Approved for public release, distribution is unlimited / The United States Navy Submarine Hydrodynamic/Hydroacoustic community is a decentralized, multiorganizational, geographically distributed enterprise. Strategic planning and management, whether formal or ad hoc, is necessary for effective functioning of any organization. However, formal strategic planning is particularly difficult in multi-organizational, geographically diverse enterprises. Enterprise-wide performance measurement and a shared understanding of enterprise performance is necessary to devise compelling and effective strategies. During the Cold War, the U.S. Navy submarine force had a clear mission and compelling goals, with resulting clarity on performance metrics. The Submarine Hydrodynamic/Hydroacoustic workforce was focused on helping the submarine force achieve these goals. In the post-Cold War era, the submarine force mission in the integrated battle space is less defined. The percentage of the military budget that can be spent on discretionary spending is decreasing. The Submarine Hydrodynamics/Hydroacoustic community has been directly impacted by the recent lack of focus and budget reductions. The purpose of this thesis is to research the past processes used to perform strategic planning for the Submarine Hydrodynamic/Hydroacoustic community, identify current strategic issues for the community, and document strategic lessons learned that can be identified through the evaluation of product successes and failures. / Civilian, United States Navy

A travers cette thèse, nous avons cherché à développer de nouvelles méthodes de mesure, basées sur la rétrodiffusion acoustique, pour estimer la concentration massique des sédiments en suspension dans les rivières. Souvent, ces sédiments présentent une distribution granulométrique bimodale, i.e. constituée d’un mélange de sédiments fins et de sable. Le principal avantage des méthodes hydroacoustiques est leur capacité à fournir des mesures avec une résolution spatiale et temporelle bien meilleure que les techniques classiques type prélèvement. L’objectif est in fine d’améliorer l’estimation du flux sédimentaire dans les cours d’eau. Des mesures acoustiques multifréquences, associées à des prélèvements physiques, ont été réalisées sur le terrain et dans une cuve expérimentale au laboratoire. Des méthodes d’inversion du signal acoustique ont été testées et développées au laboratoire sur une suspension homogène de sédiments fins. Une nouvelle méthode en particulier, combinant analyse de la rétrodiffusion et de l’atténuation acoustique, a permis de retrouver la concentration massique des sédiments avec une précision de l’ordre de ± 20 %. En rivière, une méthode mixte alliant données de calibration et inversion du signal acoustique à deux fréquences a été développée, permettant, dans certaines conditions, d’estimer la concentration des sédiments fins et du sable sur l’ensemble de la section en travers d’un cours d’eau. Ce résultat confirme la capacité de la technologie hydroacoustique à fournir une information spatiale sur la suspension. Des écarts parfois importants ont été observés entre la réponse acoustique théorique, calculée à partir des données de concentration et de granulométrie, et les mesures acoustiques sur le terrain. Il semble que ces écarts soient dus à la présence d’autres corps diffusants dans les rivières, probablement des flocs et/ou des micro-bulles d’air. Ces travaux appellent au développement d’un cadre théorique plus performant et adapté aux suspensions rencontrées en rivière. / With this PhD, we have tried to develop new measurement methods, based on acoustic backscattering, to estimate the mass concentration of suspended sediments in rivers. These sediments often show a bimodal grain-size distribution, i.e. composed of a mixture of fine and sand particles. The main advantage of hydroacoustic methods is their ability to provide measurements with a much better spatial and temporal resolution than conventional sampling techniques. The ultimate goal is to improve the sediment load estimation in rivers. Multifrequency acoustic measurements, combined with physical sampling, were carried out in the field and in an experimental laboratory tank. Acoustic inversion methods were tested and developed on a homogeneous suspension of fine sediments in the laboratory. A new method was implemented, combining the analysis of acoustic backscatter and attenuation, and led to retrieve the sediment mass concentration with a precision in the order of ± 20%. In rivers, a semi-empirical method combining calibration data and acoustic inversion at two frequencies has been developed, allowing, under certain conditions, to estimate the concentration of fine and sand sediments throughout the entire river cross-section. This result confirms the ability of hydroacoustic technology to provide spatial information on the suspension. Significant differences were frequently observed between the theoretical acoustic response, computed from concentration and particle size data, and the acoustic measurements in rivers. It seems that these differences could be due to the presence of other scatterers in rivers, probably flocs and/or air micro-bubbles. This work calls for the development of a more efficient theoretical framework suitable for river suspensions.

In this thesis we explore several topics with applications to both aero and hydroacoustics. Due to the much larger speed of sound in water compared to in air, several of the approximations used in aeroacoustics are not applicable underwater over the range of frequencies of interest. Specifically, we study the finite-chord effects on two broadband noise mechanisms: the trailing edge noise and the ingested noise problems. We start by investigating the acoustic wave diffraction by a finite rigid plate using three different methods. We compare the behaviour of the different solutions as a function of the reduced acoustic wavenumber. Our results reveal that the Mathieu function expansion is the most appropriate method as long as the reduced acoustic wavenumber is not too large. Finally, we show how the Mathieu functions can be used to build a Green's function tailored to an elliptic cylinder of arbitrary aspect ratio without relying on addition theorems. The results obtained in chapter two motivated the search for an exact solution to the trailing edge noise problem using a Mathieu function expansion. It is shown that the approximate methods used in aeroacoustics are not accurate enough for reduced acoustic wavenumbers less than unity, and for all wavenumbers near cut-off. Furthermore it is shown that, even at low Mach numbers, it is crucial to take into account the effects of convection at low frequency. Finally Lighthill's analogy is used, combined with the tailored Green's function introduced previously, to recover the two asymptotic Mach number scalings of the acoustic power for a flat plate at high frequency and low frequency. In chapter four, we introduce a novel method to solve the ingested noise problem by decomposing the pressure field into a singular part whose functional form can easily be found, and a regular part that we express using a Mathieu function expansion. It was found that finite-chord effects do have a strong impact for reduced acoustic wavenumbers less than unity, and for all wavenumbers near cut-off. The following chapter focuses on the trailing edge noise mechanism and details how the theory for a single stationary aerofoil can be applied to a rotating propeller. Due to the general geometry of a blade, we extended Amiet's model to take into account a mean flow misaligned with the blade chordline. Different semi-analytical models of wall pressure spectra are introduced and compared. We make extensive use of Brooks' data for a NACA 0012 aerofoil to obtain realistic inputs in the semi-analytical models. Finally, we introduce and compare two models of rotating blade trailing edge noise. The effects of both the angle of attack and the number of strips are then investigated. The final chapter is distinct from the rest of the thesis. We propose a model for studying the low Mach number flow noise from a 2D circular cylinder with small roughness. The method is based on using the Green's function tailored to a smooth cylinder in Curle's acoustic analogy. It was found that the main source of noise was the tonal low frequency scattering by the smooth geometry. However, it is suggested that roughness elements might be the dominant source of noise at higher frequency.

The pelagic zone of lakes is defined as the water column over the area of the lake benthos that does not receive enough light from the sun to allow macrophytes to grow. The four chapters of this thesis explore the spatial ecology of predator-prey interactions between schooling fish and their fish predators in this featureless environment. We first developed novel hydroacoustics methods to study fish and fish school swimming behaviour in the pelagic zone (Chapter 1 and 2). Then we characterized our in-situ school formation and prey movement observations using an ideal gas model to better understand the mechanisms that lead to fish and school densities during the daytime (Chapter 2 and 3). With this model we estimated the functional relationship between the schooling prey densities and predator encounter rates, and verified with empirical data a counterintuitive relationship that encounter rates decreased as overall prey densities increased (Chapter 3). The encounter rates suggested that predation within the pelagic zone might be greatly influenced by external forces if they provide spatial structure which encourages greater degrees of prey aggregation in predictable locations. In this regard we examined the predator-prey dynamics under wind and found large redistributions of prey and predators under windy conditions leading to greater aggregations in downwind locations. Further, we found that our study fish were larger in lakes that were oriented into the wind, perhaps demonstrating a benefit to fish growth under windy conditions (Chapter 4).

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This thesis is focused on the fish spatial distribution and its changes mainly during the diel cycle. In the first part, I described the fish spatial distribution in the tropical lake ecosystem of Lake Turkana. The second part deals with the fish spatial distribution in a temperate reservoir on the different spatial scales from in/offshore habitats over the fine-scale to the level of individuals. The linkage of fish distribution patterns with selected environmental variables was also evaluated.

Fisheries independent data on relatively unstudied nekton communities were used to explore the efficacy of new tools to be applied in the investigation of shallow coastal coral reef habitats. These data obtained through concurrent diver visual and acoustic surveys provided descriptions of spatial community distribution patterns across seasonal temporal scales in a previously undocumented region. Fish density estimates by both diver and acoustic methodologies showed a general agreement in ability to detect distributional patterns across reef tracts, though magnitude of density estimates were different. Fish communities in southeastern Florida showed significant trends in spatial distribution and seasonal abundance, with higher estimates of biomass obtained in the dry season. Further, community composition shifted across reef tracts and seasons as a function of the movements of several key reef species.

Mysid shrimps (Mysidacea, Crustacea) are efficient zooplanktivores in both marine and freshwater systems as well as lipid rich prey for many species of fish.  Although some efforts have been made to study the role of mysids in the Baltic Sea, very few studies have been carried out in recent time and there are still knowledge gaps regarding various aspects of mysid ecology. This thesis aims to explore some of these gaps by covering a mixture of topics. Using multifrequency hydroacoustics we explored the possibility to separate mysids from fish echoes and successfully established a promising and effective method for obtaining mysid abundance/biomass estimates (paper I). An investigation of the current mysid community in a coastal area of the northern Baltic proper (paper II) demonstrated that the formerly dominant, pelagic mysid Mysis mixta had decreased substantially (~50%) in favor for phytoplanktivorous, juvenile Neomysis integer and Mysis relicta sp. By examining different aspects of mysid behavior, we studied the vertical size distribution of mysids in the field and found that size increased with depth/declining light, irrespective of temperature; indicating that their vertical size distribution primarily is a response to predation (paper II). In paper III, a combination of ecological and genetic markers was used to investigate intraspecific differences in migratory tendency. Both marker types indicated that some part of the Mysis salemaai population is sedentary on the bottom and that this strategy is a phenotypically plastic but persistent trait, analogous to the partial migrations seen in many birds and fishes. In paper IV a temperature and weight specific respiration model was developed for the littoral Praunus flexuosus. Routine respiration was moreover elevated by post-prandial effects (specific dynamic action) for longer times than previously suggested. Consequently, ignoring such effects could significantly bias respiration measurements. / At the time of doctoral defence the following papers were unpublished and had a status as follows: Paper  2: Accepted; Paper 3: Submitted; Paper  4: Accepted