Abstract Finite element method is used to analyze the flexural vibrations of beams using Galerkin approach for both Bernoulli and Timoshenko theories.The methodology is started by integral formulation of the partial differential equations for the physical problem, and then the element stiffness, mass matrices and load vector have been obtained. Free vibrations analysis is used for the predictions of natural frequencies and mode shapes for, first flexural vibrations by classical theory, second flexural vibrations by including the effect of shear deformation and rotary inertia in the analysis. Finally, the axial and torsional vibrations, in addition to flexural vibrations, in both transverse and lateral directions together have been taken into consideration, thus the finite element equations and the element stiffness, mass, and load vector matrices have been developed for axial, torsional, and flexural vibration together.The natural frequencies are tabulated for all classical types of classical boundary conditions. The mode shapes corresponding to the natural frequencies were presented graphically. The exact solutions and results obtained by other standard methods are used for comparison with the current numerical results. The forced vibrations were introduced for the analysis of dynamic behavior of beams under several types of loading. The finite element code with Taylor series method and mode superposition for the Bernoulli and Timoshenko beams has been carried out. Numerical results are presented in the form of comparisons between the Bernoulli and Timoshenko and demonstrate how the effect of shear deformation reduced the displacement response with increasing the excitation frequency, excitation amplitude, and length of the beam. Comparisons are made with the exact and existing classical methods and checked with those obtained IVusing standard methods (ANSYS package) and are found in good agreement. It should be noted that all models of beams have always convergence to the correct solution.
أمنة احمد القلفاط (2009)

This paper investigates in detail the current status of the implementation levels of JIT key-factors and their sub-elements within the cement industry within Libya, and its implication for management within the said industry. A survey methodology has been applied in this detailed investigation using an intensive questionnaire and one-to-one interviews of the correspondent organizations. Based on the analysis of the survey findings, the results show that the implementation status of the JIT key-factors and their sub-elements are found to be in the modest levels across all the surveyed organisations, thereby indicating to opportunities for eliminating waste and improving the value chain. This paper has also pointed to crucial areas where the senior management body within this industry need to take immediate actions in order to achieve an effective and successful implementation of JIT systems. The paper also makes a contribution by providing an insight into what extent the JIT key-factors and their sub-elements are understood and implemented within the key Libyan manufacturing industry arabic 19 English 113
Rajab HOKOMA, Hala Mansour Amaigl(5-2019)

تتعرض هذه الرسالة لدراسة نظرية لنموذجين مختلفين للمجمعات الشمسية، المعدنية وغير معدنية . وذلك لتعين معاملات الأداء لهذه المجمعات مثل معامل فقد الحرارة, عوامل فقد الحرارة الكلية, الكسب الحراري, الكفاءة اليومية, واللحظية.وقد أظهرت هذه الدراسة أن المجمعات المعدنية الشمسية متفوقة من حيت معاملات الأداء على المجمعات الشمسية الغير معدنية, تحت ظروف الجريان القسري. وقد دلت هذه الدراسة أيضا على أن عوامل فقد الحرارة الكلية لكلا النموذجين تظهر تغيرا طفيفا عند التغير في معدلات التدفق. كذلك فإن معامل الفقد الحراري يعتمد بصورة كبيرة على معدل التدفق لكلا لنموذجين, عند استخدام خزانات ذات سعة صغيرة. كما تبين أيضا أن الطاقة المختزنة, في المجمعات غير المعدنية, يمكن أن يستفاد منها كطاقة حرارية مفيدة حتى بعد غياب أشعة الشمس.وقد قورنت نتائج هذه الدراسة النظرية بنتائج دراسات عملية سابقة, و وجد أن هنالك تطابقا جيدا بينهما, ما عدا تلك النتائج التي تم الحصول عليها في ساعات الصباح الباكر وساعات المساء. Abstract This thesis presents a theoretical investigation of metallic and non-metallic solar water collector models for evaluating its performance parameters. The determined parameters include heat removal factor, overall heat loss coefficients, heat gain, daily and hourly efficiencies.The present study reports that, under forced circulation test, the non-metallic collector has an inferior performance parameters when compared to that of the metallic one. It was also revealed that the overall heat loss coefficients of both collectors show weak dependence on the flow rate variations. It was also noticed that the heat removal factor for both models is more sensitive to the flow rate variations when small storage tank capacities are used.The stored energy in the non-metallic flat plate solar collector model constitutes a significant part of the useful energy, even after the diminishing of the solar intensity.Finally, a comparison of performance parameters of the theoretical and experimental studies showed good agreements for most hours of the day, except the results obtained at the early morning and late after noon hours.
نورالدين عبد الحفيظ عبود (2009)