Influence of Bubble Behavior on Flow Instability under Uniform and Non-Uniform Transverse Heat Distribution : 균일 혹은 불균일한 열 분포 하에 기포 거동이 유동 불안정성에 미치는 영향

Al-yahia, Omar Sharief Ibrahim 경북대학교 대학원 2018 국내박사

횡 방향으로 불균일 한 가열은 가열 된 표면의 몇몇 지역에서 높은 국부 열 플럭스를 강제하고 다른 지역에서는 낮은 국부 열 플럭스를 강제한다. 열유속 분포의 차이는 균일 한 가열 하에서 비교했을 때 비등 거동에 차이가 생길 수 있으며 이는 2 상 유동 불안정성에 직접적으로 반영됩니다. 따라서 본 연구는 횡 방향 열유속 분포가 기포 거동에 미치는 영향과 좁은 직사각형 채널 (2.35 mm × 54.0 mm × 566 mm)을 통한 유동 불안정성에 미치는 영향을 실험적으로 조사하고자 시도되었다 입구 온도 (35 ~ 65 ℃), 화력 (500 ~ 6,250W), 질량 유량 (0.03 ~ 0.13kg / s)과 같은 광범위한 실험 작동 조건이 상승 유로에 적용됩니다. 작동 유체는 대기압 하에서 탈염 된 물에 해당합니다. 채널은 측면에서 가열되고 다른 한면은 고속 카메라를 사용하여 거품 거동을 시각화 한 투명한 폴리 카보네이트 창입니다. 가열면은 너비 50mm, 길이 300mm의 알루미늄으로 구성됩니다. 실험은 유동 불안정성, 즉 (1) 전력 증가에 따른 일정 질량 유량 및 (2) 질량 유속 감소와 함께 일정한 힘을 달성하기 위해 두 가지 상이한 절차를 사용하여 수행된다. 결과는 두 작업 절차간에 일관성을 보여줍니다. 반면에, OIPF (Onset of Inlet Pressure Fluctuation)는 균일 한 가열 조건과 비 균일 한 가열 조건 모두에 대해 유사한 화력 및 유사한 질량 유량에서 발생합니다. 그러나, 기포 거동은 두 가지 가열 조건 사이에서, 특히 입구 압력의 변동 후에 발생률, 핵 형성 자리 밀도, 기포 이탈 직경 및 기포 이탈 빈도에 차이를 나타낸다. 따라서 압력 강하와 벽 온도 곡선은 두 가지 가열 조건 사이의 추세 차이를 보여줍니다. 균일 한 경우, 가열 된 표면의 전체 가로 방향에 균일하게 기포가 생성된다. 불균일 한 경우 더 높은 국부 열 유속에서 더 많은 기포가 발생되어 가로 방향의 속도 분포를 방해한다. 횡 방향의 버블 생성의 차이는 좁은 직사각형 채널에서의 유동 불안정성의 차이를 초래합니다. 본 연구는 실험 변수들의 영향을 기술하고 논의한다. 유입 과냉각, 질량 유속 및 유동 불안정 초기에 부과 된 열 유속. Onset of Flow Instability (OFI)의 실험 결과는 관련 상관 관계와 비교되었습니다. 그러나 많은 상관 관계가 OFI 결과를 과소 평가했으며 이는 실험 매개 변수의 차이의 결과 일 수 있습니다. 따라서 현재의 데이터와 다른 실험 데이터를 매우 정확하게 예측하는 새로운 OFI 경험적 상관 관계가 제안됩니다. 반면 버블 동적 파라미터는 기존 모델과 비교됩니다. 그 모델의 대부분은 풀 비등을 위해 개발 되었기 때문에, 우리의 실험 결과를 예측할 수는 없습니다 (과냉 흐름 비등). 따라서, 좁은 직사각형 채널을 통해 끓는 과냉 된 유동을 더 잘 예측하기위한 새로운 버블 동적 파라미터가 제안되었다. 새로운 모델은 RPI 벽 비등 모델에 적용되었습니다. ANSYS FLUENT 16.1을 사용한 CFD 시뮬레이션은 균일하고 비 균일 한 열유속 분포에 대한 새로운 모델을 검증하기 위해 채택되었습니다. 시뮬레이션 결과는 두 가열 조건에 대한 실험 동향과 유사한 거동을 보여줍니다. Transversely non-uniform heating enforces high local heat fluxes at a few areas on the heated surface and low local heat fluxes at others. Differences in the heat flux distribution may generate differences in the boiling behavior when compared with that under uniform heating, and that is directly reflected to the two-phase flow instability. Thus, the present research is attempt to experimentally investigate the influence of transverse heat flux distribution on the bubbles behavior and their effects on flow instability through a narrow rectangular channel (2.35 mm × 54.0 mm × 566 mm). A wide range of experimental operation conditions, such as inlet temperatures (35–65 °C), thermal power (500 – 6,250 W), and mass flow rates (0.03 – 0.13 kg/s), are applied to the upward flow channel. The working fluid corresponds to demineralized water under atmospheric pressure. The channel is heated from a side, and the other side is a transparent polycarbonate window from which the bubble behavior is visualized by using a high-speed camera. The heating surface is composed of aluminum with a width of 50 mm and a length of 300 mm. The experiments are performed by using two different procedures to achieve the flow instability, namely (1) constant mass flow rate with power increases and (2) constant power with mass flow rate decreases. The results show consistency between the two operation procedures. On the other hand, the Onset of Inlet Pressure Fluctuation (OIPF) occurs at similar thermal power and similar mass flow rates for both uniform and non-uniform heating conditions. However, the bubble behavior exhibit differences in the generation rate, nucleation site density, bubble departure diameter, and bubble departure frequency between the two heating conditions, especially after the fluctuation in the inlet pressure. Therefore, the pressure drop and wall temperature curves show differences in the trends between the two heating conditions. In the uniform case, bubbles are generated uniformly on the whole transverse direction of the heated surface. In the non-uniform case, more bubbles are generated at the higher local heat flux, which disturbs the velocity profile in the transverse direction. The differences in bubble generation in the transverse direction leads to differences in the flow instability in a narrow rectangular channel. The present study describes and discusses the influence of the experimental parameters; inlet subcooling, mass flow rate, and the imposed heat flux on the flow instability incipience. The experimental results of Onset of Flow Instability (OFI) have been compared with the relevant correlations. However, many correlations underestimate the OFI results, which may have been a results of differences in the experimental parameters. Therefore, a new OFI empirical correlation that predicts the present data and other experimental data within very good accuracy is suggested. On the other hand, the bubble dynamic parameters are compared with the existing models. Since most of those models were developed for pool boiling, none of them can predict our experimental results (subcooled flow boiling). Thus, a new bubble dynamic parameters are proposed for better estimation of the subcooled flow boiling through a narrow rectangular channel. The new models have been applied to the RPI wall boiling model. CFD simulation using ANSYS FLUENT 16.1 is adopted to validate the new models for uniform and non-uniform heat flux distribution. The simulation results show the similar behavior with the experimental trends for both heated conditions.

TENSIONS BETWEEN INDIVIDUAL ARTISTIC VISION AND CULTURAL IMPERATIVES IN CONTEMPORARY IRAQI MONUMENTAL SCULPTURE (SCULPTURE)

AL-KAISY, SA'AD IBRAHIM Pennsylvania State University 1990 해외박사

Optimizing roof maintenance and replacement decisions

Al-Ibrahim, Anwar North Carolina State University 2006 해외박사(DDOD)

The objective of this research is to develop a Decision Support System that helps allocation of available funds to optimize roof maintenance strategies. The Decision Support System analyzes different maintenance alternatives available for each roof element and chooses the alternative that maximizes the benefits due to savings resulting from postponing element replacement. The analysis uses the Life-Cycle Cost to calculate the Reduction in Uniform Annual Cost (RUAC) that is used as the economical decision criterion to select the most economical maintenance alternative for each roof element at different condition states. The analysis utilizes integer linear programming to optimize the selection of maintenance actions for the different elements by maximizing the RUAC under budgetary constraints. Excel and AMPL software are used to implement the analysis. This study uses the roofing systems of 28 buildings on the North Carolina State University campus as a model to develop the Decision Support System. Parameters necessary to develop the model are estimated. The analysis is tested on the available data base.

First-principles study of decagonal quasicrystals

Al-Lehyani, Ibrahim Hamdan Carnegie Mellon University 2002 해외박사(DDOD)

This thesis studies the energetics of decagonal quasicrystals using <italic>ab-initio</italic> methods. First, we extend the generalized pseudopotential theory (GPT) to treat ternary transition metal (TM) aluminides. The GPT interactions are decomposed to pair and many-body interactions that allow efficient calculations of total energies. In aluminum-rich systems treated at the pair-potential level, one practical limitation is a transition-metal over-binding that creates an unrealistic TM-TM attraction at short separations. An additional potential term is added for systems with short TM atom separations, formally folding repulsive contributions of the three- and higher-body interactions into the pair potentials. To do this, we have performed numerical <italic> ab-initio</italic> total-energy calculations using an Al-Co-Ni compound in a particular quasicrystalline approximant structure. The results allow us to fit a short-ranged, many-body correction of the form <italic>a</italic>(<italic> r</italic>₀/<italic>r</italic>)<italic><super>b</super></italic> to the GPT pair potentials for Co-Co, Co-Ni, and Ni-Ni interactions. We employ the corrected potentials to predict the structure of a decagonal quasicrystal from first-principles considerations. The resulting structure obeys a nearly deterministic decoration of tiles on a hierarchy of length scales related by powers of τ, the golden mean. Second, an investigation of matching rules in Al-Co-Cu quasicrystals using a form of tile Hamiltonian (TH) reveals several results. Phason flips that replace a star-hexagon pair with a pair of boats lower the energy. In Penrose tilings, quasiperiodicity is forced by arrow matching rules on rhombus edges. The edge orientation in Al-Co-Cu is due to Co/Cu chemical ordering. Tile edges meet in vertices with 72° or 144° angles. We find strong interactions between edge orientations at 72° vertices that force a type of matching rule. Comparisons between the <italic>ab-initio</italic> methods and pair potentials are presented. Lastly, we explore the applicability of the <italic>locally self-consistent multiple scattering method</italic> (LSMS) in the energy calculations of our quasicrystal models. This is an O(N) <italic>all-electron</italic> method, which makes calculations both faster and more accurate, in principle, than other available <italic>ab-initio</italic> methods.

Shopping destination choice : a case study of Riyadh, Saudi Arabia

Al-Dousary, Ibrahim Salih University Microfilms International 1987 국내박사

Occurrence and utilization of endogenous nitrate respiration in wastewater treatment processes

Al-Ghusain, Ibrahim Ahmed A Bell & Howell Co. 1997 국내박사

Representations of learning disabilities in Saudi Arabian elementary schools: A grounded theory study

Al-hano, Ibrahim A The University of Wisconsin - Madison 2006 해외박사(DDOD)

In 1996, learning disabilities (LD) was introduced as formal category of disability into Saudi Arabia educational system. This qualitative grounded theory study aimed at understanding how members of LD teams in 9 Saudi public elementary schools perceived and made sense of students with LD and the contexts that surround the identification process. The data were gathered through semi-structured interviews with 13 LD teachers, 10 regular classroom teachers, 9 school counselors, 6 school principals, and 3 parents. The theory developed in this study posits that, since the introduction of LD category into Saudi schools in 1996, there has been conflict over the identity of children experiencing learning difficulties in Saudi school, between, on one hand, the official LD discourse created by scientists and policymakers, and on the other the local commonsense social discourse created by people in everyday life in Saudi society. Data indicate that the points at which the two discourses tend to diverge sharply include the notion that: (1) children with LD have disability, (2) the cause of children low achievement lies within children due to neurological damage, and (3) that LD is a life-long phenomenon. By labeling otherwise normal children as disabled, the LD discourse raised complex dilemmas at the community level as well as at the individual level, where disability labels have the potential to impact a child's identity and self-worth in negative ways. In response, participants coped with the new LD category by dismissing, deemphasizing, or resisting the unfamiliar aspects of LD, which in turn affected the identification of students with LD. The identification process---via referrals, evaluation, eligibility, and remediation---is seen as a regular occurrence intended to identify students who need extra help or services rather than a process that classifies children into a category of disability. The decision-making atmosphere and the diagnosis of a child as LD generally were regarded as unproblematic.

Online-information-based learning and decision making under uncertainty

Al-Shyoukh, Ibrahim Ali Odeh University of California, Los Angeles 2007 해외박사(DDOD)

In this work, we utilize information-based learning tools for learning in unknown and complex systems. Two problems are considered. First, we study the problem of stabilizing an unknown plant using switching supervisory control. We formulate the problem as an online decision problem and use "calibrated forecasts" as a mechanism for controller selection in supervisory control. The forecasted event is whether or not a controller will be effective over a finite implementation horizon. Controller selection is based on using the controller with the maximum calibrated forecast of the reward. Assuming the existence of a stabilizing controller within the set of candidate controllers, we show that with the proposed supervisory controller, the output of the system remains bounded for any bounded disturbance, even if the disturbance is chosen in an adversarial manner. Moreover, we show that the proposed formulation provides stability guarantees even when the reward received is corrupted with (possibly infinite) zero-mean finite-variance noise. The main results are obtained for a general class of system dynamics and specialized to linear systems. Second, we propose an approach for systematic testing and learning in complex biological systems. The approach combines the use of a stochastic search algorithm and biological experiments to identify and study desired biological behaviors using external stimuli. As an example illustrating the validity of the proposed approach, we utilize the approach to study the effects of multiple drugs on the lytic-cycle induction of Kaposi's sarcoma-associated herpesvirus (KSHV). An alternate approach is also proposed where a relatively small set of sample data is experimentally evaluated and the results are used to construct a function map approximation of the input-output behavior of the biological system. To validate the alternate approach, we apply it to the same problem of KSHV reactivation. The results for the two proposed approaches indicate that they present a potential tool for systematic studying of the induced functions of complex biological systems by multiple external stimuli and for studying and developing drug therapies for several diseases.

ON MERGING SEQUENCING AND SCHEDULING THEORY WITH GENETIC ALGORITHMS TO SOLVE STOCHASTIC JOB SHOPS

AL-HARKAN, IBRAHIM M THE UNIVERSITY OF OKLAHOMA 1997 국내박사

Effect of higher prescription co-payments on clinical outcomes in patients with hypercholesterolemia in a managed care organization

Al-Zakwani, Ibrahim S University of the Sciences in Philadelphia 2005 해외박사(DDOD)

Prescription cost-sharing mechanisms have been demonstrated to reduce prescription utilization and expenditures. However, the literature evaluating the impact of prescription cost-control on actual clinical outcomes is largely unexplored. The aim of this research was to evaluate the effect of higher prescription co-payments on clinical outcomes in patients with hypercholesterolemia in a managed care organization. A retrospective, observational cohort analysis was conducted of pharmacy, medical, and laboratory claims database from a southeastern US health plan. Patients were included if they began statin therapy between 7/1/1999 and 6/30/2001, had no dyslipidemic therapy in the previous 6 months, had continuous health plan enrollment 6 months pre-index and 12 months post-index, and had both pre- and post-index lipid measurements. Patients were stratified into higher (≥$20) and lower (<$20) prescription co-payment cohorts. The primary endpoints were mean percent change in each of the lipid fractions (total cholesterol [TC], LDL-cholesterol [LDL-C], HDL-cholesterol [HDL-C], and triglycerides [TG]), NCEP-ATP-III (National Cholesterol Education Program) LDL-C goal attainment, and time to development of major adverse cardiac event (MACE). Statistical analyses were conducted using ordinary least squares, logistic, and Cox proportional hazard regression. A total of 5,476 patients were identified (<$20 = 3,157; ≥$20 = 2,319). The higher prescription co-payment cohort was associated with a significantly greater adjusted mean percent reduction in LDL-C (-26.2% vs. -25.2%; p = 0.022) and a significantly greater adjusted mean percent increase in HDL-C (1.6% vs. 0.7%; p = 0.039) when compared to the lower prescription co-payment group. There were no significant differences in mean percent change in TC and TG as well as NCEP-ATP-III LDL-C goal attainment rates between the groups. However, patients in the higher prescription co-payment cohort were associated with higher MACE events compared to those in the lower prescription co-payment group (HR 1.37; 95% CI: 1.02 to 1.85; p = 0.36). These findings indicate an association between prescription cost-sharing and the most important outcome measure of all, actual cardiac events. However, the non-significant and counterintuitive findings of the intermediate lipid laboratory outcomes as well as the potential limitations, call for substantial further research into the relationship between prescription co-payment and MACE before any definitive conclusions are made.