Aerodinamika nosive konstrukcije ovješenog mosta u uvjetima leđenja

Marušić, Ante (2014) Aerodinamika nosive konstrukcije ovješenog mosta u uvjetima leđenja. = Aerodynamic behavior of bridge cables in icing conditions. Master's thesis (Bologna) , Sveučilište u Zagrebu, Fakultet strojarstva i brodogradnje, UNSPECIFIED. Mentor: Kozmar, Hrvoje.

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Abstract (Croatian)

Efekti vjetra više od bilo kojeg okolišnog utjecaja uzrokuju štetu na građevinama. Među svim inženjerskim konstrukcijama, dugački i vitki mostovi su se pokazali kao najosjetljiviji prema utjecajima vjetra, naprezanjima i vibracijama koje on može uzrokovati. Iako se općenito smatraju relativno stabilnim pri izlaganju atmosferskom vjetru i turbulenciji, ovješeni mostovi su posebno osjetljivi zbog svojih dugačkih i fleksibilnih kabela. Prethodno su indentificirani brojni mehanizmi pobude koji uzrokuju različite tipove vibracija kabela, no posebne poteškoće zadaje stvaranje uvjeta kiše iz pridode, te generiranje leda na kablovima. Oba navedena fenomena značajno mijenjaju aerodinamičke karakteristike kablova, budući da dolazi do promjene hrapavosti površine, a i same promjene oblika presjeka. U ovom radu su proučene aerodinamičke karakteristike kablova na mostovima u uvjetima zaleđivanja. Provedeno je opširno eksperimentalno istraživanje fenomena utjecaja vjetra na kablove s ledenim pokrovom. Generiranje leda u uvjetima ledene kiše provedeno je u klimatskom zračnom tunelu. Dobivene forme leda su korištene za dobivanje digitalnog 3D modela, nakon čega se pomoću tehnologije 3D printanja dobio skalirani model kabla s ledenim pokrovom. Model je zatim testiran u aerodinamičkoj sekciji zračnog tunela, gdje su provedeni eksperimenti aerodinamičkog i aeroelastičnog odziva, vizualizacija strujanja oko kabla, mjerenja sila uslijed utjecaja vjetra, te mjerenja fokusirana na fenomen gallopinga prema Den Hartogovom modelu. Za snimanje vrtloženja zraka uslijed utjecaja kabla korištene su vruće žice konstantne temperature. Postignuti eksperimentalni rezultati pružaju nove i zanimljive podatke o aerodinamici kabela ovješenih mostova u uvjetima leđenja.

Abstract

Past few decades were influenced by a significant development in structural engineering with particular emphasis on tall buildings and long-span bridges. This development only intensified some problems which were present even in much smaller bridges, one of them for sure being wind influence. Based on available data, wind effects on structures create damage considerably larger than any other environmental influence. Of all engineering structures, long and slender bridges proved to be perhaps the most sensitive to the wind-induced structural load and fatigue. Although overall considered to be relatively stable when exposed to atmospheric wind and turbulence, cable-stayed bridges are particularly sensitive with respect to the long and flexible cables. In the past, numerous excitation mechanisms were identified causing different types of cable vibrations, whereas a particular difficulty is in creating water rivulets during the rain and ice accretion on bridge cables. Both phenomena considerably change cable aerodynamics due to altered surface roughness and cross section of the cables. The scope of this thesis is on aerodynamic behavior and oscillation characteristics of bridge cables in icing conditions. A comprehensive experimental study of wind effects on cables with ice coatings was carried out. As the existing literature on this topic is very sparse, it was important to dedicate attention to the whole process, from ice accretion to cable response and vibrations. Ice accretion in freezing-rain conditions was simulated in a climatic wind-tunnel. Obtained ice forms were used to produce digital 3D models, and thereafter the scaled sectional models of the cable were printed on a 3D printer. These models were consequently used for testing in an aerodynamic section of the wind tunnel Aerodynamic and aeroelastic tests encompassed the flow visualization, wind force measurements on the in-house developed force balance, and the measurements focused on galloping according to Den Hartog model and vortex-shedding. The vortex shedding was recorded with the constant temperature anemometry probes. The experimental results indicate some new and interesting features as compared to the data available in the literature.

Item Type: Thesis (Master's thesis (Bologna))
Uncontrolled Keywords: Ovješeni mostovi; stvaranje leda na kabelima; vibracije kabela; vjetrom uzrokovane vibracije; otkidanje vrtloga
Keywords (Croatian): Cable-stayed bridges; ice accretion on cables; cable oscillations; wind-induced vibrations; galloping; vortex shedding; wind-tunnel experiments
Date Deposited: 22 Sep 2014 18:00
Last Modified: 16 Oct 2015 12:47
URI: http://repozitorij.fsb.hr/id/eprint/2800

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