6/21/2015 2DPipelineBottomRoughness|MochammadImron

https://mochammadimron.wordpress.com/2014/01/29/2dpipelinebottomroughness/ 1/6

MochammadImronOceanengineeringstudent,15510017http://www.ocean.itb.ac.id

January29,2014

2DPipelineBottomRoughness

Leaveacomment

Now,ImstartingtouseenglishforwordsinmyblogbecauseIwanttoupgrademyenglishskillinwriting.hehehehe(Ihopenoneofyouwillbeconfusedwithmyword).Today,Iwanttoshareaboutonbottomroughness(OBR)analysis.Whatsisbottomroughness?Itsananalysistopredictthelocationofspanalongsubseapipelineafterinstallationorduringoperation.So,whatsthedifferentbetweenfreespananalysis?freespananalysisisonlydeterminethemaximumallowablelengthofpipelinethatunsupportedwhenlaidonseabed.ThecriteriaofallowablespanisdividedintoVIV(VortexInducedVibration)andULS(UltimateLimitStateorStaticCriteria).Whybottomroughnessanalysisissoimportant?Withoutbottomroughnessanalysisyoudontknowhowmanysupport(sandbag,groutbag,etc)thatyouneedtorectifyofoverspan.However,itsonlyprediction,soyouneedfurtherinspectiontoensurethelocationofoverspan.

(http://dyurindatama.files.wordpress.com/2013/02/picture4.png)

2DOBRanalysisisverysimple,youcanuseanyFEAsoftweresuchasABAQUS,ANSYS,etc..Forthisnote,IusedABAQUSFEAasmnyOBRsimulator.Thepipelinecanbemodelledusing1Delement(PIPE31H)andtheseabedcanbemodeledusinganlayticalrigidofsurface.ThecommonstepthatusedforBottomRoughnessisadoptedfromSubseaPipelines&Riserbook(2005,YongBai&QiangBai)

6/21/2015 2DPipelineBottomRoughness|MochammadImron

https://mochammadimron.wordpress.com/2014/01/29/2dpipelinebottomroughness/ 2/6

(http://dyurindatama.files.wordpress.com/2013/02/picture5.png)

AfterODBfileisproducedfromyourABAQUSFEAmachine,forthenextstepyouneedtoextractCOORD1(coordinateofpipelineKP),COORD3(waterdepthofyourBottomofPipe[BOP]),andCPRESS(ContactpressureasindicatoronlytomakesureeachnodeofpipelineBOPistouchingseabedornot).YoucanusepythonfileorextractmanuallyusingAbaqusViewer.

1. OpenyourODBfile(doubleclickyouODBfileoropenusingAbaqusViewer).Ontheleftsideyouwillseethetreeand2Xclickthestepyouwanttoextract.

2. CreatePath.Onthemenubar,pleaseclickTools>Path>Createandyoutypeyourpathname,clickOKthenyouwillfaceEditNodeListPathandpleasefillNodeLabelsyouwanttoextractthevalue,forexample1:7399(itmeansnode1tonode7399).

3. CreateXYData.ClickTools>XYData>Manager.Pleaseseepicturebelowforeasyexplanation.EachofyourXYdatashallbecopiedinMicrosoftExcel.Pleasecheckanybug/errorwithyouroutputresult.

6/21/2015 2DPipelineBottomRoughness|MochammadImron

https://mochammadimron.wordpress.com/2014/01/29/2dpipelinebottomroughness/ 3/6

(http://dyurindatama.files.wordpress.com/2013/02/picture11.png)

Beforeyoutryprocessfurtherwithyourexcelspreadsheet,youmustinterpolateyourwaterdepthofseabed(thathasbeeninputedinabaqus)againstyourCOORD1data(coordinateofpipelineKP),thenyouwillgetnewwaterdepthofseabedwithsameKPwithyourCOORD1data.DivideyourExcelspreadsheetinto2Sheets.

Inthesheetno.1youneedtosetyoursheetasasamplebelow.Youwillseeanynumberspanstart&spanendalongthepipeline.Pleasemakesureduringpipelineembedded(negativevalueofspangap)thereareanyvalueofCPRESSandviceverse.Themaximumgapvaluealongpipelinemustbeinputtedintoallowablefreespananalysis(onset/screening/fatiguecriteriaasperDNVRPF105)

6/21/2015 2DPipelineBottomRoughness|MochammadImron

https://mochammadimron.wordpress.com/2014/01/29/2dpipelinebottomroughness/ 4/6

(http://dyurindatama.files.wordpress.com/2013/02/picture1.png)

Afterthat,youhavetosort&filtereachspanstart&spanend,thencopythisKPintosheetno.2asapicturebelow.Fromeachthisformulayouwillgettheoverspanresults.PleasenoticethatthisscreeningwillusedmaximumgapvaluealongKPstartandKPend.TheminimumspangapvaluethatinfluenceVIV,is30%OD(Ref:OTCNo.4455,1983,TheInfluenceofBoundaryLayerVelocityGradientsandBedProximityOnVortexSheddingfromFreeSpanningPipeline).Somepeopleused20%OD(Ref:SumerandFredsoe,1989,HydrodynamiccsaroundCylindricalStructures)asconservatismresult

6/21/2015 2DPipelineBottomRoughness|MochammadImron

https://mochammadimron.wordpress.com/2014/01/29/2dpipelinebottomroughness/ 5/6

(http://dyurindatama.files.wordpress.com/2013/02/picture2.png)

Theanalysishasnotoveryet.First,youneedtocheckwithcentrethirdofpipelinecriteria.Iftheaveragecenterthirdofpipelinebelowallowablegapvalue,youcanignoredthisoverspanifitiscausedbyVIVonly(notULS/Staticcriteria).Butif,youwantgettheconservatismresult,youcanconsiderthisspanisoverspan(Butitwillaffectyourspanrectificationcost).Second,youneedtochecktheupliftpossibility(orlooklikeupheaval)inyourABAQUSFEAmodel.Itshouldbenothappenedbecausetheweightofpipelineandwave/currentwillforcedthisupliftsectiontodroponseabedaslateralbuckling.So,ifyouroverspanisoccurinthisupliftsection,pleaseignoreitasaspan,butyoumustchecktheintegrityofthissection(UsingLoadcontrolledCheck&DisplacementControlCheckasperDNVF101).Third,youneedtoreassessedagaineachoverspansectionwitheachgapvalueandrecalculateagaininallowablefreespanassessment,soyouwillgetnewallowablespanthatlongerthanbefore.

Your2DBottomRoughnessAnalysisisendfromhere.Butifyouwant,youcandoreanalysis(startformsheet1)withinteractivityphenomenon[duringVIV,yourspaniswillinducedvibrationwithitsneighborspan,somakethiseffectivelengthislongerthanisolatedspan].AsperDNVRPF105,youcandeterminedeachspanisakindofisolatedorinteractingspanasadiagrambelow.

6/21/2015 2DPipelineBottomRoughness|MochammadImron

https://mochammadimron.wordpress.com/2014/01/29/2dpipelinebottomroughness/ 6/6

(http://dyurindatama.files.wordpress.com/2013/02/picture3.png)

reference:

http://dyurindatama.wordpress.com/2013/02/10/2dpipelinebottomroughness/(http://dyurindatama.wordpress.com/2013/02/10/2dpipelinebottomroughness/)

PostedbymochammadimroninPersonal

CreateafreewebsiteorblogatWordPress.com.|TheSplendioTheme.

Follow

FollowMochammadImron

BuildawebsitewithWordPress.com

About these ads(http://wordpress.com/about-these-ads/)