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رجب عبدالله عبدالقادر حكومة, علي الصويعي محمد البوزيدي, عبير المبروك عبدالغفار(6-2017)

Abstract Many of the concentrating solar power (CSP) systems are expected be installed in desert locations where lack of water and sand storms might be an issue. The solar reflectors are considered to be among the main effective components. The negative effects of the harsh weather conditions, including sand storms of the desert might have strong influence on the reflector properties, leading to a decrease in the thermal performance of such solar system. This thesis studies the sand storm influence on solar reflector surfaces, where two different types of Libyan sands were considered and taken from sites suitable for the installation of CSP. These sands have different shapes, sizes and chemical compositions. Sand "A" has particle sizes that vary from 0.025 to 0.355mm, while Sand "B" has particle sizes in the range of 0.124-0.479 mm. An erosion rig was designed and built at Cranfield University, UK. the tests were conducted under different simulated sand storm conditions for both sand samples. The results have shown that Sand "A" has more severe influence than Sand "B" because the smaller particles of Sand "A" help the spread out over a larger surface area of the reflector. The higher sand storm speed has more strong impact influence, while increasing the mass quantity results in less consequences. The reflectivity of the un-cleaned surface drops by 5% in case of using Sand "A" and by 7% in case of Sand "B", both at storm speed of 21m/s with specific sand mass of 18g/m3.Sand storms with the speed exceeding 6 m/s, generate sand impact on the reflector surface causing degradation to the surface, while storms with speeds less than 6 m/s, result in wakes of suspended small particles as a consequence of the transport mechanism in the atmosphere. Sealing simulation and cleaning process, using Ultrasonic Cleaner Model, show that sand "B" makes a loss of about 3% of the surface reflectivity, due to the salt-chemical composition leading to create spots and marks on the reflector surface. However, Sand "A" has recorded no chemical reaction. Sand storm history should be taken seriously, reflector surface materials should be suitable for the sites, and cleaning operations should be considered.
عصام ميلاد اندايا (2015)

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)