Abstract Wind turbines are the means of converting wind energy into electrical energy. It is not unexpected that certain brands of horizontal wind turbines are optimally designed for certain wind speed regimes prevailing at certain sites. It has been the objective of this study to find out whether it is possible to design a wind turbine that is more suitable for a site of lower annual mean wind speed such as the western coast of Libya. In achieving this objective, use was made of a typical wind turbine aerodynamic design and performance analysis procedure together with actual wind speed data recorded at the city of Misurata.Based on the annual wind energy yield obtained from different designs of wind turbines having different rated wind speeds and different blade design tip speed ratios, this study indicates that the decrease of the rated wind speed leads to a continuous increase of annual energy yield as well as an increase of the cost of the wind turbine. Therefore the optimum value of rated wind speed for this site may only be determined as a compromise between added wind energy yield and added cost. Moreover, for any given rated wind speed this study indicates that a blade design tip speed ratio equal to six seems to be the optimum value for the given site.
محمد على نايلي (2015)

إن الكسور والشقوق الموجودة في المكمن يمكن أن تأخذ أحد شكلين، فالأول طبيعي والثاني مكتسب (محدث). وتشكلت الكسور الطبيعية بسبب النشاط التكتوني الجيولوجي المصحوب بترسيب تكوين طبقات صخور المكمن. ومع ذلك، تشكلت كسور الأصل المكتسب (المحدث) بفعل أنشطة الحفر وعمليات الإنتاج طيلة عمر المكمن. ويمكن لهذه الكسور أيا كان نوعها أن تؤثر بشكل كبير على معدل إنتاج النفط وكذلك على النفط الموجود مبدئياً في المكمن. ولذلك فإن لكل من الحجم و الشكل و الاتجاه تأثير كبير على معدل النفط وكمية المكمن. إن هدف هذه الدراسة التحقيق في تأثير خصائص هذه الكسور (الشكل، الاتجاه، الحجم) على المسامية والنفاذية الكلية للمكمن ، عندما تكون خاصيتي المكمن الفيزيائيتين لهما تأثير كبير على استرداد إنتاج النفطهذا وأجريت الدراسة عن طريق إجراء تجارب معملية على عدة عينات لبية من مكمن حجارة رملية في ليبيا. وتشمل هذه التجارب التحقيق الجيولوجي لتحديد اتجاه وشكل و كمية الكسور وكذلك تشمل نسبة الصخور الفيزيائية كالمسامية والنفاذية المتحصل عليهما من أي تحليل لبي كسرود الآبار.وأشارت نتائج التجارب إلى أن العينة اللبية مع عدد طبقات الكسور الطبيعية أبدت زيادة واضحة في النفاذية والمسامية عندما تعرضت هذه العينة لقيم إجهاد مختلفة. واستنتج أيضاً أنه عندما تتجاوز قيم الإجهاد المستخدمة على العينة اللبية في المعمل مقاومة انهيار الصخور فإن الصخور سيحصل لها قصور كامل ومن ثم انخفضت المسامية والنفاذية الملاحظة. واستنتج أيضاً أن الزيادة في مسامية و نفاذية العينة اللبية تعتبر مؤشراً على ازدياد معامل استرداد النفط من المكمن وأيضاً زيادة النفط القصوى. وقد تم اختبار العينات اللبية عند أحمال مختلفة لتحديد زيادة المسامية والنفاذية من عدمها. وقد بينت النتائج أن للعينات اللبية استجابات جيدة للقصور الذي يؤدي إلى زيادة متوسط قيمة المسامية من 9إلى 10.3% والنفاذية من 2.31 إلى 16.6 Md. Abstract Fractures or cracks that are present in the reservoir can be in two forms; the first is natural and the second is induced. The natural fractures were formed due to the geological tectonic activist accompanied with the deposition of forming of the rock reservoir layers. However the fractures of the induced origin were formed due to the drilling activities or production operations throughout the life of the reservoir. These fractures of any from can greatly affect the oil production rate as well as the oil initially in place in the reservoir. Therefore the magnitude, shape and the orientation are of great influence on the oil rate and the quantity of reservoir. The objective of this study is to investigate the effect of these fracture features (shape, orientation, magnitude) on the overall reservoir porosity and permeability, where these two reservoir physical properties have great effect on oil production of recovery. The study is carried out by conducting laboratory experiment on different core sample collected from a sandstone reservoir in Libya. The experiment includes the geological investigation for the determination of the fracture orientation, shape and quantity and also includes the physical rock proportion such as porosity and permeability obtained from either core analysis as wire line logs. The experimental results indicated that the core sample with layer number of natural fractures showed pronounced increase in permeability and porosity. When these core were subjected to different stress values. It is also concluded that when the applied stress values on the core sample in the laboratory exceed the rock collapse resistance, the rock experienced complete failure as hence the observed porosity and permeability were decreased. It is also concluded that the increase in core porosity and permeability is an indication of increasing the oil recovery factor from the reservoir as well as increasing the ultimate oil recovery. The core samples have been tested at different loads to determine whether the porosity and the permeability will increase or not. The results show that the core samples have good responses to failure which leads to increase the average porosity value from 9 to 10.3 % and the permeability from 2.31 to 16.6 mD.
زينب امبارك عيسي (2011)

In reinforced concrete design, the concrete in the tensile zone is assumed to be ineffective and increase the dead load of the structural elements. In order to reduce the self-weight, this paper examines the structural behavior of reinforced concrete beams containing lightweight concrete in the tensile region and normal weight concrete in the rest of the beam. The lightweight concrete was made from waste polystyrene. Four reinforced concrete beams were prepared with different depth of lightweight concrete. The control beam B1 consists of normal concrete. In Beams B2, B3 and B4, the depth of lightweight concrete was 25%, 50% and 75% of the total depth of the beam measured from the bottom surface respectively. A four-point bending test was conducted on all beams. The beams were loaded in increments until failure. At each load increment, the central deflection was determined. Cracks initiation and the mode of failure were observed during the experiment. The failure load was found to decreases with the increase of depth of lightweight concrete. The presence of lightweight aggregate tends to cause brittle failure. In addition, the mode of failure for reinforced concrete beams containing lightweight concrete was a shear failure. arabic 11 English 79
Hakim S. Abdelgader(6-2020)