• 한국항행학회논문지
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• 제20권3호
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• pp.196-202
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• 2016

본 논문은 초음파 거리계를 이용하는 쿼드로터 무인항공기의 고도 제어 성능 향상을 위한 정상 웨이블릿 변환 기법을 제시하였다. 쿼드로터의 수직 이착륙 시 많이 사용되는 초음파 거리계를 이용하여 지상시험을 수행하였다. 초음파 거리계는 정반사율(specular reflectance)과 음향 잡음 (acoustic noise)으로 인한 신호의 스파이크가 생긴다. 짧은 시간 간격으로 발생하는 스파이크는 시간과 주파수 영역에서의 동시 분석을 필요로 한다. 정상 웨이블릿 변환은 DWT (discrete wavelet transform)에서 다운샘플링에 의해 발생하는 문제점을 해결하기 위한 변환방법으로써 잡음제거에 DWT보다 효과적이라고 알려져 있다. 이에 초음파 거리계의 스파이크를 정상 웨이블릿 변환 기법을 이용하여 분석하였고, 실험결과 초음파 거리계의 스파이크를 효과적으로 제거할 수 있음을 확인하였다.

• Geomechanics and Engineering
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• 제34권4호
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• pp.397-408
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• 2023

Pipe pile walls are commonly used as retaining structures for excavation projects, particularly in densely populated coastal cities such as Hong Kong. Pipe pile walls are preferred in reclaimed land due to their cost-effectiveness and convenience for installation. However, the pre-bored piling techniques used to install pipe piles can cause significant ground disturbance, posing risks to nearby sensitive structures. This study reports a well-documented case history in a reclamation site, and it was found that pipe piling could induce ground settlement of up to 100 mm. Statutory design submissions in Hong Kong typically specify a ground settlement alarm level of 10 mm, which is significantly lower than the actual settlement observed in this study. In addition, lateral soil movement of approximately 70 mm was detected in the marine deposit. The lateral soil displacement in the marine deposit was found to be up to 3.4 and 3.1 times that of sand fill and CDG, respectively, mainly due to the relatively low stiffness of the marine deposit. Based on the monitoring data and site-investigation data, a 3D numerical analysis was established to back-analyze soil movements due to the installation of the pipe pile wall. The comparison between measured and computed results indicates that the equivalent ground loss ratio is 20%, 40%, and 20% for the fill, marine deposit and CDG, respectively. The maximum ground settlement increases with an increase in the ground loss ratio of the marine deposit, whereas the associated influence radius remains stationary at 1.2 times the pipe pile wall depth (H). The maximum ground settlement increases rapidly when the thickness of marine deposit is less than 0.32H, particularly for the ground loss ratio of larger than 40%. This study provides new insights into the pipe piling construction in reclamation sites.

• Structural Engineering and Mechanics
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• 제37권6호
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• pp.575-592
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• 2011

For seismic resistant design of critical structures, a dynamic analysis, either response spectrum or time history is frequently required. Owing to the lack of recorded data and the randomness of earthquake ground motion that may be experienced by structure in the future, usually it is difficult to obtain recorded data which fit the requirements (site type, epicenteral distance, etc.) well. Therefore, the artificial seismic records are widely used in seismic designs, verification of seismic capacity and seismic assessment of structures. The purpose of this paper is to develop a numerical method using Artificial Neural Network (ANN) and wavelet packet transform in best basis method which is presented for the decomposition of artificial earthquake records consistent with any arbitrarily specified target response spectra requirements. The ground motion has been modeled as a non-stationary process using wavelet packet. This study shows that the procedure using ANN-based models and wavelet packets in best-basis method are applicable to generate artificial earthquakes compatible with any response spectra. Several numerical examples are given to verify the developed model.

• Journal of Biosystems Engineering
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• 제14권2호
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• pp.85-93
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• 1989

This study was intended to develop the system which controls header height of combine automatically by means of sensing the difference between the header and the ground surface. A micro-computer was used for the controller. The sensing unit designed for the study was composed of potentiometer, oscillating link, and gage wheel. An electric-hydraulic circuit was driven by microcomputer to control header height of combine. Performance of the control system was tested by computer simulation, stationary operation of header, and traveling on the simulated ground.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2006년도 전기학술대회논문집
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• pp.61-62
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• 2006

The suppression of fluid force acting on a square prism near plane wall was studied by attaching fences on the comers of the prism. The height of the fence was 10% of the square width and the range of Reynolds number considered was $Re=2.0{\times}10^4$. The experimental parameters were the attaching position and numbers of fences, the space ratios $G/B(G/B=0.1{\sim}1.2)$ between prism and plane wall. The average drag coefficients were increased and the average hit coefficients were decreased and increased with the space ratios foulard plane wall. The drag of the prism was reduced average 7.6% with the space ratios by attaching the normal fence at the rear and upper comer and the horizontal normal fence at the rear and lower corner on the prism.

• 제어로봇시스템학회논문지
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• 제8권6호
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• pp.477-483
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• 2002

This paper deals with a workspace analysis of multi-legged walking robots in velocity domain(velocity workspace analysis). Noting that when robots are holding the same object in multiple cooperating robotic arm system the kinematic structure of the system is basically the same with that of a multi-legged walking robot standing on the ground, we invented a way ot applying the technique for multiple arm system to multi-legged walking robot. An important definition of reaction velocity is made and the bounds of velocities achievable by the moving body with multi-legs is derived from the given bounds on the capabilities of actuators of each legs through Jacobian matrix for given robot configuration. After some assumption of hard-foot-condition is adopted as a contact model between feet of robot and the ground, visualization process for the velocity workspace is proposed. Also, a series of application examples will be presented including continuous walking gaits as well as several different stationary posture of legged walking robots, which validate the usefulness of the proposed technique.

• International Journal of Aeronautical and Space Sciences
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• 제6권1호
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• pp.8-16
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• 2005

This paper describes target detection performance of millimeter wave radar that exits on non-stationary target detection schemes in the ground clutter conditions. The comparison of various CFAR process schemes such as CA(Cell-Average)-CFAR, GO(Greatest Of)/SO(Smallest Of)-CFAR, and OS(Order Statistics)-CFAR performance are applied. Using matlab software, we show the performance and loss between target detection probability and signal to noise ratio. This paper concludes the OS-CFAR process performance is better than any others and satisfies the optimal detection probability without loss of detection in the homogeneous clutter, When range bins increase.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 하계학술대회 논문집 E
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• pp.1589-1591
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• 1998

This paper presents experimental results of transient impedance characteristics investigated on the site of a large-scale grounding system using impulse current. The ground potential rise was measured while injecting an impulse current and the transient impedance was determined. As a results, the transient impedance was significantly greater than the stationary grounding resistance due to high inductance of ground conductors and leads.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2001년도 ICCAS
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• pp.30.5-30
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• 2001

This paper describes a new design of blimp having wheeled vehicle part. This system can work both on the ground using wheeled vehicle and in the air using the floating capability of the blimp part. The passive wheeled mechanism in the vehicle part enables the stable taking off, landing on as well as it is greatly helpful to keep a stationary position on the floor. On the other hand, the floating capability enables the wheeled blimp to fly freely regardless of the ground condition or obstacles. The wheeled blimp can be used as an agent robot for the tole-presence application. Using multimedia devices such as camera, speaker, LCD and microphone mounted on the blimp surface, this system can get necessary information at the local site and communicate with person from a distance. As a typical tele-presence application, the wheeled blimp is currently being developed to a tole-guidance robot working in public indoor areas such 35 exhibition halls, departments, hospitals, etc ...

• Earthquakes and Structures
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• 제18권1호
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• pp.45-56
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• 2020

The application of critical excitation method with displacement-based objective function for multi degree of freedom (MDOF) systems is investigated. To this end, a new critical excitation method is developed to find the critical input motion of a MDOF system as a synthetic accelerogram. The upper bound of earthquake input energy per unit mass is considered as a new constraint for the problem, and its advantages are discussed. Considering this constraint, the critical excitation method is then used to generate synthetic accelerograms for MDOF models corresponding to three shear buildings of 10, 16, and 22 stories. In order to demonstrate the reliability of generated accelerograms to estimate dynamic response of the structures, three target ground motions with considerable level of energy contents are selected to represent "real critical excitation" of each model, and the method is used to re-generate these ground motions. Afterwards, linear dynamic analyses are conducted using these accelerograms along with the generated critical excitations, to investigate the key parameters of response including maximum displacement, maximum interstory drift, and maximum absolute acceleration of stories. The results show that the generated critical excitations can make an acceptable estimate of the structural behavior compared to the target ground motions. Therefore, the method can be reliably implemented to generate critical excitation of the structure when real one is not available.