Applied similarity criteria in the scale-up from existing to large MSF desalination plants

Engineering and process experience deriving from various solutions in designing MSF evaporators

A hydraulic jump is the sudden transition from a high-velocity, supercritical open channel flow into a slow-moving, sub-critical flow. It is characterised by a sudden rise of the free-surface, with strong energy dissipation and mixing, large-scale turbulence, air entrainment, waves and spray. Despite recent pertinent studies, the interactions between air bubble diffusion and momentum transfer are not completely understood. In the present study, new air-water flow measurements were performed in hydraulic jumps with partially-developed flow conditions. The experiments were performed in relatively large-size facilities with phase-detection probes. Experiments were performed with identical Froude numbers, but different Reynolds numbers or different relative channel widths. In hydraulic jumps with partially-developed inflow, void fraction distributions showed the presence of an advection/diffusion shear layer in which void fraction distributions followed an analytical solution of the diffusion equation for air bubbles. This advective diffusion layer was observed only for Re1 > 2.5 E+4. For smaller inflow Reynolds numbers, the air entrainment rate was too weak and air detrainment tended to dominate the air-water flow pattern. In the developing shear region, bubble chord time distributions showed a broad range of chord times. The distributions were skewed with a preponderance of bubble chord times smaller than the mean. A cluster analysis of bubble grouping was performed. Little bubble clustering was observed. An interparticle arrival time analysis suggested however that bubble clustering may occur preferentially for small bubbles with chord times less than 3 msec. Similar experiments with identical inflow Froude numbers and relative channel widths were repeated with a true geometric scaling ratio of Lr = 2 (i.e. 2:1 scale). The results showed drastic scale effects at small Reynolds numbers in terms of void fraction, bubble count rate and bubble chord time distributions. Void fraction distributions implied comparatively greater detrainment at low Reynolds numbers leading to a lesser overall aeration of the jump roller, while dimensionless bubble count rates were drastically lower especially in the mixing layer. Bubble chord times were not scaled according to a Froude similitude. Experimental results suggested also that the relative channel width had little effect on the air-water flow properties for identical inflow Froude and Reynolds numbers within 8 < W/d1 < 22 for 0.25 < W < 0.50 m. Transverse air-water length scales were deduced from signal correlation analyses between two probes separated by a known transverse distance. In the bubbly flow region, the resulting length scale was related to the inflow depth. The dimensionless transverse length scale Z/d1 was typically between 0.25 and 0.4 irrespective of the inflow Froude and Reynolds numbers. It is a measure of transverse length scale of vortical structures advecting air bubbles in the developing shear layer.

Criteria for dynamic similarity in bouncing gaits

Dynamic similarity during human running: About Froude and Strouhal dimensionless numbers

The water entry process is relevant to a wide range of engineering applications and has been extensively investigated. Most liquids used in such studies are single-layered, and little attention has been paid to how the structure of a two-layer liquid system affects the splash and cavity formation. In this study, we use high-speed photography to experimentally investigate the water entry of a sphere after it has passed vertically through a layer of highly viscous liquid (dimethicone) at a low Froude number. We investigate the effects of different thicknesses of this dimethicone layer and find that the formation of the splash crown is closely related to both the thickness and the Froude number. In a certain range of dimethicone thickness, the height of the splash interface decreases with the increasing thickness and increases with the decreasing Froude number. The dimensionless interface height at the pinch-off time is found to have a linear relationship with the dimensionless initial velocity of the sphere. Furthermore, the formation of the cavity, including its length and pinch-off depth, depends on the Froude number. However, the pinch-off time is almost independent of the dimethicone thickness and the Froude number, and the cavity length is nearly independent of the dimethicone thickness for all Froude numbers examined.

A critical review and rethinking of hydrogen jet flame research is carried out. Froude number only based correlations are shown to be deficient for under-expanded jet fires. The novel dimensionless flame length correlation is developed accounting for effects of Froude, Reynolds, and Mach numbers. The correlation is validated for pressures 0.1–90.0 MPa, temperatures 80–300 K, and leak diameters 0.4–51.7 mm. Three distinct jet flame regimes are identified: traditional buoyancy-controlled, momentum-dominated “plateau” for expanded jets, and momentum-dominated “slope” for under-expanded jets. The statement “calculated flame length may be obtained by substitution the concentration corresponding to the stoichiometric mixture in equation of axial concentration decay for non-reacting jet” is shown to be incorrect. The correct average value for non-premixed turbulent flames is 11% by volume of hydrogen in air (range 8%–16%) not stoichiometric 29.5%. All three conservative separation distances for jet fire are shown to be longer than separation distance for non-reacting jet.

Hydrogen jet flames

In this paper, the quantitative influence of aspect ratio (B/h), and dimensionless velocity or thickness Froude number [TFN = u/√(gh)] on dimensionless ice-induced pressures (pe/ρiu2) is briefly reviewed and discussed. Since material properties of ice (E, σf, K1c) have not been reported for many data-sets, a strategy for generating appropriate material properties for ice is proposed. Two dimensionless terms for material properties of ice, {(E/σf)×[K1c/(σf√h)]} and {[K1c/(σfu)]×√[E/(ρih)]} were identified and their influence on pe/ρiu2 is discussed. It was found that (1) pe/ρiu2 on rigid vertical structures decreases with (a) increasing B/h at a rate of about 0.42, when u/√(gh) and {[K1c/(σfu)]×√[E/(ρih)]} remain constant; (b) pe/ρiu2 decreases with increasing u/√(gh) at a rate of about 1.80 when u/√(gh) is &amp;lt; about 6.0×10-3and at a rate of about 1.93 when u/√(gh) is &amp;gt; about 6.0×10-3 when B/h and {[K1c/(σfu)]×√[E/(ρih)]} remain constant. (2) Preliminary analyses of the datasets shows that pe/ρiu2 decreases with increasing {(E/σf)× [K1c/(σf√h)]} at a rate of 0.335 and 0.469 and that pe/ρiu2 decreases with increasing {[K1c/(σfu)]×√[E/(ρih)]} at a rate of 0.729 and 0.808. (3) It was also found that shapes of structures do not influence dimensionless ice-induced pressures on structures.

SummaryT0he availability of data on absenteeism for all nonsupervisory employees of a major airline for a full calendar year presented a unique opportunity for investigating some of the correlates of absenteeism. The quantitative analysis of these data was guided by two major objectives: the first was to test the prediction that the larger the size of the location (or “plant”) the higher the absenteeism, and the second was to determine how age, wage rate, seniority, and job classification were related to absenteeism with sex and “collar” held constant. The findings support the hypothesis that absenteeism is higher in larger units and thus lend credence to the notion that the characteristics of larger organizational units lead to lower levels of involvement and personal satisfaction. Other findings of the study indicate that the relationships between background factors and absenteeism are different for “blue collar” men than for other categories of employees. Among “white collar” men and women and among “blue collar” women, older, longer service, and higher paid employees are more often absent with length of service having the greatest influence. For “blue collar’ men longer length of service and higher job status are associated with lower absence rates. These findings indicate that great care should be taken in making any over‐all generalization about the factors influencing absenteeism and, particularly, that careful controls should be established in making any inferences concerning “morale” or “supervisory skill” on the basis of comparative absenteeism figures. The findings of this study, while based on data from only one company, would indicate that constructive personnel programs aimed at minimizing absenteeism should focus effort on the following work settings: larger plants, high seniority white collar personnel and blue collar women, and blue collar, male job classifications characterized by low status and little “freedom.”

By appropriate choice of reference variables, dimensionless governing equations and initial and boundary conditions of unsteady canal flow have fewer independent parameters than do their dimensioned counterparts; the same information can be expressed more compactly. With design discharge and normal depth as references, unsteady flow is governed by cross-sectional shape factors, Froude number at normal depth, and the dimensionless length, as well as initial and boundary conditions. A particular dimensionless form of the Saint-Venant equations was found to have the same appearance as the dimensioned equations. Dimensionless \ig, the ratio of weight to mass in the dimensioned real-world equations, is now related to the Froude number at normal depth in the dimensionless equations. The Manning units coefficient, normally used to express the Manning formula in English or metric systems, in the dimensionless system relates to the shape of the channel cross section under normal flow conditions. Dimensionless results are interpreted in real-world terms by specifying normal flow depth and Manning roughness. With the normal Froude number given, all pertinent dimensioned variables follow directly from dimensionless results.

The article describes mathematical model of positive-displacement hydropercussion system of single-sided back action. The principal dynamic similarity criteria found are: the reduced ratio between areas of back-stroke chamber and gas chamber; the value proportional to the ratio between potential energy of accumulator and kinetic energy of hammer; the dimensionless lengths of back stroke and gas strut. Based on numerical calculations performed within a wide range of input parameters (similarity criteria), the author has plotted nomograms of isolines of the integral input characteristics and oscillograms of dynamic characteristics, which enables revealing basic mechanisms of behavior of the discussed system in the single-blow limit cycles. In the domain of practical significance parameters, the analytically estimated dimensionless pre-blow velocity should not be higher than 810 units.

In order to establish the preventive method of big fire in urban area under strong wind , it is necessary to comprehend the general behavior of fire gas flow and fire-spread. This paper considers big fire area as a belt-shaped heat source, purposes to obtain temperature distribution of fire gas flow from this heat source under strong wind. Equations for temperature distributions are derived by determining several prameters appearing in this model, and shown as the function of dimensionless temperature (Φ), dimensionless velocity (Ω), Froude number (Fr) and ratio (x/D) of downwind distance (x) to wide (D) of the heat source. In order to examine the relation between theory and experiment, measurements of temperature and velocity are performed in a wind tunnel which is placed a belt-shaped vessel for burning alcohol, and the validity and limitation of equations are clarified by this wind tunnel test. If the steady state of fire source is assumed, it is possible to apply the proposed equation for estimating temperature distributions of fire gas flow under strong wind.

A non-human primate model of bipedal locomotion under restrained condition allowing gait studies and single unit brain recordings

Characteristics of outwardly propagating spherical flames of R134a(C2H2F4)/CH4/O2/N2 mixtures in a constant volume combustion chamber

To quickly estimate tsunami hazards along the coastline, we present a data‐driven transfer function method to reconstruct onshore tsunami hazard curves from offshore hazard curves with corresponding topographic and bathymetric data. The transfer function is approximated by a type of artificial neural network called a variational autoencoder (VAE). The VAE first encodes input data, including offshore hazard curves and topographic and bathymetric data. Once encoded, the data are represented by a normal distribution of latent variables. The VAE then uses a trained decoder to sample the distribution created by the latent variables and reconstruct a continuous hazard function at the onshore location. As a probabilistic distribution represents the encoded values, the resulting hazard curve output has inherent stochasticity. Thus, model variance can be found through many realizations of the transfer function for a single set of inputs. We developed a set of transfer functions to accurately predict the onshore hazard curves for (a) onshore flow depth, (b) Froude number (dimensionless velocity), and (c) dimensionless momentum flux. We construct two flow depth transfer functions with one version utilizing an “anchor point” taken from established site‐specific numerical modeling data. The VAEs to predict velocity and momentum flux incorporate an approach that leverages condensed topographic information around the point of interest (topographic rings). The resulting VAE's provide estimates of tsunami hazard with accuracy sufficient to perform impact and risk assessments. Overall, the transfer function method efficiently estimates onshore tsunami hazard curves, together with model uncertainty quantification, without requiring computationally expensive numerical simulations.