US3475834A - Hydraulic models - Google Patents

Description

Nov. 4, 1969 A. E. BUGG HYDRAULIC MODELS Filed March 29, 1967 United States Patent O U.S. Cl. 35-19 4 Claims ABSTRACT F THE DISCLOSURE An hydraulic model for reproducing and determining the effects of water movement consists of a tray for containing water. Means is provided for adjustably tilting the tray and for rocking the tray at adjustable cyclic rate. An indicating device continuously monitors the levels of water at a selected point in the tray and comparator means comp-ares the monitored water levels in the tray with a record of the water levels at a corresponding point in a natural area. The tilt and rocking of the tray can thus be adjusted until the water levels in the tray correspond to those on said record.

This invention relates to hydraulic models of the kind used for determining, for example, siltation and scouring effects in a river bed or in a sea bed at the estuary of a river and similar locations. The use of such models is called for whenever it is decided to carry out any engineering works which would effect a change, however slight, in the ow pattern of the water for example by the building of a dock wall or -a buttress or other support for a bridge. Before the use of models was introduced there was no way of ascertaining what effect such works could have beyond the scouring elfect in the immediate vicinity of the new structure and very serious and adverse silting or scouring sometimes occurred in places far removed from the new structure.

To overcome this difficulty various attempts have been made to seek to produce in a model over a shortened time cycle and with the use of various types of loose bed material a simulated flow cycle whereby movement of the bed material was obtained and siltation or scouring effects could be studied and unwanted effects avoided.

Such models, as they developed, assumed various forms. They can be divided roughly into two types in one of which a scale model of the site was built in a fixed tray and the rise and fall of the water to simulate the effect of the tide was produced by pumping water into `and out of the tray. In the other type, known as a rocking tray model, the volume of water in the tray was kept constant and the rise and fall of the tide was effected by rocking the model and it is to the latter type that the present invention relates.

The problem which all such models seek to solve is to represent in the model the physical changes known to recur in nature, and, by the use of loose material in the bed which could be moved by the water movement, to seek to determine how the bed of the river or sea would be moved if changes were made in the pattern of flow for example by the building of a dock wall to confine the stream or an obstruction in the stream. One of the diiculties is that the results must be repeatable or they cannot be considered to be reliable. Loose bed models often show lack of repeatability due to a number of causes such as changes in the nature of the bed material for in order to be moved by the relatively weak currents the material chosen should have a relatively low specific gravity and in use a cellular material may over a period lose its buoyancy.

Quite small changes in tidal phenomena such as in the velocity of the water can produce large changes in the behaviour of the silt as the effect on the silt may be represented by anything from the 6th to the 14th power of the change in velocity and the material used to simulate the silt must give high sensitivity and have low stability against water movement.

Hitherto in such rocking tray models the rocking has been effected manually in accordance with a xed time cycle the tray being tilted fully from one extreme position to the other and remaining so tilted during a fixed time cycle selected as hereafter explained.

It is well known that the vertical scale in such models has to be considerably exaggerated and the silt simulating material selected so that by tilting the tray, water contained within the boundary will flow back and forth over the .model of the sea or river and 'will transport the silt the object being to get the silt to settle where it will reproduce natural phenomena the whole result being capable of being performed on a shortened time scale and after that to make changes in the model so as to be able to predict changes likely to occur in nature. In a book written by Professor J. Allen which has for years been regarded as the authority for designing such models it is stated that the ratio of the shortened time cycle to the natural time cycle can be determined by the formula t/ TQM/x where t is the time cycle in the model, T the time cycle in nature, y the vertical scale and x the horizontal scale.

This formula however does not take into consideration a large number of variables which include:

(a) Boundary influences in the model which cannot reproduce or simulate the boundaries imposed by nature the boundaries in the model being the retaining walls of the tray.

(b) Non-similarity of turbulence in the model to that which would happen in nature.

(c) The fact that the translation in either direction from kinetic energy to potential energy or vice versa is different in a model to that which occurs in nature.

(d) The critical physical characteristics for silt suitable for use in a model so as to reproduce in the short model tide cycle the effects in the longer natural time cycle.

(e) The natural frequency of surge obtaining for the model as the direction of water movement is reversed at the boundary.

(f) In a rocking tray model a change of volume will cause a change in tide effect so that this factor can be made use of as one of the adjustments that can be made.

All these variables, which cannot be provided for in such a formula lead to the conclusion that the above formula, which lhas hitherto been used for calculating the time cycle, is far from perfect since no adjustment is made or suggested for taking into consideration any one or more of the above quite critical variables.`

:It is known that another difficulty exists namely kinetic energy is represented by the formula whilst turbulence is a direct function of V so that a compensation made to correct for errors in kinetic energy cannot directly provide compensation for errors in turbulence. This having been recognised, various attempts have been made to measure the velocity of ow at various points in an hydraulic model and even to provide electronic controls for changing the rate of filling or emptying a fixed tray model but such velocity measuring devices have proved to be too insensitive to small velocity changes and to be susceptible to errors caused by their own turbulence effects to a degree which impairs repeatability of models results upon which characteristic the reliability of prediction depends.

According to the present invention there is provided a method of controlling a rocking tray hydraulic model which consists in monitoring the level of liquid at at least one point in the model and changing the tilt to make the liquid depth at that point comparable with that known to exist in nature at that point at a comparable instant of time in the flow cycle. The change in the angle of tilt may be effected together with a change in the time cycle or independently thereof. The means for monitoring the change in the level may include a float and means for deflecting a light beam to amplify the changes in level and means for comparing the movement of the light beam with a graph of level changes occurring in nature so that the changes of level in the model can 'be more accurately controlled to repeat the changes known to occur in nature such graphs being easily obtained by automatic time recording gauges.

Referring to the accompanying drawing which shows diagrammatically one form of hydraulic model made in accordance with the present invention it will be seen that the model comprises a tray 2 having walls 4, 6, 8 and enclosing an area, said tray being arranged to hold water. The oor of the tray has been laid out as a model of an estuary formed mainly of a sea area 12 and land areas 14, of a river delta of which 16 is the main river course. The tray 2 is mounted on fulcrums 18 (of which only one is seen) carried on a baseboard 19 such as a table top said fulcrum being arranged transversely of the tray and towards the left hand end as seen in the drawing so that irrespective of the disposition of water in the tray the right hand end will be the heavier. The wall 8 carries a bracket 20 with which the tilting mechanism described later is adapted to engage. At the other end of the tray 2 beyond the wall 4 and secured thereto is a bar 21 carrying a counterweight 22 adjustably positioned thereon. Mounted on the wall 6 adjacent the wall 4 is a light projector consisting of a lamp 23, reflector 24 and beam focusing device 26. Secured at the other end of the wall 6 at the end wall 8 is a bracket 28 carrying at its end a vertical journal for the shaft 30 of a chart cylinder 32 said shaft carrying a bevel gear 34 engaged by a complementary bevel gear 36 carried on a shaft 38 supported in a bearing 40` carried by a bracket 42 also mounted on the bracket 28. On the chart cylinder 32 is disposed a chart 43 the graph on which has been produced by an automatic tide recorder.

The drive mechanism for tilting the tray 2 will now be described. Mounted on the baseboard 19 is a slide 50 disposed between guide blocks 52 for movement longitudinally of the baseboard 19 by means of a crank 54 the threaded shaft 56 of which is engaged with a bracket 58. A collar 60 secured against movement along the shaft 56 is secured to the end of the slide 50 the arrangement being such that turning the crank 54 will move the slide 50 either towards or away from the bracket 20. The drive mechanism is mounted on the inclined top 62 of the slide 50 and consists of a motor 64 the shaft 66 of which is coupled to a reduction gear box 68 embodying an infinitely variable gear adjustable by a knob 70. Extending laterally from the gear 'box 68 is a shaft 72 one end of which carries a cam 74 whilst the other end of the shaft 72 is coupled by a shaft 76 through universal joints 78 and 80 to the shaft 38. The shaft 76 is really two shafts telescopically arranged so as to compensate for any lengthening or shortening required when the slide 50 is moved. Obviously the two parts of the shaft are restrained from relative rotation. The cam 74 engages a cam follower 82 carried on a lever 84 pivoted at 86 on a bracket 88 mounted onthe inclined top 62 of the slide 50. The bracket 20 on the end wall 8 has a downwardly depending abutment 90 which is shown resting on the lever 84 so that raising or lowering of the lever 84 by the cam 74 will tilt the tray 2 about the fulcrum 18. The movement of the slide S0 by the crank 54 increases or decreases the amplitude of the rocking movement imparted to the tray 2. Shown connected in circuit with the motor 64 is a variable speed switch 92 so that the time cycle can be changed either by the variable gear adjustment knob 70 or the switch 92, or by adjustment of both.

On the wall 6 of the tray 2 between the focusing device 26 and the bracket 28 is mounted a bracket 94 carrying the level indicating device consisting of a oat 96 mounted on a lightweight lever 98 centrally and freely pivoted on the bracket 94 the other end' of said lever carrying a light abturator disc 100 in the center of which is a cross wire device 102 said disc being positioned so as to lie in the path of the beam from the focusing device 26 and throw an image 104 on the chart cylinder 32. The float 96 is seen positioned at the mouth of the main water channel y16 and the lever 98 is so balanced that the float 96 rests lightly on the water in said channel. As the level of water changes the image 104 of the cross wire device moves up and down the chart cylinder 32. The arcuate movement of the image would in practice be matched with the arcuate movement of the scriber of the rautomatic tide recorder.

In designing the model the float should be at the center of investigation and the fulcrum 18 should be well removed therefrom.

When the model is rst set up with the outline and the river courses all properly contoured a certain roughly estimated quantity of water is poured into the tray together with silt simulating material. The motor 8 is then started on the basis of a theoretical time cycle calculated as indicated above and the hydraulic elfect is examined to see whether silt movement approximates to what happens in nature. Obviously this is only a first approximation.

By a small adjustment of the time cycle by the infinitely variable gear adjustment knob 70 or speed control switch 92 the silt movement can be considerably affected. The effect may not be quite what is required and this is then modified by increasing or decreasing the angle of tilt imparted to the tray by turning the handle 19 to move the slide 18. Working these two adjustments in conjunction with each other any operator, after a little experience with the model, will readily be able to adjust the time and amplitude of movement of the tray so as to get a really close simulation of the silt movement combined with correct tide movement to that which occurs in nature, and the correct tide movement is ascertained when the image of the cross wires closely follows the graph on the chart 43.

In experiments which have been made with this model it has been found that a powdered low temperature carbonization product of coal sold under the trademark Coalite with carefully selected grain size serves as a satisfactory silt and that this enables repeatable results to be obtained with considerable accuracy thus enabling siltation to be predictable with considerable accuracy.

What I claim and desire to secure by Letters Patent is:

1. A method of simulating at a predetermined point in a rocking tray hydraulic model containing liquid a predetermined amplitude and 4rate of change of the liquid level comprising preparing a record of the amplitude and rate of successive changes in a liquid level to be simulated, continuously monitoring the level of liquid in the tray at said point in the tray, rocking the tray, continuously comparing the monitored amplitude and rate of the change of the liquid level at said point in the tray, due to the rocking, with said record and varying the rate of the rocking of the tray at various angles of tilt of the tray until the montored changes of amplitude and rate of the liquid level at said point in the tray correspond to the amplitude and rate of the changes of the liquid level of said record.

2. A rocking tray hydraulic model comprising a tray for containing liquid, means for tilting the tray, means for adjusting the amplitude of the tilt of the tray, means for rocking the tray, means for adjusting the cyclic rate of the rocking of the tray, record means defining a sequence of liquid levels to be simulated at a predetermined point in the tray, means for monitoring the level of liquid in the tray at said point, and a comparator for comparing the monitored level of liquid in the tray with said liquid levels defined by said record means, whereby said adjusting means can be utilized to vary the rate of the rocking of the tray at various angles of tilt of the tray until the monitored changes of amplitude and rate of the liquid level at said point in the tray correspond to the amplitude and rate of the changes of the liquid level of said record means.

3. The rocking tray hydraulic model of claim 2 in which said record means comprises a chart having marked thereon a graph of said sequence of liquid levels, in which said comparator includes indicator means connected to be moved by changes in the level of liquid in the tray monitored by the monitoring means, in which said chart is movably mounted for moving said graph relatively past said indicator means, and which includes means for moving said chart and its graph in timed relation to the rocking ofthe tray.

4. The rocking tray hydraulic model of claim 3 in which said indicator means comprises a light beam generating device mounted on the tray and obturator means mounted on the monitoring means for movement in accordance with changes in the level of liquid in the tray, said obturator means having an aperture therein with cross Wire means supported in the aperture, and said light beam generating device, said obturator means and said chart being aligned for a light beam from the generating device to project an image of the cross wire means of the obturator on the chart in various liquid-level i11- dicating positions of the obturator.

References Cited UNITED STATES PATENTS `644,068 2/ 1900 Everly 259--73 2,601,411 6/1952 McLanchlan 259-73 3,142,908 8/1964 Aunis et al. 35-19 3,253,353 5/1966 Steed et al. 35-19 3,287,967 11/ 1966 -Laurent 73-148 FOREIGN PATENTS 474,892 6/ 1929 Germany.

EUGENE R. CAPOZIO, Primary Examiner WALTER W. NIELSEN, Assistant Examiner U.S. Cl. X.R. 73-148

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