Nonlinear wave loads on a vertical cylinder     

Zeki Demirbilek  Jonathan D. Gaston 《Ocean Engineering》1985,12(5):375-385

Nonlinear contributions due to elevation of the free surface, the dynamic head, and the second-order velocity potential on the wave loads are presented in closed-form expressions. Such nonlinearities resulting from large-amplitude ocean waves are associated with the irrotational flow interacting with a fixed bottom-mounted vertical cylinder piercing the surface. These are expressed in the form of dynamic, waterline and quadratic forces all of which depend on the square of the wave amplitude. The appropriate modifications are made to both the classical Morison equation and the well-known linear diffraction theory of MacCamy and Fuchs for accounting the second-order effects.A limited comparative study is performed to verify the present theoretical derivations. In general, satisfactory agreements have been obtained with the test results from various laboratory studies by different researchers. However, under certain environmental conditions, some discrepancies still exist with the measured results.  相似文献   

Fluid-controlled crustal metasomatism within a high-pressure subducted mélange (Mt. Hochwart, Eastern Italian Alps)     

Simone Tumiati  Gaston Godard  Silvana Martin  Urs Kltzli  Damiano Monticelli 《Lithos》2007,94(1-4):148-167

The Nonsberg–Ultental Region of northern Italy contains a Palaeozoic mélange that was partially subducted during the Variscan orogeny. This mélange is constituted mainly by metapelites characterized by shale-type REE-patterns, displaying partial melting which began under high-pressure conditions. The resulting migmatites enclose minor slivers of mantle-wedge peridotites that have been incorporated into the mélange during subduction. Peridotites display important large ion lithophile elements (LILE) enrichment consequent to amphibole recrystallization contemporaneously with metapelite migmatization at P ≈ 2.7 GPa and T ≈ 850 °C in the garnet–peridotite field. Crustal and mantle (ultramafic) rocks of the mélange display the same Sm–Nd ages of about 330 ± 6 Ma, which dates both the metamorphic peak and the migmatization event. The zircon U–Pb age of the metasomatic amphibolitic contact between garnet peridotite and migmatite is identical (333.3 ± 2.4 Ma) within analytical errors. Therefore, metasomatism, migmatization and peak metamorphism are constrained to the same event. The presence of Cl-rich apatite and ferrokinoshitalite in the contact amphibolite, together with the trace-element patterns of peridotites, suggest that metasomatism was driven by Cl- and LILE-rich fluids derived from ocean water transported into the subduction zone by sediments and crustal rocks. These fluids interacted with the crust, prompting partial melting under water oversaturated conditions and partitioning LILE from the crust itself. Peridotites, which were well below their wet solidus temperature, could not melt but they recrystallized in the crustal mélange under garnet-facies conditions. Crustal fluids caused extensive hydration and LILE-enrichment in peridotites and severe Sm–Nd isotope disequilibrium between minerals, especially in the recrystallized peridotites. The proposed scenario suggests massive entrapment of crustal aqueous fluids at high-pressure conditions within subduction zones.  相似文献   

Book reviews     

Edward Proffitt  Gary R. Gaston  Gary R. Gaston  Michael Healey 《Estuaries and Coasts》1995,18(1):315-317

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The magnetotelluric phase over 2-D structures     

Gaston Fischer  L. Szarka  A. Adam  J. T. Weaver 《Geophysical Journal International》1992,108(3):778-786

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Announcement Internatioal Society for Diatom Research and Nederlands-Vlaamse Kring van Diatomisten     

Gaston Mialaret  Gilbert Landsheere  Dieter Mahr  Marcel Postic  A. Harry Passow  et al. 《Journal of Paleolimnology》1991,6(2):171-172

Announcement Internatioal Society for Diatom Research and Nederlands-Vlaamse Kring van Diatomisten  相似文献   

A strong topographic valley effect in AMT and VLF-R measurements     

Gaston Fischer 《Geophysical Journal International》1989,96(3):469-475

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Magnetotelluric observational techniques on land     

Gaston Fischer 《Surveys in Geophysics》1982,4(4):373-393

During the period since the Workshops in Sopron and Murnau we have witnessed some quite remarkable changes in the techniques employed in magnetotelluric (MT) observations. These changes have brought about significant improvements in the quality of MT data that can be gathered today. The new techniques are very likely to bring improvements in many areas beside MT, but are reviewed here in the light of the progress they have rendered possible for MT soundings on land. Three main subjects are covered in this review. The first one is concerned with the use of cryogenic or SQUID magnetometers. The new instruments are presented to the geomagnetist. An explanation of how these instruments work is given without, however, details of their operation and fabrication, and without showing that they usually have a much larger, i.e. better, signal-to-noise ratio than conventional magnetometers. Next, the method of the remote magnetic reference is examined. Originally the MT method assumed incident signals in the form of plane waves. While it is known today that incident wave amplitudes which vary linearly with distance are perfectly acceptable for MT soundings, there are many other higher order distortions of the incident signal which are not acceptable. Most of these high order or local perturbations are man-made and can seriously falsify MT data. All processes of MT data analysis try to minimize the errors caused by locally perturbed signals. But they are only partly successful, especially when the perturbations produce strong cross-power bias. The remote magnetic reference method has proved far superior in avoiding most of this cross-power as well as faulty autopower. The last section of this review deals with the use in the field of microcomputers or microprocessors. These have made it possible to process the data on the site already to such a degree that the sounding crew knows whether the sounding is proceeding satisfactorily, and can decide how best to continue the survey work. Of particular interest is digital filtering, which is especially easy with the microcomputer, and which may be used to avoid specific sources of perturbation.  相似文献