Investigación experimental del flujo aerodinámico sobre helipuertos embarcados

La investigación del flujo aerodinámico sobre helipuertos embarcados se encuentra estrechamente relacionada con la operación segura de las aeronaves, pues las condiciones del flujo que tiene lugar en ese entorno pueden exceder los límites para los que están certificadas dichas aeronaves. El ambiente aerodinámico en las inmediaciones de un barco es altamente complejo y se encuentra influenciado por gran número de factores (chimeneas, antenas, mástiles, etc.) relacionados con la configuración específica del propio barco. El flujo objeto de investigación corresponde a la estela que se desarrolla sobre la cubierta de vuelo de una fragata, el cual está fuertemente influenciado por la superestructura de la misma, y que cualitativamente es similar al flujo que tiene lugar entre edificios altos o helipuertos situados en áreas urbanas, pues comprende estructuras tipo caja, con bordes afilados, que generan flujos tridimensionales altamente turbulentos. En esta Tesis se aborda el estudio del problema desde el punto de vista experimental, mediante simulación en túnel aerodinámico y medida de las variables del campo fluido sobre maquetas de fragatas a escala reducida. Las herramientas empleadas para tal cometido, han sido técnicas experimentales, tales como la visualización del flujo, la velocimetría láser por imágenes de partículas, la anemometría láser Doppler y los scanners electrónicos de presión, que han permitido investigar el flujo problema con objeto de obtener información, y adquirir así, un conocimiento más profundo de dicho flujo. La explotación de este conocimiento, ha dado lugar al diseño de una nueva solución, basada en la modificación de geometría básica de la fragata, por medio del cambio de la curvatura del techo del hangar, permitiendo suavizar el escalón descendente que se produce aguas abajo del mismo. Las geometrías modificadas han sido ensayada en túnel mediante la misma metodología empleada para la fragata original, de modo que, ha podido establecerse un análisis comparativo, para valorar la efectividad de la solución propuesta, el cual ha mostrado resultados satisfactorios, retirando el flujo adverso de la zona de operación de helicópteros y desplazándolo hacia el hangar, donde resulta menos peligroso, de modo que se reduce la carga del piloto y los riesgos de accidente durante las operaciones a bordo de embarcaciones. ABSTRACT The investigation of aerodynamic flow above the ship’s heliports is directly related to the aircraft safe operation, because the environment flow conditions may exceed the aircraft certification limits. Aerodynamic ship’s environment is highly complex and it is influenced by a large number of factors (stacks, antennae, masts, …) related to each specific ship configuration. The flow under investigation occurs into the wake produced above the flight deck of a frigate, that is strongly influenced by the superstructure. This flow is similar to one produced around tall buildings or heliports located in urban areas, thus in both of them, the air is flowing around sharp-edges box-like structures, producing three-dimensional and highly turbulent flows. This Thesis studies the problem from an experimental point of view, by means of wind tunnel simulations and measurements of the flow field around reduced scale frigates models. Tools used in this work are the experimental techniques, as flow visualization, particle image velocimetry, laser Doppler anemometry and pressure electronic scanners. These techniques provide information about the flow in order to obtain a more complete insight of this kind of flows. The exploitation of this insight is used for the design of a new flow control concept, based on the modification of the basic frigate geometry. This new design consists in the hangar roof curvature modification that produces a smoothing of the descendent step located downstream the hangar. Modified geometries are tested in wind tunnel by means of the same methodology as the original frigate, thus a comparative analysis is established in order to perform an assessment of effectiveness. This analysis has shown good results in displacing the adverse flow from the helicopter operation path to the nearest hangar region, reducing the pilot load and the accident risks during on board operations.

A Spectral Analysis of LDA Turbulent Flow Measurements in a Ship Air Wake

Helicopters are one of the most important tactical elements in maritime operations. The necessity for an improvement in the conditions in which the landing and take-off operations are carried out leads to the study of the flow that separates from the ship?s superstructure over the flight deck. To investigate this flow a series of wind tunnel experiments have been performed by testing a sub-scale model of a generic frigate. Measurements of the flow?s velocity have been taken by means of Laser Doppler Anemometry (LDA) in five points that simulate the last path of the landing trajectory. The data obtained in these experiments is manipulated in a frequency analysis where the corresponding spectra are calculated. Onboard measurements from an actual full scale frigate are analyzed and compared with the wind tunnel results. Conclusions obtained consist of a series of illustrative values of turbulent energy frequency ranges which can be valuable for any study in this field. The comparison shows a clear similarity between both experiments, reasserting the wind tunnel measurements and its reliability.

Narrative of the voyage of H.M.S. Rattlesnake, commanded by the late Captain Owen Stanley during the years 1846-50, including discoveries and surveys in New Guinea, the Louisiade Archipelago, etc : to which is added Mr. E.B. Kennedy's expedition for the exploration of the Cape York Peninsula / by John Macgillivray.

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Commonplace book of Hector Orr, 1789-1804

Hector Orr began recording entries in this commonplace book during his first year as a student at Harvard and continued writing in the volume sporadically until 1804. The entries written while he was a student, from 1789 to 1792, include themes written on the following topics: Time, Discontent, Patriotism, Virtue, Conscience, Patience, Avarice, Compassion, Mortality, Self-knowledge, Benevolence, Morning, Anger, Profanity, Bribery, Autumn and Winter, Hermitage, Conscience and Anticipation. He also wrote detailed entries about the forensic disputations in which he and his classmates participated, explaining both the affirmative and negative positions. One of these disputations involved discussion of the Stamp Act, which was then quite recent history. Orr's entries about the disputations list the names of students involved and specify their position in the argument.

Diary of Elias Mann, 1796-1800

Elias Mann kept this diary during his undergraduate years at Harvard College. The diary begins August 17, 1796 and ends in August of 1800 and also includes several undated sheets filled with excerpts of poems. The daily entries describe many aspects of Mann's life, including not only his experiences at Harvard but also his involvement in the larger community. Entries related to life at Harvard describe club meetings (coffee club, Hasty Pudding Club and Phi Beta Kappa); trips to the theater; dinners at taverns; games and recreation, including a card game called "Loo," cribbage, backgammon, bowling, playing ball, fishing, skating and going for sleigh rides; gathering, and sometimes taking from others' gardens, food (most often plums, peaches, nuts and apples); what he ate (including one breakfast of three raw eggs and two glasses of wine); what he read (including Tristram Shandy and one of "Mrs. Ratcliffe's novels"); his friends, often mentioned by name; and academic work and formalities. In one entry he mentions the theft of several possessions from his room, and there are several entries about trips to Fresh Pond.

Letters from Timothy Pickering to his brother and father, 1797-1798

These two handwritten letters by Timothy Pickering were written on February 14, 1797 and June 14, 1798 to his brother John Pickering and his father Timothy Pickering, respectively. The letter to his brother, John, discusses mutual friends, classmate Thomas Lee, and John’s recent attendance at a sermon by Dr. Joseph Priestley. The letter from Timothy to his father includes a discussion of Timothy’s expenses and the amount of money needed to pay his debts, a request for new shoes for commencement, the news of Timothy’s invitation to join honor society Phi Beta Kappa, and a few comments on his forensics course at Harvard.

The first iron-clad naval engagement in the world : history of facts of the great naval battle between the Merrimac-Virginia, C.S.N. and the Ericsson Monitor, U.S.N., Hampton Roads, March 8 and 9 1862 /

Mode of access: Internet.

Rise der oesterreichischen fregatte Novara um die erde, in den jahren 1857, 1858, 1859, unter den befehlen des commodore B. von Wüllerstorf-Urbair.

Only first part of Botanischer theil and of Medizinischer theil published.

Expériences auxquelles ont été soumis, en 1835, a bord de la fregate la Dryade : divers objets relatifs a l'artillerie.

Contains publisher's advertising.

Impresiones del viaje de circunnavegación en la fragata blindada Numancia.

"Manuscrito presentado por el Capitán de Fragata de Ingenieros ...en el que se ha consignado la relación histórico-descriptiva de la campaña de la fragata Numancia alrededor del mundo" cf. p.[v].

Life in a man-of-war, or Scenes in "Old Ironsides" during her cruise in the Pacific.

Mode of access: Internet.

Accident on steam-ship "Princeton"... Report [of] the Committee on naval affairs, to whom were referred certain communications from the War and Navy Departments on the subject of large wrought-iron guns...

May 15, 1844. Read, and laid upon the table, and 2,000 extra copies ordered printed.

Constitution and Guerriere. Challenge of Captain Dacres [of the Guerriere. Official letters of Captains Hull and Dacres.

"Extract from the log book of an officer on the Guerriere".

Papers relating to America. Presented to the House of commons, 1809.

Papers relating to the encounter between His Majesty's ship Leopard, and the American frigate Chesapeake.--Correspondence between Mr. Secretary Canning and Mr. Pinkney, from September 23, to November 28, 1808.--Instructions to the Honourable D. M. Erskine, by Mr. Secretary Canning; and the correspondence between the Honourable D. M. Erskine, and the Honourable Robert Smith.

The Monitor and the Merrimac; both sides of the story,

Mode of access: Internet.