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QUASICONFORMAL EXTENSIONS OF STARLIKE HARMONIC MAPPINGS IN THE UNIT DISC
Hamada, Hidetaka,Honda, Tatsuhiro,Shon, Kwang Ho Korean Mathematical Society 2013 대한수학회보 Vol.50 No.4
Let $f$ be a harmonic mapping on the unit disc ${\Delta}$ in $\mathbb{C}$. We give some condition for $f$ to be a quasiconformal homeomorphism on ${\Delta}$ and to have a quasiconformal extension to the whole plane $\bar{\mathbb{C}}$. We also obtain quasiconformal extension results for starlike harmonic mappings of order ${\alpha}{\in}(0,1)$.
Behaviour of transmission line conductors under tornado wind
Hamada, Ahmed,El Damatty, Ashraf A. Techno-Press 2016 Wind and Structures, An International Journal (WAS Vol.22 No.3
Electricity is transmitted by transmission lines from the source of production to the distribution system and then to the end users. Failure of a transmission line can lead to devastating economic losses and to negative social consequences resulting from the interruption of electricity. A comprehensive in-house numerical model that combines the data of computational fluid dynamic simulations of tornado wind fields with three dimensional nonlinear structural analysis modelling of the transmission lines (conductors and ground-wire) is used in the current study. Many codes of practice recommend neglecting the tornado forces acting on the conductors and ground-wires because of the complexity in predicting the conductors' response to such loads. As such, real transmission line systems are numerically simulated and then analyzed with and without the inclusion of the lines to assess the effect of tornado loads acting on conductors on the overall response of transmission towers. In addition, the behaviour of the conductors under the most critical tornado configuration is described. The sensitivity of the lines' behaviour to the magnitude of tornado loading, the level of initial sag, the insulator's length, and lines self-weight is investigated. Based on the current study results, a recommendation is made to consider conductors and ground-wires in the analysis and design of transmission towers under the effect of tornado wind loads.
Effect of Aft-deck Length on the Performance of Serpentine Nozzle
Hamada Mohamed(하마다 모하메드),Changwook Lee(이창욱),Heeju Choi(최희주),Jeekeun Lee(이지근) 대한기계학회 2020 대한기계학회 춘추학술대회 Vol.2020 No.8
Serpentine nozzle has been widely utilized in many types of aircraft to minimize the infrared radiation emitted by high temperature parts and exhaust systems. Annular mixer was used in the infrared suppressor of exhaust system to mix the cold outside air with hot gases from the engine. The most important parameters can evaluate the performance of the nozzle with lobed mixer include mixing effectiveness, pressure loss, and pumping performance. A central plug is used at the exit of the lobed nozzle to penetrate the primary stream in the nozzle. In this study a numerical investigation of flow characteristics of the serpentine nozzle with lobed mixer was conducted. The flow characteristics such as velocity, temperature, pressure of the lobed mixer were studied. The three-dimensional model of the serpentine nozzle was used in the simulations that carried out using Star CCM software. The grid system com-posed of 8,364,993 polyhedral cells. Hot gases enter the nozzle through the core that treated as stagnation inlet at a pressure and temperature of 45023 Pa and 811.8 K, respectively. While, the cold air at pressure and temperature of 48963 Pa and 334.8 K, respectively enters via the bypass that considered as stagnation inlet. The outlet of the nozzle was treated as a pressure outlet subjected to atmospheric pressure and temperature. The nozzle body was considered as adiabatic walls with no-slip boundary conditions. The results showed that the increasing aft-deck decreased the temperature inside the nozzle and at exhausted gases that reduced the infrared temperature.
Numerical Modeling of Conical Fluidized Bed Combustors Considering Particle Slip on Wal
Hamada Abdelmotalib,Ik-Tae Im(임익태) 대한기계학회 2014 대한기계학회 춘추학술대회 Vol.2014 No.11
In this paper, the hydrodynamics and wall to bed heat transfer of a gas?solid flow in a conical fluidized bed were simulated using the Eulerian-Eulerian model. Sand with a particle diameter of 560 μm was used as a bed material, and its properties were calculated by applying the kinetic theory of granular flow (KTGF). Different amounts of slip between the particle and wall were shown by varying the specularity coefficient. The effects of specularity (0, 0.2, 0.5, and 1.0) on hydrodynamic and wall to bed heat transfer at a superficial gas velocity of 2 m/s were investigated. It was found that the wall to bed heat transfer coefficient decreases with increasing specularity coefficient. Different values of the specularity coefficient resulted in almost the same hydrodynamic behavior near the wall and the center of the bed.
Hamada, Mohanad Lateef,Alwan, Ghazwan Saud,Annaz, Abdulkader Ahmed,Irhayyim, Saif Sabah,Hammood, Hashim Shukur Materials Research Society of Korea 2021 한국재료학회지 Vol.31 No.6
Composite materials offer distinct and unique properties that are not naturally inherited in the individual materials that make them. One of the most attractive composites to manufacture is the aluminum alloy matrix composite, because it usually combines easiness of availability, light weight, strength, and other favorable properties. In the current work, Powder Metallurgy Method (PMM) is used to prepare Al2024 matrix composites reinforced with different mixing ratios of yttrium oxide (Y<sub>2</sub>O<sub>3</sub>) particles. The tests performed on the composites include physical, mechanical, and tribological, as well as microstructure analysis via optical microscope. The results show that the experimental density slightly decreases while the porosity increases when the reinforcement ratio increases within the selected range of 0 ~ 20 wt%. Besides this, the yield strength, tensile strength, and Vickers hardness increase up to a 10 wt% Y<sub>2</sub>O<sub>3</sub> ratio, after which they decline. Moreover, the wear results show that the composite follows the same paradigm for strength and hardness. It is concluded that this composite is ideal for application when higher strength is required from aluminum composites, as well as lighter weight up to certain values of Y<sub>2</sub>O<sub>3</sub> ratio.
Design Method of 2-D Lattice Digital Filters Using the Genetic Algorithm
Hamada, Nozomu,Kishida, Masahiko 대한전자공학회 1994 ISPACS:Intelligent Signal Processing and Communica Vol.1 No.1
This paper proposes design method of 2-D lattice digital filters using the Genetic Algorithm(GA). By using the GA, they are derived directly from the desired frequency response, and 2-D stable nonseparable-denominator transfer functions can be obtained. In our method, ARMA transfer functions are designed by two algorithms. One is to optimize AR and MA parameters simultaneously, and the other is to search an optimal AR parameters with fixed MA parameters, and then search an optimal MA parameters separately. Both are done by the GA, and the simulation shows that they give the simillar results.
Numerical Study on the Wall to Bed Heat Transfer in a Conical Fluidized Bed Combustor
Hamada Mohamed Abdelmotalib,Mahmoud Abdelftah Youssef,Ali Ahmed Hassan,윤석범,임익태 한국정밀공학회 2015 International Journal of Precision Engineering and Vol. No.
In this work a numerical investigation of wall to bed heat transfer, and the related flow characteristics, was conducted along a conical fluidized bed combustor with a height of 0.8 m and a cone angle of 30o. A two-fluid Eulerian-Eulerian model was used while applying Kinetic Theory for Granular Flow (KTGF) to a wall-to-bed FB reactor. The heat transfer coefficient and hydrodynamics are discussed for two different drag models, namely the Gidaspow and Syamlal-O’Brien models. Furthermore, computational calculations were carried out for a variety of inlet velocities(1.4Umf~4 Umf) and different particle sizes. The heat transfer coefficient in the bed region was evaluated and compared with that calculated by penetration theory. The bed expansion for the two models was compared with that calculated using correlations from literature in order to validate the numerical calculations. The heat transfer coefficient was found to be increasing with increasing gas velocity and decreasing with increasing particle diameter.