Jo Mar 2, 2025
Analysis of CO2 is very important in several fields including chemical industry as well as estimation of environment, monitoring of disasters, etc.
Laser spectrum technology is effective for minimal gas analysis in the fields of environment and industrial measurement. Coherent light source which can be adjusted to the narrow width of spectrum can detect an absorption line of the matter and avoid interference of signals caused by other kinds of matter.
Narrowband filter is a major element for separating fine spectrum including gas analysis. Narrowband filter for breaking broadband has a complex structure of over 60 layers. The most widely-used narrowband filter is Fabry-Perot interferometer. This filter, which has a spacer between two reflective layers, forms interference maximum for the beam that satisfies the resonance condition according to the thickness of the spacer, thus ensuring sharp spectrum transmission.
In order to analyze CO2 in a gaseous mixture, Kye Song Chol, a researcher at the Faculty of Mechanical Science and Technology, has designed a multi-layer system of the filter for selectively filtering the absorption line of CO2 gas and cutting absorption lines of other air components.
As common Fabry-Perot narrow band filters have high spectral selectivity, he designed a double Fabry-Perot filter, which has low spectral selectivity and high transmittance at reference wavelength. For broadband cutoff, he combined a double Fabry-Perot filter and a broadband filter of symmetrical period structure, thus ensuring the necessary spectral characteristics and improving manufacturability. To increase the transmittance of band on which CO2 absorption line is located, he applied the equivalent theorem of a symmetrical period coating system and the index distribution of antireflection.
This filter consists of a double Fabry-Perot narrowband filter and a wideband filter placed on both sides of the Ge substrate, which can provide the required spectral characteristics while avoiding the complex structure of more than 60 layers of the conventional one.
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Jo Feb 28, 2025
Speckle is one of the main obstacles to the application of self-mixing interferometers into practice.
Self-mixing model reflecting speckle is of great theoretical and practical significance in self-mixing interferometry.
Ho Kwang Myong, a researcher at the Faculty of Physical Engineering, has suggested an improved model for a clearer explanation of the effect of speckle on self-mixing signals, and investigated the mechanism of feedback coefficient intensity variation induced by speckle and the effects of the surface orientation on the signals.
First, he built an improved model by replacing the output mirror reflectivity with amplitude feedback fraction in an external cavity and provided equations to calculate the amplitude feedback fraction.
Then, he proved through simulations and experiments that the irregular fluctuation of the speckle affected self-mixing signal is mainly due to the orientation change rather than the longitudinal displacement.
For further information, you can refer to his paper “Improved self-mixing model reflecting speckle” in “Applied Physics B” (SCI).
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Jo Feb 27, 2025
Coastal structures such as oil platforms, wind turbines and marine energy devices are constantly exposed to the harsh environment, which requires a deep understanding of the wave interaction with coastal structures to make them reliable, safe and cost-effective.
In order to study the linear wave interaction with a bottom-mounted body near a vertical wall, Tong Phil Sung, a student at the Faculty of Shipbuilding and Ocean Engineering, has proposed a method of applying an exact DtN boundary condition on the artificial boundary for numerical analysis. First, he adopted the mirror image method to transfer the horizontally semi-infinite water domain into a horizontally infinite water domain. Then, he made an artificial boundary enveloping the original bodies and their imaginary bodies, by which the entire fluid domain is separated into an interior subregion and an exterior subregion.
He applied the proposed method to a bottom-mounted circular cylinder, and the results were in good agreement with the literature.
In addition, he has extended it to the cases of a single rounded-rectangular cylinder to consider the effect of incident angle on exciting forces.
The proposed model can be applied to study the wave interaction with a bottom-mounted marine structure with irregular configurations in front of a vertical wall like a breakwater.
You can find more details in his paper “Wave Interaction with a Bottom‑Mounted Body in Front of a Vertical Wall Using an Exact DtN Boundary Condition” in “Iranian Journal of Science and Technology, Transactions of Civil Engineering” (SCI).
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Jo Feb 25, 2025
In most ships and offshore structures, plates and stiffeners are welded together. These structures inevitably vibrate during operation under dynamic loads by the main engine, working machinery, waves, propellers, etc. Especially, resonance causes a sudden increase in the amplitude of vibrations of the structural components of ships. As a result, it may cause a tremendous hindrance to the ship’s normal operation, causing damage to the ships and great suffering to the crew’s work and living conditions. Therefore, designing the stiffened plate structure with a correct consideration of their dynamic behavior is of great significance in solving the partial stiffness and local vibration problems of the ship structure.
Intermittent welding is generally used to attach stiffeners to plate for reducing manufacturing costs and for decreasing the weight of structures and welding distortion. Intermittently welded structures are widely used in practice, but few analytical studies have been carried out on the behavior of intermittently welded stiffened plates. The only focus has been on the static analysis of the ultimate strength and collapse behavior of the intermittently welded structures and vibration problems have been rarely discussed.
Ri Yong Ho, an institute head at the Faculty of Shipbuilding and Ocean Engineering, has proposed a simplified method for analyzing the dynamic behavior of intermittently welded stiffened plates.
First, he assumed the plate and stiffener as individual beams and considered the influence of the longitudinal internal shear force per unit length at the stiffener-to-plate junction of a continuously welded stiffened plate. Then, he divided the whole span of an intermittently welded stiffened plate into welded and non-welded segments. After that, he changed the intermittently welded stiffened plate into an equivalent continuously welded one, and built a model for bending vibration analysis of the intermittently welded stiffened plate. On this basis, he formulated a governing equation for bending vibration analysis of the intermittently welded stiffened plate by the influence function method and newly developed a practical approach to solve the governing equation. He verified the validity of the proposed method by comparing it with the finite element analysis results.
If further information is needed, please refer to his paper “A study for the bending vibration analysis of the intermittently welded stiffened plate” in “Marine Structures” (SCI).
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Jo Feb 23, 2025
Recently, many researchers have paid great attention to numerical and experimental studies of the dynamic properties of composite plates and shells, which are widely applied in various engineering fields due to their unique characteristics.
Composite plates and shells with varying thickness are widely used in different industrial fields due to the advantages of their light weights and small dimensions. A common type of the external load such as earthquakes, wind and jet noise is random excitation and therefore, it is important to study the stochastic response of composite plates and shells.
Kwak Song Hun, a researcher at the Faculty of Mechanical Science and Technology, has proposed Meshfree Jacobi point interpolation (MJPI) formulation for the free vibration and stationary stochastic response analyses of a heated composite laminated plate with varying thickness and curvilinear fiber.
He employed the Hamilton’s principle and FSDT to establish the governing equations of heated composite laminated plates with varying thickness and curvilinear fiber. He derived the stiffness coefficients for composite laminated plates with varying thickness and curvilinear fiber, and expressed the thermal strains induced by the temperature difference by using the nonlinear part of the Green–Lagrange strain. He approximated the displacement components of plates by the proposed MJPI shape function. He achieved boundary conditions by three linear springs and two rotational springs distributed along the edges of plates.
He has verified the accuracy and reliability of the proposed method through the comparisons with those from available literature and finite element software.
For more information, please refer to his paper “Free vibration and stationary stochastic response analyses of heated composite laminated plate with varying thickness and curvilinear fiber using a meshfree method” in “Acta Mechanica” (SCI).
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Jo Feb 22, 2025
Scheelite ores which are often found in tungsten deposits such as skarn occasionally include other valuable sulfide minerals. The similarity between scheelite and pyrrhotite in their densities makes gravity separation more difficult and decreases the grade of scheelite concentrate.
Generally, if scheelite ores contain a great amount of pyrrhotite, pyrrhotite is first removed by magnetic separation and then, scheelites are separated by gravity separation before being sent to the consumers respectively. On the other hand, if there is a small amount of pyrrhotite in scheelite ores, pyrrhotite is separated by gravity-magnetic separation and thrown away. The magnetic separation process involves the addition of scheelites to the magnetic flocculation, leading to the loss of scheelites.
Ryom Chol Ung, a researcher at the Faculty of Mining Engineering, has proposed a method whereby the magnetic field upwardly pulls magnetic mineral particles so that heavy valuable minerals such as scheelite are concentrated while heavy gangue minerals such as pyrrotite are floated by the magnetic force and removed directly from the table. In addition, he has simulated the gravity concentration of scheelite on the table and the removal of pyrrhotite floated by the magnet force using CFD and made a comparison through experiments.
The experimental result shows that the grade and separation efficiency are 28.4% and 76.5% on the conventional table, and 65.3% and 80.1% on the magnet bar-fixed table, respectively, which means separation efficiency of the proposed method is higher.
You can find the details in his paper “Simulation of pyrrhotite removal from scheelite ore by magnetic force in table concentration” in “Journal of Mining and Environment” (EI).
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