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VIV measurements

A self-recording triaxial accelerometer (94 mm diameter and 760 mm length) powered by internal lithium batteries and with a 2 GB SD memory card was attached to the 5½ inch drill pipes at the bottom of the assembly and near the sea surface through the attachment tool before running into the hole (Fig. F2). The accelerometer measures acceleration in three axes (x, y, and z) at a sampling rate of 250 Hz, where the z-axis corresponds to the downward direction of the drill pipe (Fig. F2). A special frame was designed to secure the accelerometer to the drill pipe, with a copper sheet set between the attachment blocks and the drill pipe to prevent slipping or rotation during deployment. Self-locking nuts were used to prevent the bolts from loosening because of vibration.

During Expedition 332, acceleration measurements were recorded to monitor VIV on the drill pipe during the SmartPlug recovery at IODP Site C0010 and the LTBMS installation at IODP Site C0002 (Kopf et al., 2010). The BHA was made up and run in the hole while the Chikyu was in the low-current area (LCA) (current < ~1.5 kt), upstream and northwest (~30 miles away) of Site C0010. Two accelerometers were attached to the drill pipe (Fig. F3) while running the BHA into the water; one was attached just above the BHA and the other was attached near the sea surface. After the completion string was lowered to 1700 m drilling depth below rig floor (DRF), drifting to the target site began at a speed of ~1 kt (Fig. F4). Acceleration data were collected during the entire operation and downloaded when the instruments were recovered on deck.