Jo Nov 26, 2025
Airlift pumps are considered an effective means of lifting deep ocean water due to their several advantages such as high reliability, simple structure, low cost and convenient maintenance.
The airlift pump is a fluid machine for raising liquids or slurries through a vertical pipe by injecting compressed air into the pipe near its mid position or lower end part, and its performance is therefore related to the state of multi-phase upflow in the pipe.
Rim Un Ryong, a researcher at the Faculty of Shipbuilding and Ocean Engineering, has conducted a numerical analysis of steady air–water two-phase flow in a vertical pipe of an airlift system based on a one-dimensional multi-fluid model.
He calculated the depth distributions of 6 physical quantities such as volumetric fractions and axial velocities of two phases, air density and pressure by solving the governing equations or by integrating the vector form of nonhomogeneous ordinary differential equation for two-phase flow interval.
He applied the proposed numerical model to a 7.86-meter-long vertical pipe and compared the results with antecedent theoretical and experimental results to validate its accuracy. The results showed good agreement.
If further information is needed, please refer to his paper “Numerical analysis of air–water two-phase upflow in artificial upwelling of deep ocean water by airlift pump” in “Computers and Fluids” (SCI).
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Jo Nov 25, 2025
Ocean wave energy has great potential to cope with increasing energy demand since it is renewable, sustainable and green energy and its overall resource is estimated to be around 2TW.
Some wave energy devices can be modeled as submerged oscillating bodies, which requires a deep understanding of hydrodynamic interaction between ocean waves and submerged bodies.
Many numerical methods have been proposed for bodies in irregular or arbitrary shapes, but it is important to specify boundary conditions on a virtual cylindrical surface between mean free surface and seabed.
Rim Un Ryong, a researcher at the Faculty of Shipbuilding and Ocean Engineering, has investigated three-dimensional linear interaction between a submerged oscillating body in arbitrary shape and the regular water wave with finite depth.
First, he derived an exact Dirichlet-to-Neumann (DtN) boundary condition on a virtual cylindrical surface, where the virtual surface was chosen to enclose the body and extract an interior subdomain with finite volume from the horizontally unbounded water domain.
Then, he applied the DtN boundary condition to solve the interaction between the body and the linear wave in the interior subdomain with the boundary integral equation.
He has validated the proposed method via a submerged vertical cylinder. The result shows a good agreement with the analytical results of precedent papers.
For more information, please refer to his paper “Free surface wave interaction with a submerged body using a DtN boundary condition” in “Theoretical and Computational Fluid Dynamics” (SCI).
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Jo Nov 24, 2025
A single-tuned harmonic filter is a passive harmonic filter widely used to eliminate harmonics in power systems.
Minimizing the impedance of the filter at the corresponding harmonic frequency makes the harmonic voltage produced by the harmonic current generated by the non-linear load a minimum. This is the principle of filtering in a single-tuned harmonic filter.
While eliminating the corresponding harmonic, the single-tuned harmonic filter affects the fundamental power factor. That is because the single-tuned harmonic filter itself is capacitive at the fundamental frequency. In the past, most power systems were inductive at the fundamental frequency, so in general, their capacitive characteristics played a positive role in raising the power factor of power systems. But nowadays, with the widespread use of power electronic devices, there have been more and more loads that are non-inductive at the fundamental frequency in the power systems. In this case, using conventional single-tuned harmonic filters results in the decrement of the fundamental power factor and the increment of transmission loss. In order to overcome these disadvantages, it is necessary to develop a new type of filter that eliminates harmonics but does not influence the fundamental power factor.
Ji Kuk Ryol, an institute head at the Faculty of Electrical Engineering, has proposed a novel single-tuned harmonic filter, which can remove harmonics with the fundamental power factor unchanged.
The proposed filter can be applied to filtering the harmonics made by a load whose fundamental power factor is 1 or capacitive.
You can find more information in his paper “Novel Single Tuned Harmonic Filter not Affecting Fundamental Power Factor” in “Journal of Electrical Power & Energy Systems” (EI).
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Jo Nov 23, 2025
Sensing nitrogen oxide gas is important for measuring pollution gas and detecting pollution sources from vehicles and chemical processes in the atmosphere and for diagnosing the diseases of human body by measuring NO2 gas from breathing. Therefore, it is necessary to measure the range of dilute concentration and to develop a less power-consuming electrochemical method.
Kim Yong Hyok, a researcher at the Faculty of Electronics, has designed the structure of a new NO2 gas sensor and conducted a qualitative analysis of its performance. In addition, he has established its manufacturing process and experimentally analyzed the bias voltage properties.
The new sensor can linearly sense NO2 gas of up to 100ppm.
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Jo Nov 22, 2025
Kim Chaek University of Technology International Conference―2025 was held on the subject “Science and Technology―Power for Development and Strategic Means” from November 11 to12.
Presented there were 120-odd scientific and technological papers of great scientific value and practical significance.
Drawing some universities and scientific research institutes from several countries including Russia and China, the conference was divided into five sections: Earth and Environmental Science, Metallurgy and Material, Mechanical and Energy Engineering, Automatics and Information Technology, and Basic Science, Chemical Engineering and Bioengineering.
Many academic findings achieved in the scientific research were reported from many papers including “Effective Non-seismic Technologies for Exploring Reservoir of Oil and Gas”, “Effect of Laser Power and Scanning Speed on Properties of Laser-Induced Graphene”, “A Method for Improving Accuracy of Positioning based on RSS Model in 3D Wireless Sensor Networks”, etc.
During the conference, the university hosted a reception for the participants.
The conference served as a good occasion of exchanging valuable experiences and knowledge.
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Jo Nov 21, 2025
In marine engineering, it is prone to encounter free surface flow problems. Typically, a boat moving on water causes nonlinear free surface flows accompanied by spray. A high-speed boat, in particular, experiences considerable resistance due to the spray, and some high-speed boats such as seaplanes and hovercrafts suffer great damage in their propulsion systems. Thus, predicting nonlinear free surface flow is an important issue for developing high-speed boats with high performance.
For the simulation of free surface flows, some computational fluid dynamics approaches called mesh-based method have been proposed. These methods are suitable for the flow of low-speed boats but not suitable for high-speed boats.
Other approaches called mesh-free method or particle method have been proposed for free surface flows. Moving particle semi-implicit (MPS), smoothed particle hydrodynamics (SPH) and particle finite element method (PFEM) are typical mesh-free methods widely used for nonlinear free surface flows. In many studies, mesh-free methods have been applied successfully to lots of problems in the marine engineering field.
Pak Chol Jun, a researcher at the Faculty of Shipbuilding and Ocean Engineering, has proposed an improved MPS method with some modifications for simulating the flow around a moving body. To improve the original MPS method, he proposed the intermediate velocity of wall particles, Laplacian compensation in the domain close to the boundary, a technique to prevent fluid particles from penetrating the wall boundary, and a handling technique for the open boundary.
He applied the improved MPS method to hydrostatic pressure and sloshing problems to validate its performance. The comparison of the numerical results with the analytical results and experimental data showed that Laplacian compensation remarkably enhances the accuracy of MPS method.
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