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Article
Viscosity Effect on Stiffness of Non-conventional (Five Tilted Pads) Journal Bearing

Authors: Mohammed Oawed Atteaa Alhassany --- Ali Khalid Aldulaimy
Journal: Tikrit Journal of Engineering Sciences مجلة تكريت للعلوم الهندسية ISSN: 1813162X 23127589 Year: 2018 Volume: 25 Issue: 3 Pages: 53-57
Publisher: Tikrit University جامعة تكريت

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Abstract

In this tribological study, we highlight the effect of lubricating oil viscosity in the Multi-pads hydrodynamic journal bearings generate important improvement in characteristics of stiffness and stability in the high speed turbomachines. Depending on viscosity of oil film (three values) variation for five tilted pads bearing, each pad is pivoted and is facilitated to be tilted with small angles, by using Matlab program, we calculate the oil film thickness for convergence layer. We applied Reynold's equation and solved it's numerically by using finite difference method with 5 nodes technique to find the pressure distributed on each node in the mesh of tilted pad, then calculate stiffness coefficients. Results show that there is clear effect on stiffens with viscosity change. The increase in value of Krr (for n = 0.3) between viscosity (0.04 Pas. s) and viscosity (0.058 Pas. s) is14.33 MN/m, while the increase in Krr value between viscosity (0.058 Pas. s) and viscosity (0.087 Pas. s) is 11.37 MN/m. the increase in value the of Kss (for n = 0.3) between viscosity (0.04 Pas. s) and viscosity (0.058 Pas. s) is5.921 MN/m, while increase in Kss value between viscosity (0.058 Pas. s) and viscosity (0.087 Pas. s) is9.55 MN/m respectively. the increase in value of Ksr (for n = 0.3) between viscosity (0.04 Pas. s) and viscosity (0.058 Pas. s) is 8.95 MN/m, while the increase in Ksr value between viscosity (0.058 Pas. s) and viscosity (0.087 Pas. s) is 14.41 MN/m respectively. the increase in value of Krs (for n = 0.3) between viscosity (0.04 Pas. s) and viscosity (0.058 Pas. s) are 5.08 MN/m, while the increase in Krs value between viscosity (0.058 Pas. s) and viscosity (0.087 Pas. s) is8.19 MN/m respectively. The values of the dominate principal coefficients Krr is greater than that of Ksr, also The values of the principal coefficients Kss is greater than that of cross coupling Krs for all values of viscosity that studied. From this result, we can conclude the side effect of cross coupling coefficients (Ksr ,Krs) can be overcome by great values for principal coefficient (Krr, Kss) respectively, so we can get good improvement instability for this bearing by variation the viscosity. After that, we regarded to use high viscosity lubricant in multi-pad journal bearing to improve the performance and stability by controlling the stiffness coefficients.


Article
Analysis, Modeling, and Design of a Reliable Wide Area Network Case Study for Tikrit University Intranet

Authors: Ibrahim Khalil Sileh --- Sufyan H. Ali --- Musaria Karim Mahmood
Journal: Tikrit Journal of Engineering Sciences مجلة تكريت للعلوم الهندسية ISSN: 1813162X 23127589 Year: 2018 Volume: 25 Issue: 2 Pages: 35-39
Publisher: Tikrit University جامعة تكريت

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Abstract

This work presents the analysis and modeling of communication network used for data transmission with multi-protocols in campus network. The designed network is based on the geographical location of communication nodes. (Colleges and centers). Network optimal backbone is first designed by Kruskal algorithm. It will be subject to reliability improvement by links addition. Tie-sets method is used to evaluate the network reliability. Communication nodes are modeled using local area network (LAN), server, links, router, switch, and Firewall. Intranet will be used as communication backbone mainly to connect different communication nodes with the Principal Communication Center (PCC) where the System Server (SS) is located. The connection of Intranet to the Internet is mad via the front-end system server (SS). Tikrit University Intranet (TUI) is taking as case study in the present research. Tikrit University sites are grouped into master communication nodes. Each node is composed from several colleges, centers, and administrative sections.


Article
The Effect of Pads Number and Their Tilt Angles on the Bearing Stiffness
تأثير عدد الوسادات وزوايا ميالنها على معامل نابضية المسند

Author: Ibrahim Ali Muhsin
Journal: Tikrit Journal of Engineering Sciences مجلة تكريت للعلوم الهندسية ISSN: 1813162X 23127589 Year: 2018 Volume: 25 Issue: 4 Pages: 6-10
Publisher: Tikrit University جامعة تكريت

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Abstract

In this work a plain (conventional) and a tilted bad bearings are analyzed and studied (both have the same dimensions and work conditions). Three, four and five pads models are studied. The pads are fixed circumferentially in a manner each two close pads are separated with an angle that is the same for all the close pads.Each pad is pivoted in its trailing edge and is facilitated to be tilted around this pivot with small angles. This study was achieved for three values of tilting angles. These angles are, 0.01o, 0.011o and 0.012o. Two dimensions' form of Reynolds equation is used and solved numerically then the stiffness coefficients had been calculated. A comparison had been done between the stiffness coefficients values for the two models (tilted pads and conventional bearings). The results of this comparison was found that (for n = 0.4), are, +28%, +275%, +270 % and -100% for Ksr, Krr, Kss and Krs respectively. It was noticed that the values of the principal coefficients Krr and Kss are increased significantly while the cross coupling coefficient, (Krs) is decreased significantly and (Ksr) is increased slightly. And this is a positive sign for stability improvement. Also it was found that increasing the tilt angle (delta) cause an increase of the stiffness coefficients values. These increases (for n = 0.4 and changing the tilt angle from 0.010 to 0.011 then to 0.012 respectively) are, Krr=+50%, +47%, Kss = +40%, +32%, Ksr = +33%, +42%, and Krs = +15%, +20%. And since increasing the values of the cross coupling coefficients make the bearing stability worse, so increasing the tilt angle is not apreferable method for improving stability. Changing the number of pads is a better solution and it was found that three pads bearing is the best among them.

في هذا البحث تمت دراسة مسند تقليدي وآخر ذو وسادات قابلة لألمالة والضبط حول حافاتها األمامية. حيث ان كال المسندين لهما نفس األبعاد وظروف العمل. تمت دراسة مسند ذو ثالثة وأربعة وخمسة وسادات. في كل منها تكون الوسادات مثبته محيطياً على جسم المسند وتنحصر بينها فضاءات محيطية متساوية وفي نفس الوقت الزاوية o المركزية ألي وسادة تكون مساوية للزاوية المركزية ألي فضاء. أنجزت هذه الدراسة لثالث قيم لزاوية إمالة الوسادات. هذه القيم هي , 0.01 o و 0.011 o 012.0 . حيث تم معادلة رينولدز والتي حلت عدديا باستخدام تقنية الفروقات المحددة ومن ثم تم إيجاد معامالت النابضية لكلي المسندين (التقليدي وذو الوسادات) وكانت النتيجة كما ً استخدام يلي: لنسبة المركزية مقدارها )4.0 = n )فأن قيم معامالت النابضية األربعة Ksr ,Krr, Kss وKrs على التوالي للمسند ذو الوسادات تزيد بمقدار %28%,+275%,+270 + و%100 -على التوالي مقارنة بقيمها للمسند التقليدي . من النتائج أعاله يمكن مالحظة زيادة قيم معامالت النابضية األساسية ) Kss, Krr )ونقصان ملحوظ لمعامل النابضيةالمستعرض Krs وهذا مؤشر على تحسن أستقرارية المسند ذو الوسادات على الرغم من الزيادة القليلة للمعامل Ksr .كذلك وجد أن قيم هذه المعامالت للمسند ذو الوسادات قد o زادت بزيادة زاوية أمالة الوسادات وكما يلي: بتغيير زاوية أمالة كل وسادة من الى 0.010 o الى 0.011 o ثم 012.0 ولقيمة نسبة المركزية مقدارها )4.0 = n )فأن كل معامالت النابضية األربعة قد زادت وكما يلي: Krr قد زاد بمقدار %50% ,+47 +على التوالي، Kss قد زاد بمقدار ,%32% +40 ، +Ksr قد زاد بمقدار % 33 ,%42 .Krs قد زاد بمقدار %15%, +20 . +مادامت زيادة زاوية إمالة الوسادات يؤدي الى زيادة كل معامالت النابضية بنوعيها، األساسية ) Kss, Krr )والمستعرضــة )Ksr، Krs )لذا فأن زيادة زاوية أمالة الوسادات التعد الطريقة المفضلة لتحسين استقراريه المسند ويبقى أسلوب زيادة عدد الوسادات هو الحل األمثل لتحسين األستقرارية وبالتحديد استخدام المسند ثالثي الوسادات.


Article
Physical Properties of Gypseous Soil after Gypsum Removal using EDTA Solution

Author: Farouk Majeed Muhauwiss
Journal: Tikrit Journal of Engineering Sciences مجلة تكريت للعلوم الهندسية ISSN: 1813162X 23127589 Year: 2018 Volume: 25 Issue: 2 Pages: 68-73
Publisher: Tikrit University جامعة تكريت

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Abstract

The main structural problem in construction on gypseous soils is due to the melting of the gypsum when exposed to water. This may be creating voids in the soil leading to rearrangement of the soil structure and moving the soil particles to more stable positions. This can cause excessive settlement which directly affects superstructures. This study, investigates the influence of gypsum removing on granular soil classification. Four gypsum soil specimens were taken from Al-Qadisiyah district in Tikrit at different depths from the natural ground surface. The depths adopted were 0.75, 1.10, 2.00 and 3.30 m. The corresponding gypsum content was 42.23%, 32.50%, 8.75% and 19.82%, respectively. The EDTA solution was used to disassemble and remove the gypsum particles by washing using distilled water. The results showed that EDTA solution and washing with distilled water was an effective method to remove gypsum from granular soils. Gypsum ratio was reduced to less than 2% in all tested specimens. The percentage of organic matter was not affected, and the specific gravity of the specimens increased between 2% and 12%. The gypsum removal process affected the granular distribution curves of the soil specimens and led to a decrease in the rate of soil grain diameters. In general, classification process of the soil before and after the washing of gypsum from the soil was not affected.


Article
Effecting of Steel Fibers and Fly Ash on the Properties of Concrete
تأثير األلياف الحديدية والرماد المتطاير على خصائص الخرسانة

Authors: Mazin B. Abdul-Rahman --- Alya’a A. Ali --- Amenah M. Younus
Journal: Tikrit Journal of Engineering Sciences مجلة تكريت للعلوم الهندسية ISSN: 1813162X 23127589 Year: 2018 Volume: 25 Issue: 4 Pages: 30-36
Publisher: Tikrit University جامعة تكريت

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Abstract

In this research, the effect of the addition of fly ash particles with different weight ratios of 15%, 20%, and 25% as well as the addition steel fibers with different volume fractions of 0.25%, 0.75%, and 1.25% on the mechanical properties of concrete (compressive strength and modulus of rupture) was studied. To carry out this research, ten concrete mixes were prepared, one of which is the reference normal concrete (without any additives), the others contain steel fibers and fly ash as additives with the mentioned volumetric and weight proportions. For each type of concrete mix, three standard 150×300 mm cylinders and three standard prisms100×100×500 mm were casted, water to cementing material ratio was fixed for all concrete mixes (W/cm = 0.435) and the superplasticizer was used with ratio of 0.98%-1.22% by weight of the cementitious material in mixtures that contain steel fibers and fly ash particles as a partial replacement of cement weight. The results showed that the addition of fly ash particles had little effect on the mechanical properties of normal concrete, while the steel fibers had the greatest effect. The highest increase in compressive strength and flexural strength compared with reference concrete was 61.60% and 78.84%, respectively in the volume fractions 1.25% of steel fiber.

في هذا البحث تم دراسة تأثير إضافة جزيئات الرماد المتطاير بنسب وزنية مختلفة (15، %20، %25%) وكذك إضافة األلياف الحديدية بنسب حجمية مختلفة (25.0% ،75.0%، 25.1%)على الخصائص الميكانيكية للخرسانة اإلعتيادية في االنضغاط واالنثناء . وإلجراء هذه الدراسة تم تحضير عشر خلطات خرسانية، واحدة منها للخرسانة االعتيادية المرجعية )الخالية من المضافات(، واالخرى تحتوي على مضافات األلياف الحديدية والرماد المتطاير وبالنسب الحجمية والوزنية المذكورة أعاله. لكل نوع من ( ملم، وثالثـة مواشير قياسـية أيضا 100×100×500 )ملم، وكانت نـسـبـة الـماء الى الســمنت ثابتة ً انواع الخلطات الخرسانية تم صب ثالثة اسطوانات قياسية )150×300( في الخلطات الخرسانية كافة ومساوية الى (435.0 الملدن الفائق بنسبة ستخدم (، وأ 98.0-1.22 )%من وزن المواد السمنتية للخلطات المعززة باأللياف الحديدية والتي تحتوي على جزيئات الرماد المتطاير كاستبدال جزئي من وزن السمنت. وقد أظهرت النتائج بان اضافة جزيئات الرماد المتطاير لها تأثير قليل على الخواص الميكانيكية للخرسانة االعتيادية ، في حين كان لاللياف الحديدية التأثير األكبر، إذ كانت أعلى نسبة زيادة في مقاومة االنضغاط ، ومقاومة االنثناء بالمقارنة مع الخرسانة المرجعية هي )60.61 )% و )84.78 )%على التوالي عند النسبة الحجمية )25.1 )%لاللياف الحديدية.


Article
Ductility Improvement of R.C Beams with Large Web opening by using Reactive Powder Concrete Layers

Authors: Husain Khalaf Jarallah --- Nidaa Qassim Jassim
Journal: Tikrit Journal of Engineering Sciences مجلة تكريت للعلوم الهندسية ISSN: 1813162X 23127589 Year: 2018 Volume: 25 Issue: 3 Pages: 30-39
Publisher: Tikrit University جامعة تكريت

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Abstract

In this investigation the effect of large web opening on the on the behaver of beams made by normal concrete (NC) and reactive powder concrete (RPC) have been studied. The experimental work consists of casting and testing in flexure 12 rectangular simply supported reinforced concrete beams. The main parameters of this test are opening locations and normal concrete and RPC location with is the section. The ultimate loads, cracking loads, load -deflection behavior, skew of the openings (deflection at the two opposite corners of openings) and ductility were discussed. These results showed that increase ultimate loads (Pu) and stiffness by increase RPC layers. The using RPC layers increase ultimate load about (1-30) %. Using RPC in compression fiber is found to be more effective than using RPC in tension fiber. The cracking load of hybrid beam with one layer of RPC in compression fiber (having one opening) higher than NC beams by 48.5%. The ultimate strength was decreases with increases opening about (4-21)%, thus indicating that the stiffness decreases accordingly. Hybrid beams with RPC in tension fiber failed with less crack than those for hybrid beams with RPC in compression fiber at the same number of openings. The skew at opening of flexural zone show greater values than the skew at opening in shear zone for each beam until failure. The increase in the number of openings leads to increase in the ductility because it reduces the strength of beams.


Article
Performance Enhancement of a Darrieus Vertical Axis Wind Turbine using Divergent Ducting System

Authors: Abdullateef A. Jadallah --- Sahar R. Farag --- Jinan D. Hamdi
Journal: Tikrit Journal of Engineering Sciences مجلة تكريت للعلوم الهندسية ISSN: 1813162X 23127589 Year: 2018 Volume: 25 Issue: 3 Pages: 58-66
Publisher: Tikrit University جامعة تكريت

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Abstract

Ducting system is an effective way to potentially augment the performance of wind turbine for applications in building architectures. This paper is aimed to study one of the possible enhancement method of the vertical axis wind turbine performance. It is characterized by adding divergent duct to facilitate imparting more flow rate. The divergent duct was designed and adapted with wind turbine. The system was modelled and simulated analytically and numerically. A computer program built in MATLAB 16 to simulate the performance of system. The performance and flow are also solved numerically using ANSYS-FLUENT 17.2. Two opening angles of the divergent -duct were employed to study the behavior of air flow through divergent duct and results were compared with base vertical axis wind turbine. The duct turbine with a straight wall type diffuser demonstrate power coefficient augmentation by 24.2% and 9.09% for opening angle 20° and 12° respectively. The optimum half opening angle was attained for the diffuser. The diffuser’s length of a half of the throat opening is recommended, and its angle of opening is 20°. The diffuser was located in a stream-was direction that adequately aligned with the center of the vertical axis wind turbine. Results showed a reasonable influence on the performance of wind turbine. This technology may be used in gates and in urban areas with a relatively low wind speed regime.


Article
Experimental and Numerical Study of Heat Transfer Enhancement in a Shell and Tube Heat Exchanger using Helical Coiled Wire Inserts

Authors: Musa Mustafa Weis --- Ehsan Fadhil Abbas --- Ahmed Sami Ridha
Journal: Tikrit Journal of Engineering Sciences مجلة تكريت للعلوم الهندسية ISSN: 1813162X 23127589 Year: 2018 Volume: 25 Issue: 2 Pages: 74-79
Publisher: Tikrit University جامعة تكريت

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Abstract

An experimental work on heat transfer enhancement in a shell and tube heat exchanger by insertion of helical coiled wires into the tube bundle was conducted. Four different pitch sizes were used (4.8, 6.4, 8.0, 9.6) mm. The working fluid for both shell and tube sides of the exchanger was water. Flow arrangement used was parallel and laminar for both sides with a Reynolds number for the tube inside ranging (100-920). Variables were taken into account, including; convection heat transfer coefficient, number of heat transfer units, thermal effectiveness, and pressure drop. CFD analysis was done in order to validate the experimental results. The study results showed an increase in heat transfer coefficient on the tube side by 54% due to the use of 9.6 mm pitched inserts. Highest thermal effectiveness obtained was in the case of 9.6 mm pitch inserts. Pressure drop rose up to 260% due to inserts.


Article
Hybrid CFD-ANN Scheme for Air Flow and Heat Transfer Across In-Line Flat Tubes Array

Authors: Tahseen Ahmad Tahseen --- M. Ishak --- Khalaf Ibrahim Hamada --- M.M. Rahman --- et al.
Journal: Tikrit Journal of Engineering Sciences مجلة تكريت للعلوم الهندسية ISSN: 1813162X 23127589 Year: 2018 Volume: 25 Issue: 2 Pages: 59-67
Publisher: Tikrit University جامعة تكريت

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Abstract

Flat tubes are vital components of various technical applications including modern heat exchangers, thermal power plants, and automotive radiators. This paper presents the hybridization of computational fluid dynamic (CFD) and artificial neural network (ANN) approach to predict the thermal-hydraulic characteristics of in-line flat tubes heat exchangers. A 2D steady state and an incompressible laminar flow in a tube configuration are considered for numerical analysis. Finite volume technique and body-fitted coordinate system are used to solve the Navier–Stokes and energy equations. The Reynolds number based on outer hydraulic diameter varies between 10 and 320. Heat transfer coefficient and friction are analyzed for various tube configurations including transverse and longitudinal pitches. The numerical results from CFD analysis are used in the training and testing of the ANN for predicting thermal characteristics and friction factors. The predicted results revealed a satisfactory performance, with the mean relative error ranging from 0.39% to 5.57%, the root-mean-square error ranging from 0.00367 to 0.219, and the correlation coefficient (R2) ranging from 99.505% to 99.947%. Thus, this study verifies the effectiveness of using ANN in predicting the performance of thermal-hydraulic systems in engineering applications such as heat transfer modeling and fluid flow in tube bank heat exchangers.


Article
Effect of the Combined Pollution of Brick Industry and Sandstorms on the Performance of High Voltage Insulators and Flashover Phenomenon

Author: Israa Amer Dahham
Journal: Tikrit Journal of Engineering Sciences مجلة تكريت للعلوم الهندسية ISSN: 1813162X 23127589 Year: 2018 Volume: 25 Issue: 1 Pages: 69-73
Publisher: Tikrit University جامعة تكريت

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Abstract

Recent repeated flashovers and power outage incidents in an (400/132) kV substation, located in the Ad Diwaniyah Province, have called for extensive investigations to evaluate the effect of subsequent deposition of sandstorm and free carbon particles (soot) on the performance of HV insulators and probable flashover occurrences. In the Ad Diwaniyah Province, the insulators of the transmission lines and substations are normally subjected to sandstorms (once or twice per year). Moreover, rapid brick industry expansion (10 brick factories constructed and operated over the last ten years) within the area of the Shafeyea, where, the (400/132) kV substation is located, has also led to a noticeable industrial pollution. Porcelain and polymeric insulators were exposed to sand and soot polluted environments and the effect of pollution severity on the flashover characteristics was investigated. Flashover voltages were measured under various simulated polluted environments for both porcelain and polymeric insulators. Obtained results show that the deposition rate of soot particles is highly increased when both porcelain and polymeric insulators are already polluted with sand particles regardless of whether the sand particles are charged or not. However, moistening was found very critical to pollutant layer build-up and consequently increases the severity of pollution.

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