• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 추계학술대회논문집
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• pp.471-477
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• 2003

The floating ring seal is often used in the turbopump (TP) unit of liquid rocket engine (LRE) owing to its inherent ability of minimizing the leakage flow and superior dynamic characteristics as well. This paper describes the test results concerned with the lock-up and dynamic characteristics of the floating ring seals in the turbopump. The characteristics of the floating ring seals were extracted from the frequency response function (FRF) by instrumental variable method. The experiment was tested at 7.0MPa and 0-24,800 rpm. And the test results were introduced about the dynamic characteristics of floating ring seal related with the eccentricity and attitude angle.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 추계학술대회 논문집 학회본부 B
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• pp.697-699
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• 1999

2기가비트급 이상의 Serial-Link Chip에 적용되는 PLL의 특성은 lock-in-time이 빨라야하며 low VDD 동작을 확보해야 한다. 본 논문은 2.8기가비트급의 인터페이스 전송칩에 사용되는 PLL에 내부 전원 공급기를 설계하여 외부전원 3.3V시에 2.5V를 제공하며 이를 PFD/CP/VCO에 개별적 적용하는 제어방법 및 회로를 제안하며 이에 따르는 IPLL의 Lock-In-Time을 1mS 이내로 설계하였으며 외부동작 주파수는 100MHz이상이며 인터페이스 전송량은 2.8기가비트에 이른다. 저전압 설계를 통한 동작전류를 내부 전원 제어를 통해 순차적(Sequential Method)동작을 시킴으로 IPLL 동작시의 전류소모을 2mA이하로 제한하였다. 본 논문에서는 2.8기가비트급 인터페이스 전송칩에 적용한 IPLL의 회로 및 내부전원 공급기의 제어 방법 및 설계결과를 제안하며 이에 따르는 전송칩의 동작방법을 제안한다.

• 한국유체기계학회 논문집
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• 제4권3호
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• pp.29-38
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• 2001

The floating ring seal has the ability of minimizing clearance without the rubbing phenomenon. It is often used in the turbo pump units of liquid rocket engines due to its superior leakage performance. The exact prediction of the lock-up position of the floating ring, the leakage performance, and the rotordynamic coefficients of the seal is necessary to evaluate the rotordynamic performance of the turbo pump unit. The governing equations(which are based on the Bulk-flow Model) we solved by the Fast Fourier Transform method. The lock-up position, leakage flow rate, and rotordynamic coefficients are evaluated according to the geometric parameters of the floating ring seal.

• Journal of Mechanical Science and Technology
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• 제16권4호
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• pp.485-491
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• 2002

The gyroscopes have been used as a suitable inertial instrument for the navigation guidance and attitude controls. The accuracy as very sensitive sensor is limited by the lock-in region (dead band) by the frequency coupling between two counter-propagating waves at low rotation rates. This frequency coupling gives no phase difference and an angular increment is not detected. This problem can be overcome by the mechanical dithering. The purpose of the mechanical dithering is to suppress the dead band, oscillate the monoblock about the rotation axis and add an external rotation rate. This paper presents the theoretical considerations of the mechanical performances of dither on the basis of the loading condition and angular characteristics due to the piezoelement deformation and the validity of theoretical equations are compared through FEM (Finite Element Method) simulations.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2000년도 제15차 학술회의논문집
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• pp.125-125
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• 2000

An Empirical approach to determine a road-surface condition is presented The road-surface condition thus provided includes the detection of not only friction coefficient, but also abrupt surface-profile changes such as pitfalls and bumpers The former plays a key role in establishing the appropriate control strategy, while the latter allows to minimize unnecessary brake intervention induced by the aforementioned jut. In this paper, we use an empirically chosen variable, namely. the time-rate of change of vehicle speed estimated from the point where ABS engaged to the point where measurement taken Experimental results shoe that the proposed method is effective to infer various control variables critical for the control of ABS.

• 한국자동차공학회논문집
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• 제21권1호
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• pp.78-85
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• 2013

This paper presents the sliding mode control methods for anti-lock brake system (ABS) with the friction force observer. Using a simplified quarter car model, the sliding mode controller for ABS is designed to track the desired wheel slip ratio. Here, new method to find the desired wheel slip ratio which produces the maximum friction force between road and tire is suggested. The desired wheel slip ratio is varying according road and tire conditions to produce maximum friction force. In order to find optimum desired wheel slip ratio, the sliding mode observer for friction force is used. The proposed sliding mode controller with observer is evaluated in simulation, and the control design is shown to have high performance on roads with constant and varying adhesion coefficients.

• 한국광학회지
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• 제14권2호
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• pp.161-165
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• 2003

Master laser(ML)의 직접 변조로 생성된 여러 개의 side-bands 중 두 개의 target band게 두 개의 Slave laser(SL)가 각각 lock이 되도록 하는 side-band injection-locking 방법을 이용하여 광학적 60㎓의 밀리미터파 신호를 구현하였다 ML에 lock이 된 두 SL의 output들은 photo detection시 서로 beating하여 안정적이고 매우 깨끗한 60㎓ 신호를 생성하였다.

• Tribology and Lubricants
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• 제19권6호
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• pp.349-356
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• 2003

A damper floating ring seal with round hole pattern surfaces is suggested for better leakage control. The flat plate test of the round hole pattern surfaces has been performed to yield an empirical friction factor model. The exact predictions of the lock­up position of the damper floating ring, the leakage performance, and the rotordynamic coefficients of the seal are necessary to evaluate the rotordynamic performance of the turbo pump unit. The governing equations including the empirical friction factor model for round hole pattern surfaces are solved by the Fast Fourier Transform method. The lock­up position, leakage flow rate, and rotordynamic coefficients are evaluated according to the geometric parameters of the damper floating ring seal. Theoretical results show that the damper floating ring seals yield less leakage and better rotordynamic stability than the floating ring seal with a smooth surface.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2001년도 ICCAS
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• pp.112-112
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• 2001

An Anti-lock Brake System ABS is developed to increase the stability of vehicle and to reduce the stopping distance when braking manoeuvres by measuring the wheel and vehicle speed. An ABS mathematical model which describes the dynamics of vehicle and calculate the stopping distance, is explained in this paper. To proceed this study, a mathematical model is produced with simulink software package. Although the model considered here is relatively simple, it retains the essential dynamics of the system. The results are evaluated at the various driving or road conditions. The results from mathematical model show that ABS reduces the stopping distance at the various road conditions. This mathematical model could be ...

• 한국군사과학기술학회지
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• 제20권5호
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• pp.597-607
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• 2017

The general control method for Anti-lock Brake System(ABS) is that the wheel slip ratio is observed and the braking force is controlled in real time in order to keep the wheel slip ratio under the value of the best slip ratio. When a wheel runs on the state of the best slip ratio, the ground friction of the wheel approaches the highest value. The value of best slip ratio, theoretically, is known as the value between 10 and 20 % and it is dependant on the ground condition such as dry, wet and ice. It is an important parameter for the braking performance and affects the braking stability and efficiency. In this thesis, an experimental method is suggested, which is a reliable way to decide the best slip ratio through dynamo tests simulating aircraft taxiing conditions. The obtained best slip ratio is proved its validity by results of aircraft taxiing tests.