Relationships between various characterisations of wave tails

One can define several properties of wave equations that correspond to the absence of tails in their solutions, the most common one by far being Huygens' principle. Not all of these definitions are equivalent, although they are sometimes assumed to be. We analyse this issue in detail for linear scalar waves, establishing some relationships between the various properties. Huygens' principle is almost always equivalent to the characteristic propagation property, and in two spacetime dimensions the latter is equivalent to the zeroth order progressing wave propagation property. Higher order progressing waves in general do have tails, and do not seem to admit a simple physical characterisation, but they are nevertheless useful because of their close association with exactly solvable two-dimensional equations.Comment: Plain TeX, 26 page

Morphodynamics of transgressive coastal systems: Modeling allogenic and autogenic response to sea level rise, storms, and changes in sediment supply

Barrier islands are widespread and typically enclose landward basins connected to the ocean through tidal inlets. Low energy in the basin enables fine sediment accumulation and salt marsh formation. Sea Level Rise (SLR) causes loss of marshes due to their low elevations and inundation sensitivity. Both long-term trends in sediment supply due to SLR and episodic transfers of sediment due to storms are important to the sustainability of marshes and tidal basins. The trajectory of deltas, including the Mississippi River Delta (MRD), are also impacted by sediment supply. The redistribution of sediments (autogenic reorganization) within transgressive systems will determine their survival under projected SLR regimes (allogenic forcing). In this research, I investigate the processes driving sediment exchange and morphologic evolution on multiple timescales with process-based numerical models. Chapter 2 focuses on the long-term response of tidal basin systems to SLR. With SLR, hydrodynamics shift to flood- dominant while the ebb-delta expands. Despite the shift to residual sand import, fine sediment continues to be exported. In Chapter 3, net sediment fluxes due to storms at a conceptual basin are analyzed to determine the influence of relative phasing of tides and surges and storm characteristics. In Chapter 4, this work is extended by applying similar storms to a model of Plum Island Sound (PIS) in Massachusetts. Each of these models applies a unique approach to bed sediment partitioning to determine imported sediment provenance. Results show that surge/tidal phasing has a high influence on sediment fluxes. For the conceptual basin, storms were found to generally import sediment, while the influence of SLR on sediment flux depends on surge/tidal phasing. For the PIS model, storms are an important source of sand for the sediment-starved basin, though on net storms are unable to counteract the ebb-dominance that exports muddy sediments. Chapter 5 investigates the efficacy of enhanced sediment supply for land-building sediment diversions in the MRD. Results show that augmenting sand supplied to the delta during low flows is effective in increasing land building. Greater sediment supply encourages more-frequent autogenic reorganization of the distributary channel network, with wider distribution of sediments and greater reworkin

Nonlinear combustion instability in liquid-propellant rocket motors Final report

Mathematical models of nonlinear combustion instabilities in liquid propellant rocket engin

The Effect of Artificial Light Pollution on Orientation of Hatchling Loggerhead Sea Turtles (Caretta caretta) in the Grand Strand Region, South Carolina

Sea turtle hatchlings primarily utilize sight to detect differences in elevation and light intensity present along the horizon to navigate from the nest to the water’s edge. The addition of artificial lights can cause visual misdirection, resulting in disorientation (aimlessly wandering in circular paths) or misorientation (moving in distinct paths away from ocean). Extensive research has been done on effects of high levels of artificial light but little on effects of comparatively lower levels of artificial light on hatchling sea turtle orientation. This study examined these lower intensity areas to identify if there is a threshold of artificial light above which hatchling orientation is negatively affected. During the 2016 nesting season, a Geovision GV-FER5303 non-illuminating infrared camera recorded hatchling trajectories at twenty-one loggerhead sea turtle nests from areas varying in light intensity along the Grand Strand region of South Carolina. Individual and group dynamics for lateral range of movement, orientation deviation, and average speed were measured from each nest to determine if parameters associated with orientation were significantly affected by total and artificial radiance values present at the time of emergence. Lateral range of hatchling movement is not significantly influenced under artificial or total radiance conditions; however, deviation from seaward direction (F(2,299)=43.623, p\u3c0.001; F(3,424)=23.528, p\u3c0.001) and average speed are (F(2,495)=42.612, p\u3c0.001; F(3,648)=14.644, p\u3c0.001). Deviation from brightest light source is significant under total radiance conditions (F(3,427)=11.358, p\u3c0.001) while only marginally significant under artificial radiance conditions (F(2,300)=2.336, p=0.098). Results may help inform current management practices to enhance hatchling survival efforts near northern limit of loggerhead nesting beaches

Stability of Articulated Revetments Against Wave Attack on Shallow Soft Soil Slopes

Continuously-connected, articulated revetment systems have potential to decrease the weight of armor cover in resisting wave attack, compared to traditional designs. Modes of instability for sloping revetments include uplift, sliding, and toe roll-up. Design methods are summarized by McDonnell (1998), Pilarczyk (1998), and Herbich (1999). Russo (2003) conducted a field prototype scale investigation on performance of Articulated Concrete Mattresses (ACMs) in coastal Louisiana, which demonstrated this structure’s ability to resist a range of wave loading conditions, and inspired scoping of further research to quantify structure performance beyond known limits. Present research expanded earlier works by examining fundamental physical processes of wave loading near the theoretical threshold of structure incipient motion. The motivation for further investigation and modeling modes of failure is to: (1) demonstrate a method to support the design selection process, (2) optimize revetment dimensions when articulated block is considered the most appropriate application, and (3) meet earthen slope protection requirements with relatively low ground pressures exerted by the armor layer for use in soft soil conditions. A new structure performance metric is derived as the physically dimensionless “hydromechanic potential,” which is used to quantify structure movement as an interconnected system under wave attack. Research involved using a spectral hydromechanics analytical approach, with instrumented physical model results, to demonstrate a capability for constraining uncertainty on the behavior of revetments in specified conditions. Physical modeling was conducted based on dimensional analysis and similitude criteria. Physical modeling and spectral analysis were based on principles of hydrodynamics and structure mechanics of articulated revetment system configurations at incipient motion under irregular wave conditions. Theoretical equilibrium exists when destabilizing wave loading forces are in balance with restoring gravitational forces of the structure. Tests of prior works, conducted through traditional methods, were generally able to measure structure performance under wave attack to between 3.7 and 8 of the ratio of destabilizing-to-restoring forces. Despite being the best available physical data measurable to-date, Herbich (1999) characterized structure performance in this range for design as “doubtful”. Results of this dissertation research indicated that a new lower limit is detectable at the threshold of equilibrium based on hydromechanic potential

Building Economic Resilience: A Comparative Study of Ethnic Financing Institutions in Jewish, Japanese, and Korean American Communities

Senior Project submitted to The Division of Social Studies of Bard College

Oceanus.

v. 26, no. 3 (1983

Experimental characterization of liquid-liquid stratified flow interacting with vertical emergent cylinders

Density currents are mainly horizontal flows that are driven by density differences between contacting flows, which may result from temperature gradients, suspended solid particles or dissolved substances. These currents play an important role in nature and industry as they can have a negative environmental impact through global ocean circulation, oil spills, climate variations through water formation and the redistribution of ocean or river water. They have been widely studied since the 20th century, but despite the data acquired and the experiments carried out to date, there is still much research to be done on understanding the dynamics of density currents and their environmental impact. The present work is part of the WinTherface project that addresses the study of wind and temperature-driven mass exchange at wetland lake interfaces and its impacts on water quality through a multidisciplinary approach integrating, field, laboratory, and numerical work. The aim of the present work is to experimentally investigate how different initial current densities and the presence of vegetation interfere with the propagation and mass exchange between the current and the ambient fluid, as well as the turbulence mechanisms around a set of cylinders present in the channel. The laboratorial tests were carried out in a channel containing a set of cylinders intended to simulate rigid vegetation. The lock exchange technique was used to generate the density currents with a reduced gravity of 0.09 m/2 and 0.36 m/2. During the laboratory work several tests were carried out using the Particle Image Velocimetry (PIV) measuring technique and the image analysis technique. First the PIV system was used to measure the two-dimensional instantaneous velocity fields in two planes, these being called the side view and plan view which were situated near the cylinder array. After the PIV tests, the image analysis technique was used to mainly evaluate the mass distribution of the current. This technique consists of using a concentration of dye (Rhodamine) in the flow, allowing the understanding of the current dynamics, being able to analyse the temporal evolution of the current front, and the density, its height along the channel, as well as the entrainment evolution. It is concluded that some parameters of the current such as the height, the position of the front and the entrainment suffer a change due to the interaction with the cylinders. With the results obtained by the PIV it was observed that the interaction of the current with the set of cylinders induces a strong vertical component in the flow becoming three-dimensional. This interaction creates in the flow a set of turbulent structures dominated by a large circulation area that is evident in the approximation area of the cylinders and increases the complexity of the turbulence mechanisms in the current.As correntes de densidade são escoamentos principalmente horizontais que são impulsionados por diferenças de densidade entre escoamentos de contacto, que podem resultar de gradientes de temperatura, partículas sólidas em suspensão ou substâncias dissolvidas. Estas correntes desempenham um papel importante na natureza e na indústria, uma vez que podem ter um impacto ambiental negativo através da circulação oceânica global, derramamento de petróleo, variações climáticas através da formação de água e da redistribuição da água do oceano ou dos rios. Têm sido amplamente estudadas desde o século XX, mas apesar dos dados adquiridos e das experiências feitas até hoje, há ainda muito a pesquisar sobre a compreensão da dinâmica das correntes de densidade e o seu impacto ambiental. O presente trabalho está inserido no âmbito do projeto WinTherface que aborda o estudo da troca de massas impulsionada pelo vento e pela temperatura em interfaces de lagoas húmidas e os seus impactos na qualidade da água através de uma abordagem multidisciplinar, que integra trabalho de campo, de laboratório e numérico. O objetivo do presente trabalho é investigar experimentalmente como as diferentes densidades iniciais de corrente e a presença de vegetação interferem na propagação e troca de massa entre a corrente e o fluido ambiente, bem como os mecanismos de turbulência em torno de um conjunto de cilindros presentes no canal. Os testes laboratoriais foram realizados num canal que continha um conjunto de cilindros que pretendiam simular a vegetação rígida. Foi utilizada a técnica de lock exchange para gerar as correntes de densidade com uma gravidade reduzida de 0.09 m/2 e 0.36 m/2. Durante o trabalho laboratorial foram realizados vários testes utilizando a técnica de medição de Particle Image Velocimetry (PIV) e a técnica de análise de imagem. Primeiro foi utilizado o sistema PIV para medir o campo bidimensional de velocidade instantânea em dois planos, sendo eles o plano horizontal e o vertical, que estavam situados perto do conjunto de cilindros. Após os testes de PIV, foi utilizada a técnica de análise de imagem para avaliar principalmente a distribuição da massa da corrente. Esta técnica consiste em utilizar uma concentração de corante (Rodamina) no fluxo, permitindo a compreensão da dinâmica da corrente, podendo analisar a evolução temporal da frente da corrente e da densidade, a sua altura ao longo do canal, bem como a evolução do entrainment. Conclui-se que alguns parâmetros da corrente tais como a altura, a posição da frente e o entrainment sofrem uma alteração devido à interação com os cilindros. Com os resultados obtidos pelo PIV observou-se que a interação da corrente com o conjunto de cilindros induz uma forte componente vertical no escoamento passando a ser tridimensional. Esta interação cria no escoamento um conjunto de estruturas turbulentas dominadas por uma grande circulação que são evidentes na zona de aproximação aos cilindros e aumentam a complexidade dos mecanismos de turbulência na corrente