scholarly journals An Update on Binary Formation by Rotational Fission

2001 ◽  
Vol 200 ◽  
pp. 40-44 ◽  
Author(s):  
Joel E. Tohline ◽  
Richard H. Durisen
Keyword(s):  
Numerical Simulations ◽  
Dynamic Processes ◽  
Nonlinear Saturation ◽  
Detailed Understanding ◽  
Structure And Stability ◽  
Stability Analyses ◽  
Mode Amplitude ◽  
Binary Formation ◽  
Dynamic Growth ◽  
Axisymmetric Equilibrium

During the 1980s, numerical simulations showed that dynamic growth of a barlike mode in initially axisymmetric, equilibrium protostars does not lead to prompt binary formation, i.e., fission. Instead, such evolutions usually produce a dynamically stable, spinning barlike configuration. In recent years, this result has been confirmed by numerous groups using a variety of different hydrodynamical tools, and stability analyses have convincingly shown that fission does not occur in such systems because gravitational torques cause nonlinear saturation of the mode amplitude. Other possible routes to fission have been much less well scrutinized because they rely upon a detailed understanding of the structure and stability of initially nonaxisymmetric structures and/or evolutions that are driven by secular, rather than dynamic processes. Efforts are underway to examine these other fission scenarios.

Structure and stability analyses of collagen hydrolysate coacervates triggered by ethanol in aqueous solution

2020 ◽  
Vol 137 (48) ◽  
pp. 49600
Author(s):  
Zhijie Li ◽  
Jie Liu ◽  
Luan Zhang ◽  
Yuelong Xiao ◽  
Keyong Tang ◽  
...  
Keyword(s):  
Aqueous Solution ◽  
Collagen Hydrolysate ◽  
Structure And Stability ◽  
Stability Analyses

scholarly journals Synthesis, 3D-structure and stability analyses of NRPa-308, a new promising anti-cancer agent

2019 ◽  
Vol 29 (24) ◽  
pp. 126710 ◽  
Author(s):  
Etienne Brachet ◽  
Aurore Dumond ◽  
Wang-Qing Liu ◽  
Marie Fabre ◽  
Mohamed Selkti ◽  
...  
Keyword(s):  
3D Structure ◽  
Structure And Stability ◽  
Stability Analyses ◽  
Anti Cancer ◽  
Cancer Agent

Low-dimensional models of a temporally evolving free shear layer

2009 ◽  
Vol 618 ◽  
pp. 113-134 ◽  
Author(s):  
MINGJUN WEI ◽  
CLARENCE W. ROWLEY
Keyword(s):  
Numerical Simulations ◽  
Shear Layer ◽  
Direct Numerical Simulations ◽  
Rate Of Change ◽  
Galerkin Projection ◽  
Free Shear Layer ◽  
Nonlinear Saturation ◽  
Complex Modes ◽  
Dimensional Models ◽  
Low Dimensional

We develop low-dimensional models for the evolution of a free shear layer in a periodic domain. The goal is to obtain models simple enough to be analysed using standard tools from dynamical systems theory, yet including enough of the physics to model nonlinear saturation and energy transfer between modes (e.g. pairing). In the present paper, two-dimensional direct numerical simulations of a spatially periodic, temporally developing shear layer are performed. Low-dimensional models for the dynamics are obtained using a modified version of proper orthogonal decomposition (POD)/Galerkin projection, in which the basis functions can scale in space as the shear layer spreads. Equations are obtained for the rate of change of the shear-layer thickness. A model with two complex modes can describe certain single-wavenumber features of the system, such as vortex roll-up, nonlinear saturation, and viscous damping. A model with four complex modes can describe interactions between two wavenumbers (vortex pairing) as well. At least two POD modes are required for each wavenumber in space to sufficiently describe the dynamics, though, for each wavenumber, more than 90% energy is captured by the first POD mode in the scaled space. The comparison of POD modes to stability eigenfunction modes seems to give a plausible explanation. We have also observed a relation between the phase difference of the first and second POD modes of the same wavenumber and the sudden turning point for shear-layer dynamics in both direct numerical simulations and model computations.

scholarly journals Investigation of the roughness-induced transition: global stability analyses and direct numerical simulations

2014 ◽  
Vol 760 ◽  
pp. 175-211 ◽  
Author(s):  
Jean-Christophe Loiseau ◽  
Jean-Christophe Robinet ◽  
Stefania Cherubini ◽  
Emmanuel Leriche
Keyword(s):  
Aspect Ratio ◽  
Global Stability ◽  
Numerical Simulations ◽  
Shear Layer ◽  
Roughness Element ◽  
Three Dimensional ◽  
Direct Numerical Simulations ◽  
Low Speed ◽  
Stability Analyses ◽  
Roughness Elements

AbstractThe linear global instability and resulting transition to turbulence induced by an isolated cylindrical roughness element of height $h$ and diameter $d$ immersed within an incompressible boundary layer flow along a flat plate is investigated using the joint application of direct numerical simulations and fully three-dimensional global stability analyses. For the range of parameters investigated, base flow computations show that the roughness element induces a wake composed of a central low-speed region surrounded by a three-dimensional shear layer and a pair of low- and high-speed streaks on each of its sides. Results from the global stability analyses highlight the unstable nature of the central low-speed region and its crucial importance in the laminar–turbulent transition process. It is able to sustain two different global instabilities: a sinuous and a varicose one. Each of these globally unstable modes is related to a different physical mechanism. While the varicose mode has its root in the instability of the whole three-dimensional shear layer surrounding the central low-speed region, the sinuous instability turns out to be similar to the von Kármán instability in the two-dimensional cylinder wake and has its root in the lateral shear layers of the separated zone. The aspect ratio of the roughness element plays a key role on the selection of the dominant instability: whereas the flow over thin cylindrical roughness elements transitions due to a sinuous instability of the near-wake region, for larger roughness elements the varicose instability of the central low-speed region turns out to be the dominant one. Direct numerical simulations of the flow past an aspect ratio ${\it\eta}=1$ (with ${\it\eta}=d/h$) roughness element sustaining only the sinuous instability have revealed that the bifurcation occurring in this particular case is supercritical. Finally, comparison of the transition thresholds predicted by global linear stability analyses with the von Doenhoff–Braslow transition diagram provides qualitatively good agreement.

scholarly journals The origin of hysteresis in the flag instability

2011 ◽  
Vol 691 ◽  
pp. 583-593 ◽  
Author(s):  
Christophe Eloy ◽  
Nicolas Kofman ◽  
Lionel Schouveiler
Keyword(s):  
Numerical Simulations ◽  
Hysteresis Loop ◽  
Nonlinear Stability ◽  
Slender Body ◽  
Two Dimensional ◽  
Weakly Nonlinear ◽  
Stability Analyses ◽  
Aeroelastic Instability ◽  
Large Hysteresis ◽  
Cantilevered Plate

AbstractThe flapping flag instability occurs when a flexible cantilevered plate is immersed in a uniform airflow. To this day, the nonlinear aspects of this aeroelastic instability are largely unknown. In particular, experiments in the literature all report a large hysteresis loop, while the bifurcation in numerical simulations is either supercritical or subcritical with a small hysteresis loop. In this paper, the discrepancy is addressed. First, weakly nonlinear stability analyses are conducted in the slender-body and two-dimensional limits, and, second, new experiments are performed with flat and curved plates. The discrepancy is attributed to inevitable planeity defects of the plates in the experiments.

scholarly journals On the formation mechanism of cirrus banding: radiosonde observations, numerical simulations, and stability analyses

2021 ◽  
Author(s):  
Kazuya Yamazaki ◽  
Hiroaki Miura
Keyword(s):  
High Resolution ◽  
Numerical Simulations ◽  
Linear Stability ◽  
Numerical Experiments ◽  
Heat Budget ◽  
Shear Instability ◽  
Vertical Shear ◽  
Formation Mechanisms ◽  
Stability Analyses ◽  
Unstable Layer

AbstractThe structures and formation mechanisms of cirrus banding are investigated by analyzing radiosonde observations, conducting high-resolution numerical experiments, and performing linear stability analyses. In all 29 cases of cirrus bands that were analyzed, radiosonde observational data indicate that statically unstable layers exist. The detected banding clouds were aligned nearly parallel to the vertical shear vector in the unstable layer. In high-resolution numerical experiments using the cloud-resolving model SCALE-RM, cirrus bands forming in the outflow layer of a tropical cyclone are explicitly simulated. The existence of statically unstable layers and band-parallel background vertical wind shear are commonly identified in the simulations. Sensitivity experiments and heat budget analyses demonstrated that the unstable stratification within the cirrus clouds was maintained by the cloud-radiation interactions. To reveal the behavior of fluid instabilities in the cirrus bands, linear stability analyses in a basic state constructed from the radiosonde observations were performed. The fastest-growing disturbance is highly similar to that of the previously known thermal-shear instability in a uniform and isolated unstable layer and the results obtained by radiosonde observations and numerical simulations. All of the results consistently indicate that thermal-shear instability is responsible for the formation of cirrus banding. Our results not only follow previous modeling studies but also provide observational support, quantification of the destabilization by the cloud-radiation interactions, as well as a theoretical basis of the thermal-shear instability in a complex environment near cirrus bands.

scholarly journals Anomalous transport in discrete arcs, double layers in experiments, simulations, and space

1987 ◽  
Vol 5 (4) ◽  
pp. 589-608
Author(s):  
Robert A. Smith
Keyword(s):  
Boundary Conditions ◽  
Numerical Simulations ◽  
Numerical Investigation ◽  
Laboratory Experiments ◽  
Particle Beam ◽  
Anomalous Transport ◽  
Double Layers ◽  
Trapped Particles ◽  
Structure And Stability ◽  
Volume Ionization

This paper presents a survey of selected results of laboratory experiments and numerical simulations of plasma double layers. Emphasis is given to discrimination between features peculiar to the experimental or numerical investigation and results which may have general implications for double layers in space similar to that of laser or particle beam produced plasma. The discussion concentrates on certain aspects pertaining to dynamics, structure, and stability of double layers considering the effects of boundary conditions (trapped particles, Bohm conditions, and applied potentials), waves and turbulence, collisions, and volume ionization.

GLOBAL ALTERNATION-INDUCED PATTERNS

2002 ◽  
Vol 02 (04) ◽  
pp. R139-R159 ◽  
Author(s):  
J. BUCETA ◽  
KATJA LINDENBERG ◽  
J. M. R. PARRONDO
Keyword(s):  
Pattern Formation ◽  
Theoretical Analysis ◽  
Numerical Simulations ◽  
Amplitude Equations ◽  
Ordered Structures ◽  
Mode Amplitude

We present a review of a recently proposed mechanism for pattern formation in which deterministic or random global alternation of dynamics, neither of which exhibits patterns, induces stationary or oscillatory ordered structures. We illustrate the mechanism by means of Swift-Hohenberg-like models and implement a theoretical analysis in terms of mode amplitude equations. Numerical simulations on 1-d and 2-d lattices support our findings.

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