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Banisoleiman, Kian
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Banisoleiman, Kian
Official Name
Banisoleiman, Kian
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- PublicationProbabilistic decision basis and objectives for inspection planning and optimizationMarine and offshore engineering has long been challenged with the problem of structural integrity management (SIM) for assets such as ships and offshore platforms due to the harsh marine environments, where cyclic loading and corrosion are persistent threats to structural integrity. SIM for such assets is further complicated by the very large number of welded plates and joints, for which condition surveys by inspections and structural health monitoring become a difficult and expensive task. Structural integrity of such assets is also influenced by uncertainties associated with materials, loading characteristics, fatigue degradation model and inspection method, which have to be accounted for. Therefore, managing these uncertainties and optimizing the inspection and repair activities are relevant to improvements in SIM. This paper addresses probabilistic inspection planning and optimization by comparative analysis for a typical fatigue-prone structural detail based on reliability, life cycle cost (LCC) and value of inspection information (VoI). With the objective of clarifying the differences between the theoretical basis and objectives for probabilistic inspection optimization, three maintenance strategies for the structural detail are proposed and studied. It is found that different optimal inspection times are obtained with the objectives of reliability maximization, LCC minimization and VoI maximization. Also, planned inspection and repair can help to achieve higher reliability with fewer repairs than repair without inspection (i.e. time-based replacement). If the cost of unit inspection and repair is not negligible compared with failure consequence, it is suggested to employ the optimization objective of life cycle cost minimization, which considers the costs of SIM. The paper proposes a simple approach for quantifying the VoI, based on life cycle cost analysis for the three maintenance strategies. It is concluded that the VoI is relevant to both the optimal maintenance decision with and without inspection.
145 - PublicationUncertainty quantification and calibration of a modified fracture mechanics model for reliability-based inspection planningEfficient inspection and maintenance are important means to enhance fatigue reliability of engineering structures, but they can only be achieved efficiently with the aid of accurate pre-diction of fatigue crack initiation and growth until fracture. The influence of crack initiation on fatigue life has received a significant amount of attention in the literature, although its im-pact on the inspection plan is not generally addressed. Current practice in the prediction of fatigue life is the use of S-N models at the design stage and Fracture Mechanics (FM) models in service. On the one hand, S-N models are relatively easy to apply given that they directly relate fatigue stress amplitude to number of cycles of failure, however, they are difficult to extrapolate outside the test conditions employed to define the S-N curves. On the other hand, FM models like the Paris propagation law give measurable fatigue damage accumulation in terms of crack growth and have some ability to extrapolate results outside the test conditions, but they can only be a total fatigue life model if the initial crack size was known given that they do not address the crack initiation period. Furthermore, FM models generally introduce large uncertainties in parameters that are often difficult to measure such as initial crack size, crack growth rate, threshold value for stress intensity factor range, etc. This paper proposes a modified FM model that predicts the time to failure allowing for crack initiation period. The main novelty of the modified FM model is the calibration using S-N data (i.e., inclusive of crack initiation period) for an established criterion in fatigue life and reliability level. Sources of uncertainty associated to the model are quantified in probabilistic terms. The modified FM model can then be applied to reliability-based inspection planning. An illustrative example is performed on a typical detail of ship structure, where the optimum inspection plan derived from the proposed model is compared to recommendations by existing FM models. Results demonstrate to what extent is the optimum inspection plan influenced by the crack initiation period. The modified model is shown to be a reliable tool for both fatigue design and fatigue management of inspection and maintenance intervals.
374 - PublicationFatigue Life Assessment Methods: the Case of Ship Unloaders(2016-06-30)
; ; This paper reviews methodologies for fatigue analysis with emphasis on ship unloaders. Maintaining the performance of ship unloaders at a satisfactory level is essential for any port's operation in order to comply with the global demand of shipping and trading. Ship unloaders are subject to alternating operational loadings and to adverse environmental conditions, and as a result, they show a rapid rate of deterioration that makes them susceptible to failure by cumulative damage processes such as corrosion and fatigue. The purpose of this paper is to review key features of the most common methodologies for fatigue analysis and to underline the limitations and uncertainties involved. Finally, developments in reliability-based approaches are suggested for a more accurate fatigue assessment of ship unloaders.1428 - PublicationField characterization of location-specific dynamic amplification factors towards fatigue calculations in ship unloadersThis paper highlights the impact of dynamic amplification factors in remaining fatigue life assessment of ship unloaders. In practice, the widely accepted procedure for these structures is to carry out a fatigue life assessment envisages: (1) carrying out static analysis, (2) taking into account dynamics via the application of dynamic amplification factors, and (3) applying Miner's rule. This factor, provided by the standard, is applied to the structure as a whole without considering the vibration of each structural member individually. This paper characterizes the dynamic behavior of each element using location-based dynamic amplification factors estimated from measurements. This caters for a more accurate assessment of the structure, whilst maintaining the simplicity of the standard procedure.
439Scopus© Citations 2 - PublicationReliability-based inspection planning in view of both crack initiation and propagationFatigue cracks pose threats to the integrity of welded structures and thus need to be addressed in the whole service lives of structures. In-service inspections are important means to decease the probability of failure due to uncertainties that cannot be accounted for in the design stage. To help schedule inspection actions, the decline curve of reliability index with time needs to be known. A predictive tool is normally developed based on crack propagation models neglecting the crack initiation stage, which leads to conservative predictions for fatigue life. Inspection plans built on those predictions are far from optimal, especially for welds with relatively long crack initiation life. This paper proposes to use a fracture mechanics based reliabil-ity analysis method that takes the crack initiation stage into account via the concept of Time-To-Crack-Initiation (TTCI). The optimum inspection plan for a fatigue prone ship structural component is derived by the new approach and compared to the commonly-used method that only considers crack propagation life. Two inspection planning approaches are tested to investigate the influence of incorporating crack initiation period: (i) target reliability approach and, (ii) equidistant inspection times approach. With each planning ap-proach, two inspection methods are adopted: close visual and magnetic particle inspection. The paper con-cludes with recommendations on the inspection method and planning approach to adopt while considering and without considering the crack initiation stage.
486Scopus© Citations 7