The stability of an incompressible two-dimensional wake

1972 ◽  
Vol 51 (2) ◽  
pp. 233-272 ◽  
Author(s):  
G. E. Mattingly ◽  
W. O. Criminale
Keyword(s):  
Reference Frames ◽  
Two Dimensional ◽  
Mean Velocity ◽  
Spatial Reference ◽  
Spatial Reference Frames ◽  
The Mean ◽  
Temporal And Spatial ◽  
The Stability ◽  
Transverse Oscillations ◽  
Small Disturbances

The growth of small disturbances in a two-dimensional incompressible wake has been investigated theoretically and experimentally. The theoretical analysis is based upon inviscid stability theory wherein small disturbances are considered from both temporal and spatial reference frames. Through a combined stability analysis, in which small disturbances are permitted to amplify in both time and space, the relationship between the disturbance characteristics for the temporal and spatial reference frames is shown. In these analyses a quasi-uniform assumption is adopted to account for the continuously varying mean-velocity profiles that occur behind flat plates and thin airfoils. It is found that the most unstable disturbances in the wake produce transverse oscillations in the mean-velocity profile and correspond to growing waves that have a minimum group velocity.Experimentally, the downstream development of the wake of a thin airfoil and the wave characteristics of naturally amplifying small disturbances are investigated in a water tank. The disturbances that develop are found to produce transverse oscillations of the mean-velocity profile in agreement with the theoretical prediction. From the comparison of the experimental results with the predictions for the characteristics of the most unstable waves via the temporal and spatial analyses, it is concluded that the stability analysis for the wake is to be considered solely from the more realistic spatial viewpoint. Undoubtedly, this conclusion is also applicable to other highly unstable flows such as jets and free shear layers.In accordance with the disturbance vorticity distribution as determined from the spatial model, a description of the initial development of a vortex street is put forth that contrasts with the description given by Sato & Kuriki (1961).

scholarly journals The evolution of a thermocline effected by a turbulent stream

1995 ◽  
Vol 2 (1) ◽  
pp. 49-57 ◽  
Author(s):  
O. A. Druzhinin ◽  
V. I. Kazakov ◽  
P. A. Matusov ◽  
L. A. Ostrovsky
Keyword(s):  
Turbulent Energy ◽  
Quantitative Agreement ◽  
Marginal Stability ◽  
Mean Velocity ◽  
Induced Drag ◽  
The Mean ◽  
The Stability ◽  
Semi Empirical ◽  
Oceanic Currents ◽  
Small Disturbances

Abstract. The process of thermocline evolution under the action of turbulent stream in the upper layer is investigated in laboratory experiment in thermally stratified tank, the initial temperature profile with pronounced thermocline being similar to that observed in tropic seas. The mean velocity and turbulent energy spatial distributions have been shaped to model the hydrological conditions in strong oceanic currents or wind-induced drag currents. The experiment demonstrates the gradual deepening and transformation of thermocline in a case where no global instability took place (i.e., with Richardson numbers always exceeding 0.3-0.4). The process of thermocline evolution resulted also in recurring "bursts" of microstructure. A numerical experiment based on equations of semi-empirical theory of turbulence shows quantitative agreement with experimental data. Moreover, simple analytical solutions and numerical results show that a layer with marginal stability is formed with Richardson numbers being very close to the stability threshold, so that quite small disturbances in thermocline can result in appearance of internal waves and bursts of turbulence.

scholarly journals Reference frames in spatial communication for navigation and sports: an empirical study in ultimate frisbee players

2020 ◽  
Vol 5 (1) ◽  
Author(s):  
Steven M. Weisberg ◽  
Anjan Chatterjee
Keyword(s):  
Reference Frame ◽  
Reference Frames ◽  
Spatial Information ◽  
Spatial Reference ◽  
Spatial Reference Frames ◽  
The North ◽  
Communication Task ◽  
Spatial Communication ◽  
Spatial Domains ◽  
Ultimate Frisbee

Abstract Background Reference frames ground spatial communication by mapping ambiguous language (for example, navigation: “to the left”) to properties of the speaker (using a Relative reference frame: “to my left”) or the world (Absolute reference frame: “to the north”). People’s preferences for reference frame vary depending on factors like their culture, the specific task in which they are engaged, and differences among individuals. Although most people are proficient with both reference frames, it is unknown whether preference for reference frames is stable within people or varies based on the specific spatial domain. These alternatives are difficult to adjudicate because navigation is one of few spatial domains that can be naturally solved using multiple reference frames. That is, while spatial navigation directions can be specified using Absolute or Relative reference frames (“go north” vs “go left”), other spatial domains predominantly use Relative reference frames. Here, we used two domains to test the stability of reference frame preference: one based on navigating a four-way intersection; and the other based on the sport of ultimate frisbee. We recruited 58 ultimate frisbee players to complete an online experiment. We measured reaction time and accuracy while participants solved spatial problems in each domain using verbal prompts containing either Relative or Absolute reference frames. Details of the task in both domains were kept as similar as possible while remaining ecologically plausible so that reference frame preference could emerge. Results We pre-registered a prediction that participants would be faster using their preferred reference frame type and that this advantage would correlate across domains; we did not find such a correlation. Instead, the data reveal that people use distinct reference frames in each domain. Conclusion This experiment reveals that spatial reference frame types are not stable and may be differentially suited to specific domains. This finding has broad implications for communicating spatial information by offering an important consideration for how spatial reference frames are used in communication: task constraints may affect reference frame choice as much as individual factors or culture.

scholarly journals Testing the spatial reference frames used for manual interception

2010 ◽  
Vol 10 (7) ◽  
pp. 1063-1063
Author(s):  
J. C. Dessing ◽  
J. D. Crawford ◽  
W. P. Medendorp
Keyword(s):  
Reference Frames ◽  
Spatial Reference ◽  
Spatial Reference Frames

Space Representation in Children

2018 ◽  
pp. 13-22
Keyword(s):  
Object Representation ◽  
Reference Frames ◽  
Cognitive Strategies ◽  
Space Representation ◽  
Spatial Transformations ◽  
Scientific Debate ◽  
Spatial Reference ◽  
Spatial Reference Frames ◽  
The Central Nervous System ◽  
The Individual

With “Spatial Reference Frames” we refer to systems of coordinates by which the central nervous system encodes the relative positions of objects in space, including that of the body itself. A reference system is a way of representing the positions of the subjects / objects in space. The spatial position of an object can be represented in the brain with respect to different classes of reference points, which may be related or not to the position of the subject. In a nutshell, we can say that there are two types of transformations of space imagery: the allocentric spatial transformations, that involve a system of representation from object to object and encode information about the location of an object or its parts in relation to other objects, and egocentric spatial transformations that involve a system of subject-object representation. The human being switches from one code to another, depending on the contingent requirements, giving preference to one or another system according to a set of heterogeneous factors. The gender difference (male / female), for example, plays a key role. Even the individual cognitive strategies make use of different representations in a significantly different way. Manipulation of spatial reference systems constitute a “transnosographic trait” in various neurological and psychiatric disorders. Each of these diseases (autism, schizophrenia, epilepsy, spatial anxiety, Parkinson) reaches some of the structures involved in the manipulation of referential of different spaces. The chapter illustrates Piaget's study on the representation of space in the child and the use of different spatial coding systems, and provides a brief overview of the scientific debate following the Piagetian position.

scholarly journals Shared contributions of the head and torso to spatial reference frames across spatial judgments

Cognition ◽  
2020 ◽  
Vol 204 ◽  
pp. 104349
Author(s):  
Matthew R. Longo ◽  
Sampath S. Rajapakse ◽  
Adrian J.T. Alsmith ◽  
Elisa R. Ferrè
Keyword(s):  
Reference Frames ◽  
Spatial Reference ◽  
Spatial Reference Frames
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