Influencia de un fluido en las características dinámicas de placas circulares y casicirculares

La influencia de un fluido en las características dinámicas de estructuras se ha estudiado desde hace tiempo. Sin embargo muchos estudios se refieren a aplicaciones bajo el agua, como es el caso del sonar de un submarino por lo que el fluido circundante se considera líquido (sin efectos de compresibilidad). Más recientemente en aplicaciones acústicas y espaciales tales como antenas o paneles muy ligeros, ha sido estudiada la influencia en las características dinámicas de una estructura rodeada por un fluido de baja densidad. Por ejemplo se ha mostrado que el efecto del aire en el transmisor-reflector del Intelsat VI C-B con un diámetro de 3,2 metros y con un peso de sólo 34,7 kg disminuye la primera frecuencia en torno a un 20% con respecto a su valor en vacío. Por tanto es importante en el desarrollo de estas grandes y ligeras estructuras disponer de un método con el que estimar el efecto del fluido circundante sobre las frecuencias naturales de éstas. De esta manera se puede evitar el ensayo de la estructura en una cámara de vacío que para el caso de una gran antena o panel puede ser difícil y costoso. Se ha desarrollado un método de elementos de contorno (BEM) para la determinación del efecto del fluido en las características dinámicas de una placa circular. Una vez calculados analíticamente los modos de vibración de la placa en vacío, la matriz de masa añadida debido a la carga del fluido se determina por el método de elementos de contorno. Este método utiliza anillos circulares de manera que el número de elementos para obtener unos resultados precisos es muy bajo. Se utiliza un procedimiento de iteración para el cálculo de las frecuencias naturales del acoplamiento fluido-estructura para el caso de fluido compresible. Los resultados del método se comparan con datos experimentales y otros modelos teóricos mostrando la precisión y exactitud para distintas condiciones de contorno de la placa. Por otro lado, a veces la geometría de la placa no es circular sino casi-circular y se ha desarrollado un método de perturbaciones para determinar la influencia de un fluido incompresible en las características dinámicas de placas casi-circulares. El método se aplica a placas con forma elíptica y pequeña excentricidad. Por una parte se obtienen las frecuencias naturales y los modos de deformación de la placa vibrando en vacío. A continuación, se calculan los coeficientes adimensionales de masa virtual añadida (factores NAVMI). Se presentan los resultados de estos factores y el efecto del fluido en las frecuencias naturales. ABSTRACT The influence of the surrounding fluid on the dynamic characteristics of structures has been well known for many years. However most of these works were more concerned with underwater applications, such as the sonar of a submarine and therefore the surrounding fluid was considered a liquid (negligible compressibility effects). Recently for acoustical and spatial applications such as antennas or very light panels the influence on the dynamic characteristics of a structure surrounded by a fluid of low density has been studied. Thus it has been shown that the air effect for the Intelsat VI C-B transmit reflector with a diameter of 3,2 meters and weighting only 34,7 kg decreases the first modal frequency by 20% with respect to the value in vacuum. It is important then, in the development of these light and large structures to have a method that estimates the effect that the surrounding fluid will have on the natural frequencies of the structure. In this way it can be avoided to test the structure in a vacuum chamber which for a large antenna or panel can be difficult and expensive A BEM method for the determination of the effect of the surrounding fluid on the dynamic characteristics of a circular plate has been developed. After the modes of the plate in vacuum are calculated in an analytical form, the added mass matrix due to the fluid loading is determined by a boundary element method. This method uses circular rings so the number of elements to obtain an accurate result is very low. An iteration procedure for the computation of the natural frequencies of the couple fluid-structure system is presented for the case of the compressibility effect of air. Comparisons of the present method with various experimental data and other theories show the efficiency and accuracy of the method for any support condition of the plate. On the other hand, sometimes the geometry of the plate is not circular but almost-circular, so a perturbation method is developed to determine the influence of an incompressible fluid on the dynamic characteristics of almost-circular plates. The method is applied to plates of elliptical shape with low eccentricity. First, the natural frequencies and the mode shapes of the plate vibrating in vacuum are obtained. Next, the nondimensional added virtual mass coefficients (NAVMI factors) are calculated. Results of this factors and the effect of the fluid on the natural frequencies are presented.

Polymetallic ferromanganese deposits research on the Atlantic Spanish continental margin

Seamounts, submarine banks, volcanoes and undercurrent channels are prominent geomorphic features that have become an important target for minerals research and exploration with the goal of future exploitation. Polymetallic ferromanganese deposits are common types of mineralization on these settings. Co-rich ferromanganese crusts are important as potential resources of Mn and Co, but also Ti, Ni, Tl, REEs, PGEs, and other metals. Many seamounts and channels along the Atlantic Spanish continental margin are known to hold mineral deposits but are poorly studied. This work presents and briefly describes the most recent activities of the Spanish Geological Survey (IGME) on exploration and investigation of ferromanganese deposits along the Atlantic Spanish continental margin. Different submarine areas from the northwestern margin of the Iberian Peninsula to the west off Canary Islands have been surveyed by geophysical, sampling and underwater observations from 89 to 4000 m water depth. The mineral deposits cover a large diversity of submarine geological and geomorphical features: mud volcanoes and diapirs related to hydrocarbon seeps, seamounts associated with hot spot volcanism, hydrothermal vents in active magmatic volcanoes, structural basement highs and banks or contourite channels. Considering the collected dataset, we present the preliminary results of the study of these mineral deposits, including ferromanganese nodules and crusts and phosphate pavements and nodules, which can be considered as potential sources of raw materials.

An Overview of Geodetic Volcano Research in the Canary Islands

The Canary Islands are mostly characterized by diffuse and scattered volcanism affecting a large area, with only one active stratovolcano, the Teide?Pico Viejo complex (Tenerife). More than 2 million people live and work in the 7,447 km2 of the archipelago, resulting in an average population density three times greater than the rest of Spain. This fact, together with the growth of exposure during the past 40 years, increases volcanic risk with respect previous eruptions, as witnessed during the recent 2011?2012 El Hierro submarine eruption. Therefore, in addition to purely scientific reasons there are economic and population-security reasons for developing and maintaining an efficient volcano monitoring system. In this scenario geodetic monitoring represents an important part of the monitoring system. We describe volcano geodetic monitoring research carried out in the Canary Islands and the results obtained. We consider for each epoch the two main existing constraints: the level of volcanic activity in the archipelago, and the limitations of the techniques available at the time. Theoretical and observational aspects are considered, as well as the implications for operational volcano surveillance. Current challenges of and future perspectives in geodetic volcano monitoring in the Canaries are also presented.

Surface velocity and mass balance of Livingston Island ice cap, Antarctica

The mass budget of the ice caps surrounding the Antarctica Peninsula and, in particular, the partitioning of its main components are poorly known. Here we approximate frontal ablation (i.e. the sum of mass losses by calving and submarine melt) and surface mass balance of the ice cap of Livingston Island, the second largest island in the South Shetland Islands archipelago, and analyse variations in surface velocity for the period 2007–2011. Velocities are obtained from feature tracking using 25 PALSAR-1 images, and used in conjunction with estimates of glacier ice thicknesses inferred from principles of glacier dynamics and ground-penetrating radar observations to estimate frontal ablation rates by a flux-gate approach. Glacier-wide surface mass-balance rates are approximated from in situ observations on two glaciers of the ice cap. Within the limitations of the large uncertainties mostly due to unknown ice thicknesses at the flux gates, we find that frontal ablation (−509 ± 263 Mt yr−1, equivalent to −0.73 ± 0.38 m w.e. yr−1 over the ice cap area of 697 km2) and surface ablation (−0.73 ± 0.10 m w.e. yr−1) contribute similar shares to total ablation (−1.46 ± 0.39 m w.e. yr−1). Total mass change (δM = −0.67 ± 0.40 m w.e. yr−1) is negative despite a slightly positive surface mass balance (0.06 ± 0.14 m w.e. yr−1). We find large interannual and, for some basins, pronounced seasonal variations in surface velocities at the flux gates, with higher velocities in summer than in winter. Associated variations in frontal ablation (of ~237 Mt yr−1; −0.34 m w.e. yr−1) highlight the importance of taking into account the seasonality in ice velocities when computing frontal ablation with a flux-gate approach.

Nuevas tendencias en el proyecto de buques cableros

Esta tesis tiene como objetivo actualizar los criterios de proyecto de los buques cableros, analizando las nuevas tendencias en el uso de este tipo de barcos. Se estudian las operaciones realizadas para la instalación y reparación de los cables submarinos. Del estudio de estas técnicas se extraen unos requisitos para el proyecto. Se comprueba cómo han evolucionado a lo largo de la historia las características de los buques cableros. Comparando esta evolución con las características necesarias extraídas del estudio de las operaciones de cables, se concluyen los aspectos fundamentales a tener en cuenta por los ingenieros navales en el proyecto de estos buques cableros. Se presentan: datos concretos para el dimensionamiento, equipamiento, distribución y disposición general; soluciones utilizadas y desarrolladas por el autor para la configuración del manejo del cable de tiro del arado submarino; y se propone una disposición general más acorde con las necesidades modernas de uso de estos barcos. Todo está basado en la experiencia del autor de más de 20 años operando buques cableros de la empresa Transoceanic Cableship Company, Ltd.1 y TE Conectivity SubCom SL (antes TEMASA2), ambas filiales de la empresa norteamericana de telecomunicaciones submarinas TE SubCom, por ello su utilidad práctica queda garantizada. ABSTRACT The goal of this thesis is to update the design criteria applied to cableships by analyzing the new trends in the use of this type of ships. The methods of procedure for the installation and repair of fiber optic submarine cables are also explored. The study of these techniques draws conclusions regarding the design requirements. The evolution of the characteristics of the cableships throughout the history is also approached. The primary aspect that has to be taken into account by the naval architect is also stated, when comparing the evolution and the necessary requirements extracted from the study of cable operations. Specific data for dimensioning, outfitting, distribution and arrangement are presented, as well as solutions found and developed by the author for the tow wire handling configuration. Furthermore, a new general arrangement more in line with the modern needs for the purpose of these ships is suggested. Everything is based in the author´s experience of over twenty years in the operation of cableships owned by Transoceanic Cableship Company Ltd. and TE Connectivity SubCom SL (formerly called TEMASA), both subsidiaries of the US based company TE SubCom. For this reason, the practical value of the study is guaranteed.

A non-linear analysis of lying a floating pipeline on the seabed

In this article, a model for the determination of displacements, deformations and tensions of a submarine pipeline during the construction is presented. The process is carried out from an initial floating situation to the final laying position on the seabed. The existence of currents and small waves are also considered. Firstly, this technique, usually applied to polyethylene pipelines, is described in this paper as well as some real world examples, as well as the variables that can be modified to control the behavior of the structure. A detailed description of the actions in this process is considered, specially the ones related to marine environment, as Archimedes force, current and sea waves. The behavior of the pipeline is modeled with a non linear elasto dynamic model where geometric non linearities are taken into account. A 3-D beam model, without cross section deformation effects, is developed. Special care is taken in the numerical analysis, developed within an updated lagrangian formulation framework, with the sea bed contact, the follower forces due to the external water pressures and the dynamic actions. Finally, some subroutines are implemented into ANSYS to simulate the two dimensional case, where the whole construction process is achieved. With this software, a sensibility analysis of the bending moments, axial forces and stresses obtained with different values of the control variables in order to optimize the construction steps. These control variables are, the axial load in the pipe, the inundated inner length and the distance of the control barge from the coast.

Potential effects of gas hydrate on human welfare

For almost 30 years. serious interest has been directed toward natural gas hydrate, a crystalline solid composed of water and methane, as a potential (i) energy resource, (ii) factor in global climate change, and (iii) submarine geohazard. Although each of these issues can affect human welfare, only (iii) is considered to be of immediate importance. Assessments of gas hydrate as an energy resource have often been overly optimistic, based in part on its very high methane content and on its worldwide occurrence in continental margins. Although these attributes are attractive, geologic settings, reservoir properties, and phase-equilibria considerations diminish the energy resource potential of natural gas hydrate. The possible role of gas hydrate in global climate change has been often overstated. Although methane is a “greenhouse” gas in the atmosphere, much methane from dissociated gas hydrate may never reach the atmosphere, but rather may be converted to carbon dioxide and sequestered by the hydrosphere/biosphere before reaching the atmosphere. Thus, methane from gas hydrate may have little opportunity to affect global climate change. However, submarine geohazards (such as sediment instabilities and slope failures on local and regional scales, leading to debris flows, slumps, slides, and possible tsunamis) caused by gas-hydrate dissociation are of immediate and increasing importance as humankind moves to exploit seabed resources in ever-deepening waters of coastal oceans. The vulnerability of gas hydrate to temperature and sea level changes enhances the instability of deep-water oceanic sediments, and thus human activities and installations in this setting can be affected.