ISSN:0031-9171    

DOI:10.1063/1.3480119

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A new solution to the linearized shallow‐water wave equations is introduced for the case of cnoidal waves climbing up a plane beach. The solution is used to calculate the maximum runup. It is shown that the maximum relative runup of cnoidal waves is significantly larger than the runup of monochromatic waves with the same wave height and wavelength far from the shore. It is also shown that the maximum relative runup of cnoidal waves is not a monotonically varying function of the normalized wavelength.

ISSN:0031-9171    

DOI:10.1063/1.866575

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A three‐mode projection of the Navier–Stokes equations for nonlinear perturbations to an elliptical vortex is studied numerically. It is found that, as the Reynolds number increases, the perturbations undergo a sequence of period doublings leading to chaos according to the Feigenbaum scenario [J. Statis. Phys.19, 25 (1978); Phys. Lett.74A, 375 (1979)].

ISSN:0031-9171    

DOI:10.1063/1.867010

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The effects of electric field fluctuations on bootstrap current and resistivity in toroidal plasmas are studied in the plateau regime. A tokamak is discussed as an example. The bootstrap current density is more sensitive to the fluctuations than the plasma resistivity because the bootstrap current density depends on the poloidal mode number of the fluctuations, while plasma resistivity depends on the parallel wave vector.

ISSN:0031-9171    

DOI:10.1063/1.866581

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Stellarator transport scalings with electric field, geometry, and collision frequency in the reactor‐relevant collisionless‐detrapping regime are determined from numerical solutions of the drift kinetic equation. A new geometrical scaling, proportional to &egr;3/2trather than &egr;t&egr;1/2h, is found, where &egr;tis the inverse aspect ratio and &egr;his the helical ripple. With the new scaling, no reduction in energy confinement time is associated with large helical ripple, which provides design flexibility. Integral expressions for the particle and heat fluxes that are useful for transport simulations are given.

ISSN:0031-9171    

DOI:10.1063/1.866559

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Consider a viscous fluid, at zero Reynolds number, moving over a solid surface flat except for a random array of microscopic defects having a small area fractionc. Assuming a microscopic boundary condition of perfect slip, the macroscopic boundary condition is determined from first principles. The asymptotic structure of the solution for a random surface with finite slope is quite different from those of earlier studies in the limit of an ‘‘almost flat’’ surface. The results of this study show that very small amounts of roughness can well approximate a no‐slip boundary condition macroscopically, for example, one defect of the order of 10−9m per (10−7m)2gives a slip length of only 10−5m.

ISSN:0031-9171    

DOI:10.1063/1.866563

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The shapes and motion of immiscible bubbles in a Hele–Shaw cell driven by the motion of the surrounding fluid were studied. Six classes of steady shapes, some of which are remarkable, were observed. Multiple steady states exist over some ranges of parameters and the shape as a function of speed may slow hysteresis. The observed translational velocities do not agree with available theory, but some of the shapes are in qualitative agreement with those computed by Tanveer [Phys. Fluids29, 3537 (1986)].

ISSN:0031-9171    

DOI:10.1063/1.866566

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Nonlinear solutal convection in the melt under a planar solidifying surface is investigated in the limit of small segregation. Stationary solutions of the nonlinear problem are obtained and the preferred mode of convection is determined by a stability analysis. It is found that down‐hexagons (where motion is downward at the cells’ centers) are stable for sufficiently small amplitude &Egr;, while both down‐hexagons and squares are stable in a range of larger &Egr;. The dependence of various flow features on the segregation coefficient and the effective depth of the melt is discussed.

ISSN:0031-9171    

DOI:10.1063/1.866573

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The stability of laminar natural convection in a shallow cavity has been studied theoretically. The flow is driven by a horizontal temperature gradient between isothermal vertical sidewalls of the cavity, the top and bottom of which are insulated. It was found that for a Prandtl number (Pr) less than 0.033, shear instability causes stationary transverse cells to be formed in the flow. For larger values of Prandtl number the instability sets in as oscillating longitudinal rolls in the range 0.033<Pr<0.2; and as stationary longitudinal rolls for larger values of Pr. The importance of three‐dimensional disturbances was investigated for Pr=0.02 and they were found to be less critical than two‐dimensional ones. Finite amplitude motions of the stationary transverse cells were simulated by solving the nonlinear equations numerically with the use of pseudospectral methods. This simulation supports the calculations of the onset of the instability by linear theory, and explains why the Nusselt number decreases when secondary flows are present.

ISSN:0031-9171    

DOI:10.1063/1.866574

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Free‐streamline theory is used to analyze the deformation and dislodging by wind pressure of drops of liquid adhered by surface tension to a solid surface. The critical Weber number for droplets to be dislodged is determined as a function of advancing and receding contact angle. Graphical results for drop shape are in good agreement with observation.

ISSN:0031-9171    

DOI:10.1063/1.866576

出版商:AIP    

年代:1988

数据来源: AIP