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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Jo Nov 20, 2025
Automatic Guided Vehicles (AGVs) are material handling equipment traveling on a network guide path. AGVs can be interfaced with other equipment for production and storage. Increasing the efficiency of automatic guided vehicle (AGV) scheduling is one of the important issues to improve the productivity of manufacturing enterprises.
Ri Il Chol, a researcher at the Faculty of Automation Engineering, has established a multi-objective mathematical model for scheduling multi-load AGVs carrying production materials and cutting tool consumables.
The objective function includes three objectives: the total moving distance of AGVs, the standard deviation of AGV workload and the standard deviation of the difference between the latest delivery time and the predicted time of tasks. Then, he implemented the assignment and ordering of tasks performed by AGV by implementing neighborhood search strategy using an improved harmony search algorithm.
He has applied the proposed harmony search algorithm to a virtual manufacturing enterprise to evaluate its performance.
The computational results show that the proposed harmony search algorithm outperforms the genetic algorithm.
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Jo Nov 19, 2025
Rod coal briquette is a kind of porous material consisting of solid coal particles, liquid phase moisture, stream and air, and study of drying process of coal briquette is that of porous material.
Most researchers proposed some mathematical models of drying inside porous material by convective heat. They are classified into diffusion model, theory model based on osmosis evaporation, and models based on Whitaker’s continuum theory and non-equilibrium thermodynamics.
Study on heat and mass transfer in porous material was conducted for a long period and it developed from the basic theory of heat and moisture transfer mechanism into the modern comprehensive and logical scientific theory. However, most studies were focused on the drying of wood, grain and paper, and not on rod coal briquette.
Pak Kyong Il, a researcher at the Faculty of Metal Engineering, designed a tunnel-type dryer for reducing coal consumption while reducing the cracking of briquettes and increasing their strength by improving the thermal working state of a tunnel dryer with low recovery and high coal consumption required for drying.
Compared to the conventional dryers, the newly-designed one has many advantages. First, drying time per batch is reduced by 4h from 24h to 20h. Second, 48kg of coal is saved for drying a ton of coal briquettes. Third, cracking rate is reduced by 23%.
In addition, cold compressive strength and hot compressive strength, and hot abrasive strength are raised by 10-11% and 4-5%, respectively, to improve the quality of briquettes used for iron production in small blast furnaces.
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Jo Nov 18, 2025
Initially, automatic identification system (AIS) was proposed to avoid collision between vessels and ensure effective traffic controlling off the coast or in harbors via navigational messages among mobile terminals and base stations in the VHF maritime mobile band.
Since it used typical VHF data exchange devices, AIS terminal equipment has been used for ocean monitoring. However, most ocean monitoring systems rely on satellites and no studies have been conducted on shore-based systems.
In the case of a long distance between the ground station and vessels, the received signal intensity decreases rapidly and there are a number of small cell areas around the base station. The rapid degradation of the strength of received signals due to troposphere propagation and the packet collision due to simultaneous signal transmission are main challenges to widening the communication range of AIS systems.
In order to extend the communication range of AIS ground stations, it is necessary to amplify received signals as much as possible to transfer to feed those with sufficient signal-to-noise ratio into the demodulation part, and the demodulation part should use coherent Viterbi detector and error correction codes to reduce the packet error rate.
O Myong Guk, a researcher at the Faculty of Communications, has proposed a new packet structure using error correction codes to reduce the packet error rate at the shore station, and a scheme to correctly decode it.
The simulation and experimental results show that the proposed scheme is suitable for reducing the packet error rate and increasing the coverage area of long-range AIS systems which depend on the troposphere wave propagation.
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Jo Nov 17, 2025
Coal-bed hydraulic fracturing is a key process in coal-bed gas production and one of the important ways for improving its efficiency is to make a new kind of proppant. What is important here is to reduce its density as much as possible, maintaining its technical parameters including strength.
Activated water often used as a fracturing liquid in hydraulic fracturing of coal seam is favourable for forming a complex fracture net, with stable performance and low frictional resistance, but it is limited in hydraulic fracturing due to its low viscosity and low capacity of carrying proppants. The use of ultra-low density proppants for hydraulic fracturing can solve problems such as clogging of cracked pores after gel break of the fracturing liquid and low productivity, often encountered in hydraulic fracturing using dense sand or ceramic granular proppants, and can provide sufficient proppant carrying capacity by crystalloid solutions such as clean and cheap activated water.
In order to solve the problems of high settling rate of proppants when low-cost activated water is used as a hydraulic fracturing liquid, Yun Myong Guk, a researcher at the Faculty of Earth Science and Technology, has prepared a resin-coated ultra-low density proppant with solid slag and white fly ash as feedstock.
He has analyzed the effects of the material composition and the resin dip and coating of the proppant on its performance by X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM) and cylinder pressure methods.
The analysis results are as follows.
The packing effect was best when resin concentration was 25wt.%. When the coating resin content of the proppant dip body was 6%, the visible porosity of particles was reduced to 7.13% and its bulk density was 0.91g/cm3. The apparent density was 1.5g/cm3 and the acid solubility was 0.35%. The breakage rates were 7.3% and 9.0%, respectively under 16MPa and 20MPa closing pressure conditions.
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Jo Nov 16, 2025
Electricity is clean and efficient energy that is essential for human life and widely used. As the power demand increases, the demand for power quality is constantly increasing. The sudden voltage fluctuations in industrial production hinder the normal operation of automation devices and even cause damage to products.
In the evaluation of power quality, system frequency and voltage at the grid nodes are main indices, and the voltage, symmetry and waveform of three-phase network are auxiliary indices.
The dynamic voltage restorer (DVR) is a power electronic device used to protect the load from the shock caused by voltage fluctuations occurring in the electrical network. This device is very effective in improving power quality, compared to conventional compensating devices.
Aiming to compensate harmonics and unbalances, Jong Il Bok, a researcher at the Faculty of Electrical Engineering, has proposed a controller for standard voltage calculation of DVR and a current controller using PCI method. Then, he has verified the accuracy of a designed controller in MATLAB/Simulink environment.
The simulation results show that the dynamic voltage restorer can cope with sudden voltage fluctuations and effectively prevent factors affecting power quality such as voltage fluctuations.
And the proposed current controller can be used not only for DVR but also for AC sequences control.
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