Test 14
Free heave response of axisymmetric bodies with a round base.
By Peter K. Stansby (University of Manchester, UK), Efrain Carpintero Moreno (Ghent
(Download full test case data files here: SPHERIC_TestCase14.zip)
Introduction
Radiation damping is an important component
determining the response of floating bodies. Drag also causes damping and
cannot be separated. Radiation damping force may be estimated from a linear
radiation coefficient from a standard panel method, e.g. WAMIT, and the
remainder may be assumed to be due to drag, enabling an estimate of drag
coefficient which may be compared with reference below (Gu et al. 2018). In the
experiment without any external constraint the motion provides a clean data set
for validation of numerical models.
Flow phenomena
Radiation damping, drag, free response,
axisymmetric bodies, hemispherical/rounded base.
Geometry
Axisymmetric floats, dimensions in metres.

Boundary
conditions
The body surface is smooth aluminium.
Initial
conditions
The water is stationary initially and body is
released from rest, above or below water. The zero vertical level is when a
stationary body is floating in still water.
Discretisation
The sample rate is 200 Hz. The displacement was obtained from a Qualisys motion capture system.
Results specification
The results simply show vertical displacement
(mm) variation with time (s). They are shown in Figs.1, 2, 3 in section
Benchmark Results. The error bars show range of values across tests and the
line shows the mean values.
Results format
Three txt files with column 1 = time (s), column 2 = mean vertical displacement (mm) with sample rate of 200 Hz are:
Float 1 offset -0.074 m : “Fl1-0p074.txt”
Float 1 offset +0.076 m : “Fl2+0p076.txt”
Float 2 offset-0.088 m : "Fl2-0p088.txt"
Benchmark results
Benchmark results showing mean and error bars

Fig. 1 Displacement (mm) time history of Float 1, initial offset -74 mm (mean of 2 tests).

Fig. 2 Displacement (mm) time history of Float 1, initial offset +76 mm (one test).

Fig. 3 Displacement (mm) time history of Float 2, initial offset -88 mm (mean of 3 tests).
SPH Publications
using this Case
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References
- Gu,H., Stansby,P.,
Stallard,T., Carpintero Moreno,E. 2018 Drag, added mass and radiation damping
of oscillating vertical cylindrical bodies in heave and surge in still water,
J. Fluids Struct, 82, 343-356. doi.org/10.1016/j.jfluidstructs.2018.06.012.