Axial-flow-inducedvibrationforarodsupportedbytranslationalspringsatbothendsOriginalResearchArticle

Anaxial-flow-inducedvibrationmodelwasproposedforarodsupportedbytwotranslationalspringsatbothendsinordertoevaluatethesensitivitytospringstiffnessontheFIVforaPWRfuelrod.Fordevelopingthemodel,aone-modeapproximationwasmadebasedontheassumptionthatthefirstmodewasdominantinvibrationbehaviorofthesinglespanrod.Thefirstnaturalfrequencyandmodeshapefunctionsfortheflow-inducedvibration,calledtheFIV,modelwerederivedbyusingLagrangeʹsmethod.Thevibrationdisplacementswerecalculatedbybothofthespring-supportedrodandthesimple-supported(SS)one.Asaresult,thevibrationdisplacementforthespring-supported(50kNm−1)rodwas15–20%largerthanthatoftheSSrodwhentherodsareinaxialflowof5–8ms−1velocity.Thediscrepancybetweenbothdisplacementsbecamemuchlargerasflowvelocityincreased,andthatoftherodhavingtheshortspanlengthwaslargerthanthatoftherodhavingthelongspanlengthalthoughthedisplacementvalueitselfofthelongspanrodwaslargerthanthatoftheshortone.Thevibrationdisplacementforthespring-supportedrodappearedtodecreasewiththeincreaseofthespringconstant.Sincesinglespanbeamsupportedbythetwotranslationalspringsarefocusedoninthispaper,furtherstudywillbeneededtoreflectmorerealisticsupportingconditionsofthePWRfuelrodsuchastwospringsandfourdimplesandcrossorswirlingflowcausedbythemixingvaneofthespacergrid.