Showing papers on "Dissipation published in 1992"

On undamped heat waves in an elastic solid

Abstract: This paper is concerned with thermoelastic material behavior whose constitutive response functions possess thermal features that are more general than in the usual classical thermoelasticity. After a general development of the constitutive equations in the context of both nonlinear and linear theories, attention is focused on the latter. In particular, the one-dimensional version of the equation for the determination of temperature in the linearized theory provides an easy comparative basis of its predictive capability: In one special case where the Fourier conductivity is dominant, the temperature equation reduces to the classical Fourier law of heat conduction, which does not permit the possibility of undamped thermal waves; however,'in another special case in which the effect of conductivity is negligible, the equation has undamped thermal wave solutions without energy dissipation.

Enhanced dissipation of kinetic energy beneath surface waves

Abstract: TRANSFER of momentum from wind to the surface layer of lakes and oceans plays a central part in driving horizontal and vertical circulation of water masses. Much work has been devoted to understanding the role of waves in momentum transfer across the air–sea interface, but less is known about the energetics of the near-surface turbulence responsible for the mixing of momentum and mass into the underlying water column. In particular, it has remained unclear whether the structure of the turbulence in the surface layer can be described by analogy to wall-bounded shear flows or whether waves, either through breaking or wave–current interaction, introduce new length- and timescales which must be modelled explicitly. Here we report observations of turbulence in Lake Ontario, taken under conditions of strong wave breaking, which reveal a greatly enhanced dissipation rate of kinetic energy close to the air–water interface, relative to the predictions of wall-layer theory. Because wave breaking is intermittent, short-term measurements of the kinetic energy dissipation in the near-surface layer may therefore result in considerable underestimates, and any general treatment of upper mixed layer dynamics will have to take wave breaking explicitly into account.

Energy dissipation in shear driven turbulence.

Abstract: The Navier-Stokes equations are utilized to derive upper bounds on the turbulent energy dissipation rate for an incompressible Newtonian fluid confined between parallel comoving plates. These estimates provide a rigorous foundation for one of the basic scaling ideas of turbulence theory, namely, the independence of the dissipation rate and the viscosity at high Reynolds number. The bounds are compared to experiments on turbulence in the Couette-Taylor system.

In search of a thermodynamic description of biomass yields for the chemotrophic growth of microorganisms.

Abstract: Correlations for the prediction of biomass yields are valuable, and many proposals based on a number of parameters (Y(ATP), Y(Ave), eta(o), Y(c), Gibbs energy efficiencies, and enthalpy efficiencies) have been published. This article critically examines the properties of the proposed parameters with respect to the general applicability to chemotrophic growth systems, a clear relation to the Second Law of Thermodynamics, the absence of intrinsic problems, and a requirement of only black box information. It appears that none of the proposed parameters satisfies all these requirements. Particularly, the various energetic efficiency parameters suffer from major intrinsic problems. However, this article will show that the Gibbs energy dissipation per amount of produced biomass (kJ/C-mod) is a parameter which satisfies the requirements without having intrinsic problems. A simple correlation is found which provides the Gibbs energy dissipation/C-mol biomass as a function of the nature of the C-source (expressed as the carbon chain length and the degree of reduction). This dissipation appears to be nearly independent of the nature of the electron acceptor (e.g., O(2), No(3) (-), fermentation). Hence, a single correlation can describe a very wide range of microbial growth systems. In this respect, Gibbs energy dissipation is much more useful than heat production/C-mol biomass, which is strongly dependent on the electron acceptor used. Evidence is presented that even a net heat-uptake can occur in certain growth systems.The correlation of Gibbs energy dissipation thus obtained shows that dissipation/C-mol biomass increases for C-sources with smaller chain length (C(6) --> C(1)), and increases for both higher and lower degrees of reduction than 4. It appears that the dissipation/C-mol biomass can be regarded as a simple thermodynamic measure of the amount of biochemical "work" required to convert the carbon source into biomass by the proper irreversible carbon-carbon coupling and oxidation/reduction reactions. This is supported by the good correlation between the theoretical ATP requirement for biomass formation on different C-sources and the dissipation values (kJ/C-mol biomass) found. The established correlation for the Gibbs energy dissipation allows the prediction of the chemotrophic biomass yield on substrate with an error of 13% in the yield range 0.01 to 0.80 C-mol biomass/(C)-mol substrate for aerobic/anaerobic/denitrifying growth systems.

Measurement of the fracture energy using three-point bend tests: Part 1—Influence of experimental procedures

Abstract: Available measures of the fracture energy GF obtained with the procedure proposed by RILEM TC-50 provide values that appear to change with sample size, calling into question the possibility of considering GF as a material parameter. In this paper some possible sources of experimental errors, when the RILEM proposal is applied, are ascertained, namely the apparent energy dissipation from hysteresis in the testing equipment and energy dissipation in the lateral supports. It is concluded that either some other sources of energy dissipation are operative or that GF cannot be considered a material property.

Measurement of the fracture energy using three-point bend tests: Part 2—Influence of bulk energy dissipation

Abstract: Avialable measures of the fracture energy GF obtained with the procedure proposed by RILEM TC-50 provide values that appear to change with sample size, calling into question whether GF can be considered as a material parameter. In a previous paper, possible sources of energy dissipation from the testing equipment and lateral supports were considered. In this paper new possible sources of energy dissipation in the sample, apart from the fracture crack itself, are considered. Such dissipation will take place inside the bulk of the most stressed regions of the specimen and, if it is not taken into account, higher values of GF will be recorded than that strictly due to surface fracture energy. When this constribution and the possible energy dissipation analysed in previous work are considered, they are not enough to account for the measured size effect. If GF is to be considered a material parameter, the evaluation of the results from the RILEM method should be analysed more carefully. In any case, the dissipated energy reported here represents a non-negligible amount of GF and should be taken into account when performing measurements.

Probability distribution, conditional dissipation, and transport of passive temperature fluctuations in grid‐generated turbulence

Abstract: The evolution of the scalar probability density function (pdf), the conditional scalar dissipation rate, and other statistics including transport properties are studied for passive temperature fluctuations in decaying grid‐generated turbulence. The effect of filtering and differentiating the time series is also investigated. For a nonzero mean temperature gradient it is shown that the pdf of the temperature fluctuations has pronounced exponential tails for turbulence Reynolds number (Rel) greater than 70 but below this value the pdf is close to Gaussian. The scalar dissipation rate, conditioned on the fluctuations, shows that there is a high expectation of dissipation in the presence of the large, rare fluctuations that produce the exponential tails. Significant positive correlation between the mean square scalar fluctuations and the instantaneous scalar dissipation rate is found when exponential tails occur. The case of temperature fluctuations in the absence of a mean gradient is also studied. Here, the results are less definite because the generation of the fluctuations (by means of fine heated wires) causes an asymmetry in the pdf. The results show, however, that the pdf is close to Gaussian and that the correlation between the mean square temperature fluctuations and the instantaneous scalar dissipation rate is very weak. For the linear profile case, measurements over the range 60≤Rel≤1100 show that the dimensionless heat flux Nu is proportional to Rel0.88 and that the transition from a Gaussian pdf to one with exponential tails occurs at Nu∼31, a value close to transitions observed in other recent mixing experiments conducted in entirely different turbulent flows.

The origin of high speed solar wind streams

Abstract: Standard coronal heating mechanisms such as dissipation of acoustic waves generated in turbulent photospheric layers, or dissipative heating by current sheets and resonant absorption (see proceedings of Heidelberg conference /1/) cannot produce high speed solar wind streams We propose that the source of energy in these streams lies in the regions of strong magnetic field which define the boundaries of the chromospheric supergranulation network pattern If the magnetic field in these “trunks” is not strictly unipolar but instead also contains closed loops then the available free energy can be readily released in impulsive reconnection events (“microflares”) which give rise to high frequency hydromagnetic waves with periods of the order of or less than one second It appears necessary to invoke a strong source of relatively high frequency waves to allow substantial dissipation in the corona itself and also to heat selectively species of differing charge to mass ratios by cyclotron interactions Moreover such wave-particle interactions are also necessary to account for the detailed properties of high speed streams in which the perpendicular temperature exceeds the parallel temperature, ionic species tend to have the same temperature per unit mass and heavier species tend to move faster than the protons by about the Alfven speed It is noteworthy that the same source mechanism for generating the high frequency waves may also be responsible for an enhancement of low FIP ions if the required closed loops of magnetic flux emerge in the transition region where the temperature is between 104 and 105 °K

The measurement of turbulent surface-layer fluxes by use of bichromatic scintillation

Abstract: Scintillation measurements with a HeNe and a CO2 laser were used to derive turbulent fluxes of heat and momentum in the surface layer. This was achieved by the structure constant or dissipation technique, i.e., by relating the measured structure constants and inner scales of refractive index fluctuations to structure constants of temperature fluctuations and dissipation rates of turbulent kinetic energy, respectively, and then assuming Monin-Obukhov similarity.

Seismic-Energy Dissipation in MDOF Structures

Abstract: The seismic input energy imparted to a structure is dissipated by hysteretic behavior and other nonyielding mechanisms usually represented by equivalent viscous damping. It is generally recognized that there is a strong correlation between the energy dissipated by hysteretic action and the seismically induced level of damage. While viscous damping has a small effect on the amount of energy imparted to a structure, it has a significant influence on the amount of hysteretic energy dissipation. A parametric study is presented on the influence of the mathematical modeling of viscous damping on seismic‐energy dissipation of multidegree‐of‐freedom (MDOF) structures. The damping is modeled using mass‐proportional, stiffness‐proportional, and Rayleigh damping computed from either the initial elastic or the tangent inelastic system properties. Various structural performance indices are evaluated for bilinear hysteresis model of simple MDOF structures with different strength levels, strain hardening ratios, and dam...

Scenarios for the nonlinear evolution of alpha-particle-induced Alfvén wave instability

Abstract: Various nonlinear scenarios are given for the evolution of energetic particles that are slowing down in a background plasma and simultaneously causing instability of the background plasma waves. If the background damping is sufficiently weak, a steady-state wave is established as described by Berk and Breizman. For larger background damping rate pulsations develop. Saturation occurs when the wave amplitude rises to where the wave trapping frequency equals the growth rate. The wave then damps due to the small background dissipation present and a relatively long quiet interval exists between bursts while the free energy of the distribution is refilled by classical transport. In this scenario the anomalous energy loss of energetic particles due to diffusion is small compared to the classical collisional energy exchange with the background plasma. However, if at the trapping frequency, the wave amplitude is large enough to cause orbit stochasticity, a phase space ``explosion`` occurs where the wave amplitudes rise to higher levels which leads to rapid loss of energetic particles.

Optimum Dimensions of Extended Surfaces Operating in a Convective Environment

Abstract: This article is devoted to the review of the literature on optimum dimensions of extended surfaces losing heat by pure convection to the surroundings. The review covers straight (longitudinal) fins, annular (radial) fins, and spines of different profile shapes. The optimum dimensions for each shape are given both in terms of the volume of the material as well as the heat dissipation. The effects of tip heat loss, variable heat transfer coefficient, internal heat generation, temperature dependent thermal conductivity, base convection, and primary surface thickness on the optimum dimensions are discussed. The optimization procedure is illustrated with several numerical examples. Areas of extended surface technology where further optimization studies are needed are identified. It is hoped that the article would serve the dual purpose of the state-of-the-art as well as a pedagogical review. 24 refs., 22 figs., 9 tabs.

The interplay of tunneling, resonance, and dissipation in quantum barrier crossing: A numerical study

Abstract: We discuss the interplay of various quantum effects on barrier crossing for a one‐dimensional system with dissipation. This is based on a numerical study using a hierarchy of kinetic equations introduced by Tanimura and Kubo. The numerical work uses a grid in phase space for the Wigner distribution and deals with both the classical limit and the tunneling regimes.

A self-consistent turbulent model for solar coronal heating

Abstract: The rate of solar coronal heating induced by the slow random motions of the dense photosphere is calculated in the framework of an essentially parameter-free model. This model assumes that these motions maintain the corona in a state of small-scale MHD turbulence. The associated dissipative effects then allow a large-scale stationary state to be established. The solution for the macroscopic coronal flow and the heating flux is first obtained assuming the effective (turbulent) dissipation coefficients to be known. In a second step these coefficients are calculated by the sefl-consistency argument that they should result from the level of turbulence associated with this very heating flux

Properties of an adiabatic shear-band process zone

Abstract: The formation of adiabatie shear bands is examined with an approximate analytic model. The shear band is viewed as a propagating feature with a well-defined front. The shear band is further partitioned into a shear-band process zone within which most of the adiabatic heating and shear stress relaxation occurs, followed by a quasi-steady zone within which little dissipation occurs. Although a one-dimensional analysis of the shear-band dynamics is initially pursued, the analysis is then used to calculate properties of the inherently two-dimensional shear-band process zone. The length and width of the process zone are calculated along with the shear displacement. The model is further used to calculate the energy dissipation within the shear-band process zone and the concept of a shear-band toughness is introduced. The flow field within the vicinity of the process zone is also examined. Calculated properties of the shear-band process zone compared well with available experimental data.

Spatiotemporal intermittency and instability of a forced turbulence

Abstract: The time development of an infinitesimal disturbance and the relation to the spatiotemporal intermittency of a developed turbulence is studied by solving numerically the Navier–Stokes equation and its linearized form. A high‐symmetric flow is integrated by the use of the spectral method with 3403 effective modes to realize a developed turbulent field with Reynolds number of about 186 which is in statistically stationary state. Energy transfer in the wave‐number space is not uniform in time but quiescent and active periods of energy transfer and of the energy dissipation rate occur repeatedly in a large‐scale eddy‐turnover time. Vorticity tends to be concentrated in long thin tubelike regions and the energy dissipation field forms double peaks around a tube, which resembles a flow around a nonaxisymmetric Burgers vortex. Both the energy and the enstrophy of the disturbance field increase exponentially in time with growth rate comparable to the reciprocal of the time scale of the peak wave number of the energy dissipation spectrum. The energy spectrum of the disturbance field shows an equipartition of energy at small wave numbers including the inertial range. The disturbance vorticity field has a dipole structure at the position of a vorticity concentrated tube. The direction of this dipole structure is orthogonal to that of the energy dissipation field.

Variational Formulation of the Linear Mhd Stability of 3d-Plasmas with Noninteracting Hot-Electrons

Abstract: The linear MHD stability problem for 3D plasmas with noninteracting hot electron layers and nested magnetic flux surfaces in the absence of dissipation mechanisms is formulated in variational form. Boozer magnetic coordinates are extended to anisotropic pressure plasmas with nested magnetic flux surfaces for this purpose. A modified energy principle in which the hot electron species current is imperturbable is considered. Plasma incompressibility is imposed and thus a simplified kinetic energy is employed to determine the conditions of marginal stability. The vacuum region surrounding the plasma is treated as a shearless, pressureless and massless pseudoplasma. Fourier decomposition of the perturbations in the periodic angular variables of the magnetic coordinates is applied and a finite element discretization scheme reduces the stability problem to a special block pentadiagonal matrix eigenvalue equation which is amenable to solution with an inverse vector iteration technique. The formulation described is useful to evaluate the linear MHD stability properties of 3D plasma configurations with rigid hot electrons to global internal and external modes. The conditions for linear MHD stability to local modes are determined with the application of the ballooning mode representation to the internal plasma potential energy to derive the corresponding ballooning mode equation. The asymptotic analysis of this equation yields the Mercier criterion.

Comparative study of four passive energy dissipation systems

Abstract: Passive energy dissipation devices have the potential to increase the seismic resistance of a structure by increasing its capability to dissipate energy and by reducing the seismic demand on the structure. They offer particular promise for seismic retrofitting as well as extensive applications in new construction. This paper describes and compares earthquake simulator tests of four new types of passive energy dissipators that were performed at the Earthquake Engineering Research Center of the University of California at Berkeley. The four types of energy dissipator are a Coulomb friction damper; a self-centering friction device in which the slip load is proportional to the slip displacement; a viscoelastic shear damper; and a shape memory alloy. Two different model structures were used in the experimental studies, and the energy dissipators were incorporated as part of the bracing systems of the structures.

On the multifractal properties of the energy dissipation derived from turbulence data

Abstract: Various difficulties can be expected in trying to extract from experimental data the distribution of singularities, the f(α) function, of the energy dissipation. One reason is that the multifractal model of turbulence implies a dependence of the viscous cutoff on the singularity exponent. It is an open question if current hot-wire probes can resolve the scales implied by exponents a significantly less than 1.Two exactly soluble models are used to show how spurious scaling can occur, due to finite Reynolds number effects. In the Gaussian model the true velocity signal is replaced by independent Gaussian random variables. The dissipation, defined as the square of the difference of successive variables, has trivial scaling in so far as all the moments of spatial averages of the dissipation behave asymptotically as a uniform dissipation. Still, contamination by subdominant terms requires that scaling exponents for high-order moments be identified over an increasingly large range of scales. If the available range is limited by the Reynolds number, scaling exponents for high orders will be systematically underestimated and spurious intermittency will be inferred. Burgers’ model is used to highlight further problems. At finite Reynolds numbers, regions with no small-scale activity (away from shocks) have a residual dissipation which contributes a spurious point (α = 1,f(α) = 1). In addition, when the f(α) function is obtained by Legendre transform techniques, convex hull effects generate an entire spurious segment.Finally, Burgers’ model also indicates that the relation between exponents of structure functions and exponents of local dissipation moments, which goes back to Kolmogorov's (1962) work, leads to an inconsistency for structure functions of low positive order.

The dissipation of nonlinear dispersive waves: the case of asymptotically weak nonlinearity

Abstract: It is proved herein that certain smooth, global solutions of a class of quasi-linear, dissipative wave equations have precisely the same leading order, long-time, asymptotic behavior as the solutio...

Nonlocal triad interactions and the dissipation range of isotropic turbulence

Abstract: Detailed transfer functions T(k‖p,q), which express turbulent energy transfer rate to modes k caused by their nonlinear interactions with modes p and q, are analyzed using results of direct numerical simulations of homogeneous turbulence. A previously found phenomenological scaling for the functions T(k‖p,q), which brings them into a self‐similar form, is used to deduce the form of the energy spectrum in the dissipation range proportional to k−2 exp(−ak) and the transfer spectrum proportional to exp(−ak). A physical mechanism of the energy transfer process consistent with the self‐similarity scaling is proposed.

Estimation of cutting temperature in high speed machining

Abstract: This paper presents a study of the inverse heat conduction problem for high speed machining. A finite element method with an inverse scheme and an experimental measurement using infrared (IR) pyrometer with fiber optic are applied to predict the tool-chip interface temperature and the total heat dissipating to both tungsten carbide and ceramic inserts. A one-dimensional ellipsoidal mapping model of the cutting temperature distribution is adopted here and the average transient cutting temperature is calculated by the inverse finite element method with measured surface temperatures adjacent to the tool edge. Also the analysis of the errors coming from the sensor location and mapping model is studied. The results show the estimated cutting temperature is well convergent and agrees to other previous investigations. It is found that the thermal conductivity of the tool material has significant effect on the heat dissipation but little effect on the tool-chip interface temperature in high speed machining.

Energy dissipation in substorms

Abstract: The energy dissipated by substorms manifested in several ways is discussed: the Joule dissipation in the ionosphere; the energization of the ring current by the injection of plasma sheet particles; auroral election and ion acceleration; plasmoid ejection; and plasma sheet ion heating during the recovery phase For each of these energy dissipation mechanisms, a 'rule of thumb' formula is given, and a typical dissipation rate and total energy expenditure is estimated The total energy dissipated as Joule heat (approximately) 2 x 10(exp 15) is found about twice the ring current injection term, and may be even larger if small scale effects are included The energy expended in auroral electron precipitation, on the other hand, is smaller than the Joule heating by a factor of five The energy expended in refilling and heating the plasma sheets is estimated to be approximately 5 x 10(exp 14)J, while the energy lost due to plasmoid ejection is between (approximately) (10 exp 13)(exp 14)J

Quantum Monte Carlo simulation of the dynamics of the spin-boson model

Abstract: This paper presents the results of stationary-phase Monte Carlo simulations for the dynamics of the spin-boson problem. The problem of alternating weights ubiquitous in dynamical simulations has been solved using discretized path-integral simulations in conjunction with stationary-phase filtering techniques. Our computation covers the bulk of the parameter space, including non-zero bias and frequency-dependent dissipation. Besides a comparison with analytic predictions, we present some new results. For sub-Ohmic dissipation, the dynamics at low temperatures depends significantly on the initial preparation. In the Ohmic regime 1/2