Apparatus for reducing vibration on a ship

Details Apparatus for reducing vibration on a ship Apparatus for reducing vibration on a ship

1999-04-15

2001-02-20

Basinger, Sherman (Department: 3617)

Marine propulsion

Screw propeller

With vibration dampening

C440S001000

Reexamination Certificate

active

06190217

ABSTRACT:

The present invention relates to apparatus for reducing vibration on a ship provided with two drive shafts.
BACKGROUND OF THE INVENTION
Achieving acoustic silence is an important concern in marine vessels. For passenger ships the purpose is to improve passenger comfort, whereas for scientific ships or naval vessels, silence is an operating constraint.
It is therefore appropriate to reduce the acoustic vibration generated by water being compressed against the hull because of propeller rotation. This corresponds to the case where the ship is driven by at least two drive shafts each provided with a propeller.
It is thus known to fit each of the two shafts of a ship with an angular position encoder and to use these means to regulate the speed of rotation of the shafts so that they present an angular difference which is set to a constant reference value. This reference is the result of mechanical considerations concerning the interactions between the propellers, the water, and the hull, and these considerations are subject to a certain amount of inaccuracy. In addition, the interactions depend closely on the operating conditions of the ship. Amongst these conditions, mention can be made in particular of the power developed on a drive shaft, its speed of rotation, the burden of the ship, the speed at which it is advancing, and the temperature and the salinity of the water.
As a result, calculating such a reference value is very complex. Furthermore, the fact of adopting a reference value that is constant leads necessarily to a compromise, in other words the reference value is not always optimized for the operating conditions of the ship in any given situation.
OBJECTS AND SUMMARY OF THE INVENTION
Thus, an object of the present invention is to provide apparatus for reducing vibration which is not subject to the constraints or limitations mentioned above.
According to the invention, this apparatus as fitted to a ship provided with at least two drive shafts comprises means for servo-controlling the angular difference of the two shafts to a reference value; it further comprises calibration Means for finding an optimum angular offset between the shafts which corresponds to a vibration minimum, and control means for responding to a control signal to actuate in succession said calibration means and then said servo-control means, with said optimum angular offset being fixed as the reference value.
Thus, for given operating conditions and prior to performing conventional servo-control, a search is made for an optimum angular offset that leads to minimum vibration.
An advantageous application of the invention lies with drive shafts driven by electric motors. Under such circumstances, the apparatus comprises measurement means for deriving the angular difference from parameters concerning the power supplied to the motors.
That makes it possible to avoid using position encoders on the shafts.
In a first option, the optimum angular offset is detected by ear.
In a second option, the apparatus further includes a vibration sensor for detecting the optimum angular offset.
It is then possible to provide for the apparatus to comprise a regulation system for producing a regulation signal representative of variations in vibration level, the control means fixing this regulation signal as the reference value after fixing the optimum angular offset.
Preferably, the regulation signal represents the derivative of the fundamental level of the vibrations.
Whatever the embodiment adopted, a simple solution consists in opting for manual actuation of the control signal.
In addition, it is advantageous to design the apparatus in such a manner that the control signal is actuated following a modification to the operating conditions of the ship.
In particular, this modification may concern either the speed of rotation or else the power transmitted to one of the shafts


REFERENCES:
patent: 5049795 (1991-09-01), Moulds, III
patent: 5148402 (1992-09-01), Magliozzi et al.
patent: 5355732 (1994-10-01), Anderl et al.

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