Jo Mar 19, 2025
The deck, bottom, side shell, bulkhead structures and superstructures consist of stiffened panels and grillages, which serve as the most important components in ship structures. The ship grillage structure consisting of several girders crossing each other and a plate is a complex structural system. In a structural system consisting of several structural components with several possible failure modes, system failure generally occurs as a complex combination of failure modes.
However, as the stiffeners and transverse girders are related to each other in the ship grillage structure which consists of several stiffeners, transverse girders and plates, it is incorrect that the grillage will fail if any of the stiffeners or transverse girders fail. Therefore, the system reliability of the ship grillage should be estimated by taking account of all possible failure modes and paths of the stiffeners and transverse girders. In addition, if some stiffeners fail, the remaining (unbroken) stiffeners will be subjected to the external load, which leads to the stress redistribution for them.
Ri Yong Ho, an institute head at the Faculty of Shipbuilding and Ocean Engineering, has proposed a method for estimating the system reliability of ship grillage under combined axial compression and lateral pressure load, and estimated the structural system reliability on the buckling collapse of the bottom structure of an oil tanker.
First, he modeled the grillage into a structural system consisting of several longitudinal stiffeners and transverse girders with attached plating in parallel, respectively, and considered how the external load is distributed and transferred to the longitudinal stiffeners and transverse girders. On this basis, he estimated the reliability of each stiffener on the buckling collapse. Then, he performed an analysis of the system reliability of the ship grillage, considering the stress redistribution in the remaining unbroken stiffeners after any one of the stiffeners failed.
The results of the comparison with the literature show that the proposed method can more realistically and accurately evaluate the reliability of the structural system.
You can find the details in his paper “A method for estimating the system reliability of ship grillage structure” in “Marine Systems & Ocean Technology” (SCI).
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Jo Mar 18, 2025
PEF, a novel non-thermal processing technology, which started to be applied to liquid food processing, has the potential to be used effectively in extracting useful ingredients from microorganisms, plant cells and animal cells. Unlike heat treatment, PEF treatment can preserve the natural favor, nutrients and functions of liquid foods such as fruit juice, vegetable juice and milk. Thus, it is regarded as a technology that corresponds to the increasing demand for fresh food.
During PEF treatment, high electric field (of 10~50kV/cm with a pulse duration of 1~100㎲) is applied to the target liquid. Then, the biological cells under the PEF undergo electroporation, which makes holes in the cell membrane. As a result, the intracellular contents leak and therefore the cells die off. This is the very principle of pasteurization or extraction methods.
PEF chambers have three main kinds―parallel-plate, co-axial, and co-linear―and other kinds derived from them. Most continuous PEF systems use co-linear chamber. Its drawback, however, is the non-uniformity of processing parameters in the chamber. The non-uniformity of the electric field in the treatment chamber remarkably increases the temperature in the regions with electric field strength peaks, and the liquid food passing through this region is overheated, which produces undesirable results like quality degradation due to contamination and composition modification. On the other hand, the lower electric field could rather be responsible for under-processing and therefore increases energy consumption alone due to Joule heat.
Based on the analysis of the previous studies, Kim Jin Hak, a researcher at the Faculty of Physical Engineering, has proposed a co-linear treatment chamber with sub-electrodes to increase the uniformity of the electric field intensity distribution inside the treatment chamber and to increase the volume of the treatment chamber, and investigated the effect of the sub-electrodes on the uniformity of electric field, the average electric field strength and the throughput of chamber.
The simulations and experiments have shown that the improved treatment chamber with sub-electrodes can produce more uniform fields in the treatment space, not only to ensure the uniformity of treatment but also to increase the throughput and reduce power consumption.
For more information, please refer to his paper “Improvement in uniformity of co-linear pulsed electric field treatment chamber by sub-electrodes and its optimization” in “Journal of Food Process Engineering” (SCI).
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Jo Mar 17, 2025
With the recent increase in gold production, the manageable gold ore resources for cyanidation have been gradually depleted, and low-grade, fine-grained gold ores difficult to cyanide and refractory gold ores containing harmful impurities such as sulphur, arsenic and copper have become the main raw material for gold production. Generally, as the ultrafine gold particles are wrapped in pyrite and arsenopyrite in fine grained or disseminated form, gold particles are not exposed even if the ore is finely grinded, which results in low leaching rate for sulphur- and arsenic-rich refractory gold ores. Also, since arsenide reacts with cyanide during the leaching process and consumes the leaching agent and oxygen, it prevents gold leaching.
In order to extract gold from refractory gold ores effectively, oxidation pretreatment must be conducted prior to leaching to oxidize the sulfide-bearing gold particles and convert their physical and chemical properties.
Preoxidation of pyrite and arsenopyrite, especially to compare the oxidation mechanism and the oxidation-reduction potential of sulphur and arsenic and illustrate the effect of desulfidation and arsenic removal on the gold leaching ratio is significant for the pretreatment of the refractory gold ores containing pyrite and arsenopyrite in large quantities.
Kim Chang Sok, a researcher at the Science Engineering Institute, has investigated the thermodynamic features of preoxidation of pyrite and arsenopyrite, the main minerals of refractory gold ores, and the effect of pressure oxidation, one of the peroxidation methods, on chlorination leaching.
From the E-pH diagram of the pyriticarsenopyrite-H2O system, he has concluded that arsenopyrite under acidic conditions is more prone to wet oxidation than pyrite, and that the preoxidation process of pyrite-arsenopyrite-type gold ore can be considered with a focus on the pyrite.
For more information, please refer to his paper “Thermodynamic Behavior of Pyrite and Arsenopyrite in Preoxidation for Chlorination Leaching of Refractory Gold Concentrate” in “Journal of Chemistry” (SCI).
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Jo Mar 16, 2025
At present, the industry is developing rapidly, which results in an increased emission of toxic gases. Therefore, it is of great importance to develop inexpensive and high-performance sensors for real-time monitoring and quantification of these toxic gases in all fields including environmental monitoring, medicine, industrial processing and agriculture. Different types of chemical sensors based on polymers, carbon nanotubes, graphene, zeolites and metal oxide nanomaterials can be used to detect the emission of various toxic gases. Among them, semiconductor gassensors based on metal oxide nanomaterials have attracted a great deal of attention due to their advantages such as excellent fabrication technology, low cost, long lifetime and wide range of target gases. Furthermore, a great interest in them is the integration with complementary metal-oxide semiconductors (CMOS) or microelectromechanical system (MEMS) processes.
Titanium dioxide is an n-type semiconductor with excellent electrical properties, thus finding its wide use in photocatalysis, solar cells and sensors. The surface-to-volume ratio is large for 1D metal oxide semiconductor nanostructures such as nanowires, nanorods, nanobelts and nanofibers. These 1D nanostructures like nanowires and nanorods are widely used for gas sensors. The intrinsic properties of these nanostructures increase the effective surface area of the material by facilitating the interaction with target gas molecules and the diffusion into the material. These nanomaterials are synthesized by hydrothermal method, sol-gel method and electrostatic spinning method to be fabricated by deposition on a substrate.
Some time ago, Pak Jong Sung, a section head at the Faculty of Chemical Engineering, prepared TiO2 nanopaper (long nanowire/nanofiber membranes) similar to the conventional paper in mechanical performance by combining high-temperature hydrothermal nanofiber synthesis and paper preparation, and then characterized its structural properties. This 2D nanomaterial is in disordered arrays of nanowires/nanofibers and of highly porous structure with flexible mechanical strength, and its thickness could be controlled arbitrarily. Thus, this material exhibits intrinsic properties of nanomaterials as sensing materials as well as high chemical, thermal and mechanical stability. However, this material has low selectivity for gas sensing due to the gas sensing properties of semiconductor materials.
To overcome this shortcoming, Ri Son Ho, a student at the same faculty, has prepared a novel gas sensing material with an excellent performance using V2O5-doped TiO2 nanopaper and characterized its SO2 sensing, under the guidance of Pak Jong Sung.
This sensing material exhibited high conversion efficiency of SO2 to SO3 and sensing properties due to its flexible mechanical strength, high porosity, chemical and thermal stability and high catalytic activity of V2O5.
For more information, please refer to his paper “Sulfur dioxide gas sensor based on vanadium oxide doped TiO2 nanopaper” in “Engineering Research Express” (SCI).
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Jo Mar 14, 2025
The permanent magnet synchronous motor (PMSM) is widely used in the robotics and motion control systems due to its compact structure, low noise and high torque to inertia ratio. PMSM is a typical multivariable and nonlinear system with strong coupling and uncertain model parameters. Therefore, traditional linear control methods such as PID control cannot guarantee high control performance for PMSM systems.
Though many advanced nonlinear control methods including adaptive control, nonlinear optimal control, fuzzy logic control and neural network control have been used for PMSM systems, they have their own advantages and shortcomings.
Ri Tae Hyong, a researcher at the Robotics Institute, has proposed a full order terminal sliding mode (FOTSM) controller to solve the speed tracking problem for a PMSM system by combining RBF neural network and FOTSM control scheme.
First, in order to eliminate chattering in conventional sliding mode control (SMC), he developed a continuous FOTSM technique. Then, he designed a FOTSM speed controller based on RBF neural network, in consideration of the presence of external disturbance.
The simulations and PMSM speed control experiments by MATLAB have proved that the proposed method is effective.
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Jo Mar 13, 2025
High-intensity focused ultrasound (HIFU) has been investigated as a noninvasive surgical method for the treatment of tumors located in various tissues including brain, prostate, liver, kidney and breast. When the ultrasonic beams emitted from the transducer is focused into the target tissue, the temperature in the focal region rises above 56℃ in a short time, which results in tissue necrosis without damaging overlying or surrounding tissues.
Recent efforts in HIFU research have been focused on the treatment of uterine fibroids. Uterine fibroid is benign neoplasm that occurs in approximately three out of four menopausal women. The incidence rate of this disease in pregnant women is 25%-30%. Several treatment methods currently exist for uterine fibroids but they have some serious shortages. For instance, hormone therapy is a noninvasive method to treat fibroids but if medication is discontinued, fibroids regrow. These show that HIFU therapy is better than others.
Since the most important requirement in the HIFU therapy is safety, the consequences of the therapy must be predicted before treatments of tumors. Thus, a proper model for predicting the temperature distribution by ultrasound source in a human body is needed.
Kim Sang Jin, a researcher at the Faculty of Physical Engineering, has described and simulated geometrical and mathematical models of the thermal coagulation necrosis region caused by HIFU radiation on the human uterus for different types of transducers and frequencies.
He used two models for the HIFU simulation. In one model, only the linear parts in the Westervelt equation was considered, and in the other one, thermal conduction and viscosity were included. He compared the differences in the temperature distribution for both models, varying the shape of transducer and the frequency.
The results show the shape of transducer and the frequency greatly affect the temperature field in the uterine fibroid.
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