报告题目：Analysis of aerodynamic forces from the perspective of force element theory  

 报告人：张建成 教授（台湾大学应力学研究所）

 报告时间：2024年12月6日（周五）上午10：00-12：00

 报告地点：A18-529报告厅

 主办单位：必威西汉姆官网平台、航空航天结构力学及控制全国重点实验室、国际合作处

 报告内容摘要：

 This presentation is to briefly report the basic theory and progress of the force element theory. Since 1992, the author has proposed to analyze hydrodynamic/aerodynamic forces directly in terms of fluid elements of nonzero vorticity and density gradient (force element theory). This lecture is aimed at reviewing and adding some new results to our works on a force element theory for viscous compressible flows around a single or several finite bodies. The success lies in a judicious expression of the pressure force in terms of kinematic and thermodynamic quantities through the boundary conditions on bodies, elaborated to extract the potential force (such as added-mass) from the real viscous flow so that the force contributions associated with vorticity force and density gradient appear naturally to make a convergent force representation. Let ρ denote the fluid density,the velocity, and the vorticity. Among all the contributions, it is demonstrated that for largely separated flows about bluff bodies, there are two major source force element

 where ϕ is a (acyclic) natural potential, associated with the motion generated by the solid body moving in the negative direction of the force component under consideration. In particular, under mild conditions, our (unique) choice of ϕ enforces that the elements Re (x) and Ve (x) decay rapidly away from the body. Naturally, the contribution from Re (x) is negligible when there is only slight variation in the fluid density, while the contributions from Ve (x) is negligible when the fluid element is irrotational. Moreover, Re (x) due to density gradient becomes progressively important relative to Ve (x) due to vorticity as the Mach number increases. The present method of force analysis enables effective analysis and assessment of relative importance of individual flow structures - each consists of a region of fluid elements. The analysis could therefore be very much useful in view of the rapid growth in numerical and experimental fluid dynamics; detailed (either local or global) flow information is often available. The review proceeds with the formulation for the constant-density flow, then for the stratified fluid, and then for the general viscous compressible flows with and without turbulence, and mention some applications to flow control.  

 报告人简介： 

 After obtaining his Ph.D. degree, Dr. Chang had worked at the Lawrence Berkeley National Laboratory as a Research Associate. Since 1987, he has been a faculty member at the Institute of Applied Mechanics, National Taiwan University, Associate Professor (1987) and Professor (1993), and has been appointed a Distinguished Professor since 2007. He had held several visiting positions at California Institute of Technology (Summer 1987), University Erlangen-Nürnburg (1994-1995, Humboldt Fellow), University of California, Berkeley (Fall, 1997, NSC Visiting Program), Columbia University (Special Invitation, Fall, 1998), and HKUST (Hong Kong, Spring, 2003, Distinguished Visiting Scholar Program). From July 2005 to June 2009, Prof. Chang had held a joint appointment in Academia Sinica on mission to establish Division of Mechanics in the Research Center for Applied Sciences. From August,2009 to July, 2012, Dr. Chang had served as the Director of the Institute of Applied Mechanics, National Taiwan University. He is currently an executive member of the Center for Advanced Study in Theoretical Sciences, National Taiwan University. Prof. Chang also serves as a Taiwan representative to the General Assembly of IUTAM (International Union of Theoretical and Applied Mechanics).   

 Prof. Chang has done research works in the fields of fluid mechanics and scientific computation, specializing in vortex dynamics, unsteady flow and turbulence as well as two-phase suspension flow. In particular, he has developed the theory of force elements in hydrodynamics and aerodynamics, and recently the concept and techniques of principal spectral analysis and structural frequencies. Over the years, he has also been engaged in research on micro & nanofluidics, biological modeling and imaging techniques as well as in mechanics of micro-scale composites, 2D materials (such as grapheme, Boron Nitride), photonic band-gap materials and nano-optics/plasmonics for metallic/dielectric materials. He has published more than 160 papers in internationally renowned journals such as Journal of Fluid Mechanics, Physics of Fluids, Proc Royal Society, London, Series A, Physical Reviews, CARBON, Nanoscale, ACS Nano, Journal of Materials Chemistry A, Ultrasound in Medicine and Biology and Physics in Medicine and Biology. Over the past 38 years, Prof. Chang has supervised 28 doctoral theses and over 150 MS theses which cover a wide range of topics in applied mechanics, all in the National Taiwan University