This paper describes a case study for the causes of cracks and ruptures that emerged in the houses of the City of Shari, AlQassim region. The structures of this city built using the load wall bearings system. Loads of bearing masonry buildings usually have walls arranged at a fairly uniform spacing to carry gravity loads to the foundation without addition of columns. This study is divided to two parts; the first part discusses the field geotechnical investigation of the construction site. The second part presents the results of a parametric study for the effect of soil settlement as well as the positions and sizes of the wall openings on the existence of the wall cracks. The results showed that, the construction of houses almost at or very near to the ground surface with no rigid tie-beams under the walls which could help in resisting the differential settlement affects their safety. The opening definitely reduces the stiffness of the wall and subsequently reduces the failure load and increases deflection at the same load level. The finite difference-based code FLAC and the finite element-based code, ANSYS were used in the analysis.

The utilization of wind energy driven induction generators finds nowadays great interest. The present paper aimed at improving the performance of the induction generators at the different expected wind speeds employing control techniques from the rotor side. A set of two converters in the rotor circuit has been adjusted to inject a voltage such that the generator runs at the speed which allows the wind turbine to extract the maximum power from the wind, and at the same time to deliver the electrical power to the network at unity power factor. The double-fed induction generator has been modelled at steady-state conditions using frequency domain equivalent circuit. The performance characteristics of both double-fed induction generator (DFIG) and single-fed induction generator (SFIG) have been computed. The computed performance characteristics have revealed that the DFIG has superior performance characteristics as compared with the SFIG. The output active power of the generator has been clearly increased by double-feeding especially at wind speeds far from the base speed. Also, the DFIG nearly does not consume reactive power when compared with SFIG. Although the output power of the generator is clearly increased by doubly feeding it, the stator and rotor currents still within their rated values.

Tube Expansion is the process of reducing a tube wall by displacing the outside diameter of the tube against a fixed container such as rolling tubes into tube sheets. To assure a proper tube joint to the tubesheet, the tube wall must be reduced by a predetermined percentage. Different methods have been used to estimate the necessary amount of expansion in tube to tubesheet rolling expansion for strong tubeto-tubesheet joint. The first commonly method depends on torque and pull out strength data collection by experimentation. This method fits with small and large clearance but it suffers from cost of experiments to collect the necessary data. The second method depends on theoretically calculation of the necessary inner radius displacement that to insure proper residual contact stress. That stress gives indication the strength of the joint. This method fits with small clearance as the joint strength decreases until it vanishes as the clearance increases. This paper proposes a new method that depends on the fixed outer tube surface displacement. The finite element analysis results show that, the proposed method provides good results for both low and large clearance.

The normal contact stiffness between two polymer blocks with nominally flat surfaces in contact is investigated. Contact stiffness is experimentally determined on a tension-compression machine at small loading steps from zero to about 15 kN. The contact stiffness of steel specimens with the same dimensions as those of the polymer blocks is also investigated to examine the differences between polymers and metals. The three-dimensional surface parameters of the samples are obtained by using an optical profiler. The experimentally measured contact stiffness of Nylon shows a trend similar to that of steel, whereas Teflon and Polyimide show different trends. This discrepancy is shown to be related to the non-homogeneous distribution of surface summits on the contact area. Such a distribution may reduce the real elastic contact area, which in turn changes the surface condition from a rough to smooth contact.