Fresh cement mortar is a type of workable paste, which can be well approximated as a Bingham plastic and whose flow behavior is of major concern in engineering. In this paper, Papanastasiou＇s model for Bingham fluids...Fresh cement mortar is a type of workable paste, which can be well approximated as a Bingham plastic and whose flow behavior is of major concern in engineering. In this paper, Papanastasiou＇s model for Bingham fluids is solved by using the multiple- relaxation-time lattice Boltzmann model （MRT-LB）. Analysis of the stress growth exponent m in Bingham fluid flow simulations shows that Papanastasiou＇s model provides a good approximation of realistic Bingham plastics for values of m 〉 108. For lower values of m, Papanastasiou＇s model is valid for fluids between Bingham and Newtonian fluids. The MRT-LB model is validated by two benchmark problems： 2D steady Poiseuille flows and lid-driven cavity flows. Comparing the numerical results of the velocity distributions with corresponding analytical solutions shows that the MRT-LB model is appropriate for studying Bingham fluids while also providing better numerical stability. We further apply the MRT-LB model to simulate flow through a sudden expansion channel and the flow surrounding a round particle. Besides the rich flow structures obtained in this work, the dynamics fhi d force on the round particle is calculated. Results show that both the Reynolds number Re and the Bingham number Bn affect the drag coefficients Co, and a drag coefficient with Re and Bn being taken into account is proposed. The relationship of Bn and the ratio of unyielded zone thickness to particle diameter is also analyzed. Finally, the Bingham fluid flowing around a set of randomly dispersed particles is simulated to obtain the apparent viscosity and velocity fields. These results help simulation of fresh concrete flowing in porous media.展开更多
文摘目的 探究维持性腹膜透析(MPD)患者肺动脉高压(PAH)与细胞外水(ECW)/身体总水(TBW)水平的关系。方法 回顾性分析2019年5月至2022年5月安徽医科大学第一附属医院收住院的125例MPD患者临床资料,根据超声心动图检查肺动脉压力值分为PAH组(肺动脉压力≥35 mm Hg)75例和非PAH组(肺动脉压力<35 mm Hg)50例,比较两组的一般资料、实验室指标、超声心动图参数、人体成分分析参数。采用线性回归分析、平滑曲线拟合、受试者工作特征(ROC)曲线等方式探讨MPD患者ECW/TBW水平与PAH的相关性。结果 PAH组和非PAH组的体重指数(BMI)、收缩压、血红蛋白(HGB)、脑钠肽(BNP)、细胞外水(ECW)/身体总水(TBW)、射血分数(EF)、左室质量分数(LVMI)差异均有统计学意义(P<0.05)。多因素logistic逐步回归分析结果显示,ECW/TBW(×10^(-2))[OR=1.127,95%CI:1.005~1.265,P=0.041]是MPD患者发生PAH的独立影响因素。以PAH为状态变量,ECW/TBW(×10^(-2))为检验变量绘制ROC曲线,ECW/TBW预测PAH发生的ROC曲线下面积为0.739,其临界点为47.1×10^(-2)。ECW/TBW(×10^(-2))每升高1×10^(-2),PAH发生率升高12.7%。结论 MPD患者的PAH发生与容量状态关系密切,ECW/TBW水平升高可导致PAH的发生。
基金supported by the National Key Basic Research Program of China(Grant No.2010CB731504)the Natural Science Foundation of China(Grant Nos.11034010,11272048 and 51239006)+1 种基金European Commission Marie Curie Actions(Grant No.IRSES-294976)the State Key Laboratory of Hydroscience and Engineering(Grant No.2013-KY-2)
文摘Fresh cement mortar is a type of workable paste, which can be well approximated as a Bingham plastic and whose flow behavior is of major concern in engineering. In this paper, Papanastasiou＇s model for Bingham fluids is solved by using the multiple- relaxation-time lattice Boltzmann model （MRT-LB）. Analysis of the stress growth exponent m in Bingham fluid flow simulations shows that Papanastasiou＇s model provides a good approximation of realistic Bingham plastics for values of m 〉 108. For lower values of m, Papanastasiou＇s model is valid for fluids between Bingham and Newtonian fluids. The MRT-LB model is validated by two benchmark problems： 2D steady Poiseuille flows and lid-driven cavity flows. Comparing the numerical results of the velocity distributions with corresponding analytical solutions shows that the MRT-LB model is appropriate for studying Bingham fluids while also providing better numerical stability. We further apply the MRT-LB model to simulate flow through a sudden expansion channel and the flow surrounding a round particle. Besides the rich flow structures obtained in this work, the dynamics fhi d force on the round particle is calculated. Results show that both the Reynolds number Re and the Bingham number Bn affect the drag coefficients Co, and a drag coefficient with Re and Bn being taken into account is proposed. The relationship of Bn and the ratio of unyielded zone thickness to particle diameter is also analyzed. Finally, the Bingham fluid flowing around a set of randomly dispersed particles is simulated to obtain the apparent viscosity and velocity fields. These results help simulation of fresh concrete flowing in porous media.
