摘要:

It is shown that laboratory double layers become multiple double layers when the ratio of Debye length to system length is decreased. This result exhibits characteristics described by boundary layer theory.

ISSN:0031-9171    

DOI:10.1063/1.863702

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The parallel ion fluid velocity in the scrape‐off layer of a poloidal divertor is observed to vary inversely with the mirror ratio in the divertor’s throat for ratios ranging from 1 to 5, in good agreement with models developed for bundle divertors. The density variation on a diverted field line also agrees qualitatively with the models, but the observed electric field does not.

ISSN:0031-9171    

DOI:10.1063/1.863703

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

It is shown that drift waves can be destabilized in the presence of a nonuniform electrostatic field. This may explain the anomalous diffusion observed in tokamaks.

ISSN:0031-9171    

DOI:10.1063/1.863704

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The use of a rotating radial phase grating to carry out beam splitting and frequency shifting in a laser‐Doppler velocimeter is briefly reviewed. This technique is not new. However, the present design adds a substantial new element by using two overlapping radial gratings to produce a two‐channel system in which channel separation can be accomplished by electronic filtering of the signal from a single detector.

ISSN:0031-9171    

DOI:10.1063/1.863705

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

A two‐parameter family of exact axially symmetric solutions of the Navier–Stokes equations for vortices contained within conical boundaries is found. The solutions depend upon the same similarity variable, equivalent to the polar angle &fgr; measured from the symmetry axis, as flows previously discussed by Long and by Serrin, but are distinct from the cases they treated. The conical bounding stream surfaces of the present solution can be located at any angle &fgr;=&fgr;0, where 0<&fgr;0<&pgr;. The flows in all of these cases, when solutions exist, are finite everywhere except at the cone vertex which is a source of axial momentum, but not of volume. Solutions are of three types, flow may be (a) towards the vertex on the axis and away from the vertex at the conical boundary, (b) towards the vertex both on the axis and at the cone, or (c) away from the vertex on the axis and towards it at the bounding cone. In the first and second case, strong shear layers form on the cone walls for high Reynolds numbers. In case (c), a region of strong axial shear and strong axial vorticity forms near the axis, even for low Reynolds numbers. The qualitative nature of the possible solutions is deduced, using methods of argument due to Serrin, and examples of flows are numerically computed for cone half‐angles of &pgr;/4, &pgr;/2 (flows above the planez=0), and 3&pgr;/4. Regions of the parameter space where solutions are proven not to exist are given for the cone half‐angles given above, as well as regions where solutions are proven to exist.

ISSN:0031-9171    

DOI:10.1063/1.863706

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Calculations of a discrete nonlinear dispersive wave system show that as the degree of nonlinearity increases, the system experiences in turn, periodic, recurring, chaotic, transitional, and periodic motions. A relationship between the instability of the initial configuration and the long‐time behavior is identified. The calculations further suggest that the corresponding continuous system will exhibit chaotic motions and energy‐sharing among a narrow band of unstable modes, a phenomenon which we call ‘‘confined chaos.’’

ISSN:0031-9171    

DOI:10.1063/1.863707

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Experimental measurements of evolution of a deep‐water wave group are described. Wave groups are found to change rapidly over a few tens of wavelengths when the initial steepness 0.09≤a0k0≤0.28. The transition creates envelope solitons composed of waves with smaller steepness and lower carrier frequency than the initial state. The carrier frequencies of the envelope solitons can be downshifted as much as 25%. The transition process is irreversible, but does not lead to total randomness.

ISSN:0031-9171    

DOI:10.1063/1.863708

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

A newmodulatedpoint‐vortex model is presented for the equivalent barotropic equations of potential vorticity:qt−&psgr;yqx+&psgr;xqy=0, (q=&kgr;+&bgr;y, &kgr;=∇2&psgr;−&ggr;&psgr;). The discrete model conserves ∑m(qm0−&bgr;*ym)2in analogy with the conserved ∫ ∫&kgr;2dx dy. An analytical study is made for the general two point‐vortex system. For equal vortices, the solution has a monotonic drift ∝(−&bgr;). A comparison is made of numerical solutions of the point‐vortex model and corresponding solutions of a finite‐difference model on a periodic domain. For an initially monopolar distribution of ∇2&psgr;−&ggr;2&psgr;, anxdrift in the direction of sign (−&bgr;) and aydrift in the direction of the sign of the extremum of &kgr; is obtained in both cases that are in agreement at short times. Theydrift is associated with the development of a spreading Rossby wave wake, as a consequence of the conservation law. For a ‘‘tilted’’ dipolar region of vorticity we observe near‐periodic oscillations. The modulated point‐vortex model is also applicable to drift waves in a plasma.

ISSN:0031-9171    

DOI:10.1063/1.863709

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The equations of motion for point vortices are well known to preserve certain discrete symmetries of the initial state. The case of acenterof symmetry is considered in detail here, since this particular instance seems to have been overlooked in the classical literature. This symmetry provides a generalization of the early studies by Gro¨bli and Greenhill wherein severalaxesof symmetry are present, a case which leads to an effective one‐body problem. The center of symmetry yields an effective two‐body problem which is Hamiltonian and integrable. As an example the ‘‘double alternate ring’’ configurations, circular analogs of the vortex street introduced by Havelock, are considered. A fully nonlinear mode wherein these double rings asymptotically dissolve into freely moving vortex pairs is found analytically. The paper concludes with a discussion of the relevance of such modes to our understanding of the disintegration of vortex streets in two‐dimensional flow.

ISSN:0031-9171    

DOI:10.1063/1.863710

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The small‐amplitude waves generated by a submerged vorticity distribution on the surface of a viscous fluid are studied. The linearized initial‐value problem is considered, and a closed‐form solution for each monochromatic component is obtained. The results of the theory are illustrated by a numerical synthesis of these components for the case of a vortex filament in water.

ISSN:0031-9171    

DOI:10.1063/1.863711

出版商:AIP    

年代:1982

数据来源: AIP