• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.36 no.1
• /
• pp.43-50
• /
• 2012

The effects of parameters related to the finite element simulation of the laser shock peening(LSP) process on the residual stresses of Inconel alloy 600 steel are discussed. In particular, we focus on the maximum pressure, pressure pulse duration, laser spot size, and number of shots. It is found that certain ranges of the maximum pressure and pulse duration can produce the maximum compressive residual stresses near the surface, and thus proper choices of these parameters are important. The residual stresses are not affected by the laser spot size, provided it is larger than a certain size. The magnitudes of the compressive residual stresses and the plastically affected depths are found to increase with an increasing number of shots, but this effect is less pronounced for more shots.

• Korean Journal of Optics and Photonics
• /
• v.30 no.3
• /
• pp.87-93
• /
• 2019

Phase screens are widely used to simulate the effects of atmospheric turbulence on the phase fluctuations of a light beam. We compare three sampled-based phase-screen-generation methods (the fast-Fourier-transform, subharmonic, and covariance-matrix methods), in terms of accuracy and simulation time. We show that the covariance method generates the phase screens most accurately, with simulation time comparable to the other sampled-based methods.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.36 no.3
• /
• pp.315-324
• /
• 2012

This paper presents a numerical investigation of the deflagration-to-detonation transition (DDT) of flame acceleration by a shock wave filled with an ethylene/air mixture as the combustible gas, considering geometrical changes by using obstacles and bent tubes. The model used consists of the reactive compressible Navier-Stokes equations and the ghost fluid method (GFM) for complex boundary treatment. Simulations with a variety of bent tubes with obstacles show the generation of hot spots through flame and strong shock-wave interactions, and restrained or accelerated flame propagation due to geometrical effects. In addition, the simulation results show that the DDT occurs with a nearly constant chemical heat-release rate of 20 MJ/($g{\bullet}s$) in our numerical setup. Furthermore, the DDT triggering time can be delayed by the absence of unreacted material together with insufficient pressures and temperatures induced by different flame shapes, although hot spots are formed in the same positions.

• Journal of the Korean Geophysical Society
• /
• v.9 no.4
• /
• pp.343-349
• /
• 2006

In order to study unconsolidated sediments upstream of the Soyang Dam, seismic refraction data were recorded along five profiles of 94 m length. Receiver interval and record length were 2 m and 204 ms, respectively. Recorded data were analyzed using the traveltime tomography and delay-time methods in order to reveal sediment distribution in the investigation site. The acoustic basements are buried at approximately 14 m deep and their thickness shallows to southeast approaching to a hill. On the basement, pre-existing sediments deposited before construction of the Soyang dam lies. This sedimentary layer is composed of paleo-soil and sandy sediments. Above this layer, recent sediments comprise the top layer which is believed to have been deposited since the formation of the dam. Average thickness of this uppermost layer is approximately 1.6 m, which is much thicker than in the downstream.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.9 no.4
• /
• pp.883-889
• /
• 2005

Error backpropagation algorithm of multilayer perceptron may result in local-minima because of the insufficient nodes in the hidden layer, inadequate momentum set-up, and initial weights. In this paper, we proposed the ART-1 based fuzzy supervised learning algorithm which is composed of ART-1 and fuzzy single layer supervised learning algorithm. The Proposed fuzzy supervised learning algorithm using self-generation method applied not only ART-1 to creation of nodes from the input layer to the hidden layer, but also the winer-take-all method, modifying stored patterns according to specific patterns. to adjustment of weights. We have applied the proposed learning method to the problem of recognizing a resident registration number in resident cards. Our experimental result showed that the possibility of local-minima was decreased and the teaming speed and the paralysis were improved more than the conventional error backpropagation algorithm.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.29 no.6B
• /
• pp.538-547
• /
• 2004

Optical Burst Switched (OBS) networks usually employ one-way reservation by sending a burst control packet (BCP) with a specific offset time, before transmitting each data burst frame (BDF). Therefore, The quality of service may be degraded because contentions may lead to loss of BDFs. Especially, this phenomenon becomes more serious when burst size is longer. This necessitates an effective method of prevention to avoid burst collision in nodes. OBS networks can employ several methods to avoid such burst losses. One is that burst size is cut short to reduce burst loss probability during scheduling time. In this paper, we evaluate the burst generation and transmission using Sub-Carrier Multiplexting (SCM) in OBS networks. We propose an appropriate burst assembly architecture and transmission scheme based on SCM in OBS networks. The performance of SCM in OBS networks is examined in terms of number of Sub-Carriers per wavelength, burst loss probability, throughput, and total bandwidth of an optical fiber.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.26 no.4
• /
• pp.289-295
• /
• 1993

The present paper was investigated in the inhibitory action of vegetable and seaweed water-soluble extracts on the formation of carcinogenic N-nitrosodimethylamine(NDMA). The vegetable and seaweed extracts obtained from garlic(Allium sativum), onion(Allium cepa), green onion(Allium fistuiosum), chinese pepper(Fagara mandshurica), green pepper(Capsicum annuum), red pepper(Capsicum annuum), ginger(Zingiber officinale), carrot(Daucus carota), laver(Porphyra tenera), sea lettuce(Entero compresa), sea mustard(Undaria pinnatifida) and sea staghorn(Codium fragile) were incubated with sodium nitrite-dimethylamine mixtures at $37^{\circ}C$ under different pH conditions The formation of NDMA was reduced to $10{\sim}40\%\;and\;25{\sim}50\%$ by the addition of vegetable and seaweed extracts 30mg at pH 1.2, respectively. The inhibition degree by the extracts at pH 1.2 was similiar to that at pH 4.2 and to that by ascorbic acid at pH 1.2. The inhibitory action of the extracts against NDMA formation was not decreased by heat treatment at $80^{\circ}C$ for 10min, but decreased by the treatment of sodium borohydride. It is assumed that reducing powers of the extracts participated in their inhibitory actions.

• Proceedings of the Korean Information Science Society Conference
• /
• 2008.06b
• /
• pp.191-195
• /
• 2008

최근 데이터 방송은 새로운 콘텐츠의 부재로 어려움을 겪고 있지만 사용자 중심의 서비스와 플랫폼을 지향하는 웹 2.0의 개념과 기술의 도입을 통해 콘텐츠 활성화에 기여할 것으로 보인다. 그에 대한 기대와 요구가 있으나 구체적인 구현 사례는 존재하지 않으므로 이에 본 논문에서는 웹 2.0으로 각광받고 있는 RSS를 통해 웹에서 지속적으로 업데이트가 이루어지는 최신 정보를 별도의 수집과정 없이 데이터 방송서비스를 생성하는 시스템을 개발했다. 지상파 DMB 데이터 방송의 경우 실시간으로 업데이트가 이루어지는 콘텐츠의 경우 지속적인 반영이 어렵지만 RSS를 통해 콘텐츠를 생성함으로써 저작 단계 및 시간을 줄여 보다 웹의 다양한 내용의 최신 정보를 사용자에게 제공할 수 있다.

• Proceedings of the Optical Society of Korea Conference
• /
• 2003.02a
• /
• pp.12-13
• /
• 2003

고차조화파를 이용해 아토초 펄스를 생성시킬 수 있음은 최근 여러 연구자들에 의해 이론적으로 제시되어 왔다. 아토초 펄스의 생성은 기본적으로 고차조화파 발생을 이용하여 생성되므로 고차조화파의 연구가 선행되어야 하며, 이에 대한 연구는 이미 많은 연구자들에 의해 이루어 졌다. 초기에 Kulander 등은 Time dependent Schrdinger equation (TDSE) 을사용하여 수치적으로 계산하여 고차조화파의 이론적 분석을 수행하여 단일원자(single atom)에서 발생하는 고차 조화파의 평탄영역(plateau)과 잘림영역(cutoff) 등을 설명하였고, Corkum 등은 준고전적 (semiclassical) 원자 모델을 사용하는 물리적 모형을 제안하여 이 때 계산된 고차조화파가 실험결과 및 완전한 양자역학적 결과와 유사하게 나타남을 보였다. (중략)

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 1998.04a
• /
• pp.16-16
• /
• 1998

로켓의 추진제에는 고체 추진제와 액체 추진제를 사용하는 두 경우로 나눌 수 있는데, 액체 추진제를 사용하는 경우, 액체 연료와 액체 산화제를 다양한 방법으로 연소실내로 분사하게 된다. 이때 사용되는 injector들 중에 impingement type이 있다. 이 type은 injector의 가공이 비교적 용이하고, 혼합성능이 좋기 때문에 LOX/RP-1(Kerosin-based hydrocarbon fuel)을 사용하는 액체 로켓엔진에서 주로 사용되어 왔다. 두 액체 jet의 충돌에 의해 액막이 형성되는데, 이 액막은 가장자리로 갈수록 두께가 얇아지며 액막표면의 파는 충돌점으로부터 멀어질수록 그 진폭의 증가를 이루어 액체의 표면장력과 관성력의 균형을 깨트리며, 이 순간 액막은 rim의 형태로 분열하여 결국에는 액적을 생성하게 된다. 현재까지의 연구내용은 충돌 jet의 형태 laminar jet과 turbulent jet으로 구분된 인젝트에 관해 연구되어왔고, 특히 국내에는 이러한 구분된 충돌 jet의 분열현상에 관한 연구결과가 미흡하다. 동일한 오르피스의 경우에도 laminar jet과 turbulent jet으로 구분되어 지며, 각각의 jet의 형태에 따라 생성되는 액막의 형상 또는 다르게 생성되어 진다. 그러므로 본 연구에서는 두 구분된 jet의 경우의 분열현상을 실험적으로 분석하였다.