• 한국항공우주학회지
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• 제48권3호
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• pp.187-194
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• 2020

본 연구에서는 고도에 따른 간섭 유동과 공력특성을 파악하고, 측추력 제트에 사용된 기체의 종류에 따라 다화학종 가스제트의 확산을 고려한 유동해석을 수행하였다. 공기제트에 비해서 임의로 가정한 다화학종 가스 제트를 사용하는 경우 충격파의 위치와 제트의 확산 영역이 동체전방으로 이동한다. 이로 인해 표면의 고압영역이 앞으로 나가며 같은 조건에서 보다 높은 피칭 모멘트를 갖는다. 또한 고온효과의 적용에 따라 압력분포 예측에 차이를 보였다. 그리고 저고도의 측추력제트 유동 구조와 비교했을 때 중고도 유동조건에서 주변 대기의 낮은 밀도로 측추력 제트의 두께가 더 크며, 넓은 영역에 걸쳐 확산된다.

• The Korean Journal of Ceramics
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• 제5권3호
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• pp.270-277
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• 1999

The ballistic capability of an alumina-rich oxide armor ceramic against a shaped jet was characterized as a function of penetration depth in a layered target structure. The penetration resistance of the ceramic, based upon the determination of penetration velocity, was not equally realized throughout the depth of penetration. It was abnormally low at an early stage of penetration, followed by a sudden increase to reach ~16GPa thereafter. There was no apparent change in such a profile with respect to the lateral size of the specimen. Based upon 2-D flash x-ray radiography and 3-D Hull code simulation, the feasibility of forming a pressure-induced predamnaged zone in front of the jet tip was speculated to foster an increased penetration velocity in the initial stage penetration, resulting in the diminished penetration resistance. The disappearance of such a predamaged zone with penetration was interpreted to restore the resistance of the ceramic in the later penetration stage.

• 대한기계학회논문집B
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• 제23권5호
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• pp.577-586
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• 1999

Two problems with jet injection through the cylindrical film cooling hole are 1) penetration of jet into mainstream rather than covering the surface at high blowing rates and 2) nonuniformity of the film cooling effectiveness in the lateral direction. Compound angle injection is employed to reduce those two problems. Compound angle injection increases the film cooling effectiveness and spreads more widely. However, there is still lift off at high blowing rates. Shaped film cooling hole is a possible means to reduce those two problems. Film cooling with the shaped hole is investigated in this study experimentally. Film cooling hole used in present study is a shaped hole with conically enlarged exit and Inlet-to-exit area ratio is 2.55. Naphthalene sublimation method has been employed to study the local heat/mass transfer coefficient and film cooling effectiveness for compound injection angles and various blowing rates around the shaped film cooling hole. Enlarged hole exit area reduces the momentum of the jet at the hole exit and prevents the penetration of injected jet into the mainstream effectively. Hence, higher and more uniform film cooling effectiveness values are obtained even at relatively high blowing rates and the film cooling jet spreads more widely with the shaped film cooling hole. And the injected jet protects the surface effectively at low blowing rates and spreads more widely with the compound angle injections than the axial injection.

• 한국전기전자재료학회논문지
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• 제35권1호
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• pp.18-23
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• 2022

이젯 프린팅은 직접적인 비접촉 마이크로 팹기술의 하나로서 노즐과 기판 사이에 강한 전기장을 가함으로써 넓은 범위의 마이크로/나노패턴 어레이를 구현할 수 있는 다목적 팹공정이다. 제조된 고분자/퀀텀닷 마이이크로 패턴의 모양과 두께는 자동화된 프린트 기계에 설치된 노즐 직경과 공정에 사용된 잉크 성분에 일반적으로 정밀한 의존성을 갖는다. 본 논문의 목적은 실험 결과에 영향을 미칠 수 있는 각각의 공정 변수 효과를 설명하기 위해서 이젯 프린팅된 고분자/퀀텀닷의 전형적인 실제 예를 설명하는데 있다. 여기서 우리는 마이크로/나노 해상도로 두께가 정밀하게 제어된 고분자/퀀텀닷 패턴을 제조할 수 있는 몇 가지 이젯 프린팅 공정을 구현하였다.

• 한국지능시스템학회논문지
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• 제25권2호
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• pp.168-173
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• 2015

비행 시 외부 조건에 따라 비선형시변 동적특성을 갖는 항공기의 비행제어는 종 제어(longitudinal control)와 횡 제어(lateral control)로 나눌 수 있으며, 종 제어는 승강키(elevator)에 의한 피치(pitch)값, 횡 제어는 에일러론(aileron)에 의한 롤(roll)값과 방향키(rudder)에 의한 요(yaw)값들을 제어대상으로 삼는다. 현재까지 항공기의 안정성, 조종성 그리고 기동성을 보장하기 위한 제어시스템 개발에 많은 연구들이 활발히 진행되어 왔으나, 최근에는 다양하고 복잡한 풍동실험과 환경실험들을 필요로 하는 기존연구들과는 다른 항공기의 지능제어시스템 개발에 관련된 연구들이 이루어지고 있다. 본 논문은 대표적인 지능제어방식인 Interval Type-2 퍼지논리기법에 의한 항공기 종 제어시스템을 제시하고 F-4 제트전투기의 컴퓨터 모의실험을 통해 그 효용성을 입증한다.

• 제어로봇시스템학회논문지
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• 제12권7호
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• pp.713-718
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• 2006

Supersonic jet fighter aircraft have several different weapon loading configuration to support air-to-air combat and air-to-ground delivery of weapon modes. Especially, asymmetric loading configurations could result in decreased handling qualities for the pilot maneuvering of the aircraft. The design of the T-50 lateral-directional roll axis control laws change from beta-betadot feedback structure to simple roll rate feedback structure and gains such as F-16 in order to improve roll-off phenomena during pitch maneuver in asymmetric loading configuration. Consequently, it is found that the improved control law decreases the roll-off phenomenon in lateral axes during pitch maneuver, but initial roll response is very fast and wing pitching moment is increased. In this paper, we propose the lateral control law blending between beta-betadot and simple roll rate feedback system in order to decreases the roll-off phenomenon in lateral axes during pitch maneuver without degrading of roll performance.

• 한국해양공학회지
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• 제24권5호
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• pp.8-15
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• 2010

The flow around a two-dimensional, rectangular cylinder that is freely falling in a channel was simulated using the immersed boundary method with direct forcing to determine the interactions between the fluid and the structure. The results of the present study were in good agreement with previous experimental results. Regardless of the H/L ratio (where H and L are the height and width of the rectangular cylinder, respectively), the flow structures had essentially the same pattern as the two symmetrical circulations that form about the horizontal center of the cylinder, with those centers located at each lateral position near the wake. When the cylinder approaches very close to the bottom, a jet-like flow appeared between the bottom of the rectangular cylinder and the channel. When the jet-like flow goes through the channel, surrounding fluids are sucked into this jet, forming the secondary vortices.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.835-840
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• 2009

In this paper, confined multiple slot jet impingement with exhaust ports is investigated numerically. A flow cell, defined as volume sectioned by the impingement and confinement surfaces and the centerlines of adjacent nozzle and exhaust port, is chosen for computational domain. The effects of Reynolds number and geometrical parameters on the heat transfer performance and the flow characteristics are studied. For turbulence, the Abe-Kondoh-Nagano version of the low-Reynolds k-$\varepsilon$ model is employed. The results showed that the local Nusselt number distribution is shifted down and show poor heat transfer performance for small Reynolds number and small ratio of the lateral and axial length of flow cell. The rest of range, except the range of the shift phenomenon, can be classified into three groups by heat transfer characteristics.

• 대한조선학회논문집
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• 제48권4호
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• pp.357-362
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• 2011

It has been often reported that a water-jet propelled high speed vessel lost the course keeping ability in seaway. In this study, model tests of a high speed vessel were performed to measure the running attitude and to check the course keeping ability. The model ship may lose the course keeping ability due to bad running attitudes such as bow drop. So model tests were carried out to improve the running attitude by changing the position of longitudinal center of gravity and using appendages at the bow and the stern of a model. The position of lateral center of pressure moved toward stern and the course keeping ability was improved by modifying the transom wedge angle.

• Water Engineering Research
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• 제3권3호
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• pp.163-176
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• 2002

In this study, laboratory experiments have been performed to investigate characteristics of the velocity fields and turbulence for non-buoyant plane jet in the vicinity of the jet nozzle using PIV system. The experimental results show that, in the transition region, the lateral velocity profile is in good agreement with Gaussian distribution. However, the coefficient of Gaussian distribution, $\K_{u,}$, decreases with longitudinal distance in the transition region. The existing theoretical equation for the centerline velocity tends to overestimate the measured data in the transition region. A new equation for the centerline velocity derived by incorporating varying $k_{u}$ gives better agreement with the measured data than the previous equation. The results of the turbulence characteristics show peak values are concentrated on the shear layers. The Reynolds shear stress profile shows the positive peak in the upper layer and negative peak in the lower layer. The turbulent kinetic energy also provides double peaks at the shear layers. The peak of the Reynolds shear stress and the turbulent kinetic energy increases until x/B=8, and then it decreases afterwards.s.