The drag on a sphere moving horizontally through stably stratified salt water is measured in laboratory experiments. The increment ΔCD in drag coefficient due to the stratification is obtained as a function of a stratification parameter κ and, in principle, the usual Reynolds number R. In these experiments, where R ranges from 150 to 5000, ΔCD is insensitive to R. But, as a function of κ, ΔCD has both positive and negative values attributable respectively to lee-wave drag and to suppression of turbulence in the wake. An observed delay in flow separation also apparently results from the lee-wave drag.

Observations are made of a density current system in which salt water flows turbulently under a pool of fresh water. The density and rate of flow of the salt water are varied, resulting in varying degrees of agitation of the interface. Measurements include the interface slope, the velocity and density profiles, and the rate of mixing. Profiles of stress and effective viscosity are developed from the observations and the equation of motion. In the zone of stable stratification the effective viscosity has a minimum equal to or greater than the molecular viscosity depending upon whether the interface is laminar or agitated. Dimensionless relationships between the observed or computed quantities and the given fluid properties and flow characteristics are investigated. The principal independent variables are a Reynolds number and a Froude number. An interfacial stress coefficient is found to depend upon both. With fair accuracy, the velocity profile can be related to the interfacial stress in a manner analogous to that for turbulent flow near a rigid boundary.

Coastal processes Equilibrium bed forms Oscillatory flow Ripple growthRipple profiles Sand motion initiation Three-dimensional bed forms Waves 2Q. ABSTRACT (Vaatinum aa reveram s{«fi> ff rtexrnaeaey aad Identify by block number)The development of sand ripples in an oscillatory-flow water tunnel was observed in 104 laboratory experiments approximating conditions at the seabed under steady progressive surface waves. The period, T, and amplitude, a, of the water motion were varied over wide ranges. Three quartz sands were used, with mean grain diameters, D = 0.55, 0.21, and 0.18 millimeter.In 24 experiments, with the bed initially leveled, T was reduced until ripples appeared, and their development to final equilibrium form was observed without further change in T. (Continued) M73 EDITION OF » MOV 65 IS OBSOLETE UNCLASSIFIED SECURITY CLASSIFICATION OF THIS PAGE (When Data Ent. UNCLASSTFTRn SECURITY CLASSIFICATION OF THIS PAGE(T*7l»n Data Enterad)Profiles of two-dimensional ripples in equilibrium with the flow were generally as described by Mogridge and Kamphuis (1972) .In particular, X/a and n/a were fairly constant over a wide range of intensity of flow. However, with end crests fixed, and a varying, a profile could be "strained" into various stable forms over a considerable range of X/a. Both two-and three-dimensional final bed forms were observed. Criteria for these forms were not clearly established, but appeared to depend on both the amplitude and intensity of flow, and the grain size. UNCLASSIFIED 2 SECURITY CLASSIFICATION OF THIS PAGEflVTien Date Entered) PREFACE This report is published to improve understanding of the occurrence and form of ripples under water waves, since ripples can reduce wave height and affect sand transport.The report summarizes a laboratory study, including prototype offshore conditions, of sand ripple growth in sinusoidal flow. The results will enable the engineer to better predict and interpret equilibrium ripples in the offshore under both laboratory and field conditions.The work was carried out under the coastal processes program of the U.S. Army Coastal Engineering Research Center

Coastal processes Permeability effects Prototype tests Sand transport Water tunnel Waves 20. ABSTRACT ("Continue on reverse side H necessary and identity by block numberj The water tunnel described produces sinusoidal flow with peak velocities adjustable from to at least 30 centimeters per second for any period between 3 and 25 seconds. The tunnel is of U-tube design with the middle horizontal part comprising the test section. The vertical end parts are two cylinders with tight-fitting pistons at one end, and two reservoirs open to air at the other. The pistons are driven by a variable-speed electric motor, with an adjustable counterweight permitting operation at resonance at any period.

No abstract