• 한국추진공학회지
• /
• 제22권1호
• /
• pp.45-51
• /
• 2018

최근 이중모드 램제트 엔진에서 모드 천이는 격리부 출구 마하수의 불연속적인 변화를 일으킨다고 보고된 바 있다. 이 현상을 격리부 입구와 출구에서의 유효 유동 단면적과 압력비에 따라 나타내었으며, 이는 Non-Allowable Region (NAR)으로 설명되었지만, NAR의 발생 기구에 대한 이해는 여전히 부족한 실정에 있다. 본 연구에서는 NAR의 발생 원인에 대한 유동 메커니즘을 조사하기 위해, 앞서 수행한 수치해석 결과들의 상세 연구가 수행되었으며, 스크램제트에서 램제트로의 모드 천이발생 동안 기체역학적 특성에 대한 이해를 돕기 위해 이론해석도 수행되었다. 격리부 입구에서 유동 상태량이 수용할 수 있는 당량비의 임계값이 정해져 있는데, 이 임계값을 초과하는 당량비의 증가는 격리부 입구에서의 정압뿐만 아니라 마하수의 급격한 변화를 발생시키게 되며, 이는 NAR의 발생 원인이 된다.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2009년 춘계학술대회논문집
• /
• pp.87-89
• /
• 2009

In the present paper, transition turbulence model is applied to the NACA64(3)618 and detailed flow features are studied. The turbulence model is sensitive to the boundary layer grid quality and y+ of the grid was limited to 1. The prediction of the transition region is dependent on the local flow condition. The pressure coefficient distribution of the transition turbulence model is compared with that of the fully turbulent mode and the drag distribution of the transition turbulence model was compared with that of the wind tunnel test.

• 한국정보처리학회:학술대회논문집
• /
• 한국정보처리학회 2023년도 추계학술발표대회
• /
• pp.1141-1142
• /
• 2023

본 연구는 4륜 독립 구동·제동·조향 차량의 모드 천이 논리 알고리즘에 관한 연구로서, 일반적인 주행 스타일 외에도 다양한 주행 스타일을 가지는 차량에서 주행 모드 전환 간에 고려되어야 하는 조건들을 다룬다. 주행 모드 전환 간에 Static Transition과 Dynamic Transition이 가능하며 Static Transition 방식이 일반적이지만 저속 상태에서 차량이 충분히 정렬되어 있다면 FWS 주행, 동상 주행, 역상 주행 간의 Dynamic Transition도 가능할 것이다.

• ETRI Journal
• /
• 제32권2호
• /
• pp.195-203
• /
• 2010

A new vertical transition between a substrate integrated waveguide in a low-temperature co-fired ceramic substrate and an air-filled standard waveguide is proposed in this paper. A rectangular cavity resonator with closely spaced metallic vias is designed to connect the substrate integrated waveguide to the standard air-filled waveguide. Physical characteristics of an air-filled WR-22 to WR-22 transition are compared with those of the proposed transition. Simulation and experiment demonstrate that the proposed transition shows a -1.3 dB insertion loss and 6.2 GHz bandwidth with a 10 dB return loss for the back-to-back module. A 40 GHz low-temperature co-fired ceramic module with the proposed vertical transition is also implemented. The implemented module is very compact, measuring 57 mm ${\times}$ 28 mm ${\times}$ 3.3 mm.

• 한국음향학회지
• /
• 제19권3호
• /
• pp.26-34
• /
• 2000

본 논문에서는 선형예측 잔여신호에 대한 하모닉 벡터 여기 코딩에, 시간 대역 분리 혼합 코딩을 결합한 4kbps 음성코더를 제안한다. 하모닉 벡터 여기 코딩은 유성음 구간에서 하모닉 여기 코딩을 사용하며, 무성음 구간에 대해서는 분석-합성 구조의 벡터 여기 코딩을 사용한다. 그러나, 이러한 양단 모드 코딩 방법은 유성음과 무성음이 혼재하는 전이 구간에서는 비효과적이므로, 유/무성음 모드 코딩 이외의 새로운 방법이 요구된다. 이에, 전이 구간을 위한 시간 분리 전이 코딩을 설계하였으며, 여기서, 유/무성음 결정 알고리즘은 단위 구간 내의 유성음과 무성음의 존속기간을 결정하고, 이전 구간의 유/무성음 결정에 따라 하모닉-하모닉 코딩과 벡터-하모닉 코딩을 선택적으로 사용한다. 복호화기에서는 하모닉 크기값들의 IFFT 과정을 통해 유성음 여기신호가 효과적으로 합성되며, 무성음 여기신호는 역 벡터 양자화를 통해 만들어진다. 재 복원된 음성 신호는 중첩합산 방법에 의해 합성된다.

• 항공우주시스템공학회지
• /
• 제9권1호
• /
• pp.12-18
• /
• 2015

The inter-conversion between different control laws in flight has a lot of risk. The SWM(Switching Mechanism) including logic and stand-by mode is designed to analyze the transient response of aircraft during inter-conversion between different control laws, based on the in-house software for non-real-time and real-time simulation. The SWM applies the fader logic of TFS(Transient Free Switch) to minimize the transient response of an aircraft during the inter-conversion, and applies the reset '0' type of the stand-by mode to prevent surface saturation due to integrator effect in the disengaged flight control law. The transition time is also important to minimize the objectionable transient response in the inter-conversion, as well as the transition control law design. This paper addresses the results of non-real-time simulation for the characteristics of transient response to different transition time to select the adequate transient time, and the real-time pilot evaluation, using SSWM(Software Switching Mechanism) and HSWM(Hardware Switching Mechanism), which is met for Level 1 flying qualities and assures safety of flight.

• 전력전자학회논문지
• /
• 제25권5호
• /
• pp.333-342
• /
• 2020

Power exchanges between the grid and the battery through a bidirectional DC-DC converter are essential for DC microgrid systems. In general, the battery is charged when the grid is connected, and the system is powered by the battery when the grid is disconnected. In this mode transition, the saturation of the voltage controller slows down output response and produces large transient errors in DC link voltage. To solve this problem, a novel anti-windup design is proposed to improve anti-windup performance further. The proposed method stabilizes DC bus voltage through a wider range of battery voltage with faster transition compared with that of conventional methods. The proposed method is verified through an experimental setup composed of a 125 W laboratory-scale DC microgrid system.

• Journal of Power Electronics
• /
• 제19권3호
• /
• pp.691-701
• /
• 2019

To solve the problems in the contact charging of inspection robots, a wireless charging system for inspection robots and a control strategy are introduced in this paper. Circuit models of a wireless power system with a compound compensation circuit and a three-phase Class-D resonant inverter are set up based on circuit theory. An output voltage control method based on the equal spread regulation of the phase difference between adjacent phases and the parameter correction method in the primary compound compensation circuit are proposed. The dynamic characteristics of the key parameters varying with the secondary coil position are obtained to further investigate the adaptive location scheme during the access and exit processes of moving robots. Combining the output voltage control method and the adaptive location scheme, a transition control strategy for the standby and operation modes of the wireless charging systems for inspection robots is put forward to realize the system characteristics including the low standby power in the standby mode and the high receiving power in the operation mode. Finally, experiments are designed and conducted to verify the correctness of the theoretical research.

• 한국자동차공학회논문집
• /
• 제19권2호
• /
• pp.26-34
• /
• 2011

Hybrid powertrain systems have been developed to improve the fuel efficiency of internal combustion engines. In the case of a parallel hybrid powertrain system, an engine and a motor are directly coupled. Because of the hardware configuration of the parallel hybrid system, friction and the pumping losses of internal combustion engines always exists. Such losses are the primary factors that result in the deterioration of fuel efficiency in the parallel-type hybrid powertrain system. In particular, the engine operates as a power consumption device during the fuel-cut condition. In order to improve the fuel efficiency for the parallel-type hybrid system, cylinder deactivation (CDA) technology was developed. Cylinder deactivation technology can improve fuel efficiency by reducing pumping losses during the fuel-cut driving condition. In a CDA engine, there are two operating modes: a CDA mode and an SI mode according to the vehicle operating condition. However, during the mode change from CDA to SI, a serious fluctuation of the air-fuel ratio can occur without adequate control. In this study, an air-fuel ratio control algorithm during the mode transition from CDA to SI was proposed. The control algorithm was developed based on the mean value CDA engine model. Finally, the performance of the control algorithm was validated by various engine experiments.

• 한국전기전자재료학회논문지
• /
• 제17권10호
• /
• pp.1049-1055
• /
• 2004

Chemical Mechanical Polishing (CMP) is referred to as a three body tribological system, because it includes two solids in relative motion and the CMP slurry. On the assumption that the abrasives between the pad and the wafer could be a major reason not only for the friction force but also for material removal during polishing, the friction force generated during CMP process was investigated with the change of abrasive size and concentration of CMP slurry. The threshold point of average coefficient of friction (COF) with increase in abrasives concentration during interlayer dielectric (ILD) CMP was found experimentally and verified mathematically based on contact mechanics. The predictable models, Mode I (wafer is in contact with abrasives and pad) and Mode II (wafer is in contact with abrasives only), were proposed and used to explain the threshold point. The average COF value increased in the low abrasives concentration region which might be explained by Mode I. In contrast the average COF value decreased at high abrasives concentration which might be regarded to as Mode II. The threshold point observed seemed to be due to the transition from Mode I to Mode II. The tendency of threshold point with the variation of abrasive size was studied. The increase of particle radius could cause contact status to reach transition area faster. The correlation between COF and material removal rate was also investigated from the tribological and energetic point of view. Due to the energy loss by vibration of polishing equipment, COF value is not proportional to the material removal rate in this experiment.