The effect of variable currents on internal solitary waves

The effect of variable currents on internal solitary waves is described within the context of a variable coefficient Korteweg-de Vries (KdV) equation, and the approximate slowly varying, solitary-wave solution of this equation. The general theory which leads to the variable coefficient KdV equation is described; a derivation for the special case when the solitary wave and the current are aligned in the same direction is given in the Appendix. Using further simplifications and approximations, a number of analytical expressions are obtained for the variation in the solitary wave amplitude resulting from variable shear in the basic current or from when the basic current is a depth-independent flow which is a simple representation of a geostrophic current, tidal flow or inertial wave.

Visualization of turbulence and internal waves in a stratified fluid

A new method for measuring the density, temperature and velocity of N2 gas flow by laser induced biacetyl phosphorescence is proposed. The characteristics of the laser induced phosphorescence of biacetyl mixed with N2 are investigated both in static gas and in one-dimensional flow along a pipe with constant cross section. The theoretical and experimental investigations show that the temperature and density of N2 gas flow could be measured by observing the phosphorescence lifetime and initial intensity of biacetyl triplet (3Au) respectively. The velocity could be measured by observing the time-of-flight of the phosphorescent gas after pulsed laser excitation. The prospect of this method is also discussed.

On the behavior of gravity-waves on porous slopes

displacement thickness is lower than in the pure-gas case alone. The results indicate

Evolution and propagation of density waves on galactic disk .1. General evolution equation of wavelet and discussion of its solution

This paper presents a general self-consistent theory of evolution and propagation of wavelets on the galactic disk. A simplified model for this theory, i. e. the thin transition-layer approximation is proposed.There are three types of solutions to the basic equation governing the evolution of wavelets on the disk: (ⅰ) normal propagating type; (ⅱ) swing type; (ⅲ) general evolving type. The results show that the first two types are applicable to a certain domain on the galactic disk and a certain region of the wave number of wavelets. The third is needed to join the other two types and to yield a coherent total picture of the wave motion. From the present theory, it can be seen that the well-known "swing theory" of the G-L sheet model holds only for a certain class of basic states of galaxies.

Evolution and propagation of density waves on galactic disk .2. An approximation of the thin transition layer

In this part of the present work, a simplified model—the thin transition layer theory is proposed. The comparison of this model with the G-L sheet model is made.

Some comments on the stability theory of mhd shock waves

The stability (evolutionarity) problem for a kind of MHD shock waves is discussed in this paper. That is to solve the interaction problem of MHD shock waves with (2-dimensional) oblique incident disturbances. In other words, the result of gasdynamic shocks is generalized to the case of MHD shocks. The previous conclusion of stability theory of MHD shock waves obtained from the solution of interaction problem of MHD shock wave with (one-dimensional) normal shock wave is that only fast and slow shocks are stable, and intermediate shocks are unstable. However, the results of this paper show that when the small disturbances are the Alfven waves a new stability condition which is related to the parameters in front of and behind the shock wave is derived. When the disturbances are entropy wave and fast and slow magneto acoustic waves the stability condition is related to the frequency of small disturbances. As the limiting ease, i. e. when a normal incident (reflection, refraction) is consid...更多ered, the fast and slow shocks are unstable. The results also show that the conclusion drawn by Kontorovich is invalid for the stability theory of shock waves.

The interaction of two pairs of solitary waves in a two-fluid system

This paper deals with the interaction of solitary waves in a two-fluid system which consistsof two superimposed incompressible inviscid fluids with a free surface and a horizontal rigidbottom. Under the assumption of shallow water wave, we first derive the basic equationssuitable for the model considered, a generalized form of the Boussinesq equations, then usingthe PLK method and the reductive perturbation method, obtain the second-order approximatesolution for the head-on collision between two pairs of interface and surface solitary waves,and give their maximum amplitudes during the collision and the nonuniform phase shiftsafter the collision which lead to the distortion of the wave profiles.

Two-dimensional short surface-waves of an oscillating cylinder with arbitrary shape of cross-section

The 2-D short surface waves produced by a partially submerged cylinder which performsarbitrary oscillating motion are discussed. The uniformly valid solution which is applicableto all kinds of cylinder wall cases at waterline point is obtained. It is pointed out that thesolution obtained by Holford[J] for the vertical oscillating motion of a cylinder is incomplete.The reason why his solution cannot go over to that for the case of vertical cylinder wall atwaterline point is also pointed out.

The permanence of density waves of galaxy and the numerical investigation of waser mechanism

This paper deals with in detail the permanence of the spiral structure of galaxies andthe characters of waser mechanism. A simplified model of galaxy is adopted. Variousdynamical characters of density waves are studied using numerical calculation method. Theresults verify very well the switch character f waser and the tunnel effect of density wavesat the potential barrier of corotation circle as is shown in a previous work of the author.

Measurement of Electron Density Profile Behind Strong Shock Waves with a Langmuir Probe

At the shock velocity range of 7~9km/s, the variations of electron density behind strong normal shock waves are measured in a low-density shock tube by using the Langmuir electrostatic probe technique. The electron temperature, calculated based on Park’s three-temperature model, is used in interpreting the probe current data. The peak electron densities determined in the present experiment are shown to be in a good agreement with those predicted by Lin’s calculation. The experimentally obtained ratios of the characteristic ionization distance to the mean free path of freestream ahead of the shock wave are found to be in a good agreement with the existing experiments and Park’s calculation.

Influence of Wind and Grain Size on Migration of Asymmetric Sand Waves

Large parts of shallow seas are covered by regular seabed patterns and sand wave is one kind of these patterns. The instability of the sedimentary structures may hazard pipelines and the foundations of offshore structures. In the last decade or so, it's a focus for engineers to investigate the movement mechanism of sand waves. Previous theoretical studies of the subject have developed a general model to predict the growth and migration of sand waves, which is based on the two-dimensional vertical shallow water equations and the bed-form deformation equations. Although the relation between wave-current flow and sand bed deformation has been established, the topographic influence has not been considered in the model. In this paper some special patterns, which are asymmetric and close to the reality, are represent as the perturbed seabed and the evolution of sand waves is calculated. The combination of a steady flow induced by wind and a sinusoidal tidal flow is considered as the basic flow. Finally the relations of some parameters (grain size, etc.) and sand waves' growth and migration are discussed, and the growth rate and migration speeds of asymmetric sand waves are carried out.

Short-Term Nonlinear Response of Tension Leg Platform in Random Sea Waves

Most of the existing mathematical models for analyzing the dynamic response of TLP are based on explicit or implicit assumptions that motions (translations and rotations) are small magnitude. However, when TLP works in severe adverse conditions, the a priori assumption on small displacements may be inadequate. In such situation, the motions should be regarded as finite magnitude. This paper will study stochastic nonlinear dynamic responses of TLP with finite displacements in random waves. The nonlinearities considered are: large amplitude motions, coupling the six degrees-of-freedom, instantaneous position, instantaneous wet surface, free surface effects and viscous drag force. The nonlinear dynamic responses are calculated by using numerical integration procedure in the time domain. After the time histories of the dynamic responses are obtained, we carry out cycle counting of the stress histories of the tethers with rain-flow counting method to get the stress range distribution.

Measurement and Calculation of Vibrational Temperature behind Strong Shock Waves

In the present paper the measured values of vibrational temperature behind strong shock waves are compared with theoretical ones. The histories of vibrational temperature behind strong shock waves in a shock tube were measured using two monochromators. The test gas was pure nitrogen at 100-300Pa, and the speeds of shock waves were 5.0-6.0km/s. The electronic temperature of N-2(+) was also approximately determined from experiment and compared with the experimental vibrational temperature. The results show that the presented calculational method is effective, and the electronic energy of N2+ is excited much faster than its vibrational energy. One Langmuir probe was used to determine the effective time of region 2. The influence of viscosity in the shock tube is also analyzed.