The virtual grid method used in the embedding technique to solve the problem of finding interpolating cells of the inner and outer boundary points near joint regions was developed for calculating the viscous flows aro...The virtual grid method used in the embedding technique to solve the problem of finding interpolating cells of the inner and outer boundary points near joint regions was developed for calculating the viscous flows around a wing with control surface. The main purpose of the virtual grid is to effectively treat the geometry of the crossed facial planes at the interface, and to convert a solid wall boundary condition into an interface condition, however, no fluid flow computations are conducted within the virtual grid. Navier Stokes computations were performed for transonic flow over a clipped delta wing with control surface, and the computed results compare well with the experimental data.展开更多
In order to improve efficiency of virtual enterprise, a manufacturing grid and multilevel manufacturing system of virtual enterprise is built up. When selecting member enterprises and task assignment based on the manu...In order to improve efficiency of virtual enterprise, a manufacturing grid and multilevel manufacturing system of virtual enterprise is built up. When selecting member enterprises and task assignment based on the manufacturing grid, key activities are assigned to the suitable critical member enterprises by task decomposition, enterprise node searching and characteristic matching of manufacturing resources according to the characteristic matching strategy. By task merger, some ordinary activities are merged with corresponding key activities and assigned to corresponding critical member enterprises. However, the other ordinary activities are assigned to the related ordinary member enterprises with enterprise node searching and characteristic matching of manufacturing resources. Finally, an example of developing the artificial hip joint in the virtual enterprise is used to demonstrate that efficiency of the virtual enterprise is improved by using the manufacturing grid and the proposed strategies for member enterprise selection and task assignment.展开更多
The global water demand and supply situation is becoming increasingly severe due to water shortage and uneven distribution of water resources.The highest water demand in the energy sector is attributable to power gene...The global water demand and supply situation is becoming increasingly severe due to water shortage and uneven distribution of water resources.The highest water demand in the energy sector is attributable to power generation.With cross-country and cross-continental power grid interconnections becoming a reality,electricity trading across countries and the creation of new opportunities for re-allocation of water resources are possible.This study expands the concept of virtual water and proposes a generalized virtual water flow in an interconnected power grid system to accurately estimate water resource benefits of clean power transmission from both the production and the consumption sides.By defining the water scarcity index as a price mechanism indicator,the benefits of water resources allocation through power grid interconnections are evaluated.Taking the Africa-Asia-Europe interconnection scenario as an example,the total water saving would amount to 88.95 million m^3 by 2030 and 337.8 million m^3 by 2050.This result shows that grid interconnections could promote the development of renewable energy and expand the benefits of available water resources.展开更多
This paper addresses the problem of dynamic frequency control in a diesel-based mini-grid. It is shown that a virtual synchronous machine (VSM) can support dynamic frequency control by adding virtual inertia and dampi...This paper addresses the problem of dynamic frequency control in a diesel-based mini-grid. It is shown that a virtual synchronous machine (VSM) can support dynamic frequency control by adding virtual inertia and damping to the system. However, it is found that the typical formulation of damping power does not work properly when the grid forming gen-set operates in droop mode because of the unknown stabilization value of the grid frequency. As a solution to this problem, an estimator for the stabilization frequency that works in conjunction with the damping function of the VSM is proposed. Theoretical and experimental results provide evidence of a satisfactory performance of the proposed VSM with estimator for different values of the gen-set droop factor. The estimated stabilization frequency converges in approximately 2 s and the maximum frequency deviation during the transient is reduced in 34%, on average.展开更多
The joint grid system, which consists of the developed collar grid, the virtual grid and other grids, was used in the embedding technique to solve the problem of finding interpolating cells of the internal and externa...The joint grid system, which consists of the developed collar grid, the virtual grid and other grids, was used in the embedding technique to solve the problem of finding interpolating cells of the internal and external boundary points near the joint regions. With different boundary plane generated along different fixed surface, the collar grid obtained using hyperbolic partial equations can ensure to generate high quality grids and to provide real interpolating cells for the boundary points in the blanking regions. The virtual grid was used to convert solid wall boundary conditions into an interface condition, however, no fluid flow computations were conducted within the virtual grid. The computational result of body strake wing shows that the current developed embedding technique with joint grid system can effectively treat the geometry and can more accurately predict the flow over complexconfiguration with intersecting surfaces.展开更多
文摘The virtual grid method used in the embedding technique to solve the problem of finding interpolating cells of the inner and outer boundary points near joint regions was developed for calculating the viscous flows around a wing with control surface. The main purpose of the virtual grid is to effectively treat the geometry of the crossed facial planes at the interface, and to convert a solid wall boundary condition into an interface condition, however, no fluid flow computations are conducted within the virtual grid. Navier Stokes computations were performed for transonic flow over a clipped delta wing with control surface, and the computed results compare well with the experimental data.
文摘In order to improve efficiency of virtual enterprise, a manufacturing grid and multilevel manufacturing system of virtual enterprise is built up. When selecting member enterprises and task assignment based on the manufacturing grid, key activities are assigned to the suitable critical member enterprises by task decomposition, enterprise node searching and characteristic matching of manufacturing resources according to the characteristic matching strategy. By task merger, some ordinary activities are merged with corresponding key activities and assigned to corresponding critical member enterprises. However, the other ordinary activities are assigned to the related ordinary member enterprises with enterprise node searching and characteristic matching of manufacturing resources. Finally, an example of developing the artificial hip joint in the virtual enterprise is used to demonstrate that efficiency of the virtual enterprise is improved by using the manufacturing grid and the proposed strategies for member enterprise selection and task assignment.
基金supported by the State Grid GEIGC Science and Technology Project under the “Research on Global Energy Transition Scenario and Model Development and Application under the New Pattern of Global Environmental Protection” framework(Grant No.52450018000W)
文摘The global water demand and supply situation is becoming increasingly severe due to water shortage and uneven distribution of water resources.The highest water demand in the energy sector is attributable to power generation.With cross-country and cross-continental power grid interconnections becoming a reality,electricity trading across countries and the creation of new opportunities for re-allocation of water resources are possible.This study expands the concept of virtual water and proposes a generalized virtual water flow in an interconnected power grid system to accurately estimate water resource benefits of clean power transmission from both the production and the consumption sides.By defining the water scarcity index as a price mechanism indicator,the benefits of water resources allocation through power grid interconnections are evaluated.Taking the Africa-Asia-Europe interconnection scenario as an example,the total water saving would amount to 88.95 million m^3 by 2030 and 337.8 million m^3 by 2050.This result shows that grid interconnections could promote the development of renewable energy and expand the benefits of available water resources.
文摘This paper addresses the problem of dynamic frequency control in a diesel-based mini-grid. It is shown that a virtual synchronous machine (VSM) can support dynamic frequency control by adding virtual inertia and damping to the system. However, it is found that the typical formulation of damping power does not work properly when the grid forming gen-set operates in droop mode because of the unknown stabilization value of the grid frequency. As a solution to this problem, an estimator for the stabilization frequency that works in conjunction with the damping function of the VSM is proposed. Theoretical and experimental results provide evidence of a satisfactory performance of the proposed VSM with estimator for different values of the gen-set droop factor. The estimated stabilization frequency converges in approximately 2 s and the maximum frequency deviation during the transient is reduced in 34%, on average.
文摘The joint grid system, which consists of the developed collar grid, the virtual grid and other grids, was used in the embedding technique to solve the problem of finding interpolating cells of the internal and external boundary points near the joint regions. With different boundary plane generated along different fixed surface, the collar grid obtained using hyperbolic partial equations can ensure to generate high quality grids and to provide real interpolating cells for the boundary points in the blanking regions. The virtual grid was used to convert solid wall boundary conditions into an interface condition, however, no fluid flow computations were conducted within the virtual grid. The computational result of body strake wing shows that the current developed embedding technique with joint grid system can effectively treat the geometry and can more accurately predict the flow over complexconfiguration with intersecting surfaces.
文摘光伏等新能源及储能系统基于电力电子接口融入微电网,其低惯量问题显著,面临严峻的频率稳定风险。为了改善微电网频率动态特性,利用模型预测控制(model predictive control,MPC)协同优化外环与内环,提出了一种基于级联模型预测(cascaded model predictive control,CMPC)的虚拟同步机(virtual synchronous generator,VSG)控制策略。在外环,利用MPC的滚动优化,对输入VSG的有功功率参考值进行实时修正。在内环,优化通过两个阶段寻找最优电压矢量(voltage vector,VV)的离散空间矢量模型预测控制(discrete space vector model predictive control,DSVM-MPC)方法,减少跟踪外环输出误差,使频率控制更为精确。仿真结果表明,所提策略能够提升频率响应和限流效果,避免频率过冲。
