• 한국초전도ㆍ저온공학회논문지
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• 제26권1호
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• pp.25-30
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• 2024

High-temperature superconducting rotors offer advantages in terms of output-to-weight ratio and efficiency compared to conventional phase conduction motors or generators. The rotor can be cooled by conduction cooling, which attaches a cryocooler, and by refrigerant circulation, which uses circulating liquid or gas neon, helium and hydrogen. Recent work has focused on environmental issues and on high-temperature superconducting motors cooled with liquid hydrogen that can be combined with fuel cells. However, to ensure smooth supply and return of the cryogenic cooling fluid, a cryogenic rotational coupling between the rotating and stationary parts is necessary. Additionally, the development of a sealing structure to minimize fluid leakage applicable to the coupling is essential. This study describes the design and performance evaluation of a non-contact sealing method, specifically a labyrinth seal, which avoids power loss and heat load caused by friction in contact sealing structures. The seal design incorporates a spiral flow path to reduce leakage using centrifugal force, and computational fluid dynamics (CFD) simulations were conducted to analyze the flow path and rotational speed. A performance evaluation device was configured and employed to evaluate the designed seal. The results of this study will be used to develop a cryogenic rotational coupling with supply and return flow paths for cryogenic applications.

• Journal of Biosystems Engineering
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• 제35권3호
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• pp.163-168
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• 2010

With income growth and "well-being" trends, sales of corn has been increased recently. Corns are processed at processing facilities on the main production site. Corn processing steps include removing bract, steaming, vacuum packing, and storing. To replace manual corn bract removing, some bract removing machines were imported and used. However, the machines were abandoned shortly, because of high damaging ratio of corns. In this research, factors of successful bract removing was studied with rotating rollers and air-injection nozzles to develop corn bract removing system. The test device was composed of a cylindrical roller, an air spray nozzle, a regulator, and a motor. Designing factors were roller type, diameter of air spraying nozzle, spraying angle, and spraying pressure. The measured factors were bract removing rate and damaging rate. It was found that optimum cylindrical roller surface shape was cylindrical roller and linear grove roller. This roller shape produced lowest damaging rate. Test results of the efficacy of preprocessing showed that the air spraying after preprocessing produced highest performance. The rotational speed and inclination of the roller didn't affect the bract removing performance. Optimum injection angle of the air jet nozzle was $70^{\circ}$. To increase bract removing rate and to reduce corn damage, required injection pressure and injection nozzle diameter were decided to less than 0.4 MPa and 2.5 mm, respectively. More than 3 times of nozzle passing produced good bract removing performance and there were no significant difference between the number of passing times.

• Journal of Advanced Marine Engineering and Technology
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• 제37권1호
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• pp.121-126
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• 2013

교류기기의 속도 및 토크 제어시스템에서 전력변환장치로 사용되는 싸이클로컨버터는 저속에서 토크가 크고 제어가 간단한 장점을 가지고 있다. 또한, 정류기, 직류링크부, 인버터가 설치되지 않으므로 시스템이 간단하고 대전력 시스템에 적합하다. 현재 사용되고 있는 대형선박의 추진전동기의 구동용 전력변환장치를 싸이클로컨버터로 변경하면 시스템이 간단해지므로 설치비용을 크게 감소시킬 수 있다. 하지만 기존의 싸이클로컨버터는 전력 반도체소자의 고속 스위칭에 의한 손실이 크고 출력 전압파형이 왜곡되어서 고조파 성분이 증가하게 된다. 본 논문에서는 이러한 단점을 개선하기 위해서 1차측에 위상이 다른 2개의 입력단과 2차측에 1개의 출력단으로 구성되는 상천이 필터를 설치한다. 위상이 다른 2개의 전압파형이 더해져서 2차측으로 변압됨으로써 전압파형이 정현파에 가깝게 출력된다. 그로 인해 추진전동기에 입력되는 전압파형이 개선되고 총고조파왜형율도 크게 감소한다.

• Geomechanics and Engineering
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• 제35권5호
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• pp.487-497
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• 2023

Penetration rate (PR) and penetration depth (Pe) are crucial parameters for estimating the cost and time required in tunnel construction using tunnel boring machines (TBMs). This study focuses on investigating the impact of rock strength on PR and Pe through full-scale experiments. By conducting controlled tests on rock-like specimens, the study aims to understand the contributions of various ground parameters and machine-operating conditions to TBM excavation performance. An earth pressure balanced (EPB) TBM with a sectional diameter of 3.54 m was utilized in the experiments. The TBM excavated rocklike specimens with varying uniaxial compressive strength (UCS), while the thrust and cutterhead rotational speed were controlled. The results highlight the significance of the interplay between thrust, cutterhead speed, and rock strength (UCS) in determining Pe. In high UCS conditions exceeding 70 MPa, thrust plays a vital role in enhancing Pe as hard rock requires a greater thrust force for excavation. Conversely, in medium-to-low UCS conditions less than 50 MPa, thrust has a weak relationship with Pe, and Pe becomes directly proportional to the cutterhead rotational speed. Furthermore, a strong correlation was observed between Pe and cutterhead torque with a determination coefficient of 0.84. Based on these findings, a predictive model for Pe is proposed, incorporating thrust, TBM diameter, number of disc cutters, and UCS. This model offers a practical tool for estimating Pe in different excavation scenarios. The study presents unprecedented full-scale TBM excavation results, with well-controlled experiments, shedding light on the interplay between rock strength, TBM operational variables, and excavation performance. These insights are valuable for optimizing TBM excavation in grounds with varying strengths and operational conditions.

• 한국항공우주학회지
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• 제30권8호
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• pp.46-55
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• 2002

본 연구에서는 저가형 PC-클러스터 환경에서 운영 가능한 고속 병렬처리 기법을 활용하여 전기체 항공기 및 발사체 형상을 고려할 수 있는 천음속/초음속 비선형 플러터 해석시스템을 개발하였다. 이는 이론적으로 진보된 수치해석 기법인 전산구조동역학(CSD), 유한요소법(FEM) 및 전산유체역학(CFD) 기법을 동시에 연계하고 있으며, 각종 비행체의 공탄성안정성 설계 과정에서 공학적으로 매우 정밀한 데이터 제공이 가능하다. 개발된 공탄성 해석시스템의 뛰어난 응용성을 보이기 위해 국내에서 개발 중인 초음속 항공기의 전기체 형상에 대해 천음속/초음속 비선형 공탄성 해석을 수행하였다.

• 드라이브 ㆍ 컨트롤
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• 제16권4호
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• pp.1-8
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• 2019

The HPM (High-speed Power Matching) system is an electro-hydraulic control system. It directly controls the swash plate of the pump by selecting four-loop logic based on joystick signals, pump flow, and pressure signal to improve the efficiency and controllability of construction machines. In the NFC (Negative Flow Control) system, a typical pump control system using conventional open center type MCV, the loss is continuously generated by flow through the center bypass line even when the excavator is not in operation. Also, due to the slow response of the pump that indirectly controls the flow rate using the pressure regulator, peak pressure occurs at the start or stop of the operation. Conversely, the HPM system uses an MCV without center-by-pass flow path and the swash plate of a pump for the HPM is controlled by a high-speed proportional flow control valve. As a result, the HPM system minimizes energy loss in standby state of the excavator and enables peak pressure control through rapid electro-hydraulic control of a pump. In this paper, the concept of the HPM system algorithm is introduced and the hydraulic system efficiency is compared with the NFC system using the excavator SAT (System Analysis Tool).

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제48권5호
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• pp.241-248
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• 1999

Recently, many linear motion generators and motors are rapidly finding applications that ranges from short stroke linear motion vibrators, such as dynamic cone type loudspeakers to stirling engine driven linear reciprocating alternators, compressors, textile machines etc. The stroke-length may go up to 2m, and the maximum speed is in the range of 5 to 10m/s with oscillating frequency as high as 15 kHz. Therefore, the linear oscillating actuators(LOAs) may be considered as variable speed drivers of precise controller with stoke-length and reversal periods during the reciprocating motion. In this paper, the design, fabrication, experiments, and extraction of control parameters of a moving coil type LOA for driving of linear reciprocating motion control systems, are treated. The actuator consists of the NdFeB permanent magnets with high specific energy as the stator produced magnetic field, a coil-wrapped nonmagnetic hollow rectangular bobbin structure, and an iron core as a pathway for magnetic flux. Actually, the design is accomplished by using FEM analysis for the basic configuration of a magnetic circuit, and characteristic equations for coil design. In order to apply as the drivers of a linear motion reciprocating control system, the control parameters and circuit parameters, such as input voltage-stoke, exciting frequency-stoke, coil inductance and so on, are extracted from the analysis and experiments on concerning a fabricating LOA.

• 한국산업정보학회논문지
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• 제24권1호
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• pp.39-44
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• 2019

고온 초전도 (HTS) 발전기는 무게, 크기 및 효율의 장점 때문에 활발히 연구되어왔다. 대규모의 초전도 풍력 발전기는 매우 저속의 고토크 회전 기계이다. 이 기계에서는 높은 전자기력과 토크가 중요한 문제이다. 하나의 축에 직렬로 연결된 2개의 발전기는 고토크의 문제를 극복하기위한 하나의 해결 방안이 될 수 있다. 본 논문에서 저자는 15 MW 급 HTS 발전기를 설계하고 분석했다. 3D 유한 요소법을 사용하여 15 MW HTS 발전기의 자기장 분포 및 토크 성능을 확인하였다. 결과적으로 설계된 발전기는 기존의 발전기보다 적은 토크를 생성한다. 제시된 15 MW 초전도 발전기의 설계방식은 대용량 초전도 풍력 발전기의 제작에 있어 고토크로 인한 문제를 해결하는데 활용될 수 있다.

• Journal of Ship and Ocean Technology
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• 제6권4호
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• pp.1-12
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• 2002

A control system for an automated line heating process is developed by use of object-oriented methodology. The main function of the control system is to provide real-time heating information to technicians or automated machines. The information includes heating location, torch speed, heating order, and others. The system development is achieved by following the five steps in the object-oriented procedure. First, requirements are specified and corresponding objects are determined. Then, the analysis, design, and implementation of the proposed system are sequentially carried out. The system consists of six subsystems, or modules. These are (1) the inference module with an artificial neural network algorithm, (2) the analysis module with the Finite Element Method and kinematics analysis, (3) the data access module to store and retrieve the forming information, (4) the communication module, (5) the display module, and (6) the measurement module. The system is useful, irrespective of the heating sources, i.e. flame/gas, laser, or high frequency induction heating. A newly developed automated line heating machine is connected to the proposed system. Experiments and discussions follow.

• International Journal of Precision Engineering and Manufacturing
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• 제9권1호
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• pp.3-6
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• 2008

Electrical discharge machining (EDM) is one of the most widespread nonconventional machining processes. Recently, a low-power micro-EDM process was introduced using a cylindrical electrode. Since its development, micro-EDM has been applied effectively to micromachining, and because the device setup for this process is simple, it is suitable for a microfactory that minimizes machines to fabricate small products economically in one system. In the EDM process, however, the electrode is also removed along with the workpiece. Therefore, the electrode shape and length vary as machining progresses. In this paper, a control method using a high speed realtime voltage measurement is proposed to regulate the rate and amount of material removed. The proposed method is based on the assumption that the volume of the workpiece removed in a single discharge pulses is nearly constant. The discharge pulses are monitored and controlled to regulate the amount of material removed. For this purpose, we developed an algorithm and apparatus for counting the number of discharge pulses. Electrode wear compensation using pulse number information was applied to EDM milling in a microfactory, in which a slight tilt of the workpiece may occur. The proposed control method improves the machining quality and efficiency by eliminating the inaccuracies caused by electrode wear and workpiece tilt.