Abstract For this study, two identical single-effect of single basin solar stills are designed, fabricated, tested, and evaluated, where one of them is employed alone which is referred to as “passive still”, while the other is coupled to a flat plate solar collector introducing what so called the active still. Both are installed at the same site in Tripoli-Libya and they are oriented due to south. Measurement of various temperatures, solar intensities, humidity, wind speed and distillated water production are taken each hour for several days of August under various operating conditions. Two operational modes are considered; each of the passive and active stills is operating for the whole day. These tests were performed using seawater and water basin different depths. The water production of the active still is reported to be 6.6 L/m2.day which is higher than that of the passive still by 56 per cent approximately. The maximum daily efficiency is calculated to be 24 per cent approximately for the active still system while it is 14 per cent approximately for the passive still. Yet, the still thermal performance seems to have a complex function of geometrical, constructional, and operational conditions, site characteristics and layout details.
صالح أحمد سرابيط (2010)

Abstract This Thesis overviews the methods for calculating the stress intensity factor and employs the stress and displacement methods in the current study. The model used simulates a cracked rectangular plate which is subjected to tensile stress. The Finite element method is used to calculate inplane displacement due to applied loads. As a post processing the stress and stress intensity factor over the plate was calculated. The results show that the singularity exists at the crack tip and the components of stress and approach infinity as the crack tip approach. The comparison of the current study to theoretical and other numerical results shows a good agreement and reliability of the program. The thesis consists of five chapters, the first chapter, presents general over view and historical al review. The second chapter demonstrates the theoretical basis in fracture mechanics. The third chapter involves the numerical solution using F.E.M. The fourth chapter demonstrates a case study and the results and discussion of the obtained results. The fifth chapter concludes the work and gives recommendations.
محمد كامل الشيخ (2009)

عند تطبيق سياسات الصيانة تواجه المؤسسات الصناعية والخدمية على حدا سواء تحدى ألا وهو ماهى طريقة الصيانة المثلى والسياسة الأفضل الواجب إتباعها لصيانة النظام بالأخذ في الاعتبار التكاليف ؟ بكلمات أخرى ماهى السياسة المثلى للصيانة التي تحقق التوازن بين تقليل الأعطال والحفاظ على النظام في أحسن الظروف التشغيلية وبأقل تكلفة ممكنة للصيانة.لذلك تشكل تكلفة الصيانة دورا هاما قي عملية المفاضلة عند اختيار وتخطيط سياسات الصيانة. إن حساب تكاليف الصيانة لاى نظام من بداية تشغيله إلى نهاية عمره الافتراضي له أهمية كبيرة للمؤسسة الصناعية ، حيث يضمن لمتخذي القرار حسن التصرف في مصادر رؤؤس الأموال وهذا الأمر مهم جدا خصوصا للدول النامية نظرا لمحدودية توفر إمكانياتها . لذلك يقدم البحث نموذج رياضي مطور لتقدير التكاليف الإجمالية لسياسات الصيانة المتبعة أو المقترحة لنظام ما على طول العمر الافتراضي له ، تقدير عدد الأعطال التي يتعرض لها النظام، تقدير تكلفة المواد المطلوبة لعمليات الصيانة ، تقدير العدد الأمثل لمرات إجراء الصيانة الوقائية بكل فترة من فترات عمر النظام ، ومن خلال البحث نقوم بدراسة وتحليل تأثير العناصر المختلفة للصيانة على معايير الأداء . أيضا يعطى النموذج الرياضي المطور الوقت الأمثل لإجراء العمرة لمعدات النظام بدلا من السياسة التقليدية المتبعة ببعض المؤسسات الصناعية في الدول النامية والتي تعتمد فقط على إجراء عمرة لمعدات النظام بعد فترات زمنية ثابتة بغض النظر عن حالة النظام ومدى احتياجه فعليا لتجديد معداته .ويدعم البحث بدراسة تحليلية وعملية لنظام محطة نقل الطاقة الكهربائية بالشركة العامة للكهرباء كمثال للدراسة . Abstract Through implementation of the maintenance policies, companies face challenge with respect to system maintenance cost, which is how to keep the system in good working condition at low maintenance cost? Thus the tradeoff process between cost and performance of the system plays an important role in the selection of the maintenance policies.This research is intended to achieve the optimum maintenance policies, and to achieve the leverage between system performance and life cycle maintenance cost. It focused on accomplishing the following points:Developing a mathematical model to evaluate maintenance policies through life cycle of the system.Assessing the impact of maintenance parameters on system performance measures.Using the developed model to determine the appropriate overhauling times for the industrial enterprises, actually when the equipments should be overhauled, instead the traditional way, that is performed based on fixed number of years. The model works based on criteria's are set by enterprise's decision makers, such that if the system exceeds certain number of breakdowns through its life cycle, then system must be overhauled. This thing helps the companies saving money. Using appropriate performance measures to evaluate how well the system meets its goals based on the applied maintenance policy. Practical and analytical study of power transmission station's equipments in general electrical company of Libya was presented as a case study.
عماد مختار المصراتي (2009)