• Corrosion Science and Technology
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• 제19권1호
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• pp.37-42
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• 2020

Even though 304 low-carbon (304L) stainless steel was developed to enhance the resistance to intergranular corrosion and stress corrosion cracking, it is occasionally subject to degradation in harsh environments. The degree of sensitization (DOS) of 304L stainless steel was studied as a function of sensitization using a double-loop electrochemical potentiokinetic reactivation (DL-EPR) method. Sensitizing heat treatment was performed in an Ar atmosphere at 500℃, 600℃, and 700℃, with heat treatment times varying from 0 to 96 h. DOS was measured by the ratio of the peak current density value of the forward scan to that of the reverse scan. After the EPR experiment, the specimen surface was observed by scanning electron microscopy and energy dispersive spectroscopy. The DOS of the specimens heat-treated at 600℃ increased with heat treatment times up to 48 h and then decreased due to a self healing effect. The DOS was higher in specimens heat-treated at 600℃ than those at 500℃ or 700℃. Corrosion of the sensitized specimens occurred mainly at the δ-γ phase boundary. The corrosion morphology at the δ-γ phase boundary changed with sensitizing heat-treatment conditions due to differences in chromium activity in γ austenite and δ ferrite.

• Journal of Power Electronics
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• 제16권4호
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• pp.1513-1525
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• 2016

Rapid and accurate phase synchronization is critical for the reliable control of grid-tied inverters. However, the commonly used software phase-locked loop methods do not always satisfy the need for high-speed and accurate phase synchronization under severe grid imbalance conditions. To address this problem, this study develops a novel open-loop phase locking scheme based on a synchronous reference frame. The proposed scheme is characterized by remarkable response speed, high accuracy, and easy implementation. It comprises three functional cascaded blocks: fast orthogonal signal generation block, fast fundamental-frequency positive sequence component construction block, and fast phase calculation block. The developed virtual orthogonal signal generation method in the first block, which is characterized by noise immunity and high accuracy, can effectively avoid approximation errors and noise amplification in a wide range of sampling frequencies. In the second block, which is the foundation for achieving fast phase synchronization within 3 ms, the fundamental-frequency positive sequence components of unsymmetrical grid voltages can be achieved with the developed orthogonal signal construction strategy and the symmetrical component method. The real-time grid phase can be consequently obtained in the third block, which is free from self-tuning closed-loop control and thus improves the dynamic performance of the proposed scheme. The proposed scheme is adaptive to severe unsymmetrical grid voltages with sudden changes in magnitude, phase, and/or frequency. Moreover, this scheme is able to eliminate phase errors induced by harmonics and random noise. The validity and utility of the proposed scheme are verified by the experimental results.

• Korean Journal of Radiology
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• 제22권5호
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• pp.742-750
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• 2021

Objective: To assess the safety and clinical efficacy of percutaneous transhepatic enteral stent placement for recurrent malignant obstruction in patients with surgically altered bowel anatomy. Materials and Methods: Between July 2009 and May 2019, 36 patients (27 men and 9 women; mean age, 62.7 ± 12.0 years) underwent percutaneous transhepatic stent placement for recurrent malignant bowel obstruction after surgery. In all patients, conventional endoscopic peroral stent placement failed due to altered bowel anatomy. The stent was placed with a transhepatic approach for an afferent loop obstruction (n = 27) with a combined transhepatic and peroral approach for simultaneous stent placement in afferent and efferent loop obstruction (n = 9). Technical and clinical success, complications, stent patency, and patient survival were retrospectively evaluated. Results: The stent placement was technically successful in all patients. Clinical success was achieved in 30 patients (83.3%). Three patients required re-intervention (balloon dilatation [n = 1] and additional stent placement [n = 2] for insufficient stent expansion). Major complications included transhepatic access-related perihepatic biloma (n = 2), hepatic artery bleeding (n = 2), bowel perforation (n = 1), and sepsis (n = 1). The 3- and 12-months stent patency and patient survival rates were 91.2%, 66.5% and 78.9%, 47.9%, respectively. Conclusion: Percutaneous enteral stent placement using transhepatic access for recurrent malignant obstruction in patients with surgically altered bowel anatomy is safe and clinically efficacious. Transhepatic access is a good alternative route for afferent loop obstruction and can be combined with a peroral approach for simultaneous afferent and efferent loop obstruction.

• 한국군사과학기술학회지
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• 제24권6호
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• pp.577-590
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• 2021

In this paper, we theoretically analyzed the self-alignment/navigation performance in the accelerometer resonance state generated by dither motion of ring laser gyroscope in LINS and verified it through simulation. As a result of analysis, it is confirmed that the amplitude of the accelerometer measurement amplified in the accelerometer resonance state is decreased in the process of sampling per the navigation calculation period and that frequency is changed by the aliasing effect too. It was also analysed that the attitude error in self-alignment is determined by the amplitude/frequency of the accelerometer measurement, the gain of the self-alignment loop, and the velocity and position error in the navigation is determined by the amplitude/frequency/phase error of the accelerometer measurement. This analysis and simulation results show that the self-alignment and navigation performance is not be degraded only when the amplification factor of the accelerometer measurement in the accelerometer resonance state is 3 or less

• 대한기계학회논문집A
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• 제26권2호
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• pp.314-321
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• 2002

An endoscope is usually inserted into the human body for the inspection of the gullet, stomach, and large intestine (colon) and this may cause discomfort to patients and damage to tissues during diagnostic or therapeutic procedures. This situation necessitates a self-propelling endoscope. There are many kinds of mechanism to move in a rigid pipe. However, these methods are difficult to apply directly to the endoscope. The main reason is that human intestine cannot be considered as a uniform, straight, and rigid pipe. This paper proposes a flexible loop wheel mechanism, which is adaptable to the human intestine. This mechanism is designed and fabricated by a simple modeling, and tested by an experiment. Finally, the actuator is inserted into the pig colon.

• 한국통신학회논문지
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• 제24권6B호
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• pp.1074-1079
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• 1999

155.52 Mbps STM-1급 디지털 통신용 고성능 CMOS 리시버 칩을 설계 제작하였다. 제작된 리시버는 전송선로의 단락 또는 송신 중단 등으로 인해 데이터신호가 입력되지 않거나, 정전 발생 또는 시스템의 유지보수 등으로 인해 전원이 차단되었다가 복구될 때에도 155.52 MHz의 클락 주파수를 유지하여 항상 안정된 동작을 할 수 있는 구조로 이루어진다. 이를 위해 설계된 회로는 PLL을 기본으로 한 데이터 및 클락 복원회로 외에 데이터 감시회로와 전원 감시회로도 내장한다. 측정 결과 제작된 IC는 데이터신호가 입력되는 정상적인 상황에서뿐만 아니라, 데이터신호가 입력되지 않는 비정상적인 상황하에서도 항상 155.52 MHz의 안정된 클락을 발생시키고 있음을 알 수 있었음, PLL 루프의 실효 지터도 23 ps로 우수한 특성을 나타내었다.

• Smart Structures and Systems
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• 제6권1호
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• pp.1-16
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• 2010

This paper presents a novel smart MEMS accelerometer which employs a hybrid control algorithm and an estimator. This scheme is realized by adding a sliding-mode controller to a conventional PID closed loop system to achieve higher stability and higher dynamic range and to prevent pull-in phenomena by preventing finger displacement from passing a maximum preset value as well as adding an adaptive nonlinear observer to a conventional PID closed loop system. This estimator is used for online estimation of the parameter variations for MEMS accelerometers and gives the capability of self testing to the system. The analysis of convergence and resolution show that while the proposed control scheme satisfies these criteria it also keeps resolution performance better than what is normally obtained in conventional PID controllers. The performance of the proposed hybrid controller investigated here is validated by computer simulation.

• 한국항공우주학회지
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• 제36권7호
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• pp.674-679
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• 2008

본 논문에서는 안정된 진동을 얻기 위한 자동 이득 제어(AGC) 루프를 이용하여 자가 유지 특성을 갖는 공진형 가속도계를 설계하였다. 제안된 가속도계의 기본 원리는 가속도 입력시, 가변 진동의 진폭을 일정하게 유지시키는 방법을 이용한다. 시스템 모델링과 진동의 포락선을 고려한 루프 설계 및 변환를 통하여 다양한 가속도 입력 하에서 진동 신호의 진폭을 일정하게 유지하도록 제어기를 설계하였고, 시뮬레이션 결과를 통해 실현가능성을 확인하였다. 따라서 고안된 공진 가속도계는 산업과 민간 응용 분야에 있어서 제어용 등급의 관성 측정 시스템에 적용될 수 있을 것으로 기대한다.

• 제어로봇시스템학회논문지
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• 제4권2호
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• pp.203-208
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• 1998

This paper presents an adaptive fuzzy controller using an neural network and adaptation algorithm. Reference-model following neuro-fuzzy controller(RMFNFC) is invesgated in order to overcome the difficulty of rule selecting and defects of the membership function in the general fuzzy logic controller(FLC). RMFNFC is developed to tune various parameter of the fuzzy controller which is used for the discrete nonlinear system control. RMFNFC is trained with the identification information and control closed loop error. A closed loop error is used for design criteria of a fuzzy controller which characterizes and quantize the control performance required in the overall control system. A control system is trained up the controller with the variation of the system obtained from the identifier and closed loop error. Numerical examples are presented to control of the discrete nonlinear system. Simulation results show the effectiveness of the proposed controller.

• International Journal of Fluid Machinery and Systems
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• 제9권1호
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• pp.1-16
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• 2016

Behaviors of surges appearing near the stall stagnation boundaries in various fashions in systems of a single-stage compressor and flow-path systems were studied analytically and were tried to put to order. Deep surges, which enclose the stall point in the pressure-mass flow plane, tend to have either near-resonant surge frequencies or subharmonic ones. The subharmonic surge is a multiple-loop one containing, for example, in a (1/2) subharmonic one, a deep surge loop and a mild surge loop, the latter of which does not enclose the stall point, staying only within the stalled zone. Both loops have nearly equal time periods, respectively, resulting in a (1/2) subharmonic surge frequency as a whole. The subharmonic surges are found to appear in a narrow zone neighboring the stall stagnation boundary. In other words, they tend to appear in the final stage of the stall stagnation process. It should be emphasized further that the stall stagnation initiates fundamentally at the situation where a volume-modified reduced resonant-surge frequency becomes coincident with that for the stagnation boundary conditions, where the reduced frequency is defined by the acoustical resonance frequency in the flow-path system, the delivery flow-path length and the compressor tip speed, modified by the sectional area ratio and the effect of the stalling pressure ratio. The real surge frequency turns from the resonant frequency to either near-resonant one or subharmonic one, and finally to stagnation condition, for the large-amplitude conditions, caused by the non-linear self-excitation mechanism of the surge.