Articles in This Issue
Abstract
Composite laminate plates, fabricated by bonding fiber–reinforced layers, were dynamically analyzed under different combinations of number of layers, type of cutout, hole dimensions, angle of lamination and type of dynamic loading . This work was achieved by the well–known engineering software (ANSYS). The toughness of composite plates was evaluated in terms of the normal stress in the direction of loading at the periphery of the cutout. The toughness was found to increase by increasing the number of layers, by setting the lamination angle at around 40o,by selecting hole dimensions to width of plate ratio of around 0.4 and by employing square cutouts or avoiding triangular cutouts. Also, composite plates were found to be more strain-rate-sensitive in ramp loading, with least number of layers and with triangular type of cutout.
Abstract
Some mechanical properties of mortar (compressive strength and hardness) with sawdust replacement of sand were investigated. Cubes of 50 mm × 50 mm were prepared, the compressive strength tests were done for a replacement levels ranging (5, 10, 15, 25, 50, 75) % by volume a reference mix were also prepared for comparison this test was done after 7, 14, and 28 days while hardness test were done after 28 day for a replacement levels (0, 5, 10, 15, 25) % by volume. Result showed that the compressive strength of the specimen were decreased with higher sawdust content, hardness values were decreased slightly in the replacement levels 0, 5, 10 % while the values began to decrease noticeably in the replacement levels 15 and 25 % the hardness values were (59, 57.5, 56, 47.77 , 45.2) N/mm2 respectively A cost analysis was done, this analysis was based on a unit of mortar (1.0 m3) made from conventional materials and a modified concrete made by substituting materials with sand using sawdust
Abstract
One way of obtaining information about reliability of units is to accelerate their life by testing at higher levels of stress (such as increasing elevated temperatures or voltages). Predicting the lifetime of a unit at normal operating conditions based on data collected at accelerated conditions is a common objective of these tests. Different models of accelerated life testing are used for such extrapolations. Two statistical based models are widely used: parametric models which require a prior specified lifetime distribution, and nonparametric models that relax of the assumption of the life time distribution. The proportional odds model is a nonparametric model in accelerated life testing based on the odds function and show that it gives a more accurate reliability estimates than proportional hazard model. This paper will concentrate on the models of proportional odds nonparametric accelerated life test for reliability prediction.
Abstract
This research presented a strategy for designing a particular set of surfaces, obtained by the technique of cross-sectional design. The surfaces considered were formed by sliding a Bezier curve (profile curve), and also this research describes an automatic procedure for selective identification of sampling points in reverse engineering applications using Coordinate Measurement Machine. In addition, Matlab program have been used in the present work so as to plot the curve sections of the surfaces using transformation matrices. UGS program have been also used to connect the sections that designed in Matlab program to get the final shape of the proposed surface. It can be concluded that the whole steps task which built in the present research can be programmed in a single block of the part program that’s from it can be create any curve or surface at minimum designing time.
Abstract
This research presents a mathematical model of feed-interval scallop height, where in a machined surface there are two types of scallop height, the pick(path)-interval scallop and the feed-interval scallop. The pick-interval scallop is generated by the finite pick offset between the successive cutting paths, while the feed-interval scallop is generated by the finite increment between the successive tooth feeds. New model that describes and predicts the geometric generating mechanisms of the feed-interval scallop height have been derived using torus cutter which is commonly used in multi-axis milling machine. The machining parameters (effective tool cutter radius, feed per tooth and the magnitude of tool axis inclination angles) have been considered in theoretical and experimental work to study the effect of these parameters on this type of scallop height. From theoretical and experimental work it was found that at high-speed machining, the feed-interval scallop is more important to the surface roughness than the path-interval scallop, and the feed-interval scallop is very sensitive to the tool-axis inclination angle. The feed-interval scallop height decreased sharply and quickly within a few degrees of the tool-axis inclination to the normal workpiece surface. In general, an inclination angle equal to is good enough for all tool diameters used in the present work, namely (6,8,10 12 mm).
Abstract
In this paper, the effect of using the strengtheners on the stress and deflection under the effect of a certain weight falling on plates made of aluminum alloys (Al Mg3)has been studied. The study was carried on through two aspects; experimentally and theoretically; theoretically by using (F.E.M LS. DYNA) program. After comparing the theoretical aspect and experimental aspect, greatly- close results at point of contact were found out, as follows: When using one strengthener, the stresses reduce by (14 %) and the deflection by (70%) with comparison of without stiffener case .When using two strengtheners at the ends, stresses reduce (77%) and the deflection (65%) .When using two strengtheners 8 cm apart, stresses reduce (56 % ) and the deflection ( 18%) . When using two strengtheners 4 cm apart, stresses reduce (60 %) and the deflection (31%)
Abstract
Better understanding the innovative process of renewable energy technologies is important for tackling climate change. Concentrated solar power (CSP) is a method of electric generation fueled by the heat of the sun, an endless source of clean, free energy. Commercially viable and quickly expanding, this type of solar technology requires strong, direct solar radiation and is primarily used as a large, centralized source of power for utilities. This study has focused on the feasibility of improving concentrating solar power (CSP) plant efficiency, by manufacturing a diminished prototype. Three states were studied, coloring the central target with a selective black color, fixing a reflector with arc form behind the target, and using these two changes together. The results showed an improvement in the thermal storage varied form month to month. The maximum stored energy was gained at August with increments about 56.1%, 58.63%, 62.23 and 64.69% for ordinary target, black painting, using reflector alone and black target with reflector together, respectively compared with stored energy for March.
Abstract
The present work represents a two-dimensional numerical investigation of forced laminar flow heat transfer over a 3-rows oval-tube bank in staggered arrangement with rectangular longitudinal vortex generators (LVGs) placed behind each tube. The effects of Reynolds number (from 250 to 1500), the positions (3 in x-axis and 2 in y-axis) and angles of attack (30o and 45o) of rectangular VGs are examined. The study focuses on the Influence of the different parameters of VGs on heat transfer and fluid flow characteristics of three rows oval-tube banks. The characteristics of average Nu number and skin friction coefficient are studied numerically by the aid of the computational fluid dynamics (CFD) commercial code of FLUENT 6.3. The results showed increasing in the heat transfer and skin friction coefficient with the increasing of Re number and decreasing the relative distance of positions of LVGs. It has been observed that the overall Nuav number of three oval-tubes increases by 10–20.4% and by 10.4–27.7% with angles of 30o and 45o respectively, with increasing in the overall average of skin friction coefficient of three oval-tubes reached to 53% and 72% with two angles used respectively, in comparison with the case without VGs.
Abstract
An experimental and theoretical study has been conducted to determine the thermal efficiency of a parabolic trough solar collector. The experiments have been performed during winter and summer at Tikrit-Iraq. The solar radiation of Tikrit University was calculated theoretically and a theoretical study was performed by using FORTRAN 90 program. The dimensions and specifications of the collector were entered to the program to determine the theoretical thermal efficiency. It has been found the experimental thermal efficiency of collector is less than the theoretical one in percentage between (7-15) .So the increase in water mass flow rate leads to an increase in the thermal efficiency, and there is no significant change in thermal efficiency when the water mass flow rate becomes more than forty kilograms per hour.
Abstract
The enhancement of laminar forced convection inside helical pipes is studied numerically and compared with plain pipes. The study is achieved numerically using the (Fluent-CFD 6.3.26) software program for solving the governing equations. The heat transfer coefficient and friction coefficient are calculated using the enhancement technique and compared with the plain tube. In this research the factors that affect the enhancement technique using helical pipes are studied, these factors are the ratio of (pitch /pipe length) (SL), Reynolds number and the heat flux applied to the external surface of the pipe. The results showed that there is an increasing in the heat transfer coefficient is related to the decreasing of (SL), increasing of Reynolds number and heat flux. The performance of the helical pipes is evaluated depending on the calculation of (Enhancement ratio), and it’s found that the enhancement ratio increases as Reynolds number increases and (SL) decreases. It is found that the best enhancement ratio was (200%) at (SR=0.05), (Re=2000),(Heat flux=3000W/m2).The results are compared with the literature and there is a good agreement.
Abstract
The object of this paper was determined the thermal behavior of present and future constructs Iraqi walls at Baghdad climate region (Latitude 33.2 °N) with or without (40) mm insulating materials. The study was carried out at day (21) July for East Orientation. The obtained results were tabulated in terms of over all heat transfer coefficient, weight of the wall per unit area, wall thickness, temperature difference between outside and inside wall face and the temperature difference between inside of the room and it's inside wall surface through on. day hours and it's average values.