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 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 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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Jo Aug 30, 2024
Stress sensitivity and the elastic outer boundary (EOB) condition have a great effect on the analysis of the characteristics of fluid flow in a reservoir. When analyzing the characteristics of fluid flow, researchers considered the stress sensitivity and the EOB condition separately, not simultaneously. Therefore, errors were inevitable during the analysis of well testing.
Kim Song Chol, a section head at the Faculty of Earth Science and Technology, has established a well-testing model for the DPR, considering the stress sensitivity and the EOB condition simultaneously and presented its semianalytical solution.
First, on the basis of the consideration of the EOB condition and stress sensitivity of permeability (SSP), he built a seepage model for the DPR with the EOB by considering wellbore storage and skin. To solve this model, he changed a nonlinear partial differential equation into a linear form by introducing an effective well radius and applying Pedrosa’s transformation and perturbation transformation. Then, by applying the Laplace transformation, he obtained an analytical solution in the Laplace space, and by numerically inverting it, he obtained a solution in the real space, thus drawing the curves of pressure and pressure derivative (PPD).
By comparing the proposed model with the one with the EOB without consideration of SSP, he verified its effectiveness.
For more information, please refer to his paper “Well-Testing Model for Dual-Porosity Reservoir considering Stress-Sensitivity and Elastic Outer Boundary Condition” in “Geofluids” (SCI).
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Jo Aug 29, 2024
Developing high quality learning contents (LCs) and improving their interactions in online learning with e-learning contents is important for greater cognitive abilities of a learner.
Studies on the interactions in online learning have increased and focus has been placed on its increased effectiveness. However, there has been less discussion on the relationship of LC design to learner’s cognition. In addition, there are few qualitative data on the interactions between a learner and LC, and less has been known about the effectiveness of self-feedback in learning processes on increasing the cognitive abilities of a learner. On the other hand, non-structural interaction brings about negative results to learners and cannot improve learner’s cognition, which means less cost-effective. This clearly shows that the interactions with LCs should be improved for successful online learning and, to this end, LCs with a self-feedback structure be designed to suit the intrinsic features of a learner.
Kim Jang Hak, a section head at the Faculty of Distance Education, has designed LCs with new self-feedback structure by considering the personalized characteristics of a learner and described a method for improving learners’ cognition abilities through improved interactions between a learner and LCs.
Based on the previous research findings on feedback and interaction, he divided the learning object into knowledge unit learning nodes and managed the learning control and appropriate interactions through self-feedback. Then, he conducted an experiment to investigate what improvement was made in the learner’s cognition by putting the proposed method into practical application.
The result showed that the self-feedback is a significant factor that gives positive influence on the learner’s cognition.
You can find the details in his paper “Improving Learners' Cognition through Designing Learning Contents with Self-feedback Structure and Advanced Interaction in Online Learning” in “Informatica” (SCI).
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Jo Aug 28, 2024
In general, temperature and structural loads may generate deformation of optomechanical systems and this deformation has a negative effect on the optical performance.
To analyze and minimize the effects of this deformation on the optical performance is a very important step in optomechanical structure design.
Kim Chol Hyon, a section head at the Faculty of Physical Engineering, has presented an integrated design process for an optomechanical system based on multidisciplinary optimization.
The proposed integrated optimal design process consists of finite element analysis (FEA) by ANSYS Workbench, MATLAB optomechanical transfer program, optical analysis by ZEMAX and multidisciplinary optimization solver by Isight.
By using optimum bipod flexures, he decreased the wavefront error of the primary mirror of Cassegrain Telescope from 29.9 nm to 16.1 nm.
For more information, please refer to his paper “Multidisciplinary integrated optimal design process for Optomechanical System” in “Applied optics” (SCI).
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