In this study,a two-dimensional flow-pollutant coupled model was developed based on a quadtree grid.This model was established to allow the accurate simulation of wind-driven flow in a large-scale shallow lake with ir...In this study,a two-dimensional flow-pollutant coupled model was developed based on a quadtree grid.This model was established to allow the accurate simulation of wind-driven flow in a large-scale shallow lake with irregular natural boundaries when focusing on important smallscale localized flow features.The quadtree grid was created by domain decomposition.The governing equations were solved using the finite volume method,and the normal fluxes of mass,momentum,and pollutants across the interface between cells were computed by means of a Godunov-type Osher scheme.The model was employed to simulate wind-driven flow in a circular basin with non-uniform depth.The computed values were in agreement with analytical data.The results indicate that the quadtree grid has fine local resolution and high efficiency,and is convenient for local refinement.It is clear that the quadtree grid model is effective when applied to complex flow domains.Finally,the model was used to calculate the flow field and concentration field of Taihu Lake,demonstrating its ability to predict the flow and concentration fields in an actual water area with complex geometry.展开更多
In the case of lid-driven deep cavity flow, the effects of different resolutions of local grid refinement have been studied in the frame of multiple relaxation times (MRT) lattice Boltzmann method (LBM). In all the ca...In the case of lid-driven deep cavity flow, the effects of different resolutions of local grid refinement have been studied in the frame of multiple relaxation times (MRT) lattice Boltzmann method (LBM). In all the cases, the aspect ratio and Reynolds number are set as 1.5 and 3.200, respectively. First, the applied method is validated by comparing it with two reported works, with which agreements are reached. Then, six separate degrees of local grid refinement at the upper left corner, i.e. purely coarse grid, including 1/64, 1/32, 1/16, 1/8, 1/4 refinements of the lattice number in the width direction have been studied in detail. The results give the following indications:① The refinement degrees lower than 1/8 produce similar results;② For single corner refinement, 1/4 refinement is adequate for clearing the noises in the singularity zone to a large extent;③ New noise around the interface between coarse and fine zones are introduced by local grid refinement. Finally, refinement of entire subzone neighboring the lid is examined to avoid introducing new noises and it has been found effective.展开更多
针对数字孪生城市亟需空间统一框架与数据高效组织问题,基于地球空间剖分理论及相应的《地球表面空间网格与编码》(GJB8896-2017)、《北斗网格位置码》及《地球空间网格编码规则》等国家标准编制成果,提出发展一种数字孪生城市空间网格...针对数字孪生城市亟需空间统一框架与数据高效组织问题,基于地球空间剖分理论及相应的《地球表面空间网格与编码》(GJB8896-2017)、《北斗网格位置码》及《地球空间网格编码规则》等国家标准编制成果,提出发展一种数字孪生城市空间网格框架与GDS(Grid Data System)数据平台技术。城市多尺度立体剖分网格空间是一种地球空间的客观存在,城市万事万物在某一时间内一定落在某一或某几个网格体中,由此发展的GDS技术面向空间数据统一组织,有利于发展出面向空间建模的新型G-GIS、G-BIM等系统,是对传统GIS、BIM等面向对象建模数据系统的创新探索;有助于构建统一的空间数据框架进而实现城市多源异构数据的汇聚、关联与高效计算,对支撑数字孪生城市建设具有理论与实践意义。展开更多
基金supported by the National Natural Science Foundation of China(Grants No.51739002 and 51479064)the World-Class Universities(Disciplines)and Characteristic Development Guidance Funds for the Central Universitiesthe Priority Academic Program Development(PAPD)of Jiangsu Higher Education Institutions(Grant No.PPZY2015A051)
文摘In this study,a two-dimensional flow-pollutant coupled model was developed based on a quadtree grid.This model was established to allow the accurate simulation of wind-driven flow in a large-scale shallow lake with irregular natural boundaries when focusing on important smallscale localized flow features.The quadtree grid was created by domain decomposition.The governing equations were solved using the finite volume method,and the normal fluxes of mass,momentum,and pollutants across the interface between cells were computed by means of a Godunov-type Osher scheme.The model was employed to simulate wind-driven flow in a circular basin with non-uniform depth.The computed values were in agreement with analytical data.The results indicate that the quadtree grid has fine local resolution and high efficiency,and is convenient for local refinement.It is clear that the quadtree grid model is effective when applied to complex flow domains.Finally,the model was used to calculate the flow field and concentration field of Taihu Lake,demonstrating its ability to predict the flow and concentration fields in an actual water area with complex geometry.
基金Supported by Science and Technology Development Planning of Shandong Province,P.R.China(2016GGX104018)
文摘In the case of lid-driven deep cavity flow, the effects of different resolutions of local grid refinement have been studied in the frame of multiple relaxation times (MRT) lattice Boltzmann method (LBM). In all the cases, the aspect ratio and Reynolds number are set as 1.5 and 3.200, respectively. First, the applied method is validated by comparing it with two reported works, with which agreements are reached. Then, six separate degrees of local grid refinement at the upper left corner, i.e. purely coarse grid, including 1/64, 1/32, 1/16, 1/8, 1/4 refinements of the lattice number in the width direction have been studied in detail. The results give the following indications:① The refinement degrees lower than 1/8 produce similar results;② For single corner refinement, 1/4 refinement is adequate for clearing the noises in the singularity zone to a large extent;③ New noise around the interface between coarse and fine zones are introduced by local grid refinement. Finally, refinement of entire subzone neighboring the lid is examined to avoid introducing new noises and it has been found effective.
文摘基于虚拟同步控制(virtual synchronous generator,VSG)的构网型直驱风机(permanent magnet synchronous generator,PMSG)的控制结构决定了其轴系扭振特性必然会受到网侧动态的影响。当系统受到外界扰动时,可能会产生扭转振荡,导致系统出现低频振荡。目前,对于基于VSG的直驱风机轴系扭振特性的机理研究尚不清晰,关键制约因素仍不明确,且网侧动态对轴系阻尼的影响机理尚待解决。因此,详细分析了基于VSG的直驱风机的轴系扭振特性。首先,通过电气转矩法得出了电磁转矩-转速差的传递函数,并定义了等效阻尼系数,以定量表达电磁转矩对轴系扭振的电气阻尼作用。同时,探讨了在最大功率跟踪(maximum power point tracking,MPPT)模式下,网侧动态对电磁转矩在轴系阻尼作用中的影响机理,识别出了影响轴系阻尼的关键制约因素及其作用规律。在此基础上,提出了相应的轴系扭振抑制策略。最后,利用SIMULINK对理论分析进行了仿真验证,结果证明了理论分析的正确性和控制策略的有效性。
文摘针对数字孪生城市亟需空间统一框架与数据高效组织问题,基于地球空间剖分理论及相应的《地球表面空间网格与编码》(GJB8896-2017)、《北斗网格位置码》及《地球空间网格编码规则》等国家标准编制成果,提出发展一种数字孪生城市空间网格框架与GDS(Grid Data System)数据平台技术。城市多尺度立体剖分网格空间是一种地球空间的客观存在,城市万事万物在某一时间内一定落在某一或某几个网格体中,由此发展的GDS技术面向空间数据统一组织,有利于发展出面向空间建模的新型G-GIS、G-BIM等系统,是对传统GIS、BIM等面向对象建模数据系统的创新探索;有助于构建统一的空间数据框架进而实现城市多源异构数据的汇聚、关联与高效计算,对支撑数字孪生城市建设具有理论与实践意义。
