Numerical investigations on winglet effects on aerodynamic and aeroacoustic performance of a civil aircraft wing

Vaezi, Erfan,Fijani, Mohammad Javad Hamedi Techno-Press 2021 Advances in aircraft and spacecraft science Vol.8 No.4

The paper discusses the effect of the winglets on the aerodynamic and aeroacoustic performance of Boeing 737-800 aircraft by numerical approach. For this purpose, computational fluid dynamics and fluent commercial software are used to solve the compressible flow governing equations. The RANS method and the K-ω SST turbulence model are selected to simulate the subsonic flow around the wing with acceptable accuracy and low computational cost. The main variables of steady flow around the simple and blended wing in constant atmospheric conditions are computed by numerical solution of governing equations. The solution of the acoustic field has also been accomplished by the broad-band acoustic source model. The results reveal that adding a blended winglet increases the pressure difference near the wingtip,which increases the lift force. Also, the blended winglet reduces the power and magnitude of vorticities around the wingtip, which reduces the wing's drag force. The effects of winglets on aerodynamic forces lead to a 3.8% increase in flight range and a 3.6% increase in the maximum payload of the aircraft. Also, the acoustic power level variables on the surfaces and fields around the wing have been investigated integrally and locally.

Numerical investigations on winglet effects on aerodynamic and aeroacoustic performance of a civil aircraft wing

Vaezi, Erfan,Fijani, Mohammad Javad Hamedi Techno-Press 2021 Advances in aircraft and spacecraft science Vol.8 No.4

The paper discusses the effect of the winglets on the aerodynamic and aeroacoustic performance of Boeing 737-800 aircraft by numerical approach. For this purpose, computational fluid dynamics and fluent commercial software are used to solve the compressible flow governing equations. The RANS method and the K-ω SST turbulence model are selected to simulate the subsonic flow around the wing with acceptable accuracy and low computational cost. The main variables of steady flow around the simple and blended wing in constant atmospheric conditions are computed by numerical solution of governing equations. The solution of the acoustic field has also been accomplished by the broad-band acoustic source model. The results reveal that adding a blended winglet increases the pressure difference near the wingtip,which increases the lift force. Also, the blended winglet reduces the power and magnitude of vorticities around the wingtip, which reduces the wing's drag force. The effects of winglets on aerodynamic forces lead to a 3.8% increase in flight range and a 3.6% increase in the maximum payload of the aircraft. Also, the acoustic power level variables on the surfaces and fields around the wing have been investigated integrally and locally.

Two-dimensional and volumetric airway changes after bimaxillary surgery for class III malocclusion

Toraj Vaezi,Seyed Hossein Hosseini Zarch,Majid Eshghpour,Hamed Kermani 대한구강악안면외과학회 2017 대한구강악안면외과학회지 Vol.43 No.2

Objectives: Any change in maxilla and mandible position can alter the upper airway, and any decrease in the upper airway can cause sleep disorders. Thus, it is necessary to assess airway changes after repositioning of the maxilla and mandible during orthognathic surgery. The purpose of this study was to evaluate linear and volumetric changes in the upper airway after bimaxillary surgery to correct class III malocclusion via cone-beam computed tomography (CBCT) and to identify correlations between linear and volumetric changes. Materials and Methods: This was a prospective cohort study. CBCTs from 10 class III patients were evaluated before surgery and three months after. The Wilcoxon one-sample test was used to evaluate the differences in measurements before and after surgery. Spearman’s rank correlation coefficient was used to test the correlation between linear and volumetric changes. Results: The results show that the nasopharyngeal space increased significantly, and that this increase correlated with degree of maxillary advancement. No significant changes were found in volumes before and after surgery. A correlation was found between linear and volumetric oropharyngeal changes. Conclusion: Bimaxillary surgical correction of class III malocclusion did not cause statistically significant changes in the posterior airway space.

The fabrication of a dip- coated tin oxide thin film via solgel processing and a study of its gas sensing properties

M. R. Vaezi 한양대학교 세라믹연구소 2012 Journal of Ceramic Processing Research Vol.13 No.6

In this paper, tin oxide, SnO2, thin films were coated on soda- lime glass substrates using the simple and economic processing route such as dip coating sol- gel method. In the preparation of a stable sol, instead of using only one alcohol, a combination of some alcohols without adding any surfactant and applying non- liquid tin chloride has been used. The effect of temperature, time, and thickness of the layers were studied. The phase and structural determination of samples were obtained by X-ray diffraction (XRD) analysis. Scanning electron microscopy (SEM) images were used for size and morphological evaluation of the thin films obtained. The gas- sensor response of tin dioxide thin films was determined by electrical sheet resistance measurements. After exposing the gas to different concentrations of ethanol, the effects of temperature, gas concentration, size, shape, dispersion of crystallite and thickness of the film on the sensor response were investigated. The best sensing responses are related to a two- times deposited layer with a thickness of about 299 nm heated at 400 ο C and 600 ο C. The first detection of gas concentration was at about 27.7 ppm ethanol at 300 ο C. Also, the level of response and recovery times of this sensor were 70 and 88 s, respectively.

Effects of substrate etching, Sn+2 doping and surfactant addition on the morphology of chemically deposited zinc oxide films

Mohammad Reza Vaezi 한양대학교 세라믹연구소 2011 Journal of Ceramic Processing Research Vol.12 No.4

The effect of substrate etching by HF, doping by SnCl2 and the addition of a surfactant such as Tiron on the morphology and growth rate of zinc oxide deposits is investigated. The layer is produced on a high purity alumina (HPA) substrate by two-stage chemical deposition (TSCD) from a solution containing an ammonium zinc complex. Etching does not affect the structure of films thinner than 400 nm. It has, however, a considerable effect on the structure of films greater than 800 nm. The latter is produced by 70 times dipping of the substrate into the ZnO containing solution. It is seen that 100 times of dipping results in the formation of acicular grains on the initially formed grains. The addition of 2 drops per lit (d/l) of Tiron changes the surface morphology and causes the formation of a fine-grained structure. Further addition of Tiron causes poisoning of the nucleation stage and coarsens the grains. The same effect is observed with Sn-doping of the film. Adding more than 2% Sn as a dopant induces poisoning of the nucleation stage and hinders the formation of fine grains. Combined substrate etching and Tiron addition effects are discussed in this paper.

Synthesis of nanosized SnO/ZnO coupled oxides via co-precipitation method

M. R. Vaezi 한양대학교 세라믹연구소 2015 Journal of Ceramic Processing Research Vol.16 No.4

In this paper, SnO/ZnO nanocomposites have been produced via co-precipitation method for the first time. SnCl2, ZnCl2 and NaOH were used as precursors. The synthesized powders were characterized by X-Ray Diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), Brunauer-Emmett-Teller adsorption isotherm (BET) and X-ray florescence (XRF) analyses. Effect of synthesis temperature on the obtained phases, particle size and morphology, crystallite size and specific surface area of produced nanocomposites have been discussed. It has been shown that at lower synthesis temperature only ZnO nanocrystals could be produced, however at higher temperatures SnO/ZnO nanocomposites could be formed and this co-existence of phases affects the powders crystallite sizes, morphologies, particle sizes and specific surface areas.

CTAB assisted hydrothermal synthesis of ZnO/Co(OH)2 nano-composites: Mechanisms of synthesis and growth of composite

M. R. Vaezi 한양대학교 세라믹연구소 2014 Journal of Ceramic Processing Research Vol.15 No.6

In this paper, nano-composites of ZnO/Co(OH)2 were synthesized via Hydrothermal processing. Co(NO3)2.6H2O, Zn(NO3)2 • 4H2O (0.5 M, 200 ml) and KOH (2 M, 200 ml) were used as precursors. N_Cetyl_N,N,N,_tri methyl ammonium bromide (CTAB) was used as surfactant and its effects on the morphologie was investigated. The crystal growth mechanism was studied via Growth Unit Model and thermodynamics of cobalt oxide formation from its hydroxide under hydrothermal condition. Nano-rods and nano-hexagonals were prepared via hydrothermal synthesis with and without using CTAB, respectively. Also, the effects of hydrothermal periods on morphologies and particle growth were investigated in this paper. Xray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the products obtained.

Non-Orthogonal Multiple Access in Multi-Cell Networks: Theory, Performance, and Practical Challenges

Shin, Wonjae,Vaezi, Mojtaba,Lee, Byungju,Love, David J.,Lee, Jungwoo,Poor, H. Vincent IEEE 2017 IEEE communications magazine Vol.55 No.10

<P>Non-orthogonal multiple access (NOMA) is a potential enabler for the development of 5G and beyond wireless networks. By allowing multiple users to share the same time and frequency, NOMA can scale up the number of served users, increase spectral efficiency, and improve user-fairness compared to existing orthogonal multiple access (OMA) techniques. While single-cell NOMA has drawn significant attention recently, much less attention has been given to multi-cell NOMA. This article discusses the opportunities and challenges of NOMA in a multi-cell environment. As the density of base stations and devices increases, inter-cell interference becomes a major obstacle in multi-cell networks. As such, identifying techniques that combine interference management approaches with NOMA is of great significance. After discussing the theory behind NOMA, this article provides an overview of the current literature and discusses key implementation and research challenges, with an emphasis on multi-cell NOMA.</P>

Coordinated Beamforming for Multi-Cell MIMO-NOMA

Shin, Wonjae,Vaezi, Mojtaba,Lee, Byungju,Love, David J.,Lee, Jungwoo,Poor, H. Vincent IEEE 2017 IEEE communications letters Vol.21 No.1

<P>In this letter, two novel coordinated beamforming techniques are developed to enhance the performance of non-orthogonal multiple access combined with multiple-input multiple-output communication in the presence of inter-cell interference. The proposed schemes successfully deal with intercell interference, and increase the cell-edge users' throughput, which in turn improves user fairness. In addition, they increase the number of served users, which makes them suitable for 5G networks where massive connectivity and higher spectral efficiency are required. Numerical results confirm the effectiveness of the proposed algorithms.</P>

Cooperative Wireless Powered Communication Networks With Interference Harvesting

Shin, Wonjae,Vaezi, Mojtaba,Lee, Jungwoo,Poor, H. Vincent IEEE 2018 IEEE Transactions on Vehicular Technology VT Vol.67 No.4

<P>A cooperative wireless-powered communication network protocol is proposed, in which user far away from a hybrid access point (H-AP) is capable of harvesting wireless powers by overhearing the uplink signals of users that are relatively nearer to the H-AP, in addition to downlink signal broadcast by the H-AP. In this setting, time allocations for the downlink transmission of the H-AP and the uplink transmission for the users are jointly optimized for two different purposes. First, the <I>weighted sum-rate maximization</I> problem is solved for a given total transmission time. Then, the <I>total transmission time</I> is minimized under a minimum rate constraint, and an efficient algorithm is also presented to solve the optimal solution by a line search strategy. Numerical results demonstrate that the proposed schemes significantly increase the far user's rate, which in turn improves user fairness and transmission delay.</P>