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가솔린직접분사기관에서 흡기포트 및 피스톤의 형상에 따른 유동해석
박찬국(Chan-Guk Park),박형구(Hyung-Koo Park),임명택(Myung-Taeck Lim) 한국전산유체공학회 1999 한국전산유체공학회지 Vol.4 No.3
In this paper, the characteristics of flow resulting from the configurations of piston head and intake-port of the cylinder in a gasoline-direct-injection engine are investigated numerically. Calculations are carried out from intake process to the end of compression. GTT code which includes the third order upwind Chakravarthy-Osher TVD scheme and k-ε, turbulence model with the law of wall as a boundary condition. As a result, a piston head with a smaller radius of curvature and larger radius gives stronger reverse tumble. It is also shown that as the maximum tumble ratio increases by the configuration of the intake-port the tumble ratio at the end of compression stroke increases. It is concluded that flows at the end of compression stroke can be controlled by the optimum design of intake-port and piston head.
문맥압항진증에서 Propranolol 및 Isorsorbide-5-Mononitrate의 효과
박찬국(Chan Guk Park),정규성(Kyu Sung Chung),김만우(Man Woo Kim) 대한소화기학회 1996 대한소화기학회지 Vol.28 No.2
N/A Background/Aims: Esophageal variceal bleeding is one of the major causes of death in patients with portal hypertension, mostly due to liver cirrhosis. Surgical portal-systemic shunvs, sclero- therapy and/or pharmacological treatment are used in the primary and secondary prevention of hernorrhages in high-risk patients, but the effect of tbis therapy has not improved. A major innovation in the treatment of portal hypertension was the use of phannacologic agent.; to prevent bleeding and death from ruptured esophageal varices. Porta] pressure can be reduced by decreasing blood flow and/or vascular resistance within the portal venous system. Up to now, the medical treatment of portal hypertension has been based on the use of drugs that reduce the splanchnic blood tlow, such as vasopressin, somatostatin, and 0-adrenergic blockers. Especially, the oral administration of Isosorbide-5-rnononitrate, a preterentia] venous dilator with prolonged biological activity and no hepatic metabo]ism, caused a significant reduction in portal pressure in patients with cirrhosis. This was due in part to a decrease in hepatic vascular resistance. Hcwever, the indications for and against such therapies are not standardized and the problems caused by both hemodynamic evaluation of the response to treatment and selection of responders are still unresolved. Methods: Doppler ultrasonography(real time B-scan imaging and pulsed Doppler ultrasonographic study) represents a valuable and non-invasive method for the study nf portal hemodynamics in patients with liver cirrhosis. Twenty patients(16 males, aged 51+6) had hemo- dynamic measurements in the baseline condition Liefore and 1 day, l week, 3 weeks, aind 5 weeks after oral administration of propranolol and Isosorbide-S-Mononitrate, respectively by Doppler ultrasonography. Results: Diameter, maximal ve]ocity, cross sectional area, mean velcicity, blood flow vo]ume of porta] system were significantly reduced after drug administration(p--0,001). But the congestion index was not decreased statistically. Blood flov, volume difference between the portal vein and the sum of splenic vein and superior mesenteric vein(P-SS) was significantly reduced after drug administration(p<0.001). Conslusions: The oral adrainistration of propranolo] and Isosorbide- 5-Mononitrate achieved an effective reduction in portal hypertension with cirrhosis. When pharmacologic treatment of portal hypertension is contemplated, Doppler u]trasonography would appear to be of considerable interest because of its availability, noninvasivity and repeatability.(Korean J Gastroenterol 1996; 28:241-250)
가솔린직접분사기관에서 흡기포트 및 피스톤의 형상에 따른 유동해석
박찬국(Chan-Guk Park),박형구(Hyung-Koo Park),임명택(Myung-Taeck Lim) 한국전산유체공학회 1999 한국전산유체공학회지 Vol.4 No.3
In this paper, the characteristics of flow resulting from the configurations of piston head and intake-port of the cylinder in a gasoline-direct-injection engine are investigated numerically. Calculations are carried out from intake process to the end of compression. GTT code which includes the third order upwind Chakravarthy-Osher TVD scheme and k-ε, turbulence model with the law of wall as a boundary condition. As a result, a piston head with a smaller radius of curvature and larger radius gives stronger reverse tumble. It is also shown that as the maximum tumble ratio increases by the configuration of the intake-port the tumble ratio at the end of compression stroke increases. It is concluded that flows at the end of compression stroke can be controlled by the optimum design of intake-port and piston head.