1、第21卷第4期2006年8月实验力学JOURNALOFEXPERIMENTALMECHANICSVol/21No/4Aug/2006文章编号/100124888(2006)0420439208ADynamicLoadingDeviceforSuctionFoundationsinCentrifugeModeling3WANGShu2yun1/ZHANGJian2hong2/LUXiao2bing331/JIAOBin2tian1(1/InstituteofMechanics/ChinaAcademyofScience/Beijing100080/China；2/DepartmentofHydr
2、aulicEngineering/TsinghuaUniversity/Beijing100084/China)Abstract/Suctionbucketfoundationsarewidelyusedintheoffshoreplatformfortheexploitationoftheoffshorepetroleumandnaturalgasresources/Duringwinterseasons/icesheetsformedinBohaiBaywillimposestrongimpactandresultinstrongvibrationontheplatform/Thispap
3、erdescribesadynamicloadingdevicedevelopedonthegeotechnicalcentrifugeanditsapplicationinmodelingsuctionbucketfoundationundertheequivalentice2inducedvibrationloadings/Someexperimentalresultsarepresented/Itisshownthatwhentheloadingamplitudeisoveracriticalvalue/thesandattheupperpartaroundthebucketsoften
4、sorevenliquefies/Theexcessporepressuredecreasesfromtheupperparttothelowerpartofthesandfoundationinverticaldirectionwhiledecreasesfromneartofarawayfromthebucketssidewallinthehorizontaldirection/Largesettlementsofthebucketandthesandaroundthebucketoccurunderthehorizontaldynamicloading/Thedynamicrespons
5、esofthebucketwithsmallersizeareheavier/Keywords/suctionbucketfoundation；dynamicloadingdevice；ice2inducedvibration；centrifugemodeling0IntroductionInrecentyears/suctionbucketfoundationshavebeenappliedincreasinglyofteninoffshoreengineering(Clukeyetal1/1995；Allersmaetal2/3/1997/2000)/Thefirstadvantageof
6、suctionbucketfoundationsareattractivebecauseoftheconvenientmethodofinstallationandrepeatedlyuse/Foranexample/asuctionbucketfoundationwithadiameterof9mandaheightof10mcanbeinstalledin13hours/byusingonlyapump/Thesecondadvantageisthatitmaymobilizeasignificantamountofpassivesuctionduringuplift/Despitesev
7、eralstudiesontheinstallationandstaticbearingcapacityhavebeencarriedout/thedetailresponsesofsuctionbucketfoundationsunderdynamicloadingshaveremainedunknown(Senpereetal4/1982；Aasetal5/1992；Dymeetal6/1998)/Thedynamicloadingconditionissignificantwhensuctionbucketsareusedasthefoundationofaplatform/Wavelo
8、adingandice2induceddynamicloadingcausethefoundationtobesubjectedtocyclicloadings(Tjeltaetal7/1990；Byeetal8/1995)/Thelackofexperiencesundertheseloading333收稿日期/2005208224；修订日期/2006207210基金项目/ThisprogramissupportedbythefundofChineseOceanOilCo/andChineseAcademyofSciencesKJCX22SW2L03201(40025103)andNatio
9、nalNaturalScienceFund(No/10202024)通讯作者/鲁晓兵(1968-)/男/博士/现在中科院力学所从事岩土力学研究。E2mail/conditionsledtoaproposalforatestprogramintendedtogainadeeperunderstanding/Theconsiderableexpenseandtimeconsumingnatureofprototypetestsmeanthattheinvestigationofthebearingcapacityofrealscaledevicesunderdifferentcircumstanc
10、esisoflimitedpracticality/Itismucheasiertochangeparametersinsmallscaletests/Butproblemsariseconcerningthestress2dependentbehaviorofsoilthatthemeasuredloadingsaresolowthatmeasurementsarenotsufficientlyaccuratetovisualizedifferencesindesign/Theserestrictionscanbeovercomeifperformingthetestsinageotechn
11、icalcentrifuge/Inacentrifugethesoilstressesoverasimilardeptharethesameasintheprototypesituation/Foranexample/at100g(100timestheEarthsgravity)/asuctionfoundationwithadiameter9mandaheightof9mmaybesimulatedwithafoundationwithadiameterof0/09mandaheightof0/09m/Thescalingfactoroftheprototypetothemodelis10
12、01/Theice2induceddynamicloadingisthecontrollingloadinginBohaiBayinChina/Thistypeofhorizontaldynamicloadingistranslatedtothesoillayerbyplatformandcausestheparameters/e/g/strengthandmodulusofthesoillayer/todegrade/Asaresult/thebearingcapacityofbucketfoundationsdecreases/Therefore/itisimportantandneces
13、sarytoclarifythedynamicbehaviorofbucketfoundationsunderthistypeofloadingsinordertoprovidepracticaldesignmethodandparameters(Dingetal9/2003；Luetal10/2003)/Inthispaper/wefirstintroducedasetofdynamicloadingdevicesdesignedforsimulatingthehorizontaldynamicloadings/Thensomeexperimentalresultsoftheice2indu
14、cedcyclicbehaviorofsuctionbucketfoundationsarepresented/Theeffectsoftheloadingamplitude/thesizeofthebucketandthestructuralweightaremainlyinvestigated/Fig/1Theelectro2magneticactuator1DynamicloadingdeviceThedynamicloadingdeviceiscomposedprimarilyofanelectro2magneticactuatorasshowninFig/1/Thisactuator
15、consistsofapermanentmagnet/acylindricalsilvercoil/twocopperdisksprings/aloadcellandasteelrodconnectedtothecoil/Therearetwomaintechnicalchallengesassociatedwiththedesignoftheactuator/(1)Thecylindricalcoilissuspendedinaprefabricatedspaceinthepermanentmagnet/Thespaceisverytinyinordertoavoidmagneticloss
16、/However/sincethiscylindricalcoilmoveshorizontally/itisorthogonaltothegravitationalforce/thedeformationofthecoilunderthisgravitymaylockitinthistinyspace/Inordertoavoidthissituationalinearbearingandtwodiskspringsareinstalledtomakethecoilmovelinearlywithoutbeinglocked/Thistechniquehasbeendemonstratedt
17、obeveryeffective/(2)Theweightofthecoilshouldbeminimizedtoincreaseitsdeformationinthedirectionofloading/Silverwireisusedtoformthecylindricalcoilsoastoenhancetheperformanceandlimittheweightwithin0/5kg/Thetotalweight044实验力学(2006年)第21卷ofthedeviceis14kg/Consequently/thevibrationofthe0/5kgcoilwouldnotimpo
18、sesignificantimpactonthestrongboxwhoseweightis150kg/Thecoilmovesbackandforthtoapplycyclicloadingonthemodelbucketthrougharigidrod/Fig/2isthecontrollingsystemfortheloadingdevice/Theloadingfunctionisfedfromacomputersignalgeneratorintoaservoamplifier/Thelatterinturngeneratesthenecessaryelectricalsignals
19、tocontroltheintensityofelectriccurrentintheactuator/Theoutputfromtheactuatorintheformofloadingiscontinuouslymonitoredbytheloadingcellandfedbackthroughachargedamplifiertotheoscillograph/Outputsignalfromporepressuretransducer(PPT)andlinearvariabledisplacementtransformers(LVDT)werepassedacrossthecentri
20、fugeslip2ringandconvertedtodigitaldata/Withthisdevice/differentamplitudesandthefrequenciesofhorizontalcyclicforcesarereproducedatcentrifugalaccelerationof80g/Therefore/thescalingfactoroftheloadfrequencyoftheprototypetothemodelis180/andthescalingfactoroftheloadamplitudeoftheprototypetothemodelis64001
21、/Inthecentrifuge/thepeakcyclicloadingof100Nand64Hzrepresentsaprototypeloadingof640KNand0/8Hz/Table1showsthetechnicalspecificationsofthisactuator/Theforce2electricityrelationat80gisshowninFig/3/Tab/1TechnicalspecificationoftheelectromagneticactuatorDiameter(mm)Length(mm)Weight(kg)Frequencyrange(Hz)Pe
22、akcyclicload(N)1802601411201002CentrifugesystemconfigurationFig/4showstheconfigurationofthecentrifugeandthemodel/Theinternalareaofthealuminumstrongboxmeasures600mm350mmandheightis350mm/Thethicknessofthesiltysandis210mm/underlainby20mmcoarsesandwhichistopreventthepipingduringpenetrationofwater/Therei
23、s20mmhighwaterabovethesoilsurface/Theactuatorissupportedbytwosteelbeamsfastenedontheflange/TworodsfixthebackoftheactuatoragainstthesideofthestrongboxasshowninFig/4/AminiatureTVcamerawasattachedtotheflangeofthemodelcontainertomonitorthemotionofthemodelbucket/Themodelbucketisasteelcylinderwhichhasanex
24、ternaldiameterof60mm/aninternaldiameterof56mm/andaheightof72mm/Thedeadweightoftheplatformwassimulatedbyaballastmountedonthetopoftheshaft/ThemovementofthebucketwasmonitoredbytwoLVDTs/Whenthecentrifugemodelistestedunder80g/itsbehaviorwouldprimarilycorrespondtothatofaprototypefootingwithadiameterof4/8m
25、/144第4期WANGShu2yunetal/ADynamicLoadingDeviceforSuctionFoundationsinCentrifugeModelingFig/4Thelayoutofthemodel3PreparationoftheexperimentsTheexperimentsareperformedinthe50g2tonscentrifugeinTsinghuaUniversity/Themaximumofthecentrifugesaccelerationis200g/Thepayloadis250kgunder200g/Theexperimentalmateri
26、alisfinesandwhosespecialgravityis2/69andtheaveragegrainsdiameteris0/14mm/Thepermeabilityis510-3mm/s/Threemodelbucketsmadebysteelareusedinexperiments/Theinnerdepths(donotincludethetopcapthickness)are48mm/72mmand90mm/respectively/theinnerdiametersareall60mm/thethicknessesofthewallandthetopcapareboth2m
27、m/Afinepipewithanouterdiameterof10mm/aninnerdiameterof8mmandaheightof100mmisweldedatthecenterofthetopcap/Aslidinggroovepermittingaballmovingupanddowntoadaptthesettlementofthebucketisconnectedwiththepipeclosely/Oneendofasteelpoleisjointedwithaball/theotherendofthepoleisconnectedwiththeelectromagnetic
28、vibrationactuator/Thusthepolecannotbedraggedwhenthebucketsettles/OneLVDTislocatedatthetopofthefinepipetomeasuretheverticaldisplacement/OneLVDTislocatedatthefinepipeatthesamelevelasthatofthesteelpoletomeasurethehorizontaldisplacement/TheothertwoLVDTsarelocatedonthesandsurfacetomeasurethesettlementsof
29、thesandsurfaceatdifferentpositions/TenPPTsmadeinDruckCo/(English)/areburiedinthesandaroundandinthebucket(Fig/5)/ThePPTsarenotfixedbutsuspendedinthesand/Inordertoguaranteetherepeatability/210mmthickmodelsandlayerisdividedintofivelayerstocreateandbecompactedgentlybyhandstriking/Thiscourseiscontrolledb
30、ydrydensity/Thewaterdepthoverthesandsurfaceis1cm/Afterthedrysandsamplehasbeenprepared/thesandlayerissaturatedbypenetratingwaterintofromthebottomofthetankthroughavulva/A20mmthickcoarsesandlayerisdepositedatthebottomofthetanktoguaranteethewaterriseuniformlyandpreventingthepiping/Whenthewaterlevelisove
31、rthesandsurface/avacuumpumpisusedtopumpthegasinthesandfor38hourstoincreasethesaturation/TwotypesofPPTlayoutareadoptedinthetests/Thefirsttype/onerowPPTsaredisposedinthesandalongdepthattheactuatorsideand2mmawayfromthebucketssidewall/Theupperoneis20mmbelowthesandsurface/Theothershavea20mmdistanceonebyo
32、nefromtheuppertothelowest/Tworowsaredisposedinthesandattheoppositeside/Onerowis2mmawayfromthebucketswallandtheotherrowis52mmawayfromthebucketswall/Thesecondtype/tworowsareboth2mmawayfromthebucketssidewallontheoppositesideintheloadingdirection/ArowofPPTsaredisposedinthehorizontaldirection20mmbelowthesandsurface/ExceptforthePPTs244实验力学(2006年)第21卷
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