Transactions of the American Society of Civil Engineers Volume 51 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1903 Excerpt: ...fits the runner elot-ely, the velocity of the water will be half that of the runner. This will reduce the friction between the runner and the water to about oneeighth; but there will arise friction between the water and the case, which, lor a close lit between the runner and the case, is about equal to the friction between the runner and the water. The power to overcome the friction between the water and the case must also ccnie from the runner. The total work of friction, therefore, is approximately one-quarter of that between quiet water and the runner. Different parts of the runner have different velocities, and the formula for F must be changed accordingly. The two considerations mentioned suggest the formula W W F=S. 8pIV3 = f-f 2 p I Vs. 4 c" 4 c' The case here considered, however, is widely different from that of the flow of water in a pipe or an open channel. The results obtained by the foimula, therefore, may not correspond with the facts. Experiments with a pump arranged for running in either water or air, and driven by an electric motor of known characteristics, would be needed to determine the proper coefficients for the formula. Experiments with a metal disk and with a cylinder revolving in water would be still more suitable for ascertaining the general law of this friction. The distance of the case from the runner has probably little influence on the amount of work lost by this friction. If the case is far distant from the runner, a large part of the total friction will be internal friction in the water, and the friction between the water and the case will be correspondingly smaller. The formula is here given merely as a hypothesis of the probable law of this friction. It needs confirmation by experiment, because several steps in the argu...