The wakes of bluff objects and in particular of circular cylinders are known to undergo a ‘fast ’ transition, from a laminar two-dimensional state a t Reynolds number 200 to a turbulent state a t Reynolds number 400...
The wakes of bluff objects and in particular of circular cylinders are known to undergo a ‘fast ’ transition, from a laminar two-dimensional state a t Reynolds number 200 to a turbulent state a t Reynolds number 400. The process has been documented in several eXperimental mvestigations, but the underlying physical mechanisms have remained largely unknown so far. In this paper, the transition process is investigated numerically, through direct simulation of the NavierStokes equations at representative Reynolds numbers, up to 500. A high-order timeaccurate, miXed spectral/spectral element technique is used. It is shown that the wake first becomes three-dimensional, as a result of a secondary instability of the two-dimensional vorteX street. This secondary instability appears at a Reynolds number close to 200. For slightly supercritical Reynolds numbers, a harmonic state develops, in which the flow oscillates at its fundamental frequency (Strouhal number) around a spanwise modulated time-average flow. In the near wake the modulation wavelength of the time-average flow is half of the spanwise wavelength of the perturbation flow, consistently with linear instability theory. The vorteX filaments have a spanwise wavy shape in the near wake, and form rib-like structures further downstream. At higher Reynolds numbers the three-dimensional flow oscillation undergoes a period-doubling bifurcation, in which the flow alternates between two different states. Phase-space analysis of the flow shows that the basic limit cycle has branched into two connected limit cycles. In physical space the period doubling appears as the shedding of two distinct types of vorteX filaments. Further increases of the Reynolds number result in a cascade of period-doubling bifurcations, which create a chaotic state in the flow at a Reynolds number of about 500. The flow is characterized by broadband power spectra, and the appearance intermittent phenomena. It is concluded that the wake undergoes transit
In this article we present a new formulation for coupling spectral element discretizations to finite difference and finite element discretizations addressing flow problems in very complicated geometries. A general ite...
详细信息
The response of transport measures (Nusselt number, drag and lift force) for two- and three-dimensional flow past a heated cylinder reaching a chaotic state is investigated numerically using a spectral element discret...
The response of transport measures (Nusselt number, drag and lift force) for two- and three-dimensional flow past a heated cylinder reaching a chaotic state is investigated numerically using a spectral element discretization at a Reynolds number Re = 500. The undisturbed two-dimensional flow remains periodic at this Reynolds number, unless a suitable forcing is applied on the naturally produced system. Three-dimensional simulations establish that three-dimensionality sets in at Re almost-equal-to 200. Successive supercritical states are established through a series of period-doublings, before a chaotic state is reached at a Re almost-equal-to 500. For the two-dimensional forced flow, all transport measures oscillate aperiodically in time and undergo a "crisis," i.e., a sudden and dramatic increase in their amplitude. The corresponding three-dimensional, naturally produced chaotic state corresponds to a less drastic change of the transport quantities with both rms and mean values lower than their two-dimensional counterparts.
S. Kida, M. Takaoka, F. Hussain; Corrigendum:‘‘Reconnection of two vortex rings’’ [Phys. Fluids A 1, 630 (1989)]Comments, Physics of Fluids A: Fluid Dynamics, V
S. Kida, M. Takaoka, F. Hussain; Corrigendum:‘‘Reconnection of two vortex rings’’ [Phys. Fluids A 1, 630 (1989)]Comments, Physics of Fluids A: Fluid Dynamics, V
作者：
STIMSON, WAMARSH, MTUTTICH, RMWilliam A. Stimsonreceived his B.S. degree in mathematics from the University of Texas at El Paso in 1964
and his M.S. degree in engineering from the University of Santa Clara in 1971. He served in the U.S. Army Artillery during the Korean Conflict and subsequently was employed at IBM Huntsville Alabama until 1968 where he worked in the design of automatic control systems of the Saturn vehicle. From 1968 until 1971 he was employed at Ames Research Center Moffett Field in the design of nonlinear control systems for sounding rockets and pencil-shaped spacecraft. Following this Mr. Stimson worked at Hewlett Packard Sunnyvale California as a test engineer in automatic test systems. Since 1973 Mr. Stimson has been employed at the Naval Ship Weapon Systems Engineering Station Port Hueneme. He was a ship qualification trials project supervisor for many years and is now serving as master ordnance repair deputy program manager. Mr. Stimson is a member of the American Society of Naval Engineers and is program chairman of the Channel Islands Section. Cdr. Michael T. Marsh
USNreceived a B.S. in mathematics from the University of Nebraska and was commissioned via the NESEP program in 1970. He holds an M.S. in computer science from the U.S. Navy Postgraduate School and an MBA from the State University of New York. Cdr. Marsh has served in the weapons department of USSFrancis Hammond (FF-1067) and of USSJohn S. McCain (DDG-36). He was weapons officer aboard USSSampson (DDG-10). As an engineering duty officer Cdr. Marsh was the technical design officer for PMS-399 at the FFG-7 Class Combat System Test Center from 1978 to 1982. He is presently combat system officer at SupShip Jacksonville and has been active in the MOR program since its inception. Cdr. Marsh is also the vice chairman of the Jacksonville Section of ASNE. LCdr. Richard M. Uttich
USNholds B.S. and M.S. degrees in mechanical engineering from Stanford University. He enlisted in the Navy in 1965 serving as an electronics technician aboard USSNereus (A
The 600-ship United States Navy offers private shipyards an unprecedented opportunity for overhaul of surface combatants with complex combat systems. Recognizing the new challenge associated with the overhaul of high ...
详细信息
The 600-ship United States Navy offers private shipyards an unprecedented opportunity for overhaul of surface combatants with complex combat systems. Recognizing the new challenge associated with the overhaul of high technology combat systems in the private sector, the Navy in 1983 established the master ordnance repair (MOR) program. This program, a joint effort of the Naval Sea Systems Command (NAVSEA) and the Shipbuilders Council of America (SCA), was designed to identify and qualify those companies and private shipyards technically capable of managing combat systems work and conducting combat system testing. Standard Item 009–67 describes the role of the MOR company in combat system overhaul. It defines terms that are important to understanding the item itself, and imposes upon the prime contractor an obligation to utilize the MOR subcontractor in a managerial capacity. Specific tasks are assigned to the MOR company in planning, production, and testing. Finally, this standard item describes to the Navy planner how to estimate the size of the MOR team appropriate to the work package, a feature that will ensure that combat system bids are tailored to a specific availability.
"This book is concerned with the application of methods from dynamical systems and bifurcation theories to the study of nonlinear oscillations. Chapter 1 provides a review of basic results in the theory of dynami...
详细信息
ISBN:
(数字)9781461211402
ISBN:
(纸本)9780387908199;9781461270201
"This book is concerned with the application of methods from dynamical systems and bifurcation theories to the study of nonlinear oscillations. Chapter 1 provides a review of basic results in the theory of dynamical systems, covering both ordinary differential equations and discrete mappings. Chapter 2 presents 4 examples from nonlinear oscillations. Chapter 3 contains a discussion of the methods of local bifurcation theory for flows and maps, including center manifolds and normal forms. Chapter 4 develops analytical methods of averaging and perturbation theory. Close analysis of geometrically defined two-dimensional maps with complicated invariant sets is discussed in chapter 5. Chapter 6 covers global homoclinic and heteroclinic bifurcations. The final chapter shows how the global bifurcations reappear in degenerate local bifurcations and ends with several more models of physical problems which display these behaviors." #;#1 "An attempt to make research tools concerning `strange attractors' developed in the last 20 years available to applied scientists and to make clear to research mathematicians the needs in applied works. Emphasis on geometric and topological solutions of differential equations. Applications mainly drawn from nonlinear oscillations." #;#2
Mathematical models of the human left ventricle are presented to determine the physiological response-oriented mechanical parameters of the LV, which have diagnostic significance. These parameters are (i) the rheologi...
详细信息
Mathematical models of the human left ventricle are presented to determine the physiological response-oriented mechanical parameters of the LV, which have diagnostic significance. These parameters are (i) the rheological parameters of the left ventricular muscle, namely the instantaneous values of stiffness of series elasticity, parallel elasticity, and the stress-strain rate relationship for the contractile unit that characterizes the deviatric stress-strain response of a left ventricular muscle element, (ii) the effective modulus of the LV, and (iii) the state of stress in the LV. The rheological parameters are obtained from a continuum model of the LV whose stress state equilibrates the chamber pressure and whose strain state equals the instantaneous strains in the actual LV, obtained from instantaneous changes in the geometry of the LV (as noted from cineangiocardiography); the constitutive equations for the model incorporate the known existing rheological models for the isolated cardiac muscle. The effective moduli of the LV are obtained by correlating the fundamental frequency of vibration of a spherical model of the LV with the corresponding frequencies of the second component of the first heart sound and the third heart sound; thus the values of representative moduli (and hence indices of the left ventricular stiffnesses) at systole and diastole are obtained. The stress state in the LV is obtained by utilizing single plane cineangiocardiographic information of the irregular geometry of the LV in anteroposterior projection. Plane stress finite element analysis of this planor irregular geometry of the LV is done and the resulting stresses are reduced by a factor, heuristically determined to make allowance for the actual 3-dimensional geometry of the LV; the stresses obtained thus bring out effects of irregular boundary of varying (and at times high) curvature.
暂无评论