Print ISSN: 1813-162X

Online ISSN: 2312-7589

Volume 18, Issue 4

Volume 18, Issue 4, Autumn 2011, Page 1-103


Numerical Study of Separated Flows in Backward Facing Step by Using Collocated Grid Arrangement

Dr. Ahmed Waheed Mustafa

Tikrit Journal of Engineering Sciences, Volume 18, Issue 4, Pages 1-9

The effects of Reynolds number and the inlet height ratio on separated flow over backward facing step are investigated. The flow field is studied numerically with different inlet height ratio. The laminar flow field is analyzed numerically by solving the steady, two-dimensional incompressible Navier-Stokes equations. A collocated (non-staggered) grid is used in the momentum equations, which discretized by finite volume method, SIMPLE algorithm is used to adjust the velocity field to satisfy the conservation of mass. The range of Reynolds number is (Re = 100 - 800). The results show that at low height ratio (h/H = 0.25) and high Reynolds number the flow separated along the top wall of the channel. Good agreement with the experimental data is obtained.

The Overall Drag Losses For A Combination of Bodies

Dr. Sabah Jebour Al-Janabi

Tikrit Journal of Engineering Sciences, Volume 18, Issue 4, Pages 10-19

The objective of this work is to obtain better understanding of the flow over a combination of bluff bodies in close enough proximity to strongly interact with each other. This interaction is often beneficial in that the drag of the overall system is reduced. Proto-types for this problem come from tractor- trailer and missiles, and from various add-on devices designed to reduce their drag. Thus, an experimental investigation was carried out by placing conical frontal bodies having a base diameter of 0.65 cylinder diameter with different vertex angles (30°, 50°, 70°, and 90°). It was found that, the bluffer cone with 90° vertex angle gives the best minimum drag, which is 31% lower than the drag of the isolated cylinder. Also an interesting phenomenon was observed in that, the minimum drags for all combinations are obtained at the same gap ratio (i.e.at g/d2= 0.365).

Theoretical Study of Thermal Performance of Rock Bed Storage

Mousa Mustafa Weis; Ihsan F. Abbas; Dr. Suad H. Danok

Tikrit Journal of Engineering Sciences, Volume 18, Issue 4, Pages 20-28

In this theoretical study, heat transfer and pressure drop in two cases of rock bed thermal storage has been studied, in the first case the equivalent diameter is changed when the mass flow rate per unit area is constant, and in the second case is inversely. The unsteady numerical simulation is employed to analyze the performance of the heat flow and temperature field in the storage. While the best thermal storage is obtain at equivalent diameter is (0.01) m. and show that the relation of pressure drop is decrease with increase in equivalent diameter except in a range of (0.025 to 0.038) m is constant.

Overflow Characteristic of Cylindrical Shape Crest Weirs Over Horizontal Bed

Adnan Abdul; Emad Abdul; Wahab; Mohammad Akram; Gabbar

Tikrit Journal of Engineering Sciences, Volume 18, Issue 4, Pages 29-39

The most common types of weirs are the broad-crested weir, the sharp-crested weir, the circular crested weir and the ogee crested weir. Advantages of the cylindrical weir shape include the stable overflow pattern, the ease to pass floating debris, the simplicity of design compared to ogee crest design and the associated lower costs. In present study, it was investigated the overflow characteristics of circular weirs in laboratory for various cylinder radii of three sizes (11.4, 9.0, 6.3 cm), and the models fixed on the channel bed vertically to the direction of flow. The result shows that the increase in the ratio of head to weir radius ratio (Hw/R) value causes an increase in discharge coefficient (Cd) value for the same height of weir. It was observed that the cylinder size (i.e. radius of cylindrical weir (R)) has an effect on the (Cd). The flow magnification factor (qw/qs) increases with an increase in (Hw/R) value and values of (qw/qs) were always higher than one for all values of (Hw/R), this means that weirs of cylindrical shape performed better than those of sharp crest for any value of weir radius tested in this study.

Improvement The Transmission Efficiency For Wireless Packet Communication Systems Using Automatic Control for power And Time Slot Width Of Slotted Non persistent ISMA Protocol

Saad Meshhen Hardan

Tikrit Journal of Engineering Sciences, Volume 18, Issue 4, Pages 40-47

In packed communication systems which use a protocol, the protocol should perform the allocation of channels such that the transmission channel is used efficiently. Efficiency is usually measured in terms of channel throughput and the average transmission delay. The Slotted Nonpersistent ISMA protocol is one of random access protocols used in packed communication systems. In this research a Slotted Nonpersistent ISMA protocol Model with automatic control for power and time slot is proposed. the suggested algorithm enable the base station(access point) to control the protocol time slot length and transmission power in a dynamic way to control the normalized propagation delay d and to maintain all the uplink signals in the limit of captured power threshold (capture ratio) in order to control the throughput and the average transmission delay of the communication system by an automatic method. the computer simulation results confirm the activity of the proposed algorithm for increasing the throughput and decreasing the average transmission delay by an accepted ratios.

Optimization In Searching Daily Rule Curve At Mosul Regulating Reservoir, North Iraq Using Genetic Algorithms

Thair M. Al-Taiee

Tikrit Journal of Engineering Sciences, Volume 18, Issue 4, Pages 48-59

To obtain optimal operating rules for storage reservoirs, large numbers of simulation and optimization models have been developed over the past several decades, which vary significantly in their mechanisms and applications. Rule curves are guidelines for long term reservoir operation. An efficient technique is required to find the optimal rule curves that can mitigate water shortage in long term operation. The investigation of developed Genetic Algorithm (GA) technique, which is an optimization approach base on the mechanics of natural selection, derived from the theory of natural evolution, was carried out to through the application to predict the daily rule curve of Mosul regulating reservoir in Iraq. Record daily inflows, outflow, water level in the reservoir for 19 year (1986-1990) and (1994-2007) were used in the developed model for assessing the optimal reservoir operation. The objective function is set to minimize the annual sum of squared deviation from the desired downstream release and desired storage volume in the reservoir. The decision variables are releases, storage volume, water level and outlet (demand) from the reservoir. The results of the GA model gave a good agreement during the comparison with the actual rule curve and the designed rating curve of the reservoir. The simulated result shows that GA-derived policies are promising and competitive and can be effectively used for daily reservoir operation in addition to the rational monthly operation and predicting also rating curve of reservoirs.

Heat Transfer by Mixed Convection in the Opposing Thermally Developing Flow in a Vertical and Inclined Annulus

Ameer A. Jadoaa

Tikrit Journal of Engineering Sciences, Volume 18, Issue 4, Pages 60-70

Combined convection heat transfer in an inclined (ψ=60o) and vertical (ψ=90o) annulus has been experimentally studied for opposing thermally developing and thermally fully developed laminar air flows with adiabatic inner tube and uniformly heated outer tube (r1/r2=0.41) for Reynolds number range from 450 to 1000 and heat flux is varied from 150 W/m2 to 780 W/m2. The hydrodynamically developed condition has been achieved by using entrance section annular pipe (calming section) having the same dimensions as test section (L/Dh≈40). The mixed convection regime has been bounded by the convenient selection of Re and heat flux ranges, so that the obtained Richardson number varied approximately from 0.05 to 0.97. The average heat transfer results have been correlated with an empirical correlation by dimensionless groups as logNum against logRa/Re and compared with available literature showed that the heat transfer process in the hydrodynamically fully developed region of duct is better than that in the developing region of this duct.

Effect of Wetting and Drying Cycles on Swell/Collapse Behavior and Cracks of Fine – Grained Soils

Abdulrahman H. T. Al Zubaydi

Tikrit Journal of Engineering Sciences, Volume 18, Issue 4, Pages 71-79

Many of the soils undergo volumetric changes due to the change in the water content. Swell-shrink and collapse behavior of those soils affects the stress state in soil and the interacted structures. Shrinkage in the soil produce cracks of different patterns, and affects the swelling potential in next wetting cycle.
This study covers swelling and collapsing properties of four different soils from Mosul city. The changes in swelling and collapsing properties with respect to number of wetting and drying cycles have been investigated. Also, A shrinkage cracks have been studied with aid of digital image after each drying cycle. Number of segments and area of cracks calculated with aid of AutoCAD package.
Results indicated that, the collapse potential is influenced by soil type (soil composition) and applied loads. As the applied loads increase the collapse potential increases. For sandy soil the collapse potential decreased with increasing wetting and drying cycles, and for the clayey soils, swell potential decreased while collapse potential increased with these cycles. It has been shown that the cracks increase with wetting-drying cycles. Larger values of percent crack area to the initial sample area has been observed in the soil that contain more clay content than other types of soils.

Experimental Study of Free Convection in Coiled Tube Heat Exchanger

Harith Noori Mohammed

Tikrit Journal of Engineering Sciences, Volume 18, Issue 4, Pages 80-87

An experimental study has been conducted on steady-state natural convection heat transfer from helical coil tubes in vertical orientation. Water was used as a bath liquid without any mixing and cold water was used as a coolant fluid. A straight copper tube of 6 mm ID, 8 mm OD and 3 m length was bend to fabricate the helical coil. Four coils are used in this experiment has different curvature ratios and pitches. The data were correlated using tube diameter as the characteristic length. The results show that the overall heat transfer coefficient and Nusselt number increase when the flow rate of coolant and curvature ratio increase. The effect of coil pitch was investigated and the results show that when of the coil pitch (angle of inclination) increases Nusselt number increase. A correlation was presented to calculate the outside average Nusselt number of coil.

Heat Transfer and Fluid Flow Characteristic in banks Flat Tubes

Abdulmajeed A. Ramadhan; Amer Jameel Shareef

Tikrit Journal of Engineering Sciences, Volume 18, Issue 4, Pages 88-103

In this research a study effect of the length ratio (L/Da) and the height ratio (H/Da) for banks flat tube heat exchanger In-Line and staggered arrangement on force convection heat transfer and friction coefficient by (Fluent-CFD) numerical program.
The governing equations (mass, momentum and energy) are solving by using Finite Volume (Fluent-CFD) software for considering steady state, two dimensional, at constant heat flux with Reynold’s number (100≤Re≤8000).
The results show that increasing (H/Da), (L/Da) lead to decreasing friction coefficient and enhancement of (Nu) is at (H/Da=2) for all (L/Da) values In-line arrangement and at (H/Da =2, L/Da =5) for staggered arrangement.

The Application of Public Participation Method in Forming the Urban Future for Alchipayish City

Tikrit Journal of Engineering Sciences, Volume 18, Issue 4, Pages 1-16

Since the sixteenths of the previous century the criticizing started to face the rational methods in urban planning, urban design and architecture. Modernism had been criticized on large scale, so that the architecture of post-modern emerged; and the public participation appeared in deciding urban settlements future. This change was due to democratic methodology in dealing with societies requirements. What led to this methodology was the people tend to think of their cities future. This methodology exposed among the societies of wide sum of information's techniques, where these tools could be used as communication channels between all discipliners and planners to achieve the public participation steps.
On other side, the current methods in deciding the urban environment in Iraq still follow the centralization method, explaining this case that this public participation demands the existing of communication tools and the capability of people to use them. Here, the research problem emerged as a uncertainty of success possibility of implementing the public participation to achieve decisions in urban field, incase applied on simple Iraqi rural and urban settlements.
Alchipayish City has been chosen as a study case matching research hypotheses test due to many reasons, the most important one is its being small city, like a village contains a simple society.
The public participation applied by a workshop, by which many discipline issues discussed, deducting important results, used successfully in forming comprehensive urban plan for the city future, out of people decisions themselves. This experiment proved that it is possible to apply this methodology on simple societies.

Performance Evaluation of Wastewater Treated Plant for Ninava Drug Factory

Tikrit Journal of Engineering Sciences, Volume 18, Issue 4, Pages 17-26

In this study the characteristics of raw and treated wastewater from Ninava drug factory were evaluated. The results revealed that the strength of raw wastewater can be classified as medium concentrated wastewater with respect to its BOD5 since the average value is 231.7 mg/l. In addition a strong correlations were found between many characteristics of raw waste. The characteristics of produced effluent from waste water treatment plant of the factory were within the Iraqi specification for the disposed wastewater constraints in 1997, where the average is 7.8 for pH, 40mg/l for SS, 2.8 mg/l for PO4-3, 45 mg/l for BOD5 and 104.3 mg/l for COD. The heavy metals concentrations for both raw and treated wastewater is to be less than those of the related literatures for Tigris river, municipal wastewater and water supply in Mosul city, the average heavy metal concentrations of raw and treated wastewater were 0.5 mg/l for Iron, 0.2 mg/l for zinc and 0.005 mg/l for copper, and there is no significant difference between raw and treated heavy metal concentrations.

Using SP and SF to Lower Cement Content

Tikrit Journal of Engineering Sciences, Volume 18, Issue 4, Pages 27-39

In the present research, using different percents of superplasticizer (SP) and silica fume (SF) to improve the characteristics of concrete is performed. SP and SF are added to two types of normal concrete, the first is of mixing ratio (1:2:4) and the second is of mixing ratio (1:1.5:3).
The results show that adding SF lead to increase compressive strength for first mix by about 45.3% and 47.7% while adding SP lead to increase the compressive strength by about 43% and 41% compared to reference mix at 7 and 28 day respectively. The corresponding values for second mix are 46.7% , 49%, 44% and 43% respectively.
The maximum compressive strength when SP and SF used together can be attained when the percents of SF and SP are 5% and 3% respectively. The increase in compressive strength is about 49.3% and 48.4% for first mix, while the corresponding values for second mix are 52.4% and 51.2% as they compared to reference mix at 7 and 28 day respectively.
For Tensile strength, adding SP lead to increase it by about 29.2% and 31.6% for first and second mix respectively, while the corresponding values when adding SF are 38.1% and 40.3%. The effect of using SP and SF together on increase tensile strength is more than the effect of using each one separately. The maximum tensile strength can be attained when the percents of SF and SP are 5% and 3% respectively as they increase the tensile strength by about 38.9% and 40.7% for first and second mix.
The effect of using admixtures on cement content can be noted clearly as the maximum reduction percents are about 8.7% and 9.35% for first and second mix respectively when the percent of SP is 3%. The corresponding values are 9.4% and 11.26% when the percent of SF is 5%. Using SP and SF together at percents 3% and 5% respectively lead to reduce cement content by about 10.15% and 13.54% for first and second mix respectively.

Experimental and Theoretical Study of Natural Convection Heat Transfer between Two Inclined Concentric Cylinders Filled With Porous Media

Tikrit Journal of Engineering Sciences, Volume 18, Issue 4, Pages 40-51

Porous media have considerable importance in improvement of heat transfer and storage. This research includes an experimental and theoretical study of transient and steady state natural convection heat transfer between two inclined concentric cylinders filled with a porous medium, under condition of applying uniform heat flux on the inner cylinder and constant outer surface temperature for the outer cylinder. Glass beads was used as porous medium , the study shows that the heat dissipated ability in the inner cylinder is function of Rayligh number , and the Nusselt number increase is directly proportional with the increase in Rayligh number in the steady state .
Fluent program was used to show the heat dissipation and the flow lines inside the gap between the two cylinders in the horizontal and inclined situation, the experimental results show that the nature of the heat distribution depends greatly on Rayligh number, and the angle of inclination of the cylinders. An experimental relationship between Nu&Ra was obtained under the study conditions.

Behavior of Lime Stabilized Gypseous Soil Under Different Condition

Tikrit Journal of Engineering Sciences, Volume 18, Issue 4, Pages 52-65

This research work aims to study the variations taking place (occurring) in the strength and strain of lime stabilized gypseous soil specimens with different degree of saturation when subjected to different conditions. Those conditions include stages where by (Specimens soaked in water of 25C temperature, no soaking but specimens are at ambient temperature of 25C, soaking in water of 60C temperature and no soaking but specimens are at ambient temperature of 60C). At the above mentioned conditions the specimens were loaded with a pre-determined calculated of unconfined compressive strength, these loads were increased in a cumulative manner up to failure.
The results showed that the soil strength reduced by (21, 12 and 8%) under the 1st three envisaged conditions respectively when compare with the control original specimen. Also the temperature of the soaking water has marked effect on strength indicating an increase of (18%) in the samples in water of 60C. Contrary to the strength results the strains increased by (2.24, 1.67 and 1.44) for the same above mentioned conditions as compared to the control specimen at a primary saturation condition (94%).