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Twenty-First Symposium on NAVAL HYDRODYNAMICS
disturbances are dominant (as in model as well as prototype scales) over the body-generated disturbances.
The definition of the upstream effect does not need repetition. It is a well-known fact that there are stratification-excited mechanisms (solitons, nonlinear waves), which lead to significantly larger signal-amplitude to up-stream-distance ratios above the threshold noise level. The end-wall reflections have nothing to do with the issue because the upstream effect under unsteady circumstances (impulsive starts, turns, dives, porpoising, etc.) manifests itself almost immediately after the passage of the bow and certainly long before the waves reach the end wall and return to the probe.
The discussor has incorrectly stated that the wakes collapse at Nt=7. What we have written is this, “As the model continues to move, RC decreases at first (when the probe is over the axisymmetric cylindrical part of the body) and then increases again sharply when the probe enters the wake and reaches a maximum at about Nt=2 (ΔNt=1 corresponds to Δt=6.67s or to about 50 body diameter for this particular case). ” Immediately afterwards, the wake begins to collapse. The wake collapse is virtually complete at about Nt=7, i.e., after about 47s or about 340 body diameters.”
As to the nature of the plots, the discussor did not read the paper carefully. They are not “ensemble averaged over several runs….” The plots are ensemble averages of the data obtained simultaneously during a single run with numerous probes positioned along the axis of the body. No two runs have ever been ensemble averaged. Our data have shown that the ensemble-average of n-number of probe signals resulting from a single run is indistinguishable from the individual probe data for that same run. As noted earlier (ΔC)max/N2D is not a meaningful parameter.
In summary, it appears that the discussor read the paper rather hastily. The topology of the wakes of towed bodies of such special geometries as right circular cylinders and spheres does not generalize to slender self-propelled bodies and to more general problems of the evolution of isolated turbulent patches in stratified fluids. Our work presents, for the first time, body geometries and measurements on both fundamental and applied levels. It is hoped that future studies in stratified flows will move toward high Re and F experiments with slender self-propelled bodies. After all, spheres and right circular cylinders do not make good submarines at any speed.
The comments of the discussor gave us the opportunity to expand on several topics of scientific and practical interest and are appreciated.