توصيفگر ها :
قابليت اعتماد , تعمير و نگهداري , اثر متقابل خرابي , خرابي نرم , خرابي سخت , فرسايش , دسترس پذيري
چكيده فارسي :
سياست‌هاي نگهداري و تعميرات روش‌هايي هستند كه چگونگي برخورد با خرابي تجهيزات را بيان كرده و شامل فعاليت‌هاي تشخيص، تعمير و رفع خرابي مي‌شوند. هدف نگهداري و تعميرات عبارت است از افزايش عمر مفيد و صرفه اقتصادي تجهيزات به گونه‌اي كه با كمترين هزينه بيشترين بهره‌وري حاصل شود. فعاليت نگهداري و تعمير به دو بخش عمده تقسيم مي‌شوند: تعمير اصلاحي و نگهداري پيشگيرانه. در نگهداري پيشگيرانه با يك برنامه مشخص و از پيش تعيين شده براساس زمان، تاريخ و... به تعمير و تعويض قطعات مشخصي از سيستم جهت كاهش خرابي‌هاي اتفاقي و متداول پرداخته مي‌شود.
اهميت تداوم فعاليت سيستم‌ها و افزايش هزينه‌هاي غير مترقبه در صورت خرابي سيستم و هزينه‌هاي ناشي از توقف كار، و از طرف ديگر هزينه‌هاي گزاف بررسي‌هاي مكرر پيش از خرابي سيستم‌ها، مخارج سنگيني را به واحد مربوطه اعمال مي‌كند كه موجب كاهش سود (و در نتيجه كاهش تمايل سرمايه‌گذاران و سهام‌داران به سرمايه‌گذاري در شركت) مي‌شود. اين پژوهش در پي آن است تا از يك طرف از طريق مشخص كردن سياست بهينه براي بازرسي و تعمير و نگهداري سيستم‌ها، هم امكان خرابي و توقف كار و هم هزينه‌هاي ناشي از آن را به حداقل برساند.
در اكثر سيستم‌هاي چند مولفه‌اي، نوعي وابستگي بين مولفه‌ها وجود دارد به نحوي كه خرابي يك مولفه ممكن است باعث افزايش نرخ خرابي يا سطح فرسايش مولفه‌هاي ديگر شود. به اين نوع وابستگي بين مولفه‌ها، اثر متقابل خرابي گفته مي‌شود كه مي‌تواند به اندازه قابل توجهي در قابليت اعتماد سيستم و هزينه‌هاي تعمير و نگهداري و ... تاثير بگذارد. به طور معمول، نگهداري و تعميرات سيستم‌ها در حالت تك-خرابي مورد بررسي قرار مي‌گيرند. لذا در اين پايان‌نامه به مطالعه و بررسي روش‌هاي تعمير و نگهداري سيستم‌ها در حالت اثر متقابل خرابي پرداخته شده و سپس به دنبال به حداقل رساندن هزينه‌ي ممكن در برنامه‌هاي تعمير و نگهداري هستيم.
چكيده انگليسي :
One of the main goals in the manufacturing industries is to increase the reliability of systems and products. Therefore, various strategies have been considered to achieve this goal, among them maintenance method play an important rule. Maintenance policies are methods that describe how equipment is dealt with failures. They include diagnostic, repair and troubleshooting activities. The purpose of maintenance is to increase the useful life and economic efficiency of the equipment so that the maximum efficiency is achieved at the lowest cost. Maintenance activities are divided to two main parts: corrective repair and preventive maintenance. In preventive maintenance, with a specific and predetermined schedule based on time, date, etc., specific components of the system are repaired and replaced to reduce accidental and common failures. In the most multi-component systems, for simplicity, it is often assumed that the failure of a component has no effect on failures of the other components. However, in practice the failure of one component may affect the other components by increasing their failure rates or their degradation levels. Our aim in this dissertation, is to studying the methods of maintenance of systems with failure interaction, and subsequently to optimize it such that the possible cost in maintenance programs are minimized. In the first part of this thesis, we consider a two-component system with the interaction effect of failures such that the first component is repairable and the second component is unrepairable, but its level of performance deteriorates over time. Thus, two different failure models are considered. In the first model, the failure of the first component leads to cumulative damage to the second component and reduces its level of performance. In the second model, the failure of the first component can with a certain probability cause the failure of the second component, while the failure of the second component is devastating and causes the failure of the entire system. In both models, different maintenance policies are defined, assuming that incomplete repair is performed for the first component and complete repair is performed for the second one. Three preventive maintenance policies are considered: age-based policy, failure-number-based policy, and mixture policy. The results are provided on the system long run average maintenance cost under these different maintenance policies. In the other section of thesis, we consider a single-component system, which is affected by two types of failure: hard failure, which crashes the system if it occurs, and soft failure, which only reduces system performance. It is also assumed that there is a correlation between these two types of failure in such a way that any soft failure directly increases the risk of hard failure. In other words, there is an interaction between these two types of failure modes. To identify these two types of failures, inspections are performed periodically. Recursive equations for system reliability and availability are derived. Also for this system, optimizing the inspection time in order to reduce the average cost is examined. More precisely, this research seeks to minimize both the possibility of failure and the resulting costs by determining the optimal time to inspect systems.
