GB1592452A - Apparatus for creating waves in a body of liquid - Google Patents

Description

(54) APPARATUS FOR CREATING WAVES IN A BODY OF LIQUID (71) We, INDUSTRIAL AND COM MERCIAL ELECTRONICS LIMITED, a British Company of 63 Hampstead High Street, London NW3 1QH, do hereby declare this 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 described in and by the following statement: This invention relates to an improved apparatus for creating surface waves in a body of liquid.

Models of ships, oil rigs and harbour installations are tested with model waves in a test tank, and the apparatus for making these waves is an important part of the equipment in the test tank.

There are three popular kinds of known wave making apparatus namely the flap, the piston and the wedge and these respectively are shown diagrammatically in Figs. la, ib and ic of the accompanying drawings. The operation and descriptive name given to each will be readily understood from examination of Figs. la, ib and ic, the arrows in each figure indicating the manner in which each displacer is moved to produce the waves. In each of these known types, the displacer is connected to and moved by a drive. The simplest drive is a continuously rotating electric motor and a crank. In the known arrangements using a motor and crank drive, the wave period is set by motor speed and the stroke of the displacer is set by crank eccentricity.It is possible to connect the displacer and motor with a linkwork which allows stroke adjustment without stopping the motor, and where it is desired that the apparatus should be capable of producing any of a desired spectrum of wave types, more complicated drives using hydraulic actuator and servo-systems can be used.

In all of the known arrangements the displacer is rigid. Research has shown that the neutral orbit diameters of individual particles in a wave decrease with depth of the body of liquid and that it would be advantageous to curve the displacer active face to an exponential form.

According to the invention there is provided apparatus for creating waves in a body of liquid, comprising at least one liquid displacer means and means for moving the or each displacer means back and forth to create the waves in the body of liquid, wherein the or each displacer means is of sheet material which is compliant so as to flex as it is moved back and forth to create said waves.

Such a compliant displacer means may be used in or other wise than in association with means for controlling the movement of the displacer by reference to signal representative of the level of the body of liquid in the region of the displacer means.

The or each displacer means may be a paddle for positioning in a tank for holding the body of liquid, or in another arrangement the apparatus includes a tank for holding the body of liquid and the or each displacer means is a portion of a wall of the tank, which wall is formed of said compliant material.

Embodiments of the present invention will now be described by way of example, with reference to Figs. 2 to 7 of the accompanying diagrammatic drawings, and of which: Fig. 2 is a sectional side view of apparatus according to the invention; Fig. 3 is a side view showing a preferred method of supporting the paddle of the apparatus shown in Fig. 1; Fig. 4 is a graph showing the force/deflection characteristics of the support arrangement shown in Fig. 3; Fig. 5 is a side view showing why it is advantageous to employ a compliant paddle; and Figs. 6 and 7 are a sectional side view and a plan respectively of a test tank having a compliant wall and forming apparatus according to a further embodiment of the invention.

Referring to Fig. 2 initially, in this figure there is shown attest tank 10 having a paddle displacer 12 close to an end 14 of the tank.

The means for moving the displacer 12 between the extreme positions 12A and 12B is an electric motor 16.

Motor 16 is a printed circuit motor and is drivingly c()nneci e(l t() l re-ci reu1tiag ball screw device 18 having ail acat)r rod 2(! directly c otlpled to the paddle 12. Motor 16 is reversible and rotation of same in one direction' causes actuator 20 to move outwardly while rotation of motor 16 in the opposite direction causes actuator 20 to retract.By repeatedly reversing the motor direction the paddle 12 is oscillated between the positions 12A and 12B as sho n.

In use of the apparatus. it is the body of liquid 22 at the face 24 of paddle 12 in which the waves are to be created, and adjacent face 24 is a level or height sensing device 26 of conventional form or of a form having a self-seeking zero position in the event of overall increase or decrease in level of the tank for sensing the level of the body of the liquid 22 at the face 24 and for producing electrical signals reperesentative of such Icvel and delivering same to an amplifying and control circuit 28. This control circuit 28 controls the operation of the motor 16 and hence the position of the paddle 12. The sensing device 26 is operative for causing the dissipation of waves arriving at face 24.When the apparatus is creating waves, the level of liquid at the sensing device will rise and fall and the control circuit is set to treat this as normal. However, when a wave arrives at face 24, the level of the liquid at the face 24 will tend to deviate from the normal. Device 26 senses this and feeds back a signal to motor 16 causing it to rotate such as to move paddle 12 towards position 1 2B, thereby in effect creating space for the liquid of the incoming wave if the level is deviating by rising. If the level at face 24 deviates from the normal by dropping below the predetermined level. the same sequence of operation takes place, except that the paddle 12 is displaced in the opposite direction.

By so operating the paddle 12 it can be caused to absorb or dissipate waves arriving at face 24 which is desirable as explained hereinbefore whilst still generating waves of the pre-set amplitude and frequency.

When the displacer is not generating waves, the sensing device can be made operative to absorb incoming waves, in this case the said normal being level water.

Instead of pivoting the paddle 12 at the base of the tank 10, it may be carried by the spring arrangement illustrated in Fig. 3 which comprises a main spring blade 30 and strut spring blade 32 located to the rear of active face 24 of the paddle. By using this spring mounting arrangement, it is not necessary to provide the small body 34 of liquid at the opposite side of paddle 12 from face 24 as the spring arrangement 30. 32 gives basically similar loading characteristics to the paddle as does the body 34 of liquid.

Tlie force llefl.^ct characteristic of the sprig arrangement 3(1.32 is shown in Fig. 4 and it will be secn that up to a yielding point 36, there is only a small deflection within increasing load. A point 36 however, the Strut 4.7 in fact buckles and substantial deflection takes place even to the extent as shown in Fig. 4 that the load can be reduced and the subc;tant extension will continue.

The above description which is substantially similar to that in our co-pending application No. 15804/76 (Serial No. 1 592 451) is consistant with the paddle 12 being a rigid plate, but in fact it is of a compliant material so that it curves generally to an exponential form as shown in Fig. 5 as it is oscillated.

The paddle may be of tapering thickness to assist this effcct. This particular form of curving is desirable, as the neutral orbit diameters of particles in a wave decrease exponentially with depth into the body of liquid as shown in Fig. 5 by the dotted line circles. A suitable material for forming a compliant paddle is sheet metal.

Figs. 6 and 7 show a specific form of the present invention and in particular what is shown in these figures is a test tank 40 which as a whole is of compliant material such as heavy gauge rubber or sheet metal, and the tank is suspended by wires or ropes 42. By making the tank in this way, the material of the tank takes the loading in tension in the manner of a catenary suspension, and the tank wall experiences no bending movemcnt and one or several side walls can be used as the displacer. The wires or ropes may, under the loading, splay slightly to the vertical in order to provide horizontal force components to support the tank. The horizontal forces along the edge of the tank may be supported by ropes which are tensioned, when the tank is full, by the weight of liquid in the tank.In the arrangement shown in Fig. 7, the wall 40A has five regions 44 each in fact forming a displaccr similar to the displacer described with reference to Fig. 2, and each being provided with its sensing and displacement means as shown in Fig. 2. It will be normal in a test tank of any significant size to use a plurality of displacers side by side, and the arrangement of Fig. 7 provides an advantage over side by side displacers in that it can be utilised substantially to eliminate interference between the respective wave patterns crcated and absorbed by adjacent displacers. Furthermore. if the end two displacer regions 44 shown in Fig. 7 are used to isolate a wave pattern created by the remaining displacer regions 44, there will be effective isolation of the wave pattern by virtue of the fact that the entire wall 40A is compliant and there will be smooth transitions between each end displacer region 44 and its neighhour cven although these regions may be oscillated out of phase by any amount up to 1800 where the material of the tank permits.

WHAT WE CLAIM IS: 1. Apparatus for creating surface waves in a body of liquid, comprising at least one liquid displacer means, means for moving the or each displacer means back and forth to create the waves in the body of liquid, wherein the or each said liquid displacer means is of sheet material which is compliant so as to flex as it is moved back and forth to create said waves.

2. Apparatus according to Claim 1, wherein the or each liquid displacer means is a paddle for positioning in a tank for holding the body of liquid.

3. Apparatus according to Claim 1, including a tank for holding the body of liquid and wherein the or each displacer means is a portion of a wall of the tank, which wall is formed of said compliant material.

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

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. the tank permits. WHAT WE CLAIM IS:

1. Apparatus for creating surface waves in a body of liquid, comprising at least one liquid displacer means, means for moving the or each displacer means back and forth to create the waves in the body of liquid, wherein the or each said liquid displacer means is of sheet material which is compliant so as to flex as it is moved back and forth to create said waves.

2. Apparatus according to Claim 1, wherein the or each liquid displacer means is a paddle for positioning in a tank for holding the body of liquid.

3. Apparatus according to Claim 1, including a tank for holding the body of liquid and wherein the or each displacer means is a portion of a wall of the tank, which wall is formed of said compliant material.