• Journal of IKEEE
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• v.8 no.1 s.14
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• pp.39-46
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• 2004

This paper presents the realization schemes for a multipurpose coherent mono-pulse radar Simulator with extendable features. We developed and installed the TSG(Timing Signal Generator) board which can simulate a mechanically rotate signal of antenna, an operation timing signal of pulse radar and target signal, to operate the simulator without real target in the indoor environment. Also, with the insertion of the radar signal processor, it came to be easy to achieve the addition of radar function algorithms, to rebuild or extend the multi-DSP Architecture into the simulator. Throughout the simulation results, we verified that the designed coherent mono-pulse radar simulator can exactly display a moving target on the realistic monitor(RD 9800).

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.3
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• pp.336-345
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• 1998

The substantial loss behind axial flow rotor was generated by wake, various vortices in the hub region and the leakage vortex in the tip region. Particularly, the leakage vortex formed near blade tip was one of the main causes of the reduction of performance, the generation of noise and the aerodynamic vibration in rotor downstream. In this study, the three-dimensional flowfields in an axial flow rotor for various tip clearances were calculated, and the numerical results were compared with the experimental ones. The numerical technique was based on SIMPLE algorithm using standard k-.epsilon. model (WFM). Through calculations, the effects of the tip clearance on the overall performance of rotor and the loss distributions, and the increase in the displacement, momentum, and blade-force-deficit thickness of the casing wall boundary layer were investigated. The mass-averaged flow variables behind rotor agreed well with the experimental results. The presence of the tip leakage vortex behind rotor was described well. Although the loci of leakage vortex by calculation showed some differences compared with the experimental results, its behavior for various tip clearances was clarified by examining the loci of vortex center.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.3
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• pp.261-267
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• 2009

The spindle with a built-in motor can be used to simplify the structure of machine tool system, while the rotor has unbalance mass inevitably. Therefore, it is important to recognize the effect of unbalance mass. This paper presents analysis of dynamic behavior of a high speed spindle with a built-in motor. The spindle is supported by the angular contact ball bearings and the rotor is fixed at the middle of spindle. The spindle used in CNC automatic lathe has been investigated using combined methodologies of finite elements and transfer matrices. The Houbolt method is used for the integration of the system equations and the dynamic behavior of spindle is obtained considering unbalance mass of rotor. Results show that increasing rotational speed of spindle magnifies the whirl responses of spindle seriously. Also the whirl responses of spindle are affected by the other factors such as unbalance mass and bearing stiffness.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.12
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• pp.1238-1245
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• 2007

A very abnormal vibration was occurred at the LP(low pressure) turbine continuously during the pre-operation for a 550MW class USC(ultra super critical) steam turbine. This vibration was initiated at the rotating speed of about 3,450 rpm and then the vibration amplitude was highly increased the number by $2{\sim}3$ times with the increase of the rotating speed to the rated speed (3,600 rpm). In this paper, this abnormal vibration named spike vibration. This spike vibration was caused by the rubbing between the rotating bucket tip seal and the lower half of spill strip. Also, this paper presents the mechanism of the spike vibration and the proper method to eliminate this abnormal vibration problem. This result would be good practice to find the solution of similar high vibration in the USC steam turbines for power plant as well as industrial rotating machineries.

• Journal of the Korean Institute of Intelligent Systems
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• v.20 no.5
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• pp.603-609
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• 2010

This paper introduces an objects recognition algorithm based on SURF(Speeded Up Robust Features) and GP(Genetic Programming) based gaits generation. Combining both methods, a recognition based intelligent walking for quadruped robots is proposed. The gait of quadruped robots is generated by means of symbolic regression for each joint trajectories using GP. A position and size of target object are recognized by SURF which enables high speed feature extraction, and then the distance to the object is calculated. Experiments for objects recognition and autonomous walking for quadruped robots are executed for ODE based Webots simulation and real robot.

• Journal of the Korea Institute of Military Science and Technology
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• v.13 no.5
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• pp.717-724
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• 2010

The initial trajectory of a spheroid configuration bobbin for precision guidance has been investigated by analyzing its aerodynamic load and six-degree-of-freedom motion. The effects of changes in the spheroidal head configuration, flow angle and lateral center-of-gravity offset are numerically studied using the commercial software "FLUENT". A wind tunnel test is also conducted to validate the numerical scheme and to examine effect of the Reynolds number on the flow around the bobbin. It is shown that the size of the separation bubble formed on the surface decreases significantly when the Reynolds number is varied between 110,000 and 140,000. At a zero flow angle, an oblate spheroidal head shows relatively moderate rotation while a prolate spheroidal head shows rapid rotation. The bobbin with a spherical head shape has little effect on the flow direction; however, the oblate bobbin is sensitive to the flow angle. The roll motion of the bobbin is greatly influenced by the lateral center-of-gravity offset and maximum dispersion is observed at half of the radius.

• Journal of Navigation and Port Research
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• v.31 no.5 s.121
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• pp.325-332
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• 2007

This study develops a control algorithm on berthing/unberthing system using a joystick for ships with thrusters and a rudder. A nonlinear mathematical model for low speed maneuvering of typical container ships is used to develop a MIMO(multi-input multi-output) nonlinear control algorithm for velocity feedback joystick control. Also a virtual HILS(hardware in the loop simulation) software program for berthing/unberthing is developed to test the performance of the nonlinear and a PID control algorithm. The program is developed using LabWindow/CVI, and a user can see current position and desired trajectory of ship in a monitor, then he can control forward and yaw velocities of a ship using a joystick. The simulation results show that the nonlinear mfd the PID controller have superior performance over a simple open loop joystick control algorithm.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.121-121
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• 2009

자동차는 코너 주행 시 In-corner와 Out-corner 의 바퀴 궤적이 달라지므로, 특별한 장치가 없이 좌우 구동 측의 바퀴가 같은 속도로 회전을 하게 되면 정상적인 주행이 불가능하다. 따라서 정상적인 코너 주행이 가능 하려면, 코너 안쪽 바퀴보다 바깥쪽 바퀴가 더 빨리 회전해야 하며 이러한 회전 차를 보상받지 못할 경우 바깥쪽 바퀴가 끌리는 현상이 발생하는데 이를 방지하기 위해 디퍼렌셜 기어가 필요하다. 현재 디퍼렌셜 기어는 디퍼렌셜 케이스와 링기어를 볼트로 체결하는 조립 공법을 통해 생산되고 있다. 하지만 볼트 체결 공법은 조립을 위한 볼트와 볼트 체결을 위한 플랜지와 볼팅을 위한 홀을 가공하는 공정이 필요하기 때문에 재료비 절감 및 생산 효율 향상에 매우 불리하고 볼트체결을 위한 부분 때문에 불필요한 무게가 증가하게 된다. 따라서 본 연구에서는 이러한 기계적 체결 방식을 레이저 용접 방식으로 대체하여 재료비를 절감하고 무게 저감을 통해 주행성능을 향상시키고자 하였다. 링기어의 소재는 침탄처리강(SCM420H)이며 디퍼렌셜 케이스의 소재는 주철(GCD500)을 사용하고 있다. 주철은 용접시 용접부와 열영향부에서 마르텐사이트 조직과 레데브라이트, 시멘타이트 조직이 생성되며 고탄소 모재의 탄소 확산으로 인한 부분 혼합영역에서 탄소 합금이 생성되어 균열이 발생하는 등 용접성이 매우 좋지 않은 것으로 알려져 있다. 이러한 주철의 난용접성을 해결하는 방법으로는 고탄소 모재 용접시 발생하는 탄소의 확산을 억제하거나 예열이나 후열 처리를 통한 냉각 속도의 제어하는 방법과 오스테나이트 안정화 원소를 첨가한 필러와이어를 사용하여 용접시 마르텐사이트와 시멘타이트의 성장을 방해하는 방법 등이 이용되고 있다. 본 연구에서는 예열처리나 후열처리를 통한 주철의 용접법은 대량 생산을 통한 원가절감을 노리는 자동차 업계의 특성에 비추어 볼 때 비용이나 프로세스 구성 면에서 적용하는 것이 어려울 것이라 판단하여 Ni-base filler metal을 통한 주철의 용접법을 선택하였고 그 결과 실차에 적용하기 위한 비틀림 강성 테스트나 내구 테스트는 통과하였으나 NVH 테스트 결과 볼팅 체결 방식에 비하여 소음이 커지는 문제가 발생하고 링기어의 HAZ부가 고경화 되는 문제가 발생하였다. 때문에 용입깊이를 초기 시제품인 5mm에서 4mm로 변경시켜 입열량 감소 및 용접변형을 줄여 소음 문제를 해결하고자 하였으며 링기어의 침탄층을 1mm 절삭하여 링기어 HAZ부의 고경화 문제를 해결하고자 하였다. 이러한 용접 구조 변경이 용접변형 및 강성과 피로에 미치는 영향력을 알아보고자 용접 및 열처리 상용 소프트웨어인 SYSWELD, 구조해석 상용소프트웨어인 NX_NASTRAN, 피로 해석 상용 소프트웨어인 FEMFAT을 이용하여 시뮬레이션 하였고 실제 구조 변경한 용접 시제품과 비교, 분석하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.8C
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• pp.721-730
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• 2012

In this paper the problem of a moving control of an automatic guided vehicle(AGV) which transports a dead body to a designated cinerator safely in a crematorium, an special indoor environment, will be discussed. Since a method of burying guided lines in the floor is not proper to such an environment, a method of moving control of an AGV based on infrared ray sensors is now proposed. With this approach, the AGV emits infrared ray to the landmarks adheres to the ceiling to find a moving direction and then moves that direction by recognizing them. One of the typical problems for this method is that dead zone and/or overlapping zone may exist when the landmarks are deployed. To resolve this problem, an algorithm of recognizing double landmarks at each time is applied to minimize occurrences of sensing error. In addition, at the turning area to entering the designated cinerator, to fit an AGV with the entrance of the designated cinerator, an algorithm of controlling the velocity of both the inner and outer wheel of it. The functional correctness of our proposed algorithm has been verified by using a prototype vehicle. Our real AGV system has been applied to a crematorium and it moves automatically within an allowable range of location error.

• Journal of KIISE
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• v.42 no.6
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• pp.748-754
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• 2015

This paper proposes a sequential state estimation model consisting of continuous and discrete variables, as a way of generalizing all discrete-state factorial HMM, and gives a design of gait motion model based on the idea. The discrete state variable implements a Markov chain that models the gait dynamics, and for each state of the Markov chain, we created a Gaussian process over the space of the continuous variable. The Markov chain controls the switching among Gaussian processes, each of which models the rotation or various views of a gait state. Then a particle filter-based algorithm is presented to give an approximate filtering solution. Given an input vector sequence presented over time, this finds a trajectory that follows a Gaussian process and occasionally switches to another dynamically. Experimental results show that the proposed model can provide a very intuitive interpretation of video-based gait into a sequence of poses and a sequence of posture states.