Experiments on Surface Reconstruction for Partially Submerged Marine Structures

Over the past 10 years, significant scientific effort has been dedicated to the problem of three-dimensional (3-D) surface reconstruction for structural systems. However, the critical area of marine structures remains insufficiently studied. The research presented here focuses on the problem of 3-D surface reconstruction in the marine environment. This paper summarizes our hardware, software, and experimental contributions on surface reconstruction over the past few years (2008–2011). We propose the use of off-the-shelf sensors and a robotic platform to scan marine structures both above and below the waterline, and we develop a method and software system that uses the Ball Pivoting Algorithm (BPA) and the Poisson reconstruction algorithm to reconstruct 3-D surface models of marine structures from the scanned data. We have tested our hardware and software systems extensively in Singapore waters, including operating in rough waters, where water currents are around 1–2 m/s. We present results on construction of various 3-D models of marine structures, including slowly moving structures such as floating platforms, moving boats, and stationary jetties. Furthermore, the proposed surface reconstruction algorithm makes no use of any navigation sensor such as GPS, a Doppler velocity log, or an inertial navigation system.Singapore-MIT Alliance for Research and Technology. Center for Environmental Sensing and Modelin

Modeling and Inspection Applications of a Coastal Distributed Autonomous Sensor Network

Real time in-situ measurements are essential for monitoring and understanding physical and biochemical changes within ocean environments. Phenomena of interest usually display spatial and temporal dynamics that span different scales. As a result, a combination of different vehicles, sensors, and advanced control algorithms are required in oceanographic monitoring systems. In this study our group presents the design of a distributed heterogeneous autonomous sensor network that combines underwater, surface, and aerial robotic vehicles along with advanced sensor payloads, planning algorithms and learning principles to successfully operate across the scales and constraints found in coastal environments. Examples where the robotic sensor network is used to localize algal blooms and collect modeling data in the coastal regions of the island nation of Singapore and to construct 3D models of marine structures for inspection and harbor navigation are presented. The system was successfully tested in seawater environments around Singapore where the water current is around 1-2m/s. Topics: Inspection , Modeling , Sensor networks , ShorelinesSingapore. National Research Foundation (Singapore-MIT Alliance for Research and Technology (SMART)

Flow and air-entrainment around partially submerged vertical cylinders

In this study, a partially submerged vertical cylinder is moved at constant velocity through water, which is initially at rest. During the motion, the wake behind the cylinder induces free-surface deformation. Eleven cylinders, with diameters from $D=1.4$ to 16 cm, were tested at two different conditions: (i) constant immersed height $h$ and (ii) constant $h/D$. The range of translation velocities and diameters are in the regime of turbulent wake with experiments carried out for $4500<Re<240 \,000$ and $0.2<Fr<2.4$, where $Re$ and $Fr$ are the Reynolds and Froude numbers based on $D$. The focus here is on drag force measurements and relatively strong free-surface deformation up to air-entrainment. Specifically, two modes of air-entraiment have been uncovered: (i) in the cavity along the cylinder wall and (ii) in the wake of the cylinder. A scaling for the critical velocity for air-entrainment in the cavity has been observed in agreement with a simple model. Furthermore, for $Fr>1.2$, the drag force varies linearly with $Fr$

Soft Computing approaches in ocean wave height prediction for marine energy applications

El objetivo de esta tesis consiste en investigar el uso de técnicas de Soft Computing (SC) aplicadas a la energía producida por las olas o energía undimotriz. Ésta es, entre todas las energías marinas disponibles, la que exhibe el mayor potencial futuro porque, además de ser eficiente desde el punto de vista técnico, no causa problemas ambientales significativos. Su importancia práctica radica en dos hechos: 1) es aproximadamente 1000 veces más densa que la energía eólica, y 2) hay muchas regiones oceánicas con abundantes recursos de olas que están cerca de zonas pobladas que demandan energía eléctrica. La contrapartida negativa se encuentra en que las olas son más difíciles de caracterizar que las mareas debido a su naturaleza estocástica. Las técnicas SC exhiben resultados similares e incluso superiores a los de otros métodos estadísticos en las estimaciones a corto plazo (hasta 24 h), y tienen la ventaja adicional de requerir un esfuerzo computacional mucho menor que los métodos numérico-físicos. Esta es una de las razones por la que hemos decidido explorar el uso de técnicas de SC en la energía producida por el oleaje. La otra se encuentra en el hecho de que su intermitencia puede afectar a la forma en la que se integra la electricidad que genera con la red eléctrica. Estas dos son las razones que nos han impulsado a explorar la viabilidad de nuevos enfoques de SC en dos líneas de investigación novedosas. La primera de ellas es un nuevo enfoque que combina un algoritmo genético (GA: Genetic Algorithm) con una Extreme Learning Machine (ELM) aplicado a un problema de reconstrucción de la altura de ola significativa (en un boya donde los datos se han perdido, por ejemplo, por una tormenta) utilizando datos de otras boyas cercanas. Nuestro algoritmo GA-ELM es capaz de seleccionar un conjunto reducido de parámetros del oleaje que maximizan la reconstrucción de la altura de ola significativa en la boya cuyos datos se han perdido utilizando datos de boyas vecinas. El método y los resultados de esta investigación han sido publicados en: Alexandre, E., Cuadra, L., Nieto-Borge, J. C., Candil-García, G., Del Pino, M., & Salcedo-Sanz, S. (2015). A hybrid genetic algorithm—extreme learning machine approach for accurate significant wave height reconstruction. Ocean Modelling, 92, 115-123. La segunda contribución combina conceptos de SC, Smart Grids (SG) y redes complejas (CNs: Complex Networks). Está motivada por dos aspectos importantes, mutuamente interrelacionados: 1) la forma en la que los conversores WECs (wave energy converters) se interconectan eléctricamente para formar un parque, y 2) cómo conectar éste con la red eléctrica en la costa. Ambos están relacionados con el carácter aleatorio e intermitente de la energía eléctrica producida por las olas. Para poder integrarla mejor sin afectar a la estabilidad de la red se debería recurrir al concepto Smart Wave Farm (SWF). Al igual que una SG, una SWF utiliza sensores y algoritmos para predecir el olaje y controlar la producción y/o almacenamiento de la electricidad producida y cómo se inyecta ésta en la red. En nuestro enfoque, una SWF y su conexión con la red eléctrica se puede ver como una SG que, a su vez, se puede modelar como una red compleja. Con este planteamiento, que se puede generalizar a cualquier red formada por generadores renovables y nodos que consumen y/o almacenan energía, hemos propuesto un algoritmo evolutivo que optimiza la robustez de dicha SG modelada como una red compleja ante fallos aleatorios o condiciones anormales de funcionamiento. El modelo y los resultados han sido publicados en: Cuadra, L., Pino, M. D., Nieto-Borge, J. C., & Salcedo-Sanz, S. (2017). Optimizing the Structure of Distribution Smart Grids with Renewable Generation against Abnormal Conditions: A Complex Networks Approach with Evolutionary Algorithms. Energies, 10(8), 1097

Geomorphological map of the Tremiti Islands (Puglia, Southern Adriatic Sea, Italy), scale 1:15,000

This paper describes the Geomorphological map of the Tremiti Islands (Puglia, Southern Adriatic Sea, Italy), scale 1:15,000. The Tremiti Islands, located north of Gargano promontory's coast, are part of a complex geological area within the Adriatic basin, facing the junction between the central and southern Apennines. This area is well known for Neogenic-Quaternary stratigraphic, tectonic and seismologic aspects and is crucial for the definition of Late Quaternary Adriatic basin evolution. The map is the result of a geomorphological study carried out on the islands and the inner continental shelf around them. This study incorporates: (1) field recognition of Quaternary continental deposits and geomorphological mapping, supported by radiometric dating, focused on the morpho-lithostratigraphic correlation of deposits among the different islands and the recognition of landforms that controlled landscape evolution; (2) bathymetric analysis; (3) geomorphological analysis of data from a side scan sonar survey, ..

3D virtualization of an underground semi-submerged cave system

Underwater caves represent the most challenging scenario for exploration, mapping and 3D modelling. In such complex environment, unsuitable to humans, highly specialized skills and expensive equipment are normally required. Technological progress and scientific innovation attempt, nowadays, to develop safer and more automatic approaches for the virtualization of these complex and not easily accessible environments, which constitute a unique natural, biological and cultural heritage. This paper presents a pilot study realised for the virtualization of 'Grotta Giusti' (Fig. 1), an underground semi-submerged cave system in central Italy. After an introduction on the virtualization process in the cultural heritage domain and a review of techniques and experiences for the virtualization of underground and submerged environments, the paper will focus on the employed virtualization techniques. In particular, the developed approach to simultaneously survey the semi-submersed areas of the cave relying on a stereo camera system and the virtualization of the virtual cave will be discussed

Numerical evaluation of the free surface effect on the hydrodynamics and dynamics of underwater vehicles

The present thesis seeks to evaluate the free surface effect on the hydrodynamics and dynamics of a generic underwater vehicle (UV) in the horizontal plane. Accordingly, the captive tests, including the straight-ahead resistance, drift and rotating arm tests, are performed on the bare hull of a UV model by using numerical simulations based on URANS equations with a Reynolds stress turbulence model implemented in the commercial code STARCCM+. These tests are carried out for various submergence depths and proper ranges of UV velocity components. For the purpose of maneuverability assessment, the forces and moments arising from the velocity components obtained from the simulations of the captive tests are implemented in the equations of motion for various submergence depths. Additionally, analytical equations are used to calculate the forces and moments arising from the UV accelerations, thrust and rudder, which all are assumed to remain constant with respect to submergence depth. The obtained results show that, generally, a decrease in submergence depth causes an increase in all the forces arising from the velocity components. The results further show that approaching the free surface has a negligible effect on the lateral force and yaw moment generated by the bow and stern regions. Moreover, it is seen that with a decrease in submergence depth, the region between the UV midlength and the aft shoulder is mainly responsible for the increase or decrease in the lateral force and yaw moment acting on the UV hull. It is also observed that, with a decrease in submergence depth, due to an increase in the UV damping characteristics, the dynamic stability increases remarkably, which leads to a decrease in the UV maneuverability.A presente tese tem como objetivo avaliar o efeito da superfície livre na hidrodinâmica e dinâmica de um veículo submarino (UV) genérico no plano horizontal. Portanto, os testes cativos, incluindo os testes de reboque e de braço rotativo, são realizados num modelo UV usando as simulações numéricas baseadas nas equações de URANS com um modelo de turbulência de Reynolds implementados no código comercial STARCCM+. Estes testes são realizados nas várias profundidades de submersão e faixas apropriadas das velocidades. Para fins de avaliação de manobrabilidade, as forças e os momentos obtidos a partir das simulações dos testes cativos são implementados nas equações de movimento nas várias profundidades. Adicionalmente, as equações analíticas são usadas para calcular as forças e os momentos que surgem das acelerações, impulso e leme, os quais são assumidos constantes em relação à profundidade. Os resultados obtidos mostram que, geralmente, uma diminuição na profundidade provoca um aumento em todas as forças geradas pelas velocidades. Os resultados ainda mostram que aproximar a superfície livre tem um efeito insignificante na força lateral e no momento de yaw ambos gerados pelas regiões de proa e popa. Além disso, observa-se que, com a diminuição da profundidade, a região entre o meio do UV e o ombro de ré é o principal responsável pelo aumento ou diminuição da força lateral e do momento de yaw atuantes sobre o casco do UV. Observa-se também que, com um decréscimo na profundidade, devido a um aumento nas características de amortecimento do UV, a estabilidade dinâmica aumenta consideravelmente, o que leva a uma diminuição da manobrabilidade do UV

The Status of Eelgrass, Zostera marina, as Bay Scallop Habitat: Consequences for the Fishery in the Western Atlantic

Zostera marina is a member of a widely distributed genus of seagrasses, all commonly called eelgrass. The reported distribution of eelgrass along the east coast of the United States is from Maine to North Carolina. Eelgrass inhabits a variety of coastal habitats, due in part to its ability to tolerate a wide range of environmental parameters. Eelgrass meadows provide habitat, nurseries, and feeding grounds for a number of commercially and ecologically important species, including the bay scallop, Argopecten irradians. In the early 1930’s, a marine event, termed the “wasting disease,” was responsible for catastrophic declines in eelgrass beds of the coastal waters of North America and Europe, with the virtual elimination of Z. marina meadows in the Atlantic basin. Following eelgrass declines, disastrous losses were documented for bay scallop populations, evidence of the importance of eelgrass in supporting healthy scallop stocks. Today, increased turbidity arising from point and non-point source nutrient loading and sediment runoff are the primary threats to eelgrass along the Atlantic coast and, along with recruitment limitation, are likely reasons for the lack of recovery by eelgrass to pre-1930’s levels. Eelgrass is at a historical low for most of the western Atlantic with uncertain prospects for systematic improvement. However, of all the North American seagrasses, eelgrass has a growth rate and strategy that makes it especially conducive to restoration and several states maintain ongoing mapping, monitoring, and restoration programs to enhance and improve this critical resource. The lack of eelgrass recovery in some areas, coupled with increasing anthropogenic impacts to seagrasses over the last century and heavy fishing pressure on scallops which naturally have erratic annual quantities, all point to a fishery with profound challenges for survival