The Axial Frictional Resistance of Long Cylinders in Turbulent Flow

1959 ◽  
Vol 3 (03) ◽  
pp. 24-28
Author(s):  
K. Karhan
Keyword(s):  
Turbulent Flow ◽  
Flat Plate ◽  
Frictional Resistance ◽  
The Other ◽  
Ship Model ◽  
Transverse Curvature ◽  
Other Hand ◽  
Length And Area ◽  
Mathematical Relations

In ship-model extrapolation the frictional resistance of the ship surface is generally taken to be equal to that of the flat plate having the same length and area. Experiments carried out at several laboratories with models of different size show dearly that each model should have its own extrapolation curve. In spite of general agreement that this is so, the flat-plate extrapolation curve is still generally used. On the other hand it is not easy to derive mathematical relations for ship-form frictional resistance or to make extensive experiments for this purpose. It is obvious that a first step towards departing from the flat-plate resistance basis should be to study the effect of transverse curvature on frictional resistance.

scholarly journals Distribution of velocity and temperature between concentric rotating cylinders

1935 ◽  
Vol 151 (874) ◽  
pp. 494-512 ◽  
Keyword(s):  
Turbulent Flow ◽  
Velocity Distribution ◽  
The Other ◽  
Momentum Transport ◽  
Rotating Cylinders ◽  
Simultaneous Measurements ◽  
Other Hand ◽  
Vorticity Transport

It is not possible to distinguish between the Momentum Transport and the Vorticity Transport theories of turbulent flow by measurements of the distribution of velocity in a fluid flowing under pressure through pipes or between parallel planes. Only simultaneous measurements of temperature and velocity distribution are capable of distinguishing between the two theories in these cases. On the other hand, it will be seen later that measurements of the distribution of velocity between concentric rotating cylinders are capable of distinguishing between the two theories; in fact the predictions of the two theories in this case are sharply contrasted and mutually exclusive.

The Viscosity and Structure Viscosity of Rubber Solutions and Emulsions

1956 ◽  
Vol 29 (3) ◽  
pp. 880-887 ◽  
Author(s):  
J. Schurz
Keyword(s):  
Colloidal Solution ◽  
Mutual Effect ◽  
Extreme Case ◽  
Frictional Resistance ◽  
The Other ◽  
Structural Viscosity ◽  
Uniform Size ◽  
Dispersed Particles ◽  
Other Hand ◽  
Particle Form

Abstract It is well known that the increase of viscosity of a colloidal solution over that of the pure solvent is produced by the frictional resistance to flow of the dispersed particles. The amount of this viscosity increase depends to a great extent on the shape of the particles. If these are spheres, only the ratio of the volume of the solute to the solvent is involved (Einstein's law), while in the other extreme case, namely with fiber molecules, the particle size plays such an important role, as is known, that one can calculate the particle weight of the dispersed phase from the viscosity (Staudinger's law, Mark-Houwink equation). But not only is the viscosity of a colloidal solution influenced by the particle form, but also its structural viscosity depends on it to a great degree. It is easy to understand this. For if the structure viscosity and, consequently, the decrease of viscosity with increasing velocity gradient, result from the fact that the hydrodynamic forces in the flowing solution, on the one hand, orient and distort the dispersed particles in the moving stream, and, on the other hand, oppose an eventual intermolecular mutual effect or aggregate formation of the particles, it is easily seen that the flow forces will be able to manifest these effects all the more readily and markedly the more extended and the stiffer the dispersed particles are. Thus it can be expected that, in general, in spherical particle suspensions no structural viscosity will appear, but that this will manifest itself the more strongly the more asymmetric the particles. With rubber it is easily possible to realize two extremely different dispersion forms. Rubber emulsions, as they exist in the various latexes, are typical definite spherical suspensions, with rather large particles of very uniform size. In rubber solutions, on the other hand, say in toluene or benzene, there is a macromolecular distribution. The dispersed particles are the individual kinky fiber molecules of the rubber, which are known to have a more or less elongated form. In fact these two types of rubber dispersions behave so differently that each of them can be called a typical representative of its class.

scholarly journals Experimental and Theoretical Study of the Effect of Hull Roughness on Ship Resistance

2020 ◽  
pp. 1-10 ◽  
Author(s):  
Soonseok Song ◽  
Saishuai Dai ◽  
Yigit Kemal Demirel ◽  
Mehmet Atlar ◽  
Sandy Day ◽  
...  
Keyword(s):  
Flat Plate ◽  
Rough Surface ◽  
Frictional Resistance ◽  
Total Resistance ◽  
Roughness Effect ◽  
Surface Conditions ◽  
Ship Model ◽  
Ship Resistance ◽  
Scaling Procedure ◽  
Similarity Law

Hull roughness increases ship frictional resistance and, thus, results in economic and environmental penalties. Its effect has been prevalently predicted using the similarity law scaling procedure. However, this method has not yet been validated with experimental data using a model ship. This study presents an experimental investigation into the effect of roughness on ship resistance and provides a validation of the similarity law scaling, by using tank testing of a flat plate and a model ship. Both the plate and the ship were tested in smooth and rough surface conditions, respectively. For the rough surface conditions, sand grit (aluminum oxide abrasive powder) was applied on the surfaces of the flat plate and the ship model. The roughness functions of the rough surface were derived by using the results obtained from the flat plate tests. Using the roughness function and the flat plate towing test, frictional resistance was extrapolated to the length of the model ship following the similarity law scaling procedure. The total resistance of the rough ship model was first predicted using the extrapolated frictional resistance and the result of the smooth ship model, and then compared with the results from the rough ship model. The predicted total resistance coefficients for the rough ship model showed a good agreement with the measured total resistance coefficient of the rough ship model, thus proving the validity of using Granville's similarity law scaling to extrapolate the roughness effect on ship resistance. 1. Introduction Roughness of a ship's hull, which is often caused by hull fouling (Townsin 2003) and corrosion (Tezdogan & Demirel 2014), can dramatically increase the ship resistance and hence its fuel consumption and greenhouse gas emissions, as well as the cost associated with dry-docking (Schultz et al. 2011); Granville (1958; 1978). Accordingly, there have been numerous investigations into the roughness effect on ship resistance from the earliest times to the present (e.g., McEntee 1915; Hiraga 1934; Kempf 1937; Benson et al. 1938; Watanabe et al. 1969; Loeb et al. 1984; Lewkowicz & Das 1986; Lewthwaite et al. 1985; Haslbeck & Bohlander 1992; Schultz 1998; Schultz & Swain 1999; Schultz 2002; Schultz 2004; Andrewartha et al. 2010; Schultz et al. 2011; Demirel 2015; Demirel et al. 2017a; Demirel et al. 2019).

Hydraulics of culvert fishways V: Alberta fish weirs and baffles

1990 ◽  
Vol 17 (6) ◽  
pp. 1015-1021 ◽  
Author(s):  
N. Rajaratnam ◽  
C. Katopodis ◽  
M. A. Fairbairn
Keyword(s):  
Turbulent Flow ◽  
Key Words ◽  
Channel Flow ◽  
Laboratory Study ◽  
Open Channel ◽  
Open Channel Flow ◽  
Hydraulic Performance ◽  
The Other ◽  
Other Hand ◽  
Flow Hydraulics

This paper presents the results of a laboratory study of the hydraulic performance of fish weirs and fish baffles used by Alberta Transportation for improving the fish-passing capacity of culverts. It was found that if the longitudinal spacing of the weirs is limited to 0.6 and 1.2 times the diameter of the culvert, their performance is comparable to that of the corresponding weir and slotted-weir baffle systems, with regard to the depth of pool between the baffles as well as the barrier velocity. On the other hand, the fish baffles did not perform as well as the fish weirs under the conditions tested. Key words: culverts, fishways, baffles, turbulent flow, hydraulics, open-channel flow.

Numerical Study of Flow Through 3x3 Multiswirler Arrays With Co and Counter Swirler Arrangements

2015 ◽  
Author(s):  
Prachi Rojatkar ◽  
Milind A. Jog ◽  
San-Mou Jeng
Keyword(s):  
Flow Field ◽  
Turbulent Flow ◽  
Turbulence Model ◽  
Velocity Gradient ◽  
Recirculation Zone ◽  
Numerical Study ◽  
The Other ◽  
Combustion Performance ◽  
Other Hand ◽  
Flow Through

A numerical study of turbulent flow through 3×3 multi swirler arrangement has been performed using the realizable k-ε turbulence model on a grid with about 19 million points. All co and alternate co/counter swirler configurations comprised of radial-radial swirler with counter rotating vanes are analyzed. The offset distances of swirler exit from the base wall of confinement of 0.02D and 0.31D are considered where D is the diameter of swirler exit. For both arrangements, a strong jet is issued as the flow exits individual swirl cup. Recirculation is observed at the walls and between each swirl cup along with the formation of central toroidal recirculation zone (CTRZ) at each individual swirler. It is observed that all co swirling arrangement has a stronger more compact individual CTRZ. On the other hand alternate co and counter arrangement produces more swirler-to-swirler interactions. When the offset between swirler exit and base wall of confinement is increased to 0.31D, longer but more compact CTRZ are formed at each swirler cup. The velocity gradient for 0.31D offset case is also higher than that of 0.02D. These differences in the flow field indicate better combustion performance, fuel breakup and flame anchoring for the higher offset case.

The Dilemma of the Modern Mind and the Limits of Rules

2021 ◽  
Vol 47 (3) ◽  
pp. 21-31
Author(s):  
Alessio Tartaro ◽  
Keyword(s):  
Crucial Role ◽  
The Other ◽  
Comprehensive System ◽  
Radical Empiricism ◽  
Other Hand ◽  
Modern Mind ◽  
The One ◽  
Mathematical Relations

Starting in 1946, Polanyi begins to criticize a comprehensive system of ideas that he names positivism. His criticism is twofold. On the one hand, it has the narrow aim of pointing out the inconsistencies of a positivist account of science, according to which the essence of scientific objec­tivity lies in establishing rigorous mathematical relations between measured variables employing fixed rules. On the other hand, it examines the broad assumptions underlying this view, namely radical empiricism and skeptical doubt. The present paper analyzes both aspects of this criticism, stressing its crucial role in the development of Polanyi’s philosophy.

A study of cometary eruptions through OH radio-lines

1999 ◽  
Vol 173 ◽  
pp. 249-254
Author(s):  
A.M. Silva ◽  
R.D. Miró
Keyword(s):  
Short Duration ◽  
Growth Curves ◽  
The Other ◽  
Initial Mass ◽  
Radio Lines ◽  
Other Hand ◽  
Sudden Rise

AbstractWe have developed a model for theH2OandOHevolution in a comet outburst, assuming that together with the gas, a distribution of icy grains is ejected. With an initial mass of icy grains of 108kg released, theH2OandOHproductions are increased up to a factor two, and the growth curves change drastically in the first two days. The model is applied to eruptions detected in theOHradio monitorings and fits well with the slow variations in the flux. On the other hand, several events of short duration appear, consisting of a sudden rise ofOHflux, followed by a sudden decay on the second day. These apparent short bursts are frequently found as precursors of a more durable eruption. We suggest that both of them are part of a unique eruption, and that the sudden decay is due to collisions that de-excite theOHmaser, when it reaches the Cometopause region located at 1.35 × 105kmfrom the nucleus.

Closing the GAP—A 5Å Scanning Microscope

1969 ◽  
Vol 27 ◽  
pp. 6-7
Author(s):  
A. V. Crewe
Keyword(s):  
Normal Form ◽  
The Other ◽  
Resolving Power ◽  
Scanning Microscope ◽  
Conventional Microscope ◽  
Other Hand ◽  
Closing The Gap ◽  
Thermal Sources ◽  
Better Than ◽  
Transmission Microscope

We have become accustomed to differentiating between the scanning microscope and the conventional transmission microscope according to the resolving power which the two instruments offer. The conventional microscope is capable of a point resolution of a few angstroms and line resolutions of periodic objects of about 1Å. On the other hand, the scanning microscope, in its normal form, is not ordinarily capable of a point resolution better than 100Å. Upon examining reasons for the 100Å limitation, it becomes clear that this is based more on tradition than reason, and in particular, it is a condition imposed upon the microscope by adherence to thermal sources of electrons.

Life Beyond 1MeV

1980 ◽  
Vol 38 ◽  
pp. 30-33
Author(s):  
K.H. Westmacott
Keyword(s):  
Electron Microscopy ◽  
Past Experience ◽  
The Other ◽  
Good Case ◽  
Other Hand ◽  
The U.S

Life beyond 1MeV – like life after 40 – is not too different unless one takes advantage of past experience and is receptive to new opportunities. At first glance, the returns on performing electron microscopy at voltages greater than 1MeV diminish rather rapidly as the curves which describe the well-known advantages of HVEM often tend towards saturation. However, in a country with a significant HVEM capability, a good case can be made for investing in instruments with a range of maximum accelerating voltages. In this regard, the 1.5MeV KRATOS HVEM being installed in Berkeley will complement the other 650KeV, 1MeV, and 1.2MeV instruments currently operating in the U.S. One other consideration suggests that 1.5MeV is an optimum voltage machine – Its additional advantages may be purchased for not much more than a 1MeV instrument. On the other hand, the 3MeV HVEM's which seem to be operated at 2MeV maximum, are much more expensive.

Can the Academic Self-Concept be Positive and Realistic?

2005 ◽  
Vol 19 (3) ◽  
pp. 129-132 ◽  
Author(s):  
Reimer Kornmann
Keyword(s):  
Academic Performance ◽  
Opposite Effect ◽  
Self Esteem ◽  
Point Of View ◽  
The Other ◽  
Self Concept ◽  
High Ability ◽  
Self Image ◽  
Other Hand

Summary: My comment is basically restricted to the situation in which less-able students find themselves and refers only to literature in German. From this point of view I am basically able to confirm Marsh's results. It must, however, be said that with less-able pupils the opposite effect can be found: Levels of self-esteem in these pupils are raised, at least temporarily, by separate instruction, academic performance however drops; combined instruction, on the other hand, leads to improved academic performance, while levels of self-esteem drop. Apparently, the positive self-image of less-able pupils who receive separate instruction does not bring about the potential enhancement of academic performance one might expect from high-ability pupils receiving separate instruction. To resolve the dilemma, it is proposed that individual progress in learning be accentuated, and that comparisons with others be dispensed with. This fosters a self-image that can in equal measure be realistic and optimistic.

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