scholarly journals The Web of Micro-Structures in IC 4593

Galaxies ◽  
2020 ◽  
Vol 8 (2) ◽  
pp. 46
Author(s):  
M. Belén Mari ◽  
Denise R. Gonçalves ◽  
Stavros Akras
Keyword(s):  
Large Scale ◽  
Small Scale ◽  
Physical Parameters ◽  
Ionization State ◽  
Electron Densities ◽  
Large Scale Structures ◽  
Spatially Resolved ◽  
Morphological Component ◽  
Scale Structures ◽  
Micro Structures

In addition to large-scale structures, planetary nebulae (PNe) show small-scale structures that emit mainly in low-ionization species such as [N ii], [S ii], [O ii], and [O i], known as LISs. Here, we present the analysis of optical long-slit spectra, for three slit positions, of the PN IC 4593, which possesses a pair of knots and an isolated low-ionization knot. The motivation for this work is the need to characterize LISs completely to evaluate their impact on the PNe studies. These data allow us to derive the physical properties and ionization state for each morphological component of the nebula, including its pair of knots and individual knot. Due to the large uncertainties in the [S ii] derived electron densities, we cannot confirm any contrast between the LISs’ electron densities and the surrounding nebula, found in numerous other LISs. Though the lack of spatially-resolved physical parameters in the literature prevents further comparisons, in general, our results derived for the entire nebula agree with previous studies.

scholarly journals Design of Compliant Joints for Large Scale Structures

2020 ◽  
Author(s):  
Angela Nastevska ◽  
Jovana Jovanova ◽  
Mary Frecker
Keyword(s):  
Large Scale ◽  
Compliant Mechanisms ◽  
Compliant Mechanism ◽  
Small Scale ◽  
Nonlinear Bending ◽  
Large Scale Structures ◽  
Compliant Joints ◽  
Scale Structures ◽  
High Level ◽  
Novel Design

Abstract Large scale structures can benefit from the design of compliant joints that can provide flexibility and adaptability. A high level of deformation is achieved locally with the design of flexures in compliant mechanisms. Additionally, by introducing contact-aided compliant mechanisms, nonlinear bending stiffness is achieved to make the joints flexible in one direction and stiff in the opposite one. All these concepts have been explored in small scale engineering design, but they have not been applied to large scale structures. In this paper the design of a large scale compliant mechanism is proposed for novel design of a foldable shipping container. The superelasticity of nickel titanium is shown to be beneficial in designing the joints of the compliant mechanism.

Three-dimensional conditional structure of a high-Reynolds-number turbulent boundary layer

2011 ◽  
Vol 673 ◽  
pp. 255-285 ◽  
Author(s):  
N. HUTCHINS ◽  
J. P. MONTY ◽  
B. GANAPATHISUBRAMANI ◽  
H. C. H. NG ◽  
I. MARUSIC
Keyword(s):  
Skin Friction ◽  
High Reynolds Number ◽  
Large Scale ◽  
Three Dimensional ◽  
Streamwise Velocity ◽  
Small Scale ◽  
Large Scale Structures ◽  
Local Mean ◽  
Scale Structures ◽  
High Reynolds

An array of surface hot-film shear-stress sensors together with a traversing hot-wire probe is used to identify the conditional structure associated with a large-scale skin-friction event in a high-Reynolds-number turbulent boundary layer. It is found that the large-scale skin-friction events convect at a velocity that is much faster than the local mean in the near-wall region (the convection velocity for large-scale skin-friction fluctuations is found to be close to the local mean at the midpoint of the logarithmic region). Instantaneous shear-stress data indicate the presence of large-scale structures at the wall that are comparable in scale and arrangement to the superstructure events that have been previously observed to populate the logarithmic regions of turbulent boundary layers. Conditional averages of streamwise velocity computed based on a low skin-friction footprint at the wall offer a wider three-dimensional view of the average superstructure event. These events consist of highly elongated forward-leaning low-speed structures, flanked on either side by high-speed events of similar general form. An analysis of small-scale energy associated with these large-scale events reveals that the small-scale velocity fluctuations are attenuated near the wall and upstream of a low skin-friction event, while downstream and above the low skin-friction event, the fluctuations are significantly amplified. In general, it is observed that the attenuation and amplification of the small-scale energy seems to approximately align with large-scale regions of streamwise acceleration and deceleration, respectively. Further conditional averaging based on streamwise skin-friction gradients confirms this observation. A conditioning scheme to detect the presence of meandering large-scale structures is also proposed. The large-scale meandering events are shown to be a possible source of the strong streamwise velocity gradients, and as such play a significant role in modulating the small-scale motions.

Observation of Large-Scale Structures in Unsaturated Materials

1990 ◽  
Vol 195 ◽  
Author(s):  
J. E. Maneval ◽  
M.J. Mccarthy ◽  
S. Whitaker
Keyword(s):  
Magnetic Resonance Imaging ◽  
Nuclear Magnetic Resonance ◽  
Large Scale ◽  
Imaging Techniques ◽  
Image Data ◽  
Small Scale ◽  
Resonance Imaging ◽  
Specific System ◽  
Large Scale Structures ◽  
Scale Structures

ABSTRACTWe report here the use of nuclear magnetic resonance imaging in the observation of liquid-phase fraction distributions in a partially-wetted sample of glass beads. By combiningboth large- and small-scale imaging techniques, we can study the transition from local-averaged saturations to large-scale averaged saturations. The image data allows us to assess the utility of the large-scale measurements We comment on the reliability and generality of the measurements for our specific system.

scholarly journals Large-eddy simulation of large-scale structures in long channel flow

2010 ◽  
Vol 661 ◽  
pp. 341-364 ◽  
Author(s):  
D. CHUNG ◽  
B. J. McKEON
Keyword(s):  
Large Scale ◽  
Small Scale ◽  
Mean Velocity ◽  
Large Scale Structures ◽  
Eddy Simulation ◽  
Filter Width ◽  
Half Height ◽  
Large Eddy ◽  
The Mean ◽  
Scale Structures

We investigate statistics of large-scale structures from large-eddy simulation (LES) of turbulent channel flow at friction Reynolds numbers Reτ = 2K and 200K (where K denotes 1000). In order to capture the behaviour of large-scale structures properly, the channel length is chosen to be 96 times the channel half-height. In agreement with experiments, these large-scale structures are found to give rise to an apparent amplitude modulation of the underlying small-scale fluctuations. This effect is explained in terms of the phase relationship between the large- and small-scale activity. The shape of the dominant large-scale structure is investigated by conditional averages based on the large-scale velocity, determined using a filter width equal to the channel half-height. The conditioned field demonstrates coherence on a scale of several times the filter width, and the small-scale–large-scale relative phase difference increases away from the wall, passing through π/2 in the overlap region of the mean velocity before approaching π further from the wall. We also found that, near the wall, the convection velocity of the large scales departs slightly, but unequivocally, from the mean velocity.

Amplitude modulation of all three velocity components in turbulent boundary layers

2014 ◽  
Vol 746 ◽  
Author(s):  
K. M. Talluru ◽  
R. Baidya ◽  
N. Hutchins ◽  
I. Marusic
Keyword(s):  
Amplitude Modulation ◽  
Large Scale ◽  
Reynolds Shear Stress ◽  
Three Dimensional ◽  
Small Scale ◽  
Large Scale Structures ◽  
Scale Structures ◽  
Normal Fluctuations ◽  
High Reynolds ◽  
Cross Wire

AbstractA combination of cross-wire probes with an array of flush-mounted skin-friction sensors are used to study the three-dimensional conditional organisation of large-scale structures in a high-Reynolds-number turbulent boundary layer. Previous studies have documented the amplitude modulation of small-scale motions in response to conditionally averaged large-scale events, but the data are largely restricted to the streamwise component of velocity alone. Here, we report results based on all three components of velocity and find that the small-scale spanwise and wall-normal fluctuations ($v$ and $w$) and the instantaneous Reynolds shear stress ($-{uw}$) are modulated in a very similar manner to that previously noted for the streamwise fluctuations ($u$). The envelope of the small scale fluctuations for all velocity components is well described by the large-scale component of the $u$ fluctuation. These results also confirm the conditional existence of roll modes associated with the very large-scale or ‘superstructure’ motions.

scholarly journals Line profile variability in spectra of hot massive stars

2014 ◽  
Vol 9 (S307) ◽  
pp. 113-114
Author(s):  
Alexander Kholtygin ◽  
Natallia Sudnik ◽  
Viacheslav Dushin
Keyword(s):  
Line Profile ◽  
Large Scale ◽  
Massive Stars ◽  
Special Astrophysical Observatory ◽  
Small Scale ◽  
Astronomy Observatory ◽  
Large Scale Structures ◽  
Scale Structures ◽  
Optical Astronomy ◽  
Small Scale Structures

AbstractWe report the results of our study of the fast line profile variability (LPV) (hours – few days) in the spectra of bright OB and WR stars. All spectra were obtained with 6-m and 1-m telescope of Russian Special Astrophysical Observatory (SAO) and 1.8-m telescope of Bohyunsan Optical Astronomy Observatory, Korea (BOAO). We detected both the stochastic LPV, connected with the formation of small-scale structures in the stellar wind and the regular LPV induced by the large-scale structures in the wind.

scholarly journals Invariant solutions of minimal large-scale structures in turbulent channel flow for up to 1000

2016 ◽  
Vol 802 ◽  
Author(s):  
Yongyun Hwang ◽  
Ashley P. Willis ◽  
Carlo Cossu
Keyword(s):  
Channel Flow ◽  
Large Scale ◽  
Turbulent Channel Flow ◽  
The Self ◽  
Wall Turbulence ◽  
Small Scale ◽  
Invariant Solutions ◽  
Large Scale Structures ◽  
Turbulent Statistics ◽  
Scale Structures

Understanding the origin of large-scale structures in high-Reynolds-number wall turbulence has been a central issue over a number of years. Recently, Rawat et al. (J. Fluid Mech., vol. 782, 2015, pp. 515–540) have computed invariant solutions for the large-scale structures in turbulent Couette flow at $Re_{\unicode[STIX]{x1D70F}}\simeq 128$ using an overdamped large-eddy simulation with the Smagorinsky model to account for the effect of the surrounding small-scale motions. Here, we extend this approach to Reynolds numbers an order of magnitude higher in turbulent channel flow, towards the regime where the large-scale structures in the form of very-large-scale motions (long streaky motions) and large-scale motions (short vortical structures) emerge energetically. We demonstrate that a set of invariant solutions can be computed from simulations of the self-sustaining large-scale structures in the minimal unit (domain of size $L_{x}=3.0h$ streamwise and $L_{z}=1.5h$ spanwise) with midplane reflection symmetry at least up to $Re_{\unicode[STIX]{x1D70F}}\simeq 1000$. By approximating the surrounding small scales with an artificially elevated Smagorinsky constant, a set of equilibrium states are found, labelled upper- and lower-branch according to their associated drag. It is shown that the upper-branch equilibrium state is a reasonable proxy for the spatial structure and the turbulent statistics of the self-sustaining large-scale structures.

Wall pressure and coherent structures in a turbulent boundary layer on a cylinder in axial flow

1995 ◽  
Vol 286 ◽  
pp. 137-171 ◽  
Author(s):  
Stephen R. Snarski ◽  
Richard M. Lueptow
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Large Scale ◽  
Streamwise Velocity ◽  
Wall Pressure ◽  
Small Scale ◽  
Fluctuating Pressure ◽  
Large Scale Structures ◽  
Transverse Curvature ◽  
Scale Structures

Measurements of wall pressure and streamwise velocity fluctuations in a turbulent boundary layer on a cylinder in an axial air flow (δ/a = 5.04, Reθ = 2870) have been used to investigate the turbulent flow structures in the cylindrical boundary layer that contribute to the fluctuating pressure at the wall in an effort to deduce the effect of transverse curvature on the structure of boundary layer turbulence. Wall pressure was measured at a single location with a subminiature electret condenser microphone, and the velocity was measured throughout a large volume of the boundary layer with a hotwire probe. Auto- and cross-spectral densities, cross-correlations, and conditional sampling of the pressure and streamwise velocity indicate that two primary groups of flow disturbances contribute to the fluctuating pressure at the wall: (i) low-frequency large-scale structures with dynamical significance across the entire boundary layer that are consistent with a pair of large-scale spanwise-oriented counter-rotating vortices and (ii) higher frequency small-scale disturbances concentrated close to the wall that are associated with the burst-sweep cycle and are responsible for the short-duration large-amplitude wall pressure fluctuations. A bidirectional relationship was found to exist between both positive and negative pressure peaks and the temporal derivative of u near the wall. Because the frequency of the large-scale disturbance observed across the boundary layer is consistent with the bursting frequency deduced from the average time between bursts, the burst-sweep cycle appears to be linked to the outer motion. A stretching of the large-scale structures very near the wall, as suggested by space-time correlation convection velocity results, may provide the coupling mechanism. Since the high-frequency disturbance observed near the wall is consistent with the characteristic frequency deduced from the average duration of bursting events, the bursting process provides the two characteristic time scales responsible for the bimodal distribution of energy near the wall. Because many of the observed structural features of the cylindrical boundary layer are similar to those observed in flat-plate turbulent boundary layers, transverse curvature appears to have little effect on the fundamental turbulent structure of the boundary layer for the moderate transverse curvature ratio used in this investigation. From differences that exist between the turbulence intensity, skewness, and spectra of the streamwise velocity, however, it appears that transverse curvature may enhance (i.e. energize) the large-scale motion owing to the reduced constraint imposed on the flow by the smaller cylindrical wall.

scholarly journals The effect of small-scale forcing on large-scale structures in two-dimensional flows

1996 ◽  
Vol 98 (2-4) ◽  
pp. 321-334 ◽  
Author(s):  
Alexei Chekhlov ◽  
Steven A. Orszag ◽  
Semion Sukoriansky ◽  
Boris Galperin ◽  
Ilya Staroselsky
Keyword(s):  
Large Scale ◽  
Small Scale ◽  
Two Dimensional ◽  
Large Scale Structures ◽  
Scale Structures ◽  
Two Dimensional Flows
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