In this paper, we study the solutions for variable-order time-fractional diffusion equations. A three-point combined compact difference (CCD) method is used to discretize the spatial variables to achieve sixth-order a...In this paper, we study the solutions for variable-order time-fractional diffusion equations. A three-point combined compact difference (CCD) method is used to discretize the spatial variables to achieve sixth-order accuracy, while the exponential-sum-approximation (ESA) is used to approximate the variable-order Caputo fractional derivative in the temporal direction, and a novel spatial sixth-order hybrid ESA-CCD method is implemented successfully. Finally, the accuracy of the proposed method is verified by numerical experiments.展开更多
基于丙酮-环己烷共沸体系的压力敏感性,利用Aspen Plus软件,以年度总费用(TAC)最小为目标函数对常规、部分及完全热集成变压精馏工艺进行稳态模拟与优化,并以经济最优的完全热集成变压精馏工艺为基础,借助Aspen Plus Dynamics软件建立...基于丙酮-环己烷共沸体系的压力敏感性,利用Aspen Plus软件,以年度总费用(TAC)最小为目标函数对常规、部分及完全热集成变压精馏工艺进行稳态模拟与优化,并以经济最优的完全热集成变压精馏工艺为基础,借助Aspen Plus Dynamics软件建立多种不同控制结构,通过改变进料流量和进料组成考察了控制结构的有效性,并提出塔底热负荷/进料量比例控制与组成-温度串级控制相结合的改进控制结构。稳态模拟与优化结果表明,常规、部分和完全热集成三种工艺的最小TAC分别为3.64×10^(5),2.83×10^(5),2.76×10^(5)$/y,经济最优工艺为完全热集成变压精馏。动态响应结果表明固定回流量/进料量控制结构在响应时间方面优于固定回流比控制结构,但产品纯度未达到设计值99.9wt%;而塔底热负荷/进料量比例控制与组成-温度串级控制相结合的改进控制结构能够有效保证产品纯度在99.9wt%及以上。展开更多
In this study,we conducted numerical experiments to examine the effects of turbulence parameterization on temporal and spatial variations of suspended sediment dynamics.Then,we applied the numerical model to the Yamen...In this study,we conducted numerical experiments to examine the effects of turbulence parameterization on temporal and spatial variations of suspended sediment dynamics.Then,we applied the numerical model to the Yamen Channel,one of the main eight outfalls in the Pearl River Delta.For the field application,we implemented the k−εscheme with a reasonable stability function using the continuous deposition formula during the erosion process near the water-sediment interface.We further validated and analyzed the temporal-spatial suspended sediment concentrations(SSCs).The experimental results show that under specified initial and boundary conditions,turbulence parameterization with stability functions can lead to different vertical profiles of the velocity and SSC.The k−εpredicts stronger mixing with a maximum value of approximately twice the k−kl.The k−kl results in smaller SSCs near the surface layer and a larger vertical gradient than the k−ε.In the Yamen Channel,though the turbulent dissipation,turbulent viscosity and turbulence kinetic energy exhibit similar trends,SSCs differ significantly between those at low water and high water due to the tidal asymmetry and settling lag mechanisms.The results can provide significant insights into environmental protection and estuarine management in the Pearl River Delta.展开更多
文摘In this paper, we study the solutions for variable-order time-fractional diffusion equations. A three-point combined compact difference (CCD) method is used to discretize the spatial variables to achieve sixth-order accuracy, while the exponential-sum-approximation (ESA) is used to approximate the variable-order Caputo fractional derivative in the temporal direction, and a novel spatial sixth-order hybrid ESA-CCD method is implemented successfully. Finally, the accuracy of the proposed method is verified by numerical experiments.
文摘基于丙酮-环己烷共沸体系的压力敏感性,利用Aspen Plus软件,以年度总费用(TAC)最小为目标函数对常规、部分及完全热集成变压精馏工艺进行稳态模拟与优化,并以经济最优的完全热集成变压精馏工艺为基础,借助Aspen Plus Dynamics软件建立多种不同控制结构,通过改变进料流量和进料组成考察了控制结构的有效性,并提出塔底热负荷/进料量比例控制与组成-温度串级控制相结合的改进控制结构。稳态模拟与优化结果表明,常规、部分和完全热集成三种工艺的最小TAC分别为3.64×10^(5),2.83×10^(5),2.76×10^(5)$/y,经济最优工艺为完全热集成变压精馏。动态响应结果表明固定回流量/进料量控制结构在响应时间方面优于固定回流比控制结构,但产品纯度未达到设计值99.9wt%;而塔底热负荷/进料量比例控制与组成-温度串级控制相结合的改进控制结构能够有效保证产品纯度在99.9wt%及以上。
基金Supported by the Scientific Research Start-up Funds of Guangdong Ocean University(Grant No.060302032202).
文摘In this study,we conducted numerical experiments to examine the effects of turbulence parameterization on temporal and spatial variations of suspended sediment dynamics.Then,we applied the numerical model to the Yamen Channel,one of the main eight outfalls in the Pearl River Delta.For the field application,we implemented the k−εscheme with a reasonable stability function using the continuous deposition formula during the erosion process near the water-sediment interface.We further validated and analyzed the temporal-spatial suspended sediment concentrations(SSCs).The experimental results show that under specified initial and boundary conditions,turbulence parameterization with stability functions can lead to different vertical profiles of the velocity and SSC.The k−εpredicts stronger mixing with a maximum value of approximately twice the k−kl.The k−kl results in smaller SSCs near the surface layer and a larger vertical gradient than the k−ε.In the Yamen Channel,though the turbulent dissipation,turbulent viscosity and turbulence kinetic energy exhibit similar trends,SSCs differ significantly between those at low water and high water due to the tidal asymmetry and settling lag mechanisms.The results can provide significant insights into environmental protection and estuarine management in the Pearl River Delta.
