Scattering of an eddy advected by a current towards a topographic obstacle

2000 ◽  
Vol 402 ◽  
pp. 211-223 ◽  
Author(s):  
MELVIN E. STERN
Keyword(s):  
Dipole Moment ◽  
Constant Velocity ◽  
Grazing Incidence ◽  
Plane Motion ◽  
Basic Flow ◽  
Homogeneous Fluid ◽  
Azimuthal Mode ◽  
Main Effect ◽  
A Current ◽  
Stratified Model

Contour dynamics is used to compute the two-dimensional (f-plane) motion of an initially circularly symmetric barotropic eddy with piecewise-uniform vorticity as it is advected around a circular obstacle by a uniform upstream current. For grazing incidence of this ‘shielded’ eddy (compensating positive and negative vorticity) the main effect of the vortex images (inside the obstacle) is to change the speed of those particles in the outer portion of the eddy that are closest to the obstacle; a lesser velocity is induced on the oppositely signed vortices near the eddy centre. The result is a systematic separation of the centroids of the ± vortices in the eddy, and the eddy emerges far downstream with an invariant dipole moment (m = 1 azimuthal mode). This causes the eddy to move with a constant velocity V normal to the uniform basic flow. The ratio of the numerically computed V to the accompanying far-field dipole moment agrees with a previous analytical theory for a completely isolated eddy subjected to a small-amplitude m = 1 initial disturbance. The scattering effect might be realizable in a rotating homogeneous fluid by translating a cylinder relative to an otherwise stationary eddy. Application to a density-stratified model is suggested.

scholarly journals Conditions for a pure toroidal dipole source

2021 ◽  
Vol 2015 (1) ◽  
pp. 012027
Author(s):  
Adrià Canós Valero
Keyword(s):  
Dipole Moment ◽  
Current Distribution ◽  
Electric Dipole ◽  
Spherical Surface ◽  
Physical Significance ◽  
Dipole Source ◽  
Multipole Moments ◽  
Physical Origin ◽  
First Time ◽  
A Current

Abstract Recently, the physical significance of dynamic toroidal multipoles in the context of electrodynamics has been put under discussion. Indeed, the latter can be shown to arise simply from a Taylor series of the exact source (Cartesian) multipole moments. The split into elementary and toroidal parts was demonstrated to lead to an unphysical result were forbidden components of the momentum transform of the current could radiate into free space. In this contribution, we elaborate the conditions that a current distribution must necessarily satisfy to be considered a ‘pure’ toroidal dipole source. We demonstrate for the first time that symmetry prevents such current distribution to radiate as an elementary electric dipole moment, without leading to an unphysical result. Thus, while both elementary electric dipole and toroidal dipoles are indistinguishable outside the source, they display topologically distinct characteristics within the smallest spherical surface enclosing the source itself and have different physical origin. Based on our results, a pure ‘toroidal’ source can be designed. We believe the outcome of our investigations will help clarify further the formal meaning of the toroidal multipoles.

scholarly journals The modulation of short gravity waves by long waves or currents

1988 ◽  
Vol 29 (4) ◽  
pp. 410-429 ◽  
Author(s):  
R. Grimshaw
Keyword(s):  
Gravity Waves ◽  
Finite Amplitude ◽  
Basic Flow ◽  
Long Waves ◽  
Water Current ◽  
Kinematic Equation ◽  
Local Dispersion ◽  
Short Waves ◽  
First Case ◽  
A Current

AbstractThe modulation of short gravity waves by long waves or currents is described for the situation when the flow is irrotational and when the short waves are described by linearised equations. Two cases are distinguished depending on whether the basic flow can be characterised as a deep-water current, or a shallow-water current. In both cases the basic flow has a current which has finite amplitude, while in the first case the free surface slope of the basic flow can be finite, but in the second case is small. The modulation equations are the local dispersion relation of the short waves, the kinematic equation for conservation of wave crests and the wave action equation. The results incorporate and extend the earlier work of Longuet-Higgins and Stewart [10, 11].

Elastic Flexible Cable in Plane Motion Under Tension

1959 ◽  
Vol 26 (4) ◽  
pp. 587-593
Author(s):  
Wen-Hsiung Li
Keyword(s):  
Partial Differential Equations ◽  
Elastic Waves ◽  
Constant Velocity ◽  
Plane Motion ◽  
Transverse Waves ◽  
Longitudinal Waves ◽  
Flexible Cable ◽  
Quasilinear Partial Differential Equations ◽  
Sharp Fronts ◽  
Infinite String

Abstract The motion and stresses of a non-Hookian elastic flexible cable in plane motion under tension are described with four simultaneous quasilinear, partial differential equations which are totally hyperbolic. The propagation of the longitudinal elastic waves and the transverse waves are described by the four characteristics. From the characteristic equations, solutions for simple longitudinal waves and simple transverse waves are obtained for uniform Hookian cables. The problem of an infinite string moved at one point with a constant velocity can be solved. Solutions also have been obtained for the interaction of transverse and longitudinal waves with sharp fronts.

Dynamic Ride-Up and Crushing of Short Ice Ridges on Conical Structures

1991 ◽  
Vol 113 (1) ◽  
pp. 70-73
Author(s):  
R. P. Nordgren ◽  
M. M. Winkler
Keyword(s):  
Constant Velocity ◽  
Equations Of Motion ◽  
Plane Motion ◽  
Maximum Force ◽  
Typical Problem ◽  
Crushing Strength ◽  
Flexural Failure ◽  
Type Contact ◽  
Conical Structure ◽  
Design Loads

An analysis is presented for the plane motion of an ice ridge being pushed up a faceted conical structure by a floe moving at constant velocity. The effect of crushing of the ridge against the rigid structure is included by means of an idealized crushing model. The effect of changing buoyancy is included in the analysis. The plane, rigid-body equations of motion are solved numerically for finite displacement and rotation of the ridge. A quasi-static flexural model is used to determine conditions for failure of the ridge in lengthwise bending. Numerical results for a typical problem are presented and discussed. The impulsive-type contact force at initial impact depends strongly on impact velocity and ice-crushing strength. However, the maximum force on the structure usually occurs later after the ridge has ridden up on the structure. This force is nearly independent of velocity. For realistic crushing strengths, the maximum force is significantly lower than in our previous static analysis of ridge ride-up without crushing. With consideration of lengthwise flexural failure, the dynamic ride-up model is applied to the development of design loads for a 40-deg conical structure.

Analysis of Wake Interaction of Oscillating Platform With Four Columns

2019 ◽  
Author(s):  
Shinichiro Hirabayashi ◽  
Murilo M. Cicolin ◽  
Rodolfo T. Gonçalves ◽  
Gustavo R. S. Assi ◽  
Hideyuki Suzuki
Keyword(s):  
Particle Image Velocimetry ◽  
Constant Velocity ◽  
Particle Image ◽  
Hydrodynamic Force ◽  
Water Channel ◽  
Circulating Water ◽  
Image Velocimetry ◽  
Wake Interaction ◽  
The Difference ◽  
A Current

Abstract The effect of wake interaction on the hydrodynamic force was experimentally investigated. A scaled platform model with four columns was subjected to a current in the circulating water channel with constant velocity. The diameter of each column was 75 mm, and the aspect ratio (defined by the ratio between the column draft and diameter) was 1.5. The spacing ratios, (defined by the ratio between the distance of column centers and diameter) were 3 and 4. The platform was forced to oscillate with different frequencies and amplitudes. Flow around columns was measured by using Particle Image Velocimetry (PIV). The difference of hydrodynamic forces on each column was discussed concerning the effect of wake interaction among columns.

Resolving Crystallites in Zirconium Oxide Films

1969 ◽  
Vol 27 ◽  
pp. 140-141
Author(s):  
R.A. Ploc
Keyword(s):  
Electron Microscope ◽  
Inelastic Scattering ◽  
Zirconium Oxide ◽  
Oxide Films ◽  
Optic Axis ◽  
Objective Lens ◽  
Microscope Objective ◽  
Linear Optic ◽  
A Current ◽  
Microscope Objective Lens

The optic axis of an electron microscope objective lens is usually assumed to be straight and co-linear with the mechanical center. No reason exists to assume such perfection and, indeed, simple reasoning suggests that it is a complicated curve. A current centered objective lens with a non-linear optic axis when used in conjunction with other lenses, leads to serious image errors if the nature of the specimen is such as to produce intense inelastic scattering.

Structure of Palladium Single-Crystal Films Prepared by Flash Evaporation onto (001) NaCl Substrates

1970 ◽  
Vol 28 ◽  
pp. 456-457
Author(s):  
L. E. Murr ◽  
G. Wong
Keyword(s):  
Single Crystal ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
High Rate ◽  
Flash Evaporation ◽  
Optimum Load ◽  
Single Crystal Films ◽  
Crystal Films ◽  
A Current

Palladium single-crystal films have been prepared by Matthews in ultra-high vacuum by evaporation onto (001) NaCl substrates cleaved in-situ, and maintained at ∼ 350° C. Murr has also produced large-grained and single-crystal Pd films by high-rate evaporation onto (001) NaCl air-cleaved substrates at 350°C. In the present work, very large (∼ 3cm2), continuous single-crystal films of Pd have been prepared by flash evaporation onto air-cleaved (001) NaCl substrates at temperatures at or below 250°C. Evaporation rates estimated to be ≧ 2000 Å/sec, were obtained by effectively short-circuiting 1 mil tungsten evaporation boats in a self-regulating system which maintained an optimum load current of approximately 90 amperes; corresponding to a current density through the boat of ∼ 4 × 104 amperes/cm2.

Novel magneto-optical recording materials: Bi-substituted garnet films

1991 ◽  
Vol 49 ◽  
pp. 776-777
Author(s):  
Takao Suzuki ◽  
Hossein Nuri
Keyword(s):  
Grain Size ◽  
Amorphous Film ◽  
Nitrogen Atmosphere ◽  
Optical Recording ◽  
Garnet Film ◽  
Media Noise ◽  
Garnet Films ◽  
Order Of Magnitude ◽  
A New Technique ◽  
A Current

For future high density magneto-optical recording materials, a Bi-substituted garnet film ((BiDy)3(FeGa)5O12) is an attractive candidate since it has strong magneto-optic effect at short wavelengths less than 600 nm. The signal in read back performance at 500 nm using a garnet film can be an order of magnitude higher than a current rare earth-transition metal amorphous film. However, the granularity and surface roughness of such crystalline garnet films are the key to control for minimizing media noise.We have demonstrated a new technique to fabricate a garnet film which has much smaller grain size and smoother surfaces than those annealed in a conventional oven. This method employs a high ramp-up rate annealing (Γ = 50 ~ 100 C/s) in nitrogen atmosphere. Fig.1 shows a typical microstruture of a Bi-susbtituted garnet film deposited by r.f. sputtering and then subsequently crystallized by a rapid thermal annealing technique at Γ = 50 C/s at 650 °C for 2 min. The structure is a single phase of garnet, and a grain size is about 300A.

Record Wear Studies by Scanning Electron Microscopy

1968 ◽  
Vol 26 ◽  
pp. 364-365
Author(s):  
M.D. Coutts ◽  
E.R. Levin ◽  
J.G. Woodward
Keyword(s):  
Electron Microscopy ◽  
Constant Velocity ◽  
Peak Velocity ◽  
Great Depth ◽  
Depth Of Focus ◽  
Sweep Frequency ◽  
Transmission Electron ◽  
Test Record ◽  
Lateral Mode ◽  
Scanning Electron

While record grooves have been studied by transmission electron microscopy with replica techniques, and by optical microscopy, the former are cumbersome and restricted and the latter limited by lack of depth of focus and resolution at higher magnification. With its great depth of focus and ease in specimen manipulation, the scanning electron microscope is admirably suited for record wear studies.A special RCA sweep frequency test record was used with both lateral and vertical modulation bands. The signal is a repetitive, constant-velocity sweep from 2 to 20 kHz having a duration and repetitive rate of approximately 0.1 sec. and a peak velocity of 5.5 cm/s.A series of different pickups and numbers of plays were used on vinyl records. One centimeter discs were then cut out, mounted and coated with 200 Å of gold to prevent charging during examination. Wear studies were made by taking micrographs of record grooves having 1, 10 and 50 plays with each stylus and comparing with typical “no-play” grooves. Fig. 1 shows unplayed grooves in a vinyl pressing with sweep-frequency modulation in the lateral mode.

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