Jo Sep 29, 2025
Fractal interpolation function (FIF) is a function which interpolates a given data set and whose graph is a fractal set. In 1986, M. F. Barnsley introduced the FIF using an iterated function system (IFS). Ever since, many researchers have studied the FIFs and applied them to a lot of scientific fields such as computer graphics, function approximation, signal processing, metallurgy, earth science, surface physics, geography, geology, medical science, chemistry, etc.
Rakotch contraction is the generalization of Banach contraction, which implies that the use of Rakotch’s fixed point theorem enables modeling of more objects than the use of Banach’s fixed point theorem. Moreover, hidden variable recurrent fractal interpolation functions (HVRFIFs) with Hölder function factors are more general than fractal interpolation functions (FIFs), recurrent FIFs and hidden variable FIFs with Lipschitz function factors.
Ro Chung Il, a researcher at the Faculty of Applied Mathematics, has demonstrated that HVRFIFs can be constructed using the Rakotch’s fixed point theorem, and investigated the analytical and geometric properties of those HVRFIFs.
Firstly, he constructed nonlinear hidden variable recurrent fractal interpolation functions with Hölder function factors on the basis of a given data set using Rakotch contractions. Next, he analyzed the smoothness of the HVRFIFs and showed that they are stable for the small perturbations of the given data. Finally, he obtained the lower and upper bounds for their box-counting dimensions.
If further information is needed, please refer to his paper “Analytical properties and the box-counting dimension of nonlinear hidden variable recurrent fractal interpolation functions constructed by using Rakotch’s fixed point theorem” in “Applied Mathematics and Computation” (SCI).
...
Jo Sep 28, 2025
It is well known that cylindrical shell structures are widely used in many industrial fields including mechanical, aerospace, ship building, chemical and architectural industries. Typical examples are fuselage in the aerospace industry or submarines in the shipping industry, and vessels in the chemical industry. In the structures of these examples, various types of composite materials are being applied, either due to their performance or structural requirements. In addition, these structures will be worked in different environments and load conditions.
Generation of vibrations leads to noise. Therefore, there have been many studies to analyze the vibration and acoustic characteristics of these structures and as a result, various shell theories have been proposed. Based on these shell theories, studies have been carried out to develop solution methods with high computational accuracy and computational efficiency for vibration analysis of laminated composite cylindrical shells.
However, the study of the vibro-acoustic analysis of stepped cylindrical shells is limited, and what is more, there is no study of acoustic analysis.
U Ju Hyok, a researcher at the IT Institute, has analyzed the vibro-acoustic responses of laminated composite multi-stepped cylindrical shells immersed in fluid medium by applying the energy and spectral boundary element method.
He has verified the accuracy and reliability of the proposed method by comparing it with the results obtained by references. Then, he has conducted several numerical analyses to provide the influence of geometry, material properties, boundary condition, fluid medium and force types on vibro-acoustic behaviors of the laminated composite multi-stepped cylindrical shells.
For more information, please refer to his paper “Vibro-Acoustic Response Analysis of Laminated Composite Multi-Stepped Cylindrical Shells Immersed in Fluid Medium” in “Journal of Vibration Engineering & Technologies” (SCI).
...
Jo Sep 26, 2025
In the wireless recharge sensor network (WRSN), charging scheduling is to schedule charging tasks by employing a mobile charger (MC).
Drawing up the charging schedule of a MC which maximizes the network lifetime by determining the most suitable charging location and charging time is a consistent and invariant guideline for on-demand charging scheme in WRSNs.
To this end, Ri Man Gun, an institute head at the Faculty of Communications, has proposed a new charging scheduling scheme based on an integrated FCNP-VWA-PROMETHEE (iFCVP).
This scheme first assigns relative weights to the multi-criteria characterizing the charging request nodes with FCNP, and compensates them with VWA to make more accurate weights. These weights are then used to select the most suitable next-to-be-charged location by the PROMETHEE. Together with determination of the charging order, the partial charging time at the selected charging locations are reasonably determined using the weights assigned by FCNP-VWA by considering the trade-off between the performance metrics.
The results of the extensive simulation show that the proposed scheme gives superior performance over several existing integrated MCDM methods.
For more information, you can refer to his paper “iFCVP: an integrated FCNP-VWA-PROMETHEE method for on-demand charging scheduling in WRSNs” in “Proceedings of Ninth International Congress on Information and Communication Technology” (EI).
...
Jo Sep 25, 2025
Scientific operation of production processes with quantitative evaluation of sensory characteristics is important for improving product quality in the food industry. In order to achieve the target quality in the production processes with controllable parameters, the set-point of process parameters must be controlled to suit the operating conditions. In food production processes where the quality is represented as sensory characteristics, it is particularly important to quantitatively evaluate the quality of products.
Set-point control methods include intelligent supervisory control, case-based reasoning, etc. In addition to rule-based reasoning, case-based reasoning that utilizes operation expertise and cases to infer similar solutions corresponding to similar conditions has been widely applied to the optimal operation of industrial processes.
One of the major challenges in applying case-based reasoning to the set-point control of industrial processes is to constantly adapt the case base to the changing characteristics of processes, thus increasing the accuracy of reasoning. There was a methodology to solve this problem, which failed to deal with updating the case base with operational experience and new knowledge obtained during the online operation of industrial processes.
Song Kwang Rim, a researcher at the Faculty of Automation Engineering, has proposed a new method for online updating and addition of case base and applied it to the set-point control of a rolled cake production process.
First, he presented an approach for quantitatively evaluating the rolled cake based on the sensory quality. Second, he proposed an interactive method of acquiring knowledge from operator’s experiences and adapting the case base according to the behavior of the process and the quantitatively evaluated quality level.
The comparative experiments for validation show that the proposed method results in 4.1% improvement in the ratio of good products.
You can find the details in his paper “Acquisition of adaptive knowledge in case-based reasoning for the online set-point control of industrial process” in “Third International Conference on Communications, Information System, and Data Science (CISDS 2024)” (EI).
...
Jo Sep 24, 2025
Hazardous industrial wastewater usually contains many toxic heavy metals such as chromium, nickel, copper, zinc, lead, cadmium and mercury. The discharge of industrial wastewater containing such heavy metals without being treated not only destroys the ecological environment but also produces a negative effect when it enters animal or human bodies.
Chromium is one of the metals used in the industrial processes including stainless steel and alloy steel production, pulp production, electroplating, textile industry, metal refining, tanning, glass industry, petroleum refining, etc. Trivalent chromium existing in the waste water is generally produced from inorganic pigments, glass preparation, ceramics, etc., and it may be produced by reduction of hexavalent chromium in reducing atmosphere. Chromium ions are toxic heavy metal ions, which seriously contaminate soil and water. Therefore, it is very important to remove chromium ions in the wastewater before it is discharged into rivers or lakes.
Chromium, like other metals, can be treated in various ways such as chemical precipitation, ion exchange, membrane filtration, solvent extraction, electrochemical processes, biological methods and photo catalysis. Recently, adsorption method has been widely applied to wastewater treatment due to its simple operation and low cost.
Ri Kyong Hun, a researcher at the Faculty of Mining Engineering, has investigated the preparation of inorganic adsorbents for removing heavy metals from wastewater and other scientific and technological problems for efficient removal of chromium in wastewater by the adsorbents.
He worked on the synthesis of heavy metal adsorbents by low-temperature hydrothermal synthesis method to prepare nanocrystalline inorganic adsorbents (erdite) of 80nm in diameter and 100nm in length at 90℃ for 24h under the conditions of S/Fe > 3 and OH-/Fe > 20.
From the experiments to use the mother liquid back to the synthetic experiments, he has confirmed that a little addition of only Na2S·9H2O to the mother liquid makes it possible to effectively synthesize erdite. The removal efficiency of these sorbents for Cr(III) is above 99.8%.
...
Jo Sep 23, 2025
Active disturbance rejection control (ADRC) is one of the notable disturbance and uncertainty estimation and attenuation techniques.
Kim Ho, dean of the Faculty of Automation Engineering, has proposed a method based on the maximum sensitivity index, with an attempt to solve the problems arising in the parameter tuning of ADRC.
Then, he has applied it to the temperature control of a water glass reaction tank subject to strong model uncertainties and disturbances.
First, he built a mathematical model of a water glass reaction tank by using the identification technique based on the step response signal, and designed a second-order linear active disturbance rejection controller based on it. Then, based on the maximum sensitivity index, he presented a formula of tuning the parameters of the second-order linear active disturbance rejection controller to achieve robustness, and verified its effectiveness using MATLAB.
As a result, he has concluded that the proposed formula is suitable when the non-delay is less than 0.3, and that time delay compensation techniques such as Smith predictor should be applied when the non-delay is more than 0.3 as the time delay is not negligible.
...