A master thesis from Aalborg University
Regn\vind inducerede vibrationer af skåstags-kabler
[Rain\wind induced vibrations of stay cables]
Author(s)
Term
4. term
Education
Publication year
2009
Submitted on
2009-06-16
Pages
58 pages
Abstract
Rain/wind induced vibrations for the most severe natural load on cables used as support will be examined. The theory behind rain/wind induced vibrations on stay-cables will be outlined, based on the present available literature. A numerical quasi-static multi degree of freedom model of a stay cable is developed and a load model is established to implement the rain/wind induced aeroelastic loading on the cable. Four different types of damping mechanisms are considered for mitigation of the rain/wind induced vibrations. Active control of the axial forces by an actuator at the lower cable support point is initially considered. The control in the remaining three types is based on a perpendicular connection between the damping mechanism and the cable, at a constant distance away from the lower cable support point. Here, passive viscous damping is introduced where the damping coefficient is tuned to the first in-plane cable mode of vibration. Semi-active MR-damping is introduced with the objective to reduce the vibration response from passive viscous control. Finally, active control by use of the pole placement method is analysed. Furthermore, the active control by pole placement is supported by integral control in order to remove a static offset of the cable displacement from the applied mean wind. Special attention is brought to evaluate the relative effectiveness of the considered damping mechanisms. Practical considerations, general theory, and control algorithms with regard to the mentioned control strategies are handled.
Regn/vind-inducerede vibrationer for de mest alvorlige naturbaserede belastninger på kabler vil blive undersøgt. Teorien bag regn/vind-inducerede vibrationer på skråstags-kabler vil blive skitseret, baseret på den foreliggende tilgængelige litteratur. En numerisk kvasistatisk multifrihedsgrads model for et skråstags-kabel er udviklet og en lastmodel er oprettet for at simulere regn/vind inducerede aeroelastiske belastninger på kablet. Fire forskellige typer af dæmpningsmekanismer analyseres for dæmpning af regn/vind inducerede vibrationer. Aktiv kontrol med aksiale kræfter ved en aktuator i den lavere kabel understøtning, er i første omgang undersøgt. Kontrol i de resterende tre typer er baseret på en vinkelret forbindelsen mellem dæmper mekanismen og kablet, ved en konstant afstand fra den nederste kabelunderstøtning. Her er passiv viskos dæmpning indført hvor dæmpnings koefficienten er indstillet til den første svingningsform for kablet, i dets eget plan. Semi-aktiv MR-dæmpning er indført med det formål at reducere vibrationer i forhold til passiv viskos kontrol. Endelig er aktiv kontrol ved brug af pol allokerings metoden analyseret. Desuden er den aktive kontrol med pol allokering understøttet af integral kontrol for at fjerne en statisk flytning af kablet forårsaget af den statiske vindlast. Særlig opmærksomhed er tillagt vurderingen af den relative effektivitet af de betragtede dæmpnings mekanismer. Praktiske overvejelser, generelle teorier og kontrol algoritmer med henvisning til de nævnte kontrol strategier er håndteret.
Keywords
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