• Title/Summary/Keyword: Pressure

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Application of Pressure Correction Method to CFD Work for 8 Centrifugal Compressor Impellers (압력보정법을 이용한 8개의 원심압축기 임펠러 CFD의 적용 연구)

  • Oh, Jongsik;Ro, SooHyuk;Hyun, YongIk
    • 유체기계공업학회:학술대회논문집
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    • pp.226-235
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    • 2000
  • Two representative finite volume methods, i.e., the time marching method and the pressure correction method, were applied to 8 centrifugal compressor impeller flows, with low to very high level of pressure ratio, among which 7 impellers' experimental performance is given in the open literature. The present study is focused on the prediction differences from both methods, developed by the authors, in the pressure correction method's point of view. In all cases, the time marching method gives a satifactory solution, but the pressure correction method does not. Up to about $18\%$ less level of total-to-total pressure ratio is predicted by the pressure correction method as the level of the impeller pressure ratio increases up to about 10. The drop of total pressure ratio is caused by the underestimation of static pressure rise which seems to be attributed to inappropriate linearization and discretization of the pressure/density coupling terms in the pressure correction equation.

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A study on the effect of injection pressure and ambient pressure for the growth of impinging spray (충돌 분무의 성장에 미치는 분사압과 배압의 영향에 관한 연구)

  • Cha, Geon-Jong;Seo, Gyeong-Il;Kim, Deok-Jul
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.21 no.11
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    • pp.1458-1465
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    • 1997
  • This study investigated the effects of pressure on the growth of an impinging spray. We obtained the frozen images which were scattered by Nd ; YAG laser light (pulse width : 7 ns) using synchronization circuit made in the laboratory. For an impinging spray a growth of the penetration length was progressed with increase of the injection pressure but an ambient pressure restrained its growth. The effect of an ambient pressure on penetration was larger than that of an injection pressure. The pressure ratio had an effect on the penetration growth rate. The thickness growth rate depended on both the injection pressure and the ambient pressure compositively. A lower injection pressure or a higher ambient pressure was required for spatial distribution of impinging spray.

The Effect of Auricular Acupuncture Therapy on Blood Pressure (이침시술이 혈압에 미치는 영향)

  • 이진구;이영구;윤희식
    • The Journal of Korean Medicine
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    • v.24 no.2
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    • pp.12-18
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    • 2003
  • Objectives : Hypertension is very prevalent disease, and causes serious cardiovascular complications. Nowadays optimal hypertension treatment is emphasized to reduce the incidence of cardiovascular complications. Auricular acupuncture therapy is economical, safe and effective. Its clinical application is various, and it can be used to control blood pressure. So The effect of auricular acupuncture therapy was investigated. Daily variation of blood pressure during needle-embedded period and variation of blood pressure by blood pressure classification were observed. Methods : The auricular acupuncture points we used were Gangapjeom (降壓點), Sinmun (神門), Gyogam (交感), Sim(心), and Icheom (耳尖). Auricular acupuncture needles were embedded for three days. Blood pressure was checked four times per day and the mean obtained. Results : The following results were obtained : 1. During needle-embedded period, systolic and diastolic blood pressure decreased. Blood pressure decreased most significantly 2 days after treatment. 2. The change of blood pressure in the higher blood pressure group was more remarkable than that of the lower blood pressure group. Conclusions : Through this research, auricular acupuncture therapy is considered as an effective and safe method to lower blood pressure.

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Method for Determination of Maximum Allowable Pressure of Pressure Vessel Considering Detonation (폭굉을 고려한 압력용기 최대허용압력 결정방법의 제안)

  • Choi, Jinbok
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.31 no.5
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    • pp.235-241
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    • 2018
  • The internal pressure is a critical parameter for designing a pressure vessel. The static pressure that a pressure vessel must withstand is usually determined according to the various codes and standards with simple formula or numerical simulations considering the geometric parameters such as diameter and thickness of a vessel. However, there is no specific codes or technical standards we can use practically for designing of pressure vessels which have to endure the detonation pressure. Detonation pressure is a kind of dynamic pressure which causes an impulsive pressure on the vessel wall in a extremely short time duration. In addition, it is known that the magnitude of reflected pressure at the vessel wall due to the explosion can be over twice the incident pressure. Therefore, if we only consider the reflected pressure, the design of the pressure vessel can be too conservative from the economical point of view. In this study, we suggest a practical method to evaluate the magnitude of maximum allowable pressure that the pressure vessel can withstand against the detonation inside a vessel. As an example to validate the proposed method, we consider the pressure vessel containing hydrogen gas.

Borehole stability analysis in oil and gas drilling in undrained condition

  • Wei, Jian-Guang;Yan, Chuan-Liang
    • Geomechanics and Engineering
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    • v.7 no.5
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    • pp.553-567
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    • 2014
  • Borehole instability during drilling process occurs frequently when drilling through shale formation. When a borehole is drilled in shale formation, the low permeability leads to an undrained loading condition. The pore pressure in the compressed area near the borehole may be higher than the initial pore pressure. However, the excess pore pressure caused by stress concentration was not considered in traditional borehole stability models. In this study, the calculation model of excess pore pressure induced by drilling was obtained with the introduction of Henkel's excess pore pressure theory. Combined with Mohr-Coulumb strength criterion, the calculation model of collapse pressure of shale in undrained condition is obtained. Furthermore, the variation of excess pore pressure and effective stress on the borehole wall is analyzed, and the influence of Skempton's pore pressure parameter on collapse pressure is also analyzed. The excess pore pressure decreases with the increasing of drilling fluid density; the excess pore pressure and collapse pressure both increase with the increasing of Skempton's pore pressure parameter. The study results provide a reference for determining drilling fluid density when drilling in shale formation.

Real-Time Pressure-Measuring System for Evaluating the Depth of Pulse (맥진 깊이 판단을 위한 실시간 압력 측정기)

  • Cho, Jong Ho;Kim, Dae Bok;Kim, Gi Wang
    • Journal of Physiology & Pathology in Korean Medicine
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    • v.27 no.3
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    • pp.313-317
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    • 2013
  • In order to standardize the pressure/depth against radial artery, the externally-applied-pressure measuring system was fabricated and evaluated. Based on the resistance-variable characteristic of the very thin($10{\mu}m$) film conductive tape along the pressure of a tip of a examiner's hand, this system was designed. The change of the pressure was processed through voltage regulator and Matlab S/W, then showed on computer monitor. The signal output through voltage regulator, and Matlab S/W was evaluated on various conditions. The evaluation was executed on these cases; an examiner slowly increases and decreases the pressure, rapidly increases and decreases the pressure, sequentially increases and decreases the pressure, sustains the pressure, micro-changes the pressure. As a pulse examiner varies the pressure on the radial artery of the examinee, the system's real-time output consistently varies according to the pressure. From the results, it is concluded that this system consistently shows the pressure of the tip of a examiner's hand in real time without interrupting the evaluation of the radial artery pulse. Therefore this system is expected to standardize the value of the pressure/depth externally applied by an examiner.

A Developement of Ultra High Pressure Injection Equipment for Study on Diesel Spray Characteristics with Ultra High Pressure (극초고압 디젤분무특성 해석을 위한 극초고압 단발분사장치의 개발)

  • 정대용;이종태
    • Transactions of the Korean Society of Automotive Engineers
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    • v.11 no.5
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    • pp.50-59
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    • 2003
  • It was known that high pressure injection is an effective method to enhance thermal efficiency and decrease exhaust emissions in diesel engines. If injection pressure becomes ultra high, it is predicted that there may be a suitable injection pressure which the enhancement rate of spray characteristics is moderate. Also, there may be a limit injection pressure which spray characteristics is reversed and get worse. But these are unknown. To investigate a suitable injection pressure and a limit injection pressure, ultra high pressure injection equipment(UHPIE), which can realize the injection pressure of 3,200bar, was developed. UHPIE is a basic apparatus of single shot injection, and ultra high pressure was achieved by second stage rapid compression in short time. From the evaluation of UHPIE, a injection curve like a conventional diesel engine(jerk type) was realized. Also, it was proved that repetition of experiment was excellent. Therefore it was found that there was no problem to perform the study on the ultra high pressure injection with UHPIE. Consequently, the foundation of the study on ultra high pressure injection could be established.

A Study on the Pressure-travel Curve of 5.56mm Rifle Obtained from the Empirical Base Pressure Factor (탄저압력계수를 이용한 5.56mm 소총의 압력-이동거리 곡선 산출)

  • Lee, Sang-Kil;Lee, Gang-Young
    • Journal of the Korea Institute of Military Science and Technology
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    • v.10 no.3
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    • pp.208-216
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    • 2007
  • As the propellant mass is being accelerated out of the gun chamber along with the projectile, a continuous pressure gradient exists between the end of chamber and the base of the projectile. For this reason, the base pressure-travel curve is very important to design a conventional gun barrel in the interior ballistics, but it is not obtained briefly by empirical or theoretical method. In this paper, a simple relation between chamber pressure and base pressure was determined by the factor of base pressure(Cb) obtained from the experimental method. The simple relation gives a reasonable prediction for the reduction of pressure between the breech and the base of projectile owing to the axial gradient in the gun tube. The predictions have been validated by the infrared screen sensor and the PRODAS(PROjectile Design and Analysis System) for interior ballistic systems. Therefore, the base pressure-travel curve could be calculated from the chamber pressure measured by piezoelectric sensor. The base pressure-travel curve obtained from the simple relation offers initial information to gun barrel designer and is used for calculation of muzzle velocity.

Alternating Pressure Profile Characteristics of Powered Pressure Ulcer Preventing Devices (동력형 욕창예방제품의 교대부양 압력 프로파 특성)

  • Won, Byeong-Hee;Song, Chang-Seop
    • Journal of the Ergonomics Society of Korea
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    • v.29 no.4
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    • pp.639-646
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    • 2010
  • The APAM's quantitative effectiveness and comparative study in preventing and treating pressure ulcer has not been sufficiently evaluated mainly because of uncertainty of pressure load input and lack of interpretation of dynamic perfusion recovery characteristics of soft tissue. The purpose of this paper was to quantify and analyze the alternating pressure characteristics of APAM as a preventive measure for pressure ulcers. To quantify the alternating load to human body, we introduced alternating pressure profile concept and developed parametric model of the profile. Regarding pressure level and cycle time, 3 global and 7 local periodic parameters were used to define the profile such as light, standard, typical and heavy duty profile shape. Pressure impulse ratio of light duty is the lowest but pressure fluctuation is significantly high. For the same duty shape, contact conditions are changed with alternating cycle time and more dramatically in shorter alternating cycle time conditions. We can conclude that if we use shorter alternating cycle time on APAM's operation we can get more positive effects regarding to inflated contact time condition. We proposed the quantitative methods on tissue viability study of external loading by simultaneous measurement of interface pressure and tissue perfusion with proper alternating pressure profile conditions.

Hemodynamic effects of induced overtransfusion of blood in dogs (과량수혈이 혈역학에 미치는 영향)

  • 기노석
    • Journal of Chest Surgery
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    • v.17 no.3
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    • pp.418-423
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    • 1984
  • Appreciation of the large volume deficits which may occur in surgical or trauma patients due to blood loss has led to vigorous transfusion techniques designed to overt hypovolemic shock and ischemic damage to vital organs which may develop in minutes during the hypovolemic state. In a significant proportion of patients treated with massive rapid blood or fluid transfusion, hypervolemia occurs and life threatening pulmonary edema may develop. Especially, hypervolemia may occur during transfusion for preventing development of the so-called low output syndrome following cardiac surgery. However, the most effective indicator which reveals the adequate level of transfusion is not settled yet. The present study was aimed to compare the effectiveness of the indicators suggested thus far and to determine the most sensitive one. Eight dogs were experimentally studied in terms of left atrial pressure, pulmonary arterial systolic pressure, central venous pressure, mean systemic arterial pressure and heart rate before and after induced hypervolemia with infusion of 600ml heparinized homologous blood. Immediately after induced overtransfusion of the blood, pulmonary arterial systolic pressure increased 75.0%, in omparison with the control before transfusion, left atrial pressure 58.8%, central venous pressure 44.6%, and mean systemic arterial pressure 10.1%, one hour after transfusion, pulmonary arterial systolic pressure 40.0%, left atrial pressure 21.2%, central venous pressure 14.5%, and mean systemic arterial pressure 3.2%, central venous pressure 14.5%, and mean systemic arterial pressure 3.2%, respectively. Heart rate showed no significant change throughout the experiment. These result suggested that the changes of the pulmonary arterial systolic pressure is the most sensitive indicator for detection of hypervolemia during blood transfusion.

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