Showing papers on "Dissipation published in 1978"

Energy loss and set-up due to breaking of random waves

Abstract: A description is given of a model developed for the prediction of the dissipation of energy in random waves breaking on a beach The dissipation rate per breaking wave is estimated from that in a bore of corresponding height, while the probability of occurrence of breaking waves is estimated on the basis of a wave height distribution with an upper cut-off which in shallow water is determined mainly by the local depth A comparison with measurements of wave height decay and set-up, on a plane beach and on a beach with a bar-trough profile, indicates that the model is capable of predicting qualitatively and quantitatively all the main features of the data

The Simulation of Three-Dimensional Convective Storm Dynamics

Abstract: A new three-dimensional cloud model has been developed for investigating the dynamic character of convective storms. This model solves the compressible equations of motion using a splitting procedure which provides numerical efficiency by treating the sound wave modes separately. For the subgrid turbulence processes, a time-dependent turbulence energy equation is solved which depends on local buoyancy, shear and dissipation. First-order closure is applied to nearly conservative variables with eddy coefficients based on the computed turbulence energy. Open lateral boundaries are incorporated in the model that respond to internal forcing and permit gravity waves to propagate out of the integration domain with little apparent reflection. Microphysical processes are included in the model using a Kessler-type parameterization. Simulations conducted for an unsheared environment reveal that the updraft temperatures follow a moist adiabatic lapse rate and that the convection is dissipated by water loadin...

Energy loss and set-up due to breaking random waves

Abstract: A description is given of a model developed for the prediction of the dissipation of energy in random waves breaking on a beach. The dissipation rate per breaking wave is estimated from that in a bore of corresponding height, while the probability of occurrence of breaking waves is estimated on the basis of a wave height distribution with an upper cut-off which in shallow water is determined mainly by the local depth. A comparison with measurements of wave height decay and set-up, on a plane beach and on a beach with a bar-trough profile, indicates that the model is capable of predicting qualitatively and quantitatively all the main features of the data.

The steady-state format of global climate

Abstract: It can be proved for certain small-scale convective heat transfer processes that the preferred steady-state mode is one of maximum entropy production. The constraint is more or less equivalent to one of maximum kinetic energy dissipation or of maximum convective heat transport. Evidence is accumulating that the same constraint may apply on the much larger scale of the earth-atmosphere system. The concept is accepted as the basis of a purely thermodynamic model of the mean annual global climate. The model allows a prieri calculation of the broad-scale geographic distributions of cloud, surface temperature, horizontal energy fluxes in the ocean and in the atmosphere, net radiant energy inputs, etc. The agreement with observation strongly supports the basic concept. It suggests also that, to the extent allowed by the degrees of freedom in the dynamics, the partition of atmospheric and oceanic energy flow is determined by a requirement to equalize the local dissipations in the two media.

Dissipation in Two-Dimensional Superfluids

Abstract: Dissipation of energy by a thin film of $^{4}\mathrm{He}$ on an oscillating planar substrate arises both from motion of free vortices and from polarization of bound pairs. Starting from a Langevin equation for vortex diffusion, and taking into account production of free vortices from bound pairs, we estimate this dissipation in various regimes of frequency, amplitude of vibration, and temperature.

Ratio of scalar and velocity dissipation time scales in shear flow turbulence

Abstract: Various studies of thermal turbulence in thin shear flows are re‐examined in order to evaluate the ratio of the time scale of the scalar‐fluctuation field to that of the velocity‐fluctuation field. In all cases considered it is found that the ratio is nearly uniform with a value close to 0.5.

A depth-averaged mathematical model for the near field of side discharges into open-channel flow

Abstract: A two-dimensional mathematical model is described for the calculation of the depth-averaged velocity and temperature or concentration distribution in open-channel flows, an essential feature of the model being its ability to handle recirculation zones. The model employs the depth-averaged continuity, momentum and temperature/concentration equations, which are solved by an efficient finite-difference procedure. The ‘rigid lid’ approximation is used to treat the free surface. The turbulent stresses and heat or concentration fluxes are determined from a depth-averaged version of the so-called k, e turbulence model which characterizes the local state of turbulence by the turbulence kinetic energy k and the rate of its dissipation e. Differential transport equations are solved for k and e to determine these two quantities. The bottom shear stress and turbulence production are accounted for by source/sink terms in the relevant equations. The model is applied to the problem of a side discharge into open-channel flow, where a recirculation zone develops downstream of the discharge. Predicted size of the recirculation zone, jet trajectories, dilution, and isotherms are compared with experiments for a wide range of discharge to channel velocity ratios; the agreement is generally good. An assessment of the numerical accuracy shows that the predictions are not influenced significantly by numerical diffusion.

Accurate calculations of the forward drop and power dissipation in thyristors

Abstract: Four-layer power thyristors are analyzed using exact numerical solutions of the full set of semiconductor device equations together with the heat-flow equation Included in the analysis are the physical mechanisms of carrier-carrier scattering, Auger and SRH recombination, and band-gap narrowing The experimental current-voltage curves for three-thyristor structures are compared with the theoretical predictions and are shown to be in good agreement The limiting effects on device behavior of the physical mechanisms noted above, including heat-sink thermal impedance, are investigated over the range of device operating conditions The distribution of power dissipation throughout the device is shown and compared with the distribution of recombination in the device The theory of calculating power dissipation in a semiconductor is also discussed

A Possible Mechanism for the Formation of Hurricane Rainbands

Abstract: In a model of hurricane rainbands as linear waves on a barotropic mean vortex, it is possible to derive two conservation laws for the perturbations: both the azimuthally integrated Reynolds torque exerted by the waves and the ratio of the azimuthally integrated radial wave energy flux to the intrinsic frequency are constant with radius for a steady wave field without dissipation or cumulus heating. The latter of these conditions can be invoked to explain the amplification of a class of waves that sustains a flux of energy directed into the vortex center and one of angular momentum directed out of it. The intrinsic phase propagation in the tangential direction is against the mean flow, but it is not fast enough to prevent the waves from being advected slowly downwind in the cyclonic sense. The Doppler shift leads to an increase in the intrinsic frequency toward the center and, in consequence of the second conservation law, to an amplification of the wave energy flux, as well as a large increase in...

Propagation of perturbations in a gas-liquid mixture

Abstract: The present investigation has been performed over a wide range of the dimensionless parameters characterizing the process of propagation of pressure perturbations in a gas-liquid mixture; these are the Reynolds number, and a dispersion parameter responsible for the relation between the values of dispersion and signal intensity. The values of the above parameters were changed mainly by varying the initial perturbation. The results obtained show a complete agreement between the Burgers-Korteweg-de Vries model and the real process of propagation of long-wave perturbations in a liquid with gas bubbles. In addition to signal propagation with the formation of monotonic and oscillatory shock waves, the propagation of signals in the form of solitary waves (solitons) and wave packets was observed experimentally. Data have been obtained on signal damping, energy dissipation and the influence of mixture viscosity on the signal evolution.

Intermittency effects in a numerical simulation of stationary three-dimensional turbulence

Abstract: A Navier-Stokes direct spectral simulation code was modified to produce stationary and nearly isotropic turbulence in three dimensions. An approximate - energy spectrum was maintained over the entire range of wavenumbers by simultaneously driving the fluid and supplementing the ordinary viscosity with a subgrid-like energy sink in the last 15 yo of the spectrum. Half-tone and contour plots of the fluctuations in the vorticity, rate-of-strain tensor and helicity show increasing ‘ spottiness’ as the system evolves in time. Probability distributions and cross-correlations among these three quantities were also obtained. The flatness factor of the longitudinal velocity derivative, the longitudinal structure functions and the fluctuations in the locally averaged dissipation rate are consistent with some degree of intermittency, but do not unambiguously demonstrate its presence in the simulated A ows.

High-field electronic conduction in insulators

Abstract: The quantum theory of electronic transport phenomena in large electric fields in highly dissipative media is critically examined. Serious conceptual problems and computational difficulties arise because neither the field nor the dissipation can be treated as a perturbation. We review a decade-old calculation of the velocity acquired by an electron in a finite electric field in a polar crystal and subsequent work which expanded our understanding of our method and results. A key feature of the earlier work was that in a single curve of electric field vs velocity, all the expected phenomena appeared, including a threshold field for producing hot electrons, in quantitative agreement with experiment, and a decreasing rate of energy loss with velocity for very fast electrons. A more recently studied problem, that of electron acceleration below the threshold field will be discussed. This problem is very important since such acceleration is the necessary precursor of ionization and breakdown. The physical significance of dissipation processes far from thermal equilibrium will also be mentioned.

Microscopic calculation of friction in heavy ion reaction using linear response theory

Abstract: We present a realistic calculation of the frictional coefficients for28Si+20Ne system using the two-center shell model on the basis of the linear response theory Adopting the center separationR and the deformationδ as collective variables we study the dependence of frictional coefficients γ RR , γ Rδ and γδδ on those variables, for various values of the neck parameterɛ, the temperatureT and the smearing widthΓ The direct application of the linear response theory to the two-center potential gives non-vanishing friction for the simple translational motion of the two fragments even when they are far apart A method to avoid this energy dissipation is proposed and is used in the calculation Results show that the form factor of the frictional force is surface-peaked and the peak becomes lower as the prolate deformation or neck formation increases Temperature dependence is mild, but is not negligible We compare our γ RR and γδδ with other models

The Modeling of Tidal Flow in a Channel Using a Turbulence Energy Closure Scheme

Abstract: A parameterization scheme is developed that is suitable for the modeling of turbulence in marine systems and an application is made to the determination of the tidal structure in an elongated channel The model is used to investigate the practicality of the frequently employed depth-integrated technique and conclusions are drawn about the customary bottom stress parameterization inherent in that approach Additionally, it is shown that the value of the roughness length of the elements at the floor of the channel is of importance in determining the frictional dissipation in the model and an evaluation is made of the tidally induced residual flow in the channel

Numerical study of the return of axisymmetric turbulence to isotropy

Abstract: The spectral method of Orszag and Patterson (1972a, b) is used here to study pressure and velocity fluctuations in axisymmetric, homogeneous, incompressible, decaying turbulence at Reynolds numbers Re λ [less, similar] 40. In real space 32 3 points are treated. The return to isotropy is simulated for several different sets of anisotropic Gaussian initial conditions. All contributions to the spectral energy balance for the different velocity components are shown as a function of time and wavenumber. The return to isotropy is effected by the pressure-strain correlation. The rate of return is larger at high than at low wavenumbers. The inertial energy transfer tends to create anisotropy at high wavenumbers. This explains the overrelaxation found by Herring (1974). The pressure and the inertial energy transfer are zero initially as the triple correlations are zero for the Gaussian initial values. The two transfer terms are independent of each other but vary with the same characteristic time scale. The pressure-strain correlation becomes small for extremely large anisotropies. This can be explained kinematically. Rotta's (1951) model is approximately valid if the anisotropy is small and if the time scale of the mean flow is much larger than 0·2 L f /v, which is the time scale of the triple correlations (L f = integral length scale, v = root-mean-square velocity). The value of Rotta's constant is less dependent upon the Reynolds number if the pressure-strain correlation is scaled by v 3 /L f rather than by the dissipation. Lumley and Khajeh-Nouri's (1974) model can be used to account for the influence of large anisotropies. The effect of strain is studied by splitting the total flow field into large- and fine-scale motion. The empirical model of Naot, Shavit and Wolfshtein (1970) has been confirmed in this respect.

The Wiener-Hermite expansion applied to decaying isotropic turbulence using a renormalized time-dependent base

Abstract: The problem of decaying isotropic turbulence has been studied using a Wiener-Hermite expansion with a renormalized time-dependent base. The theory is largely deductive and uses no modeling approximations. It has been found that many properties of large-Reynolds-number turbulence can be calculated (at least for moderate time) using the moving-base expansion alone. Such properties found are the spectrum shape in the dissipation range, the Kolmogorov constant, and the energy cascade in the inertial subrange. Furthermore, by using a renormalization scheme, it is possible to extend the calculation to larger times and to initial conditions significantly different from the equilibrium form. If the initial spectrum is the Kolmogorov spectrum perturbed with a spike or dip in the inertial subrange, the process proceeds to eliminate the perturbation and relax to the preferred spectrum shape. The turbulence decays with the proper dissipation rate, and several other properties are found to agree with measured data. The theory is also used to calculate the energy transfer and the flatness factor of turbulence.

Soliton and Generation of Tail in Nonlinear Dispersive Media with Weak Dissipation

Abstract: Propagation of a soliton and generation of a tail by the soliton are investigated analytically and numerically for Korteweg-de Vries equation with dissipation term. The analytical solution obtained by the modified conservation laws shows that the amplitude and velocity of a soliton change in time due to the dissipation. At the same time, a non-soliton part–a tail–appears in the solution. The structure of a tail depends on the dissipation term. Numerical solutions confirm qualitatively the validity of the analytical solution. An overtaking collision of two solitons is also examined numerically.

Radiation damping of inertial oscillations in the upper ocean

Abstract: Turbulent motions within the wind-mixed layer, which is advected by near-surface inertial oscillations, excite internal gravity waves in the underlying ocean layers. Momentum transport in the radiated wave field results in a drag force on the inertial currents. Because the magnitude of the inertial currents is large compared with the turbulence intensity, the resultant rate of dissipation of inertial oscillation energy is approximately equal to the energy flux in the radiated wave field. Using linear internal wave theory, asymptotic results are derived for the energy flux in terms of the Brunt-Vaisala frequency N below the mixed layer, the magnitude U0 of the inertial current, the integral length scale l of the mixed-layer turbulence and the mean-square displacement 〈ζ20〉 of the base of the mixed layer. For representative conditions, we estimate an energy flux of 1-10 erg/cm2 s into relatively short (wavelength of order 2πU0/N) high frequency (of order, but less than, N) internal waves. The resultant decay times for inertial oscillation energy range from a day to a week or so, in agreement with reported observations on the decay of inertial oscillations in the upper ocean. The estimated energy flux is comparable in magnitude to estimates for other internal wave generation mechanisms, indicating that, in addition to being a significant sink of inertial energy, this process may locally represent a significant source of internal wave energy in the open ocean.

Production of entropy and viscous damping of anisotropy in homogeneous cosmological models: Bianchi type-I spaces

Abstract: We investigate world models in which strong initial anisotropies are damped out by viscous dissipation at temperatures lower than 1012K. The corresponding entropy production is calculated and is proved to be simply related to the initial anisotropy. The radiation entropy increases up to a factor 1010 in those models in which the big bang starts atT∼-1010 K. In all cases here investigated the volume expansion is dominated by viscosity in a «superviscous stage» preceding a Kasner epoch. In these models, despite of very different initial conditions, the anisotropy of the cosmic background radiation is approximately the same, namely ΔT/T∼-4·10−7 at the present epoch.

Nonlinear instability of electromagnetic drift waves

Abstract: A pair of electromagnetic drift waves is shown to be excited simultaneously by an induced Cerenkov emission by electrons. The instability is shown to be explosive. However, its property is different from the ordinary explosive instability involving three wave interactions with a negative energy wave pump. The instability here is excited by the inverted population of electrons (inverse Landau damping) and is less sensitive to the frequency mismatch or dissipation. The nonlinear growth rate is shown to exceed the linear growth rate at a reasonably small level of wave amplitude. A magnetic field perturbation is essential for this process.

Modified one-body nuclear dissipation

Abstract: We study a modification of the one-body dissipation mechanism for the conversion of energy of collective nuclear motion into internal single-particle excitation energy. One-body nuclear dissipation is a consequence of the long mean free path of nucleons inside a nucleus, and arises from nucleons colliding with the moving boundary of the nucleus rather than with other individual nucleons. In our modification, which attempts to incorporate self-consistency, the dissipation rate is proportional to an integral over the nuclear surface of the square of the normal component of the normal derivative of the velocity. The resulting properties of this dissipation are qualitatively similar to those of ordinary two-body viscosity rather than to those of the original one-body dissipation. In particular, for small oscillations about a sphere the dissipation rate increases with increasing multipole degree, and in fission this dissipation leads to more elongated scission shapes and to decreased fission-fragment kinetic energies. By adjusting the parameter that specifies the magnitude of this dissipation, we are able to reproduce adequately the experimental most probable fission-fragment kinetic energies for the fission of nuclei throughout the Periodic Table.

Bottom dissipation in finite-depth water waves

Abstract: The dissipation of wave energy by various bottom mechanisms plays an important role in the spectral transformation of waves as they propagate from deep to shallow water. Three bottom dissipation mechanisms are discussed. The bottom friction mechanism is investigated in detail and a method for calculating the friction coefficient is proposed. The method is tested by comparison with field measurements. Dissipation due to percolation and bottom motion are also discussed. The magnitude of dissipation rates induced by the different mechanisms are compared under various wave and bottom conditions.

Heavy ion collisions at intermediate energy

Abstract: Two types of measurement are proposed for the analysis of heavy ion collisions in the range of energy of 20-200 MeV/A. First, measurement of the longitudinal component of the kinetic energy of the collision products characterizes the impact parameter of the collision. The distribution in this quantity allows the dissipation in the theoretical models to be determined. A second kind of measurement is that of the coefficients of a spherical harmonic expansion of the angular distribution of the products. Besides giving independent information on the impact parameter and reaction dynamics, measurement of these coefficients offers the possibility of measuring the stiffness of the equation of state of nuclear matter. These ideas are explored in the context of a hydrodynamic model for the collision. In the purely hydrodynamic model there is a large measurable asymmetry in the angular distribution, but the dependence on the equation of state is small.

Linear and nonlinear contributions to the growth and decay of the large-scale atmospheric waves and jet stream

Abstract: To study the growth and decay of the atmospheric wave motions in middle latitudes, we have analyzed the mechanism for the kinetic energy change in wavenumber domain, and computed the composite average of each term in the kinetic energy equation at various stages in the life cycle of the atmospheric waves. It is found that for the first 1 to 2 days the extra-long waves of wavenumbers 1 and 3 grow by receiving kinetic energy from other finite amplitude waves through nonlinear interactions; in the next 1 to 2 days, they grow by gaining energy through nonlinear interactions and converting available potential to kinetic energy. These waves then maintained their peak energy for 3 to 4 days through the balance between the energy supply from conversion of available potential energy to kinetic energy and nonlinear interactions, and the energy lost by dissipation. The contribution of nonlinear interactions then changes to negative; and in the next 3 to 4 days, the waves decay by losing energy through nonlinear interactions and dissipation. The average life cycle of these extra-long waves is about 10 to 11 days. Similar results have been found with regard to the synoptic-scale waves of wavenumbers 4 to 8. They also intensify by receiving energy and decay by losing energy through nonlinear interactions among finite amplitude waves. Nevertheless, the conversion of the available potential energy to kinetic energy plays a more important role in the growing stage of the synoptic-scale waves than for the extra-long waves. The average life cycle for the synoptic-scale waves is about 6 to 8 days. It is interesting to note that the characteristics of waves of wavenumber 2 are quite different from those of the other waves. In all stages of its life cycle, the contribution of nonlinear interactions is negative and the conversion term always has large positive values. We have also analyzed the intensification and decay of the subtropical jet stream, and found that it is greatly affected by the convergence and divergence of eddy momentum flux. The fluctuations of the net momentum flux are mainly contributed by the synoptic-scale waves of wavenumbers 4 to 8. DOI: 10.1111/j.2153-3490.1978.tb00814.x

The damping of solitary waves

Abstract: The bottom mean resistance coefficient for the flow of solitary waves is derived from considerations of energy dissipation, and is obtained from measurements of the attenuation of wave amplitude al...