Sinuous Structure Research Articles

Stability Analysis of the Volcanic Cave El Mirador (Galápagos Islands, Ecuador) Combining Numerical, Empirical and Remote Techniques

El Mirador de los Túneles is a tube-shaped volcanic cave with a sinuous structure in the Galápagos Islands formed due to cooled near-surface lava flows. Since this natural formation is considered a tourist site, a large number of people frequent it daily; however, its safety conditions have not yet been defined by a comprehensive geotechnical study. In this research, a stability analysis was carried out by combining both empirical methodologies based on geomechanical classifications using Barton’s Q Index and the recently created Cave Geomechanical Index (CGI), and numerical modeling through the finite element method. In addition, three-dimensional modelling was performed using the remote photogrammetric technique Structure from Motion (SfM) to create the numerical calculation sections and dimensions of the different critical parts of the cave. The results of the analysis showed that there is evidence of instability and subsidence along the tunnel. Furthermore, the geotechnical parameters obtained from the different methods complemented each other, resulting in more realistic engineering representation of the subsurface environment. Finally, a graph showing the two empirical methodologies Barton’s Q Index and CGI, with the addition of the Factors of Safety (FoS) obtained from the modeling is presented.

Evidence that uniform momentum zones originate from roughness sublayer structure interactions in fully rough channel turbulence

Fully rough wall-sheared turbulence is composed of an inner and outer layer, the former occupied by sinuous structures sustained by the well-known autonomous inner cycle, the latter occupied by inclined parcels of momentum deviations relative to the average. The outer-layer structures are also known as uniform momentum zones (UMZs), where the presence of successive UMZs manifests instantaneously with a distinct ‘staircase’ pattern in streamwise velocity. Direct numerical simulation (DNS) of fully rough channel turbulence was recently used to interpret UMZs as wakes originating from antecedent bluff-body-like interactions within the inner layer (Anderson & Salesky, J. Fluid Mech., vol. 906, 2020, A8). Wake-scaling arguments agreed precisely with instantaneous results from DNS. Foremost among these results was evidence that the instantaneous wall-normal gradient of streamwise velocity exhibited scaling of ${\sim }x_3^{-1/2}$ , where $x_3$ is wall-normal location; this is in contrast to logarithmic scaling, which requires the wall-normal gradient of streamwise velocity to scale as ${\sim }x_3^{-1}$ . Herein, wake-scaling arguments have been advanced and compared against results from wall-modelled large-eddy simulation (LES). New results from the ‘bottom up’ wake-scaling arguments agree with LES results, such that the shear associated with the instantaneous staircase-like streamwise velocity follows a clear trend. We have leveraged conditional sampling during LES – predicated upon instantaneous low-frequency, high-magnitude surface stress values known to correspond to large-scale inertial-layer coherence – to further assess the predictive value of the wake-scaling arguments. Model results compare favourably.

Palaeoecological Analysis of Trace Fossil Sinusichnus sinuosus from the Middle Triassic Guanling Formationin Southwestern China

The Luoping Biota discovered from the early Middle Triassic (Anisian) Guanling Formation of southwestern China represents a fully recovered shallow marine ecosystem, marking the end point of Early Triassic biotic recovery following the end-Permian mass extinction. Contemporaneously preserved are prolific trace fossils, which offer good opportunities to understand the palaeoecology of marine invertebrates from a fully recovered shallow marine ecosystem. Here we present a newly discovered sinuous branching burrow from the fossil-bearing unit in Member Ⅱ of the Guanling Formation. Several features, including the horizontal regular sinuous nature, the branching pattern, typical H-junction, and the small wavelength/amplitude ratio of these sinuous structures within the burrow systems justify assignment of these traces as Sinusichnus sinuosus, a trace possibly produced by decapod crustaceans. Close association of S. sinuosus with Rhizocorallium commune suggests a deposit-feeding strategy of these trace makers. The newly reported Anisian material from the Guan-ling Formation in Luoping represents first report of Sinusichnus from South China. The global record of Sinusichnus occurrence suggests that these burrows might have an older history than Early Middle Triassic.

Simulating Fine-Scale Marine Pollution Plumes for Autonomous Robotic Environmental Monitoring

Marine plumes exhibit characteristics such as intermittency, sinuous structure, shape and flow field coherency, and a time varying concentration profile. Due to the lack of experimental quantification of these characteristics for marine plumes, existing work often assumes marine plumes exhibit behavior similar to aerial plumes and are commonly modeled by filament based Lagrangian models. Our previous field experiments with Rhodamine dye plumes at Makai Research Pier at Oahu, Hawaii revealed that marine plumes show similar characteristics to aerial plumes qualitatively, but quantitatively they are disparate. Based on the field data collected, this paper presents a calibrated Eulerian plume model that exhibits the qualitative and quantitative characteristics exhibited by experimentally generated marine plumes. We propose a modified model with an intermittent source, and implement it in a Robot Operating System (ROS) based simulator. Concentration time series of stationary sampling points and dynamic sampling points across cross-sections and plume fronts are collected and analyzed for statistical parameters of the simulated plume. These parameters are then compared with statistical parameters from experimentally generated plumes. The comparison validates that the simulated plumes exhibit fine-scale qualitative and quantitative characteristics similar to experimental plumes. The ROS plume simulator facilitates future evaluations of environmental monitoring strategies by marine robots, and is made available for community use.

Acoustic-vortex interaction in reacting wakes near the global hydrodynamic stability limit

This study experimentally characterizes the effect of acoustics on the vortex dynamics in reacting wakes. This work is motivated by the problem of combustion instabilities, where the natural combustor acoustics excite hydrodynamic instabilities of the flow that, in turn, induce heat release oscillations. Time resolved PIV, Mie scattering, and chemiluminescence imaging measurements are obtained in a reacting wake facility with acoustic excitation. Measurements and analysis are performed where the acoustic frequency is varied relative to the global mode frequency. We observe that the acoustic waves excite a varicose mode of vortex shedding, which is locked into the acoustic frequency. When the acoustic frequency is close to the natural global hydrodynamic frequency of the wake, we observe resonance, which manifests as very rapid amplification of these shed vortices as they convect downstream. Interestingly, in the resonant case, the vortices stagger from the varicose structure deposited by the acoustic waves and assume a sinuous structure that resembles the hydrodynamic global mode. A linear, local stability analysis, together with a nonlinear analysis, help elucidate the physics that govern the vortex staggering. The study counterintuitively concludes that the resonance, due to the change from varicose to sinuous structure, may help alleviate combustion instability.

Spatio-temporal linear stability analysis of stratified planar wakes: Velocity and density asymmetry effects

This paper explores the hydrodynamic stability of bluff body wakes with non-uniform mean density, asymmetric mean density, and velocity profiles. This work is motivated by experiments [S. Tuttle et al., “Lean blow off behavior of asymmetrically-fueled bluff body-stabilized flames,” Combust. Flame 160, 1677 (2013)], which investigated reacting wakes with equivalence ratio stratification and, hence, asymmetry in the base flow density profiles. They showed that highly stratified cases exhibited strong, narrowband oscillations, suggestive of global hydrodynamic instability. In this paper, we present a local hydrodynamic stability analysis for non-uniform density wakes that includes base flow asymmetry. The results show that increasing the degree of base density asymmetry generally has a destabilizing effect and that increasing base velocity asymmetry tends to be stabilizing. Furthermore, we show that increasing base density asymmetry slightly decreases the absolute frequency and that increasing the base velocity asymmetry slightly increases the absolute frequency. In addition, we show that increasing the degree of base density asymmetry distorts the most absolutely unstable hydrodynamic mode from its nominally sinuous structure. This distorted mode exhibits higher amplitude pressure and velocity oscillations near the interface with the smaller density jump than near the one with the bigger density jump. This would then be anticipated to lead to strongly non-symmetric amplitudes of flame flapping, with much stronger flame flapping on the side with lower density ratio. These predictions are shown to be consistent with experimental data. These comparisons support the analytical predictions that increased base density asymmetry are destabilizing and that hydrodynamic velocity fluctuation amplitudes should be greatest at the flame with the lowest density jump.

JET MOTION, INTERNAL WORKING SURFACES, AND NESTED SHELLS IN THE PROTOSTELLAR SYSTEM HH 212

HH 212 is a nearby (400 pc) highly collimated protostellar jet powered by a Class 0 source in Orion. We have mapped the inner 80" (~ 0.16 pc) of the jet in SiO (J=8-7) and CO (J=3-2) simultaneously at ~ 0.5 resolution with the Atacama Millimeter/Submillimeter Array at unprecedented sensitivity. The jet consists of a chain of knots, bow shocks, and sinuous structures in between. As compared to that seen in our previous observations with the Submillimeter Array, it appears to be more continuous, especially in the northern part. Some of the knots are now seen associated with small bow shocks, with their bow wings curving back to the jet axis, as seen in pulsed jet simulations. Two of them are reasonably resolved, showing kinematics consistent with sideways ejection, possibly tracing the internal working surfaces formed by a temporal variation in the jet velocity. In addition, nested shells are seen in CO around the jet axis connecting to the knots and bow shocks, driven by them. The proper motion of the jet is estimated to be ~ 115+-50 km/s, comparing to our previous observations. The jet has a small semi-periodical wiggle, with a period of ~ 93 yrs. The amplitude of the wiggle first increases with the distance from the central source and then stays roughly constant. One possible origin of the wiggle could be the kink instability in a magnetized jet.

TRACKING THE GEYSERS OF ENCELADUS INTO SATURN’S E RING

We examine Cassini Imaging Science Subsystem images of the E ring taken over a period of almost 7 yr, from 2006 September to 2013 July, in which long, sinuous structures dubbed tendrils are present. We model these structures by numerically integrating the trajectories of particles launched from the sources of the most active geysers recently located along the four main fractures crossing the south polar terrain of the moon, and producing from these integrations synthetic images that we then compare to the real ones. We include the effects of charging and the electromagnetic forces on the particles in addition to the gravity of Saturn and Enceladus. We demonstrate that these structures are produced by the highest velocity particles erupting from the most active geysers and entering Saturn?s orbit, and not perturbations of E ring particles by Enceladus. The detailed structures of the tendrils change with the orbital position of Enceladus, a finding likely to be the result of the diurnal variability in the source activity.

Large-scale flat-lying isoclinal folding in extending lithosphere: Santa María de la Alameda dome (Central Iberian Massif, Spain)

The exhumation mechanisms of deep-seated continental crust can be constrained by analyzing the structural and metamorphic imprints left in lithological ensembles. The Santa Maria de la Alameda dome formed during the collision of Gondwana and Laurussia in late Paleozoic time and is located in the Central Iberian Zone of the Iberian Massif (Spain). Rocks of the dome are part of the autochthonous Gondwanan sections of the Variscan belt, and they occur in the Variscan hinterland. The lithostratigraphy of the dome consists of metasedimentary rocks alternating with orthogneiss massifs showing irregular and sinuous structure. The metamorphic record indicates peak pressures indicative of lower-crust depths followed by isothermal decompression to middle-upper-crust levels. Exhumation resulted in the exposure of different crustal levels (represented by subsolidus vs. supersolidus mineral assemblages). The exhumation was accompanied by initial layer-parallel stretching and subsequent large-scale isoclinal folding developed in a heterogeneous, flat-lying shear zone with top-to-the-SE kinematics. SE-directed shearing and lateral extensional flow occurred in response to thermomechanical disequilibrium of previously thickened orogenic crust, probably assisted by coeval accretion of tectonic slices and lithospheric bending about a vertical axis. Positive feedback among partial melting, exhumation, and crustal attenuation resulted in the formation of a NE-SW–trending, migmatite-cored dome, and in refolding of early isoclinal folds and an associated axial surface regional foliation. The dome formed beneath a set of extensional detachments and was reshaped by WNW-ESE upright folds during later convergent deformation. The latter event brought in further instabilities throughout the belt, triggering in this region the development of a late extensional detachment under low-grade metamorphic conditions (top-to-the-S kinematics). The development of a regional train of flat-lying isoclinal folds is presented here as the macrostructural expression of the combination of vertical and lateral extensional flow, both of which are particularly common in orogens worldwide.

A magnetic anomaly associated with an albedo feature near Airy crater in the lunar nearside highlands

We describe a strong crustal magnetic anomaly, recently identified in Lunar Prospector magnetometer data, that is associated with a previously unreported albedo feature near the crater Airy in the lunar nearside highlands. Other workers have demonstrated a correlation between magnetic anomalies and the enigmatic bright markings known as lunar swirls. We have used Earth‐based telescopic spectra and Clementine multispectral images to investigate the compositional and optical maturity characteristics of the Airy swirl. The Airy albedo feature does not exhibit the complex sinuous structure of well‐known swirls such as the Reiner Gamma Formation, but does possess a bright loop and central dark lane. Another strong magnetic anomaly, in the Apollo 16/Descartes region, corresponds to a simple diffuse bright albedo spot. On this basis we suggest that a continuum of swirl morphologies exists on the Moon, with the Airy feature representing an intermediate or incipient swirl form.

MORPHOLOGICAL CHANGES IN MITOCHONDRIAL AND CHLOROPLAST NUCLEOIDS AND MITOCHONDRIA DURING THECHLAMYDOMONAS REINHARDTII(CHLOROPHYCEAE) CELL CYCLE1

Morphological changes in the organellar nucleoids and mitochondria of livingChlamydomonas reinhardtiiDang were examined during the cell cycle under conditions of 12:12 light:dark. The nucleoids were stained with SYBR‐Green I, and the mitochondria were stained with 3,3‐dihexyloxacarbocyanine iodide. An mocG33 mutant, which contains one large chloroplast nucleoid throughout the cell cycle, was used to distinguish between the mitochondrial and chloroplast nucleoids. Changes in the total levels of organellar DNA levels were assessed by real‐time PCR. Each of the G1, S, M, and Smt,cp phases was estimated. At the start of the light period, the new daughter cells were in G1and contained about 30 mitochondrial and 10 chloroplast nucleoids, which were dispersed and had diameters of 0.1 and 0.2 μm, respectively. During the G1phase of the light period, and at the start of the S phase, both nucleoids formed short thread‐like or bead‐like structures, probably divided, and increased continuously in number, concomitantly with DNA synthesis. The nucleoids probably became smaller due to the decrease in DNA of each particle and were indistinguishable. The cells in the S and M phases contained extremely high numbers of scattered nucleoids. However, in the G1phase of the dark period, the nucleoids again formed short thread‐like or bead‐like structures, probably fused, and decreased in number. The mitochondria appeared as tangled sinuous structures that extended throughout the cytoplasm and resembled a single large mitochondrion. During the cell cycle, the numbers of mitochondrial nucleoids and sinuous structures varied relative to one another.

Modal impedances of planar, non-complementary, N-fold symmetric antenna structures

Planar N-arm rotationally symmetric antennas are commonly used in applications that demand wideband, multiple-mode, dual-polarization, and conformal geometries. Antennas included in this category are spirals, log-periodic dipole arrays, bow-tie antennas, and sinuous structures. An analytic expression for the modal impedances of these complementary planar structures has been available for many years. This paper extends the theory to non-complementary planar /V-fold symmetric antennas, and provides equations valid for any arm-to-gap width ratio, arm width, expansion rate, and low-loss electrically thin substrate materials. The equations are based on quasi-TEM coplanar stripline theory, and provide a band-averaged approximation of the input impedance of the antenna for each characteristic mode of operation. Predicted modal impedances are compared to spiral antenna measurements. In addition, a procedure for accurately measuring the dielectric constant of the substrate material is discussed.

Vortex shedding modeling using diffusive van der Pol oscillators

A simple model for the near wake dynamics of slender bluff bodies in cross-flow is analyzed. It is based on a continuous distribution of van der Pol oscillators arranged along the spanwise extent of the structure and interacting by diffusion. Diffusive interaction is shown to be able to model cellular vortex shedding in shear flow, the cell size being estimated analytically with respect to the model parameters. Moreover, diffusive interaction succeeds in describing qualitatively the global suppression of vortex shedding from a sinuous structure in uniform flow. To cite this article: M.L. Facchinetti et al., C. R. Mecanique 330 (2002) 451–456.

Hubble Space Telescope Images of the HH 111 Jet.

view Abstract Citations (105) References (51) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Hubble Space Telescope Images of the HH 111 Jet. Reipurth, Bo ; Hartigan, Patrick ; Heathcote, Steve ; Morse, Jon A. ; Bally, John Abstract We have observed the classic Herbig-Haro jet HH 111 with the Wide Field and Planetary Camera 2 aboard the Hubble Space Telescope (\HST) through narrow-band filters isolating Hα and [S II]lambda lambda6716 ,6731 emission. The new images fully resolve the body of the jet into a series of small bow shocks, which we conclude form as fast jet material overruns slower, previously ejected jet material. Collisionally excited Hα emission that originates from a series of sharp arcs indicate the locations of shock fronts in the jet. The [S II] emission typically follows Hα in a cooling zone behind the shocks. In some, but not all cases, a Mach disk appears within the bow shocks. Some Balmer arcs form complete bow shocks, while others are one-sided. The jet has a pronounced sinuous structure which we ascribe to variations in the velocity and angle of ejection from the embedded driving source. The faintness of the shocks that propagate outside the jet beam suggests that the surrounding medium has a much lower density than the jet. The major bow shocks along the flow, HH 111L and V, each show a sharp leading edge which is especially bright in Hα . As with other Hα arcs in the flow, we argue that this emission is collisionally excited at the shock fronts. Extended [S II]-bright layers offset from the leading Hα emission in each bow shock appear to indicate the post-shock cooling zones. Bright, low-excitation knots located along the jet axis and nested within the bow shocks may form part of the Mach disk in each working surface. HH 111L is resolved into at least two distinct bow-shaped arcs. Future \HST\ observations may clarify as to whether we are observing two bow shocks merging in this object. The new images enable us to reexamine the molecular outflow in HH 111. Weak shocks along the periphery of the jet appear to accelerate a tube of slow CO gas along the base of the HH 111 jet. High-velocity CO and H_2 emission observed along the axis of the jet likely originates in jet gas that has cooled and become molecular. The three extended jets thus far observed by \HST\ (HH 34, HH 47, and HH 111) share several morphological characteristics which are best explained if variation in both velocity and direction produce most of the observable shocks in the flows. In all cases, the jets move into the wake of previously ejected jet material, and form shocks where they overrun slower jet gas. All three jets show faint Balmer arcs along the periphery of the jet beams, which may indicate a common mechanism by which their associated CO outflows are accelerated. Publication: The Astronomical Journal Pub Date: August 1997 DOI: 10.1086/118509 Bibcode: 1997AJ....114..757R Keywords: STARS: PRE-MAIN SEQUENCE; ISM: JETS AND OUTFLOWS full text sources ADS | data products SIMBAD (30) MAST (1) ESA (1)

Numerical simulation of 2D jets with time-dependent direction of ejection

Jets from young stars often show sinuous structures or apparent changes of direction in the plane of the sky. These effects can be interpreted as being the direct consequence of a time-dependent direction of ejection from the source. To analyse this possible interpretation, we have computed adiabatic and non-adiabatic 2D jets from sources with a time-dependent ejection direction. From these numerical simulations, we have obtained a qualitative description of the general characteristics of such flows. We have also obtained emission-line intensity maps which appear to share at least some of the observational characteristics of stellar jets. A simulation of the complete structure of an adiabatic wiggling jet is presented. From it we extract information about the general structure, velocities, the shock formation and evolution, knot formation and motion, and finer structure at the head of the jet. A ‘close-up’ of the body of a non-adiabatic wiggling jet is also presented. Maps of emission from this flow are calculated and compared with observational data.

G359.3–0.82: An Unusual Radio Source

An unusual radio source exhibiting an axisymmetric, cometary morphology was recently reported by Yusef-Zadeh and Bally (1987) near the Galactic center. This source, G359.3–0.82, consists of a bright head containing a compact source followed by a tail exhibiting sinuous structure. Radio emission is highly polarized and has a nearly flat spectrum between λ6cm and λ20cm. Its location in the sky, spectrum, and lack of resemblance to any other extragalactic radio source suggested to us that this radio source is a Galactic object possibly lying near the Galactic center. New high-reslolution radio images obtained using the VLA confirm the remarkable morphology and strengthen the distinction between G359.3–0.82 and any known extragalactic radio source. The characteristics of G359.3–0.82 suggest that it may be a nonthermal radio wake produced by an object moving through the interstellar medium at a high relative velocity.

Optical study of a possible bipolar flow associated with Herbig-Haro 12

The region near HH 12 in NGC 1333 has been imaged at V, R, I, and H-alpha using the CCD detector at the Kitt Peak National Observatory 0.9 m telescope. The H-alpha frame reveals a narrow, sinuous structure which extends over a projected distance of 0.3 pc and which emanates from a star which appears to be a T Tauri object of type M0-M2. Velocities along this structure were obtained both north and south of the star. The morphology of this structure as well as the measured velocities suggest that it may be an optical manifestation of a highly collimated bipolar outflow which excites the object heretofore identified as HH 12.

Theory of instantaneous sinuous structure in turbulent buoyant plumes

This paper reports a theory which explains the flickering motion of turbulent plumes as well as their large-scale sinuous structure. The theory is based on the fact that the inviscid region of the plume (the “plume column”) possesses elastic properties analogous to those of elastic rods subjected to longitudinal compression. It is shown that the straight plume column is not stable and buckles. The distance between two consecutive elbows is proportional to the local plume diameter, in other words, the shapes of all buckled plumes are geometrically similar. A buckled plume collapses periodically due to the interaction of its lateral elbows with the stagnant ambient. This interaction is responsible for the intermittent formation of large-scale buoyant eddies on the periphery of the turbulent plume.

SEGMENTATION OF ISLAND ARCS AND APPLICATION TO PETROLEUM GEOLOGY†

Island arcs are commonly depicted as smoothly curved or sinuous structures. This presentation almost certainly is incorrect. Most island arcs, perhaps all, are composed of more or less straight segments whose trend changes direction suddenly at specific hinge or boundary zones; these zones seem to consist of multiple transverse faults. Each straight segment itself is cut by transverse faults. The presence of the transverse structural systems is evident from geological and geophysical data.Examples of segmentation include island arcs in Indonesia, the Philippines, Solomons, New Hebrides, Kuril‐Kamchatka, Lesser Antilles, Central America, Mexico, Tonga, Alaska, Japan, Chile, Andaman‐Nicobar Islands, New Britain, Marianas, Greece, and the Himalayas. The fracture system may be related to structural, morphological, or movement aspects of an underthrusting slab, or it may be the result of movement in the backdeep or of the overthrusting sheet in general. Some of the transverse faults may be old ones that have been rejuvenated within the island‐arc area.Transverse structural systems seem to have had a pronounced effect on the petroleum accumulations of island‐arc regions, both from a stratigraphic and structural viewpoint; they therefore affect petroleum‐exploration procedures. Such systems are also likely to be found in ancient basins that went through an island‐arc stage. Knowledge of the segmentation of island arcs should aid future exploration.

Finite-element model for possible isostatic rebound in the Grand Canyon

In parts of the Grand Canyon a sinuous anticlinal structure in the Muav Limestone trends along the Colorado River and dips away from the river course. If the structure was there before the canyon was created, it appears that parts of the Colorado River channel coincide with the axis of the anticline. A model study based on the concept of finite elements shows that a possible mechanism for the folding of the Muav Limestone is elastic rebound caused by relief from overburden pressure as material was eroded to form the canyon.