Unlike the pier scour in bridge waterways,the local scour at offshore monopile foundations should take into account the effect of wave-current combination.Under the condition of wave-current coexistence,the water-soil...Unlike the pier scour in bridge waterways,the local scour at offshore monopile foundations should take into account the effect of wave-current combination.Under the condition of wave-current coexistence,the water-soil interfacial scouring is usually coupled with the pore-pressure dynamics inside of the seabed.The aforementioned wave/current-pile-soil coupling process was physically modeled with a specially designed flow-structure-soil interaction flume.Experimental results indicate that superimposing a current onto the waves obviously changes the pore-pressure and the flow velocity at the bed around the pile.The concomitance of horseshoe vortex and local scour hole around a monopile proves that the horseshoe vortex is one of the main controlling mechanisms for scouring development under the combined waves and current.Based on similarity analyses,an average-velocity based Froude number(Fra)is proposed to correlate with the equilibrium scour depth(S/D)at offshore monopile foundation in the combined waves and current.An empirical expression for the correlation between S/D and Fra is given for predicting equilibrium scour depth,which may provide a guide for offshore engineering practice.展开更多
细观孔隙结构是控制多孔介质渗透率的主要因素之一.采用高分辨率工业显微CT,分别对砂雨法成样南京粉砂、振捣干法成样南京粉砂、鄂尔多斯油砂、自贡砂岩和砂雨法成样玻璃珠扫描成像.三维重构后选取尺寸为300体素的表征单元体(Representa...细观孔隙结构是控制多孔介质渗透率的主要因素之一.采用高分辨率工业显微CT,分别对砂雨法成样南京粉砂、振捣干法成样南京粉砂、鄂尔多斯油砂、自贡砂岩和砂雨法成样玻璃珠扫描成像.三维重构后选取尺寸为300体素的表征单元体(Representative Element Volume,REV),基于最大球算法提取出REV的16种孔隙结构参数,并采用格子波尔兹曼方法计算出各REV渗透率.采用灰色关联度方法,分析了平均配位数、平均孔径、最大/小孔径等16个细观孔隙结构参数对多孔介质渗透率影响的主、次关系及其权重.结果表明,16种孔隙结构参数对渗透率的影响从大到小依次为:孔隙平均体积、孔隙最大体积、平均中值喉道、喉道平均半径、孔隙平均半径、喉道最大半径、平均喉道长度、孔隙最大半径、孔隙率、孔隙最小体积、孔喉平均配位数、孔隙截面积平均形状因子、喉道截面积平均形状因子、孔隙最小半径、孔喉比与喉道最小半径.可为岩土介质细观尺度渗流分析提供参考.展开更多
以咸水层封存二氧化碳(CO_2)为研究背景,利用流体体积函数(Volume of Fluid,VOF)多相流模型建立孔隙尺度多孔介质计算模型,研究了超临界二氧化碳(Sc-CO_2)注入到含水多孔介质中的两相运移规律。对比分析了毛细管数、地质封存压力、Sc-C...以咸水层封存二氧化碳(CO_2)为研究背景,利用流体体积函数(Volume of Fluid,VOF)多相流模型建立孔隙尺度多孔介质计算模型,研究了超临界二氧化碳(Sc-CO_2)注入到含水多孔介质中的两相运移规律。对比分析了毛细管数、地质封存压力、Sc-CO_2注射温度、两相表面张力系数、接触角等因素对两相运移速率以及驱替效率的影响,同时将不同毛细管数下的驱替效率与实验数据进行了对比。研究结果表明,随着毛细管数的增大,驱替效率先减小然后趋于稳定,数值模拟与实验数据吻合良好;在同一孔隙率下,在壁面表现为亲水性时,壁面润湿性越好,驱替速率越快,但驱替效率有所下降;同时毛细管数越小、地质封存压力越低、注射温度越高、张力系数越小驱替速率越快,且驱替效率越高。展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.1123201210872198)the National Basic Research Program of China("973"Project)(Grant No.2014CB046204)
文摘Unlike the pier scour in bridge waterways,the local scour at offshore monopile foundations should take into account the effect of wave-current combination.Under the condition of wave-current coexistence,the water-soil interfacial scouring is usually coupled with the pore-pressure dynamics inside of the seabed.The aforementioned wave/current-pile-soil coupling process was physically modeled with a specially designed flow-structure-soil interaction flume.Experimental results indicate that superimposing a current onto the waves obviously changes the pore-pressure and the flow velocity at the bed around the pile.The concomitance of horseshoe vortex and local scour hole around a monopile proves that the horseshoe vortex is one of the main controlling mechanisms for scouring development under the combined waves and current.Based on similarity analyses,an average-velocity based Froude number(Fra)is proposed to correlate with the equilibrium scour depth(S/D)at offshore monopile foundation in the combined waves and current.An empirical expression for the correlation between S/D and Fra is given for predicting equilibrium scour depth,which may provide a guide for offshore engineering practice.
文摘为了研究高频纳秒脉冲电场(ns PEFs)杀伤肿瘤细胞的机理,结合笛卡尔传输网格(CTL)和动态电穿孔等效电路模型对1个典型的2维多细胞系统在ns PEFs作用下的穿孔特性进行了仿真。利用Pspice仿真软件建立了该多细胞系统电路模型,并分析了其穿孔数量和穿孔半径变化特性。首先施加了10个场强、频率和脉宽分别为5k V/cm、1 MHz和500 ns的高频纳秒脉冲到该多细胞系统模型,结果表明随脉冲个数增加穿孔区域分布变化不大,而穿孔半径分布有明显的累积效应,细胞外膜和细胞核膜上部分孔的半径逐渐增大。同时比较了电场强度为3、5和10 k V/cm时该系统中穿孔数量和最大孔径随脉冲个数增加的变化情况。结果显示场强增加时穿孔数量明显增加,特别是场强从3 k V/cm提高到10 k V/cm时,系统整个细胞核膜从未穿孔到穿孔数量增加到2.658 4×105个。另外,穿孔半径仍然存在累积效应。仿真结果说明适当参数的高频ns PEFs能使细胞核膜发生穿孔,并起到扩大细胞部分穿孔半径的作用,可为后续实验研究选择高频纳秒脉冲参数提供依据。
文摘细观孔隙结构是控制多孔介质渗透率的主要因素之一.采用高分辨率工业显微CT,分别对砂雨法成样南京粉砂、振捣干法成样南京粉砂、鄂尔多斯油砂、自贡砂岩和砂雨法成样玻璃珠扫描成像.三维重构后选取尺寸为300体素的表征单元体(Representative Element Volume,REV),基于最大球算法提取出REV的16种孔隙结构参数,并采用格子波尔兹曼方法计算出各REV渗透率.采用灰色关联度方法,分析了平均配位数、平均孔径、最大/小孔径等16个细观孔隙结构参数对多孔介质渗透率影响的主、次关系及其权重.结果表明,16种孔隙结构参数对渗透率的影响从大到小依次为:孔隙平均体积、孔隙最大体积、平均中值喉道、喉道平均半径、孔隙平均半径、喉道最大半径、平均喉道长度、孔隙最大半径、孔隙率、孔隙最小体积、孔喉平均配位数、孔隙截面积平均形状因子、喉道截面积平均形状因子、孔隙最小半径、孔喉比与喉道最小半径.可为岩土介质细观尺度渗流分析提供参考.
文摘以咸水层封存二氧化碳(CO_2)为研究背景,利用流体体积函数(Volume of Fluid,VOF)多相流模型建立孔隙尺度多孔介质计算模型,研究了超临界二氧化碳(Sc-CO_2)注入到含水多孔介质中的两相运移规律。对比分析了毛细管数、地质封存压力、Sc-CO_2注射温度、两相表面张力系数、接触角等因素对两相运移速率以及驱替效率的影响,同时将不同毛细管数下的驱替效率与实验数据进行了对比。研究结果表明,随着毛细管数的增大,驱替效率先减小然后趋于稳定,数值模拟与实验数据吻合良好;在同一孔隙率下,在壁面表现为亲水性时,壁面润湿性越好,驱替速率越快,但驱替效率有所下降;同时毛细管数越小、地质封存压力越低、注射温度越高、张力系数越小驱替速率越快,且驱替效率越高。
