It happened about 10 years ago. At the beginning of autumn in 1984, an alarming report was received from a new one-propeller Soviet VICTOR m class attack nuclear submarine which operated in the Pacific Ocean. The commanding officer reported that the submarine could not keep a certain depth when she was sailing underwater. On zero angle of the big horizontal stem planes the submarine was surfacing. To keep a depth she had to have a balancing angle of these planes of 8-9 degrees dive. Control of the submarine by her small stem horizontal planes, as it took place usually on high speeds, was completely impossible because of their insufficient effectiveness with zero angle of big stem horizontal planes.
It was known that approximately three years before an analogous phenomenon was observed on a submarine of this class. The efforts of specialists which studied it then had been directed to discover any possible hull form and appendage deviations from blueprints. But putting this submarine in a floating dock did not provide measurable results because the floating dock caved in. The cause of the phenomenon had not been cleared up.
After the submarine left the dock, balancing angles had become normal. The question had disappeared. An enigma stayed …
And now it was an analogous picture: big balancing angles of big stern horizontal planes. The fleet called the submarine distorted and she had been removed from regular service and fleet exercises.
To clarify the problem a special group of experts, with participation of the author of this article, had been established which directed tests of the submarine’s maneuverability by determination of balancing parameters.
After providing neutral buoyancy and careful trimming without speed, the running of the submarine was analyzed in the range of speeds from 2 to 27 knots in the depths which eliminated any influence of the surface and the bottom. The submarine was controlled either manually or automatically by big stem horizontal planes. The planes’ position was recorded every 10 seconds during 3 minutes of settled horizontal run, both from sensors of the automatic control systems and mechanical indicators of big stem horizontal planes’ deflections. Furthermore, by means of a diver after sea trials, correspondence of planes’ positions and mechanical indicators had been checked. The inspection of the underwater part of the submarine by divers did not show any damage or deviations of the hull’s form and appendage shapes.
As a result, the sea trials established that an inherent submarine trim moment can be compensated only by deflection of big stem horizontal planes to 8-11 degrees of dive at all the speeds, or by pumping water from stem trim tank to bow trim tanks, providing dynamic trim of about 0 .5 degrees. So the sea tests only defined more exactly the big stem horizontal planes’ angles but they did not establish their cause. An enigma of the distorted submarine remained. Her normal service was impossible.
The commission concluded that the submarine had hydrodynamic asymmetry of the flow round her hull and appendages and recommended that the sub be measured once more, this time in a drydock. Some commission members assumed that distortion of the submarine had reached more than three feet on the whole of her length.
At the end of 1984 the submarine was put in such a dock. For measuring and analyzing the situation the most experienced experts were invited. The results of their measurements did not show any deviations from blueprints. What to do? To launch the submarine? And maybe it would happen again? The cause had not been determined! Why on high speeds does a sinking force up to 100 tons press on the stem?
In the process of discussing that problem, the author of this article proposed that the force appeared through differences in flow around the upper and lower surfaces of the stem horizontal stabilizers and planes. They are attached to the hull wings with an axis-symmetrical profile, they are trapezoidal in the horizontal planes with areas of 25 square meters on each side including horizontal planes.
He suggested that difference of the flow was stipulated by presence only on upper surfaces of acorn-like, horny-like (with sharp edges) foulage, with heights of 8-10 millimeters in amounts of 10-15 per square decimeter, and above them covered by green, soft slime-like seaweeds.
He also suggested that this roughness braked current on the upper surface, and he framed a hypothesis that in accordance with the well known Bernoulli’s principle:
ρ v2/2 + p = const
(where v – speed and p – pressure) an increase in the speed of a fluid produces a decrease of pressure and a decrease in the speed produces an increase in pressure, the teduction of flow speed on the upper surface in comparison with the lower surface led to a big sinking force which resulted in unacceptable balancing angles.
But such an explanation did not get support from hydrodynamics. Because it was known in aerobydromechanics that increased roughness increases only force of resistance but does not induce an additional force directed normally toward the rough surface.
In the light of the fact that nobody suggested an alternative explanation, it was decided to clean the upper side of the stern horizontal surfaces from foulage. It was done in the drydock.
The following sea tests confirmed correctness of that decision: the balancing angles and trims of the submarine became normal.
So was discovered the enigma of the so-called distorted submarine. By the way, she distorted for a very simple reason: the upper surface of her horizontal planes and stabilizers had been painted, mistakenly, not by non-foutage but by usual paint. The similar situation took place on the previous submarine three years before.
Because of a defect in shipbuilding technology the author by chance was able to discover a new effect in aerohydromecbanics.
It was negative for a submarine, but if to provide an increased roughness, for example, on the lower surface of a plane, it could be used for getting of additional lifting force.
Subsequent tests in the aerodynamics tubes of the Central Shipbuilding Krylov’s Institute (Russia) of various planes with different roughness bad proved that. The first result had been published by the author in the magazine Soviet Physical Reoorts (1991, vol. 36(51), pp. 373-376) and other magazines and had been patented.
Further study of this phenomenon showed that in addition to the considered case, it can be used in hydrofoils and hovercraft&. A case happened when a hydrofoil could not run on her properly working foil because of a viscous thin coating of cellulose on the upper side of the plane. It is reasonable to take into account this effect relating to surface ships. Sometimes their hulls get uneven fouling and it leads to significant balancing angles of their rudders.
It is possible to use that phenomenon in technology purposeful-ly in designing of hydraulics, steam and gas turbines, propellers, turbopumps, ventilators, and torpedoes.
Even such candidates as cars and space shuttle ships can be considered: the first ones-for increasing of the force which can press them down improving stability; the last ones-for increasing of the lift force by means of more burning of their lower side (growing roughness) when they are entering into more dense layers of atmosphere.
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