• 대한기계학회논문집
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• 제15권2호
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• pp.677-684
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• 1991

A numerical analysis is performed about the effects of aspect ratio on natural convective heat transfer from a vertical isothermal cylinder of 0.deg. C immersed in cold pure water. The results of analysis include velocity profiles, temperature profiles and mean Nusselt number of the steady flow region. As aspect ratio of vertical cylinder increases, the flow and heat transfer characteristics of vertical isothermal cylinder approach to those of vertical isothermal flat plate. Numerical solutions obtained for Rayleigh number and aspect ratio indicate the cylinders can be classified as short cylinder and long cylinder. In the cases of short cylinder and long cylinder, new heat transfer correlations are presented. Here, the coefficient values C of new heat transfer correlations are presented as the function of density extremum parameter $R^*/. Numerical results show that theoretical results are in close agreement with experimental results.ts.

• 한국소음진동공학회논문집
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• 제27권2호
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• pp.234-242
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• 2017

단순지지-자유 경계조건과 좁은 슬롯을 포함한 짧은 후판 실린더의 음향방사 특성을 검토하였다. 유한요소 해석을 통해 얻어진 샘플 실린더(슬롯 포함)의 진동 모드를 동일한 치수의 슬롯이 없는 균일 실린더의 진동 모드들의 선형 합으로 근사화하였다. 이렇게 얻어진 근사적인 진동 모드를 기준으로 (1) 레일리 적분을 이용한 직접 계산, (2) 균일 실린더의 음향 모드들을 이용한 모드전개법 등 두 방법을 적용하여 샘플 실린더의 음향 모드들을 정의하였다. 이 결과를 이용하여 음향파워, 최대음압, 지향성 선도 등 부가적인 특성을 계산한 다음, 전체 결과를 경계요소법을 이용한 수치해석 결과와 비교하여 검증하였다. 이 결과를 바탕으로, 제시된 두 가지 방법을 이용하여 짧은 비대칭 후판 실린더의 음향방사 특성을 비교적 정확하게 예측할 수 있음을 알 수 있다. 이 방법들은 다른 형태의 비대칭성 및 경계조건을 가진 실린더에도 확대 적용 가능할 것으로 판단되며 이를 통해 실린더 형태의 실제 부품들에서 방사되는 소음을 저감방안 도출도 가능할 것으로 기대된다.

• 한국자동차공학회논문집
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• 제5권4호
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• pp.219-224
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• 1997

A transient short-hot-wire technique has been presented for simultaneous measurements of the thermal conductivity and diffusivity of fluids under the microgravity condition. Two-dimensional heat conduction equations for concentric cylinders with various radius ration and length-diameter ratio have been solved numerically by taking account of the heat capacity of the inner cylinder. A unique relation between the non-dimensional temperature of inner cylinder and Fourier number is obtained for a wide range of thermal properties of the fluids, because the relation if found to be almost independent of these properties. Then the characteristic could be utilized as a masterplot to evaluate both the thermal conductivity and diffusivity. In principle, this method is proved to have an error within 1% for both of these properties.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2002년도 춘계학술대회 논문집
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• pp.435-439
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• 2002

In the pneumatic system, pneumatic cylinder is wildly used to factory automation. In general, Pneumatic cylinder problems are occured with colliding to stroke end part at which piston collide to end-cap, head cap and tube when piston is loading. This appearances have a short life of cylinder and is due to system destruction. This study examines the dynamic characteristics of pneumatic cushioning cylinder and cushion sleeve design. At head part cushion chamber for the vertical experimental, The decisions of cushioning effect and the results of the experimental research are obtained to the followings: i) The cushioning effects could acqure to the reserch, if the compressible energy is more than kinetic ones. ii) The collision of piston and head cover could acqure to the research, if the kinetic energy is more than compressible iii) If the load increase to the rolling car, the cushion region pressures would increase and the dynamic force.

• 한국자동차공학회논문집
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• 제9권3호
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• pp.9-17
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• 2001

This paper is the second of 3 companion papers which investigate axial stratification process. In-cylinder fuel behavior has been investigated in the port injected Sl engine by visualizing for the purpose of understanding stratification. Planar laser light sheet from an Nd:YAG laser has been illuminated through the transparent quartz cylinder of the single cylinder optical engine and the Mie scattered light has been captured through the quartz window in the piston head with an ICCD camera. Fuel has been replaced with an air-ethanol mixture to utilize atomized fuel spray fur the visualization purposes. This results have been compared with steady flow concentration measurement. For low/medium swirl port, the early injection makes such a fuel distribution state that is upper-rich, middle-lean and lower-rich along the combustion chamber and cylinder by tumbling motion. On the other hand, the late injection induces upper-rich, middle-lean and lower-rich state due to the short fuel penetration.

• International Journal of Automotive Technology
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• 제6권1호
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• pp.1-8
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• 2005

Recently, the HSDI (High Speed Direct Injection) diesel engine has been spotlighted as a next generation engine because it has a good potential for high thermal efficiency and fuel economy. This study was carried out to investigate the in-cylinder flow characteristics generated in a HSDI diesel engine with a 4-valve type cylinder head. The four kinds of cylinder head were manufactured to elucidate the effect of intake port geometry on the in-cylinder flow characteristics. The steady flow characteristics such as coefficient of flow rate $(C_{f})$, swirl ratio (Rs), and mass flow rate (m,) were measured by the steady flow test rig and the unsteady flow velocity within a cylinder was measured by PIV. In addition, the in-cylinder flow patterns were visualized by the visualization experiment and these results were compared with simulation results calculated by the commercial CFD code. The steady flow test results indicated that the mass flow rate of the cylinder head with a short distance between the two intake ports is $13\%$ more than that of the other head. However, the non-dimensional swirl ratio is decreased by approximately $15\%$. As a result of in-cylinder flow characteristics obtained by PIV and CFD calculation, we found that the swirl center was eccentric from the cylinder center and the position of swirl center was changed with crank angle. As the piston moves to near the TDC, the swirl center corresponded to the cylinder center and the velocity distribution became uniform. In addition, the results of the calculation are in good agreement with the experimental results.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.1303-1308
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• 2008

In this study, we researched how to estimate life-stress relationship and acceleration factor through performing accelerated life test and analyzing it. The purpose of this study is to predict life of pneumatic cylinder within short time which is widely used in automation manufacturing line. In design of accelerated life test, we selected operating pressure and load that have the most influence on main failure mode of pneumatic cylinder as accelerated factor. We used two-way factorial design for arranging of test condition to accelerated factor and accelerated level.

• 한국해양공학회지
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• 제37권6호
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• pp.225-237
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• 2023

In this study, numerical simulations for a single fixed truncated circular cylinder in regular waves were conducted to investigate the nonlinear wave run-up under various dampers and wave period conditions. The present study used the volume of fluid (VOF) technique to capture the air-water interface. The unsteady Reynolds-averaged Navier-Stokes (URANS) equation with the k- 𝜖 turbulence model was solved using the commercial computational fluid dynamics (CFD) software STAR-CCM+. First, a systematic spatial convergence study was conducted to assess the performance and precision of the present numerical wave tank. The numerical scheme was validated by comparing the numerical results of wave run-up on a bare truncated cylinder with the experimental results, and a good agreement was achieved. Then, a series of parametric studies were carried out to examine the wave run-up time series around the truncated cylinder with single and dual dampers in terms of the first- and second-order harmonic and mean set-up components. Additionally, the local wave field and the flow velocity vectors adjacent to the cylinder were evaluated. It was confirmed that under short wave conditions, the high position of the damper led to a noticeable increase in the wave run-ups with significant changes in the first- and second-order harmonic components.

• 대한조선학회논문집
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• 제50권2호
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• pp.111-119
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• 2013

The concept of the natural frequency is useful for understanding the characters of oscillating systems. However, when a circular cylinder floating horizontally on the water surface is heaving, due to the hydrodynamic forces, the system is not governed by the equation like that of the harmonic one. In this paper, in order to shed some lights on the more correct use of the concept of the natural frequency, a problem of the heaving circular cylinder is analyzed in the frequency domain. Previously, it was thought that the theory of Ursell (1949) could not be used to get the added mass and wave-making damping for short waves, however, they were obtained by applying an accurate collocation method to the theory in this study. Using the so developed numerical method, we found the added mass and wave-making damping of the circular cylinder for the entire range of the frequency. Then, the MCFR(Modulus of Complex Frequency Response) was used to locate the frequency corresponding to the local maximum of MCFR and we define it as the natural frequency. Comparing our results with the previous investigation, we found that the pressure distribution on the cylinder gets close asymptotically to that of a cylinder in infinite fluid OR close to that of the cylinder, that the approximation of the natural frequency by Lee (2008) is different from our new value only by 0.64%, and that the approximation of the heaving system by an equivalent damped harmonic oscillation is not proper by the reason that is clearly shown from the comparison of the shape of the corresponding MCFRs.

• 한국자동차공학회논문집
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• 제2권5호
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• pp.66-73
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• 1994

The configuration effects of a tumble adaptor which transforms tumble into swirl on the intake tumble characterization under steady flow condition have been investigated by LDV measurement The following parameters were involved to test their effects on tumble-swirl conversion characteristics ; the cylinder height and its bottom shape, measuring position in the swirl induction pipe, and the relative direction of the induction pipe. The short cylinder height and the flat bottom of the tumble adaptor were found effective for the generation of tumble in the cylinder, allowing higher tumble-swirl conversion efficiency.