Studies and models of sediment transport in the bottom boundary layer require knowledge of the bottom roughness as a parameter affecting the suspension and transport of sediment. Knowledge of this ...has often been quite imprecise since measurements could only be made from diver observations or camera pictures at times when the water was clear.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
A statistical model is developed describing a random field of internal waves passively oscillating a random, locally horizontally uniform temperature finestructure. The model allows one to examine ...the effects of finestructure upon all relevant measurable statistical quantities of the temperature field as a function of the vertical scale of the finestructure. Also, the effects of the time variation of the finestructure itself are considered. The model was fit to data obtained during the 3-week Mid-ocean Acoustic Transmission Experiment (MATE) in summer 1977 near Cobb seamount in the northeastern Pacific. Various spectra and coherences estimated from temperature time series and vertical profiles were used to make an assessment of the finestructure as well as establish the consistency of the model. Temperature variance measured at frequencies above the local Vaeisaelae frequency was used to estimate the magnitude of the high vertical wavenumber finestructure. The contribution of the finestructure effects to the internal wave frequency spectrum was found to be about a factor of 10 less than that of internal waves advecting a constant temperature gradient.
A buoy/mooring designed to measure waves with a surface-following buoy was instrumented with an ADCP and water property sensors. Compliant elastic elements at the top of the mooring allow the buoy to ...move freely with the waves without having to accelerate the mooring and heavy instrumentation. About 710 N (160 lbf.) of midwater flotation at the bottom of the elastic elements help keep the lower part of the mooring taut. The elastic elements provided about 1.3 kN (300 lbf.) of mooring pretension, and, depending on the horizontal current and the wave activity, the tension at the buoy could rise to about 3.5 kN (800 lbf.). Computer modeling of the mooring showed no vertical and minimal horizontal motion in the lower part of the mooring and reasonable tensions that would allow the buoy to follow the waves. Data from the accelerometer in the buoy (telemetered to shore in real-time), the SeaCats in-line and ADCP near the bottom were of high quality. The mooring was recovered by releasing a float from mid-depth that brought a line to the surface from below the elastic elements to allow the mooring (with sensors) and anchor to be retrieved. Validation of the accelerometer wave observations with a near-surface moored waves ADCP showed good agreement and indicates that the waves ADCP technology may be used for deeper water waves observations from subsurface moorings.
The University of New Hampshire has a submerged four grid mooring system off the coast of New Hampshire. To better understand the deployed grid system, a finite element model was built and field ...measurements of static tensions were taken. The purpose of the finite element model was to better understand the sensitivity of the system to anchor placement. An individual anchor was moved around the designed deployment location to better understand the grid tensions distribution. To take field measurements in the submerged system, a diver deployable instrument was designed. Field measurements reflect upon the accuracy of anchor placement and the effectiveness of the grid
Thesis (Ph. D.)--Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Ocean Engineering; and the Woods Hole Oceanographic Institution), 1998.
Making moored observations in the world's oceans is a difficult task at best. During the past 30 years, great advances have been made and much data collected in the deep ocean. As present-day ...problems and interests focus on the continental shelf, particularly on the inner shelf, it has become apparent that mooring technologies developed and used successfully in the deep ocean cannot always be transferred successfully to shallower water applications. Surface moorings often fail prematurely in very shallow waters due to wear in the mooring hardware and cyclic fatigue failure in mooring components. Also, sensors and solar panels on the buoy suffer damage due to high wave activity during times of high currents. The compliance added by a nylon rope in a deep ocean mooring to reduce this wear and shock loading cannot be carried directly to coastal regions, except with the use of elastic tether technology.
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