An Engineering Approach to the Variable Fluid Property Problem in Free Convection

An analysis is made for the variable fluid property problem for laminar free convection on an isothermal vertical flat plate. For a number of specific cases, solutions of the boundary layer equations appropriate to the variable property situation were carried out for gases and liquid mercury. Utilizing these findings, a simple and accurate shorthand procedure is presented for calculating free convection heat transfer under variable property conditions. This calculation method is well established in the heat transfer field. It involves the use of results which have been derived for constant property fluids, and of a set of rules (called reference temperatures) for extending these constant property results to variable property situations. For gases, the constant property heat transfer results are generalized to the variable property situation by replacing beta (expansion coefficient) by one over T sub infinity and evaluating the other properties at T sub r equals T sub w minus zero point thirty-eight (T sub w minus T sub infinity). For liquid mercury, the generalization may be accomplished by evaluating all the properties (including beta) at this same T sub r. It is worthwhile noting that for these fluids, the film temperature (with beta equals one over T sub infinity for gases) appears to serve as an adequate reference temperature for most applications. Results are also presented for boundary layer thickness and velocity parameters

Kolmogorov Similarity Hypotheses for Scalar Fields: Sampling Intermittent Turbulent Mixing in the Ocean and Galaxy

Kolmogorov's three universal similarity hypotheses are extrapolated to describe scalar fields like temperature mixed by turbulence. By the analogous Kolmogorov third hypothesis for scalars, temperature dissipation rates chi averaged over lengths r > L_K should be lognormally distributed with intermittency factors I that increase with increasing turbulence energy length scales L_O as I_chi-r = m_T ln(L_O/r). Tests of Kolmogorovian velocity and scalar universal similarity hypotheses for very large ranges of turbulence length and time scales are provided by data from the ocean and the Galactic interstellar medium. The universal constant for turbulent mixing intermittency m_T is estimated from oceanic data to be 0.44+-0.01, which is remarkably close to estimates for Kolmogorov's turbulence intermittency constant m_u of 0.45+-0.05 from Galactic as well as atmospheric data. Extreme intermittency complicates the oceanic sampling problem, and may lead to quantitative and qualitative undersampling errors in estimates of mean oceanic dissipation rates and fluxes. Intermittency of turbulence and mixing in the interstellar medium may be a factor in the formation of stars.Comment: 23 pages original of Proc. Roy. Soc. article, 8 figures; in "Turbulence and Stochastic Processes: Kolmogorov's ideas 50 years on", London The Royal Society, 1991, J.C.R. Hunt, O.M. Phillips, D. Williams Eds., pages 1-240, vol. 434 (no. 1890) Proc. Roy. Soc. Lond. A, PDF fil

Measurement of Vibration and Noise During the Installation of Rammed Aggregate Piers

The objective of the study was to record and evaluate ground vibration and noise generated during the installation of rammed aggregate piers (RAPs). Summarized are ground vibration and noise induced by the ramming equipment (i.e. the hydraulic break hammer and rammer) during the installation of forty-five RAPs at a single site. Data were collected during the entire installation process for each pier, which allowed for the measurement of ground vibration and noise levels for periods when the ramming equipment was positioned at different depths within the RAP. Measurements were also taken at different horizontal distances from the ramming equipment and RAP being installed. The entire data set consists of over 160 ground vibration measurements and over 260 noise measurements. Peak ground velocities measured during the study ranged between approximately 0.5 and 15 millimeters per second for horizontal distances ranging between 1.5 and 10.5 meters. Corresponding vibration frequencies ranged between approximately 20 and 60 Hz. Measured noise levels ranged between approximately 82 and 111 dBA for measurement locations between approximately 1.5 and 10.5 meters from the hammer. Overall, these measured ground vibrations and noise levels are moderate in nature and below those typically generated during pile driving

Earthquake Input Motions for Physical Model Tests

The results from several dynamic centrifuge experiments are presented in this paper; the experiments were performed as part of a study to assess the influence of local site conditions on earthquake ground motions. Medium dense dry sand and saturated soft clay models were subjected to the accelerogram recorded at Santa Cruz during the 1989 Loma Prieta Earthquake. Scaled versions of the input motion were used to shake the soil models; in addition, different time steps were used in order to study the effects of frequency content of the input motion. The results confirm that the characteristics of the input motion and the soil model combine to have important effects on soil response. This fact must be recognized when selecting input motions for physical model tests

Strain Gradients in Epitaxial Ferroelectrics

X-ray analysis of ferroelectric thin layers of Ba1/2Sr1/2TiO3 with different thickness reveals the presence of internal strain gradients across the film thickness and allows us to propose a functional form for the internal strain profile. We use this to calculate the direct influence of strain gradient, through flexoelectric coupling, on the degradation of the ferroelectric properties of thin films with decreasing thickness, in excellent agreement with the observed behaviour. This work highlights the link between strain relaxation and strain gradients in epitaxial films, and shows the pressing need to avoid strain gradients in order to obtain thin ferroelectrics with bulk-like properties.Comment: 4 pages, 3 embedded figures (1 color), revTex