Showing papers on "Dissipation published in 1977"

Rheology of concentrated disperse systems and minimum energy dissipation principle. i. viscosity-concentration relationship.

Abstract: For concentrated disperse systems, exhibiting newtonian behaviour, a new viscosity-concentration relationship is deduced from the optimization of viscous energy dissipation. Comparison with several theoretical and experimental investigations gives satisfactory agreement up to packing concentrations.

Flux Measurements, Flux Estimation Techniques, and Fine-Scale Turbulence Measurements in the Unstable Surface Layer Over Land.

Abstract: An AFCRL-UCSD joint experiment in Minnesota in 1973 has provided a comparison of direct and indirect measurements of the surface-layer fluxes of momentum, heat and moisture under unstable conditions. The direct momentum and heat flux measurements of the two groups agreed well, and also agreed well with values inferred by the direct dissipation technique. The moisture flux estimates from the inertial-dissipation technique also agreed well with the directly measured values. Several of the important terms in the budgets of turbulent kinetic energy and turbulent scalar variances were evaluated directly. The imbalance (or pressure transport) term in the energy budget was estimated, and the ratio of the imbalance term to the dissipation term determined from the present experiment agrees well with the Kansas results. The dissipation rate of temperature variance exceeded its production rate, in contrast with the Kansas results, implying an imbalanced temperature variance budget. Several possible contribu...

Coupled piano strings

Abstract: The fact that a piano typically has not one, but two or three strings tuned to a given pitch, and that these sets of strings cross the bridge at (almost) the same point, leads to significant dynamical coupling among their vibrations. Since the dominant dissipation mechanism is the non‐rigidity of the bridge, the rate of energy loss by one string is radically affected by the way that its partners are vibrating; for example, an “antisymmetric” vibration of a pair of strings is much longer‐lived than a “symmetric” one. This fundamental phenomenon is complicated by a number of factors, including (a) slight differences in the natural frequencies of the individual strings; (b) a bridge admittance which has a reactive as well as a resistive part; (c) two possible polarizations of the string vibration; and (d) hammer irregularities which cause nonidentical initial excitations of the strings. In this paper we develop theoretical predictions of the way that the rate of energy transmission from strings to bridge, as a function of time, depends on the various parameters mentioned; we then compare these predictions with experimental measurements of beats and “aftersound” under various conditions. Our data shows the time‐dependence of each polarization of string vibration amplitude, as well as the resulting sound pressure level, covering a dynamic range of 70 dB from the moment of hammer impact until the signal is lost in the noise. The agreement with theory is excellent. On the basis of this understanding we also explain the function of the una corda pedal in controlling the aftersound, point out the stylistic possibilities of a split damper, and explore the way in which an excellent tuner can use the fine tuning of the unisons to make the aftersound more uniform from note to note.

Parameterization of the Turbulent Energy Budget at the Top of the Daytime Atmospheric Boundary Layer

Abstract: The budget of turbulent kinetic energy at the base of the inversion which caps the daytime atmospheric boundary layer depends on the lapse rate of potential temperature in the air aloft. The principal gain term in the energy budget is turbulent transport of kinetic energy, the principal loss term is buoyant conversion of kinetic energy into potential energy. The contributions made by these and other terms in the energy budget need to be parameterized for applications to inversion-rise prediction schemes. This paper contains a detailed analysis of the effects of dissipation near the inversion base, which leads to reduced entrainment if the air aloft is very stable. The parameterized energy budget also includes the Zilitinkevich correction, the influence of mechanical energy production near the inversion base, and modifications needed to incorporate cases in which the surface heat flux is negligible. Extensive comparisons of the theoretical model with experimental data indicate that a simplified tr...

Inelastic responses of reinforced concrete structures to earthquake motions

Abstract: Two basic characteristics of reinforced concrete structures play an important role in determining response to strong ground motions. They are the changes in stiffness and energy dissipation capacity. Both can be related to the maximum displacement. Results of dynamic tests of reinforced concrete frames are used to illustrate the effects on dynamic response of changes in stiffness and energy dissipation capacity. It is shown that maximum inelastic response can be interpreted in terms of linearly elastic analysis by reference to a fictitious linear structure whose stiffness and damping characteristics are determined as a function of the assumed or known maximum displacement. This leads to a simplified method for estimating the design base shear taking account of inelastic response. The object of this paper is to describe basic phenomena of energy dissipation in reinforced concrete structures subjected to strong ground motion, and to present a simplified method for estimating the design base shear corresponding to inelastic response.

The energy dissipation in sheared coagulated sols

Abstract: The observed energy dissipation in coagulated sols subjected to a shear flow can be explained by assuming that the basic units of flow are elastic flocs which are slightly deformed during collisions because of the stretching of the particle bonds within a floc by a few tenths of a nanometer. Liquid inside perforated structures is generally considered immobile, but during the deformation of the flocs some internal liquid movement occurs. Although the amount of internal liquid movement is rather small, of the order of 1%, it is sufficient to account for the observed energy dissipation.

Heating of Coronal Plasma by Anomalous Current Dissipation.

Abstract: It is shown that there exist heating mechanisms which connect the observed radiative properties of the inner corona in a simple way to the underlying solar magnetic field. The mechanisms considered involve the generation and consequent dissipation of coronal currents. It is argued that the spatially and temporally inhomogeneous nature of the erupting solar magnetic field is an essential element of coronal heating. Unlike heating theories conceived in the context of the 'homogeneous' corona, this class of current heating models incorporates the observed stochastic coronal structuring at the onset, and does not view it as a complication of an otherwise straightforward model. Attention is given to the generation of coronal currents, the flux-tube emergence, the gradual growth and decay of active regions, the energetics of current dissipation, current sheath geometry and heat transport, and anomalous current dissipation.

Magnetic dynamo action in two-dimensional turbulent magneto-hydrodynamics

Abstract: Two-dimensional magnetohydrodynamic turbulence is explored by means of numerical simulation. Previous analytical theory, based on non-dissipative constants of the motion in a truncated Fourier representation, is verified by following the evolution of highly non-equilibrium initial conditions numerically. Dynamo action (conversion of a significant fraction of turbulent kinetic energy into long-wavelength magnetic field energy) is observed. It is conjectured that in the presence of dissipation and external forcing, a dual cascade will be observed for zero-helicity situations. Energy will cascade to higher wave numbers simultaneously with a cascade of mean square vector potential to lower wave numbers, leading to an omni-directional magnetic energy spectrum which varies as 1/k 3 at lower wave numbers, simultaneously with a buildup of magnetic excitation at the lowest wave number of the system. Equipartition of kinetic and magnetic energies is expected at the highest wave numbers in the system.

Electrodynamics at Metal Boundaries with Inclusion of Plasma Waves

Abstract: The energy theorem of electrodynamics is cast in a form which yields expressions for the energy current and energy dissipation of a combined field of transverse and longitudinal waves when the longitudinal field is described in the hydrodynamic approximation. This has consequences concerning the boundary conditions for transverse and plasma waves at metal-metal interface and the photoemission yield.

Elastic wave propagation in a highly scattering medium - A diffusion approach

Abstract: The propagation of elastic waves in the moon, where the first seismograms were characterized by the presence of a long coda attributed to strongly scattered waves, is modeled with the aid of the time-dependent equation of radiative transfer. The average energy density as a function of time and space is described by the diffusion equation with linear dissipation on the assumption that all the energy present has been scattered many times and the time and distance scales of the problem are long compared to the scales of the scattering process. Ultrasonic experiments in the laboratory confirm the applicability of the formalism.

Numerical Computation of Flow in Rotating Ducts

Abstract: A finite-difference procedure is employed to predict the turbulent flaw in ducts of rectangular cross-section, rotating about an axis normal to the longitudinal direction. The flows were treated as “parabolic”; and the turbulence model used involved the solution of two differential equations, one for the kinetic energy of the turbulence and the other for its dissipation rate. Agreement with experimental data is good for a constant-area duct at low rotation, but less satisfactory for a divergent duct at larger rotation. It is argued that a “partially-parabolic” procedure will be needed to predict the latter flow correctly.

Stabilization of the Alfvén wave instability in a two-component tokamak

Abstract: The stabilization of the Alfven wave instability in a two-component tokamak is investigated theoretically. It is assumed that the instability is caused by fast ions which form in the tokamak when fast neutral atoms are injected into it. Dissipation through collisions with trapped electrons is considered to be a stabilizing factor. The method developed by Timofeev for considering initial perturbations is employed. It is shown that the influence of dissipation through collisions with trapped electrons on the "local" growth rate of the instability of an ion beam is insignificant in cases of practical interest. Such collisional dissipation is also insignificant as regards the evolution of initial perturbations if the thermal spread of the beam is not too great. It can, however, play an appreciable role in the case of very diffuse beams. This opens up the possibility of suppressing Alfven instability by injecting into a tokamak neutral atoms with a broad energy spectrum.

Energy Dissipation Within Intermittent Clear Air Turbulence Patches

Abstract: Mean dissipation rates of kinetic energy in the lower stratosphere are estimated from data obtained with an instrumented, superpressure, constant-level balloon launched to measure the vertical wind shear at 200 mb. The flight record shows that while the balloon was located above a mountainous region localized patches of turbulence were encountered. The record is divided into 20 periods. The structure function is calculated over each period and, under the hypothesis of an inertial subrange, the mean dissipation is in turn estimated over each period. Our calculations indicate that the mean dissipation rate of kinetic energy can vary to a great extent over distances as short as a few tens of kilometers. Thus, when the shear layer breaks down, the mean dissipation rate can be 10 times higher than just before or after the event. It can also be 100 times higher within moderately intense clear air turbulence patches than in very weak intensity turbulence zones. These results show the sporadic nature of ...

An investigation of nonlinear transmission lines and shock waves

Abstract: Results of a study carried out on a carefully constructed laboratory model of a nonlinear transmission line are reported. These results are compared with those obtained using a computer model, and the two sets of results are shown to be in close agreement. Furthermore, a detailed study of energy balance associated with shock waves indicates that there is no per se energy loss associated with the shock wave formation and in the limit when the line dissipation (R and G parameters) is reduced to zero the system conserves energy. The observed phenomena are fully accounted for by quantitative consideration of the phenomena in the wake of the shock front. It is shown that the 'energy loss', encountered with the classical model, can be accounted for by the energy stored in the AC component of the oscillations formed in the wake of the shock front.

Linear hydrodynamical equations coupled with radiative transfer in a non-isothermal atmosphere

Abstract: A method coupling the hydrodynamical equations and radiative transfer in a realistic solar model atmosphere is described. The influence of the temperature gradient of the model and the radiative dissipation is pointed out. The effect of the large temperature gradient is important in the layers where the optical depth τ5000 is greater than 0.5; the ratio between the amplitude of the temperature and the velocity fluctuations decreases with the altitude by a factor 2 between τ = 1 and τ = 0.5 and in the case of the acoustic waves, the phase shift between these fluctuations is small. The radiative energy loss in the thick layers (τ 5000 = 1) leads to a decrease of the vertical phase velocity of the waves and to a damping of their amplitudes in the layers of intermediate optical depth (10-2 < τ5000 < 0.5). The effect of the dissipation is negligible in the thin layers (τ5000 < 10-2).

Mechanisms of damping

Abstract: Bridges subjected to dynamic testing have commonly shown relatively small variation of damping (expressed as the effective instantaneous logarithmic decrement) with amplitude This is clearly closer to the theoretical solution for viscous or idealised hysteretic damping than to the solution of the classic simple friction-damped system Nevertherless, the magnitude of the observed damping is such that in many cases friction must make a major contribution to the dissipation of the energy of oscillation Some indication is given of the possible magnitude of hysteretic effects, including cases where an apparently hysteretic behaviour arises although the actual dissipative mechanism is frictional To assist understanding of the way practical factors modify the classic friction damping model, the results are presented of an extended analysis of the effect of friction in more complex system /Author/

Dynamics of some single flux quantum devices

Abstract: In this paper and the following one, the properties of two systems operating with single flux quanta are calculated. The first system is a quantron (a one-junction interferometer) with a Josephson gate as a junction. By a proper change of its critical current in time, the switching of quantron stable states can be controlled by a small external flux much less than Qo. This "Parametric Quantron" can be used as the basic cell of a Single Quantum Logic System. The most wonderful property of this device is that the energy dissipation during one logical step (PT factor) can be much less than the thermal energy kgT and is limited by quantum effects only: PT2">02h.

Thermal loading of natural streams

Abstract: The impact of thermal loading on the temperature regime of natural streams is investigated by mathematical models, which describe both transport (convection-diffusion) and decay (surface dissipation) of waste heat over 1-hour or shorter time intervals. The models are derived from the principle of conservation of thermal energy for application to one- and two-dimensional spaces. The basic concept in these models is to separate water temperature into two parts: (1) excess temperature due to thermal loading and (2) natural (ambient) temperature. In order to formulate a linear decay model for excess temperature, the equations for back radiation, evaporation, and conduction, derived from the Lake Hefner study of U.S. Geological Survey, are linearized with reference to an arbitrary base temperature. It is shown that the resulting surface dissipation coefficient is predominantly influenced by wind speed and the mass-transfer coefficient of evaporation. Longitudinal dispersion is neglected in both transport models. Comparison of observed and calculated temperatures in seven natural streams shows that the models are capable of predicting transient temperature regimes satisfactorily in most cases. Mass-transfer coefficients of evaporation in streams are much higher than those commonly used for long-term calculations in a lake. Factors such as ground-water accretion, abrupt changes in thermalmore » loading, and unstable atmospheric conditions are found to have significant impacts on water temperature regimes. The dissipation of excess heat in natural streams is a gradual process frequently extending over a long downstream distance. For five out of the seven study reaches, the remaining excess heat at a point nearly 30 kilometers downstream was more than 50% of the initial thermal load.« less

Fluid mechanics of copper: Viscous energy dissipation in impact welding

Abstract: The aim of this paper is twofold; to explain the parametric bounds for successful impact welding, and thereby to confirm the existence of a new region V of inviscid fluid behavior of metals. The assumption of two regions of fluid behavior (viscid and inviscid) has previously permitted a description of wave formation in impact welding and has provided an estimate of about 107 s−1 for the critical strain rate dividing the two regimes. The model is extended here to a consideration of viscous energy dissipation. It is predicted that for sufficiently high impact velocities there will be some melting, and that for sufficiently low velocities the dissipation will prevent the formation of the reentrant jet needed to remove surface impurities and permit a bond to form. In this way upper and lower bounds to a bonding region are established. Fits to data of Cu‐Cu bonding provide two estimates of the coefficient of viscosity, 102 and 2.2×102 N s m−2. These values of the critical strain rate and viscosity combine to give a critical strength of (1–2.2) ×109 N m−2. A theoretical value of 1.2×109 N m−2 lies in this range.

Theoretical Evaluation of Rigid Baffles in Suppression of Combustion Instability

Abstract: An analytical technique for the prediction of the effects of rigid baffles on the stability of liquid propellant combustors is presented. This analysis employs both two and three dimensional combustor models characterized by concentrated combustion sources at the chamber injector and a constant Mach number nozzle. An eigenfunction-matching method is used to solve the linearized partial differential equations describing the unsteady flow field for both models. Boundary layer corrections to this unsteady flow are in a mechanical energy dissipation model to evaluate viscous and turbulence effects within the flow. An integral instability relationship is then employed to predict the decay rate of the oscillations. Results of this analysis agree qualitatively with experimental observations and show that sufficient dissipation exists to indicate that the proper mechanism of baffle damping is a fluid dynamic loss. The response of the dissipation model to varying baffle blade length, mean flow Mach number, oscillation amplitude, baffle configuration, and oscillation mode is examined.

The Shear Properties of Poly (N-Alkyl Methacrylates) in Concentrated Contacts

Abstract: The paper describes experiments where thin films of polymers are deposited on smooth rigid substrates and rigid smooth sliders are slid over the organic films. The influence of temperature and pressure on the interfacial shear properties of a range of poly n-alkyl methacrylates is presented. The behavior of these materials is compared with that of polythenes. The effect of progressively increasing the length of the hydrocarbon side chain moiety in the methacrylates is investigated; the behavior of the polythenes is regarded as the limiting case for infinitely long hydrocarbon side chains. The data are treated using a very simple plastic flow model based on viscous energy dissipation. The parameters obtained for this model are then considered in terms of the likely molecular processes occurring during sliding. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference held in Miami Beach, Florida, October 21–23, 1975