• International Journal of Fuzzy Logic and Intelligent Systems
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• v.5 no.2
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• pp.124-130
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• 2005

Obstacle avoidance of underwater robots based on a modified virtual force field algorithm is proposed in this paper. The VFF(Virtual Force Field) algorithm, which is widely used in the field of mobile robots, is modified for application to the obstacle avoidance of underwater robots. This Modified Virtual Force Field(MVFF) algorithm using the fuzzy lgoc can be used in moving obstacles avoidance. A fuzzy algorithm is devised to handle various situations which can be faced during autonomous navigation of underwater robots. The proposed obstacle avoidance algorithm has ability to handle multiple moving obstacles. Results of simulation show that the proposed algorithm can be efficiently applied to obstacle avoidance of the underwater robots.

• Journal of Computing Science and Engineering
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• v.8 no.3
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• pp.157-172
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• 2014

Contemporary embedded systems often use NAND flash memory instead of hard disks as their swap space of virtual memory. Since the read/write characteristics of NAND flash memory are very different from those of hard disks, an efficient page replacement algorithm is needed for this environment. Our analysis shows that temporal locality is dominant in virtual memory references but that is not the case for write references, when the read and write references are monitored separately. Based on this observation, we present a new page replacement algorithm that uses different strategies for read and write operations in predicting the re-reference likelihood of pages. For read operations, only temporal locality is used; but for write operations, both write frequency and temporal locality are used. The algorithm logically partitions the memory space into read and write areas to keep track of their reference patterns precisely, and then dynamically adjusts their size based on their reference patterns and I/O costs. Without requiring any external parameter to tune, the proposed algorithm outperforms CLOCK, CAR, and CFLRU by 20%-66%. It also supports optimized implementations for virtual memory systems.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.21 no.1
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• pp.1-14
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• 2009

Linear-tracked typhoons were simulated to investigate the effect of parameter sensitivity at Gyeongnam coastal zone. To do this, appropriateness of the linear-tracked MAEMI(0314) was tested and 175 scenarios were simulated on the basis of virtual MAEMI. The results show surge heights are relatively large at Masan and Tongyeong, and it can be attributed to topographical effects. At Masan, 2.5 m-surge height is probable with the same intensity but slightly different track from the real typhoon MAEMI. At the other stations, surge heights induced by real MAEMI are nearly same as the maximum heights of the virtual typhoons, which indicates the real track of the typhoon MAEMI was almost the most severe one. Surge heights caused by the barometric effect are higher than those by the wind effect, and the former effect shows the maximum at the eye of typhoon.

• Journal of Korea Multimedia Society
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• v.23 no.1
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• pp.15-23
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• 2020

Recently, the increase in the elderly population due to an aging society has led to a relative increase in senile diseases such as vascular dementia or Alzheimer's disease, and the social burden for rehabilitation has increased. In addition, studies have been conducted for the risk assessment and prevention of musculoskeletal disorders. The purpose of this study is to suggest a system that can be used to help with dementia prevention training by tracking the movement of motion and virtual reality contents for the risk factors of musculoskeletal disorders of the elderly. We propose a training method for preventing dementia through musculoskeletal motion analysis algorithm and virtual reality content. Through motion recognition algorithm based on motion region design, we will track and analyze the moving radius of the target joint. The purpose of this study is to calculate and evaluate scores based on the time to accomplish the goals on virtual reality contents for the prevention of musculoskeletal disorders and the support of dementia prevention training, and the degree of difficulty, and to analyze the correlation between the results of performing K-MMSE and VR contents.

• Journal of Power Electronics
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• v.19 no.5
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• pp.1224-1234
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• 2019

Hybrid rotor position estimation methods that integrate a fundamental model and high frequency (HF) signal injection are widely used for the wide speed-range sensorless control of interior permanent-magnet synchronous machines (IPMSMs). However, the direct transition of two different schemes may lead to system fluctuations or system instability since two estimated rotor positions based on two different schemes are always unequal due to the effects of parameter variations, system delays and inverter nonlinearities. In order to avoid these problems, a seamless transition strategy to define and construct a virtual q-axis inductance is proposed in this paper. With the proposed seamless transition strategy, an estimated rotor position based on a fundamental model is forced to track that based on HF signal injection before the transition by adjusting the constructed virtual q-axis inductance. Meanwhile, considering that the virtual q-axis inductance changes with rotor position estimation errors, a new observer with a two-phase phase-locked loop (TP-PLL) is developed to accurately obtain the virtual q-axis inductance online. Furthermore, IPMSM sensorless control with maximum torque per ampere (MTPA) operations can be tracked automatically by selecting the proper virtual q-axis inductance. Finally, experimental results obtained from an IPMSM demonstrate the feasibility of the proposed seamless transition strategy.

• Journal of the Korea Computer Graphics Society
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• v.29 no.3
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• pp.149-158
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• 2023

HMD, which is applied with the latest technology, minimizes motion sickness with high-resolution displays and fast motion recognition, and can accurately track location and motion. This can provide an environment where you can immerse yourself in a virtual three-dimensional space, and virtual reality contents such as disaster simulators and high-risk equipment learning spaces are developing using these characteristics. These advantages are also applicable in the field of basic science education. In particular, expanding the concepts of electric and magnetic fields in physics described by existing two-dimensional data into three-dimensional spaces and visualizing them in real time can greatly help improve learning understanding. In this paper, realistic physical education environments and contents based on three-dimensional virtual reality are developed and the developed learning contents are experienced by actual learning subjects to prove their effectiveness. A total of 46 middle school and college students were taught and experienced in real time the electric and magnetic fields expressed in three dimensions in a virtual reality environment. As a result of the survey, more than 85% of positive responses were obtained, and positive results were obtained that three-dimensional virtual space-based physical learning could be effectively applied.

• Journal of the Korean Society of Systems Engineering
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• v.1 no.2
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• pp.19-25
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• 2005

Tilting train has been developed to increase the operational speed of the trains on conventional lines which have many curves. The train are tilted at curves to compensate for unbalanced carbody centrifugal acceleration to a greater extent than compensation produced by the track cant, so that passengers do not feel centrifugal acceleration and thus trains can run at higher speed at curves. This paper developed PDM(product data management) to make a system engineering of TTX(Tilting Train eXpress) with maximum operation speed of 180 km/h.

• Proceedings of the KSR Conference
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• 2004.10a
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• pp.423-429
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• 2004

The concurrent engineering technologies have been broadly used in the field of the design, testing, manufacturing and maintenance works to reduce development time and costs. For this purpose, many design environments with the product data management system, the virtual engineering system and web database system are developed. In this research, we developed the driving simulator of the KTX(Korea Train Express) as a basic study for building the concurrent engineering design environment of rolling stock. The virtual track was developed from the Seoul to the Busan and the Daejeon to Mockpo to generate immersible driving environment. Also. fault generation systems were developed to educate drivers of the KTX. We expect to reduce the time and costs of newly developed rolling stock using the design environment developed in the research.

• ETRI Journal
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• v.34 no.3
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• pp.466-469
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• 2012

In this letter, we propose a dual autostereoscopic display platform employing a natural interaction method, which will be useful for sharing visual data with users. To provide 3D visualization of a model to users who collaborate with each other, a beamsplitter is used with a pair of autostereoscopic displays, providing a visual illusion of a floating 3D image. To interact with the virtual object, we track the user's hands with a depth camera. The gesture recognition technique we use operates without any initialization process, such as specific poses or gestures, and supports several commands to control virtual objects by gesture recognition. Experiment results show that our system performs well in visualizing 3D models in real-time and handling them under unconstrained conditions, such as complicated backgrounds or a user wearing short sleeves.

• Journal of the Korea Society for Simulation
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• v.21 no.1
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• pp.81-88
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• 2012

In the M&S filed, The Battle Lab is available for acquisition, design, development tool, validation test, and training in the weapon system of development process. Recently, the Battle Lab in the military of Korea is still in an early stage, in spite of importance of battle lab construction. In the environment of network centric warfare, a practical use of the M&S which is connecting live, virtual and constructive model can be applied to all field of System Engineering process. It is necessary thar the Battle Lab is not restricted by time and space, and is possible for the technical implementation. In this paper, to guarantee the interoperability of live and virtual simulation, virtual simulators connect live simulators by using the tactical data link. To guarantee the interoperability of virtual and constructive simulation, both virtual simulators and constructive simulators use the RTI which is the standard tool of M&S. We propose the System that constructed the Air Defence Battle Lab. In case of the approach of target tracks, The Air Defence Battle Lab is the system for the engagement based on a command of an upper system in the engagement weapon system. Constructive simulators which are target track, missile, radar, and launcher simulator connect virtual simulators which are MCRC, battalion, and fire control center simulators using the RPR-FOM 1.0 that is a kind of RTI FOM. The interoperability of virtual simulators and live simulators can be guaranteed by the connection of the tactical data links which are Link-11B and ATDL-1.