Free-Fall Penetrometer (FFP) testing is an easy and rapid test procedure for seabed sediment characterization favorable to conventional geotechnical testing mainly due to its cost-effectiveness. Yet, FFP testing results are interpreted using empirical correlations, but difficulties arise to understand soil behavior under the high-strain rate (HSR) loading effects during rapid FFP penetration. The numerical simulation of FFP-soil interaction is also challenging. This study aims to numerically analyze FFP testing of saturated loose sands using the particle-based Material Point Method (MPM). The numerical analysis was conducted by simulating calibration chamber FFP tests on saturated loose quartz sand. The numerical results using quasi-static properties resulted in a reaction of the sand softer than the actual calibration chamber test. This implied the necessity of considering HSR effects. After performing parametric analyses, it was concluded that dilation plays an important role in the response of sand-water mixtures. Comparison of dry and saturated simulations showed that FFP penetration increases when the soil is dry and tends to develop a general bearing capacity failure mechanism. This is because the pore water increases the stiffness of the system and due to the increased strength that develops in saturated dilative sands when negative pore pressures develop. Local bearing failure mechanism is observed in all saturated simulations. Finally, numerical CPT (quasi-static) and FFP tests were used to examine the strain rate coefficient used in practice (K); and a consistent range between 1 to 1.5 was obtained. / Master of Science / Accurate characterization of seabed sediments is crucial to understand sediment mobilization processes and to solve nearshore engineering problems such as scouring around offshore structures. Its portability, low testing effort, and repeatability make FreeFall Penetrometer (FFP) testing a highly cost-effective sediment characterization test. Nevertheless, due to the complex penetration mechanism of FFPs in soils (e.g., high-strain rate effects due to rapid FFP loading), converting FFP output into practical information is complicated, and it heavily relies on empirical correlations. This thesis presents a numerical analysis of FFP testing on saturated sand using the Material Point Method. First, the simulation results were compared with laboratory tests. Later, a parametric study was performed to understand the effect of different material parameters on the FFP response and to highlight in a simplified manner the effects of rapid loading on the sand behavior. Additional simulations in dry sand (without water) revealed that dry conditions provide larger FFP penetrations than saturated ones for the same material parameters. Lastly, the strain rate coefficient, which is a parameter required in one of the most common empirical methods for converting FFP output into geotechnical parameters, was back-calculated. The results were consistent with values used in practice for similar conditions.

Geotechnical sediment properties such as moisture content, relative density, bearing capacity, and undrained shear strength have been discussed in the context of coastal sediment dynamics. However, these properties have rarely been assessed in their respective relevance or quantitatively related to sediment transport and erodibility. Also, to date there is no framework available for collecting direct measurements of these properties for estimating initiation of motion and erosion rates. Here, it is postulated that improving the ability to measure geotechnical sediment properties in energetic foreshore environments can improve our ability to predict coastal response to climate change. Through a series of field measurements, the research presented here (1) provides a framework for conducting geotechnical measurements of beaches, (2) advances portable free fall penetrometer (PFFP) data analysis in intertidal environments through the introduction of an impact velocity dependent strain-rate correction factor, (3) relates textural and sediment strength properties derived from PFFP measurements to an erosion rate parameter and hydrodynamically driven bed-level change, and (4) uses PFFP measurements to develop a sediment classification scheme in terms of soil behavior and erosion behavior for a mixed sediment type Arctic environment. Relationships between sediment properties other than grain size, most significantly void ratio, and erodibility parameters highlight the relevance of these measurements in geomorphodynamically active sandy beach environments. For the cohesive sediments in the Arctic, undrained shear strength was also related to an erosion rate parameter, allowing for a categorical framework for erodibility classification to be developed. The cohesive framework was combined with the relationships developed for sandy sediments and used to highlight areas of active sediment transport in the context of local morphodynamic and ice gouging processes. Finally, a simple case study showed how implementing in-situ erodibility parameters was important for long-term morphological modelling. The results represent a step forward in our ability to predict and mitigate climate change related issues from coastal erosion. / Doctor of Philosophy / Climate change driven impacts on coastal environments include increasing frequency and severity of storms, coastal erosion, and inundation of populated areas. Specifically for Arctic environments, warming has caused more sediment to be introduced into coastal waters as well as accelerated rates of permafrost melting and shoreline retreat and decreases in sea ice. One aspect of understanding how these changes will continue to affect coastal communities and our ability to predict climate change effects is understanding the role of sediment properties on sediment erosion and shoreline change. Physical and geomechanical (strength) properties of coastal sediments are important for a variety of coastal applications but have rarely been investigated in the context of quantifying, predicting, and assessing erosion, specifically in the context of field measurements. Towards this end, a series of field surveys were conducted along the coast of North Carolina at a sandy beach, and in Harrison Bay, Alaska, an Arctic coastal zone with both sandy and muddy sediments. Tools for taking physical samples of the beach and seabed, measuring the sediment strength, among other properties in place were used to characterize the local sediments. Once a framework was developed for characterizing the type of sediment, the measured properties were then related to measurements of erosion rate from a series of laboratory experiments performed on physical samples taken from the sites. Finally, one of the instruments for measuring sediment strength both on land and in the water was used to develop classification schemes for seabed sediments in terms of their erodibility. The results of this work highlight the importance of geotechnical properties for coastal sediment transport processes, reveal new relationships between sediment properties and properties quantifying erosion behavior, and offer a framework for future research to classify erodibility of coastal environments in the field with a single piece of equipment. Overall, the work presented here contributes to our ability to measure, quantify, and predict coastal response to climate change.

In-situ geotechnical testing of surficial sediment layers in areas of active sediment dynamics can provide essential information about physical and geotechnical variations of sediment properties with regards to active sediment remobilization processes. For example, portable free fall penetrometers (PFFPs) can assist with the detection of mobile sediment layers. They are easy to deploy, and can provide a large spatial coverage in a time- and cost-effective manner. However, they often struggle to provide more detailed information about the properties of mobile sediment layers due to a lack of calibration and validation in existing data sets. Currently, existing sediment samplers often disturb, or ignore the uppermost sediment layers. Simultaneous sediment sampling and geotechnical profiling is needed to fill this gap, and to drive data interpretation forward. A field investigation of surficial sediments was conducted in the wetland waterways of coastal Louisiana in 2014. In-situ tests were conducted using PFFP, and disturbed sediment samples were collected in selected locations. The results allowed us to map changes in sediment strength and stratification, and correlate the geotechnical results to local site characteristics. However, the need for high quality sediment samples for calibration and validation was emphasized by the results. Three different sediment sampler add-on units targeting mobile layers were designed and manufactured based on lessons-learned from the literature. The designs were tested in the laboratory and in the field (Yakutat, Alaska and York River, Virginia) in 2017. The samples were analyzed to understand the influence of different sampler characteristics on collected sample quality, and, to define mobile layer sampler characteristics that enable simultaneous geotechnical testing and the collection of high quality samples. Following field survey campaigns in the York River, Virginia in 2016 allowed to assess surficial sediment layer characteristics and behavior based on a coupled analysis of geotechnical data from in-situ PFFP tests and the sedimentological data collected using box cores and the novel sediment sampler. In summary, novel strategies and instrumentation to carry out simultaneous sediment sampling and geotechnical profiling of seabed surface layers were tested, and new pathways for geotechnical data analysis for the investigation of mobile seabed layers were presented. / PHD

Portable Free Fall Penetrometers (PFFPs) are lightweight tools used for rapid and economic characterization of surficial subaqueous sediments. PFFPs vary in weight, shape and size with options for using add-on units. The different configurations enable deployments in various environments and water depths, including the nearshore zone where conventional methods are challenged by energetic hydrodynamics and limited navigable depth. Moreover, PFFPs offer an opportunity to reduce the high site investigation costs associated with conventional offshore geotechnical site investigation methods. These costs are often a major obstacle for small projects serving remote communities or testing novel renewable energy harvesting machines. However, PFFPs still face issues regarding data analysis and interpretation, particularly in energetic sandy nearshore areas. This includes a lack of data and accepted analysis methods for such environments. Therefore, the goal of this research was to advance data interpretation and sediments characterization methods using PFFPs with emphasis on deployments in energetic nearshore environments. PFFP tests were conducted in the nearshore areas of: Yakutat Bay, AK; Cannon Beach, AK; and the U.S. Army Corps of Engineers' Field Research Facility's beach, Duck, NC. From the measurements, the research goal was addressed by: (1) introducing a methodology to create a regional sediment classification scheme utilizing the PFFP deceleration and pore pressure measurements, sediment traces on the probe upon retrieval, and previous literature; (2) investigating the effect of wave forcing on the sediments' behavior through correlating variations in sediment strength to wave climate, sandbar migration, and depth of closure, as well as identifying areas of significant sediment mobilization processes; and (3) estimating the relative density and friction angle of sand in energetic nearshore areas from PFFP measurements. For the latter, the field data was supported by vacuum triaxial tests and PFFP deployments under controlled laboratory conditions on sand samples prepared at different relative densities. The research outcomes address gaps in knowledge with regard to the limited studies available that investigate the sand geotechnical properties in energetic nearshore areas. More specifically, the research contributes to the understanding of surficial sediment geotechnical properties in energetic nearshore areas and the enhancement of sediment characterization and interpretation methods. / PHD

La mémoire présente une étude numérique des trajectoires non-verticales d’objets en chute ou en ascension libre dans un fluide newtonien initialement au repos. Une méthode numérique originale combinant une discrétisation spatiale spectrale et la décomposition du domaine a été implémentée à cet effet. Le code obtenu a été exploité pour apporter de nouvelles connaissances sur des objets fixes et objets libres. Pour les objet fixes, ellipsoïdes et cylindres, l’étude très complète des divers états de la transition a permis d’établir un lien entre le scénario de transition de la sphère et du disque infiniment mince. La simulation numérique d’objets libres a apporté des résultats très complets sur la chute de disques minces et de cylindres de faible épaisseur. Plusieurs questions soulevées dans les travaux précédents ont trouvés des réponses claires. Une étude paramétrique exhaustive, jamais abordée précédemment, portant sur des ellipsoïdes est décrite dans le dernier chapitre du mémoire. / The manuscript presents a numerical study of non-vertical trajectories of bodies fallingor rising freely in a Newtonian fluid initially at rest. The original numerical methodcombining a spectral spatial discretization and the decomposition of the domain wasimplemented. The developed code was used to study fixed and freely moving objects. Forthe fixed bodies, spheroids and cylinders, a very complete study of various transitionalregimes was carried out and established a link between the transition scenario of a sphereand of a disc. The numerical simulation of free bodies brought about the results onpath instabilities of discs and cylinders of small thickness. Several questions raised inprevious studies were clearly answered. An exhaustive parametric study, that has never beentaken up before, of freely moving spheroids is described in the last chapter of the manuscript.

Dissertação(mestrado) - Universidade Federal do Rio Grande, Programa de Pós-Graduação em Engenharia Oceânica, Escola de Engenharia, 2010. / Submitted by Lilian M. Silva (lilianmadeirasilva@hotmail.com) on 2013-04-15T00:06:33Z No. of bitstreams: 1 baldez,a.l.pdf: 8426528 bytes, checksum: 47e41efbe0e6ba9d1074f9667287d13a (MD5) / Approved for entry into archive by Bruna Vieira(bruninha_vieira@ibest.com.br) on 2013-06-10T18:46:55Z (GMT) No. of bitstreams: 1 baldez,a.l.pdf: 8426528 bytes, checksum: 47e41efbe0e6ba9d1074f9667287d13a (MD5) / Made available in DSpace on 2013-06-10T18:46:55Z (GMT). No. of bitstreams: 1 baldez,a.l.pdf: 8426528 bytes, checksum: 47e41efbe0e6ba9d1074f9667287d13a (MD5) Previous issue date: 2010 / Este trabalho tem por objetivo o desenvolvimento, construção e testes preliminares de um penetrômetro de queda livre para a caracterização de solos marinhos. O aparelho tem por finalidade medir as características de resistência do solo oceânico, através da medição e analise da desaceleração imposta ao penetrômetro após o seu impacto com o fundo. Este tipo de equipamento evita os elevados custos envolvidos em outros tipos de ensaios e na obtenção de amostras do fundo em condições de elevado risco e dificuldades naturais impostas pelas condições locais do mar. O dispositivo tem o formato de um aerofólio Joukowski simétrico (formato de gota), que consiste de duas partes: a primeira onde fica o acelerômetro e o chumbo granulado e a segunda onde há um conector que liga o acelerômetro a um cabo de dados e daí a um computador portátil que realiza a aquisição de dados. O penetrômetro pode ser lançado de certa altura acima da superfície da água, entra na água e mobiliza resistência hidrodinâmica durante a queda livre. Após choca-se contra o fundo marinho mobilizando resistências ao cisalhamento do solo sendo desacelerado até o repouso. Para os testes de funcionamento do equipamento foi utilizada a marina do Rio Grande Yacht Club localizado na cidade de Rio Grande - RS. Nos testes foram obtidos sinais de desaceleração registrados pelo acelerômetro que foram integrados numericamente duas vezes, a primeira obtendo dados de velocidade e na segunda dados de deslocamento percorrido pelo penetrômetro. Os dados assim coletados permitiram uma estimativa do perfil de resistência ao cisalhamento do solo marinho ao longo do comprimento penetrado,observando que o penetrômetro adquiriu a velocidade terminal sendo mensurada em torno de 5,7 m/s e o deslocamento máximo registrado obtido na marina foi de 5 metros. / This study aims at developing, constructing and testing a free fall penetrometer for the characterization of marine soils. The objective of this device is to measure the strength characteristics of the marine soil, through the measurement and the analysis of the deceleration imposed by its impact on the bottom.This kind of equipment reduces high costs involved in other tests and in the collection ofsamples on the bottom under bad sea conditions regarding risks and natural obstacles. The device was shaped as a symmetric Joukowski airfoil (the shape of a drop) which consists of two parts: one of them holds the accelerometer and the granulated lead and the other one has a connector that links the accelerometer to a data cable, and then, to a portable computer which collects the data. The penetrometer can be launched from a certain height above the water surface, and then penetrates into the water and mobilizes hydrodynamic resistance during the free fall. When it hits the bottom of the sea, it mobilizes shear strength and decelerates until it rests. The tests with the equipment were carried out in the marina at the Rio Grande Yacht Club located in Rio Grande, RS, Brazil. The tests got deceleration signals which wererecorded by the accelerometer and were integrated twice numerically in order to collectdata on the velocity and on the displacement of the penetrometer. These data enabled the estimate of the shear strength profile of the marine soil along the length in which penetration occurred. The datashow that the velocity of the penetrometer reached about 5.7 m/s and thatthe maximum displacement recorded in the marina was 5 meters.

La thèse présente une étude numérique des instabilités de trajectoires de sphères, d'ellipsoïdes aplatis et de bulles en mouvement libre sous l'action de la gravité, de la poussée d'Archimède et des forces hydrodynamiques. Le chapitre sur les sphères reprend, complète et étend l'étude numérique de Jenny et al. (2004) en se concentrant sur la transition au chaos et sur les trajectoires chaotiques. Les résultats montrent la différence entre le scénario de transition au chaos de sphères de faible et de grand rapport de densité. Plusieurs grandeurs statistiques sont proposées afin de fournir une caractérisation quantitative des états chaotiques. Elle permettent de mettre en relation les états ordonnées et chaotiques et offrent une possibilité de comparaison objective de données aléatoires d'origine numérique ou expérimentale. L'étude, très extensive, du comportement d'ellipsoïdes aplatis établit le lien entre les disques et les sphères en faisant varier l'aplatissement des objets depuis infiniment plat jusqu'à presque sphérique. Les huit diagrammes d'état présentés permettent de comprendre l'effet de la forme des ellipsoïdes sur le scénario de transition. Le cas d'ellipsoïdes presque sphériques montre que de faibles imperfections de la forme peuvent avoir in impact significatif sur les trajectoires de sphères de très faible rapport de densité. Pour les bulles considérées dans la limite de rapport de densité et viscosité az/liquide nul, l'étude se concentre sur l'analyse de stabilité linéaire et aboutit à la courbe de stabilité marginale dans le plan des paramètres nombre de Bond – nombre de Galilée en tenant compte de la déformation des bulles au moment de la perte de leur axisymétrie. Plus deux décades de nombres de Bond, entre 0,1 et 20, sont couvertes. Les résultats montrent clairement l'effet de la déformation de la bulle sur le seuil de l'instabilité. / The thesis presents a numerical study of path instabilities for spheres, oblate spheroids and bubbles moving freely under the effect of the gravity, buoyancy and hydrodynamic forces. For spheres, the parametric study of Jenny et al. (2004) is revisited, improved end extended with a special focus on the chaotic states. The results reveal that the effect of density ratio responsible for different oblique oscillating states of low and high frequencies has a significant impact both on the onset of chaos and on the behavior of fully chaotic states. Several quantitative statistical quantities are proposed and shown to be relevant for establishing the relation between chaotic and ordered states and for an objective comparison of random data of numerical or experimental origin. The extensive study on freely moving spheroids establishes the link between disks and spheres by varying the aspect ratio of spheroids from infinitely flat to almost spherical. The state diagrams provided for eight different aspect ratios of spheroid show in detail how the transition scenario varies depending of the body shape. The investigation of almost spherical spheroids reveals the specificities of the dynamics of light imperfect spheres.For the deformable gas bubble in the limit of zero gas/liquid density and viscosity ratio, a marginal stability curve is given in the two-parameter plane of the Galileo and the Bond number indicating the critical Galileo numbers for the loss of stability of vertical trajectories. The numerical investigation covers more than two decades of Bond number going from 0.1 to 20. The results clearly show the crucial role of the surface deformation.

Purpose - The paper presents a theoretical framework that describes the aerodynamics of a falling maple (Acer pseudoplatanus) seed. --- Methodology - A semi-empirical method is developed that provides a ratio stating how much longer a seed falls in air compared to freefall. The generated lift is calculated by evaluating the integral of two-dimensional airfoil elements using a preliminary falling speed. This allows for the calculation of the definitive falling speed using Blade Element Momentum Theory (BEMT); hereafter, the fall duration in air and in freefall are obtained. Furthermore, the input-variables of the calculation of lift are transformed to require only the length and width of the maple seed. Lastly, the method is applied to two calculation examples as a means of validation. --- Findings - The two example calculations gave percentual errors of 5.5% and 3.7% for the falling speed when compared to measured values. The averaged result is that a maple seed falls 9.9 times longer in air when released from 20 m; however, this result is highly dependent on geometrical parameters which can be accounted for using the constructed method. --- Research limitations - Firstly, the coefficient of lift is unknown for the shape of a maple seed. Secondly, the approximated transient state is yet to be verified by measurement. --- Originality / Value - The added value of this report lies in the reduction of simplifications compared to BEMT approaches. In this way a large amount of accuracy is achieved due to the inclusion of many geometrical parameters, even though simplicity is maintained. This has been accomplished through constructing a simple three-step method that is fundamental and essentially non-iterative.