A pressure-based algorithm for the prediction of cavitating flows is presented.The algorithm employs a set of equations including the Navier-Stokes equations and a cavitation model explaining the phase change between ...A pressure-based algorithm for the prediction of cavitating flows is presented.The algorithm employs a set of equations including the Navier-Stokes equations and a cavitation model explaining the phase change between liquid and vapor.A pressure-based method is used to construct the algorithm and the coupling between pressure and velocity is considered.The pressure correction equation is derived from a new continuity equation which employs a source term related to phase change rate instead of the material derivative of density Dρ/Dt.This pressure-based algorithm allows for the computation of steady or unsteady,2-D or 3-D cavitating flows.Two 2-D cases,flows around a flat-nose cylinder and around a NACA0015 hydrofoil,are simulated respectively,and the periodic cavitation behaviors associated with the re-entrant jets are captured.This algorithm shows good capability of computating time-dependent cavitating flows.展开更多
Background For patients undergoing off-pump coronary artery bypass grafting （OPCABG）, it is important to establish a hemodynamic monitoring system to obtain powerful parameters for better intraoperative treatment. T...Background For patients undergoing off-pump coronary artery bypass grafting （OPCABG）, it is important to establish a hemodynamic monitoring system to obtain powerful parameters for better intraoperative treatment. This study aimed to observe the clinical feasibility of arterial pressure-based cardiac output （APCO） for cardiac output （CO） monitoring and to evaluate the correlation between APCO and pulmonary artery catheter （PAC） for CO measurement for patients undergoing OPCABG intraoperatively. Methods Fifty patients of American Society of Anaesthesiologists （ASA） classification Ⅱ-Ⅲ, undergoing elective OPCABG at Beijing Anzhen Hospital were randomly enrolled into this study. All patients were assigned to CO monitoring by PAC and APCO simultaneously. Patients with pacemaker, severe valvular heart disease, left ventricular ejection fraction （EF） 〈40%, cardiac arrhythmias, peripheral vascular disease, application of intra-aortic balloon pump （IABP） and emergent diversion to cardiac pulmonary bypass were excluded. The radial artery waveform was analyzed to estimate the stroke volume （SV） and heart rate （HR） continuously. CO was calculated as SV × HR; other derived parameters were cardiac index （CI）, stroke volume index （SVI）, systemic vascular resistance （SVR）, and systemic vascular resistance index （SVRI）. PAC was placed via right internal jugular vein and the correct position was confirmed by PAC waveforms. Continuous cardiac output （CCO）, CI and other hemodynamic parameters were monitored at following 5 time points： immediate after anesthesia induction （baseline value）, anastomosis of left internal mammary artery to left anterior descending artery （LAD）, anastomosis of left circumflex （LCX）, anastomosis of posterior descending artery （PDA） and immediate after sternal closure. Results In the 50 patients, preoperative echocardiography measured left ventricular EF was （52.8±11.5）%, and 35 patients （70%） showed regional wall motion abnormalities. The correlation coefficient of CO monitored by APCO and PAC were 0.70, 0.59, 0.78, 0.74 and 0.85 at each time point. The bias range of CI monitored from both APCO and PAC were （0.39±0.06） L.minl.m2, （0.48±0.12） L.min^-1.m2, （0.26±0.06） L.min1.m-2, （0.27±0.06） L.min-l.m2, （0.30＋0.05） L.min-l.m2 at each time point. The results of SVR by two hemodynamic monitoring techniques had good correlation during OPCABG. The variation trends of SVR were opposite comparing with the results of CO. SVR collected from PAC obtained the highest value of （1220.0±254.0） dyn.s.cm5 at PDA anastomosis, but the highest value obtained from APCO was （1206.0±226.5） dyn.s.cm-5 in LCX anastomosis. Conclusions APCO is feasible in hemodynamic monitoring for patients undergoing OPCABG The results of hemodynamic monitoring derived from APCO and PAC are closely correlated. Its characterizations of timely, accurate and continuous display of hemodynamic parameters are also obviously demonstrated in the present study.展开更多
This paper presents a simplified dynamic method based on the definition of field capacity. Two soil hydraulic characteristics models, the Brooks-Corey （BC） model and the van Genuchten （vG） model, and four soil dat...This paper presents a simplified dynamic method based on the definition of field capacity. Two soil hydraulic characteristics models, the Brooks-Corey （BC） model and the van Genuchten （vG） model, and four soil data groups were used in this study. The relative drainage rate, which is a unique parameter and independent of the soil type in the simplified dynamic method, was analyzed using the pressure-based method with a matric potential of -1/3 bar and the flux-based method with a drainage flux of 0.005 cm/d. As a result, the relative drainage rate of the simplified dynamic method was determined to be 3% per day. This was verified by the similar field capacity results estimated with the three methods for most soils suitable for cultivating plants. In addition, the drainage time calculated with the simplified dynamic method was two to three days, which agrees with the classical definition of field capacity. We recommend the simplified dynamic method with a relative drainage rate of 3% per day due to its simple application and clearly physically-based concept.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant No. 10602030)the National Key Basic Research Program of China (973 Program, Grant No. 2009CB724303)the Fundamental Research Funds for the Central Universities (Grant No. 2010QNA4015)
文摘A pressure-based algorithm for the prediction of cavitating flows is presented.The algorithm employs a set of equations including the Navier-Stokes equations and a cavitation model explaining the phase change between liquid and vapor.A pressure-based method is used to construct the algorithm and the coupling between pressure and velocity is considered.The pressure correction equation is derived from a new continuity equation which employs a source term related to phase change rate instead of the material derivative of density Dρ/Dt.This pressure-based algorithm allows for the computation of steady or unsteady,2-D or 3-D cavitating flows.Two 2-D cases,flows around a flat-nose cylinder and around a NACA0015 hydrofoil,are simulated respectively,and the periodic cavitation behaviors associated with the re-entrant jets are captured.This algorithm shows good capability of computating time-dependent cavitating flows.
文摘Background For patients undergoing off-pump coronary artery bypass grafting （OPCABG）, it is important to establish a hemodynamic monitoring system to obtain powerful parameters for better intraoperative treatment. This study aimed to observe the clinical feasibility of arterial pressure-based cardiac output （APCO） for cardiac output （CO） monitoring and to evaluate the correlation between APCO and pulmonary artery catheter （PAC） for CO measurement for patients undergoing OPCABG intraoperatively. Methods Fifty patients of American Society of Anaesthesiologists （ASA） classification Ⅱ-Ⅲ, undergoing elective OPCABG at Beijing Anzhen Hospital were randomly enrolled into this study. All patients were assigned to CO monitoring by PAC and APCO simultaneously. Patients with pacemaker, severe valvular heart disease, left ventricular ejection fraction （EF） 〈40%, cardiac arrhythmias, peripheral vascular disease, application of intra-aortic balloon pump （IABP） and emergent diversion to cardiac pulmonary bypass were excluded. The radial artery waveform was analyzed to estimate the stroke volume （SV） and heart rate （HR） continuously. CO was calculated as SV × HR; other derived parameters were cardiac index （CI）, stroke volume index （SVI）, systemic vascular resistance （SVR）, and systemic vascular resistance index （SVRI）. PAC was placed via right internal jugular vein and the correct position was confirmed by PAC waveforms. Continuous cardiac output （CCO）, CI and other hemodynamic parameters were monitored at following 5 time points： immediate after anesthesia induction （baseline value）, anastomosis of left internal mammary artery to left anterior descending artery （LAD）, anastomosis of left circumflex （LCX）, anastomosis of posterior descending artery （PDA） and immediate after sternal closure. Results In the 50 patients, preoperative echocardiography measured left ventricular EF was （52.8±11.5）%, and 35 patients （70%） showed regional wall motion abnormalities. The correlation coefficient of CO monitored by APCO and PAC were 0.70, 0.59, 0.78, 0.74 and 0.85 at each time point. The bias range of CI monitored from both APCO and PAC were （0.39±0.06） L.minl.m2, （0.48±0.12） L.min^-1.m2, （0.26±0.06） L.min1.m-2, （0.27±0.06） L.min-l.m2, （0.30＋0.05） L.min-l.m2 at each time point. The results of SVR by two hemodynamic monitoring techniques had good correlation during OPCABG. The variation trends of SVR were opposite comparing with the results of CO. SVR collected from PAC obtained the highest value of （1220.0±254.0） dyn.s.cm5 at PDA anastomosis, but the highest value obtained from APCO was （1206.0±226.5） dyn.s.cm-5 in LCX anastomosis. Conclusions APCO is feasible in hemodynamic monitoring for patients undergoing OPCABG The results of hemodynamic monitoring derived from APCO and PAC are closely correlated. Its characterizations of timely, accurate and continuous display of hemodynamic parameters are also obviously demonstrated in the present study.
基金supported by the National Natural Science Foundation of China(Grants No.51179083 and 91225302)
文摘This paper presents a simplified dynamic method based on the definition of field capacity. Two soil hydraulic characteristics models, the Brooks-Corey （BC） model and the van Genuchten （vG） model, and four soil data groups were used in this study. The relative drainage rate, which is a unique parameter and independent of the soil type in the simplified dynamic method, was analyzed using the pressure-based method with a matric potential of -1/3 bar and the flux-based method with a drainage flux of 0.005 cm/d. As a result, the relative drainage rate of the simplified dynamic method was determined to be 3% per day. This was verified by the similar field capacity results estimated with the three methods for most soils suitable for cultivating plants. In addition, the drainage time calculated with the simplified dynamic method was two to three days, which agrees with the classical definition of field capacity. We recommend the simplified dynamic method with a relative drainage rate of 3% per day due to its simple application and clearly physically-based concept.
