• Journal of Ocean Engineering and Technology
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• v.11 no.3
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• pp.107-115
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• 1997

비성형 동력학계로 모델링된 부유수송체의 동적응답을 조사하고 그 운동의 안정성을 해석하였다. 종동요 모우드의 고유주파수가 횡동요 모우드의 고유주파수의 두배가 되는, 즉, 2:1 내부공진 혹은 자기계수공진인 조건하에서, 이부유수송체는 한 운동 모우드의 직접가진에 의해 간접가진된 다른 모우드가 대진폭 응답을 보일 수 있음을 밝혔다. 또항, 종동요 모우드의 감쇠력은 비교적 넓은 범위의 운동에 대해 선형적임에 반해, 횡동요 모우드의 감쇠력은 점성의 영향이 대단히 커서 비선형성이 대단히 강한 것으로 알려져 왔다. 이 문제를 수학적으로 모델링하기 위하여, 종동요 모우드의 운동방정식에는 선형및 제곱형의 합의 형태인 감쇠력 모형을 사용하였다. 다중척도법을 사용하여 이 두가지 운동 모우드의 주기적 응답및 그의 안정성에 미치는 제곱형 비선형 횡동요 감쇠력의 영향을 밝혔다. 조우주기가 횡동요 모우드의 고유주기와 근사한 경우에 대하여 이 비선형계의 응답을 구하고 주파수-응답 곡선으로 나타내었다.

• The KIPS Transactions:PartB
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• v.19B no.1
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• pp.31-36
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• 2012

In recent years, there has been increasing interest in recommender systems which provide users with personalized suggestions for products or services. In particular, researches of collaborative filtering analyzing relations between users and items has become more active because of the Netflix Prize competition. This paper presents the reinforcement learning approach for collaborative filtering. By applying reinforcement learning techniques to the movie rating, we discovered the connection between a time sequence of past ratings and current ratings. For this, we first formulated the collaborative filtering problem as a Markov Decision Process. And then we trained the learning model which reflects the connection between the time sequence of past ratings and current ratings using Q-learning. The experimental results indicate that there is a significant effect on current ratings by the time sequence of past ratings.

• The KIPS Transactions:PartC
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• v.17C no.4
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• pp.385-390
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• 2010

Fair and efficient bandwidth allocation methods using the coalition game theory and the bargaining game theory following the axiomatic approach have been proposed when sending nodes with different traffic input rate try to share the bandwidth. These methods satisfy the axiomatic fairness provided by the mathematical ground of the game theories. However, since the axioms of the two game models are different from one another, the allocated bandwidths to each sending nodes become different even in the same communication environments. Thus, in this paper, we model the bandwidth allocation problem with these game theories, and quantitatively compare and analyze the allocated bandwidth and loss rate of each sending nodes in various communication environments. The results show that the bargaining game allocates relatively less bandwidth to a node with a higher sending rate than that with a lower sending rate while coalition game allocates bandwidth according to the sending rate of each node.

• School Mathematics
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• v.14 no.1
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• pp.109-134
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• 2012

The purpose of this study is to develop authentic assessment model and example tools of mathematics teaching and learning. By reviewing literature researches, we set up the definition of authentic assessment in mathematics education, checked the criterian of authentic assessment tasks and mathematical activities. We searched various assessment models of mathematics teaching and learning, project assessment proceeding model, and criterian of project assessment, and checked various project tasks of the authentic assessment. And we developed authentic assessment model and example tools of mathematics teaching and learning. The model is applied project tasks in the form of being integrated with class to high school students, with high school mathematics especially. Furthermore, we carried the test of content validity for a validity of developed tasks for experts in studies of mathematics education. The result is that authentic assessment model and example tools of mathematics teaching and learning has an significance in mathematics education and can be used to judge whether students are doing 'real' mathematics or not, keeping the applicability in the form of being integrated with class.

• Journal of Korea Multimedia Society
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• v.8 no.11
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• pp.1421-1431
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• 2005

There are two methods in 3-D sound reproduction: a surround system, like 3.1 channel method and a binaural system using 2-channel method. The binaural system utilizes the sound localization principle of a human using two ears. Generally, a crosstalk between each channel of 2-channel loudspeaker system should be canceled to produce a natural 3-D sound. To solve this problem, it is necessary to trace a head movement. In this paper, we propose a new algorithm to correctly trace the head movement of a listener. The Proposed algorithm is based on the detection of face and eye. The face detection uses the intensity of an image and the position of eyes is detected by a mathematical morphology. When the head of the listener moves, length of borderline between face area and eyes may change. We use this information to the tracking of head movement. A computer simulation results show That head movement is effectively estimated within +10 margin of error using the proposed algorithm.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.12
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• pp.1152-1160
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• 2007

In this paper we deal with a design of integral sliding mode controller to reject the disturbance force acting on the suspension system in the magnetically levitated system which is propelled by the linear induction motor. The control scheme comprises an integral controller which is designed for achieving zero steady-state error under step disturbances, and a sliding mode controller which is designed for enhancing robustness under plant uncertainties. A proper continuous design signal is introduced to overcome the chattering problem. The disturbance force produced by the linear motor is formularized by using a curve fitting of the experimental raw data. Computer simulations show the effectiveness of the designed integral sliding mode controller to reject the disturbance force.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.5 no.7
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• pp.1314-1320
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• 2001

DC motors have widely been used in the field of variable-speed driving system since it is easy to control flux and torque of the motors precisely but it is hard to check and maintain those periodically. In addition, there are difficulties in high power and high speed running due to rectifying limit of commutator, and are a lot of restrictions in installation. Therefore, speed control in BLDC(Brushless DC) motors have seriously been studied for a long while. In this paper, a mathematical model of BLDC motor driven by PWM inverter is developed. Dynamics and steady-state characteristics of BLDC motor are simulated and analyzed with a series of experiments for the parameter estimation : torque, speed, phase voltage and current.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2001.05a
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• pp.408-413
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• 2001

DC motor has widely been used in the field of variable-speed driving unit since it is easy to control flux and torque precisely but it is troublesome to check and maintain periodically. In addition, there are difficulties in hish power and high speed running due to rectifying limit of commutator, and are a lot of restrictions in installation. Therefore, speed control in BLDC(Brushless DC) motor has seriously been studied for a long while. In this paper, a mathematical model of BLDC motor driven by PWM inverter is developed. Dynamics and steady-state characteristics of BLDC motor are simulated and analyzed with a series of experiment for the parameter estimation : torque, speed, phase voltage and current.

• Bulletin of the Society of Naval Architects of Korea
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• v.27 no.1
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• pp.73-83
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• 1990

A theorectical method is presented for the calculation of the effective wake in an axisymmetric sheared inflow. The effective wake is essential in the design of optimal propulsor and in the reduction of propulsor induced vibration and noise. The nominal wakes are mathematically modelled and the effective wakes are calculated using the computer program developed on the basis of the linear momentum theory. The results show that shear effects arc dominant near the hub and the effective wakes reveal some differences near the hub for the moderately and heavily loaded propulsors but they arc well coincided with the other experimental or theorectical results for the lightly loaded propulsors. To improve the results it may be necessary to consider nonlinear terms neglected in this study and body boundary condition on hub.

• Journal of the Korea Society for Simulation
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• v.27 no.4
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• pp.27-45
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• 2018

The terrestrial communication network and the underwater acoustic communication network have very different communication characteristics each other in operational environments, communication media, propagation delay, frequency bandwidth, transmission speed, bit error rate, and so on. These different characteristics cause some different address schemes and different maximum transmission units and, as a result, these differences must form certainly obstacles to the intercommunication between a terrestrial communication network and an underwater acoustic communication network. In this paper, we presents a method to use the virtual addresses to resolve the interconnection problem caused by different address schemes between a terrestrial communication network and an underwater acoustic communication network, and, through a mathematical modeling, we analyze the performance on the message transceiving delay time in the underwater environment.