Governing equations, experiments, and the experimentalist

It is argued that the most important test of the understanding of any experiment is whether or not the results are consistent with the equations and boundary conditions believed to govern the flow. If they are not, then either the measurements are incorrect, the equations or boundary conditions are wrong, or the experiment performed was not the one believed to have been done. It is suggested that many apparently contradictory experimental results are, in fact, the result of the latter and have not been recognized as such because of a failure to apply the governing equations to the data. The arguments are supported by examples from turbulent shear flow experiments.     

The art and science of foam bubbles

Art and science become inevitably intertwined in our appreciation of nature's forms. This concept is demonstrated by the creative team responsible for the cover images of Nonlinear Dynamics, Psychology, and Life Sciences. Denis Weaire, Stefan Hutzler, Wiebke Drenckhan form a leading international collaboration with photographers Tim Durham and Michael Boran that explores the physics of bubble patterns. The images they generate capture and manipulate the striking aesthetic impact of foam bubbles. Furthermore, the foams exhibit a balance between simplicity and intricacy that symbolizes many of the complex systems that permeate nature and society.     

On the hidden beauty of the proper orthogonal decomposition

The proper orthogonal decomposition theorem (Loève, 1955) of probability theory has been proposed by Lumley (1967, 1972, 1981) for detection of spatial coherent patterns in turbulent flows. More specifically, the decomposition extracts deterministic functions from second-order statistics of a random field and converges optimally fast in quadratic mean (i.e., in energy). The technique can be made completely deterministic in the sense that it can be applied to spatially and temporally evolving flows. The remarkable property of this deterministic decomposition is not only in its optimal convergence (as emphasized before) but also in its space/time symmetry which permits access to the spatiotemporal dynamics. The flow is decomposed into both spatial and temporal orthogonal modes which are coupled: each space component is associated with a time component partner. The latter is the time evolution of the former and the former is the spatial configuration of the latter. This generalizes the notion of spatial and temporal structures which can be followed through the various instabilities that the flow undergoes as Reynolds number increases. It also provides a nonlinear dynamics tool for spatiotemporal dynamical systems and can be used for bifurcation detection and analysis as well as dimension and degree of complexity estimates.Dedicated to Professor J.L. Lumley on the occasion of his 60th birthday.This work was supported by an NSF/PYI award MSS89-57462, and partially by a NATO Grant No. 900265 which are gratefully acknowledged.     

浅论力学研究中的一些思维方法与力学美

浅论力学研究中的对偶互补(阴阳互补)与对称性、简单性、顺向思维与逆向思维、以及力学美等问题.     

Fluidization science, its development and future

By revisiting the three stage theory for the progress of science proposed by Taketani in 1942, the footmarks of fluidization research are examined. The bubbling and fast fluidization issues were emphasized so that the future offluidization research can be discussed among scientists and engineers in a wider perspective. The first cycle of fluidization research was started in the early 1940s by an initial stage of phenomenology. The second stage of structural studies was kicked off in the early 1950s with the introduction of the two phase theory. The third stage of essential studies occurred in the early 1960s in the form of bubble hydrodynamics. The second cycle, which confirmed the aforementioned three stages closed at the turn of the century, established a general understanding of suspension structures including agglomerating fluidization, bubbling, turbulent and fast fluidizations and pneumatic transport; also established powerful measurement and numerical simulation tools.After a general remark on science, technology and society issues the interactions between fluidization technology and science are revisited. Our future directions are discussed including the tasks in the third cycle, particularly in its phenomenology stage where strong motivation and intention are always necessary, in relation also to the green reforming of the present technology. A generalized definition of ＇fluidization＇ is proposed to extend fluidization principle into much wider scientific fields, which would be effective also for wider collaborations.     

文科类学生理科素质培养的教学研究及实践

利用开设《力学与现代生活》公共选修课的教学实践,研究针对文科类学生的基础、兴趣以及公共选修课的跨越式目的要求,进行课程及教学内容的优选、教学方法的创新、课堂过程管理方式的调整、考试方式的改革以及问卷调查与考试成绩的分析等方面,如何面向文科类学生开设自然科学及工程技术类公共选修课程,培养其综合素质,拓宽学生的知识面,完善其知识结构,提高跨学科类公共选修课的教学质量,切实达到通识教育课程的教学目的.     

Development,current state of the art,and applications of local interaction theory. Review

Local interaction theory comprises studies based on the representation of the force and thermal characteristics of the action of a medium on a body at a certain point on its surface as functions of the local velocity, the angle between the velocity direction and the normal to the surface, and the global parameters, which are constant at all points on the surface.In this review, we will trace the history of the theory and analyze the main results concerning the development of particular local interaction models, the calculation of the integral characteristics and the determination of optimal body shapes, the general properties of the model and practical methods based on them, and nontraditional fields of local model application.Along with the general results, we will focus on the most important fields of local model application, such as aerodynamics, gasdynamics, and rarefied gas dynamics.Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 3, pp. 3–18, May–June, 1996.     

普及是科学的目的和归宿——纪念《力学与实践》创刊30年

1953年在南京市第八中学上高中时,我读了一本关于航空的科普译著小册子,所说飞机为什么能飞的道理,激发了我对流体力学的兴趣.为学习流体力学, 1954年我考入了北京大学数学力学系.所以,我是在科学普及著作的影响下,进入力学学习和工作的.     

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从珲论力学的教学现状出发,通过在课程内容和教学方法等方面进行的改革,取得了一定的成效,使得课程建设梃朝着精品课程的方向发展,对提高教学质量和培养学生的创新能力具有重要意义.     

The art of shock waves and their flowfields

The visualization of compressible flows is a mature science that has significantly contributed to many advances in fluid mechanics. Numerous visualization records have been generated, many of which are not only noteworthy for their physical content, but also for their aesthetic appeal. Images of shock waves and their flowfields, primarily obtained with density-sensitive visualization methods, not only provide valuable information about the physical mechanisms of flows, but often have the qualities of works of art. This paper reviews briefly the role of these visualizations in science and their possible position in an art environment, while trying to establish a little-explored link between the elements of compressible fluid dynamics and some features found in various works of art.      

Nonlinear targeted energy transfer: state of the art and new perspectives

Nonlinear Dynamics - Following a brief review of current progress in the field of nonlinear targeted energy transfer (TET), we discuss some general ideas and methods in this field and describe...     

Methods of nonlinear statistical dynamics: The state of the art and prospects

Conclusion Our research permits us to draw the following conclusions. As our survey of methods for nonlinear statistical dynamics showed, at the present time, there is no universal approach (with the exception of efficient Monte Carlo methods) for obtaining reliable estimates of the probability of rare events in nonlinear monoparametric systems. From Proc. General Meeting of the National Committee of Ukraine on Theoretical and Applied Mechanics (Kiev, May 14, 1996). Translated from Prikladnaya Mekhanika, Vol. 33, No. 8, pp. 64–72, August, 1997.     

On backstresses,overstresses, and internal stresses represented on the mesoscale

The notions ‘backstress’, ‘effective stress’, ‘overstress’ and ‘equilibrium stress’ are given clear physical meaning by confronting their use with the use of internal stresses represented on the mesoscale as tensorial internal variables. Our way of modeling creep and relaxation is newly presented and agreement with experimental findings demonstrated. It is shown that in the case of a monotonic uniaxial deviatoric loading, the relation of the macroscopic stress to the ‘backstress’ or ‘equilibrium stress’ equals the relation of the acting force to that part of this force that is sustained by the infrastructure of barriers that do not undergo plastic deformation or rheological flow.     

Process and meaning: nonlinear dynamics and psychology in visual art

Creating and viewing visual art are both nonlinear experiences. Creating a work of art is an irreversible process involving increasing levels of complexity and unpredictable events. Viewing art is also creative with collective responses forming autopoietic structures that shape cultural history. Artists work largely from the chaos of the unconscious and visual art contains elements of chaos. Works of art by the author are discussed in reference to nonlinear dynamics. "Travelogues" demonstrates continued emerging interpretations and a deterministic chaos. "Advice to the Imperfect" signifies the resolution of paradox in the nonlinear tension of opposites. "Quanah" shows the nonlinear tension of opposites as an ongoing personal evolution. "The Mother of All Things" depicts seemingly separate phenomena arising from undifferentiated chaos. "Memories" refers to emotional fixations as limit cycles. "Compassionate Heart," "Wind on the Lake," and "Le Mal du Pays" are a series of works in fractal format focusing on the archetype of the mother and child. "Sameness, Depth of Mystery" addresses the illusion of hierarchy and the dynamics of symbols. In "Chasadim" the origin of worlds and the regeneration of individuals emerge through chaos. References to chaos in visual art mirror the nonlinear complexity of life.     

Massimo Guiggiani: The science of vehicle dynamics: handling,braking, and ride of road and race cars

Guiggiani’s book titled “The Science of Vehicle Dynamics. Handling, Braking, and Ride of Road and Race Cars” is an excellent contribution to the comprehension of vehicle dynamics both for undergraduate students and experts in the field. Despite 50 years of books on vehicle dynamics, this work has the merit to propose new concepts and interpretations with its rigorous approach which does not leave nothing either to mere intuition or for granted.