Browsing by Author "Ripken, John F."

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An Acoustic Study of Gaseous Micro-Bubbles In Boundary Layers and Propeller Wakes
(St. Anthony Falls Hydraulic Laboratory, 1962-12) Ripken, John F.; Killen, John M.
This report deals with exploratory tests to measure the nature of the free gas which occurs in natural water due to the dynamic disturbance of a ship. Acoustic attenuation measurements serve to show that micro gas bubbles are evolved from dissolved gases by the shear dynamics of a boundary layer and that the rate of evolution increases as some function of the intensity and duration of the disturbance and of the pressure, viscosity, and gas content of the water. The tests were conducted in the Laboratory, in large scale simulations of a ship's boundary layer and propeller, and in wakes of actual ship propeller's. These exploratory tests indicate the need for more extensive tests in sea water under a wide variety of naval operating conditions. Such tests are necessary to a better determination of the role that these bubbles play in cavitation and acoustic detection problems.
Analysis of a Hydroacoustic Gravity Flow Facility
(St. Anthony Falls Laboratory, 1984-09) Arndt, Roger E.; Wetzel, Joseph M.; Bintz, David W.; Ripken, John F.
Two preliminary designs of a hydroacoustic gravity flow facility have been developed for a Ship Silencing Laboratory, DTNSRDC, by Dr. George F. Wis1icenus. It was desired to attain a test section velocity of 60 fps for a 90 sec time period. As the facility will be used for acoustic measurements, cavitation-free flow is a necessity. After a test run has been completed, the water is returned by a pump in a separate line back to the head tank. To ma~imize usage of the facility, the recycling time between runs should be kept short. As part of the overall development program, the Laboratory has been asked to carry out some preliminary calculations on the proposed designs to further establish feasibility and to independently evaluate the designs. The calculations included an estimate of head loss in the system and an elementary transient analysis. An alternate configuration also has been suggested for consideration.
Design Studies for a Closed-Jet Water Tunnel
(St. Anthony Falls Hydraulic Laboratory, 1951-08) Ripken, John F.
A variable-pressure water tunnel, which is a testing facility analogous to a wind tunnel, is a useful tool in the study of cavitation or hydrodynamic characteristics of underwater bodies. This paper includes general, selective, hydrodynamic design studies for the construction of a large closed-jet water tunnel, together with experimental model test data and design analysis of a specific selection of flow components. Each flow component is critically examined with regard to its influence on test section flow quality, cavitation, susceptibility, and energy head loss. Included are studies of the test section, contraction, diffuser, vaned elbows, and pump. Presentation in chapters devoted to single flow components simplifies the treatment and increases adaptability of the findings to conduit design problems other than water tunnels.
Evaluation Studies of the United States Rubber Company Wave Blanket and Wave Trap
(St. Anthony Falls Hydraulic Laboratory, 1960-08) Ripken, John F.
Inherent in Man's use of large bodies of water is the need for sheltered area protected from destructive force of gravity waves. In natural harbors this protection is provided by structures which absorb or reflect the energy of these waves. The structures vary from long sloping beaches of fine sand to vertical cliffs of massive rock. The sloping beaches of fine sand to vertical cliffs of massive rock. The sloping beach largely dissipates the wave energy in viscous fluid action whereas the bluff structure serves mainly to reflect the wave energy back toward the source.
Experimental Flow Studies With the Dual-Screen Cooling Water Intake Assembly ("Riser") for the James H. Campbell Electric Power Generating Plant, Unit No. 3
(St. Anthony Falls Laboratory, 1978-12) Stefan, Heinz G.; Dahlin, Warren Q.; Ripken, John F.; Wood, Addison; Winterstein, Tom
Flow characteristics inside and outside of a dual-screen cooling water intake assembly ("riser") for the James H. Campbell Unit No.3 were observed and measured in hydraulic models at scales of 1:3 and 1:12. Risers consist of dual cylindrical screens with horizontal axis and solid endplates mounted on a T-assembly which is supported by a 3.5 ft diameter vertical withdrawal pipe. Pressure losses within the assembly, approach flow velocity patterns and approach flow velocities on the screen surface were investigated. A total headloss coefficient of 4.6 resulting in an equivalent full-scale headloss of 8.0" of water at a withdrawal rate of 29.44 ofs through the assembly was measured in the model. Flow patterns towards single and multiple risers were observed by dye tracing techniques. Approach flow velocities were measured on the surface of the 1: 3 scale riser model. The highest velocities were found near the center of the screen and the lowest ones near the projecting endplates. Maximum local velocities exceeded calculated average velocity by about 30 per cent.
Experimental Studies of a Hydrofoil Designed for Supercavitation
(St. Anthony Falls Hydraulic Laboratory, 1956-09) Ripken, John F.
Thin hydrofoils specifically designed to operate under conditions of extreme cavitation have been tested in a free-jet water tunnel to determine their performance characteristics in two-dimensional flow. The hydrodynamic forces acting on the foil section were evaluated from pressure distribution measurements, and related cavitation observations were made. The force studies indicated favorable performance but established the necessity for providing a very thin and sharp leading edge. The small rounding of the leading edges tested obscured possible correlation with the basic theory of the foil design employed.
An Experimental Study of Flexible Floating Breakwaters
(St. Anthony Falls Hydraulic Laboratory, 1960-10) Ripken, John F.
Earlier studies had indicated that moored flexible bags positioned slightly below the water surface and filled with a liquid or a gas could attenuate the height of gravity water waves. The studies reported herein describe large and small scale laboratory tests evaluating the attenuation effects and mooring forces for various bag configurations. A breakwater composed of a moored row of lean, floating cylindrical bags filled with water provided excellent wave attenuation with moderate mooring forces. This type of breakwater appeared suitable for practical development of temporary wave protection works. Submerged bags filled with air also provide good attenuation action but involved a substantial structural system for mooring.
Hydraulic Model Studies for Modifications of the Cooling Water Intake for Unit No. 4 - Clay Boswell Plant of the Minnesota Power and Light Company
(St. Anthony Falls Laboratory, 1978-04) Wetzel, Joseph M.; Ripken, John F.
The Minnesota Power and Light Company (MP&L), an investor owned public utility, has an existing steam-electric generating plant located on Black- water Lake in Itasca County near the City of Cohasset in Northcentral Minnesota. The plant has an intake and pumping station drawing water from the lake. The intake supplies cooling and other water for existing plant Units #1 and #2, each of which is rated at 70 MW. These units employ an open circulating cooling water system and return the heated water to Black- water Lake. The station also includes service pumps which supply makeup water for plant Unit #3. Unit #3 is rated at 350 MW and employs a closed circulating water system with mechanical draft wet cooling tower. Unit #4 will employ a closed circulating water system with a cooling tower. The existing intake pumping station, comprised of two intake sumps, is to be modified to provide water for all four steam units. The modifications will necessitate the replacement of some existing pumps with larger pumps and a rearrangement of the service water pumps. The four existing main circulating water pumps and the traveling screens for intake Units 1 and 2 are not to be replaced. The proposed design modifications of the intake were prepared by Ebasco Services, Inc., Atlanta, Georgia. This report is a brief resume of hydraulic model studies which were carried out at the St. Anthony Falls Hydraulic Laboratory (SAFHL) to clarify and validate the hydraulic performance of the proposed modifications.
Model Experiments for the Design of a Sixty Inch Water Tunnel Part II
(St. Anthony Falls Hydraulic Laboratory, 1948-09) Ripken, John F.; Holdhusen, James S.
A recirculating type of water tunnel is designed to produce a steady stream of fluid having uniform velocity and pressure in the test section. However, the tendency of the recirculating system is to produce variations in velocity from point to point across a section of flow due to growth of the boundary layer. Superimposed on this variation of velocity in space is a variation of velocity in time caused by turbulence in the stream. The necessity of diverting the stream through 360 degrees and of adding energy by means of a rotary impeller introduces the possibility of superposition of steady large-scale turbulence on the stream, but correct design of elbows and pump can effectively eliminate this source of velocity variation.
A New Facility for Evaluation of Materials Subject to Erosion and Cavitation Damage
(St. Anthony Falls Laboratory, 1965-03) Ripken, John F.; Killen, John M.; Crist, Scott D.
For nearly forty years various investigators have attempted to develop and routinely employ test procedures which would realistically evaluate the service resistance of fabricated materials exposed to erosion by water impact. These evaluations were necessary for the design selection of materials for steam turbine blades, for hydraulic machinery, and more recently for underwater ship appendages and for aircraft windshields.
Non-Newtonian Pipe Friction Studies with Various Dilute Polymer Water Solutions
(St. Anthony Falls Laboratory, 1964-06) Ripken, John F.; Pilch, Meir
This study extends existing data on the frictional drag reducing influence of long-chain polymers in dilute water solutions. Studies were conducted with both fresh and sea water in capillary tubes and pipes with a size range of 100 diameters and covering the laminar, transition, and turbulent regimes with N↑Re up to 8 x 105. Fifteen types of test additives were used, including Polyhall, Polyox, Westco Guar, and fish slime. Test temperatures ranged from 40° to 85° F. Dilute solutions ranging down to 10 ppm concentration exhibited remarkable friction reductions at high shear rates as a near-laminar type of flow. Data correlation was hampered by diameter, temperature, and concentration effects not resolved by existing flow parameters based on power law theory. Shear degradation effects were evaluated.
Reduction of Cavitation Damage by Surface Treatment
(St. Anthony Falls Laboratory, 1966-07) Ripken, John F.
It was rationalized, with limited supporting evidence, that most damage due to cavitation stems from cavities which are the consequence of outgassing nuclei growing from fissures in a body's surface. To minimize this damage, it was proposed that body surfaces be treated to reduce the number and activity of these surface faults. Vibratory cavitation damage tests of specimens treated to seal, neutralize, or compress the test surface indicated that these protective measures were inadequate for the severe conditions of a vibratory test. Light shot peening of a work hardening stainless steel prior to cavitation exposure substantially reduced the normal rate of cavitation erosion.
Research and Development Studies for a Low-Level Free-Air Velocity Measuring System
(St. Anthony Falls Hydraulic Laboratory, 1957-04) Ripken, John F.; Killen, John M.
This report describes the development effort involved in creating an instrument capable of measuring the speed (0 to 50 fps) and direction of an air-flow vector at any selected point ranging from 0 to 1000 ft above the earth's surface. The sensitive instrument element was an electrically heated thermistor rod producing an electrical signal variation as a result of the convective cooling action of the measured air flow. The electrical signal from the elevated instrument station was conveyed to the ground readout station by a transmission cable. The instrument was stably supported and selectively positioned in the air flow by a tethered kite-type balloon. The development resulted in a complete and practical field measuring instrument having good accuracy and response.
Research and Development Studies for a Low-Level Wind-Measuring System
(St. Anthony Falls Hydraulic Laboratory, 1955-12) Ripken, John F.; Killen, John M.
This report describes the research and development effort involved in creating an instrument capable of measuring the speed and direction of winds ranging from 1 to 50 ft per sec at any selected point between 0 and 1000 ft above the earth's surface. The sensitive instrument element was an electrically heated Thermistor rod producing an electrical signal variation as a result of the convective cooling action of the measured wind. The electrical signal from the elevated instrument station was conveyed to the ground indicator station by a transmission cable. The instrument was stabily supported and selectively positioned in the wind by a tethered kite-type balloon.
Shear and Diffusion in a Large Boundary Layer Injected with Polymer Solution
(St. Anthony Falls Laboratory, 1970-02) Wetzel, Joseph M.; Ripken, John F.
Experimental studies involving velocity profile measurements and polymer diffusion measurements were made in a plane boundary layer with length varying up to 40 feet, thickness varying up to 15 inches, and Reynolds number varying up to 8 x 10^7. Aqueous solutions of Polyox WSR-301 of 250 to 2000 ppm were injected tangentially at the boundary near the origin of a boundary layer having a stream velocity of 18 fps. Diffusion of the polymer from the boundary up into the boundary layer was evaluated from profiles made by sampling with withdrawal tubes located at various stations along the flow axis. A fluorescent marker dye was used for the evaluation. Velocity measurements served to define the profile and permitted profile extrapolation to the boundary for boundary shear evaluations. The maximum drag reduction of 35 per cent over a 40-foot boundary length exposed to V = 18 fps occurred with an injection of 0.004 lb/sec of polymer per foot width, which resulted in a downstream wall concentration of about 30 ppm. A flush-mounted hot-film sensor was calibrated for both water and polymer flows in a gravity-flow pipe facility. The calibration curve was influenced by the addition of polymer. Measurements of the zero crossings and frequency spectra of the turbulent fluctuations, as well as velocity profiles, were made for various polymer concentrations in the commercially rough pipe. Zero crossings were found to correlate with the square root of the wall shear stress.
The St. Anthony Falls Hydraulic Laboratory Gravity-Flow Free-Jet Water Tunnel
(St. Anthony Falls Hydraulic Laboratory, 1959-08) Silberman, Edward; Ripken, John F.
A unique facility for studying cavitation phenomena has been developed at St. Anthony Falls Hydraulic Laboratory of the University of Minnesota in the form of a gravity-flow free-jet water tunnel which makes use of the 50-ft drop in the Mississippi River at the Falls where the Laboratory is situated. The tunnel is an outgrowth of projects sponsored by the Office of Naval Research and is used for experimental studies of cavities under an exceptionally wide range of conditions, especially at small cavitation numbers. both axially symmetric and two-dimensional test sections have been provided.
Steady-State Cavity Studies in a Free-Jet Water Tunnel
(St. Anthony Falls Hydraulic Laboratory, 1955-07) Self, Morris W.; Ripken, John F.
A water tunnel with a 10-in. diameter test stream directed vertically downward through an air-filled chamber of variable pressure (free jet) has been used to study steady-state cavities. The low ambient pressures available in the free jet permitted cavitation studies in a range of σ = 0.01 to 0.30 on selected conical, spherical, and disk-headed bodies. This report describes certain characteristics of the steady-state cavities created by the selected bodies including cavity shape, internal pressures, and re-entrant internal jets. The cavity data are compared with related work by Reichardt.
Studies of the Reduction of Pipe Friction with the Non-Newtonian Additive CMC
(St. Anthony Falls Hydraulic Laboratory, 1963-04) Ripken, John F.; Pilch, Meir
This study extends existing data to better clarify the manner in which the addition of a small quantity of long-chain polymer chemical additive to water can remarkably reduce the frictional resistance to flow. The material sodium carboxymethylcellulose was added to fresh water and subjected to pipe friction tests under a wide range of shear rates, additive concentration, and temperature conditions. The frictional data are characterized by application of the power law expression for non-Newtonian fluids.
A Study of the Fragmentation of Rock by Impingement with Water and Solid Impactors
(St. Anthony Falls Laboratory, 1972-02) Ripken, John F.; Wetzel, Joseph M.
Based on findings in other research areas it was reasoned that water slugs of substantial size (up to 1/2 lb) traveling at moderate velocities (< 800 fps) could impinge on rock with fragmenting pressure. To substantiate this reasoning, a compressed air launching gun was designed and built and an extensive series of impact tests was made on a steel-mounted pressure transducer and on sandstone and limestone targets. In a very few tests pressure values measured on the steel target exceeded the nominal compressive load limits of the rocks, but on actual rock targets significant fragmentation failed to occur. The basic difficulty was related to an inability to maintain a suitable air-water interface on a traveling water slug containing high kinetic energy. This, together with higher-than-anticipated dynamic failure values in the rook, prevented effective fragmentation. Pilot tests which replaced the water with spherical slugs of steel (3/16 to 2 in. diam.) resulted in spalling fragmentation and excellent specific energy values. Minimum values of specific energy appeared to occur with velocities below 500 fps. However, the evidence for the 2-inch spheres was limited by the fact that the 12-inch target cubes (sandstone, granite, basalt) shattered at velocities below 400 fps. The tests suggest that moderate-velocity large slugs of water are not satisfactory for fragmentation of rock, but heavy large-sized solid impactors are very effective at moderate velocities.
A Study of The Influence of Gas Nuclei on Scale Effects and Acoustic Noise for Incipient Cavitation in a Water Tunnel
(St. Anthony Falls Hydraulic Laboratory, 1959-09) Ripken, John F.; Killen, John M.
Cavitation inception studies made on models in a recirculating water tunnel fail to correlate with similar studies on prototype bodies. This report considers the effect which free-gas nuclei in the water may contribute to this problem. Cavitation model tests were conducted using new instrumentation to measure the amount and size of the gas nuclei present in the flow. The inception of cavitation and the acoustic noise resulting from cavitation were both determined to be profoundly influenced by the character of the gas nuclei present in the liquid.

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