• Title/Summary/Keyword: Transition stream

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Completed Stream Cipher by Cellular Automata - About Cellular Automata rule 30 - (Cellular Automata 기초로 형성된 Stream Cipher - Cellular Automata rule 30을 중심으로 -)

  • Nam, Tae-Hee
    • Journal of the Korea Computer Industry Society
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    • v.9 no.2
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    • pp.93-98
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    • 2008
  • In this study, analyzed principle about stream cipher that is formed to Cellular Automata foundation. Cellular Automata can embody complicated and various principle with simple identifying marks that is State, Neighborhood, Transition Rules originally. Cellular Automata is hinting that can handle encipherment smoothly using transition rule. Create binary pad (key stream) by Cellular Automata's transition rule 30 applications in treatise that see therefore, and experimented ability of encryption and decryption because using stream cipher of symmetric key encryption way of password classification.

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Practical Patching for Efficient Bandwidth Sharing in VOD Systems

  • Ha Soak-Jeong
    • Journal of Korea Multimedia Society
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    • v.8 no.12
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    • pp.1597-1604
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    • 2005
  • Recursive Patching is an efficient multicast technique for large-scale video on demand systems and recursively shares existing video streams with asynchronous clients. When Recursive Patching initiates a transition stream, it always makes a transition stream have additional data for the worst future request. In order to share a VOD server's limited network bandwidth efficiently, this paper proposes Practical Patching that removes the unnecessary data included in the transition stream. The proposed Practical Patching dynamically expands ongoing transition streams when a new request actually arrives at the server. As a result, the transition streams never have unnecessary data. Simulation result confirmed that the proposed technique is better than Recursive Patching in terms of service latency and defection rate.

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Development of k-$\epsilon$ model for prediction of transition in flat plate under free stream with high intensity (고난류강도 자유유동에서 평판 경계층 천이의 예측을 위한 난류 모형 개발)

  • Baek, Seong Gu;Lim, Hyo Jae;Chung, Myung Kyoon
    • 유체기계공업학회:학술대회논문집
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    • 2000.12a
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    • pp.337-344
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    • 2000
  • A modified k-$\epsilon$ model is proposed for calculation of transitional boundary layer flows. In order to develop the eddy viscosity model for the problem, the flow is divided into three regions; namely, pre-transition region, transition region and fully turbulent region. The pre-transition eddy-viscosity is formulated by extending the mixing Length concept. In the transition region, the eddy-viscosity model employs two length scales, i.e., pre-transition length scale and turbulent length scale pertaining to the regions upstream and the downstream, respectively, and a university model of stream-wise intermittency variation is used as a function bridging the pre-transition region and the fully turbulent region. The proposed model is applied to calculate three benchmark cases of the transitional boundary layer flows with different free-stream turbulent intensity ( $1\%{\~}6\%$ ) under zero-pressure gradient. It was found that the profiles of mom velocity and turbulent intensity, local maximum of velocity fluctuations, their locations as well as the stream-wise variation of integral properties such as skin friction, shape factor and maximum velocity fluctuations are very satisfactorily Predicted throughout the flow regions.

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Multimode Boundary-Layer Transition on an Airfoil Influenced by Periodically Passing Wake under the Free-stream Turbulence (자유유동 난류 하의 주기적 통과 후류의 영향을 받는 익형 위 경계층 천이)

  • Park Tae-Choon;Jeon Woo-Pyung;Kang Shin-Hyoung
    • Proceedings of the KSME Conference
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    • 2002.08a
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    • pp.687-690
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    • 2002
  • Multimode boundary-layer transition on a NACA0012 airfoil is experimentally investigated under periodically passing wakes and the moderate level of free-stream turbulence. The periodic wakes are generated by rotating circular cylinders clockwise or counterclockwise around the airfoil. The free-stream turbulence is produced by a grid upstream of the rotating cylinder, and its intensity(Tu) at the leading edge of the airfoil is $0.5\;or\;3.5\;{\%}$. The Reynolds number ($Re_c$) based on chord length (C) of the alrfoil is $2.0{\times}10^5$, and Strouhal number ($St_c$) of the passing wake is about 0.7. Time- and phase-averaged streamwise mean velocities and turbulence fluctuations are measured with a single hot-wire probe, and especially, the corresponding wall skin friction is evaluated using a computational Preston tube method. The wake-passing orientation changes pressure distribution on the airfoil in a different manner irrespective of the free-stream turbulence. Regardless of free-stream turbulence level, turbulent patches for the receding wakes propagate more rapidly than those for the approaching wake because adverse pressure gradient becomes larger. The patch under the high free-stream turbulence ($Tu=3.5{\%}$) grows more greatly in laminar-like regions compared with that under the low background turbulence ($Tu=0.5{\%}$) in laminar regions. The former, however, does not greatly change the original turbulence level in the very near-wall region while the latter does it. At further downstream, the former interacts vigorously with high environmental turbulence inside the pre-existing transitional boundary layer and gradually lose his identification, whereas the latter keep growing in the laminar boundary layer. The calmed region is more clearly observed under the lower free-stream turbulence level and for the receding wakes. The calmed region delays the breakdown further downstream and stabilizes more the boundary layer.

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Prediction of Bypass Transition Flow on Surface with Changing Pressure Gradient (압력구배가 변하는 표면 위의 Bypass 천이 유동의 예측)

  • Baek-Seong-Gu;Chung, Myung-Kyoon;Lim, Hyo-Jae
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.26 no.6
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    • pp.823-832
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    • 2002
  • A modified $textsc{k}$-$\varepsilon$model is proposed for calculation of transitional boundary-layer flows with changing pressure gradient. In order to develop the model for this problem, the flow is divided into three regions; pre-transition region, transition region and fully turbulent region. The effect of pressure gradient is taken into account in stream-wise intermittency factor, which bridges the eddy-viscosity models in the pre-transition region and the fully turbulent region. From intermittency data in various flows, Narashima's intermittency function, F(${\gamma}$), has been found to be proportional to $\chi$$^{n}$ according to the extent of pressure gradient. Three empirical correlations of intermittency factor being analyzed, the best one was chosen to calculate three benchmark cases of bypass transition flows with different free-stream turbulence intensity under arbitrary pressure gradient. It was found that the variations of skin friction and shape factor as well as the profiles of mean velocity in the transition region were very satisfactorily predicted.

A New k-$\varepsilon$ Model for Prediction of Transitional Boundary-Layer Under Zero-Pressure Gradient (압력 구배가 없는 평판 천이 경계층 유동을 예측하기 위한 k-$\varepsilon$모형의 개발)

  • Baek, Seong-Gu;Im, Hyo-Jae;Jeong, Myeong-Gyun
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.25 no.3
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    • pp.305-314
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    • 2001
  • A modified model is proposed for calculation of transitional boundary layer flows. In order to develop the eddy viscosity model for the problem, the flow is divided into three regions; namely, pre-transition region, transition region and fully turbulent region. The pre-transition eddy-viscosity is formulated by extending the mixing length concept. In the transition region, the eddy-viscosity model employs two length scales, i.e., pre-transition length scale and turbulent length scale pertaining to the regions upstream and the downstream, respectively, and a universal model of stream-wise intermittency variation is used as a function bridging the pre-transition region and the fully turbulent region. The proposed model is applied to calculate three benchmark cases of the transitional boundary layer flows with different free-stream turbulent intensity (1%∼6%) under zero-pressure gradient. It was found that the profiles of mean velocity and turbulent intensity, local maximum of velocity fluctuations, their locations as well as the stream-wise variation of integral properties such as skin friction, shape factor and maximum velocity fluctuations are very satisfactorily predicted throughout the flow regions.

Wake-Induced Boundary Layer Transition on an Airfoil at Moderate Free-Stream Turbulence (자유유동 난류강도에 따른 익형 위 후류유도 경계층 천이의 거동)

  • Park, Tae-Choon;Kang, Shin-Hyoung;Jeon, Woo-Pyung
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.30 no.9 s.252
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    • pp.921-928
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    • 2006
  • Wake-induced boundary-layer transition on a NACA0012 airfoil with zero angle of attack is experimentally investigated in periodically passing wakes under the moderate level of free-stream turbulence. The periodic wakes are generated by rotating circular cylinders clockwise or counterclockwise around the airfoil. The free-stream turbulence is produced by a grid upstream of the rotating cylinder, and its intensities $(Tu_{\infty})$ at the leading edge of the airfoil are 0.5 and 3.5%, respectively. The Reynolds number (Rec) based on chord length (C) of the airfoil is $2.0{\times}10^5$, and Strouhal number (Stc) of the passing wake is about 1.4. Time- and phase-averaged streamwise mean velocities and turbulence fluctuations are measured with a single hot-wire probe, and especially, the corresponding wall skin friction is evaluated using a computational Preston tube method. The patch under the high free-stream turbulence $(Tu_{\infty}=3.5%)$ grows more greatly in laminar-like regions compared with that under the low turbulence $(Tu_{\infty}=0.5%)$ in laminar regions. The former, however, does not greatly change the turbulence level in very near-wall region while the latter does it. At further downstream, the former interacts vigorously with high environmental turbulence inside the pre-existing transitional boundary layer and gradually loses its identification, whereas the latter keeps growing in the laminar boundary layer. The calmed region is more clearly observed under the lower free-stream turbulence level and with the receding wakes.

Suppression of Wake Transition and Occurrence of Lock-on Downstream of a Circular Cylinder in a Perturbed Flow in the A-mode Instability Regime (A-mode 불안정성 영역에서 교란유동장에 놓인 원형실린더 후류의 천이지연과 유동공진의 발생)

  • Kim, Soo-Hyeon;Bae, Joong-Hun;Yoo, Jung-Yul
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.31 no.8
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    • pp.702-710
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    • 2007
  • Direct numerical simulation (DNS) is performed to investigate suppressed wake transition and occurrence of lock-on in the wake of a circular cylinder disturbed by sinusoidal perturbation at the Reynolds number of 220 (A-mode instability regime). The sinusoidal perturbation, of which the frequency is near twice the natural shedding frequency, is superimposed on the free stream velocity. It is shown that the wake transition behind the circular cylinder can be suppressed due to the perturbation of the free stream velocity. This change causes a jump in the Strouhal number from the value corresponding to A-mode instability regime to the value corresponding to retarded wake transition regime (extrapolated from laminar shedding regime) in the Strouhal-Reynolds number relationship. As a result, vortex shedding frequency is locked on the perturbation frequency depending not on the natural shedding frequency but on the modified shedding frequency.

Aero-Optical Diagnostic Technique for the Hypersonic Boundary Layer Transition on a Flat Plate

  • Li, Ruiqu;Gong, Jian;Bi, Zhixian;Ma, Handong
    • International Journal of Aerospace System Engineering
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    • v.2 no.2
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    • pp.6-9
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    • 2015
  • A new cross disciplinary conception of transitional aero-optics is built up during analyzing and measuring the linkage between the hypersonic boundary layer transition on a flat plate and the jittering characteristics of the small-aperture beam through that boundary layer. Based on that conception, the Small-Aperture Beam Technique (SABT) and high-speed Imaging Camera System (ICS) used in aero-optical studies are considered as new techniques for the assessment of the hypersonic transition in the boundary layer on a flat plate. In the FD-20 gun tunnel, for the free stream parameters with Mach number of 8 and unit Reynolds number of $1{\times}10^7$ (1/m), those two optical techniques are used to measure the jitter of the small-aperture beam. At the same free stream parameters, the distribution of the heat transfer along the centerline of the flat plate is also measured by the thin film resistance gauge technique. The results show the similarity of the increase trend between the heat transfer and the jitter of the small-aperture beam in the transitional region. It helps us to surmise that it may be feasible to diagnose the transition in a hypersonic boundary layer on a flat plate by means of those above optical techniques.

The transition of successive traditional pharmacological theory (역대(歷代) 전통약리학설(傳統藥理學說)의 변천(變遷))

  • Kim, Nam-Il
    • Korean Journal of Oriental Medicine
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    • v.11 no.1
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    • pp.33-42
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    • 2005
  • Traditional pharmacological theory was not built in a day. It had been changing in the past, still changing in the present day and will be changing in the future. The transition was made by criticism, modification and complements through countless debates. Therefore, we can learn the systematic stream of traditional pharmacology and logical construction and make an estimate of the changes in the future, by looking at the debates and the transition of pharmacological theory.

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