Underwater Implosion of Cylindrical Metal Tubes

Abstract

The basic physics of the underwater implosion of metal tubes is studied using small scale experiments and finite element simulations. A series of under-water implosion experimentshave been conducted with thin-wail aluminum alloy 6061-T6 tubes. The nominal tube dimensions are 2.54 cm outside diameter and 30.48 cm length. Two cylinders collapsed at their natural buckling pressure of 6895 kPa gauge pressure (1000 psig). Two additional cylinders were caused to implode at 6205 kPa gauge pressure (900 psig) using an initiator mechanism. Each of the four cylinders faiied with a mode 2 shape (collapsed shape is fiat with two lobes). The near field pressure time-history in the water is measured at a radial distance of 10.16 cm (4in.)from the centerline at three points along the cylinder's length. The pressure time-histories show very similar behavior between the cylinders which buckled naturally and those which were mechanically initiated at 90% of the buckling pressure. To aid in understanding the physical implosion phenomena, a computational model is developed with a fiuid-structure-interaction finite element code (DYSMAS). This model is validated against the experimental data, and it is used to explain the features of the implosion pressure pulse and how it is physically created.

Study of dynamic underwater implosion mechanics using digital image correlation

“…The DIC results at this instant show that the contact has spread along the major diameter of the specimen at the centre and approximately 30% of the length of the specimen has made wall contact. Such large peaks have been observed previously by several researchers [1][2][3]8]. Turner & Ambrico [3] observed through numerical simulations that this large pressure spike occurs around the time when the width at the centre of the implodable volume exhibits contact, similar to the experimental results shown here.…”

“…As u(t) is zero at the start of the implosion process (t = T − ) and must vanish at the end of implosion (t = T + ), it implies (from equation (3.2)) that Thus, as long as the waves generated in implosion can be approximated as spherical (similar to the conclusion of Turner & Ambrico [3]), …”

“…The plot Thus, the highest pressure spike is the result of a sudden increase in the contact area growth rate, causing the largest change in momentum of water against the wall, eventually leading to the highest pressure spike. Turner & Ambrico [3] suggested that the highest pressure spike corresponds to the time when collapse in the implodable volume extends to the complete width at the centre. Since both the highest rate of increase in contact area and also the extension of collapse along the width in cylindrical tubes occur at the same time, both arguments can explain the occurrence of the highest pressure.…”

“…This process, which is known as 'implosion', has been of interest in the area of underwater acoustics because such implosions can be used as an alternative to underwater explosions (UNDEX), which are commonly used as an underwater sound source [1,2]. However, there are situations in which an implosion is undesirable as the pressure wave generated during the implosion can damage adjacent structures or initiate implosion of adjacent enclosed shells [3][4][5]. The implosion of several photo-multiplier tubes (PMTs) initiated by accidental implosion of a single PMT in the Super-Kamiokande neutrino laboratory in Japan in 2001 sparked a renewed interest in studying the pressure waves generated by an underwater implosion [6].…”

The implosion of cylindrical shell structures in a high-pressure water environment

“…Ambrico & Turner [14] investigated the pressure waves resulting from the underwater implosion of models created from aluminium cylinders. The models imploded in mode 2.…”