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This study attempts to obtain more detailed knowledge of failures of wind turbines (WTs) by using the German '250 MW Wind' test program database. Specific objectives are to show the reliability of some major components and to analyze how their design has advanced through time, what the main failures are, and which technologies have proven to work. Within the program, reports on operation and maintenance are analyzed with respect to WT type, size, and technologies used. This paper presents a comparison of component reliability through time, with respect to their technology. The results show significant differences in reliability for certain subcomponents depending on the size of the WT and especially on the type of power control. For instance, induction generators show half the annual failure rate compared to synchronous generators. The study also includes failures of other components that are affected or added due to the use of the components being analyzed. In general, the results show that failure rates of WTs decrease with time. Most of the data show a short period of 'early failures' and later a long period of 'random failures.' However, this is not the case for the megawatt class: As technology is introduced into the market, WTs show a longer early failure behavior, which has not yet become stable. Furthermore, large turbines, included in the database analyzed, show a significantly higher annual failure rate of components, per WT. This may be due to the immature technology of the WTs included in the database. [DOI: 10.1115/1.2936235] Keywords: reliability, maintenance, failures, wind turbines

Background: When endoscopic retrograde cholangiopancreatography (ERCP) guided bile duct biopsy fails to demonstrate malignancy, it remains unclear how to manage patients with presumably malignant strictures. Aims: To evaluate the value [...]

One of the crucial issues for developing computer aided conceptual design system is representation of functions which represent designers' intention. Representing functions is also crucial not only for representing design objects but also for describing conceptual design processes, in which designers operate mainly functional concepts. Namely, function is a key concept to integrate object modeling and process modeling in design. In this paper, first we extend the FBS (Function-Behavior-State) diagram, which we have already proposed, by introducing three additional concepts for representing a function; namely, function body that represents designers' intention directly, function modifier that qualifies a function body, and objective entity on which the function body occurs. This extended FBS diagram, called FBS/m (modifier) diagram, enables us to represent designers' intention more precisely than the original FBS diagram. Then, we propose an FEP (Functional Evolution Process) model to represent design processes. In the FEP model, the FBS model of a design object is evolved through three steps, i.e., functional actualization, functional evaluation and functional operation. Functional actualization depicts a process to obtain physical descriptions from functional description. Functional evaluation is a process to measure realizability of functions of the design object. Functional operation is a process to operate functions to improve the design. based on the FEP model we analyze an actual design process, and show that the FEP model is suitable for representing designers' intention along with design processes.