Based on Buckingham＇s π-Theorem, dimensional analysis has achieved considerable success over the past near-century. Model testing has long been a powerful tool in both scientific studies and engineering applications...Based on Buckingham＇s π-Theorem, dimensional analysis has achieved considerable success over the past near-century. Model testing has long been a powerful tool in both scientific studies and engineering applications. However, the prototype objects are becoming more and more complicated nowadays, and many of the prototype systems can contain several sub-systems. The conventional theories on model-prototype similarity and dimensional analysis have only limited application since the π-Theorem itself does not distinguish between the original system and subsystems. This is particularly true in the field of structural dynamics, where the structure is often modeled as a multi-degree-of-freedom system. In this paper, we attempt to show that, if a system can be decoupled into several nontrivial subsystems, then, in each subsystem, the number of π-terms will be reduced and therefore simplify the model testing. On the other hand, if a system cannot be decoupled into subsystems, then using model testing with reduced π-term analysis, both experimentally and theoretically, may introduce severe errors.展开更多
Based on their differences in physical characteristics and time-space scales,the ocean motions have been divided into four types in the present paper：turbulence,wave-like motion,eddy-like motion and circulation.Apply...Based on their differences in physical characteristics and time-space scales,the ocean motions have been divided into four types in the present paper：turbulence,wave-like motion,eddy-like motion and circulation.Applying the three-fold Reynolds averages to the governing equations with Boussinesq approximation,with the averages defined on the former three sub-systems,we derive the governing equation sets of the four sub-systems and refer to their sum as ＂the ocean dynamic system＂.In these equation sets,the interactions among different motions appear in two forms：the first one includes advection transport and shear instability generation of larger scale motions,and the second one is the mixing induced by smaller scale motions in the form of transport flux residue.The governing equation sets are the basis of analytical/numerical descriptions of various ocean processes.展开更多
火箭基组合循环(Rocket Based Combined Cycle,RBCC)推进系统是极具发展前景的组合动力方案,而模态转换阶段是RBCC发动机工作的关键环节,关系到整个推进系统的成败和效率。RBCC发动机的不同工作模态具有显著的分类特征,重点总结了引射/...火箭基组合循环(Rocket Based Combined Cycle,RBCC)推进系统是极具发展前景的组合动力方案,而模态转换阶段是RBCC发动机工作的关键环节,关系到整个推进系统的成败和效率。RBCC发动机的不同工作模态具有显著的分类特征,重点总结了引射/亚燃与亚燃/超燃两个关键转换阶段,综述相关特性与机理的研究进展,汇总实验与数值模拟方面的研究成果。与双模态超燃冲压发动机相比,RBCC发动机由于内含火箭射流,在模态平稳转换控制上具备优势。结合以等离子体为代表的新型多场燃烧耦合控制方式,RBCC发动机成为了当前超声速燃烧流动控制的研究热点。在总结相关进展的基础上,对未来的模态过渡研究提出了建议。展开更多
文摘Based on Buckingham＇s π-Theorem, dimensional analysis has achieved considerable success over the past near-century. Model testing has long been a powerful tool in both scientific studies and engineering applications. However, the prototype objects are becoming more and more complicated nowadays, and many of the prototype systems can contain several sub-systems. The conventional theories on model-prototype similarity and dimensional analysis have only limited application since the π-Theorem itself does not distinguish between the original system and subsystems. This is particularly true in the field of structural dynamics, where the structure is often modeled as a multi-degree-of-freedom system. In this paper, we attempt to show that, if a system can be decoupled into several nontrivial subsystems, then, in each subsystem, the number of π-terms will be reduced and therefore simplify the model testing. On the other hand, if a system cannot be decoupled into subsystems, then using model testing with reduced π-term analysis, both experimentally and theoretically, may introduce severe errors.
基金Project supported by the National Natural Science Foundation of China (Grant Nos.40776020,41106032)the National Basic Research Program of China (973 Program,Grant Nos.G1999043800,2006CB403600,2010CB950404 and 2010CB950300)
文摘Based on their differences in physical characteristics and time-space scales,the ocean motions have been divided into four types in the present paper：turbulence,wave-like motion,eddy-like motion and circulation.Applying the three-fold Reynolds averages to the governing equations with Boussinesq approximation,with the averages defined on the former three sub-systems,we derive the governing equation sets of the four sub-systems and refer to their sum as ＂the ocean dynamic system＂.In these equation sets,the interactions among different motions appear in two forms：the first one includes advection transport and shear instability generation of larger scale motions,and the second one is the mixing induced by smaller scale motions in the form of transport flux residue.The governing equation sets are the basis of analytical/numerical descriptions of various ocean processes.
文摘火箭基组合循环(Rocket Based Combined Cycle,RBCC)推进系统是极具发展前景的组合动力方案,而模态转换阶段是RBCC发动机工作的关键环节,关系到整个推进系统的成败和效率。RBCC发动机的不同工作模态具有显著的分类特征,重点总结了引射/亚燃与亚燃/超燃两个关键转换阶段,综述相关特性与机理的研究进展,汇总实验与数值模拟方面的研究成果。与双模态超燃冲压发动机相比,RBCC发动机由于内含火箭射流,在模态平稳转换控制上具备优势。结合以等离子体为代表的新型多场燃烧耦合控制方式,RBCC发动机成为了当前超声速燃烧流动控制的研究热点。在总结相关进展的基础上,对未来的模态过渡研究提出了建议。
