• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.5
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• pp.984-991
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• 1988

Liquid column separation occurs when the valve on the pipeline is closed rapidly in an oil hydraulic system. In this case two-step pressure rise is sometimes observed in a comparatively short pipeline. In this study the two-step pressure rise phenomenon was investigated experimentally and theoretically. The experiments showed that maximum pressure values during two-step pressure rise might exceed extremely the values computed by the theory of rigid-liquid-column separation. So the two-step pressure rise phenomenon appears one of important factors of pipe strength design. From the theoretical considerations based on the experimental and numerical results, the mechanism of two-step pressure rise phenomenon could be explained clearly.

• Applied Biological Chemistry
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• v.39 no.1
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• pp.95-98
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• 1996

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.05a
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• pp.289-292
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• 2008

Highly over-expanded nozzle of the rocket engines will be excited by non-axial forces due to flow separation at sea level operations. Since rocket engines are designed to produce axial thrust to power the vehicle, non-axial static and/or dynamic forces are not desirable. Several engine failures were attributed to the side loads. Present work investigate the unsteady flow in an over-expanded rocket nozzle in order to estimate side load during a shutdown/starting. Numerical computations has been carried out with density based solver on multi-block structured grid. Present solver is explicit in time and unsteady time step is calculated using dual time step approach. AUSMDV is considered as a numerical scheme for the flux calculations. One equation Spalart-Allmaras turbulence model is selected. Results presented here is for two nozzle pressure ratio i.e. 100 and 20. At 100 NPR, restricted shock separation (RSS) pattern is observed while, 20 NPR shows free shock separation (FSS) pattern. Side load is observed during the transition of separation pattern at different NPR.

• Journal of Ocean Engineering and Technology
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• v.15 no.2
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• pp.1-5
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• 2001

A study on the new active type oil-water separation system including the oil-water separation system of magnetic film was carried out. Separation system is composed of several active types of circulating oil separation steps and one magnetic film separation step at final stage. At the magnetic separation step, ferrofluid easily forms a weak magnetic mixture with oil, which is from the water by magnetic field gradient. The vessel has been designed to run at the maximum speed of 25 knots. And two typical forms of SWATH and Catamaran have been studied as a new type of oil recovery vessel.

• Proceedings of the Membrane Society of Korea Conference
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• 1995.04a
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• pp.45-45
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• 1995

Filtration, one of the most important process in the various industrials, is defined as the separation of two or more compounds from a fluid by passing the mixture refers to the separation of solid, immisible particles from liquid or gaseous mixture. Membrane filtration which is a type of filtration extends it's application further to include the separation, concentration, and filtration. The main objective of this investigation is the preparation of organic solvents-resistant polyimide membranes by using phase inversion technique and their application as a UF membrane. Specially, the dope solution was prepared from the newly developed method. The newly developed method is that the dope solution was directly prepared from the polyimide solution which was prepared by the modified one-step polymerization. The effects of the parameters for membrane preparation such as the casting solution composition and the casting conditions were investigated and the performance and chemical stabfiity of membrane are going to be tested.

• Journal of Korean Society for Atmospheric Environment
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• v.9 no.1
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• pp.101-106
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• 1993

In order to separate the Freon-12 and air mixture$(CF_2Cl_2/Air=0.1/99.9 vol.%)$ by pressure swing adsorption (PSA), the breakthrough curve was experimentally observed in a fixed bed adsorption column. A single adsorber was packed with various adsorbents such as, the activated carbon(S-AC, W-AC) and the molecular sieve(MS-5A, MS-13X). The order of appearance of breakthrough curve is MS-5A > MS-13X > W-AC > S-AC. The activated carbon was found to be more effective adsorbent for separating Freon-12 from the mixture than the molecular sieve was. From the experimental data obtained by the separation of Freon-12 gas out of the air stream in the steady-state PSA process cycle, whose size is the same one of column used for the breakthrough curve observation, it has been confirmed that Freon-rich gas could be obtained from the purge step of PSA and Freon-free air could be obtained from the adsorption step of PSA cycle.

• Journal of Microbiology and Biotechnology
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• v.17 no.11
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• pp.1751-1757
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• 2007

Elastin-like polypeptides (ELPs) undergo a reversible inverse phase transition upon a change in temperature. This thermally triggered phase transition allows for a simple and rapid means of purifying a fusion protein. Recovery of ELPs-tagged fusion protein was easily achieved by aggregation, triggered either by raising temperature or by adding salt. In this study, levansucrase has been used as a model enzyme in the development of a simple one-step purification method using ELPs. The levansucrase gene cloned from Pseudomonas aurantiaca S-4380 was tagged with various sizes of ELPs to functionally express and optimize the purification of levansucrase. One of two ELPs, ELP[V-20] or ELP[V-40], was fused at the C-terminus of the levansucrase gene. A levansucrase-ELP fusion protein was expressed in Escherichia coli $DH5{\alpha}$ at $37^{\circ}C$ for 18 h. The molecular masses of levansucrase-ELP[V-20] and levansucrase-ELP[V-40] were determined as 56 kDa and 65 kDa, respectively. The phase transition of levansucrase-ELP[V-20] occurred at $20^{\circ}C$ in 50 mM Tris-Cl (pH 8) buffer with 3 M NaCl added, whereas the phase transition temperature ($T_t$) of levansucrase-ELP[V-40] was $17^{\circ}C$ with 2 M NaCl. Levansucrase was successfully purified using the phase transition characteristics of ELPs, with a recovery yield of higher than 80%, as verified by SDS-PAGE. The specific activity was measured spectrophotometrically to be 173 U/mg and 171 U/mg for levansucrase-ELP[V-20] and levansucrase-ELP[V-40], respectively, implying that the ELP-tagging system provides an efficient one-step separation method for protein purification.

• 한국전산유체공학회:학술대회논문집
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• 2007.10a
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• pp.194-199
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• 2007

IB (immersed boundary) method is one of the prominent tool in computational fluid dynamics for the analysis of flows over complex geometries. The IB technique simplyfies the solution procedure by eliminating the requirement of complex body fitted grids and it is also superior in terms of memory requirement. In this study we have developed numerical code (FOTRAN) for the analysis of 2D flow over a cylinder using IB technique. The code is validated by comparing the wake lengths and separation angles given by Guo et. al. We employed fractional-step procedure for solving the Navier-Stokes equations governing the flow and discrete forcing IB technique for imposing boundary conditions. Also we have developed a 3D code for the backward-facing-step flow and flow over a sphere. The reattachment length in backward-facing-step flow was compared with the one given by Nie and Armaly, which has proven the validity of our code.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.4
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• pp.780-788
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• 1989

An experimental study has been performed to investigate the process from nonequilibrium state to equilibrium state in redeveloping turbulent boundary layer beyond separation-reattachment using pitot tube and hot-wire anemometer. The model sued in the experiment has the form of a backward facing step which is assembled by a two-dimensional 4:1 half elipse and a plate. Measurements are carried out up to a distance of about 50 step height downstream of the step, where the reattachment observed at about x/h=6.5. The profiles of the shape factor H the Clauser parameter G and the coefficient of friction $C^{f}$ exhibited the characteristics similar to those of the equilibrium turbulent boundary layer from x/h=25, and the profiles of the trubulent quantities did from x/h=35. However, the wake region of the boundary layer does not seem to recover the equilibrium turbulent boundary layer even at x/h=50. By considering the distributions of the intermittency factor it has been noted that the turbulence structure changes gradually from a mixing layer to a turbulent boundary layer along downstream direction after reattachment. This becomes clearer as we analyse the one-dimensional energy spectra and the dissipation energy spectra which are measured and caculated at various downstream positions after the backward facing step.p.

• Phonetics and Speech Sciences
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• v.3 no.1
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• pp.87-94
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• 2011

The decision directed (DD) approach is widely used to determine a priori SNR from noisy speech signals. In conventional speech enhancement systems with a DD approach, a priori SNR is estimated by using only the magnitude components and consequently follows a posteriori SNR with one frame delay. We propose a phase-dependent two-step a priori SNR estimator based on the minimum mean square error (MMSE) in the log-mel spectral domain so that we can consider both magnitude and phase information, and it can overcome the performance degradation caused by one frame delay. From the experimental results, the proposed estimator is shown to improve the output SNR of enhanced speech signals by 2.3 dB compared to the conventional DD approach-based system.