• 대한조선학회논문집
• /
• 제52권6호
• /
• pp.460-470
• /
• 2015

In general ships and FPSOs, roll damping is very small and consequently roll motion is very large at the roll resonance frequency. Proper evaluation of the roll damping coefficient at the resonance frequency is an important task in the study of roll motion and usually it is done by the analysis of free roll decay tests. The relative decrement method based on energy relation has been used mainly for the evaluation of roll damping coefficient from the roll decay test so far. As another method, the logarithmic decrement method based on equivalent linear decay assumption can be used for the same purpose and it is relatively simple. In this paper, both of the relative decrement method and the logarithmic decrement method are used for the evaluation of roll damping coefficient including quadratic damping from the free roll decay tests, and their results are cross-checked for verifying the obtained damping coefficients. Through applications to a box-type floating body equiped with bilge keels, it is shown that the two methods give almost the same damping coefficients in a practical view point and the cross-check of their results is to be a good tool to prevent a possible error. And also the quantitative effects of the bilge keels on the roll damping of box-type floating body are shown and discussed.

• 한국정밀공학회지
• /
• 제30권10호
• /
• pp.1087-1093
• /
• 2013

In this study, a measurement method of double ball-bar is proposed to measure the geometric errors of an ultra-precision roll mold machine tool. A volumetric error model of the machine tool is established to investigate the effects of the geometric errors to a radius error and a cylindricity of the roll mold. A measurement path is suggested for the geometric errors, and a ball-bar equation is derived to represent the relation between the geometric errors and a measured data of the double ball-bar. Set-up errors, which are inevitable at the double ball-bar installation, also are analyzed and are removed mathematically for the measurement accuracy. In addition, standard uncertainty of the measured geometric errors is analyzed to determine the experimental condition. Finally, the proposed method is tested and verified through simulation.

• 대한기계학회논문집A
• /
• 제40권12호
• /
• pp.1005-1011
• /
• 2016

기어소음의 근본적인 원인은 전달오차로 인해 발생하게 된다. 전달오차는 기어가 맞물릴 때 발생하는데 크게 정적전달오차와 동적전달오차가 있다. 이러한 오차들은 기어 이빨의 처짐 또는 치면 마찰에 의해 발생하고 이 요인들이 원인이 되어 기어 시스템에 진동이 발생하게 된다. 그리고 이 진동이 기어의 축으로 이동하게 되어 축을 떠받치고 있는 베어링에 전달되고 베어링에 전달된 가진은 최종적으로 기어의 케이싱으로 이동하게 되어 소음을 방출하게 된다. 본 논문에서는 이러한 전달오차에 의해 발생하는 최대 굽힘응력을 가지는 롤각을 찾기 위한 응력해석을 수행되었다. 본 논문에서는 이론적 바탕으로 설계되어 인볼류트 곡선을 가진 기어와 수정된 치형을 가진 기어의 전달오차에 대한 해석을 진행하였다. 또한, 급작스러운 작동이나 큰 백래쉬로 인해 발생하는 충격강도에 대한 영향을 알아보기 위해 유한요소해석을 통해 각각 정적 최대굽힘응력과 동적 최대굽힘응력의 결과를 이용하여 충격인자 값을 예측해 보았다.

• 한국정밀공학회지
• /
• 제15권8호
• /
• pp.145-155
• /
• 1998

An $H{\infty}$ controller with a roll eccentricity filter is proposed to alleviate the effect of entry thickness variation and roll eccentricity occured in rolling stands themselves of tandem cold mills. A robust controller to the disturbances is designed by H$_{\infty}$ control techniques, which can reflect the input direction of disturbances and the knowledge of disturbance spectrum in the frequency domain. First, fundamental problems in tandem cold mills such as process transport delay inherent in the exit thickness measurement and the feedforward loading of roll eccentricity signals on the exit thickness be overcome by the roll eccentricity filtering and the compensation for the error of gaugemeter thickness estimator. And non-satndard $H{\infty}$ control problem caused by the selection of weighting function having poles on the $J{\omega}$-axis is discussed. The resultant controller composed by an $H{\infty}$ controller and an estimator for the roll eccentricity is evaluated through computer simulations. The effectiveness of the proposed control method is compared to that of the conventional LQ controller method and a feedforward controller for the roll eccentricity, which has been already studied.

• 조명전기설비학회논문지
• /
• 제24권9호
• /
• pp.56-61
• /
• 2010

Scanning head has used to detect the error signal in register controller. However the resolution of the system is not enough for E-printing(Electronic-paper printing). In this paper, the register mark shapes and process techniques are studied using a smart camera which can detect the register mark and calculate the printing error. With these, a register controller within 10[um] of error range is developed for e-printing system and confirmed with experiments.

• The Journal of the Acoustical Society of Korea
• /
• 제16권2E호
• /
• pp.47-54
• /
• 1997

This paper presents two results on intersymbol interferences in baseband digital communication over an additive white Gaussian noise channel-the interferences due to mismatched square-root raised-cosine filters, in which the filters have different roll-off factors, and / or due to sampling-time jitter. The result for the mismatched filters is that even the jitter-free sampling causes intersymbol interference and it is negligibly small for a wide range of signal-to-noise ratio up to 10dB, for the roll-off factor ranging from 0.2 to 0.5, the mismatch loss being within 0.1dB from the optimum at around 10-6 .For jitter interference an approximation formula for the bit error probability is derived in case of the matched filters, which shows how the roll-off factors and the amount of jitter affect the system performance. The formula is reasonably accurate.

• 제어로봇시스템학회:학술대회논문집
• /
• 제어로봇시스템학회 1996년도 한국자동제어학술회의논문집(국내학술편); 포항공과대학교, 포항; 24-26 Oct. 1996
• /
• pp.1083-1086
• /
• 1996

Cold rolling mill process in steel works uses stands of rolls to flatten a strip to a desired thickness. At cold rolling mill process, precalculation determines the mill settings before a strip actually enters the mill and is done by an outdated mathematical model. A corrective neural network model is proposed to improve the accuracy of the roll force prediction. Additional variables to be fed to the network include the chemical composition of the coil, its coiling temperature and the aggregated amount of processed strips of each roll. The network was trained using a standard backpropagation with 4,944 process data collected from no.1 cold rolling mill process from March 1995 through December 1995, then was tested on the unseen 1,586 data from Jan 1996 through April 1996. The combined model reduced the prediction error by 32.8% on average.

• 소성∙가공
• /
• 제8권6호
• /
• pp.583-590
• /
• 1999

New forward slip model has been developed for the precise prediction of rolling speed in the hot strip finishing mill. Besides those influential factors such as neutral point, work roll diameter, friction coefficient, bite angle and the thickness at each side of entry and delivery of the rolls, roll torque was specifically taken into account in this study. To consider the effect of width change on forward slip, calibration factors obtained from rolling torque has been added to new prediction model and refining method has also been developed to reduce the speed unbalance between adjacent stands. The application of the new model showed a good agreement in rolling speeds between the predictions and the actual measurements, and the standard deviation of prediction error has also been significantly reduced.

• 한국시뮬레이션학회논문지
• /
• 제28권2호
• /
• pp.131-137
• /
• 2019

현대전이 내전과 대테러전과 같은 국지전 양상으로 변화하면서, 탐색기를 포함한 정밀 유도무기의 운용 비중이 점점 증가하고 있다. 영상탐색기는 상대적으로 저가이며, 다양한 운용환경에 적용이 가능하다. 다만 유도무기에 적용되는 영상추적기술은 유도탄의 비행 환경 하에서 표적 추적을 수행해야하므로 상당히 고난이도의 기술이 요구된다. 그 중 유도탄의 롤은 다른 거동에 비해 탐색기 영상에 큰 변화를 주게 되어 영상 추적 성능을 크게 저하시킬 수 있다. 롤은 외란 및 비행 제어 오차로 항상 발생할 수밖에 없으나, 영상 추적 및 체계 성능에 영향을 주지 않는 수준을 판단하여 구성품의 오차 관리를 해야 한다. 하지만 표적의 영상 특성 및 영상 추적기의 높은 비선형성으로 단순한 기준으로 성능 예측을 한다는 것은 매우 어려운 일이다. 본 연구에서는 영상탐색기가 적용된 정밀유도무기의 M&S 환경을 구축하고, 유도탄의 롤 거동이 영상 추적 및 체계 성능에 미치는 영향을 분석하였다. 또한 오차 분석을 통해 유도무기 성능보장을 위해 요구되는 구성품의 규격을 도출하였다.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2008년도 춘계학술대회 논문집
• /
• pp.117-118
• /
• 2008