• 한국분무공학회지
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• 제1권2호
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• pp.16-23
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• 1996

In case of a high-speed D.I. diesel engine. the injected fuel spray is unavoidable that the impinging on the wall of piston cavity and in this case the geometry of piston cavity has a great influence on the atomization structure and air flow fields. In the field of combustion and in many other spray applications, there are clear evidence of correlation between spray structure and emission of pollutants. Ordinary, the combustion chamber of driving engine have unsteady turbulent flow be attendant on such as the change of temperature, velocity and pressure. So the analysis of spray behavior is difficult. In this study, a single spray was impinged on each cavity wall at indicated angle in a quiescent atmosphere at room temperature and pressure, as being the simplest case, and 3 types of piston cavity such as Dish, Toroidal and Re-entrant type was tested for analyzing the influence of cavity geometry. And hot wire probe was used for analyze non-steady flow characteristics of impinging spray, and to investigate the behavior of spray, the aspects of concentration c(t), standard deviation $\sigma(t)$ and variation factor (v.f.) was measured with the lapse of time.

• 대한기계학회논문집B
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• 제21권1호
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• pp.140-152
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• 1997

A simultaneous measurement of the wall skin friction and near-wall streamwise velocity fluctuations is performed using hot film and hot wire anemometers to investigate the relation between them. Near-wall turbulence statistics measured with a hot-wire probe are in good agreement with previous results. Turbulence properties of the wall skin friction fluctuations measured with a hot film also show fairly good agreements with those measured by others except that rms level is lower in the present study. Long-time averaged space- time correlations show that the wall skin friction is highly correlated with a turbulence structure which is tilted from the wall in the streamwise direction. Tilting angles are obtained from the phase shifts between the wall skin-friction and streamwise velocity fluctuations. The convection velocity of the near-wall streamwise velocity obtained from the space-time correlation is in good agreement with that from the direct numerical simulation database.

• 대한기계학회논문집B
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• 제31권8호
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• pp.718-723
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• 2007

The new concept spark plug was developed to study its influence on the combustion characteristics of SI engine. It has pre-ignition chamber in the lower end of spark plug and flame hole, in which fresh mixture gas can be introduced without any fuel supply system. This spark plug was tested with a commercial SI engine. Fuel consumption rate, emission gas and MBT timing were measured in the engine dynamometer for various flame hole numbers, hole positions, hole sizes of the pre-ignition chamber of the spark plug. And average flame propagation speed was measured by using the head gasket ionization probe in single cylinder engine. The new concept spark plug induces fast bum in combustion compared with the conventional spark plug, and MBT(Minimum advance for Best Torque) timing was retarded about $3{\sim}5^{\circ}$ crank angle. The flame hole number, hole direction and volume of pre-ignition chamber were found to influence the combustion characteristics.

• 한국가시화정보학회지
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• 제1권1호
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• pp.64-74
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• 2003

An experimental study was carried out to investigate the effect of periodic blowing and suction on a turbulent boundary layer. Particle image velocimetry (PIV) was used to probe the characteristics of the flow. The local forcing was introduced to the boundary layer via a sinusoidally-oscillating jet issuing from a thin spanwise slot. Three forcing frequencies (f$^{+}$=0.044, 0.066 and 0.088) with a fixed forcing amplitude (A$^{+}$=0.6) were employed at $Re_{=690. The effect of the forcing angles ($\alpha$=60$^{\circ}$ , 90$^{\circ}$ and 120$^{\circ}$ ) was investigated under the fixed forcing frequency (f$^{+}$=0.088). The PIV results showed that the wall region velocity decreases on imposition of the local forcing. Inspection of phase-averaged velocity profiles revealed that spanwise large-scale vortices were generated in the downstream of the slot and persist further downstream. The highest reduction in skin friction was achieved at highest forcing frequency (f$^{+}$=0.088) and a forcing angle of $\alpha$=120$^{\circ}$. The spatial fraction of the vortices was examined to analyze the skin friction reduction.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.1228-1231
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• 2005

This paper reports about the development of scanning probe microscopy (SPM) tip with multi-walled carbon nanotube (MWNT). For making a carbon nanotube (CNT) modified tips, AC electric field which causes the dielectrophoresis was used for alignment and deposition of CNTs to the metal coated SPM tip. By dropping the MWNT solution and applying an electric field between an SPM tip and an electrode, MWNTs which were dispersed into a diluted solution were directly assembled onto the apex of the SPM tips due to the attraction by the dielectrophoretic force. In this paper, we investigate experimental conditions about the alignment of the CNT to tip axis according to the change of the angle between a tip and an electrode. Experimental results are presented, and then fabricated CNT tips are showed and measurement results for 15nm gold particles are compared with that of the conventional silicon tip.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2011년도 한국우주과학회보 제20권1호
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• pp.31.4-32
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• 2011

The previous KRISS profilometer design used an aluminum profile structure to which a bar-type reference mirror subsystem and the measurement subsystem are mounted. The earlier design suffers from low stiffness as shown from the first resonance mode of 45.1 Hz. The improved mechanical design we describe in this study replaces the aluminium profile structure with a granite structure of $1340{\times}220{\times}230$ in dimension. The finite element analysis results for the revised design show 0.001 degree in probe contact angle variation. The first resonance mode was computed to 91.2 Hz that is much better than 45.1 Hz from the previous design. We describe the improved design, structural analysis results and how these results would satisfy the form accuracy requirement of 1 ${\mu}m$ PV.

• 전기학회논문지P
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• 제59권2호
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• pp.222-231
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• 2010

This paper presents numerical analysis of measurement errors of ground electrode using the fall-of-potential method. In order to analyze ground resistance error according to the positions of auxiliary probes, firstly, national and international standards were researched. Secondly, numerical ground resistance error of hemispheric electrode was analyzed according to the locations of auxiliary probes and the angle between probes. Then, error-reduced positions of auxiliary probes were shown according to the distance to auxiliary current probe versus ground electrode size. Finally, error compensation method was presented. The results presented in this paper provide useful information regarding ground resistance error of alternative positions of auxiliary probes in case that the auxiliary probes could not be located at the proper position in such cases as there are buildings, roadblock or underground metallic pipe at that position.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.333-333
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• 2013

The poor conductivity of poly (3,4-ethylene dioxythiophene): poly (styrenesulfonate) (PEDOT:PSS) film hinders to use for a flexible electrode in solar cells. In this report we demonstrate that the conductivity of PEDOT:PSS film can be enhanced by modifying structures in a mixture of PEDOT: PSS aqueous solution and various organic solvents such as polar protic (2-propanol, methanol, ethanol, formic acid) and aprotic solvents (acetone and acetonitrile). To comparatively study the structural effects on the resulted electrical properties, the films are spin-coated on glasses and ITO. At the same time, a contact angle goniometer is used for clarifying a mechanism of wettability of PEDOT (hydrophobic) and PSS (hydrophilic) on the observed conductivity. The structures and electrical properties are investigated by FE-SEM (Field Emission Scanning Electron Microscopy), AFM (Atomic Force Microscopy), and 4-point probe, respectively.

• Biotechnology and Bioprocess Engineering:BBE
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• 제8권4호
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• pp.227-232
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• 2003

A self-assembled monolayer of protein G was fabricated to develop an immunosensor based on surface plasmon resonance (SPR), thereby improving the performance of the antibodybased biosensor through immobilizing the antibody molecules (lgG). As such, 11-mercaptoundecanoic acid (11-MUA) was adsorbed on a gold (Au) support, while the non-reactive hydrophilic surface was changed through substituting the carboxylic acid group (-COOH) in the 11-MUA molecule using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrocholide (EDAC). The formation of the self-assembled protein G layer on the Au substrate and binding of the antibody and antigen were investigated using SPR spectroscopy, while the surface topographies of the fabricated thin films were analyzed using atomic force microscopy (AFM). A fabricated monoclonal antibody (Mab) layer was applied for detecting E. coli O157:H7. As a result, a linear relationship was achieved between the pathogen concentration and the SPR angle shift, plus the detection limit was enhanced up to 10$^2$ CFU/mL.

• 전기학회논문지
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• 제64권1호
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• pp.188-195
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• 2015

This paper presents measurement error reduction technique of touch and step voltage of grounding system based on numerical analysis. When measuring touch and step voltage of grounding system, auxiliary current probes should be located at suitable places. However, the auxiliary probes can not be located at suitable places in such cases as there are buildings and pavements. Therefore, in this paper, we provided measurement error reduction technique of touch and step voltage of grounding system according to the positions of auxiliary probes and angle between auxiliary probes. Also, measurement error analyses of touch and step voltage of grounding system have been conducted using more than one current probe. Based on these analyses, recommended positions of auxiliary probes within allowable measurement errors were presented.