Wind Pressure Distribution,Wind-induced Buckling,and Sloshing Behavior Of Large Steel Cylindrical Floating-roof Tanks

To meet the rising demand for enormous oil storage,large cylindrical steel tanks have been extensively developed in recent decades,generally with external floating roofs.The structure is featured by small height-diameter ratios and large diameter-thickness ratios,hence the lateral stiffness of the shell is weak.The floating roof is attached to the shell by sealing devices,which could be damaged by excessive local pressures or deformations.In hazards such as hurricanes,tropical cyclones,and earthquakes,damage to practical oil tanks with floating roofs has been widely documented,with or without contained liquid,leading to huge financial and environmental losses.The damage occurs mainly on the shell and sealing devices around the floating roof,resulting from extreme wind loads or sloshing of contained liquid.Thus,it is of tremendous practical value to evaluate wind loads,wind-induced buckling,and sloshing of large external floating roof tanks with varied liquid levels.In relevant literature,external wind loads of isolated tanks have been explicitly stated,while internal wind loads or group effects are rarely examined.Wind-induced buckling analyses have been performed mostly on empty tanks,using wind loads from design codes.The change of liquid levels and wind loads is usually ignored.As for sloshing,most study has been undertaken on tanks with relatively large height-diameter ratios or rigid walls,and the change of liquid levels is rarely considered.In this dissertation,4 typical practical large floating roof cylindrical tanks are taken as research objects.Methods such as wind tunnel test(WTT),computational fluid dynamics(CFD),finite element analysis(FEA),and shaking table test are conducted to explore wind loads,wind-induced buckling,and sloshing in diverse situations.Results of the dissertation can provide reference to the design and risk assessment of tanks.This dissertation consists of 3 parts,which are presented as follows.Considering 3 floating roof tanks with respective volumes of 50000 m~3,125000m~3,and 150000 m~3,118 cases of WTT and 62 cases of CFD are performed to get internal wind pressures on the shell of tanks with varying liquid levels,and to validate the possibility of utilizing CFD in research of this sort.Besides,nonlinear static FEAs are conducted to obtain the change of critical static loads of shells with liquid levels,adopting internal wind loads from WTT and Eurocode.The influence of change of internal wind loads is discussed,and advice for sustained liquid levels under extreme wind conditions are given.In addition,based on pressure time history data from WTT,nonlinear dynamic FEAs are conducted to obtain critical dynamic wind loads of 3empty tank shells.Effects of fluctuating wind loads are discussed correspondingly.Considering the square-arrangement tank group consisting of 4 identical floating roof tanks with a volume of 100000 m~3,234 cases of WTT and 62 cases of CFD are performed to get external wind pressures on empty and full tank groups under various wind angles and spacing.The influence of wind stiffening rings on the vertical distribution of external wind loads and the viability of employing CFD in research of this kind are examined.Effects of wind angles and spacing are investigated by observing streamlines from CFD.External wind pressure distributions that may threaten structural safety are recognized.Besides,nonlinear FEAs are conducted,adopting external wind loads from grouped tanks(that may threaten the structural safety),the isolated tank,and Eurocode.The influence of grouping effects on the wind resistance of shells is discussed.Considering the floating roof tank with a volume of 50000 m~3,60 cases of shaking table tests are conducted under various excitations and liquid levels.Responses such as sloshing heights,dynamic liquid pressures on the shell,tank wall vibration,and deformation are obtained.Effects of periods and amplitudes of excitations,roof conditions,and liquid levels are discussed.Besides,3 numerical models are established,comprising a scaled rigid model,a full-scale rigid model,and a full-scale soft model.Numerical analyses utilizing the Coupled Eulerian-Lagrangian method are undertaken to obtain the sloshing of the contained liquid.The reliability of both experimental and numerical method is confirmed.Meanwhile,the effect of wall flexibility is discussed.