Morrison Archie T.

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Archie T.

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  • Thesis
    Development of the BASS rake acoustic current sensor : measuring velocity in the continental shelf wave bottom boundary layer
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1997-06) Morrison, Archie T.
    Surface swell over the continental shelf generates a sheet of oscillatory shear flow at the base of the water column, the continental shelf wave bottom boundary layer. The short periods of surface swell sharply limit the thickness of the wave boundary layer, confining it to a thin region below an oscillatory, but essentially irrotational, core. For a wide range of shelf conditions, the vertical extent of the wave boundary layer does not exceed 2.5 cm and is commonly less. The extreme narrowness of this boundary layer is responsible for high levels of bottom stress and turbulent dissipation. Even in relatively mild sea states, the wave induced bottom shear stress can be sufficient to initiate sediment motion. The wave bottom boundary layer plays an important role in the processes of sediment entrainment and transport on the continental margins. This thesis documents the development, testing, and field use of a new instrument, the BASS Rake, designed to measure velocity profiles in the wave boundary layer. The mechanical design supports multiple measurement levels with millimeter vertical spacing. The mechanical design is integrated with an electronic interface designed to permit flexible acquisition of a suite of horizontal and vertical velocity measurements without sacrificing the electronic characteristics necessary for high measurement accuracy. The effects of velocity averaging over the sample volume are calculated with a model of acoustic propagation in a scattering medium appropriate to the scales of a single differential travel time axis. A simpler parametric model of the averaging process is then developed and used to specify the transducer characteristics necessary to image the wave boundary layer on the continental shelf. A flow distortion model for the sensor head is developed and the empirical determinations of the Reynolds number, Keulegan-Carpenter number, and angular dependencies of the sensor response for the laboratory and field prototypes is presented. The calibrated sensor response of the laboratory prototype is tested against concurrent LDV measurements over a natural sand bed in a flume. The single measurement accuracy of the BASS Rake is higher than that of the LDV and the multiple sample volumes confer other advantages. For example, the ability of the BASS Rake to image vertically coherent turbulent instabilities, invisible to the LDV, is demonstrated. Selected data from a twenty-four day field deployment outside the surf zone of a local beach are presented and analyzed. The data reveal regular reworking of the sand bed, the generation and modification of sand ripples, and strong tidal modulation of the current and wave velocities on semi-diurnal, diurnal, and spring/neap time scales. The data set is unique in containing concurrent velocity time series, of several weeks duration, with coverage from 1 cm to 20 cm above the bottom.
  • Preprint
    Autonomous Microbial Sampler (AMS), a device for the uncontaminated collection of multiple microbial samples from submarine hydrothermal vents and other aquatic environments
    ( 2006-01-11) Taylor, Craig D. ; Doherty, Kenneth W. ; Molyneaux, Stephen J. ; Morrison, Archie T. ; Billings, John D. ; Engstrom, Ivory B. ; Pfitsch, Don W. ; Honjo, Susumu
    An Autonomous Microbial Sampler (AMS) is described that will obtain uncontaminated and exogenous DNA-free microbial samples from most marine, fresh water and hydrothermal ecosystems. Sampling with the AMS may be conducted using manned submersibles, Remotely Operated Vehicles (ROVs), Autonomous Underwater Vehicles (AUVs), or when tethered to a hydrowire during hydrocast operations on research vessels. The modular device consists of a titanium nozzle for sampling in potentially hot environments (>350°C) and fluid-handling components for the collection of six independent filtered or unfiltered samples. An onboard microcomputer permits sampling to be controlled by the investigator, by external devices (e.g., AUV computer), or by internal programming. Temperature, volume pumped and other parameters are recorded during sampling. Complete protection of samples from microbial contamination was observed in tests simulating deployment of the AMS in coastal seawater, where the sampling nozzle was exposed to seawater containing 1x106 cells ml-1 of a red pigmented tracer organism, Serratia marinorubra. Field testing of the AMS at a hydrothermal vent field was successfully undertaken in 2000. Results of DNA destruction studies have revealed that exposure of samples of the Eukaryote Euglena and the bacterium S. marinorubra to 0.5 N sulfuric acid at 23°C for 1 hour was sufficient to remove Polymerase Chain Reaction (PCR) amplifiable DNA. Studies assessing the suitability of hydrogen peroxide as a sterilizing and DNA-destroying agent showed that 20 or 30% hydrogen peroxide sterilized samples of Serratia in 1 hr and destroyed the DNA of Serratia, in 3 hrs, but not 1 or 2 hrs. DNA AWAY™ killed Serratia and destroyed the DNA of both Serratia and the vent microbe (GB-D) of the genus Pyrococcus in 1 hour.
  • Thesis
    System identification and state reconstruction for autonomous navigation of an underwater vehicle in an acoustic net
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1994-01) Morrison, Archie T.
    Closed loop control of an underwater vehicle in an acoustic position net requires an accurate hydrodynamic model of the vehicle. The model is essential to the control algorithm design process. Further, it is an integral part of the observer used to generate complete state estimates from the position measurements. An experimental apparatus and numerical analysis technique for vehicle system identification during the thruster induced hover limit cycle are described. Detailed comparisons to other techniques are made and extension of the technique to four degrees of freedom with coupling is discussed. A model of the Remotely Operated Vehicle Hylas is determined. The model determined by the system identification procedure is then used in the designs of a state estimator and controller for trajectory following by the vehicle. The algorithms are initially evaluated in a numerical simulation. Tests are made for stability, trajectory following performance, and accuracy of the state estimator under varying system and environmental conditions. Finally, the results of vehicle trials are presented. System stability and accurate trajectory following under the control of the algorithms are demonstrated using ROY Hylas. The high accuracy level of the simulation is also demonstrated by the trials and directions for continued research are discussed.