Jo Apr 6, 2023
Recently, large floating structures such as oil storage facilities and floating airports have appeared for the purpose of utilizing sea space and exploiting ocean resources. Many researchers have been developing artificial protective structures such as submerged breakwaters to prevent or decrease the actions of incident wave towards a coast. Therefore, it is necessary to estimate wave motion at a place where such structures are installed, and it is also important to consider the cases of undulated seabeds or bathymetric regions.
Rim Un Ryong, a researcher at the Faculty of Shipbuilding and Ocean Engineering, has studied three-dimensional water wave motion over undulated seabeds. For wave motion in sea water of finite depth, a fluid domain is usually unbounded horizontally but bounded vertically by free water surfaces and seabeds.
To study local wave motion over undulated regions only, he suggested a novel Dirichlet-to-Neumann (DtN) boundary condition on an artificial cylindrical surface by which a fluid domain is divided into an interior region with finite volume and an exterior region. Then, he applied the DtN boundary condition and other boundary conditions on mean free water surfaces and undulated seabeds in order to determine the solution to wave motion in the interior region by using Boundary Integral Equation (BIE). Upon verification of a submerged square cylinder, he extended the present model to the case of an array of rounded-rectangular cylinders or circular paraboloidal shoals.
The proposed model can be applied to assess wave motion over an undulated seabed when an undulated region is local and its surrounding region is horizontal and unbounded.
More information about this is found in his paper “An exact DtN artificial boundary condition for motion analysis of water wave with undulated seabed” in “Wave Motion” (SCI).
...
Jo Apr 3, 2023
The knotty problems in displacement reconstruction based on self-mixing (SM) technique are estimation of self-mixing interferometry parameters and normalization of SM signals (SMSs) since they are all very time-consuming and based on complex algorithms. This has an unfavorable effect on the real-time and low-cost natures of an SM displacement sensor.
Kim Chol Hyon, a researcher at the Faculty of Physical Engineering, has presented a simple method of displacement retrieval with a high resolution, which does not require any parameter estimation and normalization.
According to his study, when C changes during the operation of a self-mixing sensor, a single fringe, in a strict sense, does not correspond to a half wavelength and, therefore, this causes inaccuracy in displacement reconstruction. On the basis of it, he has proposed a very simple method called fringe scaling for displacement reconstruction, which does not require any normalization of SMSs and parameter estimation. This method provides a high resolution of λ0/10 and in addition, it can be employed for all feedback regimes including weak, moderate and strong regimes.
The proposed method is based on the scaling of individual fringes in SMSs and speckle noise proof. The simplicity of the method will make a great contribution to lowering the cost of SM displacement sensors and improving their reliability and resolution.
For more information, please refer to his paper “Normalization-free displacement reconstruction method based on fringe scaling” in “Applied optics” (SCI).
...
Jo Mar 30, 2023
A research team led by Kye Myong Ho, an institute head at the Faculty of Metal Engineering, has developed an energy dispersive X-ray fluorescence (EDXRF) analyzer.
The analyzer has several advantages: nondestructive analysis without any chemical reagents, simultaneous analysis of several elements in a short time, very simple structure, wide range of concentration standardless analysis and convenience in use.
It is made up of a high voltage power unit, an x-ray tube, a semiconductor detector, a multi-channel pulse height analyzer, a control circuit, a vacuum pump and analysis software.
The maximum power of the x-ray tube is 50W and the energy resolution of the semiconductor detector is 149eV. The analyzer enables measurement in the vacuum and its measuring time is below 5 minutes.
The analytical software is used for instrument control, qualitative analysis, semi-quantitative analysis, calibration curve drawing and quantitative analysis.
In the software, the voltage and current of the x-ray tube are set according to elements, and fluorescence spectrum is collected. Semi-quantitative analysis is available by standardless analysis. For semi-quantitative analysis, the kind of sample must be selected before measuring. You can also make a quantitative analysis by a standard curve. First, you should select the standard curve for a sample, and then quantitative analysis result is presented.
EDXRF analyzer can be widely used for analysing element concentration of substances such as alloy, mineral, cement, precious metals and catalyzers in the fields like metal, chemical, building materials, mining industries, prospecting and archaeology.
...
Jo Mar 29, 2023
A research team led by Kim Hyong Chol, a researcher at the Faculty of Shipbuilding and Ocean Engineering, has developed a dredging vessel for building tideland banks with the soil on the ocean floor.
The dredging vessel can remarkably increase the construction speed of tideland banks in the absence or shortage of mountainous soil, and carry out continuous work without being affected by rising tide and falling tide.
The dredger consists of a hull, two back side shovel excavators, a bunker, a main belt conveyor, an intermediate belt conveyor, a ground tackle, etc.
The two back side shovel excavators, separated from the front of the hull to the left and right sides, perform the function of digging the soil on the ocean floor up into the bunker.
The excavation width of the ocean floor is set to be larger than the hull width and the excavation depth is set to form a section larger than the section of a bank.
The main belt conveyor lays the excavated soil on the bank. The main belt conveyor is installed vertically to one side so that the dredging vessel can move along the bank to dig up soil onto the bank. To ensure the safety of the bank, the dredging vessel works 30m away from the bank, so the main belt conveyor is longer than 30m.
In order to keep a balance with the two excavators, the main belt conveyor is set up on the stern, and the intermediate belt carrying the soil in the bunker to the main belt conveyor is placed on the central longitudinal section of the hull.
This dredging vessel is characterized by its structure in which excavation and transport are carried out by one boat, and by its operation whereby at the time of high tide, it works on the tidal water, and at the time of low tide it floats on the water left in the pool excavated by itself, regardless of tidal current.
This dredging vessel can be efficiently used to build tideland banks, tidal power stations and other dams on the water areas whose floors are exposed during low tides.
...
Jo Mar 28, 2023
A research team led by Cha Pong Il, a section head at the Faculty of Mechanical Science and Technology, has developed a multi-rotor UAV that could enjoy wide use in agriculture.
The agricultural multi-rotor UAV is a piece of battery-powered up-to-date mechanical equipment for scattering various agricultural chemicals and fertilizers, and taking and transmitting the photographs of crops.
Iron-shell construction is used for its safe operation under 15-kilogram effective load.
Its specification is as follows.
Flight velocity: 5-10m/s
Flight altitude: 3-10m
Endurance: 15-20 minute
Effective mass : 15㎏
Take-off mass: 40㎏
Working area (1 time): 1 hectare
Temperature condition: -10~40℃
The effectiveness of the agricultural multi-rotor UAV is as follows.
Scattering of agricultural chemicals, fertilizer and seeds by a multi-rotor UAV enhances working efficiency remarkably, about 100 times higher than by human. It will do all kinds of harmful work like agricultural chemical spray, which leads to the improvement of working conditions for farmers. It consumes no fuel, so it is environmentally-friendly.
...
Jo Mar 26, 2023
Although it appears that enough researches have been made as regards the estimation of the optical feedback factor C of a self-mixing interferometer, no method of the C estimation can ensure its reliability if the operation of the self-mixing displacement sensor covers the strong feedback regime with fringe loss due to large displacement of a target.
That is the main reason why the precision of the sensor degenerates for measurement of large displacement.
Kim Chol Hyon, a researcher at the Faculty of Physical Engineering, has proposed a novel C estimation method called region tracking for C value, which is indispensable for measurement of long-range displacement, and demonstrated its fidelity experimentally.
He classified the fringe loss which arises in moderate and strong feedback regimes into an individual fringe loss and a collective fringe loss. Then, he clarified that the individual fringe loss is induced due to the hysteresis of the self-mixing effect and the collective fringe loss due to the minimum line width mode competition principle.
The displacement reconstruction based on the proposed region tracking method ensures better precision than a half wavelength, depending on the method of displacement retrieval. The approach presented will make a great contribution to further improvement of the accuracy of the self-mixing displacement sensor for large displacement.
For more information about this, please refer to his paper “Improvement of precision of self-mixing displacement sensor based on region tracking for large displacement” published in “Optics Communications” (SCI).
...
