Jo May 17, 2024
Continuous casting is widely used for production of steel slab. The main problem is that if the stress and strain exceed a threshold value, steel slab will be cracked as the layer of steel slab depends on variable thermodynamic load in the solidification process.
The main cause of steel slab crack is the thermal stress that is generated by uneven temperature distribution during the solidification of molten steel.
Ri Yong Hwa, a researcher at the Faculty of Aerospace Engineering, proposed a method of determining the optimum heat transfer coefficient to prevent thermal crack of slab, on the basis of the identification of the cause of crack by analysis of unsteady thermal stress in the continuous casting of the slab whose width is relatively long for its height.
He analyzed unsteady temperature field and thermal stress of 800×150mm2 steel slab in the continuous casting process by using ANSYS to find out the reasons why steel slab is cracked. The analysis revealed that the reason is that the layer is not thick enough to withstand the thermal stress and the static pressure of the molten steel in the height direction of this band, and that all the thermal stresses on the surface exceed the yield limit of 1.9Mpa.
Then, based on the band analysis data and the optimization algorithm in the continuous casting process, he determined the reasonable coefficient of band heat transfer to prevent the crack of the steel slab by using ANSYS-workbench.
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Jo May 15, 2024
The vortex street flow meter is an instrument that measures a flow rate in the pipe line by measuring the frequency of vortex streets in the wake of a vortex generator located perpendicular to the flow direction in the pipe line. When Reynolds number reaches a specific value in the pipe line through which fluid runs, alternate vortex street occurs in the wake of the vortex generator and the generating frequency of this vortex street is in proportion to flow velocity. Therefore, the generating frequency is used for prediction of flow rate. The frequency depends on the type of generator.
The vortex street flowmeter has good accuracy and stability in flow measurement, but they are not widely used for low flow rate due to the small vortex frequency signal when the diameter of a pipe line is small or flow rate is low. In industrial pipe lines, flows with Re below 2×104 are often found, so in such cases, the vortex street flowmeter cannot guarantee measurement accuracy.
Compared to other types of vortex generators, a triangular prism-shaped vortex generator is now used in most vortex street flowmeters because it is easier to make and has better stability in vortex separation.
Jong Ji Song, a researcher at the Faculty of Mechanical Science and Technology, has solved and optimized hydrodynamic problems arising in the design of a triangular prism-shaped vortex generator available in the low discharge domain with minimum pressure loss.
First, he analyzed the influence of the structural parameters of the vortex generator such as thickness and width on the vortex generation and fluid flow by CFD simulation of the vortex flow around the triangular prism-shaped vortex generator. As a result, he found that with great thickness, the vortex generator easily generates vortex but has large flow resistance, and its great width is not good for generation of vortex and its narrow width cannot guarantee the stability of vortex. Next, on the basis of this analysis of the vortex generation and the flow loss in the pipe line, he determined the structural parameters of the triangular prism-shaped vortex generator available in the low discharge domain by optimization with BP neural network and genetic algorithm.
The proposed CFD simulation method and the optimization of structural parameters can also be applied in the design of vortex generators of any shape.
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Jo May 14, 2024
As the rotary angular sensor is important for measuring accurate positions and directions, it plays an important role in various applications such as robotic controller, camera and industrial machines.
At present, lots of angular position sensors such as simple resistive potentiometers, capacitive potentiometers, optical sensors and magnetic sensors are in use, and optical sensors which operate in visible light or infrared light offer the advantages of contactless measurement and insensitivity to electric and magnetic fields. So, an optical angular sensor has become recognized as an indispensable displacement/position sensor due to its high resolution, light weight and excellent immunity to electromagnetic interface.
Jo Myong Jin, a researcher at the Semiconductor Institute, has proposed an absolute rotary angular sensor with a nonlinear transparent disc. This rotary angular sensor is of transparent type and it has a nonlinear transparent disc between light source and LDRs. This sensor consists of five elements, that is, light source, a shaft coupled nonlinear transparent disc, a lens, a pair of light dependent resistors (LDR) and a signal processing circuit. In this sensor, absolute rotary angle is measured by output resistance of double LDRs which has a linear change by nonlinear transparency of the disc in the whole measurement range (from 0° to 360°) according to the characteristics of LDR’s resistance via irradiance. Its operation principle is similar to that of a resistive potentiometer.
The advantage of the sensor is that it is immune to shock and vibration as it has a nonlinear transparent disc instead of a binary coded disc and a large gap distance between the disc and the optical sensor. Another advantage is that as the output signal of LDRs is analogue, its resolution is determined by the A/D converter in the signal processing circuit. Therefore, this rotary angular sensor provides a high resolution in the range of 0~360°.
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Jo May 11, 2024
Every country and every nation in the world have their own manners of salutation.
However, hardly any of them are like ours, which satisfactorily and clearly expresses politeness to people in different social standings and age ranges.
From olden times, our people have observed the proprieties by either making a deep bow or bowing their heads when they see or part from one another.
According to our greeting etiquette, a deep bow is supposed to be made to the elders and seniors respectfully with some polite words for their health, and a slight bow to the people of the same age. Lowering one’s heads is appropriate for greeting younger ones.
Josonjol, the morally superior, hygienically impeccable and cultured greeting manners of our own style, is the best of all.
How our country could be widely known to the world as a country of courteous people in the East is also attributable, to some extent, to the fact that the people had created and constantly developed such admirable greeting etiquette.
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Jo May 10, 2024
Nowadays numerical simulation is an essential tool for stability analysis of mining engineering, and constructing a more realistic numerical model is important to ensure the accuracy and reliability of mining engineering design.
In recent years, many researchers have made significant progress in the study to quickly obtain more realistic structural elements of stopes and to apply them to production practice by performing numerical simulations of mining areas with FLAC3D. However, the model construction parts in these programs are quite difficult to use for building large and complex 3D mining models, particularly, for multi-seam and multi-boundary geological bodies.
Han Un Chol, a researcher at the Science Engineering Institute has proposed a new method of quickly converting a 3D solid model into a numerical one for stability analysis of geotechnical and mining structures by combining ANSYS, FLAC3D and SURPAC.
First, he carried out a detailed analysis of the data structure used in these three programs and presented a transformation technique between the data. Then, he converted the integrated 3D solid model made by SURPAC into a numerical model of ANSYS, and meshed it as tetrahedral elements, and consecutively, converted the meshed model of ANSYS into a grid model of FLAC3D for numerical simulation.
Finally, he applied the proposed method to numerical analysis of pillar stability in the sublevel open stopes in the target mine. It was shown that the model transformation time can be reduced to 1/50 and the accuracy of the numerical model can be increased by more than 20%.
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Jo May 9, 2024
Steamed rice cake (paeksolgi in Korean where paek means ‘white’) is named after its colour which is as white as snow. It was first introduced as paeksolgo in “Kyuhapchongso”, a book of the early nineteenth century.
Snow-white steamed rice cake reflects our people’s honesty and faithfulness. Steamed rice cake has been regarded as indispensable for several occasions like a party given to a hundred-day-old baby, the first birthday of a baby, a wedding, etc.
The custom of preparing steamed rice for hundred-day-old babies is associated with parents’ wish for them to grow up healthily and honestly like snow-white steamed rice cake.
Sharing with neighbors the dishes including steamed rice cake prepared for the day, Korean people have exchanged congratulatory remarks and shared joy with one another for good harmony and unity. Such beautiful characteristics are still being handed down.
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