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Research Papers

Underwater Implosion of Cylindrical Metal Tubes

[+] Author and Article Information
Stephen E. Turner

e-mail: Stephen.e.turner1@navy.mil

Joseph M. Ambrico

e-mail: Joseph.ambrico@navy.mil
Naval Undersea Warfare Center
1176 Howell Street
Bldg 990, Code 4121
Newport, RI 02841

Manuscript received September 13, 2011; final manuscript received May 25, 2012; accepted manuscript posted June 7, 2012; published online October 29, 2012. Assoc. Editor: John Lambros.

This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States. Approved for public release; distribution is unlimited.

J. Appl. Mech 80(1), 011013 (Oct 29, 2012) (11 pages) Paper No: JAM-11-1333; doi: 10.1115/1.4006944 History: Received September 13, 2011; Revised May 25, 2012; Accepted June 07, 2012

The basic physics of the underwater implosion of metal tubes is studied using small scale experiments and finite element simulations. A series of underwater implosion experiments have been conducted with thin-wall 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 failed with a mode 2 shape (collapsed shape is flat 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 fluid-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.

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Figures

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Fig. 1

Test stand shown with mechanical initiator

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Fig. 2

Sensor locations for all test

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Fig. 3

Collapsed shape of the cylinder from test 1. Note: the other tests are similar.

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Fig. 4

Total pressure at the cylinder ends (sensors 1 and 3) and at the middle (sensor 2) in test 1

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Fig. 5

Comparison of the pressure from tests 1 and 2 measured at the cylinder middle (sensor 2)

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Fig. 6

Comparison of the pressure from tests 3 and 4 measured at the cylinder middle (sensor 2)

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Fig. 7

Structure model from the coupled DYSMAS simulation of the aluminum cylinder implosion experiments

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Fig. 8

Material model fit for 6061-T6 aluminum extruded tube test data [14]

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Fig. 9

Fluid model from the coupled DYSMAS simulation of the aluminum cylinder implosion experiments showing the boundary conditions on the grid

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Fig. 10

Comparison of the final collapsed shape from the experiment and from the DYSMAS analysis for test 1. Note that the DYSMAS model has been reflected three times.

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Fig. 11

Pressure time-histories at the cylinder center (sensor 2) for tests 1 and 2 compared with DYSMAS simulation

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Fig. 12

Pressure time-histories at the cylinder center (sensor 2) for tests 3 and 4 compared with the DYSMAS simulation

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Fig. 13

Pressure contours from the DYSMAS simulation showing the cylinder during the collapse phase, prior to contact (2000–10,000 kPa contour range)

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Fig. 14

Pressure contours from the DYSMAS simulation showing the first point of contact reached at center of cylinder (2000–10,000 kPa contour range)

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Fig. 15

Pressure contours from the DYSMAS simulation when contact reaches the edge of the cylinder in the transverse (Y) direction (2000–20,000 kPa contour range)

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Fig. 16

Pressure contours from the DYSMAS simulation showing the collapse moving along cylinder axis toward end (2000–20,000 kPa contour range)

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Fig. 17

Pressure contours from the DYSMAS simulation showing the collapse reaching cylinder end (2000–20,000 kPa contour range)

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Fig. 18

Pressure time histories from the DYSMAS simulation of tests 1 and 2 at the cylinder center at various standoff distances from the (undeformed) surface of the tube (standoff distances indicated as multiples of the tube radius)

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Fig. 19

Results from the simulation of tests 1 and 2 for the decay rate of the positive peak implosion pressure with standoff distance from the (undeformed) tube surface, at the center of the cylinder it two directions

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