Tennant, Jeffrey S.

Russian experimenters Kozlov and Leonenko have reported substantial drag reduction on a sphere using a "bill" or "spike" extending from the body upstream into the flow. A systematic series of experiments was conducted to determine the extent of the reduction and to identify the parameters of the reported drag reduction effect. The tests were performed in the Florida Atlantic University Ocean Engineering Department's Aerolab wind tunnel. A sphere was fitted with tapering bills of various lengths, base diameters, and bill/sphere fillet radii. Experiments indicated that the effect was restricted to Reynolds numbers below 4.0 x 10^5 and that the drag of the sphere/spike combination was actually increased at Reynolds numbers greater than this. A smoke generator was used to visualize the drag reduction mechanism, which appears to be a recirculating cell at the base of the sphere/spike intersection.

The transition of two dimensional flow within a crack
with oscillating wall is studied experimentally to establish
the role of the parameters involved. Multiple instabilities
in the fluid are produced by the motion of the oscillating
wall. For a better understanding of the flow structure and
displaying in the whole flow field at a time, flow
visualization was used. Frequency, amplitude, and crack
width were systematically varied. The present study shows
that, in general, the frequency and crack width play a role
in the transition process at low frequencies of
oscillations. However, amplitude becomes progressively
important at its higher range. Results also show that the
flow changes its character approximately after a Reynolds
number 11420. After that the transition process continues
until the Reynolds number 34322 which is the upper limit of
variation of frequency (Reynolds number) in the present
study.

The objectives of this investigation were: (1) to find the relationship
between the sand movement velocity and the force induced using
a small model basin, (2) to find and build a sand transport meter and
apply the relation from (1) together to measure the velocity fluctuation
and quantity of sand movement on the beach. The idea of model basin
comes from the fluidized bed concept. Using this model, the complicated
influences that happen during the field measurement can be prevented,
and a prime relation can be applied to the field measurement.
In the model basin experiment, the force induced by the drag is
related to the velocity of power around 0. 62. In the field measurement
on the beach, the initial goal could not be reached because of the
appearance of the unexpected low frequency signal which was initiated
by the wave motion itself. However, the device and idea of this experlment
were proven to be good and feasible.

The objectives of this investigation were - 1) design and build a
turbulence current meter capable of measuring velocity fluctuations in
a geophysical scale flow and 2) the measurement of such flow including
subsequent analysis of near bottom turbulence. An unique device capable
of sensing velocity fluctuations in the region 25cm above the bottom was
constructed based on concepts original to the study of turbulence. A
review of previous equipment and research is included for a comparison.
The instrument's usefulness was illustrated in the open channel flow of
a tidal estuary by its ability to detect the horizontal velocity field.
The data obtained for the turbulence shows large variation in velocity
of the lateral component on the order of 50-75% of the "mean" current
speed. Digital filtering of the data reveals distinct structures of
high energy, intermittent in their nature and analogous to "bursting".
The energy spectrum of the longitudinal component follows the predicted
slope of -1 for over two decades (.01 to 1.3 + Hz).

A theoretical study was conducted to determine the relationships between
the major controlling factors in the heat exchangers in an Ocean Thermal
Energy Conversion system. A digital computer model was developed to
simulate and analyze the system. Variations in the thermophysical properties
of the seawater and working fluid were considered in the analysis.
Effects of variation in excess temperature differential on phase
change heat transfer rates were also considered. The net power output
of the system was determined from a Rankine cycle analysis. The results
of this investigation show the necessity of a Rankine cycle analysis and
the inclusion of fluid property variations. A significant difference
can be seen in the net power output of such a system per dollar invested
in the heat exchangers projected by this analysis and the analysis of
other investigators which have not considered these factors.

An investigation was conducted to determine the relationship
between hydrodynamic boundary layer parameters and biofouling
growth rates. A summary of previous investigations of hydrodynamic
effects on biofouling is presented. Wall shear stress
is shown to be an important parameter and is described in
detail. A submersible water tunnel was designed to allow
investigation of a flat plate subject to a uniform flow of
seawater. Parallel flow past a flat plate with a laminar
boundary layer was used to ensure that experimental conditions
existed in which a known wall shear stress distribution was
establised. Tests were conducted off Virginia Key in Miami,
Florida. The results of the experiments clearly indicate the
existance of a threshold value of shear stress which inhibits
the attachment of the macrofouler under study, the acorn
barnacle (Balanus spp.). Reported growth rates from other
investigations are presented to substantiate results. Recommendations
are made for additional hydrodynamic investigations
in dealing with biofouling.

This research explores carbon dioxide transport in life support helmet annular space using new theoretical and experimental techniques. Increased transport from next generation helmets is necessary to allow reduction of fresh gas flow and associated noise. Conventional helmet noise interferes with communications and some underwater helmets even approach hearing threshold shift levels. Helmet flow is three dimensional, unsteady, and turbulent; this research is the first known effort to identify the fundamental mechanisms of CO2 transport. An analytical model is developed which predicts average inhaled CO2 concentration for generic helmet geometry using a mixing volume approach. The model includes sensitivity to supply flow, breath rate, metabolic CO2 production, inhalation and exhalation mixing volumes, and breathing symmetry. Numerical sensitivity analysis using the model indicates optimum design paths. Nominal head-helmet-lung geometry is identified. An experimental nominal model was developed which supports inhaled concentration measurements with air-CO2 or water-dye as working fluids. Water modeling provides flow visualization which is used to identify complex convective and turbulent CO2 transport mechanisms. Correlation of water-dye and air-CO2 results indicates conditions when molecular diffusion of CO2 is significant. The research was directed primarily toward diving helmets but is applicable to spacesuit and firefighter helmets, as well as any situation involving mass transport in a periodic mixing chamber. New analytical and experimental models are substantially more accurate than the conventional steady state helmet mixing model, and provide direction for improved helmet design.