Anexpertsystemforpredictingaerationperformance

AnexpertsystemforpredictingaerationperformanceofweirsbyusingANFISAhmetBaylara,*,DavutHanbayb,EmrahOzpolataaFiratUniversity,CivilEngineeringDepartment,Elazig,TurkeybFiratUniversity,ElectronicandComputerScienceDepartment,Elazig,TurkeyAbstractAfreeoverfalljetfromaweirplungingintodownstreamwatercausesentrainmentoftheairbubblesifthefreeoverfalljetvelocityexceedsacertaincriticalvalueandhenceaerationoccurs.Thisstudyinvestigatesthefreeoverfalljetsfromtriangularsharp-crestedweirsandeffectontheirairentrainmentrateandtheaerationefficiency.Anexpertsystembasedonadaptivenetworkbasedfuzzyinferencesystem(ANFIS)wasobtainedforpredictingairentrainmentrateandaerationefficiencyofweirs.TheperformanceofANFISmodelwascomparedwithmultinonlinearandlinearregressionmodels.ThereweregoodagreementsbetweenthemeasuredvaluesandthevaluesobtainedusingtheANFISmodel.2007ElsevierLtd.Allrightsreserved.Keywords:ANFIS;Aerationefficiency;Airentrainmentrate;Weir1.IntroductionInanaturalsetting,oxygenisaddedtowaterbyatmo-sphericdiffusionatthesurface,bywindcirculationandbyphotosynthesis.Photosynthesisaccountsformostoftheoxygeninwater.Theoxygencontentofwaterincreaseswithincreasingatmosphericpressureanddecreasingtem-peratureandsalinity.Theamountofoxygeninwaterismeasuredasmilligramsperliterdissolvedoxygen.Oxygenisanaturalcleanser.Itisthekeyingredientforqualitywater.Thelevelofdissolvedoxygenisoneofthebestindicatorsofoverallwaterquality.Oxygenisaneces-saryelementtoallformsoflife.Adequateoxygenlevelsarenecessarytoprovideforaerobiclifeformswhichcarryonnaturalstreampurificationprocesses.Asdissolvedoxygenlevelsinwaterdropbelow5.0mg/L,aquaticlifeisputunderstress.Thelowertheconcentration,thegreaterthestress.Oxygenlevelsthatremainbelow1–2mg/Lforafewhourscanresultinlargefishkills.Totaldissolvedoxy-genconcentrationsinwatershouldnotexceed110%.Con-centrationsabovethislevelcanbeharmfultoaquaticlife.Hydraulicstructuresincreasetheamountofdissolvedoxygeninariversystem,eventhoughthewaterisincon-tactwiththestructureforonlyashorttime.Thesamequantityofoxygentransferthatnormallywouldoccuroverseveralkilometersinarivercanoccuratasinglehydraulicstructure.Theprimaryreasonforthisacceler-atedoxygentransferisthatairisentrainedintotheflowintheformofalargenumberofbubbles.Theseairbubblesgreatlyincreasethesurfaceareaavailableformasstransfer.Thephysicalprocessofoxygentransferoroxygenabsorp-tionfromtheatmosphereactstoreplenishtheusedoxygen.Thisprocesshasbeentermedre-aerationoraeration.Aerationperformanceofhydraulicstructureshasbeenstudiedexperimentallybyanumberofinvestigators.ThesestudiesarereviewedbyWilhelms,Gulliver,andParkhill(1992),Chanson(1995),Ervine(1998),andGulliver,Wilhelms,andParkhill(1998).Recently,BaylarandBaga-tur(2000,2001a,2001b,2006),Baylar,Bagatur,andTuna(2001a,2001b),Baylar(2002,2003),BaylarandEmiroglu(2002,inpress),andEmirogluandBaylar(2003a,2003b,2005)investigatedweirshavingdifferentcross-sectional0957-4174/$-seefrontmatter2007ElsevierLtd.Allrightsreserved.doi:10.1016/j.eswa.2007.08.019*Correspondingauthor.Tel.:[phone];fax:[phone].E-mailaddress:abaylar@firat.edu.tr(A.Baylar).(2008)1214–1222ExpertSystemswithApplicationsgeometryanddemonstratedthattheairentrainmentrateandtheaerationefficiencyofweirschangeddependingonweirshapes.Neuralnetworkandadaptivenetworkbasedfuzzyinfer-encesystem(ANFIS)arewidelyusedinvariousareasofwater-relatedresearches(ASCE,2000;Kisi,2004a,2004b;Hanbay,Turkoglu,&Demir,2006a,Hanbay,Turkoglu,&Demir,2006b,2007;Abolpour,Javan,&Karamouz,2007;Baylar,Hanbay,&Ozpolat,2007).Inthispaper,ANFISmodelwasdevelopedtodetermineairentrainmentrateandaerationefficiencyoftriangularsharp-crestedweirs.2.AirentrainmentmechanismsbyweirsErvine,McKeogh,andElsawy(1980)statedthatplung-ingjetflowsentrainairintothereceivingpoolwhentheimpactvelocityofthejetexceedsacriticalvalue.Theinceptionvelocityforaturbulentwaterjetiscommonlyobservedtobeabout1m/s,butisaffectedbythesizeofdisturbancesonthesurfaceofthejet.Ervineetal.(1980)suggestedfourmechanismsforairentrainmentdependingoncircularwaterjetturbulence.Tsang(1987)adaptedthesetothecurrentobservationsofoverfalljetsfromnor-malandparallelweirs.Tsang(1987)classifiedmechanismsofairentrainmentassmooth,rough,oscillatinganddisin-tegrated.Adescriptionofthesestagesisgiveninthefollowing.2.1.Smooth,solidjetsThemajorsourceofairsupplyisvisualizedasathinlayersurroundingthejetandcarriedintothewateruponimpact,andthereforeairentrainmentcapacityislimited.Thewatersurfaceinthereceivingpoolisrelativelyundis-turbed(seeFig.1a).2.2.Rough,solidjetsTheairsupplycanbeconsideredascominglargelyfromsmallairpocketsentrappedbetweenthejetsurfacerough-nessandthereceivingwater.Atimpact,thejetproducesripplesonthepoolsurface.ComparedtotheTypeAmech-anismundersimilarconditions,thisresultsinshallowerbubblepenetrationdepthbutincreasedentrainmentrate,becausethebubblesaremoredenselypackedinthebipha-siczone(seeFig.1b).2.3.OscillatingjetsandthoseapproachingdisintegrationTheprimaryairsourceorigina