Jo Aug 21, 2022
An inductive conductivity sensor is based on electromagnetic induction and it has some advantages such as robust structure and low manufacturing cost over conductive sensors. These sensors have no bare metal electrodes directly contacted with solutions, so they are free from damage by chemical corrosive solutions such as sulphuric acid and sodium hydroxide.
A transformer type sensor has robust structure and good linearity. It is easy to install and convenient to use in the industrial field. Using these characteristics, Kang Hwi Song, a section head at the Faculty of Electronics, has designed a new type transformer inductive conductivity sensor (TICS).
TICS has one or more magnetic cores. Its permeability values change with temperature and pressure. It is very important to compensate or eliminate the effects of magnetic core permeability change for improving the sensing performance.
TICS consists of a drive coil, a sense coil and a temperature sensor. Applying alternating voltage to the drive coil induces an ionic electric current in the solution around the sensor. This ionic electric current also induces an electric current in the sense coil which is proportional to the conductivity of the solution. Here, the two coils are encapsulated by chemical-resistant plastic material that protects them from corrosive electrolytes.
The equivalent loss resistances of the drive coil and the sense coil depend on both their turn number and frequency. From the investigation into the new model, he set the rational turn numbers as 10 each. The signal voltage was hardly affected when the drive frequency over 10kHz was used. As frequencies higher than 10kHz may cause magnetic loss, 10kHz was selected as a drive frequency.
In a word, it is important to use magnetic cores which have high permeability and small magnetic loss. He selected HS10 as the most suitable magnetic core for his purpose.
The drive coil and the sense coil are fixed on the PCB and welded to the lead wire. The main body encapsulates the two coils and PCB. The seal ring, fixing cap and gland are assembled each other. The seal ring and gland are for waterproof structure and the fixing cap is for the tank. Each part is fabricated of ABS plastic by a 3D printer. ABS plastic material has high chemical resistance and high water resistance and it is cheap. The thickness of the main body is 2 mm.
This sensing device is cheap and consumes less power. It also has simple circuitry, good linearity, high sensitivity and wide measuring range.
You can find more information in his paper “A new design of inductive conductivity sensor for measuring electrolyte concentration in industrial field” presented to the SCI Journal “Sensors and Actuators A: Physical”.
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Jo Aug 13, 2022
A research group led by Kim Sun Il, a researcher at the Faculty of Metal Engineering, has introduced his invention, an intelligent laser bird repeller with a deep neural network.
By comparison with existing repellers, the system of this bird repeller, whose design and database are based on sufficient experimental research into birds in various kinds and sizes, is programmed to undergo constant update, thus ensuring greater efficiency in bird detection and classification.
It detects birds by means of a camera, decides the mode of attack suitable for the detection results and sends signals to the laser driver device before attacking.
It consists of three parts ― a laser attack unit combined with an outdoor monitoring camera, a laser driver unit and a computer processing unit.
The laser attack unit consisting of the bunch of green (532nm), blue (420nm) and red (650nm) lasers of 1W is embedded in the outdoor monitoring camera. Once an image is sent to the computer, it detects and tracks the bird and sends a signal to the bird repeller device using artifical intelligence technology. This device emanates laser light driver signals according to the kind and size of birds and the intensity of light dependent on the weather change.
The interface consists of monitor, statistics, log, main setting, etc.
With 98.7% detection rate and 95.3% repelling rate, the fully automated system is applicable to all places including farms, fish farms, orchards and airfields that are exposed to the damage by birds.
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Jo Aug 9, 2022
Yu Chung Sim, a lecturer at the Faculty of Applied Mathematics, has studied a method to increase the convergent speed of global optimization.
The filled function method is an effective method to get the global optimization solution to multi-dimensional optimization problems.
One of the major problems to be solved in the search for a global optimization solution to multi-dimensional optimization problems is how to escape from the given local minima into a better one.
To solve this problem, a number of methods including Orbit method and Tunneling method have been investigated. Among them the filled function method has been admitted as an effective one and thus, it has been undergoing further study.
The filled function method was first applied to unconstrained nonlinear programming problems, followed by constrained nonlinear programming problems, non-smooth optimization problems and discrete optimization problems.
At present, in order to improve the effectiveness of the global optimization solution search algorithm using a filled function, many scientists have been looking for methods to combine various methods including the filter method and the interior point method with the filled function method.
The main problem of the filled function method is how to construct an auxiliary function called filled function at the given local minima of the objective function obtained from every repetition of the algorithm.
For this, filled functions with one parameter and those with two parameters were proposed, but they are difficult to control when they have more parameters
Recently, a new filled function method that skips the process where they used to get better minima by minimizing an objective function from the local minima of the filled function in the prior algorithms is being applied to continuous optimization problems.
As seen above, you can see that the filled function method can be applied to the global optimization problems arising in practice if we introduce filled functions with few parameters in the continuous optimization problems as well as discrete optimization problems, non-convex optimization problems and non-smooth optimization problems.
Therefore, she has proposed a new filled function that comes from the idea that an objective function and a filled function have the same stationary points and applied it to finding a global minimum solution to constrained nonlinear programming.
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Jo Aug 5, 2022
Ri Yong Ho, a section head at the Faculty of Heat Engineering, has been working hard to make further achievements since he developed a speed control device of a turbo coupling which is widely used in the speed change coupling of a large rotating machine.
The device consists of a turbo coupling, a speed control instrument and a distributed control system.
The fluid coupling, a power transfer device of a rotating machine, can control speed, has a wide control range and has good control characteristics. With a good power transfer characteristic, it can raise energy efficiency.
To use the turbo coupling’s speed control function, we must get a correct understanding of the turbo coupling’s working principle before designing and making a speed control instrument based on it.
The oil system of a turbo coupling consists of a lubricating oil system and a hydraulic oil system. The lubricating oil system functions as a supplier to provide lubricating oil to the coupling’s gears and medals while the hydraulic oil system controls rotating speed. The deeper the coupling is submerged in the oil, the larger the viscosity of oil gets and the faster the output rotating speed gets. The depth of the oil depends on the height of the dipper pipe.
The flow control piston controls oil discharge which passes through the turbo coupling.
The depth of the dipper pipe piston controls the rotating speed; the flow control piston controls the amount of hydraulic oil discharge to allow the turbo coupling to work.
The speed control instrument consists of a rotating motor that converts the control system’s command into the rotation angle, and cam accessories. The rotating motor receives 4~20mA current signals from the control system and in proportion to it, rotates the axis in the range of 0~150°, feeds it back to the control system in proportion to the rotated angle.
Two cams are installed on the axis of the conversion device, and they press on the fluid control piston and the dipper pipe piston individually according to the rotated angle. The main components of the conversion device are the two cams.
Based on the piston’s working principle, the working cycle, the size and installation conditions of the speed control instrument, the cam’s curve radii are decided as follows.
The fluid control cam’s radius: min = 96mm, max =115mm.
The dipper pipe cam’s radius: min = 96mm, max =117mm.
If the above-mentioned turbo coupling is installed between the main feed pump and the motor of the 210MW boiler-turbine block, it controls the rotating speed of the feed pump, which enables to control the output water pressure and the drum level of the boiler.
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Jo Aug 4, 2022
Even though there exist a great number of nations in the world, hardly any of them are like the Korean nation, which built their own state early in ancient times and has developed adorning their history based on one and the same blood and language.
One of the ancient relics that reflect the superiority of the Korean national culture is a pipha-shaped dagger.
Made in the first Korean state founded by King Tangun, pipha-shaped daggers are representative relics that are still unearthed on the Korean Peninsula and all other areas where ancient Koreans used to live. The name pipha-shaped dagger comes from its shape that resembles an ancient musical instrument pipha (a kind of oriental lute). Its birthplace is Pyongyang.
The pipha-shaped dagger representative of the culture in the first half period of Ancient Korea has peculiar features that make a clear distinction from those used by other ethnic groups in the neighbouring countries in those days in respect of structure, quality, shapes of blade and haft, designs engraved on the blade, etc.
The most distinctive one is the plane shape of the blade. The blade looks elegant with a sharp end, graceful curves at both cutting edges and a sharp protrusion in the middle or above the middle. A number of daggers of various types and structures have been discovered in the countries and regions that are proud of world-famous ancient civilization, but none of them looks like the original pipha-shaped dagger.
Another feature is its original structure. Those made and used in other countries and regions in ancient times were all cast bodily. Unlike them, pipha-shaped daggers were assembled with individually cast blades, hafts and fitters. In other words, they were built-up daggers while others were monolithic units. This demonstrates that the techniques of making and processing bronze ware owned by ancient Koreans reached a high level.
Pipha-shaped daggers have charming ornamental designs, too. Others found abroad had few ornaments and if any, the ends of hafts were decorated with no more than the shapes of heads of animals and birds. Pipha-shaped daggers, in contrast, were embossed with various sophisticated designs and ornaments on the blades, hafts, and fitters.
That is why the world people say that a pipha-shaped dagger is not a mere weapon but ‘a piece of sophisticated craftwork’.
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Jo Aug 3, 2022
A research group led by Choe Yong Chol, a researcher at the Faculty of Mining Engineering, has been employing his new method of reducing the amount of harmful explosion gas by using vermiculite and acidic deposits of mine water.
Introducing this technology, you can increase the power of explosion much higher than before thanks to the increase in the work ability resulted from the evaporation of combined water in vermiculite as well as the increase in brisance resulted from the increase in explosive density. At the same time, you can reduce the emission of harmful explosion gas such as CO and NOx by adsorption of expanded vermiculite, absorption of water separated from vermiculite and oxidation of metallic oxides in vermiculite at high temperature of explosion.
This method has two stages; manufacturing stage where vermiculite that passed through crushing, separating and distributing processes and acidic deposits of mine water are mixed, and application stage where they are admixed with explosives.
Explosive additives are made with vermiculite of 0.1mm~1.5mm in granulation size and acidic deposits of mine water less than 0.05mm in granulation size in the proportion 3:1. This mixture and Expanded Ammonium Nitrate Explosives are mixed evenly in a ratio of one to five and put into blasting cartridges before use.
Most of the acidic deposits of mine water consist of ferric hydroxide(Fe(OH)3) and basic ferric sulphate(Fe(OH)SO4). In vermiculite, some metallic oxides such as ferric oxide make up about 5.5%, which is less than those contained in acidic deposits of mine water. Trihydric ferric salt and ferric oxides serve as oxidizers that oxidize CO and NO in explosion gas to CO2 and NO2 respectively.
Vermiculite contains about 15% of interformational water which is not changed between micaceous layers at low temperatures but converted into water vapor at over hundreds of degrees. This interformational water removes harmful gases by absorbing soluble gases like NO2, N2O3, N2O4, etc. produced from explosive reactions and from oxidation by trihydric ferric constituents in the additives.
Vermiculite has a strong cation exchange ability. Its cation exchange capacity and base absorption capacity increases by 1.5 times at high temperatures. Thus, at high explosion temperatures vermiculites are expanded and the absorption ability for harmful explosion gas is further increased.
When explosives are mixed with vermiculites and acidic deposits of mine water that are heavier than constituents of explosives, the charge density of explosives increases. Consequently, the detonation velocity and pressure increase and the dynamic explosion power of explosives gets higher.
Vermiculite has a maximum of 18% of interformational and combined waters, which are changed into water vapour at the moment of explosion and expanded thousands of times in volume. It results in a considerable increase in the volume of explosion gas and in the explosion pressure of explosives, which leads to the increase in the static power and blast effects.
If this additive(vermiculit and acidic deposit of mine water) makes up 20% in explosives, removal rate for CO and NOx gases can be more than 93% and 85% respectively. The explosion power of explosives remains similar to or gets higher than before.
With the introduction of this method to all kinds of blasting operations such as driving, you can save a considerable amount of explosives and make a contribution to protecting the environment and improving working conditions by reducing the emission of harmful explosion gas.
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