Vortex-Induced Vibration Current Tank Tests of Two Equal Diameter Cylinders Offset From Tandem

Two equal diameter ABS cylinders, offset from tandem, were subjected to uniform and sheared flows in a current tank at subcritical Reynolds numbers. Both tubes were filled with a saltwater solution to produce a specific gravity of 1.38. An accelerometer in each cylinder was used to measure the vortex-induced vibration response, which primarily varied between the third and seventh transverse bending modes. The cylinders were spaced at 3 to 20 diameters in the in-line direction and at 0, 0.5, and 1.0 diameter in the offset direction. Test results indicate that a downstream cylinder, for a pure tandem (no offset) configuration, experiences less vibration than the upstream cylinder when the upstream cylinder rms displacement is larger than about 0.35D. Offsets of 0.5 and 1.0 times the outside diameter produce lower vibration of the downstream cylinder relative to that of the upstream cylinder.