Jo Jan 11, 2024
The idea of using both gain and phase in robust control theory was proposed and studied by several researchers in 1980s. Especially, the robust control theory based on gain-phase information (GP robust control theory), which started to be studied in 1999 produced new concepts like Ψ-control, H∞/Ψ-control and GP mixed sensitivity control and opened up a new stage for development of robust control theory.
However, all the researches considered only Single Input Single Output (SISO) system. So, it is very important to find a solution to the Ψ-control problem for Multi Input Multi Output (MIMO) system.
Pak Kwang Hae, a researcher at the Faculty of Automation Engineering, has proposed a new solution to Ψ-control problem for SISO system and laid methodological foundations for finding a solution for MIMO system.
To verify the efficiency and applicable possibility of the designed control system, he newly designed an automotive fuel control system and compared it with previous methods through computer simulations.
The results proved that the proposed method is effective and available in practice.
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Jo Jan 9, 2024
Water is commonly used for industry, agriculture and office and domestic consumption. Water shortage is one of the most worrying problems and it is related to poor management and inefficient use of water resources. Therefore, efficient use and monitoring of water are very important. Here, water level sensing is of key importance. Many physical properties of water like relative electrical permittivity, resistivity, thermal conductivity, buoyancy, hydraulic pressure, absorption of radiation, surface reflection of sound or light waves, etc. are used for water level sensing.
Although a variety of structures of capacitive water level sensor and low capacitance probing techniques have been proposed, it is still important to develop a new type which is more convenient, flexible, simple, low-cost and easy to make for widespread application in homes and offices.
Kim Chol Man, a section head at the Faculty of Earth Science and Technology, has proposed a new low-cost capacitance-type water level sensor and low capacitance probing technique. Unlike the conventional low capacitance probing techniques which involve analog circuits such as AC-bridge, negative impedance converter, analog switch, oscillator, multiplexer, phase shifter, etc., his method is based on a direct capacitance-to-time conversion principle by a single microcontroller unit (MCU).
For test and verification, he made a prototype water level controller. The results of the experiments showed that the repeatability and linearity of the sensor are satisfactory within the tolerable limit of 0.5% full scale.
The prototype water level controller is simple and cheap enough for home and office use.
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Jo Jan 8, 2024
Seed mutagenesis can be classified into cross-breeding and artificial mutagenesis.
Crossing, a technique for producing new varieties of seeds by crossing seeds in different genera, species and varieties requires a lot of time and labor although it is cheap.
Artificial mutation, a technique that activates mutagens in seeds, takes less time and labor and it does not cost much to make a device for it. But its drawback is that mutant seeds reveal low availability.
Another artificial mutation method is based on transgenic technique. It is excellent because target genes are injected, but it is very expensive and complicated.
Therefore, Kang Myong Hyok, a researcher at the Faculty of Physical Engineering, based on the analysis of the physical factors of mutation, has developed a device that can serve as a mutagen with simultaneous action of more than two physical factors.
The physical factors he applied are pulsed high-voltage electric field that can change electrical properties of living organisms, shock wave that can momentarily provide energy strong enough to destroy cell membranes, and strong ionization field to make the surrounding environment a strong active field from an inert field stabilized in the growth activity.
He also obtained experimental results for determining suitable operation parameters necessary for mutation.
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Jo Dec 28, 2023
The empirical Bayes approach has become a common method in statistical situations. It is a statistical method for successive Bayes decisions when prior distribution is unknown but many past data are given. The inference for truncation parameters is important for evaluation of upper or lower bounds of population, so it has been studied extensively. Many authors have considered the case of one-sided truncated distribution but in practice, we face the case of two-sided one, too.
Ri Sung Hyon, a section head at the Faculty of Applied Mathematics, has investigated empirical Bayes estimation for truncation parameters of two-sided truncated distribution under squared error loss.
First, he constructed the empirical Bayes estimators of truncation parameters using size two samples and proved the asymptotic optimality of the estimators. Then, he proved that the probability of reverse estimation converges to zero as sample size goes to infinity. Finally, he presented an example to show the soundness of his theoretical results and conducted a simulation on the performance of the proposed empirical Bayes estimators.
The new proposal of using size two samples could be extended to the case of multi-dimensional truncated distributions defined on hyper-cubic domain.
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Jo Dec 27, 2023
Comminution of agglomerates is an essential part in preparing raw materials in a lot of production processes, consuming a great amount of energy. Nowadays, demand for energy is further increasing in the world and environmental protection problems require us to reduce energy consumed for comminution. To solve this problem, we have to further study a breakage process of agglomerates to accurately estimate the breakage energy consumed for crushing agglomerates into requested grain size.
Knowledge on breakage pattern and breakage energy of agglomerate under different conditions is very important for control and optimization of comminution processes. Therefore, making a practical agglomerate model is the key to studying breakage processes of agglomerates and deciding technical parameters of crushers.
The common feature of these studies is that the experimental results of many agglomerate models were analyzed statistically because the arrangement of particles forming an agglomerate model is random and stochastic. It needed a lot of time for DEM simulation.
Hong Sok Gun, a researcher at the Faculty of Mining Engineering, has proposed a new method of making an agglomerate model by means of discrete element method (DEM) according to the crystal structure of mineral material by the principle of closest packing in the crystallography and of determining the microproperty of agglomerate models by back analysis fitting the cumulative mass fraction of breakage product, one of the external expressions of agglomerate breakage. In this new model, the packing efficiency 0.74 and coordination number 12 are nearly the same as those in natural minerals.
His method can be used not only to express the breakage process of an object but also to predict the breakage energy. In addition, it can remarkably reduce simulation time, one of the difficulties in DEM simulation, as there is no need to make many agglomerate models due to no-randomness and no need for a statistical analyzing method.
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Jo Dec 26, 2023
Diffusion combustion is widely used in conventional diesel engines, and heat release rate and formation of harmful substances are determined by the mixing characteristics of diesel spray.
Both fuel atomization and spray characteristics are keys to improving diesel combustion and emission performance. In a combustion chamber with certain geometry, the process of fuel spray and mixing has a great impact on the combustion and emissions.
In a DI diesel engine, the centers of the combustion chamber and the injector are eccentric and the injector inclines gently. Therefore, in order to improve the fuel/air equivalence ratio distribution, it is important to analyze the effect of spray parameters such as spray angle, spray direction and number of spray holes suitable for the combustion chamber type.
In order to improve the quality of mixture, to boost combustion effects and to reduce the emission of exhaust gas, Hwang Kon, an institute head at the Faculty of Shipbuilding and Ocean Engineering, has analyzed the effect of spray angle in a reentrant combustion chamber and determined the best spray angle.
He simulated and investigated mixture formation and combustion processes at different spray angles in diesel engines by using AVL-FIRE code.
The main findings can be summarized as follows:
(a) Spray angle has a great influence on the fuel/air equivalence ratio in the combustion chamber and in-cylinder temperature distribution, and it also concerns the combustion process and emissions.
(b) The combustion performance parameters imply that increase in spray angle up to 160° is suitable and at that time emission is minimized.
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