deterministic approach, but not being excessively restrictive.?depth requirements; access channel; probabilistic; optimization!Civil Engineering and GeosciencesHydraulic EngineeringPorts and Waterways)uuid:519b5492935649148391c39614a2567dDhttp://resolver.tudelft.nl/uuid:519b5492935649148391c39614a2567d:Cost optimal river dike design using probabilistic methodsBischiniotis, K.RKok, M. (mentor); Jonkma<n, S.N. (mentor); Jommi, C. (mentor); Kanning, W. (mentor)nThis research follows a fully probabilistic approach in order to estimate the optimal design for a river dike crosssection, taking into account the investment costs. From the theory studied, the failure mechanisms that contribute most to the failure of river dikes are identified. These are overflowing, wave overtopping, piping and inner slope stability. The most important design variables of the dike crosssection dimensions are set and following probabilistic design methods, the probability of failure of many different dike crosssections is estimated based on the abovementioned failure mechanisms. The aim of the study is to develop a generic method that automatically estimates the failure probabilities of many river dike crosssections and gives the one with the least cost, taking into account the boundary conditions and the requirements that are set by the user.river dike; cost optimal; optimization; overflowing; piping; macroinstability; DGeoStability; matlab; crosssection; probabilistic
20140122 Water Management and engineering
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