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An Investigation into the use of Strain Rosettes for the Measurement of Propagating Cyclic Strains

  • Vernon A. Squire (a1)

Abstract

An investigation into the feasibility of using a strain rosette to measure the principal strains and to locate the principal axes for a propagating strain wave is carried out for the particular application of a flexural-gravity wave in sea ice. It is found that the separation of the instruments in the rosette is extremely critical and, for a physically realizable rosette, errors are unavoidable if strain is to be monitored continuously. An alternative approach is proposed employing frequency-domain analysis and in particular a running-power spectral density. The method is demonstrated with data obtained from strainmeters on fast ice in Notre Dame Bay, Newfoundland. Two distinct wave components are found to be present of period 6 s and 13s. and it is shown with 99.9% confidence that they are propagating in different directions.

Résumé

On a conduit une recherche sur la faisabilité de l'utilisation d'une rosette de déformation pour mesurer les principales déformations et pour situer les directions principales d'un tracé d'ondes en mouvement, dans le cas particulier d'une onde de flexion-gravité dans une glace de mer. On trouve que la séparation des instruments dans la rosette est extrêmement délicate et que, pour une rosette physiquement réalisable, les erreurs sont inévitables s'il est nécessaire d'afficher la déformation en continu. On propose une solution de rechange en employant l'analyse du domaine de fréquences et en particulier de la densité spectrale. On a essayé la méthode avec des données obtenues par des capteurs de déformation sur la glace fixée dans Notre Dame Bay, Newfoundland. Deux ondes composantes distinctes ont été trouvées de périodes 6s et 13 s et l'on montre avec une confiance de 99,9% qu'elles se propagent dans des directions différentes.

Zusammenfassung

Für die spezielle Anwendung auf eine schwerkraftinduzierte Biegungswelle in Meereis wurde eine Untersuchung liber die Zweckmàssigkeit des Gebrauchs von Spannungsrosetten zur Messung der Hauptspannungen und zur Lokalisierung der Hauptaehsen einer fortschreitenden Spannungswelle angestelll, Es ergibt sieh, dass der ràumlicher Abstand der Messinstrumente in der Rosette ausserordentliche Bedcutung besitzt und dass in physikalisch realisierbaren Rosrtten unvermeidliche Messfehler auftreten, wenn die Spannung kontinuierlich aufgezeichnet werden soil. Es wird deshalb ein anderes Verfahren vorgeschlagen, das die Frequenzbereichsanalyse und besonders die fortlaufende spektrale Wirkungsdichte heranzieht.' Dtesc Méthode wird anhand von Daten vorgefuhrl, die von Dehnungsmessern auf dem Festeis in der Notre-Dame-Bay von Neufundland stammen. Es lassen sich zwei verschiedene Wellenkoniponenten mit Perioden von 6 s und 13 s feststellen und es wird mit einer Zuverlâssigkeit von 99,9% gezeigt, dass sie sich in verschie-denen Richtungen fortpflanzen.

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Copyright

References

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Allan, A. J., and Squirt, V. A., In press. Naturally induced surfacestrain in fast ice. C-CORE Publication (Memorial University of Newfoundland. Centre for Cold Ocean Resources Engineering).
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An Investigation into the use of Strain Rosettes for the Measurement of Propagating Cyclic Strains

  • Vernon A. Squire (a1)

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