GB1589768A

GB1589768A - Hydraulic damping units

Info

Publication number: GB1589768A
Application number: GB4531676A
Authority: GB
Original assignee: National Research Development Corp UK; National Research Development Corp of India
Current assignee: National Research Development Corp UK; National Research Development Corp of India
Priority date: 1977-10-17
Filing date: 1977-10-17
Publication date: 1981-05-20

Description

(54) IMPROVEMENTS IN AND RELATING TO HYDRAULIC DAMPING UNITS (71) We, NATIONAL RESEARCH DE VELOPMENT CORPORATION, a British Corporation established by Statute, of Kingsgate House, 66-74 Victoria Street, London, S.W.1, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to hydraulic damping units and more particularly to arrester apparatus incorporating such units usable to apply a retarding force on a moving ship.

In its broadest aspect the present invention comprises a piston and cylinder hydraulic damping unit in which the piston rod is provided by a flexible cable and in which the cable is surrounded by a collapsible seal isolating the cable from the volume swept out by the piston during operation of the device.

The seal may, for example, be telescopic.

Preferably a conduit is provided for the feed back of operating liquid from one side of the piston to the other during operation of the device.

The device of the present invention has a particular applicaffon as part of an arrester apparatus for ships e.g. on canals, for use on those occasions where through misjudgement or faulty equipment the ship is approaching a lock at too great a speed to stop in time without outside help.

Thus according to another aspect of the invention a ship arrester apparatus comprises a hydraulic damping unit according to the present invention and locating means adapted to extend a cable across the path of an oncoming ship. In operation of the apparatus the ship will displace the cable and the damping unit is thereby operated to apply a retarding force on the cable and the ship.

When present, the conduit of the damping unit preferably takes the form of a manifold connected with the cylinder by a number of branch pipes. A substantial resistance to flow through the pipes is provided either by the pipes themselves or by constrictions associated with the pipes. Preferably the branch pipe spacings and/or the relative flow resistances are so chosen that in operation the damping unit applies a more or less constant retarding force on the piston over a large part of its working stroke.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which Figures 1 and 2 show a schematic vertical section and plan view of an arrester apparatus according to the present invention; Figure 3 is a vertical section of a damping unit according to the present invention and for use in the apparatus of Figures 1 and 2, Figure 4 is an elevation of a resetting device for use with the unit of Figure 3; and Figure 5 is a graph illustrating the performance characteristics of the unit shown in Figure 3.

Thus referring first to Figures 1 and 2, an arrester apparatus 10 according to the present invention includes two identical damping devices 12 and 14 according to the invention and a cable and float assembly 16 located upstream of lock gates 18 in a canal 20 (Figure 2). The end portions of the cable provide the piston rods for devices 12 and 14.

Figures 1 and 2 show the arrester apparatus in its operative and inoperative positions respectively. Referring first to Figure 2, the cable and float assembly 16 comprises the cable from device 12 tensioned against a lightweight boom 225 and carrying a number of spaced floats 232. Reference numeral 228 indicates a guide surface for the cable and numeral 226 indicates a pivot about which the boom can rotate to span the width of the lock.

When lock gates 18 have been closed and a vessel (22) is approaching the lock at too great a speed, the lock keeper operates a drive mechanism (not shown) to rotate the boom 225 from its inoperative positions through a 90" arc to the operative position shown (for the cable) in Figure 1.

In this latter position the cable from absorber 14 is rigidly fixed to the cable on the boom by means of a locking mechanism 24 one half of which is retained against the lock wall and the other half of which is carried by the boom where it is fixed to the cable and float assembly. Reference numeral 230 indicates the guide block for the cable from absorber 14.

When the cables from both sides of the canal are positively locked together, the boom 225 is rctracted into the recess 234 in the lockwall 20 and the arrester system is fully operational. This operative position is shown in Figure 1 and is indicated by chain lines 16' in Figure 2.

The normal stopping position for a vessel will be upstream of the boom recess but if a vessel should stray beyond this point, whether it contacts the arrester cables or not, it will be necessary to retract the vessel to the normal stopping position in order to remove the arrester cables.

If a vessel completely or partially extends the absorber cables then, after retraction of the vessel, the cables will have to be re covcred either from the bottom of the canal or from their partially submerged position to the freely floating condition. This is achieved by reset equipment resetting each damping device to its initial position.

When conditions upstream of the lock gates 18 are satisfactory and the cables are required to be removed, the boom is rotated out across the canal. When the boom contacts the locking mechanism 24, this releases the cable from absorber 14 from the arrester assembly and picks up this latter so that it can be returned to the stowed position in the lockwall recess. After stowing, the main lock gates 18 are opened to allow free passage of the vessel out of the canal.

The damping devices 12, 14 can be mounted either vertically, as shown, or horizontally. Their construction can best be seen from Figure 3 which shows device 12 with its piston at the uppermost position. In essence the unit comprises a hydraulic pistonicylinder assembly (piston 26 moving in cylinder 28) with the cable 216 providing the piston rod. Using the cable in this way, it is possible considerably to reduce the installation length required for the described device compared to a unit using a rigid piston rod. This advantage is especially important for a device in which the piston stroke is large.

in the embodiment shown, the cable 216 is isolated from the cylinder space 30 beneath the piston by a telescopic seal 32 extending between the underface of the piston and the base support plate 34 for the cylinder. The seal comprises several tubular units such as unit 35. These have retaining flanges (such as flange 36) at their lower vends and ring seals (such as seal 38) at their upper ends. An abutment 40 for piston 26 ensures that under no circumstances can the telescopic seal be damaged by piston 26 at the end of its downwards travel.

In an alternative embodiment (not shown) the stranded non-rotational cable 216, shown in Figure 3, is replaced by a locked coil cable. Because this latter has a substantially cylindrical outer section, the telescopic seal 32 can be replaced by a simple compression type seal at the aperture of base plate 34.

Abutment 40 can then, if desired, be at a correspondingly lower position. The principal drawbacks of this alternative embodiment are the relatively high cost of locked coil cable and the reduced flexibility of this type of cable.

Returning now to the illustrated embodiment, a manifold 42 is joined by branch pipes 44 with an aperture 45 above piston 26 and with a number of apertures 46 spaced apart along the cylinder wall below the piston. Each aperture 46 houses an outwardly narrowing orifice 48 throttling the flow of hydraulic liquid from space 30 into the manifold during the downward travel of the piston. The nozzle areas are progressively of smaller cross-sectional area the lower they are in the cylinder, so that the total discharge area available for the liquid displaced by piston 26 decreases in a roughly exponential fashion at the piston moves down the cylinder. Conveniently the branch pipes and nozzles in the upper two thirds of the apparatus are uniformly spaced apart by a first amount (e.g. 1 foot) whereas those in the lower third are unifirmly spaced apart by, say, half this amount. This enables the decrease in discharge area to approach more closely an exponential form where this matters most i.e. during the last part of the piston's travel.

Tn an alternative version (not shown) the constrictions are located in the pipes 44 rather than in the cylinder walls. The illustrated version is normally to be preferred however firstly because the nozzles are readily accessible for replacement if a different damping characteristic is required and secondly because they confine the high pressure region of the system to the piston cylinder arrangement.

In the position shown in Figure 3 the piston is held in place by a retainer cable 50 passing over a pulley 52 to a winch 54.

As viewed in Figure 3, the winch must be able to freewheel in a clockwise sense on the attainment of a tension in the retainer cable slightly in excess of that produced by the piston assembly in its illustrated position.

An alternative retainer system is shown in Figure 4 where, after passing over pulley 52, cable 50 passes under a second pulley 55 and has its free end secured to a flange 56 at the top of the cylinder casing. A hydraulic jack 58 connected between the spindle of this second pulley and base plate 34 tensions cable 50 to hold the piston in the position shown in Figure 3. In use, the operation characteristics of the jack 58 are the same as those of winch 54 and the jack will freely expand to allow substantially unhindered movement of the cable when a sufficient increase in cable tension is experienced.

Figure 5 shows typical performance curves 100, 101, for a ship arrester system as shown in Figures 1 and 2. For these two curves, the y-axis indicates the tension in cable 216 and the x-axis indicates the stroke of the piston. Curve 100 shows the load/stroke characteristics for a ship with a 0 bow angle and curve 101 shows the characteristics for a ship with a 30 bow angle. In this latter case some of the retarding effect of cable 216 will of course be lost by the cable riding down the inclined front edge of the bow. Point A on the graph indicates the situation when the bow of the ship has just engaged the cable. During the next 10 feet or so of the ship's travel it will draw the cable along with it and piston 26 will be pulled down to the top aperture 46 (parts AB of the curves). During this part of the piston stroke, all the apertures 46 are available for the discharge of hydraulic fluid from beneath the piston and this liquid is readily fed back through the manifold to the upper part of cylinder 28. This means that the piston is initially able to feed out cable at a speed at which it will exert little or no retarding force on the ship i.e. the cable is initially "riding" the blow of the ship's impact on the cable. Thereafter piston 26 excludes the apertures 46 one by one from the discharge path of the fluid. The throttling effect of nozzles 46 is proportional to the square of the velocity of the liquid passing through them so that as the piston slows down the available nozzle area available must diminish at a corresponding rate to enable a more or less constant retarding force to be applied by cable 216 to ship 22 (part BC of the curve 100 and part BD of the curve 101).

With a 0 bow angle, the loading on the cable will have been reduced substantially to zero by the time the cable has moved the piston 26 into engagement with abutment 40 (point D on curve 100), but in the other cases, for the 30 bow angle represented by curve 101 for example, this will not be so and the cable must be sufficiently strong to take the final strain until the ship has been brought finally to rest.

The velocities of the two types of ship considered above are shown in curves 102 (0 bow angle) and 103 (30 bow angle).

For these two curves the x-axis has the same significance as with curves 100, 101 but the y-axis now indicates the velocity of piston 26.

WHAT WE CLAIM IS: 1. A piston and cylinder hydraulic damping unit in which the piston rod is provided by a flexible cable and in which the cable is surrounded by a collapsible seal isolating the cable from the volume swept out by the piston during operation of the device.

2. A damping unit as claimed in Claim 1 in which the seal is telescopic.

3. A damping unit as claimed in any preceding claim in which a conduit is provided for the feed back of operating liquid from one side of the piston to the other during operation of the device.

4. A damping unit as claimed in Claim 3 in which the conduit takes the form of a manifold connected with the cylinder by a number of branch pipes.

5. A damping unit as claimed in Claim 4 in which a substantial resistance to flow through the pipes is provided either by the pipes themselves or by constrictions associated with the pipes.

6. A damping unit as claimed in Claim 5 in which the spacings and/or the relative flow resistances are so chosen that in operation the damping unit applies a more or less constant retarding force on the piston over a large part of its working stroke.

7. A ship arrester apparatus comprising a hydraulic damping unit according to any preceding claim and locating means adapted to extend a cable across the path of an oncoming ship.

8. A hydraulic damping unit substantially as hereinbefore described with reference to Figure 3 of the accompanying drawings.

9. A damping unit as claimed in Claim 8 in combination with a resetting device substantially as hereinbefore described with reference to Figure 4 of the accompanying drawings and adapted to operate with the performance characteristics illustrated by Figure 5 of the accompanying drawings.

10. A ship arrester apparatus substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

56 at the top of the cylinder casing. A hydraulic jack 58 connected between the spindle of this second pulley and base plate 34 tensions cable 50 to hold the piston in the position shown in Figure 3. In use, the operation characteristics of the jack 58 are the same as those of winch 54 and the jack will freely expand to allow substantially unhindered movement of the cable when a sufficient increase in cable tension is experienced.

Figure 5 shows typical performance curves 100, 101, for a ship arrester system as shown in Figures 1 and 2. For these two curves, the y-axis indicates the tension in cable 216 and the x-axis indicates the stroke of the piston. Curve 100 shows the load/stroke characteristics for a ship with a 0 bow angle and curve 101 shows the characteristics for a ship with a 30 bow angle. In this latter case some of the retarding effect of cable 216 will of course be lost by the cable riding down the inclined front edge of the bow. Point A on the graph indicates the situation when the bow of the ship has just engaged the cable. During the next 10 feet or so of the ship's travel it will draw the cable along with it and piston 26 will be pulled down to the top aperture 46 (parts AB of the curves). During this part of the piston stroke, all the apertures 46 are available for the discharge of hydraulic fluid from beneath the piston and this liquid is readily fed back through the manifold to the upper part of cylinder 28. This means that the piston is initially able to feed out cable at a speed at which it will exert little or no retarding force on the ship i.e. the cable is initially "riding" the blow of the ship's impact on the cable. Thereafter piston 26 excludes the apertures 46 one by one from the discharge path of the fluid. The throttling effect of nozzles 46 is proportional to the square of the velocity of the liquid passing through them so that as the piston slows down the available nozzle area available must diminish at a corresponding rate to enable a more or less constant retarding force to be applied by cable 216 to ship 22 (part BC of the curve 100 and part BD of the curve 101).

With a 0 bow angle, the loading on the cable will have been reduced substantially to zero by the time the cable has moved the piston 26 into engagement with abutment 40 (point D on curve 100), but in the other cases, for the 30 bow angle represented by curve 101 for example, this will not be so and the cable must be sufficiently strong to take the final strain until the ship has been brought finally to rest.

The velocities of the two types of ship considered above are shown in curves 102 (0 bow angle) and 103 (30 bow angle).

For these two curves the x-axis has the same significance as with curves 100, 101 but the y-axis now indicates the velocity of piston 26.

WHAT WE CLAIM IS: 1. A piston and cylinder hydraulic damping unit in which the piston rod is provided by a flexible cable and in which the cable is surrounded by a collapsible seal isolating the cable from the volume swept out by the piston during operation of the device.
2. A damping unit as claimed in Claim 1 in which the seal is telescopic.
3. A damping unit as claimed in any preceding claim in which a conduit is provided for the feed back of operating liquid from one side of the piston to the other during operation of the device.
4. A damping unit as claimed in Claim 3 in which the conduit takes the form of a manifold connected with the cylinder by a number of branch pipes.
5. A damping unit as claimed in Claim 4 in which a substantial resistance to flow through the pipes is provided either by the pipes themselves or by constrictions associated with the pipes.
6. A damping unit as claimed in Claim 5 in which the spacings and/or the relative flow resistances are so chosen that in operation the damping unit applies a more or less constant retarding force on the piston over a large part of its working stroke.
7. A ship arrester apparatus comprising a hydraulic damping unit according to any preceding claim and locating means adapted to extend a cable across the path of an oncoming ship.
8. A hydraulic damping unit substantially as hereinbefore described with reference to Figure 3 of the accompanying drawings.
9. A damping unit as claimed in Claim 8 in combination with a resetting device substantially as hereinbefore described with reference to Figure 4 of the accompanying drawings and adapted to operate with the performance characteristics illustrated by Figure 5 of the accompanying drawings.
10. A ship arrester apparatus substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.