• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.39 no.7
• /
• pp.605-611
• /
• 2011

Shimmy is a self-excited vibration in lateral and torsional directions of a landing gear during either the take-off or landing. It is caused by a couple of conditions such as a low torsional stiffness of the strut, a free-play in the landing gear, a wheel imbalance, or worn parts, and it may make the aircraft unstable. This study was performed for an analysis of the shimmy stability on a small aircraft. A nose landing gear was modeled as a linear system and characterized by state-equations which were used to analyze the stability both in the frequency and time-domain for predicting whether the shimmy occurs and investigating a good design range of the important parameters. The root-locus method and the 4th Runge-Kutta method were used for each analysis. Because the present system has a simple mechanism using a friction to reinforce the stability, the friction, a non-linear factor, was linearized by a describing function and considered in the analysis and observed the result of the instability reduction.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.19 no.3
• /
• pp.207-216
• /
• 1999

A phased array is a multi-element piezoelectric device whose elements are individually excited by electric pulses at programmed delay time. One of the advantages of using phased array in nondestructive evaluation (NDE) application over conventional ultrasonic transducers is their great maneuverability of ultrasonic beam. There are some parameters such as the number and the size of the piezoelectric elements and the inter-element spacing of the elements to design phased array transducer. In this study, the characteristic of ultrasonic beam for phased array transducer due to the variation of the number of elements has been simulated for ultrasonic SH-wave on the basis of Huygen's principle. Ultrasonic beam directivity and focusing due to the change of time delay of each element were discussed due to the change of the number of piezoelectric elements. It was found that ultrasonic beam was much more spreaded and hence its sound pressure was decreased as steering angle of ultrasonic beam was increased. In addition, the ability of ultrasonic bean focusing decreased gradually with the increase of focal length at the same piezoelectric elements. However, the ability of beam focusing was improved as the number of consisting elements was increased.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.23 no.8
• /
• pp.936-942
• /
• 2019

Autonomous driving of drone indoor must move along a narrow path and overcome other factors such as lighting, topographic characteristics, obstacles. In addition, it is difficult to operate the drone in the hallway because of insufficient texture and the lack of its diversity comparing with the complicated environment. In this paper, we study an autonomous drone navigation using Convolution Neural Network(CNN) in indoor environment. The proposed method receives an image from the front camera of the drone and then steers the drone by predicting the next path based on the image. As a result of a total of 38 autonomous drone navigation tests, it was confirmed that a drone was successfully navigating in the indoor environment by the proposed method without hitting the walls or doors in the hallway.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.5 no.3
• /
• pp.76-85
• /
• 1997

The understeer characteristics of four wheel steering system(4WS system) in a high speed region have a negative effect upon the yaw velocity, leading to a decrease in the handling ability of vehicle. As a result, even if the side slip angle of vehicle can be kept up a minimum, a driver must compensate a decrease in yaw velocity by increasing the steering wheel angle in order to track the desired vehicle path. In this study, to keep the side slip angle of vehicle at zero and achieve a suitable yaw velocity in vehicle motion, a full active 4WS system(FA 4WS system) with actively steerable front and rear wheels is presented based on a nonlinear vehicle model and a model following control of yaw velocity. And the analysis results show the fat that, besides the excellent stability of vehicle, the FA 4WS system is able to realize better handling performance of vehicle than the previous 4WS systems in the high speed region.

• The Journal of the Acoustical Society of Korea
• /
• v.21 no.5
• /
• pp.478-484
• /
• 2002

Linear towed arrays (LTA) have a nonlinear shape due to tow vessel motion, ocean swells and currents. By reasons of nominally linear shape, various towed array shape estimation techniques have been developed since the perturbed shape cause the error in target detection. In this paper,, we propose the beamforming method for the perturbed LTA with simple structure. The proposed method linearizes a nonlinear phase of steering vector with position information measured by two reference sensors. It can be proved using some properties of Markov transition matrix, and iteration number of linearization process is decided by variance of cross phase difference. As a result of computer simulation in the ocean environment, beampattern of the proposed method is almost same with the ideal case in my type of array shape. In the signal-to-noise ratio (SNR) performance simlation, the DOA estimation performance of the proposed beamforming method is evaluated, and the comparison with Bartlett beamformer of the LTA shows that the proposed method can estimate. the spatial characteristic of sources more accuracy.

• Journal of Energy Engineering
• /
• v.8 no.1
• /
• pp.95-100
• /
• 1999

대우자동차는 1992년 이래로 전기자동차 개발사업을 추진하고 있으며 1996년에는 전기자동차의 Fleet 운영시험을 위해 10대의 씨에로 개조형 전기자동차를 제작하였다. 이 씨에로 전기자동차에는 고성능 연축전지, 교류유도전동기, 탑재형 충전기 및 전동조향배력장치 등이 장착되어 있으며 고등기술연구원에서는 전기자동차의 Fleet 운영시험의 일환으로 시외 일반도로 운행조건에서 전기자동차의 에너지비용을 조사하기 위한 연구를 수행하였다. 두 대의 씨에로 전기자동차를 용인시와 안성군 지역의 일반도로에서 1998년 4월부터 운행하였으며 이 운행시험 결과를 바탕으로 일반도로 주행조건에서 씨에로 전기자동차의 에너지비용과 동급의 가솔린자동차인 씨에로 1.5DOHC A/T 차량의 에너지비용을 계산하였다. 두 대의 전기자동차중 한 대의 연비는 5.7 km/kWh이었으며, 다른 한 대의 연비는 5.8 km/kWh이었다. 이에 비해 가솔린자동차의 연비는 13.7 km/l로 년간 20,000 km를 주행한다고 가정할 때 가솔린자동차의 년간 주행비용은 전기자동차의 3.4∼18.0배가 되는 것으로 나타났다. 이 시험을 통해 향후 전기자동차의 개발을 위해 유용하고 가치있는 많은 데이터를 얻었다.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
• /
• 2007.12a
• /
• pp.138-140
• /
• 2007

폰툰형 레저보트는 쌍동식 또는 삼동선식의 안전성이 확보된 선체와, 다양한 기능을 만족할 수 있는 상부구조로 구성, 건조비 뿐만 아니라 레저 접근성이 용이한 보트로서, 해양레저 선진국에서는 내수면뿐만 아니라 해수면에서도 함께 즐길 수 있는 가족형 레저보트로 인식되어 최근 보급이 확대되고 있는 추세이다. 그러나 폰툰형 레저보트는 최적의 공간활용을 위해 사각모양의 갑판형태로 인해 유체의 저항에 취약한 단점이 있다. 이로 인해 선저형상, 추진시스템 및 조향운전장치 뿐만아니라 선수선저부의 슬래밍 충격에 대비한 구조강도 등 체계적인 연구를 통한 개발이 필요하다. 이에 본 연구에서는 2가구 4인 가족단위로 함께 즐길 수 있는 안전성이 높고, 낚시, 스쿠버 둥을 위한 편의시설이 확보한 선형 최적형상 연구 및 구조강조 해석을 통한 9인승 규모의 폰툰형 레저보트를 개발하고자 한다.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.4 no.2
• /
• pp.209-220
• /
• 1996

In this paper, dynamic performance of 4WD/4WS Electric-driven vehicles is investigated. A coupled dynamic model is introduced for longitudinal, lateral and yawing motion of 4WD/4WS vehicles. Based on the coupled model, dynamic performance is analyzed for steady-state steering, acceleration steering and brake steering, respectively. These non steady-state cornering analysis is important for non-paved road maneuvering, trajectory projection for armored vehicle and future AVCS(Advanced Vehicle Control System) technology. Simulation results are obtained based on a simulink module for the introduced model.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.25 no.7
• /
• pp.1039-1046
• /
• 2001

Among the automotive steering systems, an Electric Power Assisted steering (EPAS) system utilizes an electronically controlled electric motor to provide steering assistance to the driver. The key components of the EPAS system are torque sensor, ECU (Electronic Control Unit), and DC Motor. The most important component of the EPAS is the torque sensor. The conventional torque sensor has complicated mechanical mechanism of torque detection. However, we suggest a non-contact torque sensor for EPAS using Maluss polarization law. It was found that the sensor exhibited not only excellent linearity but also superior characteristics of hysteresis, temperature and vibration.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.5 no.1
• /
• pp.195-206
• /
• 1997

In this study, a simulation tool is developed in order to investigate non steadystate cornering performance of 4WD/4WS vehicles. The 4WD/4WS vehicles are modeled as a 8-th order dynamic system which includes complex non-linear vehicle dynamics and tire models. The vehicle models are constructed into a modulated simulation tool and are utilized for analyzing cornering performance such as combined braking and steering, cornering on the icy read and $\mu$-split braking, The whole analysis is done with the simulation tool which consists of a number of subsystems and offers graphic environment. Simulation results show that this tool is useful and cost-effective in the dynamic analysis of the combustion-engine vehicles as well as electrically driven vehicles.