2673 KB47 KB199920252014Popplewell, NeilShah, Arvind H.Stoyko, Darryl K.številka:5letnik:60str. 349-362, SI 66ISSN:0039-2480COBISSID:13449755URN:URN:NBN:SI:doc-RX5PM8VJenZveza strojnih inženirjev in tehnikov Slovenije et al.Strojniški vestnikcevifrekvenca odrezasingularnostultrazvočni valovizarezeReflection and transmission coefficients from rectangular notches in pipes|The use of a single, non-dispersive ultrasonic guided wave mode is one important approach to monitoring a structure's health. It is advantageously non-destructive with the ability of propagating over tens of metres to detect a hidden defect. The dimensional assessment of a defect, on the other hand, requires reflection coefficients for two or more such modes. Multiple modes may be excited simultaneously by applying a short pulse to a structure%s external surface. This situation is examined here for a circular, hollow and homogeneous, isotropic pipe having negligible damping and an open rectangular notch. A finite element model is employed in a region around a notch. It is coupled to a wave function expansion in the two adjacent, effectively, semi-infinite pipes. Representative longitudinal and flexural modes are investigated for different notch dimensions. A nonaxisymmetric notch, unlike an axisymmetric notch, introduces a plethora of cross modal couplings that lead to more singularities in a reflection coefficient's frequency dependence. There is, however, a common pattern to these distinctive singularities. It is conjectured that singularities corresponding to propagating modes may enable a notch to be detected and its dimensions determinedUporaba posamezne, nerazpršene lastne oblike ultrazvočnega vala predstavlja pomemben pristop pri spremljanju razvoja poškodb v strukturi. Bistveno prednost tega pristopa k neporušnemu testiranju predstavlja zmožnost zaznave poškodb na razdaljah več deset metrov. Za določitev lokacije poškodbe je potrebno pridobiti koeficiente odboja za dve ali več lastnih oblik. Sočasno vzbujanje večih lastnih oblik se izvede s kratkim udarnim impulzom na zunanjo površino strukture. Opisan način je v članku uporabljen na primeru votle okrogle cevi iz homogenega in izotropnega materiala z zanemarljivim dušenjem ter odprto pravokotno zarezo. V območju zareze je uporabljen model končnih elementov, ki je sklopljen z razširitvijo valovne funkcije v dveh sosednjih polneskončnih cevehTEXTznanstveno časopisjejournalsSlovenian National E-content AggregatorNational and University Library of SloveniaUniverza v Ljubljani, Fakulteta za strojništvo