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
Based on surface mount products virtual assembly technology,the solder joint reliability of plastic ball grid array (PBGA) was studied. Four process parameters,including the upper pad diameter,the stencil thickness,th...Based on surface mount products virtual assembly technology,the solder joint reliability of plastic ball grid array (PBGA) was studied. Four process parameters,including the upper pad diameter,the stencil thickness,the chip weight on a single solder joint and the lower pad diameter were chose as four control factors. By using an L25(56) orthogonal array the PBGA solder joints which have 25 different process parameters’ levels combinations were designed. The numerical models of all the 25 PBGA solder joints were developed and the finite element analysis models were setup. The stress and strain distribution within the PBGA solder joints under thermal cycles were studied by finite element analysis,and the thermal fatigue life of PBGA solder joint was calculated using Coffin-Manson equation. Based on the calculated thermal fatigue life results,the range analysis was performed. The results of study show that that the impact sequence of the four factors from high to low on the fatigue life of PBGA solder joints are the stencil thickness,the upper pad diameter,the lower pad diameter and the chip weight on a single solder joint; the best level combination ofprocess parameters that results in the longest fatigue life is the lower pad diameter of 0.6 mm,the stencil thickness of 0.175 mm,the chip weight on asingle solder joint of 28×10 -5 N and the upper pad diameter of 0.5 mm.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
In this paper,an experiment method for the Manufacturing Grid application system development in the single personal computer environment is proposed.The characteristic of the proposed method is constructing a full pro...In this paper,an experiment method for the Manufacturing Grid application system development in the single personal computer environment is proposed.The characteristic of the proposed method is constructing a full prototype Manufactur- ing Grid application system which is hosted on a single personal computer with the virtual machine technology.Firstly,it builds all the Manufacturing Grid physical resource nodes on an abstraction layer of a single personal computer with the virtual machine tech- nology.Secondly,all the virtual Manufacturing Grid resource nodes will be connected with virtual network and the application software will be deployed on each Manufacturing Grid nodes.Then,we can obtain a prototype Manufacturing Grid application system which is working in the single personal computer,and can carry on the experiment on this foundation.Compared with the known experiment methods for the Manufacturing Grid application system development,the proposed method has the advantages of the known methods,such as cost inexpensively,operation simple,and can get the confidence experiment result easily.The Manu- facturing Grid application system constructed with the proposed method has the high scalability,stability and reliability.It is can be migrated to the real application environment rapidly.展开更多
This paper studies the voltage, phase and current tracking strategy to eliminate voltage and current mutations when the virtual synchronous generator is switching between grid-connected and islanded. By using these st...This paper studies the voltage, phase and current tracking strategy to eliminate voltage and current mutations when the virtual synchronous generator is switching between grid-connected and islanded. By using these strategies the inverter can realize secondary frequency regulation and voltage regulation. If the phase is near 0 or 2π a little disturbance may made the PLL output a big error, so a new PLL is proposed by this paper. A sine module is added in the PLL to avoid this error. In order to verify the strategy proposed by this paper a simulation model is built in Matlab/Simulink. The simulation results show that the control strategy can realize seamless switching.展开更多
This paper combines semantic web technology with business modeling and yields semantic business model that is semantically described in terms of roles and relationships. The semantic business model can be used to disc...This paper combines semantic web technology with business modeling and yields semantic business model that is semantically described in terms of roles and relationships. The semantic business model can be used to discover grid services by means of automation tools. The gap between business goals and grid services is bridged by role relationships and compositions of them, so that the virtual organization evolution is supported effectively. Semantic business model can support virtual organization validation at design stage rather than at run-time stage. The designers can animate their business model and make initial assessment of what interactions should occur between roles and in which order. The users can verify whether the grid service compositions satisfy business goals.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Funded by Science Foundation of Guangxi Zhuang Autonomous Region (No.02336060) .
文摘Based on surface mount products virtual assembly technology,the solder joint reliability of plastic ball grid array (PBGA) was studied. Four process parameters,including the upper pad diameter,the stencil thickness,the chip weight on a single solder joint and the lower pad diameter were chose as four control factors. By using an L25(56) orthogonal array the PBGA solder joints which have 25 different process parameters’ levels combinations were designed. The numerical models of all the 25 PBGA solder joints were developed and the finite element analysis models were setup. The stress and strain distribution within the PBGA solder joints under thermal cycles were studied by finite element analysis,and the thermal fatigue life of PBGA solder joint was calculated using Coffin-Manson equation. Based on the calculated thermal fatigue life results,the range analysis was performed. The results of study show that that the impact sequence of the four factors from high to low on the fatigue life of PBGA solder joints are the stencil thickness,the upper pad diameter,the lower pad diameter and the chip weight on a single solder joint; the best level combination ofprocess parameters that results in the longest fatigue life is the lower pad diameter of 0.6 mm,the stencil thickness of 0.175 mm,the chip weight on asingle solder joint of 28×10 -5 N and the upper pad diameter of 0.5 mm.
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.
基金Funded by the Open Project in Hubei Digital Manufacturing Key Laboratory under Grant NO.SZ0413the Sunshine Young Project in Wuhan City of China under Grant No.20055003059-5.
文摘In this paper,an experiment method for the Manufacturing Grid application system development in the single personal computer environment is proposed.The characteristic of the proposed method is constructing a full prototype Manufactur- ing Grid application system which is hosted on a single personal computer with the virtual machine technology.Firstly,it builds all the Manufacturing Grid physical resource nodes on an abstraction layer of a single personal computer with the virtual machine tech- nology.Secondly,all the virtual Manufacturing Grid resource nodes will be connected with virtual network and the application software will be deployed on each Manufacturing Grid nodes.Then,we can obtain a prototype Manufacturing Grid application system which is working in the single personal computer,and can carry on the experiment on this foundation.Compared with the known experiment methods for the Manufacturing Grid application system development,the proposed method has the advantages of the known methods,such as cost inexpensively,operation simple,and can get the confidence experiment result easily.The Manu- facturing Grid application system constructed with the proposed method has the high scalability,stability and reliability.It is can be migrated to the real application environment rapidly.
基金Acknowledgements： This work is supported by grants from the National Natural Science Foundation of China （Grant No. 90104002 ＆ 2003CB314800） and by Computer Software Lab of Siehuan Normal University.
文摘This paper studies the voltage, phase and current tracking strategy to eliminate voltage and current mutations when the virtual synchronous generator is switching between grid-connected and islanded. By using these strategies the inverter can realize secondary frequency regulation and voltage regulation. If the phase is near 0 or 2π a little disturbance may made the PLL output a big error, so a new PLL is proposed by this paper. A sine module is added in the PLL to avoid this error. In order to verify the strategy proposed by this paper a simulation model is built in Matlab/Simulink. The simulation results show that the control strategy can realize seamless switching.
基金Supported bythe National Basic Research Programof China (973 Program) (1999032710)
文摘This paper combines semantic web technology with business modeling and yields semantic business model that is semantically described in terms of roles and relationships. The semantic business model can be used to discover grid services by means of automation tools. The gap between business goals and grid services is bridged by role relationships and compositions of them, so that the virtual organization evolution is supported effectively. Semantic business model can support virtual organization validation at design stage rather than at run-time stage. The designers can animate their business model and make initial assessment of what interactions should occur between roles and in which order. The users can verify whether the grid service compositions satisfy business goals.
