Jo Apr 28, 2023
A research team led by Kim Sung Ri, a section head at the Faculty of Mechanical Science and Technology, has carried out a CFD simulation on a vertical turbine flowmeter with air and hydrogen and compared the meter factors. Then, they have conducted research on improving its starting characteristic in a low flowrate domain.
Generally, the meter factors of a turbine flowmeter for different densities of gases are different.
To fix this problem, they carried out a CFD simulation on a vertical turbine flowmeter that employs air and hydrogen as working media, and analyzed the effect of the density of gas on meter factors.
First, they created a geometrical model and mesh, and performed a CFD simulation by ANSYS Fluent using an SST κ-ω turbulence model. The result showed that as the density of air is much higher than hydrogen, the zero-load rotational speed of air is much higher than that of hydrogen for the same flowrates, and in contrast, the meter factor of air is smaller than that of hydrogen. It also showed that the meter factor of hydrogen had nonlinearity in a low flowrate domain, while the meter factor of air was almost constant over the whole flowrate domain.
Second, they carried out CFD simulations on vertical turbine flowmeters with 2 and 6 inlet channels, respectively, and analyzed the effect of the number of inlet channels on the starting characteristic. The result showed that in case of 2 channels, the zero-load rotational speed in a low flowrate domain was much higher than in case of 6 channels and the meter factor had linearity.
In conclusion, adjusting the area of an inlet channel is a good method for improving the performance of gas flowmeters, and in particular, this method is the most effective for measuring low-density gas in a low flowrate domain.
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Jo Apr 27, 2023
Many crashing accidents of helicopters and multicopters are attributable to the propellers plunging into a vortex ring state. Therefore, safe operation of a helicopter or a multicopter needs a thorough study on the vortex ring of a propeller and the vortex ring state.
Though many studies have been conducted on a vortex ring and its state, few of them deal with the cause of a vortex ring and determination of the critical descent velocity.
Myong Song Nam, an institute head at the Faculty of Mechanical Science and Technology, has determined the cause of the vortex ring of a descending propeller and the critical descent velocity by CFD method.
He used the MRF(Moving Reference Frame) method of Fluent for adequate prediction of the wake flows of a propeller.
The simulation showed that the origin of the vortex ring is not the vorticity line, but the interaction between the wake stream tube and the surrounding air, and that as the position of the vortex ring core varies with the increase in the descent velocity, the vortex ring approaches the propeller and consequently, the propeller enters into a vortex ring state and the vortex ring sharply moves above the propeller. Then, he predicted the boundary value of the descent velocity at which the propeller enters into a vortex ring state. The vortex ring state relates closely to the position of a vortex ring core or the thrust, which starts to vary suddenly at about 4.2m/s of descent velocity.
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Jo Apr 26, 2023
U Yong Nam, a section head at the Robotics Institute, has developed a tower clock.
The tower clock is composed of a driving ball-worm gearing box (1:84) and a clock gearing box (reduction ratio of the hour hand and the minute hand 1:12). The accuracy of the clock is ensured by the side clearance and the motion smoothness of the driving ball-worm gearing box.
When the worm shaft rotates in the driving ball-worm gearing box, the rolling balls in the circular workspace between the worm and the worm wheel transfer torque to the ball-worm wheel. Then, the balls circulate along the ball recirculation passage through 2~3 teeth. At the input and output of the passage is a piece to guide the balls back smoothly. And there is a ball-bush to stop the balls from dispersing.
The control system is composed of a main clock and terminal clocks calibrated by the national standard time. The control device consists of a digit I/O part, a serial communication part, a display, control buttons, and a power circuit.
The terminal clocks receive time pulses through RS-485 communication every 30s from the main clock and send them to the drive module to drive the motor.
The large-size tower clock with a ball-worm gearing box has several advantages.
First, it is much easier to achieve the dimensional accuracy and the assembling accuracy of the gearing box than a clock with a planetary gearing box.
Second, its service life is semipermanent or permanent.
Third, it ensures a high degree of accuracy and it is easy to operate.
It will find use at the front gates of factories and enterprises, in the waiting rooms of stations, and at public places.
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Jo Apr 24, 2023
U Yong Nam, a section head at the Robotics Institute, has developed a manned omnidirectional vehicle for carrying books.
Controlled by a librarian, the vehicle moves in narrow corridors between large bookshelves with lots of books to find ordered books and carry them to a conveyor.
The vehicle consists of four omnidirectional wheels, reduction motors, dampers, a control panel, a book basket, a chair, and batteries. The control panel has a monitor, a joystick, and a tablet PC, so the librarian can monitor and control all the states of the vehicle on it.
The four omnidirectional wheels and four DC motors which drive every wheel independently are installed on the vehicle. Each wheel has dampers for safe travel.
The omnidirectional wheels rotate clockwise or counterclockwise according to operation commands and the vehicle moves to a designated position running forward, backward and laterally or turning on the spot.
The vehicle goes in three stages of velocity: 2m/s (first), 1.5m/s (second) and 1m/s (third).
The vehicle is useful in libraries or storehouses with narrow corridors.
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Jo Apr 23, 2023
A research team led by Kim Sung Nam, an institute head at the Faculty of Information Science and Technology, has developed a game program by using cellular automata, which enables study of artificial life.
It is not too much to say that the history of evolution of life is just that of its adaptation to the changing environment. The environment acts on organisms as an input signal. It is hard for them to survive if they fail to receive the signals. Organisms analyse the input of the environment and seek to cope with it.
This artificial life game uses cellular automata to make sure that life moves alive and grows for a long time by changing the life or death rule. This program has an environment for simulation of an artificial life game, and offers diversity of patterns that are generated as the shape and transition rule of 2 dimensional cellular automata are changed.
They have laid a scientific foundation for the realization of a life machine by enabling the game program to give the most concise and persuasive explanation of cellular automata so that people with no professional knowledge of it can understand it.
The program consists of a simulation and application block, a pattern generation block for providing the diversity of patterns by varying the shape of 2-dimensional cellular automata, and a storage and management block for storing and managing the periodic and nonperiodic patterns of a life machine generated by changing environment.
Not only does the program help you to understand the essence of life in the education of artificial life, it can be applied to the sectors of electronics industry and textile engineering.
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Jo Apr 21, 2023
A research group led by Choe Kyong Chol, a lecturer at the Faculty of Materials Science and Technology, has established a casting process of a backing roller for a cement kiln on the basis of an effect analysis of factors on the quality of large steel castings.
For its design, two things should be taken into consideration ― it is a large and massive steel casting (tens of tonnes) and its thick walls could cause mass effect.
Therefore, what is important for the establishment of casting processes is proper design of casting plans, design of inner chill, selection of molding material and inoculation of molten metal.
They considered the contraction amount as 1.8% according to the chemical composition of a backing roller to calculate the gating system and they used ProCAST2016 to simulate the flow and solidification of molten metal to design a proper casting plan.
Both riser and chill were used at the same time to ensure directional solidification due to the great height of castings.
The weight of inner chill was set to be 2% of pouring weight of casting and its dimensionφ20mm in diameter.
Rahung silica sand was used as molding material (about 5mm in diameter). The coating was made by magnesia clinker (about 2mm in thickness).
Boron, titanium and rare earths were added to the molten metal to raise the quality of a backing roller and to reduce mass effect.
The backing roller has a tensile strength of over 550 MPa, an elongation of 12% and a hardness of about HB180.
This casting process can be used for manufacturing massive large steel castings.
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