Automatic Installation For The Transversal Balancing Of A Ship

Abstract

In an automatic installation for balancing a ship by means of the so-called "balanced tanks" method, the actual rate of flow of the liquid being transferred from either tank to the other is measured through the pressure differential between the two tanks. The differential between the "ordered" rate of flow and the actual rate of flow is computed by a comparison circuit. The instantaneous value of the differential rate of flow is used for adjusting the rate of flow of the variable delivery pump which is inserted in a conduit connecting the two tanks serially.

Description

This invention relates to an installation for the transversal balancing of a ship.

Antirolling stabilizing installations for ships are known, of the king comprising activated fins. In such installations, one or more the kind of fins jut out of the sides of the ship and, being more or less inclined with respect to the fluid fillets which impings of the ship as it goes on, impart to the ship a torque intended to counteract the heeling torque due to the sea waves.

The mechanical or electronic computer which controls the fins generally comprises sensing members for the angular motion, such as a bank indicator, a gyroscope and an angular accelerometer, which detect at every instant of time, the heeling of the ship. The computer sends to the fins a signal, as a function of the detected values, said signal being called an "ordered thrust" signal which is intended instantaneously to balance the motion of the ship. The command for a certain thrust, sent by the computer to the actuators, is translated into the rotation, through a certain angle, of the two fins, the left and the right, obviously in opposite directions so as to generate a torque for counteracting the rolling motion of the ship. These actuated fin installations, while are very satisfactory stabilizers at ship speeds near the cruising speed, or, in limiting conditions, up to 10 knots approximately, are inefficient when the ship is stationary or travels at a reduced speed.

Stabilizing installations are also known, which are called "balanced tank" installations, which provide for at least a couple of tanks situated on the same perpendicular to the longitudinal plane of symmetry of the ship and at equal distances therefrom (more particularly arranged on the ship sides), said tanks being filled with a liquid (preferably fresh water) which can be transferred from either tank to the other through at least one conduit equipped with pumping means adapted to transfer the liquid from either tank to the other at an instantaneous rate of flow which is determined by a signal, called"ordered rate of flow" signal, which is a function of the angle of tilt, of the speed of tilt and of the tilt acceleration of the ship with respect to the balanced position of the ship. This signal is obtained, again, by means of a bank indicator, a gyroscope, and an angular accelerometer and is The ordered rate of flow signal which actuates the pumping means (in practice a conventional variable delivery pump) so that they transfer the liquid from either tank to the other at such a rate as to counteract the tilting torque and to restore the ship to its balanced trim.

These "balanced tank" installations, while are unable, at high speeds, to replace the actuated fin installations due to the greater power they require (which entail higher running costs), are conversely very efficient when the speeds are low and when the ship is stationary, more particularly whenever it is desired to embark a line of railway cars which advance on a track placed laterally of the ship, in the case of ferries, or, anyhow, when embarking very heavy and unbalanced loads.

However, also in the case of such balanced tank installations, the stabilization when the ship is stationary or is caused to advance at a low speed, is not perfect, since it is not possible to provide a hydraulic, variable delivery pumping means which is adapted to give a sufficiently linear and repeatable law of variation, under any working conditions, of the actuated rate of flow versus the ordered rate of flow.

An object of the present invention is to provide a balanced tank stabilizing installation, particularly adapted to provide a balanced tank stabilizing installation, particularly adapted to provide a balancing action when embarking heavy loads on a stationary ship, which ensure an improved stabilizing effect by reducing the influence of the unavoidable errors of actuated rate of flow versus the ordered rate of flow on the stabilization.

The object of the invention is achieved by measuring the actuated rate of flow and converting it into a signal which is compared with the ordered rate of flow signal, the latter being in turn a function of the tilt angle, the speed and acceleration of the tilting motion, to originate a differential signal which is the control signal for the pumping means aforementioned. It is apparent that by so doing and rendering the transfer function from actuated rate of flow and ordered rate of flow, a function which is inverse with respect to that between the ordered rate of flow signal and the actuated rate of flow signal, there is a comparison between the signal relating to the ordered rate of flow and the signal related to the actuated rate of flow, said comparison having a tendency toward varying the control signal for the pumping means as a function of the variation of the actuated rate of flow, as originated by possible disturbances. On the other hand, the ship itself, together with the bank indicator, the gyroscope and the accelerometer, ensures the translation between the actuated rate of flow and the signal of unbalance, so that there are two feedback rings which ensure, as a whole, the stabilization, instant of time for instant of time, of the ship against the unbalances due to the embarkation of unbalancing loads and/or sea waves and against possible disturbances which would tend to render the law, which binds the actuated rate of flow to the ordered rate of flow, variable.

The features of the present invention will be better understood from the following detailed description of its general layout and of a preferred embodiment of the member which translates the actuated rate of flow into a comparison signal with the unbalance signal. Said description, which is given by way of example only and is not a limitation, reference will be had to the accompanying drawings, wherein:

FIG. 1 is a diagrammatical showing, in cross-sectional view, of a ship equipped with a balanced tank installation according to this invention.

FIG. 2 is a diagrammatical block showing of an installation according to the invention.

FIG. 3 is a diagrammatical showing of a preferred embodiment of the member which measures the actuated rate of flow and converts it into the ordered rate of flow signal.

FIG. 1 shows a ship, 1, subjected to a tilting torque due to a load 2 (such as a train during embarkation) applied laterally with respect to the plane of longitudinal vertical symmetry of the ship. To the sides of the ship, and on the same perpendicular to said plane of symmetry, are affixed two tanks 3 and 4 filled with fresh water and in mutual communication by means of a duct 5 which contains a pump 6 adapted to transfer variable rates of flow of water from either tank to the other.

It is apparent that, under such circumstances, by actuating the pump 6 so as to transfer thereby water from the tank 3, which lies at a level lower than that of the tank 4, a balancing torque is originated, which tends to balance the tilting torque due to the action of the load 2. By increasing the volume of water transferred through the duct 5, the balancing torque will be proportionally increased; so that, since the larger is the tilting torque, the larger the necessary balancing torque will be, the result is that the larger is the tilting torque, the greater should be the rate of flow through the duct 3 and thus the rate of flow of the pump 6 in order to transfer the necessary volume of water within a given time.

The stabilizing installation according to the invention has exactly the function of establishing a connection between the tilting torque and a pump-actuating signal so as to produce an increase of the rate of flow as the tilting torque is increased, and vice versa. Moreover, since it is virtually impossible, due to the presence of unavoidable disturbances, to obtain a constant and straightforward relationship between the rate of flow "ordered" to the pump and the rate of flow which is obtained in practice, the installation provides for a comparison between the ordered rate of flow and the actual rate of flow, the result giving the pump-actuating signal (or, better to speak, the signal for operating the pump actuator). By so doing, the influence of said disturbances of the operation of the pump are reduced by the introduction of the feedback effect.

The general block diagram of an installation according to the invention is shown in FIG. 2, where the general reference numeral 7 indicates a block which represents the ship as a whole: this block receives at its input a tilting torque C' and a balancing torque C" as determined by the actual rate of flow Q" through the duct 5, and gives, at its output, an angle of tilt .phi., an angular or tilt speed .phi. and an angular or tilt acceleration .phi.. More particularly, the block 7 can be thought as being split into an integrator 8, wherein the actual rate of flow Q" is integrated and converted into the balancing torque C", a differentiator 9, where the difference between the tilting torque C' and the balancing torque C' is computed, and a block 10 wherein the differential C is converted into an angle .phi., and angular speed .phi. and an angular acceleration .phi..

Past the block 7 there is a block 11, which can be called a "processor," where the outputs from the block 7 are converted into an electric signal f(Q') indicating the rate of flow Q' as ordered to the pump 6 to restore the ship to the desired trim. The block 11 comprises a bank indicator 12, which converts into an electric signal f (.phi.) the angle of tilt .phi. of the ship, a gyroscope 13, which converts into an electric signal f (.phi.) the speed of tilt of the ship, an angular accelerometer 14, which converts into an electric signal f (.phi.) the tilting acceleration .phi. of the ship, and lastly a mixer 15 which receives, as its inputs, said signals f (.phi.), f (.phi.) and f (.phi.) and converts them into a consolidated electric signal f ) which, as recalled above, indicates the ordered rate of flow Q'.

The processor 11 is followed, in turn, by a differentiator, 16, wherein the differential is computed between the electric signal f (Q') and another electric signal f (Q"): the latter is obtained, by translation, carried out in a transducer 17 having a transfer function which is inverse of that of the assembly formed by the pump 6, the pump actuator and the duct 5, of the actual rate of flow Q" as given by the pump 6. The electric signal E obtained by the difference between the above-mentioned signals f (Q') and f (Q") is applied to the input of a block 18 which represents the assembly composed by the pump 6 (indicated herein by a block 20), the pump actuator (indicated here at block 19) and the duct 5 (indicated herein by the block 21). The output from the block 18, which is a function of the features of the component parts of the block and the disturbances D connected therewith, represents the actual rate of flow Q" through the duct 5 which connects the balancing tanks 3 and 4.

The operation of the installation of FIG. 2 is as follows: as the ship undergoes a tilting torque, such as that due to an unbalancing load 2, as is the case in FIG. 1, it tends to heel on a side. The instantaneous values of the angle, the speed and the acceleration (signals .phi., .phi., .phi. emerging from the block 7 of FIG. 2) are sensed by the bank indicator 12, the gyroscope 13 and the angular accelerometer 14 included in the processor 11, whose outputs determine, at the output of the processor an electric signal f (Q') which represents the rate of flow ordered to the pump 6 to restore the ship's trim.

The signal f (Q') causes the actuator 19 to control the pump 6 so as to transfer the water from the lower level tank (tank 3 in the case of FIG. 1) to the higher level tank (tank 4 in the case of FIG. 1) through the duct 5 at a rate of flow which, in theory at least, should equal the ordered rate of flow Q'. The presence of the disturbances D, however, acts in such a way that the actual rate of flow through the duct 5 is Q", different from Q': as the disturbances D are continually variable, the law binding Q" to Q' is not always the same and the balancing action would not be quick and accurate, as it is desirable, if there would be no feedback as formed by the branch comprising the transducer 17. On the contrary, the transducer senses the actual rate of flow Q" and converts it into an electric signal f (Q") which is subtracted from the signal f (Q') to produce a signal E of the actuation error of the actuator 19 and thus of the pump 6. The presence of the feedback formed by the transducer 17, which has, as mentioned above, an inverse function of transfer with respect to that of the block 18 so as to render the signals f (Q') and f (Q") analog, tends to render linear and constant the relationship which binds the actual rate of flow to the ordered one.

The actual rate of flow Q", furthermore, is integrated by the integrator 8 comprised in the block 7 which represents the ship and the result of such an integration is a balancing torque C" which, subtracted from the tilting torque C' gives a resultant torque C: the latter determines the new angle of tilt of the ship and thus, as described above, the new ordered rate of flow. The equality between the torques C' and C" will indicate that the balancing has taken place and the ship has been restored to its normal trim.

As has been repeatedly outlined in the foregoing, the novelty of this invention with respect to the conventional balanced tank installations consists in the introduction of the feedback between the actuated rate of flow and the ordered rate of flow. The most characteristic block of the diagram of FIG. 2 is thus formed by the transducer 17 which converts the actuated rate of flow Q" into an electric signal f(Q") which is representative of it. Said transducer should thus include means for measuring the actuated rate of flow and means for converting the measured rate of flow into an electric signal. This rate of flow could be measured with a flowmeter introduced into the duct 5, but it would be an unacceptable mechanical resistance in that it would increase the delay of the whole system. In the installation according to the invention, the rate of flow is measured by deriving the level differential between the two tanks, a difference of level which is measured, in turn, by arranging on the bottom of the two tanks two pressure transducers and computing the differential between the outputs thereof.

FIG. 3 shows the diagram of a member which, from two pressure measurements, just derives an electric signal relating to the instantaneous rate of flow between the two tanks. The diagram comprises a DC differential amplifier 22 having a high gain and whose positive input is connected via a resistor 23 to an input terminal 24, the latter being connected to the output of the pressure transducer 65 applied to either tank of the ship, for example to tank 4, as diagrammatically shown in FIG. 1, whereas the negative input of the differential amplifier is connected, through a resistor 25 to an input terminal 26 which is connected to the output of the pressure transducer 66 applied to the other tank. The two inputs of the amplifier 22 are then connected to one another by a variable resistor 27. The feedback is established by a resistor 28 inserted between the output and the negative input of the amplifier.

The output of the amplifier 22 is connected to the input of a differentiator consisting of a differential amplifier 29, having a high gain and equipped with an RC feedback, and an assembly resistor 30-capacitance 31 whose constant of time determines the constant of time of the differentiator. More exactly, the capacitor 31 is inserted between the output of the amplifier 22 and the negative input of the amplifier 29, whereas the resistor 30 is inserted between said negative input and the ground. The positive input to the amplifier 29, in turn, is earthed through a resistor 32. Its output is also earthed through the set of two fixed resistors 33 and 34 and a variable resistor 25. The feedback is established by the parallel connection of a capacitor 36 and a series formed by a fixed resistor 37 and a variable resistor 38, said parallel being inserted between the negative terminal of the amplifier 29 and the point of junction of the resistors 34 and 35.

The diagram of FIG 3 also comprises a ring modulator 39 comprises two windings 40 and 41 mutually connected by four diodes 42, 43, 44 and 45, which are cross coupled. The winding 40, which has a central earthed tap, is the secondary winding of a transformer 46 whose primary winding 47 is fed by an AC voltage (preferably, 115 volts, 400 c.p.s.) applied between an input terminal 48 and the ground, through the series of two resistors 49 and 50, a resistor 51 being connected in parallel to the series formed by the resistor 50 and the winding 47. The winding 41, which has, in turn, a central tap connected via a resistor 52 to the point of junction between the resistors, 33 and 34, is, conversely, the primary winding of a transformer 53 whose primary winding 54 is inserted in series comprising also a resistor 55 which connects to ground the negative input of a further high-gain differential amplifier 56 whose positive input is grounded through the resistor 57 and to the negative input through a variable resistor 58. The feedback is formed by the series connection of a fixed resistor 59 and a variable resistor 60 connected between the output and the negative input. The output of the assembly of FIG. 3 consists of a terminal 61 connected to the output of the amplifier 56 through a transformer 62 having the two windings, i.e. the primary 63 and the secondary 64 with an earthed terminal.

The operation of the assembly of FIG. 3 is as follows.

The block 67, which comprises the amplifier 22, computes the difference between the two pressure signals sent to the inputs 24 and 26 from the pressure transducers 65 and 66, and the result of this operation (which is a level differential) is differentiated and converted into a measure of rate of flow by the differentiator 68, comprising the amplifier 29 and having as its constant of time the product of the parameters of the resistor 30 and the capacitor 31. The sign of the differential coefficient will be either positive or negative according to whether the pressure sensed by the transducer 65 is increased or decreased over the one sensed by the transducer 66.

The signal thus obtained goes to modulate the AC signal which is present at the input of the ring modulator 39, originating an AC modulated signal whose amplitude is proportional to the differential coefficient of the difference of the signals emitted by the pressure transducer. The modulating signal will be in phase with the AC carrier when the output of the differentiator 68 is positive (i.e. the pressure in the tank 4 is increased with respect to that in the tank 3), whereas it will be in phase opposition when the output of the differentiator 68 is negative (i.e. the pressure in the tank 4 is decreasing with respect to that in the tank 3). The reason why this modulation has been introduced is connected to the fact that differential amplifiers and processors for AC signals (more particularly 400c.p.s.) are available, which have already been applied in the art and are an advantage over those operated with DC. The block 69, comprising the amplifier 56, has the function of supplying power to the signal f (Q") which is available at the output 61.

Claims

The transducer of FIG. 3 has been shown and described herein to illustrate how it is possible to measure the actuated rate of flow of the pump 6 of FIG. 1 and to convert it into an electric signal f(Q") which can be compared with the electric signal f(Q') representative of the ordered rate of flow for the pump 6. It should be clearly understood, however, that such actuated rate of flow could also be measured otherwise, without departing from the scope of the invention as defined by the appended claims.

1. An automatic installation for transversally balancing a ship, of the kind comprising at least a couple of tanks situated on the same perpendicular to the longitudinal vertical plane of symmetry of the ship and at equal distances from said plane, said tanks containing a liquid which can be transferred from either tank to the other at an instantaneous rate of flow which is determined by a signal, called ordered rate of flow signal, which is a function of the angle of tilt, of the speed of tilt and the acceleration of tilt of the ship with respect to the balanced trim thereof, characterized in that it comprises means for measuring the actual rate of flow through said duct and converting it into a signal analog to the ordered rate of flow signal and comparing the signal thus obtained with said ordered rate of flow signal so as to obtain a differential signal whose instantaneous value determines the instantaneous actuated rate of flow as given by said pumping means.

2. An automatic installation according to claim 1, characterized in that the function of transfer between said actual rate of flow and the signal which can be compared with said ordered rate of flow signal is the inverse of the function between said differential signal and said actual rate of flow.

3. An automatic installation according to claim 3, characterized in that the measurement of the actual rate of flow is obtained by differentiation of the pressure differential between the two tanks.

4. An automatic installation according to claim 3, characterized in that said measurement is taken by means of an electronic device comprising a differential amplifier and a differentiator connected to one another in a cascade connection, the inputs of said differential amplifier being fed with signals obtained by translating the pressures in each of said two tanks.

5. An automatic installation according to claim 4, characterized in that the output signal of said differentiator is applied as a modulating signal to an AC-fed modulator.

6. An automatic installation according to claim 5, characterized in that the modulated signal issuing from said modulator is power amplified.

7. An automatic installation according to claims 1 to 6, characterized in that the rate-of-flow signal is derived from the tilt angle, the tilting speed and the tilt acceleration of the ship by mixing the signals issuing from a bank indicator, a gyroscope and an angular accelerometer installed on said ship.