• IEMEK Journal of Embedded Systems and Applications
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• v.15 no.3
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• pp.149-157
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• 2020

Regarding previously-developed drone simulators, it was easy to check their flight stability or controlling functions based on the condition that their weight was fixed from the design. However, the drone is largely classified into two types that is the one with the fixed weight whose purpose is recording video with camera and racing and another is whole weight-variable during flight with loading the articles for delivery and spraying pesticide though the weight of airframe is fixed. The purpose of this thesis is to analyze the structure of drone and its flight principle, suggest dynamics-model-based simulator that is capable of simulating weight-variable drone and develop the simulator that can be used for designing main control board, motor and transmission along the application of weight-variable drone. Weight-variable simulator was developed by using various calculation to apply flying method of drone to the simulator. First, ground coordinate system and airframe-fixing coordinate system were established and switching matrix of those two coordinates were made. Then, dynamics model of drone was established using the law of Newton and moment balance principle. Dynamics model was established in Simulink platform and simulation experiment was carried out by changing the weight of drone. In order to evaluate the validity of developed weight-variable simulator, it was compared to the results of clean flight public simulator against existing weight-fixed drone. Lastly, simulation test was performed with the developed weight-variable simulation by changing the weight of drone. It was found out that dynamics model controlled various flying positions of drone well from simulation and the possibility of securing the optimum condition of weight-variable drone that has flying stability and easiness of controlling.

• The Journal of the Korea institute of electronic communication sciences
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• v.15 no.3
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• pp.533-542
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• 2020

In this study, we developed a PC - based motorcycle simulator based on the development technology of the virtual patrol motorcycle training system. In order to get the impression that the motorcycle simulator is operating in a realistic way, it is important to have a reliable signal transmission and operation feeling between the driver and the simulator. In order to achieve this, we developed a system that can apply the sub-systems of the actual vehicle to the motorcycle simulator in order to generate the same operation feeling as the actual vehicle. Based on these results, We have developed a method for generating a feedback queue. Vehicle dynamics simulates real-time vehicle motion by receiving input from a steering wheel, accelerating / decelerating pedal, etc. operated by a driver on a vehicle simulator and transmitting the result to a visual and acoustic system, It is the central element of the simulator to generate. I want to summarize the main requirements of simulation dynamics.

• Tuberculosis and Respiratory Diseases
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• v.81 no.3
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• pp.216-221
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• 2018

Background: The number of immigrants with tuberculosis (TB) increases each year in South Korea. Determining the transmission dynamics based on whole genome sequencing (WGS) to cluster the strains has been challenging. Methods: WGS, annotation refinement, and orthology assignment for the GenBank accession number acquisition were performed on two clinical isolates from Chinese immigrants. In addition, the genomes of the two isolates were compared with the genomes of Mycobacterium tuberculosis isolates, from two native Korean and five native Chinese individuals using a phylogenetic topology tree based on the Multiple Alignment of Conserved Genomic Sequence with Rearrangements (Mauve) package. Results: The newly assigned accession numbers for two clinical isolates were CP020381.2 (a Korean-Chinese from Yanbian Province) and CP022014.1 (a Chinese from Shandong Province), respectively. Mauve alignment classified all nine TB isolates into a discriminative collinear set with matched regions. The phylogenetic analysis revealed a rooted phylogenetic tree grouping the nine strains into two lineages: strains from Chinese individuals and strains from Korean individuals. Conclusion: Phylogenetic trees based on the Mauve alignments were supposed to be useful in revealing the dynamics of TB transmission from immigrants in South Korea, which can provide valuable information for scaling up the TB screening policy for immigrants.

• Journal of Veterinary Science
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• v.22 no.5
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• pp.71.1-71.12
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• 2021

Background: African swine fever (ASF) is a hemorrhagic fever occurring in wild boars (Sus scrofa) and domestic pigs. The epidemic situation of ASF in South Korean wild boars has increased the risk of ASF in domestic pig farms. Although basic reproduction number (R₀) can be applied for control policies, it is challenging to estimate the R₀ for ASF in wild boars due to surveillance bias, lack of wild boar population data, and the effect of ASF-positive wild boar carcass on disease dynamics. Objectives: This study was undertaken to estimate the R₀ of ASF in wild boars in South Korea, and subsequently analyze the spatiotemporal heterogeneity. Methods: We detected the local transmission clusters using the spatiotemporal clustering algorithm, which was modified to incorporate the effect of ASF-positive wild boar carcass. With the assumption of exponential growth, R₀ was estimated for each cluster. The temporal change of the estimates and its association with the habitat suitability of wild boar were analyzed. Results: Totally, 22 local transmission clusters were detected, showing seasonal patterns occurring in winter and spring. Mean value of R₀ of each cluster was 1.54. The estimates showed a temporal increasing trend and positive association with habitat suitability of wild boar. Conclusions: The disease dynamics among wild boars seems to have worsened over time. Thus, in areas with a high elevation and suitable for wild boars, practical methods need to be contrived to ratify the control policies for wild boars.

• Journal of Satellite, Information and Communications
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• v.7 no.3
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• pp.8-15
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• 2012

Adaptive transmission technique is an effective means to counter-measure rain attenation that is one of the most significant factors degrading link quality in satellite communication systems. This paper introduces a simulator for adaptive transmission technique to compensate rain attenuation. In the simulator, a dynamic rain attenuation model is loaded, which was developed to synthesize Korean rain attenuation dynamics at a frequency band of Ka. It is a Markov chain model with rain attenuation parameters extracted from the rain attenuation data measured per second. In addition, various transmission schemes are embedded so that a user defined simulations can be performed. This paper demonstrates simulation results of adaptive schemes in comprison with fixed schemes, and show the efficiency of the adaptive schemes to compensate the rain attenuation.

• Tribology and Lubricants
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• v.30 no.6
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• pp.337-342
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• 2014

The reduction of drag torque is an important research issue in terms of improving transmission efficiency. Drag torque in a wet clutch occurs because of the viscous drag generated by the transmission fluid in a narrow gap (clearance) between the friction plate and a separate plate. The objective of this paper is to observe the effects of the friction plate area and the clearance on the drag torque using finite element simulation. The two-phase flow of air and oil fluid is considered and modeled for the simulation. The simulation analysis reveals that as the rotational speed increases, the drag torque generally increases to a critical point and then decreases sharply at a high speed regime. The clearance between the two plates plays an important role in controlling drag torque peak. An increase in the clearance causes a decrease in shear stress; thus, the drag torque also decreases according to Newton's law of viscosity. An observation of the effect of the area of contact between transmission fluid and friction plate shows that the drag torque increases with the contact area. The flow vectors inside the flow channel present clear evidence that the velocity of the fluid flows is faster with a larger friction plate, that is, in the case of a larger contact area. Therefore, the optimum size of the friction plate should be determined carefully, considering both the clutch performance and drag reduction. It is expected that the results from this study can be very useful as a database for clutch design and to predict the drag torque for the initial design with respect to various clutch parameters.

• Nuclear Engineering and Technology
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• v.56 no.10
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• pp.4365-4374
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• 2024

Utilizing first-order beam dynamics models is adequate for studying the beam properties during the conceptual design of a cyclotron-based proton therapy beamline. After finishing lattice design, particle-matter interaction simulations for passive elements (e.g., degrader, collimators, energy slit) are required. The cascade simulation is used for lattice updates in each iteration, which is complicated. In addition, when the models involve particle tracking and particle-matter interaction, their optimization process is time-consuming. Therefore, this study proposes a start-to-end modeling method using Monte Carlo Beam Delivery Simulation (BDSIM) software that considers more realistic factors, such as particle-matter interaction and the realistic vacuum chamber, to precisely evaluate working parameters, along with an efficient optimization method that utilizes multi-objective Bayesian optimization (MOBO) to improve transmission efficiency. Taking the Huazhong University of Science and Technology proton therapy facility (HUST-PTF) as an example, beam loss along the beamline is located, quantified, and subsequently reduced by tuning the quadrupole strengths based on MOBO. The results show that: (i) By considering the particle-matter interaction and the realistic vacuum chamber, the precision in the prediction of the beam properties is improved; (ii) After optimization, the transmission efficiency of the entire beamline is relatively increased by an average of 6.52 % under different energy settings, especially 11.39 % at 70 MeV.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.54-55
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• 2010

Vacancy defects in graphene can be created by electron or ion irradiation and those induce ripples which can change the electronic properties of graphene. Recently, the formation of defect structures such as vacancy defects and non-hexagonal rings has been reported in the high resolution transmission electron microscope (HR-TEM) of reduced graphene oxide [1]. In those HR-TEM images, it is noticed that the dislocations with pentagon-heptagon (5-7) pairs are formed and diffuses. Interestingly, it is also observed that two 5-7 pairs are separated and diffuse far away from each other. The separation of 5-7 pairs has been known to be due to their self-diffusion. However, from our tight-binding molecular dynamics simulation, it is found that the separation of 5-7 pairs is due to the diffusion of single vacancy defects and coalescence with 5-7 pairs. The diffusion and coalescence of single vacancy defects is too fast to be observed even in HR-TEM. We also implemented Van der Waals interaction in our tight-binding carbon model to describe correctly bi-layer and multi-layer graphene. The compressibility of graphite along c-axis in our tight-binding calculation is found to be in excellent agreement with experiment. We also discuss the difference between single layer and bi-layer graphene about vacancy diffusion and reconstruction.

• International Journal of Aeronautical and Space Sciences
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• v.6 no.2
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• pp.23-32
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• 2005

An experimental control system is proposed for the attitude control of a simplified 2-DOF helicopter model. The main rotor is a rigid one, and the fuselage is simply supported by a fixed hinge point where the longitudinal motion is decoupled from the lateral one since the translations and the rolling rotation are completely removed. The yaw trim of the helicopter is performed with a tail rotor, by which the azimuthal attitude can be adjusted on the rotatable post in the yaw direction. The robust sliding mode control tracking a given attitude angle is proposed based on the flight dynamics. A pitch damper is inserted for the control of pitching angle while the compensator to reaction torque is used for the control of azimuth angle. Several parameters of the system are selected through experiments. The results shows that the proposed control method effectively counteracts nonlinear perturbations such as main rotor disturbance, undesirable chattering, and high frequency dynamics.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.340-340
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• 2010

Various structures of vacancy defects in graphene layers and carbon nanotubes have been reported by high resolution transmission electron microscope (HR-TEM) and those arouse an interest of reconstruction processes of vacancy defects. In this talk, we present reconstruction processes of vacancy defects in a graphene and a carbon nanotube by tight-binding molecular dynamics (TBMD) simulations and by first principles total energy calculations. We found that a structure of a dislocation defect with two pentagon-heptagon (5-7) pairs in graphene becomes more stable than other structures when the number of vacancy units is ten and over. The simulation study of scanning tunneling microscopy reveals that the pentagon-heptagon pair defects perturb the wavefunction of electrons near Fermi level to produce the $\sqrt{3}\;{\times}\;\sqrt{3}$ superlattice pattern, which is in excellent agreement with experiment. It is also observed in our tight-binding molecular dynamics simulation that 5-7 pair defects play a very important role in vacancy reconstruction in a graphene layer and carbon nanotubes.