135 research outputs found
Effects of geometry and gas composition on swirling flow
Get PDFLean premixed swirl stabilised combustion is regarded as one of the most successful technologies for flame control and NOx reduction in gas turbines. Important characteristics of these flows are good mixing, flame stability through the formation of a Central Recirculation Zone, and low emissions at lean conditions as a consequence of the low operating temperature. This project presents a series of experiments and numerical simulations using commercial software (ANSYS) to determine the behaviour and impact on the blowoff process at various swirl numbers, nozzle geometries and gas compositions at same power outputs using confined and open conditions. Experiments were performed using a generic premixed swirl burner. The Central Recirculation Zone and the associated turbulent structure contained within it were obtained through CFD analyses providing details of the structures and the Damkölher Number (Da) close to blowoff limits. The results show how the strength and size of the recirculation zone are highly influenced by the blend and nozzle geometry, with a shift of Da and turbulence based on carbon-hydrogen ratio, shearing flows and Reynolds number. The Central Recirculation Zone was also measured and correlated to the blowoff phenomenon. A trend was found between the CRZ size/strength, the different compositions of gases used and the burner nozzle. Chemical kinetic analyses were carried out using PRO-CHEMKIN to determine flame speeds and chemical properties needed for CFD calculations. Experiments were performed using Phase Locked PIV and High Speed Photography. The Central Recirculation Zone and its turbulence were measured and correlated providing details of the structure close to blowoff. It was found that the nozzle angle has a small effect on the LBO at low flow rates using all mixtures. During the tests, the Coanda effect was observed with some geometries, thus further research was carried out regarding the transition of this phenomenon. It was found that the process occurs at a particular geometry and step size, with a shift in frequency produced by the leading structure due to the entrainment of air and strength of the latter. Stability of the flow occurs after a Coanda Vortex Breakdown (COVB) has occurred, a process similar to the one observed in the central region of the flow under regular swirling open flames. As the step size is increased, the COVB will evolve into a slower Trapped Vortex (TV
Narratives and outcomes of the uprisings in Syria and Bahrain
No full textThe narratives deployed by the political elites and the opposition groups in Syria and Bahrain has undergone a process of evolution since the onset of the Arab Spring. The examination of the cases of Syria and Bahrain is useful from a methodological perspective, since it enables us to determining the nuances that come about from the manner in which the Arab Spring unfolded in the region. This dissertation attempts to unite a diverse range of elements to present a comprehensive analysis of the nature of revolutionary consciousness, the nature of Arab transnational collective action movements in an era of globalization, and the mechanisms governing the evolutions of protest rhetoric. This dissertation draws attention to the particular ways in which language and rhetoric are used on both sides of the struggle and the ways in which rhetoric changes in response to the expectation of an international audience.Ph.D.Includes bibliographical referencesby Hesham Abdulaziz A. Alamma
Heat Transfer Characteristics for Natural Convection through Inline and Staggered Horizontal Banks of Tubes
No full textAbstract: In the present study, heat transfer characteristics of natural convection of air through 7x7 horizontal bank of tubes of 1cm diameter are studied numerically using Ansys-Fluent CFD code. Both the inline and staggered arrangements are considered. The study is carried out under constant heat generation in the tubes. The study is carried out at different spaces between the tubes in both the horizontal (longitudinal) and vertical (transverse) directions. The results of thermal and flow fields are obtained for each case. The effect of the longitudinal and transverse distances, SL and ST respectively, between the tubes on heat transfer is obtained for both the cases of inline and staggered arrangements. The studied range of both SL and ST is 1.2 to 4 cm. The results show that the heat transfer rate increases and the temperature decreases as a result of increasing the distance between the tubes in both the longitudinal and transverse directions. The effect of the longitudinal distance between the tubes on heat transfer is more pronounced than the corresponding effect of the transverse distance. Staggered arrangement has better heat transfer characteristics than the inline arrangement. Two correlations relating Nusselt number with tube spacing, one for the inline arrangement and the other for the staggered, were derived from the present results. Ideal tube spacing for the studied range of SL and ST was determined for the two arrangements.
Keywords: Heat transfer, horizontal tube bank, inline and staggered.
Title: Heat Transfer Characteristics for Natural Convection through Inline and Staggered Horizontal Banks of Tubes
Author: Abdelfatah Abdelmaksoud, Hesham Elbakhshawangy
International Journal of Novel Research in Electrical and Mechanical Engineering
ISSN 2394-9678
Vol. 10, Issue 1, September 2022 - August 2023
Page No: 39-53
Novelty Journals
Website: www.noveltyjournals.com
Published Date: 18-January-2023
DOI: https://doi.org/10.5281/zenodo.7547534
Paper Download Link (Source)
https://www.noveltyjournals.com/upload/paper/Heat%20Transfer%20Characteristics-18012023-2.pdfInternational Journal of Novel Research in Electrical and Mechanical Engineering, ISSN 2394-9678, Novelty Journals, Website: www.noveltyjournals.co
One-year mortality rate after hip fracture in the western region of Saudi Arabia A retrospective cohort study
No full text
SPECIAL FOCUS: TRAUMA
One-year mortality rate after hip fracture in the western region of Saudi Arabia: A retrospective cohort study
Al-Hebshi, Amro MDa; Hegaze, Adel MDa; Mustafa, Hesham N. MDb; Tash, Bayan MBBCha; Sawan, Dana MBBCha; Al-Faris, Khalid MBBCha
Author InformationCurrent Orthopaedic Practice 31(2):p 115-119, March-April 2020. | DOI: 10.1097/BCO.0000000000000841
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Abstract
Background:
The mortality rate of elderly patients who sustain a hip fracture is high compared to the general population. Identifying risk factors can help predict patients at risk of hip fracture to reduce the mortality rate. No studies have shown the mortality rate of patients with hip fractures in the western region of Saudi Arabia. Therefore, this study aimed to identify the risk factors associated with the mortality of patients with hip fractures admitted to the King Abdulaziz Hospital and compare the results with other studies.
Methods:
The mortality rate (within 1 yr or less) in 177 patients over the age of 60 yr who were admitted to the university hospital between July, 2007, and September, 2012, with hip fractures was retrospectively studied. The patients were assessed with regard to gender, age, type of hip fracture, and type of surgical intervention.
Results:
The overall mortality rate 1 yr after hip fracture was 12.43%, and the mean age was 77.77 yr old. The risk factors most associated with mortality were as follows: advanced age (71 to 80 and 81 to 90 yr old), male, peritrochanteric (extracapsular) fracture, and operative fixation with dynamic hip screw.
Conclusions:
The mortality rate of patients with hip fractures within 1 yr has a high-risk potential, especially for male patients over 71 yr of age with peritrochanteric (extracapsular) fractures. Surgical treatment with dynamic hip screw also was shown to be a risk factor between the different treatment options.</p
Study of Outputs Power of Broadly Tunable InGaAsp/InP AMQW Lasers
Get PDFTitle: Study of Outputs Power of Broadly Tunable InGaAsp/InP AMQW Lasers, Author: Hesham Enshasy, Location: MillsBroadly tunable InGaAsP/InP asymmetric multiple quantum well (AMQW) ridge waveguide laser diodes suffer from low output power. The output power problem of the AMQW laser diodes limits the use of these lasers in certain applications. Both theoretical and experimental studies were carried out in this work to understand the reasons behind this output power problem and to put forth solutions to this problem. As a starting point a commercial beam propagation method (BPM) optical simulator was used to optimize the confinement factor of the laser diodes. The laser diode output power almost doubled as a result of optical confinement optimization, which opens the door for improvement from electrical and thermal optimization. A commercially available partial differential equation solver, FlexPDE, was used to solve the main electronic and thermal equations and simulate a laser diode device. The FlexPDE simulations -which were validated with published data-showed poor current injection efficiency to the center of the device active region. The FlexPDE simulations showed that the main reason for this poor current injection efficiency is the ridge structure. Since the ridge structure is an essential part of this type of laser diode, effort was put forth to reduce the effect of the ridge structure on the current injection efficiency. Both simulation and experimental data showed that extending the doping profile closer to the active area would improve significantly the output power. On the other hand, a proposed forced electrical confinement method showed potential to improve the output power of the device theoretically and experimentally. The over all output power improvement went from a range of 2-5 m W to a range of 15-18 m W as a result of this study. A discussion of the two distinct output power profiles is included in the study, while detailed explanations of the dip in the power profile supported by experimental data are reported. A new method of distance measurement using one of the first, optimized, broadly tunable InGaAsP/InP short-external-cavity diode lasers is reported. Non-linear, least squares fitting method was used to extract estimates of distance from the raw data. This fitting method together with the wide tuning range (100 nm) made it possible to achieve sub-micron resolution of distance even in the presence of noise.ThesisDoctor of Philosophy (PhD
Correction to: Naturally occurring radioactive materials (NORM) concentration and health risk assessment of aerosols dust in Nicosia, North Cyprus (Journal of Radioanalytical and Nuclear Chemistry, (2024), 333, 3, (1073-1082), 10.1007/s10967-023-09346-w)
No full textThe article “Naturally occurring radioactive materials (NORM) concentration and health risk assessment of aerosols dust in Nicosia, North Cyprus”, written by Hesham M. H. Zakaly, Akbar Abbasi, Nouf Almousa and Ahmet Savaşan, was originally published Online First without Open Access. After publication in volume 333, issue 3, page 1073–1082, the author decided to opt for Open Choice and to make the article an Open Access publication. Therefore, the copyright of the article has been changed t
The use of CO2 to improve stability and emissions of IGCC combustors
No full textThe use of gas for power generation is likely to increase in the medium term. Also, the introduction of new fuels will ensure a higher generation with lower emissions under continuous operation. These scenarios lead to the conclusion that there will be a considerably more diverse range of fuel supply. However, the use of these new fuels contrasts with recent experiences of global operators who report increasing emissions and difficult combustion dynamics with even moderate variations in their fuel characteristics. Clearly there are significant challenges for fuel flexible gas turbines, particularly emission control, combustor dynamics and flame stability.
Trials using a power derivative gas turbine combustor and a high hydrogen content fuel produced unusual flashback events, in that flashback was induced by either leaning of the fuel mixture by the increase of combustion air, or by a change in composition through the reduction of methane pilot fuel. The introduction of CO2 through the combustors pilot injector prevented flashback from occurring under these circumstances. The resulting reduction of temperature in the combustion zone, indicated by lower burner tip temperatures causes a reduction in the emissions of nitrous oxides, whilst there is minimal effect on the effective turbine inlet temperature, only a 2.3% reduction.
Investigations using a ‘generic’, radial swirl burner and stereo PIV demonstrated how the flashback depended on a combination of flow structure augmentation and changes in mixture burning rate. The injection of methane or CO2 had differing effect on these parameters of the combustion zone, but both produced combinations that facilitated stability
RETRACTED ARTICLE: Effects of dexamethasone on foetal Doppler flow velocimetry
No full textWe, the Editor and Publisher of Journal of Obstetrics and Gynaecology, have retracted the following article: Ahmed M. Nofal, Tarek M. Sayyed, Hesham S. Mahmoud & Tamer Y. Atia (2021). Effects of dexamethasone on foetal Doppler flow velocimetry. Journal of Obstetrics and Gynaecology, 41 (3), 390–394. DOI: 10.1080/01443615.2020.1742677. Since publication, significant concerns have been raised about the statistical analysis in the article. When approached for an explanation, the authors fully cooperated and provided their data, but they have not sufficiently addressed the concerns raised, and concerns remain about the statistical methods in the article. As verifying the validity of published work is core to the integrity of the scholarly record, we are therefore retracting the article. The corresponding author listed in this publication has been informed. The authors do not agree with the retraction. We have been informed in our decision-making by our policy on publishing ethics and integrity and the COPE guidelines. The retracted article will remain online to maintain the scholarly record, but it will be digitally watermarked on each page as ‘Retracted’
Project Risk Management during Construction Stage According to International contract (FIDIC)
No full textAbstract: Whereas the construction industry represents a significant proportion of national income in comparison with other industries, and project management during the construction stage has a very important role through which most of the project cost is spent out, therefore the project management team has to use the best techniques in project management to get the best results. Risk Management which requires more time and effort in the preliminary stage in order to avoid or mitigate risks that may occur during construction, all project stakeholders are taking responsibility for risks during the construction stage, so it is important to take care of risk management and allocation between client and contractor according to contractual terms and conditions to achieve the project. There are many types of contracts that govern the relationship between the contractual parties either locally or internationally, study proposed FIDIC contracts to govern the relationship during construction. Study proposed risk management process to Plan Risk Management, Identify Risks, Risk Allocation, Perform Qualitative Risk Analysis, Perform Quantitative Risk Analysis, Implement Risk Responses, and Monitor. Instead of Plan Risk Management, Identify Risks, Perform Qualitative Risk Analysis, Perform Quantitative Risk Analysis, Implement Risk Responses, Monitor Risks, as mentioned in PMBOK 6th edition. risk management flow chart for governance during the construction, and automate project risk management reports and interactive dashboard that demonstrate project progresses.
Keywords: construction industry, project management team, Risk Management.
Title: Project Risk Management during Construction Stage According to International contract (FIDIC)
Author: Rizk Elimam A. Younis, Hesham Abdelkhalek, Ahmed Mohammed Abdelalim
International Journal of Civil and Structural Engineering Research
ISSN 2348-7607 (Online)
Vol. 10, Issue 2, October 2022 - March 2023
Page No: 76-93
Research Publish Journals
Website: www.researchpublish.com
Published Date: 13-February-2023
DOI: https://doi.org/10.5281/zenodo.7635679
Paper Download Link (Source)
https://www.researchpublish.com/papers/project-risk-management-during-construction-stage-according-to-international-contract-fidicInternational Journal of Civil and Structural Engineering Research, ISSN 2348-7607 (Online), Research Publish Journals, Website: www.researchpublish.co
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