Jo Sep 12, 2024
Fluid flow and heat transfer problems in porous media are widely applied in drying, filtration, preservation of agricultural products, fluidized bed reactors, etc.
Today, a significant amount of work has been focused on the numerical simulation of the problems involving non-equilibrium heat and mass transfer. Especially, Computational Fluid Dynamics (CFD) is used to simulate such problems.
Recently, there have been several studies on the numerical modeling of diverse problems involving heat and mass transfer including drying. In this respect, heat and mass transport equations have been proposed to model different heat and mass transfer problems based on the thermal non-equilibrium assumption.
However, few studies have been proposed on non-equilibrium heat and mass transfer models for prediction of drying process using commercial software FLUENT.
Choe Song Gun, a section head at the Faculty of Heat Engineering, has developed a numerical formulation for modeling non-equilibrium heat and mass transfer inside porous media and solved the equations by using FLUENT. To achieve the objective, he reformed the moisture transport equation and energy transport equation for the solid matrix of porous media into a user-defined scalar equation type in FLUENT. In addition, he redefined the properties of solid and some terms of these equations in consideration of the coefficients and terms of UDS equation in FLUENT.
Then, he compared the calculation results and the experimental results in order to check the validity of the reformation of the model and equations. The deviations between them are less than 3% in heat transfer and less than 8% in mass transfer. The results show that his predictions follow the expected trends with respect to temperature and velocity at inlet.
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Jo Sep 10, 2024
Wireless sensor network (WSN) is one of the most popular areas of research due to the constant improvement in the field of wireless technology and embedded system. Now, WSNs are extensively deployed in every area such as industry, civilian and military applications. These applications include monitoring, tracking, event detection and disaster management. The long term usefulness of WSN mainly relies on the lifetime of sensor nodes. The lifetime of SN mainly depends on its battery source. Since these batteries can be hardly replaceable, the improvement in the lifetime of WSNs can be achieved through the conservation of battery energy. In order to achieve this purpose, it is very important to design an energy-efficient routing protocol for efficient use of the limited energy of WSNs.
Many researchers applied the concept for clustering of sensor nodes and efficient routing to conserve the energy of sensor nodes and these techniques significantly improved the lifetime of WSN. LEACH (Low Energy Adaptive Clustering Hierarchy), the first adaptive hierarchical clustering routing protocol that considers energy saving, comprises two phases i.e. setup phase and steady phase.
But LEACH protocol has some critical drawbacks: It does not consider residual energy of a node, so a node with low energy can be selected as a cluster head. Also, due to randomized election of cluster heads, it is possible that elected cluster heads very close to each other might cause congestion in particular areas.
To solve the critical problem due to residual energy in LEACH, some protocols similar to LEACH, but considering residual energy of nodes were introduced. Nevertheless, LEACH based protocols considering residual energy of nodes can never deal with irregular election of cluster heads.
In response to the above issue, Kim Chol Man, a researcher at the Faculty of Information Science and Technology, has presented an improved cluster head election algorithm using residual energy and network address of nodes.
This algorithm is based on LEACH and considers both remaining energy and network address of nodes to revise the cluster head threshold equation. He assigned the network addresses of nodes by distributed address assignment mechanism (DAAM) of ZigBee. As he used the network address of a node in the threshold equation, the cluster type created in a new round is similar to the old cluster type. In addition, he dynamically changed the upper limit of the interval that generates random numbers to optimize the number of cluster heads.
He evaluated the performance of the proposed LEACH-NA using network Simulation platform NS-2. The simulation results demonstrate that the proposed algorithm shows better performance than the existing ones in terms of network lifetime and energy conservation, and the number of cluster heads in every round is more stable than other algorithms based on LEACH.
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Jo Sep 9, 2024
Mausoleum of King Wang Kon (founder of Koryo, 877-943) is in Haeson-ri, Kaesong City, DPRK.
Thanks to the wise guidance of President
On one side before the gate stands a monument to the reconstructed mausoleum of King Wang Kon, founder of Koryo.
Entering through the gate, you face a sacrifice chamber and a monument pavilion. Go past them and you will finally get to the typical Koguryo-style earth-covered stone grave on a raised platform.
At the four corners are stone tigers with offertory tables, stone posts, stone lanterns, etc. before them.
On the second and third platforms, which are situated a little lower than the mausoleum stand apart in two rows eight close vassals including those of merit who contributed to the founding of the dynasty.
The entrance to the grave chamber is a stone door. In the center of the chamber is a bier of large plate stones. On the left and right under the walls are long stands for display of relics and on the eastern, western and northern walls are painted with bamboos and pines.
Many kinds of relics like a jeweled buckle, buckle-shaped metal fittings, a bronze kettle, a gilt-bronze sedentary statue, etc. have been found in the mausoleum and its surroundings.
The magnificently reconstructed mausoleum is making a great contribution to educating the working people and young boys and girls in patriotism, as a priceless historical and cultural site.
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Jo Sep 6, 2024
Ozone has strong oxidation ability and very strong reactivity with organic and inorganic substances. It also leaves no secondary contaminants, which makes it applicable in a variety of ways in many fields including chemical industry, medicine, light industry, agriculture, water treatment, etc.
With the expansion of application of ozone generators over a long period since its appearance, the power supply of ozone generation has been made in various types and many achievements have been made in the research for power quality improvement.
Nowadays, an ozone generator based on dielectric barrier discharge (DBD) is popular and the high-voltage and high-frequency inverter power supply is essential in power mode.
Hwang Kum Song, a researcher at the Nano Physics Engineering Institute, has proposed a method for a feedback control of the discharge current in a DBD type high-frequency and high-voltage power supply to keep the discharge intensity of the ozone generator constant and to improve the power efficiency.
He mapped the discharge current model of the DBD inverter source, which is subject to strong nonlinearity and model uncertainty, to a dynamic linearization (DL) model to design a model-free adaptive control (MFAC) algorithm, and conducted a simulation on Matlab Simulink. He designed an MFA controller with the control object equivalent to the simplest dynamic linear model.
The strong nonlinearity and model uncertainty inherent in the control objective reduce the control effectiveness of conventional control approaches (PID control or fuzzy-PID control) and complicates the application of intelligent control approaches.
However, MFAC method, which requires no model of a plant and only controls the input and output data of the system, is more effective in constant-current control of the DBD ozone generator. MFA controller based on compact form dynamic linearization is convenient for implementation because of its simple structure and low computational cost. In addition, optimizing the parameters of the model-free adaptive controller can achieve more flexible adaptation of the controller, eliminate most of the overshoot and improve the response speed.
The simulation results showed the improved effectiveness of the model-free adaptive controller compared to the PID controller or the fuzzy-PID controller.
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Jo Sep 5, 2024
Kyongdang was a civilian education establishment of the Koguryo age.
Koguryo people, regardless of their high or low social standings, liked learning, so they built a large house called kyongdang for educating young people including children.
The education at kyongdang was aimed at cultivating patriotism and talent, and courage and strength.
Those who attended kyongdang learnt to read and acquired knowledge of history and other fields day and night.
In addition, they built up their physical strength, training in several military arts like archery, horse riding, swordsmanship, etc.
It has been said that many kyongdang graduates with literary and military accomplishments played a big part in the battles against foreign invaders.
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Jo Sep 4, 2024
Parallel manipulators are closed-loop mechanical structures presenting very good performance in terms of accuracy, rigidity and ability to move large loads. Generally, the mechanism has two platforms: one is attached to the fixed reference frame and the other performs arbitrary motions in its workspace. Some moving legs similar to those of serial robots connect the moving platform to the fixed platform. Spherical joints, revolution joints or prismatic joints connect the elements of the robot to one another.
Recently, much effort has been devoted to the kinematic and dynamic analysis of fully parallel manipulators. The dynamic analysis was usually conducted by analytical methods of classical mechanics in which projection and resolution of equations on the reference axes are written in a considerable number of cumbersome, scalar relations and the solutions are rendered by large-scale computation together with time-consuming computer codes.
Pang Thae Jin, a researcher at the Robotics Institute, has established a new method for inverse dynamic analysis of a 3-DOF parallel manipulator with three actuators using an approach based on the principle of virtual work.
The new approach is far more efficient, and it can eliminate all forces of internal joints and directly determine the time-history evolution of torques and powers required by the three actuators.
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