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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Jo Feb 21, 2025
Microbubbles are widely used in various fields including fishing industry, agriculture, chemical industry and light industry in the world and brisk researches have been conducted to improve their performance.
There are several methods for generating microbubbles, depending on their principles and applications. They are largely divided into two modes―one is liquid flow accompanying and the other is non-liquid flow accompanying. Liquid flow accompanying includes swirl jet, mechanical high-speed cutting, pressurized melting and Venturi, and non-liquid flow accompanying includes fluid oscillation, ultrasonic, electrolytic, etc.
Compared with the methods described above, the pressurized-dissolved microbubble generator has the advantage of high bubble generation and relatively small and uniform size distribution.
Han Il Song, a researcher at the Nano Science and Technology Institute, has manufactured a large microbubble generator that can be widely applied in various fields including wastewater treatment, sewage treatment and fishery by generating relatively small and uniform microbubbles at high density by means of a pressurized solution method.
The pressurized-dissolved microbubble generator used for pulp mill effluent treatment has the advantage of low cost and operating cost but very high efficiency of microbubble generation.
The new-type microbubble generator consists of a mixing tank, a circulating water pump, a Venturi air inlet, a pressurized tank, and a swirl jet nozzle.
The Venturi air intake unit, which is located at the inlet of the circulating water pump, is equipped with a flow control valve to provide a flow rate of 45-50L/min of air to be sucked.
The application of a pressurized-dissolved microbubble generator to pulp effluent treatment resulted in pulp recovery of more than 92% and the residual pulp content in the wastewater discharged after treatment of less than 0.002%.
At present, a large pressurized-dissolved microbubble generator has been introduced into pulp wastewater treatment to recover residual pulp in wastewater with higher efficiency than 92%, thus contributing greatly to recycling pulp and protecting the ecological environment.
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Jo Feb 20, 2025
It is very important to improve the quality of communication lines.
Communication lines, that is, telephone lines should have not only high electrical conductivity but also high strength.
The use of copper-coated wires with low resistivity as communication wires has become a worldwide trend.
The wire used for communication should have a low wire resistance, as well as a good current flow, and a limited diameter wire should be coated with a copper deposit of a certain thickness.
Therefore, the crystal should be compact and the thickness should be uniform.
The wire used as a telephone wire is very thin with the diameter of 0.235-0.24 mm, so it cannot be used at high temperatures and it must have a certain thickness to obtain appropriate resistivity. If it is too thin or too thick, its resistivity increases.
Kim Kyong Chol, a section head at the Faculty of Chemical Engineering Faculty, has designed and established a high-speed continuous copper coating process for producing wire by depositing copper of uniform thickness on the surface of a steel wire by the electroplating method at the time of continuous draw of steel wire.
To ensure the copper plating layer thickness of 0.015mm on the steel wire, he set the plating process in two stages and fixed the anode contact at 2m intervals, and carried out degreasing, neutralization, plating and passivation continuously.
For constant immersion length in the plating solution, he set the reciprocating of wire to be 1.5 times.
When the number of outgoing wires is 6 and the outgoing speed is 10~15m/min, the resistance value of the steel wire copper coating is 1.6~2Ω/m, and the resistivity is 0.08~0.1Ω·mm2/m.
The proposed method is widely used in the units for copper plating of 0.2-0.5mm steel wire, especially in the plants for producing copper coating steel wire for communication.
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Jo Feb 19, 2025
Fractional calculus is a branch of mathematics that deals with the differentiation and integration of any arbitrary order. Fractional differential equations have been widely applied to the analysis of complex systems such as material mechanics, anomalous diffusion, wave propagation and turbulence analysis, and researches on this field have attracted more and more attention in recent years. The variable order fractional calculus is the extension of the constant order fractional calculus. Here, fractional order is expressed not as a constant but in the form of a function of time or space variables.
Variable order fractional derivatives have significant advantages over constant order fractional derivatives in analyzing and controlling various physical systems including a nonlinear viscoelasticity oscillator.
Since numerical schemes with high degree of accuracy for variable order fractional derivatives can improve the accuracy of calculations and reduce computational cost, developing these numerical schemes is of great practical importance.
O Chol Won, a researcher at the Faculty of Applied Mathematics, has presented an explicit finite difference method for a space-time Riesz-Caputo variable order fractional wave equation.
He has proved that the explicit finite difference scheme is stable under certain constraints and estimated global truncation error. The numerical example shows the efficiency of the proposed finite difference scheme.
For further details, you can refer to his paper “An Explicit Finite Difference Approximation for Space-Time Riesz–Caputo Variable Order Fractional Wave Equation Using Hermitian Interpolation” in “NUMERICAL ANALYSIS AND APPLICATIONS” (SCI).
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