• 한국정밀공학회지
• /
• 제17권9호
• /
• pp.145-150
• /
• 2000

Out-of-sphericity is degree of deformation of an air bearing sphere deviated from a perfect sphere. This paper investigates numerically the effect of out-of-sphericity error on the radial stiffness of an air bearing Three types of out-of-sphericity modes are considered. in this study the stiffness is calculated from pressure distribution at the bearing surface which is obtained by solving th Reynolds equation. in some cases large out-of-sphericity errors are found to improve the stiffnesses of air bearings. This implies that an air bearing of perfect hemispheres is not necessarily of the best performance. Thus much labor and cost in manufacturing air bearings can be saved, In addition the radial stiffness of an air bearing depends greatly on the application direction.

• Journal of the Korean Wood Science and Technology
• /
• 제27권4호
• /
• pp.15-19
• /
• 1999

Three wood coffins of Chosun Dynasty period buried about 450 years ago were excavated in the sound condition in Andong area in the early 1998. The proprietors of wood coffins were grandparents, Mr. Myoung Jong Lee and Mrs. Mun, and their grandson, Mr. Eung Tae Lee, and the social standing of their family was known to belong to the nobility in those days by the clan genealogy. All the wood coffins investigated through light microscopy had same anatomical characteristics as follows: abrupt to somewhat abrupt tracheid transition from earlywood to latewood; normal longitudinal and horizontal resin canals with thin-walled epithelium; tylosoids in resin canals; bordered pits frequently in 1 row on radial walls of tracheids; 1 or 2 window-like pits per cross-field; uniseriate and fusiform rays; heterogeneous rays composed of body ray parenchyma cells and marginal ray tracheids or homgeneous rays composed of only ray tracheids; dentate ray tracheids; occasional trabeculae traversing tracheids in radial direction. Based on theses microscopic characteristics, all the wood coffins were identified to be Korean red pine (Pinus densiflora) or Korean black pine (Pinus thunbergii). Korean black pine growing naturally in coastal area might not be probable because the site of excavation, Andong area, was mountainous and inland area of Korea Thus, Korean red pine was thought to be the possible species for the wood coffins because of its natural distribution through the Korean Peninsula and the easy availability.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2003년도 추계학술대회
• /
• pp.1121-1126
• /
• 2003

Strength evaluation was carried out for the fillet and oil hole of crankshaft of medium speed diesel HiMSEN engine to verify initial concept design. Alternating torque obtained from torsional vibration analysis and radial force due to firing pressure were applied. It was assumed that the maximum alternating torque and radial force occur simultaneously. Weak points in view of fatigue are proceeding fillet and crank pin fillet area and the minimum normalized fatigue safety factor is 1.17 at crank pin fillet. The fatigue strength of the oil hole was evaluated to verify the effect of the surface roughness of the oil hole. As results, the specific level of the inner surface roughness and the polishing depth of the oil hole for sufficient fatigue strength was suggested. The maximum stress value and stress distribution at the inner surface of the oil hole can be easily estimated at initial design stage by the newly developed method.

• 한국생산제조학회지
• /
• 제21권3호
• /
• pp.401-407
• /
• 2012

The recent manufacturing process in the thin wafers and flat panel necessitate new approaches to reduce handling fragile and surface-sensitive damage of components. This paper presents a new pneumatic levitation for non-contact handling of parts and substrates. This levitation can achieve non-contact handling by blowing air into an air pressure pick-up head with radial passages to generate a negative pressure region. Negative pressure is caused by the radial air flow by nozzle throat and through holes connecting to the bottom region. The numerical analysis deals with the levitational motion with different design factors. The dynamic motion is examined in terms of force balance(dynamic equilibrium) occurring to the flow field between two objects. The stable equilibrium position and the safe separation distance are determined by analyzing the local pressure distribution in the fluid motion. They make considerable design factors consisting the air pressure pick-up head. As a result, in case that the safe separation distance is beyond 0.7mm, the proposed pick-up head can levitate stably at the equilibrium position. Furthermore, it can provide little effect of torque, and obtain more wide picking region according to the head size.

• 한국자동차공학회논문집
• /
• 제12권4호
• /
• pp.1-11
• /
• 2004

Combustion and fuel distribution characteristics of heavy duty engine with the liquid phase LPG injection(LPLI) were studied in a single cylinder engine, Swirl ratio were varied between 1.2, 2.3, and 3.4 following Ricardo swirl number(Rs) definition, Rs=2.3 showed the best results with lower cycle-by-cycle variation and shorter burning duration in the lean region while strong swirl(Rs=3.4) made these worse for combustion enhancement. Excessive swirl resulted in reverse effects due to high heat transfer and initial flame kernel quenching. Fuel injection timings were categorized with open valve injection(OVI) and closed valve injection(CVI). Open valve injection showed shorter combustion duration and extended lean limit. The formation of rich mixture in the spark plug vicinity was achieved by open valve injection. With higher swirl strength(Rs=3.4) and open valve injection, the cloud of fuel followed the flow direction and the radial air/fuel mixing was limited by strong swirl flow. It was expected that axial stratification was maintained with open-valve injection if the radial component of the swirling motion was stronger than the axial components. The axial fuel stratification and concentration were sensitive to fuel injection timing in case of Rs=3.4 while those were relatively independent of the injection timing in case of Rs=2.3.

• Korea-Australia Rheology Journal
• /
• 제19권2호
• /
• pp.89-95
• /
• 2007

The flow characteristics of chicken blood in a micro-tube with a $100{\mu}m$ diameter are investigated using a micro-Particle Image Velocimetry (PIV) technique. Chicken blood with 40% hematocrit is supplied into the micro-tube using a syringe pump. For comparison, the same experiments are repeated for human blood with 40% hematocrit. Chicken blood flow has a cell-free layer near the tube wall, and this layer's thickness increases with the increased flow speed due to radial migration. As a hemorheological feature, the aggregation index of chicken blood is about 50% less than that of human blood. Therefore, the non-Newtonian fluid features of chicken blood are not very remarkable compared with those of human blood. As the flow rate increases, the blunt velocity profile in the central region of the micro-tube sharpens, and the parabolicshaped shear stress distribution becomes to have a linear profile. The viscosity of both blood samples in a low shear rate condition is overestimated, while the viscosity in a high shear rate range is underestimated due to radial migration and the presence of a cell-depleted layer.

• 유체기계공업학회:학술대회논문집
• /
• 유체기계공업학회 2004년도 유체기계 연구개발 발표회 논문집
• /
• pp.225-231
• /
• 2004

Scroll compressor has been used extensively for refrigeration since the early 1980's for its improved efficiency, greater reliability, smoother operation, lower noise and vibration. And also, nowadays, the scroll mechanism is used for expander even though in niche market yet. But scroll expander has not been used for high-temperature and high-pressure gas, because the continuous expansion of the gas causes a wide range of temperature distribution over the whole scroll wrap that leads to differential thermal expansion of scroll elements, which results in system vibrations, noise and efficiency losses. For the scroll expander to produce power more efficiently, all of radial and radial clearances between scroll wrap must be the same. In order to reduce differential thermal expansion in addition to improvements in thermal efficiency and specific power, we propose a scroll expander with heating structure. Heat-pipe heating structure is considered as the most effective method to heat the scroll expander at a uniform temperature. This paper includes some results of preliminary study of the scroll expander with heating structure and proposals of their systems for power generation and refrigeration.

• Animal cells and systems
• /
• 제16권2호
• /
• pp.114-120
• /
• 2012

In echinoderms, the SALMFamide neuropeptides sharing the SxL/FxFamide motif seem widespread throughout the phylum and may be important signalling molecules that mediate various physiological functions. Recent identification of S1 and its analogues, MagS3 and MagS4, along with the S2 analogue, MagS2 from the starfish $Marthasterias$ $glacialis$, indicated that SALMFamides in the class Asteroidea are more diverse than previously thought. Further, isolation of the neuropeptides from the radial nerve cord and studies on pharmacological actions of the neuropeptides on the cardiac stomach warrant studies on the tissue distributions of these peptides in both the nervous and digestive systems. In the present study, antisera raised against an S1 analogue, KYSALMFamide, and an S2 analogue, KYSGLTFamide, were used to localize the distribution patterns of the S1- and S2-like immunoreactivities (S1-IR/S2-IR) in the nervous and digestive systems of the starfish. In the nervous system, cell bodies in the ectoneural part were immunostained for both S1 and S2 peptides, while in the digestive system, the basiepithelial plexus and mucosal cell bodies were immunoreactive. These immunocytochemical data support the notion that the SALMFamides may play a neuroendocrine role in mediating feeding behaviour of the starfish. Further studies including identification of peptide binding sites and differential expression pattern of mRNAs encoding the peptides are required to elucidate their physiological functions.

• 대한용접접합학회:학술대회논문집
• /
• 대한용접접합학회 2005년도 춘계학술발표대회 개요집
• /
• pp.285-287
• /
• 2005

During fabrication of deck house block in passenger ships, the problem of unexpected large deformation and distortion frequently occurs. In this case, line and spot heating method were widely used to correct the distortion of thin plate structure. Spot heating was especially used for the case under 5mm thickness. Few papers are available on the working conditions of spot heating method but only little information on deformation control. In this study, evaluation was carried out on the temperature distribution of spot heating methods using FEA and practical experiments for various heating time. IIn FEA, heat input model was established using Tsuji's double Gaussian heat input mode (Tsuji, I., 1988). This model was verified by comparing with experimental data. Also radial shrinkage and angular distortion due to spot heating were determined and compared with experimental results. Thermo elasto-plastic analysis was performed using commercial FE code, MSC/MARC. Radial shrinkage and angular distortion were measured using 3D measuring apparatus. Based on these results, simplified analysis model for deformation by spot heating was established.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
• /
• 한국우주과학회 2009년도 한국우주과학회보 제18권2호
• /
• pp.29.4-30
• /
• 2009

Extra-tidal feature of the globular clusters such as tidal tails and halos can be a crucial evidence of the merging scenario of the Galaxy formation in the dynamical point of view. To search for such an extra-tidal feature of globular clusters located in the Galactic bulge(RGC<3kpc), we obtained wide-field near-infrared JHKs images of 6 metal-poor ([Fe/H]<-1.0) clusters and 3 metal-rich ([Fe/H]>-1.0) clusters. Observations were carried out using IRSF 1.4m telescope and SIRIUS near-infrared camera, during 2006~2007. The obtained images have a total maximum field-of-view of ~ $21'\times 21'$. To select clusters' member stars and minimize the field star contaminations, we applied CMD masking algorithm. Smoothed surface density contour maps with selected stars for each cluster show overdensity features around the tidal radius and beyond. Also, radial surface density profiles within the tidal radius of the clusters show an overdensity feature as a change of slope of the radial profile. The results add further observational constraints of the formation of the Galactic bulge.