Jo Jul 27, 2023
Analytic hierarchy process (AHP) is a well-known attribute weighting method in multi attribute decision-making. Its major requirement is to satisfy the consistency of pairwise matrix (PM).
To meet these requirements, Yang Won Chol, a researcher at the Faculty of Materials Science and Technology, proposed a new consistency improvement method of PM based on consistency ratio (CR) decreasing rate. In this method, the CR decreasing rates of all the PMs reconstituted by replacing all elements of the PM with the lower and upper neighbouring 9-point scales are calculated, and an element with maximum CR decreasing rate is found before it is modified to its lower or upper neighbouring scale.
Then, he developed a third order approximate polynomial for random consistency index by least square method. It enables determination of the RI value according to the number of attributes without a numerical table.
Finally, he proposed a final PM determination method and a final attribute weighting method with decision makers’ levels in consideration, on the basis of the CR values of individual PMs, when several decision makers perform their own pairwise comparisons.
With two numerical examples, he tested the performances of the proposed and some previous consistency improvement methods.
The results demonstrate that the proposed method improves the consistency of PM better and faster with smaller amount of modification than that of the previous methods, while it modifies the elements of the PM to 9-point scales necessarily.
He has applied the proposed method to hip joint prosthesis material selection to verify that the proposed method may be widely used in practical applications of AHP.
More information about this is found in his paper “Consistency Improvement Method of Pairwise Matrix Based on Consistency Ratio Decreasing Rate and Attribute Weighting Method Considered Decision Makers’ Levels in Analytic Hierarchy Process: Application to Hip Joint Prosthesis Material Selection” in “Mathematical Problems in Engineering” (SCI).
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Jo Jul 26, 2023
Attention to ship energy efficiency and CO2 emission is significantly increasing.
Both are related to fuel consumption and they can be assessed by ship energy efficiency operational indicator (EEOI).
Jon Min Hyok, a section head at the Faculty of Shipbuilding and Ocean Engineering, has developed a formula for estimation of an operational carbon intensity indicator (CII) and an optimal model of ship’s route and operational speed to minimize the EEOI with navigational environment and ship’s safety in consideration.
He developed a formula for estimation of CII, assuming that it is a function of ship’s main particulars such as block coefficient, and the ratio of operation speed to design speed of the ship.
For navigational environment, he considered wave and wind, which greatly influence ship’s performance including resistance and seakeeping.
For ship’s safety, he considered motion sickness incidence (MSI), one of the seakeeping indices.
Particle Swarm Optimization (PSO) algorithm was adopted to solve the model.
He illustrated the proposed method with a numerical example, comparing with full-scale data. The comparison results showed the proposed method can effectively reduce CO2 emission and improve ship energy efficiency.
If further information is needed, please refer to his paper “Optimization of ship energy efficiency considering navigational environment and safety” published in “Proceedings of the 5th International Conference on Numerical Modelling in Engineering (NME 2022)”.
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Jo Jul 24, 2023
Although there are many advantages in SEM measurement methods at ultra-low and low accelerating voltages, it is very important to select a proper accelerating voltage in a wide range from ultra-low accelerating voltage to high one (30kV) according to the purpose of observation of samples.
Studies on imaging of CNTs/polymers have been made within 0.3~5kV of accelerating voltages by FE-SEM with an in-lens detector, but few studies on observation of the surface microstructure of CNTs were conducted by SEM equipped with standard second electron detectors.
Pak Il Man, a section head at the General Assay Office, has performed a theoretical analysis on observation of the microstructure of CNT surface and observed the image of microstructure of CNT surface by Quanta 200 SEM, thus proposing a new method for selecting a proper accelerating voltage.
First, considering the theoretical resolution of Quanta 200 SEM and the size of electron-CNTs interaction range according to acceleration voltage, he made a theoretical study on selection of a proper accelerating voltage.
Second, he performed an observation of SEM images of CNTs at various accelerating voltages.
The effects of energy of the incident electron on the size of the electron-CNTs interaction range and the resolution of SEM were theoretically investigated. As a result, in the case of microstructure observation of CNTs surface by SEM, the most proper accelerating voltage was in the range of 5~10kV.
Through the experiments based on it, he found that the accelerating voltage of 7.5kV enables us to get the sharpest image of the microstructure of CNT surface.
More information is available in his paper “Optimization of the Accelerating Voltage in the Fine Structure Observation of Carbon Nanotube Surface by SEM” in “International Journol of Research and Scientific Innovation” (EI).
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Jo Jul 22, 2023
Hong Won Chol, a researcher at the Faculty of Electrical Engineering, has developed a high-power induction channel furnace (ICF) for melting steel.
Induction channel furnaces (ICF) are widely used for melting, superheating and heat preservation of ferrous and nonferrous metals because of their low power consumption and operation cost. However, thermal stresses in the refractory channel caused by high temperature, premature erosion of the channel due to the flow of molten metal, and failure of the inductor make it difficult to repair them.
He proposed a design of a three-phase channel and an inducer of a new type of ICF for steel melting, and analyzed temperature distribution of the channel by coupling simulations on electromagnetism-heat-fluid, by COMSOL Multiphysics 5.4 and Taguchi method.
An induction channel furnace (ICF) has been widely utilized for melting, refining and heat preservation of metal owing to its advantages such as higher power factor, less power consumption and less stirring of molten metal because the magnetic induction line follows the closed core.
In general, ICF is composed of induction units with iron core, an inductor winding, a channel, and a metal pot. The induction units are assembled verticality to a furnace body, and are separable when the furnace is under repair. The induction units of the proposed ICF are of horizontal type or inclination type, and have no need for separation, so it is easy to repair.
The proposed furnace provides 1 200kW of power, 1.5t/h of output, 1 000V of voltage of inductor (primary winding), 750kW•h/t of power consumption and 4h of cycle of production turns.
This type of furnace, when introduced to the production and refining of steel, cast iron and nonferrous metal, might bring a large profit in operation by saving electrical energy and improving the quality of metals.
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Jo Jul 20, 2023
It is very important to improve rapidity and correctness of analysis.
A powerful chemical imaging analysis system by AI technology has been developed by a research team led by Ri Ok I, a lecturer at the Faculty of Distance Education, and Kim Yong Ok, a section head at the Faculty of Chemical Engineering. They introduced deep learning technology, a branch of mechanical learning that has been accepted as an innovative one in the field of AI technology in recent years, thus making it labor- and cost-effective.
They first developed a method of extracting the main colour from a solution image taken by a camera and converting it into RGB values.
Then, they built a neuron network by deep learning technology. Learning data for the engine should be more than ten thousand sheets but construction of as many experimental data is not easy, so experimental data had to undergo processing for improving learning efficiency.
Finally, they designed it so that the RGB values are put into the engine and output values are processed to show analysis results.
On the basis of this, they developed an analysis system for Android-based smart phones or tablet PCs.
They applied the system to the analysis of Ni plating solution.
The result showed that analysis of plating solutions could be conducted promptly and easily any time with high accuracy without recourse to any kind of chemical reagents and analytical apparatus, and that it can be used by non-professionals too.
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Jo Jul 19, 2023
Today, exhaustion of fossil fuel and serious environmental pollution earnestly require active use of renewable energy resources such as wind, geothermal and solar energies for power generation.
Particularly, geothermal resources with low temperature heat source have been developed extensively for power generation all over the world by using the Organic Rankine Cycle.
A research group led by Ri Hung Nam, a section head at the Faculty of Heat Engineering, has developed a 50kW geothermal power generation system that harnesses hot spring water.
The system consists of an evaporator, a steam turbine, a condenser, a preheater, a hot spring water pump, a working fluid pump and a cooling water pump and so on. NH3 (R717) is used as working fluid.
In the evaporator, the hot spring water from the intake well by the pump produces steam by heating working fluid with low boiling point from the preheater. The high pressure saturated vapor from the evaporator expands through the steam turbine to the pressure of condenser. At the same time, it drives the turbo-generator to generate electricity. In the condenser, the working fluid is condensed with the help of the cooling water.
The condensed working fluid is fed to the preheater by the pump.
In the preheater the working fluid from the condenser is heated to be saturated liquid with an evaporating temperature by the hot spring water from the evaporator. Hot spring water from the preheater is used for heating of a building. And the heated working fluid in the preheater enters into the evaporator and then the above cycle is repeated.
This system has horizontal bundle heat exchangers (evaporator, condenser and preheater) and a single impulse stage steam turbine.
In the evaporator hot spring water flows into the tube and working fluid evaporates outside. In the preheater, working fluid flows into the tube and hot spring water flows out of it.
In the condenser, cooling water flows into the tube and working fluid vapor is condensed outside.
The system saves 120~180t/h of coal a year and it can contribute to the prevention of global warming. It is available in all areas with over 70℃ of heat sources such as hot spring and wasted heat.
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