VNU Journal of Science: Mathematics - Physics

Aerodynamic problems in general are often difficult to solve by analytics analysis. Experimental or numerical simulation can be used to analyze these computational models. However, due to the large expenses required in the experimental method, the numerical method is more preferred. This paper presents the modeling and simulating processes of computational fluid dynamic (CFD) problem on a aircraft wing model, using typical section as NACA 2412 airfoil. This wing model might be chosen in the future experimental design. ANSYS Fluent is used to analyze the pressure and velocity distribution on the surface of wing. The lift and drag forces are also determined by ANSYS Structural. Additionally, the coefficients of lift and drag forces can be calculated through the data obtained when the relative velocity inlet between the airflow and airfoil changes from 0 to 50 m/s. The numerical results shown are compatible with those of the theory, thus suggesting a reliable alternative to predict the aerodynamic characteristics of the tested wing model in fabricating the Unmanned Aircraft Vehicles (UAVs).Keywords: Aerodynamic, airfoil, lift and drag, UAVs.

Abstract: The capture and storage of gases for the applications of energy, environment, and biomedicine are closely related to the major concerns of the modern world about energy crisis, air pollution and global warming, and human’s health. Many materials and techniques have been developed to tackle these widespread issues, in which metal-organic frameworks (MOFs) – a new class of porous materials with exceptionally high surface areas – have emerged as the most promising candidate for the capture and storage of gases based on the adsorption of gases on the surface of MOFs. This article provides a short overview of the current status in the capture and storage of gases within the structure of MOFs.Keywords: Metal – organic frameworks, gas storage, hydrogen, carbon dioxide, methane, nitric oxide.

In this research, the dependence of the velocities and the absorption coefficients of ultrasonic waves propagated in 1018 low carbon steel on temperature range from 0 oC to 50 oC was investigated. The coefficients of the temperature dependence of the ultrasonic longitudinal wave and ultrasonic shear wave were estimated to be -0.8 m/s.oC and -0.44m/s.oC, respectively. The acoustic impedances of this carbon steel were also investigated and effected much by temperature. Simultaneous, the effect of temperature on the acoustic impedances and ultrasonic attenuations of the motor oil was also determined. As the results, reflection and transmission coefficients at the interface between the carbon steel and motor oil were estimated. It is concluded that the ultrasonic attenuation of the motor oil is one of the main reasons for the behavior of the ultrasonic absorption coefficients propagated in the steel sample.Keywords: Ultrasonic, Nondestructive Testing, Reflection and Transmission coefficients, Longitudinal Wave, Shear Wave, Ultrasonic Velocity, Low carbon steel, Ultrasonic Attenuation, Reflection and Transmission Coefficients, Pulse-echo Technique

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In this work, Morse potential parameters of bcc crystals have been calculated based on the calculation of volume per atom and atomic number in each elementary cell, as well as the energy of sublimation, the compressibility and the lattice constant. They are used for studying the anharmonic interatomic effective potential, local force constant in XAFS (X-ray Absorption Fine Structure) theory. Numerical results for Fe, W and Mo are found to be in good agreement with experiment and with those of other theories.Keywords: Morse potential parameter, effective potential, local force constant, bcc crystals.

This paper presents the results of study, design and manufacture of a searching and satellite auto-tracking system used for mobile receiver. This system applies both the traditional proportional integral derivative (PID) control and the fuzzy PID control methods. Firstly, the PID controller was designed by Ziegler-Nichols tuning method to obtain control parameters. Then, a fuzzy controller was applied to tuning online parameters of the PID controller. In order to apply for mobile satellite receiver, the tracking control system has been designed, fabricated on a PCB board. Simulated and experimental results indicate that the system performances obtain from applying the fuzzy PID controller was better than traditional PID controller.   Keywords: Satellite tracking system, step-tracking algorithm, PID controller, Fuzzy controller, satellite communication.

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