• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.05a
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• pp.69-72
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• 2002

The high temperature deformation behavior of SiCp/2124Al composite and 2124Al alloy was investigated by hot compression test in a temperature ranged $400~475^{\circ}C$ over a strain rate ranged $10^{-3}~1s^{-1}$. The billets of 2124Al alloy and SiCp/2124Al composite were fabricated by vacuum hot pressing process. The stress-strain curve during high temperature deformation exhibited a peak stress, and then the flow stress decreased gradually into a steady state stress with increasing the strain. It was found that the flow-softening behavior was attributed to the dynamic recovery, local dynamic recrystallization and dynamic precipitation during the deformation. The precipitation phases were identified as S' and S by TEM diffraction pattern. Base on the TEM inspection, the relationship between the Z-H parameter and subgrain size was found based on the experiment data. The dependence of flow stress on temperature and strain rate could be formulated well by a hyperbolic-sinusoidal relationship using the Zener-Hollomon parameter.

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.138-138
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• 2011

GTL(Gas to Liquid) 합성유 생산 공정은 크게 합성가스 개질공정(reformer), FT 반응공정, upgrading 공정으로 구성된다. 본 연구에서는 FT 반응기에 유입되는 합성가스의 생산공정인 개질공정 최적화 시뮬레이션을 수행하였다. 기존에 HYSYS 공정 모사 tool로 구현한 개질공정 모델에 dynamic simulation을 적용하여 공정 운전 시간 변화에 따른 온도/압력/조성의 일정범위 별 생산 가스의 성분비를 모사하고자 한다. Dynamic 공정 시뮬레이션은 모사 대상 공정의 운전 시간 별 결과값 변화를 산출할 수 있는 방법으로 기존 정상상태(steady-state) 시뮬레이션에 비해 현실 공정의 운전 변수를 보다 더 정확하게 반영할 수 있는 장점이 있다. 본 시뮬레이션은 1bpd급 GTL 파일럿 플랜트의 설계 자료를 근거로 수행되었으며, 향후 운전 데이터를 feedback하여 최적의 운전 매뉴얼 도출자료로 활용코자 한다. 아울러, 다음의 시간 변화별 모사 결과 데이터들을 산출하고 공정의 최적운전 조건을 분석하고자 한다. - 시간에 따른 공정의 온도/압력 변화, 이에 연동되는 반응기 출구의 1) $H_2$/CO 비율, 2) $CH_4$ conversion, 3) $CO_2$ conversion 본 연구의 결과 데이터를 1bpd급 GTL 플랜트 내 합성가스 개질공정의 운전조건 최적화에 적용코자 하며, 이는 개질반응기의 안정적인 연속운전을 통한 GTL 통합공정의 운전 효율향상에 기여 가능하리라 기대된다. 향후 개질공정의 후단공정인 FT 합성공정 시뮬레이션 과업과 연계하여 GTL 통합공정 시뮬레이션 및 최적화에 따른 실증 규모의 스케일업 기반 데이터를 마련할 수 있을 것이다.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.8 no.3
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• pp.386-396
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• 1996

The dynamic characteristics of a condenser are numerically studied for the control of air-conditioning systems. The important factors, such as the refrigerant flow rate and refrigerant temperature, air velocity and air temperature at the condenser inlet, are incorporated into the analysis. This study was focused on the analysis of dynamic responses by transfer function method in the condenser. Block diagrams were made through analytic transfer function, and dynamic responses are evaluated on Bode diagrams in the frequency response. These results may be used for determining an optimum design parameters in an actual component and total systems. Also, the mathematical models, frequency response and steady state response may be used to increase understanding, to obtain useful information for its commercialization, to evaluate the hardware and the optimum design parameters, the design control system and to determine the best controller setting for the refrigeration and air conditioning systems.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.436-442
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• 2012

In the process of liquid rocket engine design, obtaining method of the dynamic characteristics of engine should be emphasized typically to determine the control logic and algorithms of the throttle valves in the propellant feed pipeline. However, determining the dynamic characteristics of an engine through the autonomous test is very hard and laborious, so that the numerical approach is prevailing. In this study, using the previously developed dynamic analysis model of the engine around the steady state, we introduced a disturbance to this model, and obtained the dynamic response in the time domain. And by applying the well-known Levy method to this temporal response, we could deduce the transfer function of that system that can give us various information of engine and can be manipulated to design the control system.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.34 no.3
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• pp.294-301
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• 1998

Towing performance of a midwater trawl system was examined aboard the training ship KAYA(2900ps) at the East Sea using the midwater trawl gear that had been designed and manufactured in accordance with the vessel. In this experiment, the trawl system data, the towing speed, the length and tension of the warp, net mouth height, and the depth of otter boards and net were measured and analyzed. The results are as follows: 1. In case of heaving in the warp with constant towing speed, the tension was suddenly increased and then again was reduced and after returned to the original steady state tension. At this time, net height was reduced a bit by ascension of ground rope, but returned to it’s original value. In the case where the warp was paid out, the tension was suddenly decreased and after increased and then returned to the tension of the original state, and the net height was greatly increased instantly by the sinking of the ground rope and then returned to the steady state 2. In the case of increased towing speed mm constant warp length, the tension was increased, and reducing the net height, the gear depth was decreased. On the other hand, in the case where towing speed was reduced, the tension was reduced and the gear depth and net height was increased. 3. Otter boards show a swing motion in the scope of 5~ 10m continuously. Otter boards responded to the state change of the trawl system at first, and then the motion of the net appeared. 4. The depth of net center was about 20m deeper than that of the otter boards, it shows about 0.4 times the warp length at the 4knots towing speed.

• Nuclear Engineering and Technology
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• v.55 no.2
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• pp.460-474
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• 2023

A simple but accurate mathematical model is crucial for dynamic simulations and controller design of helical coil once-through steam generator (OTSG). This paper presents a three-region movable boundary dynamic model of the helical coil OTSG. Based on the secondary side fluid conditions, the OTSG is divided into subcooled region (two control volumes), two-phase region (two control volumes) and superheated region (three control volumes) with movable boiling boundaries between each region. The nonlinear dynamic model is derived based on mass, energy and momentum conservation equations. And the linear model is obtained by using the transfer function and state space transformation, which is a 37-order model of five input and three output. Validations are made under full-power steady-state condition and four transient conditions. Results show good agreements among the nonlinear model, linear model and the RELAP5 model, with acceptable errors. This model can be applied to dynamic simulations and controller design of helical coil OTSG with constant primary-side flow rate.

• Journal of Power Electronics
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• v.15 no.3
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• pp.763-774
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• 2015

This study investigates the inherent influence of a DC-link voltage controller on both DC-link voltage control and the compensation performance of a three-phase, four-wire shunt active power filter (APF). A nonlinear variable-parameter DC-link voltage controller is proposed to satisfy both the dynamic characteristic of DC-link voltage control and steady-state compensation performance. Unlike in the conventional fixed-parameter controller, the parameters in the proposed controller vary according to the difference between the actual and the reference DC-link voltages. The design procedures for the nonlinear voltage controller with variable parameters are determined and analyzed so that the proposed voltage controller can be designed accordingly. Representative simulation and experimental results for the three-phase, four-wire, center-spilt shunt APF verify the analysis findings, as well as the feasibility and effectiveness of the proposed DC-link voltage controller.

• Journal of the Korea Society of Computer and Information
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• v.6 no.1
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• pp.67-73
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• 2001

This paper proposes a new scheduling algorithm for broadband ATM access network. The existed scheduling algorithms (Train, Chao. Dynamic scheduling algorithm) have high cell loss rate and waste channel. These proposed mechanism utilize to control of multimedia services based on the quality of service level of the input traffic This paper suggests a functional architecture of scheduling and the scheduling algorithm to satisfy various QoS requirements. The performance measures of interest, namely steady-state cell loss probability and average delay, average delay, are discussed by simulation results.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.2
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• pp.283-290
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• 2002

In this paper, we consider the dynamic electromechanical behavior of an eccentric Yoffe permeable crack in a piezoelectric ceramic strip sandwiched between two elastic orthotropic materials under the combined anti-plane mechanical shear and in-plane electrical loadings. Fourier transforms are used to reduce the problem to the solution of two pairs of dual integral equations, which are then expressed to a Fredholm integral equation of the second kind. The initial crack propagation orientation for PZT-5H piezoceramics is predicted by maximum energy release rate criterion.

• Proceedings of the Korea Technical Association of the Pulp and Paper Industry Conference
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• 2004.04a
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• pp.97-106
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• 2004

The paper making process itself is a typical nonlinear process with complicated dynamics. In the application of advanced control-methods especially for the grade change operations the nonlinear process is linearized to give suitable linear models to be used in the control strategies. However, the use of the linear model is limited within short range containing steady-state operating conditions for grade change operation. In this paper a bilinear model for the nonlinear grade change processes is presented. We can see that the dynamic behavior for grade change operations can be effective analyzed by using multivariable bilinear model.