http://hdl.handle.net/1721.1/7846 http://hdl.handle.net/1721.1/49765 A parallel hypothesis method of autonomous underwater vehicle navigation LaPointe, Cara Elizabeth Grupe This research presents a parallel hypothesis method for autonomous underwater vehicle navigation that enables a vehicle to expand the operating envelope of existing long baseline acoustic navigation systems by incorporating information that is not normally used. The parallel hypothesis method allows the in-situ identification of acoustic multipath time-of-flight measurements between a vehicle and an external transponder and uses them in real-time to augment the navigation algorithm during periods when direct-path time-of-flight measurements are not available. A proof of concept was conducted using real-world data obtained by the Woods Hole Oceanographic Institution Deep Submergence Lab's Autonomous Benthic Explorer (ABE) and Sentry autonomous underwater vehicles during operations on the Juan de Fuca Ridge. This algorithm uses a nested architecture to break the navigation solution down into basic building blocks for each type of available external information. The algorithm classifies external information as either line of position or gridded observations. For any line of position observation, the algorithm generates a multi-modal block of parallel position estimate hypotheses. The multimodal hypotheses are input into an arbiter which produces a single unimodal output. If a priori maps of gridded information are available, they are used within the arbiter structure to aid in the elimination of false hypotheses. (cont.) For the proof of concept, this research uses ranges from a single external acoustic transponder in the hypothesis generation process and grids of low-resolution bathymetric data from a ship-based multibeam sonar in the arbitration process. The major contributions of this research include the in-situ identification of acoustic multipath time-of-flight measurements, the multiscale utilization of a priori low resolution bathymetric data in a high-resolution navigation algorithm, and the design of a navigation algorithm with a flexible architecture. This flexible architecture allows the incorporation of multimodal beliefs without requiring a complex mechanism for real-time hypothesis generation and culling, and it allows the real-time incorporation of multiple types of external information as they become available in situ into the overall navigation solution. Thesis (Ph. D.)--Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Mechanical Engineering; and the Woods Hole Oceanographic Institution), 2009. Includes bibliographical references (p. 275-284). Wed, 29 Oct 2008 22:58:59 GMT http://hdl.handle.net/1721.1/49764 Forward sound propagation around seamounts : application of acoustic models to the Kermit-Roosevelt and Elivs seamounts Kim, Hyun Joe The Basin Acoustic Seamount Scattering Experiment (BASSEX) of 2004 was conducted to measure forward-scattering around the Kermit-Roosevelt Seamount Complex in the Northeast Pacific. The BASSEX experiment was focused on the bathymetric effects on acoustic propagation, in particular, on direct blockage, horizontal refraction, diffraction, and scattering by the seamounts. A towed hydrophone array, with 64 sensors cut for 250Hz (3m spacing), was used to measure the signals transmitted from the aforementioned broadband sources at many locations around the Kermit-Roosevelt and Elvis seamounts. Utilizing the measured broadband signals from the towed array, the size of the shadow zone was obtained. The measured data in the BASSEX experiment strongly support the understanding of the complicated phenomena of sound propagation around the seamounts. In addition, the experimental data could be used to validate current 2D and 3D theoretical models and develop new models to properly realize the sound propagation with such complicated phenomena. In this thesis, the reconciliation between the measured pulse arrivals from the BASSEX experiment and various two-dimensional (2D) and three-dimensional (3D) theoretical models is carried out to investigate the physical characteristics of the sound propagation around seamounts: First, the 2D Parabolic Equation (PE) model and the 2D ray tracing model are used to reconcile each ray arrival with the BASSEX experiment in terms of arrival time and grazing angle. (cont.) We construct a sound speed field database based on the sound speed profiles from the BASSEX experiment, World Ocean Atlas (WOA) 2005, and CTD casts using the objective analysis. Second, 3D broadband sound propagation around a conical seamount is investigated numerically using the 3D spectral coupled-mode model (W. Luo, PhD Thesis, MIT, 2007). Since the calculation of 3D broadband pulses with the spectral coupled-mode model requires extensive computation time, a parallel program is developed with a clustered computing system to obtain results in reasonable time. The validation of the 3D spectral coupled-mode model is performed by a series of comparisons between the various 2D and 3D models for a shallow-water waveguide. The Kermit-Roosevelt seamount is modeled by a simple conical seamount for the 3D model. The computed 3D broadband pulses for the modeled conical seamount are compared with those from the BASSEX experiment and the 2D PE simulation. Through this analysis, we examine the limit of the application of the sound propagation models and improve the efficiency of the 3D sound propagation model using parallel computing to obtain a broadband pulse in a reasonable amount of time. Thesis (Ph. D.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Mechanical Engineering; and the Woods Hole Oceanographic Institution), 2009. Includes bibliographical references (p. 271-277). Wed, 29 Oct 2008 22:58:59 GMT http://hdl.handle.net/1721.1/49763 Effect of traveling waves on Vortex-Induced Vibration of long flexible cylinders Jaiswal, Vivek, Ph. D. Massachusetts Institute of Technology Offshore marine risers and pipelines, exposed to ocean currents, are susceptible to Vortex-Induced Vibration (VIV). Accurate prediction of VIV is necessary for estimating the fatigue life as well as for taking corrective measures to prevent the vibrations. State of the art response prediction methods work reasonably well for short flexible cylinders vibrating at frequencies corresponding to low mode numbers (below the tenth mode). However, for long structures, which respond above the tenth mode, lack of experimental data has until recently impeded progress. Results will be presented from recent field experiments conducted in the Gulf Stream and Lake Seneca, NY. These experiments have provided an opportunity for new insights about the VIV of long flexible cylinders, responding at high mode numbers. The experimental results also include insights on the use of VIV suppression devices such as helical strakes. The experiments reveal that the dominant response of long flexible cylinders is often in the form of traveling waves. High spatial density fiber optic strain gauge measurements are used to obtain estimates of the phase speed of the waves, the response amplitude and the added mass coefficient. The mean added mass coefficient for the bare cylinder is shown to be approximately one and the maximum response amplitude is found to be approximately one diameter. A Green's function, response prediction method, is introduced which is able to emulate both the standing and traveling wave properties observed in the experimental data. (cont.) A novel approach to modeling the excitation force as a combination of standing and traveling wave components is shown to predict the measured response very well. The method is also able to account for high localized damping that result from the use of response suppression devices, such as helical strakes. Many marine risers are composed of nested concentric steel pipes. The relative motion of these concentric pipes in the presence of confined liquids introduces unusual dynamic properties, including the potential for beneficial effects as dynamic absorbers. Numerical and theoretical models are developed as a preliminary step in the design of dynamic absorbers for deep water risers. Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2009. Includes bibliographical references (p. 155-160). Wed, 29 Oct 2008 22:58:59 GMT http://hdl.handle.net/1721.1/49762 Bio-inspired fluid locomotion Chan, Brian, 1980- We have developed several novel methods of locomotion at low Reynolds number, for both Newtonian and non-Newtonian fluids: Robosnails 1 and 2, which operate on a lubrication layer, and the three-link swimmer which moves in an unbounded fluid. Robosnail 1 utilizes lubrication pressures generated in a Newtonian fluid under a steadily undulating foot to propel itself forward. Tractoring force and velocity measurements are in agreement with analytic and numerical solutions. Robosnail 2, modeled after real land snails, uses in-plane compressions of a flat foot on a mucus substitute such as Laponite or Carbopol. Robosnail 2 exploits the non-Newtonian qualities (yield-stress, shear thinning) of the fluid solution to locomote. The glue-like behavior of the unyielded fluid allows Robosnail 2 to climb up a 90 degree incline or inverted 180 degree surfaces. The three-link swimmer is a device composed of three rigid links interconnected by two out-of-phase oscillating joints. It is the first experimental test that successfully demonstrates that a swimmer of its kind can translate in the Stokes limit. Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2009. Includes bibliographical references (leaves 95-99). Wed, 29 Oct 2008 22:58:59 GMT