• Ocean Systems Engineering
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• 제10권4호
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• pp.373-397
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• 2020

Heave compensation is a vital part of various marine and offshore operations. It is used in various applications, including the transfer of cargo between two vessels in the open ocean, installation of topsides of an offshore structure, offshore drilling and for surveillance, reconnaissance and monitoring. These applications typically involve a load suspended from a hydraulically powered winch that is connected to a vessel that is undergoing dynamic motion in the ocean environment. The goal in these applications is to design a winch controller to keep the load at a regulated height by rejecting the net heave motion of the winch arising from ship motions at sea. In this study, we analyze and compare the performance of various control algorithms in stabilizing a suspended load while the vessel is subjected to changing sea conditions. The KCS container ship is chosen as the vessel undergoing dynamic motion in the ocean. The negative of the net heave motion at the winch is provided as a reference signal to track. Various control strategies like Proportional-Derivative (PD) Control, Model Predictive Control (MPC), Linear Quadratic Integral Control (LQI), and Sliding Mode Control (SMC) are implemented and tuned for effective heave compensation. The performance of the controllers is compared with respect to heave compensation, disturbance rejection and noise attenuation.

• 한국인터넷방송통신학회논문지
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• 제11권3호
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• pp.175-179
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• 2011

본 논문에서는 모바일 환경에서의 음성인식 개선에 관한 내용으로 기존의 HMM에서 특징보상기법을을 적용한 방식으로 예측잡음이 아닌 실제 오염된 데이터를 적용하여 인식모델을 잡음상황에 맞도록 적응시키는 모델적응 HMM을 사용하였다. 음성인식 시 기존의 방법에서는 주변노이즈를 고려하지 않은 참조패턴을 사용하였으나 본 연구에서는 주변노이즈를 고려한 참조패턴을 생성하여 인식률을 향상 시키는 방법으로 모바일 환경에서의 음성 인식률을 향상 시켰다.

• 한국공작기계학회논문집
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• 제17권3호
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• pp.128-132
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• 2008

The noise levels and individual employee noise exposure levels within a factory will determine the need for hearing conservation program. The difficulty in not having an effective hearing conservation program is the risk of hearing loss that employees may sustain. In the last few years the claims for hearing loss compensation have grown due to class action litigation brought against the employer and companies that have equipment in the factory alleged to have caused hearing loss. The Blower in the factory generates the noise of 98.3dB(A) in the frequency range of 2,000Hz, which may cause occupational hearing loss. By designing close type enclosures which are made of absorption material, about 24.4dB(A) reduction has been in the factory. It is demonstrated that this kind of enclosures can be effectively used to reduce the noise in the factory.

• 한국군사과학기술학회지
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• 제6권2호
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• pp.55-64
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• 2003

Underwater acoustic noise measurement is an essential element for vulnerability assessment of modern naval platforms. But during the last few decades environmental conditions have drastically changed due to the gradually increasing sea ambient noise level and decreasing submarine radiated noise level. A real-time underwater acoustic measurement system with vertical line array is designed for the quiet submarine radiated noise assessment in challenging environment. This system has a constant directivity index in measurement frequency range and accurate tracking capability for the transmission loss compensation and navigation aids inside the submarine. This system has been validated at sea and used several times for the submarine noise measurement.

• 방송공학회논문지
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• 제21권4호
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• pp.472-483
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• 2016

본 논문에서는 MC-FRUC(Motion Compensated Frame Rate Up-Conversion) 에서 사용될 수 있는 주파수 영역에서의 블로킹 현상(blocking artifacts) 검출 알고리즘을 제안한다. MC-FRUC 알고리즘은 블록 단위로 움직임 벡터를 계산하여 움직임 보상을 수행함으로써 블록 경계선 주변에서 블로킹 현상이 발생할 수 있다. 본 논문에서는 효율적인 블로킹 현상 검출을 위해 보간된 영상(interpolated frame)의 주파수 성분을 분석하여 블록경계에서 블록킹 현상을 감소시킨다. 실험결과에서 제안된 알고리즘이 기존의 FRUC 방법보다 더 나은 주관적 화질을 보인다. 제안한 방법은 또한 기존의 BDMC(Bi-Directional Motion Compensation) 대비 평균 약 0.45 dB PSNR(Peak Signal to Noise Ratio)이 향상되었다.

• 한국음향학회지
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• 제23권6호
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• pp.473-480
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• 2004

본 논문에서는 잡음 환경에서 강인한 음성 인식을 위하여 음성 모델을 기반으로 하는 효과적인 특징 보상 기법을 제안한다. 제안하는 특징 보상 기법은 병렬 결합된 혼합 모델 (PCMM)을 기반으로 한다. 기존의 PCMM 기반의 기법은 시간에 따라 변하는 잡음 환경을 반영하기 위하여 매 음성 입력마다 복잡한 과정의 혼합 모델 결합이 필요하다. 제안하는 기법에서는 다중의 혼합 모델을 보간하는 방법을 채용함으로써 시간에 따라 변하는 배경 잡음에 대응할 수 있다. 보다 신뢰성 있는 혼합 모델 생성을 위하여 데이터 유도 기반의 방법을 도입하고, 실시간 처리를 위하여 프레임에 동기화된 환경 사후 확률 예측 과정을 제안한다. 다중 모델로 인한 연산량 증가를 막기 위하여 혼합 모델을 공유하는 기법을 제안한다. 가우시안 혼합 모델 사이에 통계학적으로 유사한 요소들을 선택하여 공유에 필요한 공통 모델을 생성한다. Aurora 2.0 데이터베이스와 실제 자동차 주행 환경에서 수집된 음성 데이터베이스에 대한 성능 평가를 실시한다. 실험 결과로부터 제안한 기법이 모의 환경과 실제 잡음 환경에서 강인한 음성 인식 성능을 가져오고 연산량 감소에 효과적임을 확인한다.

• Investigative Magnetic Resonance Imaging
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• 제23권2호
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• pp.114-124
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• 2019

Purpose: We investigate biases in the assessments of left ventricular function (LVF), by compressed sensing (CS)-cine magnetic resonance imaging (MRI). Materials and Methods: Cardiovascular cine images with short axis view, were obtained for 8 volunteers without CS. LVFs were assessed with subsampled data, with compression factors (CF) of 2, 3, 4, and 8. A semi-automatic segmentation program was used, for the assessment. The assessments by 3 CS methods (ITSC, FOCUSS, and view sharing (VS)), were compared to those without CS. Bland-Altman analysis and paired t-test were used, for comparison. In addition, real-time CS-cine imaging was also performed, with CF of 2, 3, 4, and 8 for the same volunteers. Assessments of LVF were similarly made, for CS data. A fixed compensation technique is suggested, to reduce the bias. Results: The assessment of LVF by CS-cine, includes bias and random noise. Bias appeared much larger than random noise. Median of end-diastolic volume (EDV) with CS-cine (ITSC or FOCUSS) appeared -1.4% to -7.1% smaller, compared to that of standard cine, depending on CF from (2 to 8). End-systolic volume (ESV) appeared +1.6% to +14.3% larger, stroke volume (SV), -2.4% to -16.4% smaller, and ejection fraction (EF), -1.1% to -9.2% smaller, with P < 0.05. Bias was reduced from -5.6% to -1.8% for EF, by compensation applied to real-time CS-cine (CF = 8). Conclusion: Loss of temporal resolution by adopting missing data from nearby cardiac frames, causes an underestimation for EDV, and an overestimation for ESV, resulting in underestimations for SV and EF. The bias is not random. Thus it should be removed or reduced for better diagnosis. A fixed compensation is suggested, to reduce bias in the assessment of LVF.

• Smart Structures and Systems
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• 제25권5호
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• pp.569-580
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• 2020

The identification of delays and delay compensation are critical problems in real-time hybrid simulations (RTHS). Conventional delay compensation methods are mostly based on the assumption of a constant delay. However, the system delay may vary during tests owing to the nonlinearity of the loading system and/or the behavioral variations of the specimen. To address this issue, this study presents an adaptive delay compensation method based on a discrete model of the loading system. In particular, the parameters of this discrete model are identified and updated online with the least-squares method to represent a servo hydraulic loading system. Furthermore, based on this model, the system delays are compensated for by generating system commands using the desired displacements, achieved displacements, and previous displacement commands. This method is more general than the existing compensation methods because it can predict commands based on multiple displacement categories. Moreover, this method is straightforward and suitable for implementation on digital signal processing boards because it relies solely on the displacements rather than on velocity and/or acceleration data. The virtual and real RTHS results show that the studied method exhibits satisfactory estimation smoothness and compensation accuracy. Furthermore, considering the measurement noise, the low-order parameter models of this method are more favorable than that the high-order parameter models.

• Investigative Magnetic Resonance Imaging
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• 제22권4호
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• pp.209-217
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• 2018

Purpose: The objective of this study was to obtain improved susceptibility weighted images (SWI) of the cervical spinal cord using respiratory-induced artifact compensation. Materials and Methods: The artifact from $B_0$ fluctuations by respiration could be compensated using a double navigator echo approach. The two navigators were inserted in an SWI sequence before and after the image readouts. The $B_0$ fluctuation was measured by each navigator echoes, and the inverse of the fluctuation was applied to eliminate the artifact from fluctuation. The degree of compensation was quantified using a quality index (QI) term for compensated imaging using each navigator. Also, the effect of compensation was analyzed according to the position of the spinal cord using QI values. Results: Compensation using navigator echo gave the improved visualization of SWI in cervical spinal cord compared to non-compensated images. Before compensation, images were influenced by artificial noise from motion in both the superior (QI = 0.031) and inferior (QI = 0.043) regions. In most parts of the superior regions, the second navigator resulted in better quality (QI = 0.024, P < 0.01) compared to the first navigator, but in the inferior regions the first navigator showed better quality (QI = 0.033, P < 0.01) after correction. Conclusion: Motion compensation using a double navigator method can increase the improvement of the SWI in the cervical spinal cord. The proposed method makes SWI a useful tool for the diagnosis of spinal cord injury by reducing respiratory-induced artifact.

• Smart Structures and Systems
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• 제14권3호
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• pp.327-345
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• 2014

This paper presents a composite control strategy for the active suppression of vibration due to the unknown disturbances, such as external excitation, harmonic effects and control spillover, as well as high-frequency accelerometer measurement noise in the all-clamped stiffened plate. The proposed composite control action based on the modal approach, consists of two contributions including feedback part and feedforward part. The feedback part is the well-known PID controller, which is widely used to increase the structure damping and improve its dynamic performance close to the resonance frequencies. In order to get better performance for vibration suppression, the weight matrixes is optimized by chaos sequence. Then an improved disturbance observer (IDOB) as the feedforward compensation part is developed to enhance the vibration suppression performance of PID under various disturbances and uncertainties. The proposed IDOB can simultaneously estimate the various disturbances dynamically as well as measurement noise acting on the system and suppress them by feedforward compensation design. A rigorous analysis is also given to show why the IDOB can effectively suppress the unknown disturbances and measurement noise. In order to verify the proposed composite control algorithm (IDOB-PID), the dSPACE real-time simulation platform is used and an experimental platform for the all-clamped stiffened plate active vibration control system is set up. The experimental results demonstrate the effectiveness, practicality and strong anti-disturbances ability of the proposed control strategy.