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Title: Compilation report on the effects of distortion: from the writings of John J. Franco and James E. Glover
Authors: Pokrefke, Thomas J.
Keywords: Distorted depth
Distorted velocity
Fixed-bed models
Froude relationships
Lightweight bet material
Model distortion
Movable-bed model
Publisher: Coastal and Hydraulics Laboratory(U.S.)
Engineer Research and Development Center (U.S.)
Series/Report no.: ERDC/CHL TR ; 05-3.
Description: Technical report
In the 1930s, 1940s, and 1950s, the U.S. Army Engineer Waterways Experiment Station (WES) conducted several series of studies to investigate the effects of distortion, differing horizontal and vertical scales, on physical model results. This report presents the portion of those investigation conducted from 1954 to 1961. The results had not been previously published; however, the two WES researchers, the late Messrs. John J. Franco and the late James E. (Ed) Glover, had prepared various unpublished documents of these investigations. Therefore, this report is a compilation of those writings and supporting data, as well as this author’s conclusions and applicability of the effects of distortion investigations to physical, movable-bed models using lightweight bed materials. The investigations conducted by Franco and Glover involved two specific series of tests. Those series were: a.Plan A, Series 1. These tests were conducted using distortions of 0, 2, 4, 6, 8, and 10. The horizontal scale used was 1:200 with subsequent vertical scales of 1:200, 1:100, 1:50, 1:33.33, 1:25, and 1:20, respectively. The tests were conducted following the Froude criteria to determine the appropriate velocity and discharge scales for these tests. b.Plan A, Series 2. These tests were conducted using distortion ratios of 0, 2, 3, and 4. The horizontal scale used was 1:400. This series of tests was conducted somewhat different than Series 1, with the velocity held constant at the 0-distortion value and the depth varied from the 0-distortion to the 4-distortion value. The depth was then held at the 4-distortion value and the velocity varied from the 0-distortion to the 4-distortion value. Some of these tests were conducted with the Froudian scale relationships not followed to isolate either velocity or depth of flow impacts. The results of the two series of tests conducted by Franco and Glover indicate that: a.Based on the Series 1 tests, the effects of distortion on the results of models of a straight reach are negligible unless the flow is affected by a bend upstream. b.Based on the Series 1 tests, flow around bends is affected by model distortion, and the effect extends for a considerable distance downstream depending upon the amount of distortion. c.Based on the Series 1 tests, the current directions in models with distortions of 4 and higher and with curvilinear flow is affected to the degree that the influence extends to the downstream model limits. d.Based on the Series 2 tests, the currents in a bend would be deflected toward the concave side of the channel as the linear-scale distortion is increased. The effect of distortion was generally progressive up to a point where the alignment of the currents was affected or controlled by the wall along the concave side of the bend. When this point was reached, increasing the distortion appeared to have little effect on the alignment of the currents. e.Based on the Series 2 tests, with the same channel roughness, the factors varied as the model was distorted were velocity and depth. The test results with constant depth and with constant velocity indicated that changes in the width-depth ratio of the channel was the principal cause of the deviation in the alignment of currents in a bend. f.Based on the Series 2 tests, increasing the roughness of the model channel as the distortion was increased would tend to reduce the effect of distortion. These results also tended to indicate that use of surface roughness sufficient to entirely overcome the effect of distortion would be impracticable.
Rights: Approved for public release; distribution is unlimited.
Appears in Collections:Technical Report

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