Regn\vind inducerede vibrationer af skåstags-kabler
Translated title
Rain\wind induced vibrations of stay cables
Authors
Gadegaard, Claus ; Jensen, Jesper
Term
4. term
Education
Publication year
2009
Pages
58
Abstract
Vi undersøger regn/vind-inducerede vibrationer, som er blandt de mest alvorlige naturbaserede belastninger på kabler. Teorien bag regn/vind-inducerede vibrationer på skråstagskabel skitseres med udgangspunkt i den tilgængelige litteratur. Vi udvikler en numerisk, kvasistatisk multifrihedsgradsmodel af et skråstagskabel samt en lastmodel, der simulerer regn/vind-inducerede aeroelastiske belastninger. Vi analyserer fire måder at dæmpe (reducere) vibrationer på: 1) Aktiv kontrol med aksiale kræfter via en aktuator ved den nederste kabelunderstøtning. 2) Tre løsninger med en vinkelret forbindelse mellem dæmper og kabel i en fast afstand fra den nederste understøtning: passiv viskos dæmpning, hvor koefficienten tunes til kablets første svingningsform i eget plan; semi-aktiv MR-dæmpning (magnetorheologisk), der kan justere modstanden for at opnå bedre reduktion end passiv kontrol; samt aktiv kontrol ved brug af polallokering (pole placement). Den aktive polallokeringskontrol suppleres med integral kontrol for at fjerne statisk forskydning forårsaget af statisk vindlast. Særlig opmærksomhed gives til at vurdere den relative effektivitet af de betragtede mekanismer, og vi behandler praktiske forhold, grundlæggende teori og kontrolalgoritmer for disse strategier.
We investigate rain/wind-induced vibrations, which are among the most severe natural loads on cables. The theory of rain/wind-induced vibrations on a stay cable is outlined based on available literature. We develop a numerical, quasi-static multi-degree-of-freedom model of a stay cable and a load model to simulate rain/wind-induced aeroelastic loading. We analyze four ways to damp (reduce) vibrations: 1) Active control using axial forces applied by an actuator at the lower cable support. 2) Three solutions with a damper connected perpendicularly to the cable at a fixed distance from the lower support: passive viscous damping, with the coefficient tuned to the cable’s first in-plane mode; semi-active MR damping (magnetorheological), which can adjust resistance to achieve better reduction than passive control; and active control using the pole-placement method. The active pole-placement control is supplemented with integral control to remove static displacement caused by static wind load. Special attention is paid to assessing the relative effectiveness of the considered mechanisms, and we address practical aspects, general theory, and the control algorithms for these strategies.
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Keywords