Transient three-dimensional-patterned ripples appear during deformation of a two-dimensional ripple field under wave-induced oscillatory flow

2009 ◽  
Vol 34 (6) ◽  
pp. 839-847 ◽  
Author(s):  
T. Sekiguchi
Keyword(s):  
Oscillatory Flow ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Wave Induced

scholarly journals Assessing the Impact of the Tropopause on Mountain Waves and Orographic Precipitation Using Linear Theory and Numerical Simulations

2015 ◽  
Vol 72 (2) ◽  
pp. 803-820 ◽  
Author(s):  
Nicholas Siler ◽  
Dale Durran
Keyword(s):  
Numerical Simulations ◽  
Linear Theory ◽  
Three Dimensional ◽  
Orographic Precipitation ◽  
Two Dimensional ◽  
Tropopause Height ◽  
Atmospheric Conditions ◽  
Mountain Waves ◽  
Wave Induced ◽  
The Impact

Abstract The partial reflection of mountain waves at the tropopause has been studied extensively for its contribution to downslope windstorms, but its impact on orographic precipitation has not been addressed. Here linear theory and numerical simulations are used to investigate how the tropopause affects the vertical structure of mountain waves and, in turn, orographic precipitation. Relative to the no-tropopause case, wave-induced ascent above the windward slope of a two-dimensional ridge is found to be enhanced or diminished depending on the ratio of the tropopause height to the vertical wavelength of the mountain waves—defined here as the “nondimensional tropopause height” . In idealized simulations of flow over both two-dimensional and three-dimensional ridges, variations in are found to modulate the precipitation rate by roughly a factor of 2 under typical atmospheric conditions. The sensitivity of precipitation to is related primarily to the depth of windward ascent but also to the location and strength of leeside descent, with significant impacts on the distribution of precipitation across the range (i.e., the rain-shadow effect). Using a modified version of Smith and Barstad’s orographic precipitation model, variations in are found to produce significant rain-shadow variability in the Washington Cascades, perhaps explaining some of the variability in rain-shadow strength observed among Cascade storms.

scholarly journals Double-Diffusive Convection in a Stochastic Shear

2015 ◽  
Vol 45 (12) ◽  
pp. 3155-3167 ◽  
Author(s):  
Timour Radko ◽  
James Ball ◽  
John Colosi ◽  
Jason Flanagan
Keyword(s):  
Internal Waves ◽  
Phase Distribution ◽  
Three Dimensional ◽  
Vertical Shear ◽  
Two Dimensional ◽  
Salt Fingers ◽  
Diffusive Dynamics ◽  
Wave Induced ◽  
The Impact ◽  
Double Diffusive

AbstractAn attempt is made to quantify the impact of stochastic wave–induced shears on salt fingers associated with internal waves in the ocean. The wave environment is represented by the superposition of Fourier components conforming to the Garrett–Munk (GM) spectrum with random initial phase distribution. The resulting time series of vertical shear are incorporated into a finger-resolving numerical model, and the latter is used to evaluate the equilibrium diapycnal fluxes of heat and salt. The proposed procedure makes it possible to simulate salt fingers in shears that are representative of typical oceanic conditions. This study finds that the shear-induced modification of salt fingers is largely caused by near-inertial motions. These relatively slow waves act to align salt fingers in the direction of shear, thereby rendering the double-diffusive dynamics effectively two-dimensional. Internal waves reduce the equilibrium vertical fluxes of heat and salt by a factor of 2 relative to those in the unsheared three-dimensional environment, bringing them close to the values suggested by corresponding two-dimensional simulations.

scholarly journals TURBULENT OSCILLATORY FLOW OVER RIPPLES AT HIGH REYNOLDS NUMBERS FOR PETA-SCALE SIMULATIONS

2018 ◽  
pp. 95
Author(s):  
Guillermo Oyarzun ◽  
Athanassios Dimas
Keyword(s):  
Coastal Zone ◽  
High Performance ◽  
Oscillatory Flow ◽  
Three Dimensional ◽  
Small Scale ◽  
Poisson Solver ◽  
Execution Model ◽  
High Reynolds ◽  
Wave Induced ◽  
The Impact

Surface waves in the coastal zone induce oscillatory flow motions in the vicinity of the seabed. These wave-induced coastal flows interact with the sandy seabed and modify the bed shape by generating coherent small-scale bed structures, which are generally known as ripples. The presence of ripples in oscillatory flows is important due to the impact they have on the seabed roughness and how they affect the near-bed boundary layer hydrodynamics. Simulations of higher and more real-scale Reynolds number (Re) require the use of supercomputers in order to obtain results in a reasonable amount of time. However, the constant evolution of the computing facilities makes the development of parallel algorithms a rather difficult task. The objective of the proposed research is to advance in the comprehension of coastal processes utilizing high performance computing (HPC) for the numerical simulation of the three-dimensional, turbulent flow, which is induced in the coastal zone by wave propagation. In particular, our CFD code (SimuCoast) has been developed using a hybrid MPI+OpenACC execution model that increases its scalability and allows it to engage the vast majority of high-end supercomputers. Special attention has been paid in the parallelization strategy of the Poisson solver that is the most computational demanding operation.

Three-dimensional oscillatory flow over steep ripples

2000 ◽  
Vol 412 ◽  
pp. 355-378 ◽  
Author(s):  
P. SCANDURA ◽  
G. VITTORI ◽  
P. BLONDEAUX
Keyword(s):  
Oscillatory Flow ◽  
Three Dimensional ◽  
Nonlinear Effects ◽  
Boundary Layer Separation ◽  
Vortex Structures ◽  
Two Dimensional ◽  
Free Shear Layer ◽  
Dimensional Flow ◽  
Continuity Equations ◽  
Two Dimensional Flow

The process which leads to the appearance of three-dimensional vortex structures in the oscillatory flow over two-dimensional ripples is investigated by means of direct numerical simulations of Navier–Stokes and continuity equations. The results by Hara & Mei (1990a), who considered ripples of small amplitude or weak fluid oscillations, are extended by considering ripples of larger amplitude and stronger flows respectively. Nonlinear effects, which were ignored in the analysis carried out by Hara & Mei (1990a), are found either to have a destabilizing effect or to delay the appearance of three-dimensional flow patterns, depending on the values of the parameters. An attempt to simulate the flow over actual ripples is made for moderate values of the Reynolds number. In this case the instability of the basic two-dimensional flow with respect to transverse perturbations makes the free shear layer generated by boundary layer separation become wavy as it leaves the ripple crest. Then the amplitude of the waviness increases and eventually complex three-dimensional vortex structures appear which are ejected in the irrotational region. Sometimes the formation of mushroom vortices is observed.

Centrifugal instability of an oscillatory flow over periodic ripples

1990 ◽  
Vol 217 ◽  
pp. 1-32 ◽  
Author(s):  
Tetsu Hara ◽  
Chiang C. Mei
Keyword(s):  
Oscillatory Flow ◽  
Sandy Beach ◽  
Three Dimensional ◽  
Small Region ◽  
Oscillating Flow ◽  
Two Dimensional ◽  
Steady Streaming ◽  
Centrifugal Instability ◽  
Two Dimensional Flow ◽  
Finite Slope

An oscillating flow over a sandy beach can initiate and enhance the formation of bed ripples, with crests perpendicular to the direction of the ambient oscillation. Under certain circumstances, bridges may develop to span adjacent ripple crests, resulting in a brick pattern. It has been suggested that the onset of this transition is due to a three-dimensional centrifugal instability of an otherwise two-dimensional flow over periodic long-crested ripples. Here we analyse theoretically such an instability by assuming that the ripples are rigid and smooth. Two complementary cases are studied. We first consider a weak ambient oscillation over ripples of finite slope in Case (i). The three-dimensional disturbance is found to be localized in a small region either along the crests or along the troughs. In Case (ii) we analyse finite oscillations over ripples of mild slope. The region influenced by the instability is now comparable with a ripple wavelength and the unstable disturbance along adjacent ripples may interact with each other. Four types of harmonic and subharmonic instabilities are found. The associated steady streaming close to the ripple surface shows various tendencies of possible sand accumulations, some of which appear to be qualitatively relevant to the initiation of brick-patterned ripples.

Numerical investigation of the oscillatory flow around a circular cylinder close to a wall at moderate Keulegan–Carpenter and low Reynolds numbers

2009 ◽  
Vol 627 ◽  
pp. 259-290 ◽  
Author(s):  
PIETRO SCANDURA ◽  
VINCENZO ARMENIO ◽  
ENRICO FOTI
Keyword(s):  
Circular Cylinder ◽  
Oscillatory Flow ◽  
Three Dimensional ◽  
Hydrodynamic Forces ◽  
Transverse Force ◽  
Vortex Structures ◽  
Time Development ◽  
Two Dimensional ◽  
Wide Range ◽  
Three Dimensional Simulations

The oscillatory flow around a circular cylinder close to a plane wall is investigated numerically, by direct numerical simulation of the Navier–Stokes equations. The main aim of the research is to gain insight into the effect of the wall on the vorticity dynamics and the forces induced by the flow over the cylinder. First, two-dimensional simulations are performed for nine values of the gap-to-diameter ratio e. Successively, three-dimensional simulations are carried out for selected cases to analyse the influence of the gap on the three-dimensional organization of the flow. An attempt to explain the pressure distribution around the cylinder in terms of vorticity time development is presented. Generally, the time development of the hydrodynamic forces is aperiodic (i.e. changes from cycle to cycle). In one case (Re = 200), when the distance of the cylinder from the wall is reduced, the behaviour of the flow changes from aperiodic to periodic. When the cylinder approaches the wall the drag coefficient of the in-line force increases in a qualitative agreement with the results reported in literature. The transverse force is not monotonic with the reduction of the gap: it first decreases down to a minimum, and then increases with a further reduction of the gap. For intermediate values of the gap the decrease of the transverse force is due to the reduction of the angle of ejection of the shedding vortices caused by the closeness of the wall; for small gaps the increase of the transverse force is due to the strong interaction between the vortex system ejected from the cylinder and the shear layer generated on the wall.Three-dimensional simulations show that the flow is unstable with respect to spanwise perturbations which cause the development of three-dimensional vortices and the distortion of the two-dimensional ones generated by flow separation.In all the analysed cases, the three-dimensional effects on the hydrodynamic forces are clearly attenuated when the cylinder is placed close to the wall.The spanwise modulation of the vortex structures induces oscillations of the sectional forces along the axis of the cylinder which in general are larger for the transverse sectional force. In the high-Reynolds-number case (Re = 500), the reduction of the gap produces a large number of three-dimensional vortex structures developing over a wide range of spatial scales. This produces homogenization of the flow field along the spanwise direction and a consequent reduction of the amplitudes of oscillation of the sectional forces.

Morphology of the forced oscillatory flow past a finite-span wing at low Reynolds number

2007 ◽  
Vol 571 ◽  
pp. 327-357 ◽  
Author(s):  
K. PARKER ◽  
K. D. VON ELLENRIEDER ◽  
J. SORIA
Keyword(s):  
Reynolds Number ◽  
Oscillatory Flow ◽  
Three Dimensional ◽  
Wake Flow ◽  
Half Cycle ◽  
Two Dimensional ◽  
Reynolds Stresses ◽  
Trailing Edge ◽  
Finite Span ◽  
Spanwise Vorticity

A study of the morphology of the vortical skeleton behind a flapping NACA0030 wing with a finite aspect ratio of 3, is undertaken. The motivation for this work originates with the proposal that thrust can be efficiently produced by flapping aerofoils. The test condition corresponds to a Strouhal number of 0.35, Reynolds number, based on aerofoil chord, of 600 and an amplitude of flapping, equal to the chord length of the wing. This test condition corresponds to the optimal thrust-producing case in infinite-span flapping wings. This study investigates the effect of wing three-dimensionality on the structure of the wake-flow. This is accomplished here, by quantitatively describing the spatio-temporal variations in the velocity, vorticity and Reynolds stresses for the finite-span-wing case.Preliminary flow visualizations suggest that the presence of wingtip vortices for the three-dimensional-wing case, create a different vortical structure to the two-dimensional-wing case. In the case of a two-dimensional-wing, the flow is characterized by the interaction of leading- and trailing-edge vorticity, resulting in the formation of a clear reverse Kármán vortex street at the selected test condition. In the case of a three-dimensional-wing, the flow exhibits a high degree of complexity and three-dimensionality, particularly in the midspan region. Using phase-averaged particle image velocimetry measurements of the forced oscillatory flow, a quantitative analysis in the plane of symmetry of the flapping aerofoil was undertaken. Using a triple decomposition of the measured velocities, the morphological characteristics of the spanwise vorticity is found to be phase correlated with the aerofoil kinematics. Reynolds stresses in the direction of oscillation are the dominant dissipative mechanism. The mean velocity profiles resemble a jet, indicative of thrust production. Pairs of strong counter-rotating vortices from the leading- and trailing-edge of the aerofoil are shed into the flow at each half-cycle. The large-scale structure of the flow is characterized by constructive merging of spanwise vorticity. The midspan region is populated by cross-sections of interconnected vortex rings.

High Resolution Microscopy of Multi-Layered Biological Crystals

1982 ◽  
Vol 40 ◽  
pp. 80-83
Author(s):  
H.A. Cohen ◽  
T.W. Jeng ◽  
W. Chiu
Keyword(s):  
High Resolution ◽  
Low Dose ◽  
Three Dimensional ◽  
Data Interpretation ◽  
Two Dimensional ◽  
Biological Objects ◽  
Density Maps ◽  
Density Map ◽  
Complex Crystal ◽  
High Resolution Microscopy

This tutorial will discuss the methodology of low dose electron diffraction and imaging of crystalline biological objects, the problems of data interpretation for two-dimensional projected density maps of glucose embedded protein crystals, the factors to be considered in combining tilt data from three-dimensional crystals, and finally, the prospects of achieving a high resolution three-dimensional density map of a biological crystal. This methodology will be illustrated using two proteins under investigation in our laboratory, the T4 DNA helix destabilizing protein gp32*I and the crotoxin complex crystal.

Instrumentation For Quantitative Microscopy

1977 ◽  
Vol 35 ◽  
pp. 206-209
Author(s):  
B. Ralph ◽  
A.R. Jones
Keyword(s):  
Volume Fraction ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Automatic Data ◽  
Phase Volume Fraction ◽  
Statistical Confidence ◽  
Resultant Data ◽  
Automatic Data Collection ◽  
Third Dimension ◽  
Evolution Of Microstructure

In all fields of microscopy there is an increasing interest in the quantification of microstructure. This interest may stem from a desire to establish quality control parameters or may have a more fundamental requirement involving the derivation of parameters which partially or completely define the three dimensional nature of the microstructure. This latter categorey of study may arise from an interest in the evolution of microstructure or from a desire to generate detailed property/microstructure relationships. In the more fundamental studies some convolution of two-dimensional data into the third dimension (stereological analysis) will be necessary.In some cases the two-dimensional data may be acquired relatively easily without recourse to automatic data collection and further, it may prove possible to perform the data reduction and analysis relatively easily. In such cases the only recourse to machines may well be in establishing the statistical confidence of the resultant data. Such relatively straightforward studies tend to result from acquiring data on the whole assemblage of features making up the microstructure. In this field data mode, when parameters such as phase volume fraction, mean size etc. are sought, the main case for resorting to automation is in order to perform repetitive analyses since each analysis is relatively easily performed.

Sign in / Sign up

Export Citation Format

Share Document