• Title/Summary/Keyword: Characteristic Pressure

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CFD Analysis on the 2nd Cylinder Discharge line in Hydrogen Reciprocating Compressor

  • Lee, Gyeong-Hwan;Woo, Ju-Sik;Shin, Yong-Han;Jeong, Hyo-Min;Chung, Han-Shik
    • Journal of Advanced Marine Engineering and Technology
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    • v.34 no.5
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    • pp.695-702
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    • 2010
  • Numerical analysis information will be very useful to improve fluid system. General information about an internal gas flow is presented by numerical analysis approach. Relating with hydrogen compressing system, which have an important role in hydrogen energy utilization, this should be a useful tool to observe the flow quickly and clearly. Flow characteristic analysis, including pressure and turbulence kinetic energy distribution of hydrogen gas coming to the cylinder of a reciprocating compressor are presented in this paper. Suction-passage model is designed based on real model of hydrogen compressor. Pressure boundary conditions are applied considering the real condition of operating system. The result shows pressure and turbulence kinetic energy are not distributed uniformly along the passage of the Hydrogen system. Path line or particles tracks help to demonstrate flow characteristics inside the passage. The existence of vortices and flow direction can be precisely predicted. Based on this result, the design improvement, such as reducing the varying flow parameters and flow reorientation should be done. Consequently, development of the better hydrogen compressing system will be achieved.

Effect of Nozzle Hole Number on Atomization Characteristics of DME Fuel Spray using High Pressure Injector (고압 인젝터의 노즐 홀 수가 DME 연료분무의 미립화 특성에 미치는 영향)

  • Lee, Jongtae;Lee, Sanghoon;Chon, Mun Soo
    • Journal of ILASS-Korea
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    • v.19 no.4
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    • pp.216-220
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    • 2014
  • This paper presents effect of nozzle hole number on atomization characteristic of DME fuel spray using three different type of injector having the hole number of 6, 7 and 8. For this study, PDPA(phase Doppler particle analyzer) experiment was performed in terms of $T_{ASOE}$ under various injection pressure. To compare general trend of atomization characteristic, the law data were ensemble averaged based on $T_{eng}$ of 0.2 ms. Results showed that the droplet diameter in terms of SMD(Sauter Mean Diameter) was reduced as increase in injection pressure. Increasing the number of hole lead to reduce in droplet diameter, but no significant reduction in diameter was observed between hole number of 7 and that of 8. In addition, increasing the number of hole resulted in decrease in droplet velocity which is considered as the effect of reduction in spray momentum due to decreasing of fuel quantity per each hole.

Three-Dimensional Flow Analysis around Rolling Stock with Square Cross Section Using Low Re ${\kappa}-{\epsilon}$ (사각 단면을 갖는 철도차량 주위의 3차원 유동해석)

  • Jang, Yong-Jun
    • Journal of the Korean Society for Railway
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    • v.9 no.6 s.37
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    • pp.772-777
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    • 2006
  • Three-dimensional numerical study is performed for the flow analysis around the rolling stock with square cross section (Mugungwha train model). The height (H) of rolling stock is considered as the characteristic length and the total length of rolling stock is 40 which correspond to 1/2 unit of rolling stock. The gap between the surface and rolling stock is 0.17H which is average value. The relative velocity between the surface and rolling stock is assumed to be zero and Re=10,000 based on the characteristic length. Low Re ${\kappa}-{\epsilon}$[15] is employed for the calculation of turbulence which resolve all the way to the solid surface (laminar sub-layer). Large flow separation occurred at the front head of train and a pair of vortex is generated on both top and side of rolling stock. The behavior of vortices on the top of the rolling stock is believed to affect the performance of the pantograph which should be intensively investigated. The difference between the high pressure in the front stagnation region of train and the low pressure in the rear separated region causes a large pressure drag. A large pair or vortex are generated in the rear of train and the size of vortex is increased more than the size of cross section of train.

Measuring Thresholds of Serum Lipid Level related to Hypertension and Age Using Receiver Operating Characteristic Curve in Korean Adult

  • Kim, Seong-Gil;Park, So-Hyun
    • Journal of the Korean Society of Physical Medicine
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    • v.9 no.3
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    • pp.301-305
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    • 2014
  • PURPOSE: The purpose of this study was to determine the optimal thresholds of serum lipid level related to hypertension according to age in Korean adults. METHODS: In total, 564 adults who visited the health examine center in general hospital were included. The blood pressure and lipid profiles of low density lipoprotein cholesterol(LDL), high density lipoprotein cholesterol (HDL), triglyceride(TG) were measured. Receiver operating characteristic (ROC) curve were used to establish optimal thresholds between blood pressure and lipid profiles. RESULTS: The optimal TG cutoff value were 110.50(mg/dl) in the 18-39 and 81.50(mg/dl) in the 40-59 age group, and optimal cutoff value of LDL were 126.50(mg/dl) in the 40-59 age group and 111.00(mg/dl) in the 60 and over age group. There was a negative correlation between HDL and hypertension, a higher HDL decreased hypertension. The optimal cutoff value of HDL was 49.50(mg/dl) in the 18-39 age group. CONCLUSION: The thresholds of hypertension were lower in LDL and TG with aging. This result indicated that elderly people needs to concern more about their lipid profiles to maintain healthy cardiovascular function.

The Characteristic of a Hydrostatic Extrusion of Magnesium Alloy(AZ31) - II (Mg 합금(AZ31)의 열간 정수압 압출 특성에 관한 연구(II))

  • Seo Y. W.;Jeong H. G.;Na K. H.;Yoon D. J.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2005.05a
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    • pp.144-147
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    • 2005
  • In hydrostatic extrusion the billet in the container is extruded through a die with a liquid acting as a pressure medium, instead of by the direct application of the load by a ram. And the extrusion pressure can be affected by the flow stress and they are affected by the temperature. So in this study the temperature is the main issue with a extrusion ratio and a half die angle. As extrusion temperature goes down from $300^{\circ}C$ to $200^{\circ}C$, tensile strength goes up to 310MPa. Because velocity of extrusion is higher than the conventional extrusion, there is another characteristic in the sense of microstrure. The temperature was sotted to $300^{\circ}C,\;250^{\circ}C,\;200^{\circ}C$, respectively. There is a increase of extrusion pressure abot $15\%$.

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Multidisciplinary Design Optimization for Acoustic Characteristics of a Speaker Diaphragm (스피커 진동판의 음향특성 다분야통합최적설계)

  • Kim, Sung-Kuk;Lee, Tae-Hee;Lee, Surk-Soon
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2004.11a
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    • pp.763-766
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    • 2004
  • Recently, various acoustic artifacts that contains speaker have been produced such as cellular phone. Speaker consists of diaphragm generating sound and coil vibrating diaphragm. Generally, good speaker means that it has a wide frequency range, high output power rate to input power and flat sound pressure level in specified frequency range. Acoustic characteristic was estimated through the experiment and computer simulation, or sound power was controlled with acoustic sensitivity in a natural frequency range fer last decade. However, the flatness of sound pressure level has not been considered to enhance the sound quality of a speaker. Tn this study, a method for speaker design is proposed for a good acoustic characteristic, which is flatness of SPL(sound pressure level) and wideness between the first and second natural frequency. SYSNOISE is used fer acoustic analysis and ANSYS is used for harmonic response analysis and modal analysis. Optimization for acoustic characteristics of a speaker diaphragm is performed using ModelCenter. All analyses are done within a frequency domain. And we confirm that the experimental and computational simulations have similar trend.

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Condensation oscillation characteristic of steam with non-condensable gas through multi-hole sparger at low mass flux

  • Dandi Zhang;Lili Tong;Xuewu Cao
    • Nuclear Engineering and Technology
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    • v.55 no.2
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    • pp.780-791
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    • 2023
  • To study oscillation characteristic of steam and non-condensable gas direct contact condensation through multi-hole sparger at low mass flux, a series of experiments of pure steam and mixture gas condensation have been carried out under the conditions of steam mass flux of 20-120kg/m2s, water temperature of 20-95 ℃ and mass fraction of non-condensable gas of 0-5%. The regime map of pure steam condensation through multi-hole sparger is divided into steam chugging, separated bubble, aggregated bubble and escaping aggregated bubble. The bubbles behavior of synchronization in the same hole columns and desynchronized excitation between different hole columns can be found. The coalescence effect of mixture bubbles increases with water temperature and non-condensable gas content increasing. Pressure oscillation intensity of pure steam condensation first increases and then decreases with water temperature increasing, and increases with steam mass flux increasing. Pressure oscillation intensity of mixture gas condensation decreases with water temperature and non-condensable gas content increasing, which is significantly weaker than that of pure steam condensation. The oscillation dominant frequency decreases with the rise of water temperature and non-condensable gas content. The correlations for oscillation intensity and dominant frequency respectively are developed in pure steam and mixture gas condensation at low mass flux.

Numerical studies of the failure modes of ring-stiffened cylinders under hydrostatic pressure

  • Muttaqie, Teguh;Thang, Do Quang;Prabowo, Aditya Rio;Cho, Sang-Rai;Sohn, Jung Min
    • Structural Engineering and Mechanics
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    • v.70 no.4
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    • pp.431-443
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    • 2019
  • The present paper illustrates a numerical investigation on the failure behaviour of ring-stiffened cylinder subjected to external hydrostatic pressure. The published test data of steel welded ring-stiffened cylinder are surveyed and collected. Eight test models are chosen for the verification of the modelling and FE analyses procedures. The imperfection as the consequences of the fabrication processes, such as initial geometric deformation and residual stresses due to welding and cold forming, which reduced the ultimate strength, are simulated. The results show that the collapse pressure and failure mode predicted by the nonlinear FE analyses agree acceptably with the experimental results. In addition, the failure mode parameter obtained from the characteristic pressure such as interframe buckling pressure known as local buckling pressure, overall buckling pressure, and yield pressure are also examined through the collected data and shows a good correlation. A parametric study is then conducted to confirm the failure progression as the basic parameters such as the shell radius, thickness, overall length of the compartment, and stiffener spacing are varied.