Abstract:
In order to generate waves in a volume of water ( 12 ) of an aquarium, it is proposed that a storage container ( 22 ) which extends beyond the surface of the volume of water ( 12 ) should be provided in the aquarium ( 10 ). Using a pump ( 32 ), water is periodically pumped from the water container ( 10 ) into the storage container ( 22 ) and returned from the storage container ( 23 ) into the aquarium ( 10 ). The energy delivered to the water during this leads to fluctuations in the position of the free surface ( 14 ) of the volume of water ( 12 ) and in-phase operation of the pump ( 32 ) provides stronger surface displacements in the aquarium ( 10 ), which are comparable with a wave in open water and which expose the plants and living beings in the aquarium to an alternating mechanical load.

Description:
BACKGROUND OF THE INVENTION 
   The invention relates to a method for generating waves in an aquarium and to a device therefor. 
   The water in aquaria is normally circulated constantly through a filter for cleaning purposes by using a pump. Although this does lead to flows of water, they are negligibly small. 
   It is furthermore known to set up a stronger flow in such aquaria by making pumps extract water directly from the volume of water contained in the aquarium and return it directly into this volume of water. 
   For many applications, it is actually preferable to be able to replicate waves in an aquarium. Waves are distinguished in that volumes of water move to and fro periodically. These oscillating movements of the water lead to corresponding alternating loads on plants and animals contained in the water. 
   SUMMARY OF THE INVENTION 
   In order to make these alternating loads available in an aquarium as well, the present invention relates to a method and to a device for generating waves in the restricted space of an aquarium. 
   The invention makes use of the fact that water is a liquid which has relatively low internal friction. The energy needed in order to generate a wave process can therefore be introduced as small portions into the volume of water, and the intended amplitude of the wave can be achieved by means of the total time duration of the energy input. This makes it possible to deliver the kinetic and/or potential energy by using structures which have compact dimensions. This is preferable with a view to the aquaria installed in living rooms, since extra equipment is perceived as aesthetically unpleasing there. 
   Preferred refinements of the invention are given in the dependent claims. 
   One refinement of the invention is preferable with a view to setting up waves as rapidly as possible with little energy input. The frequency at which the water level fluctuates in the aquarium in question is measured, and the energy delivery can then be synchronised accordingly. 
   One refinement is preferable with a view to generating stronger waves. 
   One method ensures that waves are not built up too strongly, and in particular that water does not escape from the aquarium. 
   One refinement of the invention is also preferable with a view to minimal input of energy. 
   In the device, volumes of liquid are displaced while delivering potential optionally as well as kinetic energy, by raising a subvolume of the water in the storage container to a level which is higher than the free level of the water in the aquarium. This volume can then be returned into the aquarium under the effect of gravity, with kinetic energy optionally also being imparted to it by the delivery instrument. 
   As an alternative, a volume of water lying below the free level of the water in the aquarium may be pumped and allowed to flow back after switching off the delivery instrument. 
   The delivery instrument may thus operate only intermittently and allow water to flow back in the periods of time between the working cycles. The delivery instrument may also have a reversible direction of rotation, however, and expel water from the storage container and deliver it into the storage container in successive half-cycles. With this procedure, the kinetic energy necessary in order to set up stronger waves is delivered to the water in a shorter time. 
   In both cases, it is favourable for the delivery instrument to have only a small flow resistance. 
   A pump having a propeller which as a delivery element is distinguished by a high throughput with a low pressure build-up. Such a pump can also be used equally well in both working directions. 
   The refined invention wherein the propeller which is enclosed by a pump housing provided with through-openings in the circumferential wall and has an axial delivery piece is preferable with a view to delivered water flows which are as laminar as possible. 
   The refinement of the invention wherein the through-openings are designed as axial slots which are distributed in the circumferential direction and distributed equally is also used to avoid turbulence. 
   Another refinement of the invention has the advantage that the interior of the storage container is substantially isolated from the volume of water in the aquarium. 
   Another refinement of the invention makes it possible to arrange the storage container, and the delivery instrument belonging to it, close to the normal surface of the aquarium so that a large part of the volume of water remains unperturbed. 
   A device wherein a level monitor is arranged at the upper end of the storage container ensures that more water can be moved into the storage container that is expedient in order to introduce potential energy. 
   The device can be constructed so that the delivery instrument is immersed only very little into the volume of water in the aquarium, where it is visible. 
   The refinement of the invention ensures very effective transfer of motion energy to the water contained in the aquarium. 
   If the waves are generated by a device comprising a tilting bearing provided for the aquarium and a drive engaged on the aquarium, then virtually all the interior of the aquarium can remain free of equipment. A device as indicated in claim  18  can also be retrofitted to aquaria which are already being used. 
   A tilting bearing can be implemented without mechanical work on the aquarium. 
   A tipping drive is distinguished by very compact dimensions in the vertical direction. This drive can therefore be arranged at the bottom of the aquarium. 
   The two cooperating discs of the drive then form a compact unit with smooth faces. 
   The effect achieved by one of the refinements of the invention is that, on the one hand, a friction lock is obtained between the working part of the tipping mechanism and the aquarium and, on the other hand, the drive connection between the tipping drive and the aquarium permits smaller tilting between the drive and the aquarium. 
   A tipping drive having a pressure actuator which is selectively pressurized or relieved of pressure is distinguished by a particularly straightforward and robust mechanical structure, and low production costs. 
   The refinement wherein the pressure actuator is a deformable monobloc element is then preferable with a view to a further simplified structure and good reliability of the drive, with low costs. 
   The pressure actuator being enclosed by two telescopic parts ensures that the drive then has an attractive exterior and is protected against transverse loads. 
   Another refinement of the invention makes it possible to vary the intensity and shape of the waves generated in the aquarium in a straightforward way. 
   A controller is then distinguished by a straightforward structure. The delivery instrument or tilting drive is operated by a clock generator, the frequency of which is preferably adjustable, with a frequency at which the intended wave amplitude is obtained according to observation of the resulting waves. 
   In a device wherein the control end interacts with at least one level detector the program control can actually establish the oscillating frequency of the wave in the aquarium from the output signal of the level detector connected to it, and can tune it according to its operation. 
   Another refinement of the invention allows straightforward adaptation of the position of the level detector to the water level conditions respectively encountered in the aquarium. 
   Waves generated in the aquarium would also move to and fro the food which is added to the aquarium at predetermined time intervals, and make it settle on plants, stones etc. in the container. One effect achieved by a refinement of the invention is that the wave generation can be suspended for a predetermined length of time. This avoids the aforementioned loss of food. 
   For much aquarium stock, it is also preferable not to generate waves during the night. 
   One refinement of the invention makes it possible to adapt the wave generator in a very straightforward way to the respective filling level of the aquarium. The wave generator should be arranged so that the one hand it can take in as much water as possible from the interior of the aquarium and, on the other hand, it is always immersed in the volume of water even with the strongest waves which are generated in the aquarium. 
   The effect achieved by one refinement of the invention is that an inlet, and outlet, a dirt extractor or the like essentially operate equally when there are waves and when the water is still. 
   Strong waves can be generated even in large aquaria. 
   The refinement of the invention wherein one of two wave generators operates at different frequencies can then influence the waveform. On the one hand, particularly abrupt wave profiles can be generated by superposition of the long-wave and short-wave components; on the other hand (with an appropriate amplitude and phase relation) it is also possible to set up short-wave flows of smaller amplitude. 
   Essentially periodic waves are then also obtained by a device wherein one of the two wave generators operates at twice the frequency of the other wave generator. 
   The refinements of the invention wherein the two wave generators lie close together and their flow axes are aligned parallel or are arranged on opposite walls with their flow axes pointing towards each other are preferable with a view to generating large amplitudes by wave units which reinforce one another. 
   Another refinement of the invention allows fine control over the amplitude of the waves being generated. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be explained in more detail by exemplary embodiments with reference to the drawings, in which: 
       FIG. 1  shows a vertical section through an aquarium having a wave generator; 
       FIG. 2  shows an axial view of a pump housing of a delivery pump, which is part of the wave generator shown in  FIG. 1 ; 
       FIG. 3  shows a block diagram of a controller for the wave generator shown in  FIG. 1 ; 
       FIG. 4  shows a similar representation to  FIG. 1 , but in which a modified wave generator is shown; 
       FIG. 5  shows a similar view to  FIG. 1 , but showing a wave generator arranged outside the aquarium; 
       FIG. 6  shows a vertical section through a small-range linear drive, which may be used in the wave generator according to  FIG. 5 ; 
       FIG. 7  shows a vertical section through a modified small-range linear actuator, which may also be used in the wave generator according to  FIG. 5 ; 
       FIG. 8  shows a similar view to  FIG. 1 , in which a further modified wave generator working inside the aquarium in shown; 
       FIG. 9  shows a view of an aquarium which is provided with two wave generators arranged on one of its narrow sides; 
       FIG. 10  shows a similar view to  FIG. 9 , but in which one wave generator is arranged on each of the narrow sides of the aquarium; and 
       FIG. 11  shows a schematic side view of a wave generator and the way in which it is fastened to an aquarium wall. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   In  FIG. 1 , the reference  10  denotes an aquarium in which there is a volume of water  12 . Its free surface  14  is aligned horizontally in the absence of any extraneous effects. 
   In order to set up conditions in the volume of water similar to those encountered when there are waves in open water, a wave generator denoted overall by  16  is arranged in the aquarium  10  and periodically moves the surface  14  of the volume of water  12  to and fro in oscillation during operation, between two extreme positions which are indicated at  18  and  20  in the drawing, respectively by dashes and by dots and dashes. 
   The wave generators are generally arranged on a narrow side of the aquarium. There, they may also be placed in a corner where they do not impede the view. The wave generators may, however, also be arranged in an end section of the aquarium which is covered on the outside by a shade. 
   It can be seen that there is a region in the middle of the aquarium where the water level changes little or not at all. In this region, a suction tube S via which a pump P takes in water near the surface dips into the upper layer of the volume of water. This water is sent by the pump P through a filter F and is fed back via a return line R into a lower region of the volume of water in the aquarium  10 . 
   The wave generator  16  comprises a storage container  22 , which has a cylindrical circumferential wall  24  and a bottom wall  26 . A window  28 , into which a delivery piece  30  of a delivery pump  32  is fitted essentially hermetically, is formed in the lower section of the circumferential wall  24 . The delivery piece  30  is carried by the end face of a pump housing  34 , which has a multiplicity of slotted through-openings  36  distributed equally in the circumferential direction in its circumferential wall. 
   Inside the pump housing  34 , there is a rotor denoted overall by  38  which has a hub  40  and propeller blades  42 , distributed equally in the circumferential direction, which are carried by the latter. The hub  40  is linked in rotation with the shaft of a variable-direction electric motor  44 . 
   The electric motor  44  is supplied with energy, and has its direction of rotation controlled, by a control unit  48  via a line  46 . 
   As another input signal, the control unit  48  receives the actual position of the surface  14 , as measured at a point near the edge. To this end, a level sensor  50  which has a float  52  interacting with the surface  14  is provided. 
   Another signal which the control unit  48  receives is the output signal of a level switch  54 , which is fitted in the storage container  22  and responds when the level inside the water, container has reached a predetermined level  56 . 
   Generally speaking, the control unit  48  operates so that it uses the output signal of the level sensor to determine which wave phase the surface  14  is currently in. As a function of this phase, the control unit  48  operates the delivery pump  32  so that potential or kinetic energy is delivered in-phase to the subvolume of water oscillating intermediate storage container  22  and the volume of water  12 . 
   Specifically, potential energy is delivered to the water when it is raised by the delivery pump  32  to a level inside the storage container  22  which is higher than the surface  14 , and kinetic energy is delivered to the water when it flows back from the upper region of the storage container  22  into the interior of the aquarium  10 , in which case the delivery pump  32  may also be run in the opposite sense in which the rotor  38  increases the flow rate of the water. 
   For lower energy input, however, the water may also be allowed to flow back from the storage container  22  merely under the effect of gravity. The delivery pump  32  designed as a propeller pump presents only a small resistance to such a return flow. 
   Such a propeller delivery pump  32  for use in a seawater aquarium with a volume of about 400 to 2000 litres may typically have a delivery power of between 2000 and 10000 litres per hour, with a delivery height corresponding to a water column of 20 to 30 cm. 
   If the water is intended to be further accelerated as it flows back, by operating the delivery pump  32  in reverse, then a stabilizing cross  58  as shown in  FIG. 2  is preferably also provided in the delivery piece  30  of the delivery pump  32 . In this exemplary embodiment, it comprises four thin plates lying in radial planes. 
     FIG. 3  shows a block diagram of the control unit  48 . 
   The output of the level sensor  50  is connected to the input of an amplitude measuring loop  60 . The latter contains an A/D converter and a memory, which is switched forward at a predetermined time interval and is dimensioned overall so that it can display one to three full periods of the surface movement. The amplitude of the surface movement is determined from this and sent as a digital signal to a control computer  62 . 
   The output of the level sensor  50  is furthermore connected to a phase and frequency measuring loop  64 . This is constructed similarly as the amplitude measuring loop  60 , in relation to digitising and storing measurement values, but the stored measurement data are with a view to the period and the phase relation of the output signal of the level sensor  50 . The corresponding results are likewise sent to an input of the control computer  62 . 
   This is also used to drive a voltage-controlled oscillator  66 . The output signal of the latter is sent to a controllable phase shifter  68 . The control terminal thereof is connected to an output of the control computer  70 . 
   The output signal of the phase shifter  68  is sent to a pulse encoder  70  which, generally speaking, operates so that it cuts a portion of adjustable width from the half-wave of the output signal of the phase shifter  68 . This may, for example, be done by using a controllable amplitude discriminator. The pulse-width control terminal of the pulse encoder  70  is connected to another output of the control computer  62 . 
   The control computer  62  furthermore interacts with a data memory  72  in which successive data triplets of amplitude, frequency and pulse width are stored. 
   By using these stored data and the reported actual values of amplitude and frequency, the control computer  62  then maximize the amplitude of the surface movement of the volume of water. This is done firstly by varying the phrase relation (control signal for the phase shifter  68 ) and then by varying the activation time of the delivery pump  32  (control signal for the pulse encoder  70 ). 
   Another input of the control computer  72  is connected to an input unit  74 , which is shown as a keypad. 
   When a setpoint value entered here for the amplitude of the wave in the aquarium  10  is reached then the maximization of the wave amplitude is ended, that is to say operation is thereafter continued with the equivalents for phase relation and pulse width unless a drop in amplitude necessitates readjustment of the phase relation and pulse width. 
   A last input of the control computer  62  is furthermore connected to the output signal of the level switch  54 . When this responds, then the trailing edge of a pulse generated by the pulse encoder  70  is always generated, which avoids overfilling the storage container  22 . 
   In the modified exemplary embodiment according to  FIG. 4 , components which have been already explained above with reference to  FIGS. 1 to 3  are still provided with the same reference numbers. These components will not again be described in detail below. 
   A displacing plate  76 , whose edge can be moved essentially fluid-tightly in the manner of a piston inside the storage container  22 , is arranged inside the storage container  22  instead of the delivery pump  32 . For the purpose of the present application, it may be assumed that the storage container  22  has a somewhat unrounded, for example elliptical cross section so that the displacing plate  76  is guided securely against rotation by the storage container  22 . 
   The displacing plate  76  is carried by a threaded spindle  78 , which interacts with a nut  80 . The latter is held by an axial bearing (not shown) and is likewise driven by an electric motor  44  whose direction of rotation is reversible. The electric motor  44  is driven similarly as described above with reference to  FIG. 3 . 
   In the wave generator shown in  FIG. 4 , kinetic energy is thus delivered to the volume of water in the aquarium  10  essentially by the downward movement of the displacing plate  76 . 
   If no very great efforts are made with a view to the sealing between the edge of the displacing plate  76  and the inner surface of the storage container  22 , the displacing plate can be raised again with air flowing into the space between the displacing plate and the water surface. The water then flows back under gravity through the window  28 . 
   If there is a good seal between the displacing plate  76  and the storage container  22 , then water will be sucked from the aquarium into the storage container  22  during the upward movement of the displacing plate  76  so that kinetic energy is likewise delivered to the volume of water during the upward movement of the displacing plate  76 . 
   The movement of the displacing plate  76  is matched by the control unit  48  to the surging of the water in the aquarium  10 , similarly as described in the first exemplary embodiment in connection with the operation of the delivery pump  32 . 
   In the exemplary embodiment according to  FIG. 5  as well, components which have already been described above are provided with the same reference numbers. These components need not again be described in detail below. 
   In the exemplary embodiment according to  FIG. 5 , the wave generator  16  is arranged outside the aquarium. 
   The aquarium  10  is arranged with its right-hand section in  FIG. 5  on a bearing rib  82 , which is designed as a rail having a sector-shaped cross section. This may extend over essentially the entire depth of the aquarium  10 , and a central rail section may be milled. 
   A base  84 , the length of which can be controlled, is provided in the end of the aquarium  10  placed on the left in  FIG. 5 . 
   As shown by  FIGS. 5 and 6 , the base  84  has a fixed lower base plate  86 , which carries a central bearing pin  88 . 
   A lower cam disc  90 , which has a central bore  92  fitting the bearing pin  88 , is mounted so that that it can rotate on the latter. A lower end face of the cam disc  90  is flat and cooperates with the end wall of a bearing chamber  91  which is formed in the base plate  86 . An upper end face of the cam disc  90  is provided with a cam surface  93  which, for example, may have a sinusoidal profile. 
   A complementary underlying cam surface  94  of an upper cam disc  96  cooperates with the cam surface  93  of the lower cam disc  90 . It also has a central bore  98  which fits the bearing pin  88 . An upper end face  100  of the cam disc  96  is flat. 
   The end face  100  carries an elastic support  102  which fulfils two functions: on the one hand, it fixes the upper cam disc  96  securely against rotation on the lower side of the aquarium  10  and, on the other hand, it allows the lower side of the aquarium  10  to tilt on the base  84 . 
   The lower cam disc  90  is provided on its circumference with ring gear  104  which engages with a pinion  106 . The pinion  106  is mounted in a pinion chamber  108  of the base plate  86  and is connected to the shaft of the electric motor  44 . 
   An elastic support  110  provided on the lower side of the base plate  86  provides secure and smooth placement of the base  94  on a support surface  112 . 
     FIG. 7  shows an alternative of a base  84  with a controllable height. It comprises two cooperating telescopic parts  114 ,  116 , each of which is in the form of a shallow cylindrical bowl. A diaphragm motor  118  made of elastomeric material is fitted inside the space delimited by the telescopic parts  114 ,  116 . 
   The diaphragm motor  118  is connected to the output of a pressure pump  120 , which takes in from a storage container  122 . The pressure pump  120  is controlled similarly to the operation of the electric motor  44  in the exemplary embodiment according to  FIG. 6 . 
   The interior of the diaphragm motor  118  can furthermore be connected to the storage container  122  by means of a solenoid valve  124 . The solenoid valve  124  is also controlled by the control unit  48  (generally speaking by the negative half-wave of the output signal of the phase shifter  68 ). 
   The pressurization and pressure release of the diaphragm motor  118  are controlled so that energy is delivered to the water in the aquarium in a correct phase relation with the surging of the water in the aquarium. 
   The exemplary embodiment according to  FIG. 7  also differs from the one in  FIG. 6  in that the upper end face of the base  84  (the upper-lying bottom of the upper telescopic part  114 ) is in the shape of a cap, as shown at  126 . The support  102  may therefore be obviated. 
   In the exemplary embodiment according to  FIG. 8  as well, components which have been already described are still provided with the same reference numbers. 
   Inside the aquarium  10 , there is a vertical displacing plate  128  which has a sleeve  130  at the upper end which extends over a guide rod  132  carried by the upper edge of the aquarium. 
   The displacing plate  128  furthermore carries a nut  134 , the axis of which is parallel to the axis of the sleeve  130 . The nut  134  interacts with a threaded spindle  136  which is in turn driven via toothed wheels  137 ,  139  by an electric motor  44 , which is likewise fixed to the upper edge of the aquarium  10 . 
   The electric motor  44  is driven similarly to the electric motor working on the horizontal displacing plate  76  in  FIG. 4 . 
   Wave-like displacements of the surface  14  of the volume of water  12  are again obtained by movement of the displacing plate  128 . 
   In the aquarium  10  shown in  FIG. 9 , two wave generators  16 - 1  and  16 - 2  are placed on the right-hand narrow wall. Their delivery pieces  30  are aligned parallel. 
   The wave generators  16 - 1  and  16 - 2  are connected to supply terminals “1” and “2” of the control unit  48 . The latter has a knob “1” on a console for each of the two wave generators  16 - 1  and  16 - 2 , by which the intensity of the water flow delivered by the wave generator can be adjusted, and a knob “P” by which the phase relation of a packet of water delivered by the wave generator can be adjusted. 
   The control unit  48  furthermore has other output terminals “−1” and “−2”, not required in the exemplary embodiment according to  FIG. 9 , at which the inverted output signals of the terminals “1” and “2” are provided. 
   The control unit shown in  FIG. 9  operates generally speaking so that it makes the two wave generators  16 - 1  and  16 - 2  deliver packets of water and take water back into their storage containers essentially synchronously. The water flows generated by the wave generators  16 - 1  and  16 - 2  are therefore added together. Waves with a large amplitude can thus be generated in long aquaria  10  by the arrangement shown in  FIG. 9 . 
   The different adjustability of the intensity and phase relation of the water flows delivered by the wave generators  16 - 1  and  16 - 2  can be used to compensate for differences in the propagation behaviour for these water flows, which are due to different contouring and different flow resistances of the content of the aquarium (sand piles, plants etc.). 
   The oscillation frequency of the volume of water contained in them, and the maximum achievable or recommendable wave height will be compiled below for some aquaria. 
   
     
       
             
             
             
             
             
             
           
             
             
             
             
             
             
             
           
         
             
                 
             
             
               1. 
                 
                 
                 
                 
                 
             
             
               2. 
               Dimensions (L × B × H) 
               3. 
               Frequency 
               4. 
               Max wave height 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               5. 
                 
                 
               6. 
                 
               7. 
                 
             
             
               8. 
               70 × 50 × 50 
               cm 
               9. 
               0.45 s 
               10. 
               40 mm 
             
             
               11. 
               100 × 70 × 60 
               cm 
               12. 
               0.56 s 
               13. 
               35 mm 
             
             
               14. 
               120 × 70 × 60 
               cm 
               15. 
               0.63 s 
               16. 
               35 mm 
             
             
               17. 
               150 × 100 × 60 
               cm 
               18. 
               0.83 s 
               19. 
               30 mm 
             
             
               20. 
               180 × 100 × 60 
               cm 
               21. 
               0.86 s 
               22. 
               30 mm 
             
             
               23. 
               220 × 80 × 50 
               cm 
               24. 
               1.10 s 
               25. 
               25 mm 
             
             
               26. 
               200 × 80 × 65 
               cm 
               27. 
               1.15 s 
               28. 
               25 mm 
             
             
                 
             
           
        
       
     
   
   Wave formation by superposition is particularly preferable for aquaria with a length of more than two metres. Besides the aforementioned fundamental oscillation, the half-period is also used. One generator is thus operated with a frequency which is about 1.1 s for a 2 m aquarium, and a second wave generator is operated with a frequency of about 0.55 s, i.e. twice the frequency. 
   The superposition of waves with a different wavelength also makes it possible to influence the waveform. It is thus possible to generate particularly strong waves, raise waves with steep fronts or even generate waves which are distributed in the form of fine ripples over the surface. 
   In order to switch off the wave generation during the night, the control unit  48  may interact with a sensor  148  responsive to ambient light or the aquarium illumination. When this establishes that the illumination has fallen below a predetermined level, it makes the control unit  48  suppress the output of activation signals to the wave generator/wave generators. 
   As an alternative, it is also possible for the amplitude of the wave produced at night merely to be reduced on the basis of the output signal of the sensor  148 . 
   When light strikes the sensor  148  again, whether daylight or light from the aquarium illumination, then the wave generator  16  is turned on again. 
   The control unit  48  furthermore has a button  150  which is pressed when fish in the aquarium need to be fed. The button  150  activates a timer (not shown in detail) in the control unit  48  which suppresses the wave generation for a predetermined length of time, which may be about 10 minutes in practice. In this way, food scattered over the surface of the water remains close to where it was scattered, and is not washed into water plants or decorative objects. 
   After the length of time specified by the timer has elapsed, the wave generator is automatically turned on again. 
   If desired, the output terminals “−1” and “−2” providing the inverted signals on the control unit  48  may be omitted, and the inverted signals may be applied if required by using jumpers on the normal output terminals. 
   An amplified flow of water is obtained in the exemplary embodiment according to  FIG. 10 . Now however, the two wave generators  16 - 1  and  16 - 2  are arranged on the two mutually opposite narrow sides of the aquarium. The two delivery pieces  30  of the wave generators now face towards each other. In order to obtain a flow amplification with this geometry, the wave generator  16 - 2  is now connected to the output terminal “−2” of the control unit  48 . 
     FIG. 11  shows the way in which a wave generator  16  is fitted to the wall of an aquarium  10 . A guide rail  138  is fastened to the upper end of the aquarium wall using a screw clamp  140 . A support slide  142  runs in the guide rail  138 . It can be fixed using a clamp screw  144  once it is in the correct position. 
   of the wave generator  16  is supported on the inside of the aquarium wall by an elastomeric support part  146 , which has a similar geometry to a sucker. 
   The height of the wave generator  16  can in this way be adjusted, and it can be secured to the aquarium while being exactly parallel to the wall of the aquarium. 
   The immersion depth of the wave generator  16  is adjusted so that, on the one hand, no water reaches the lid of the storage container and, on the other hand, the delivery pump  32  never emerges from the water, which would produce undesirable noise. 
   The control unit  48  may itself also be secured to the wall of the aquarium  10 . This may be done, for example, by using self-adhesive plastic hook strips. 
   With the wave generators as described above, in aquaria which may typically have a volume of from 200 to 1200 litres, it is possible to generate waves and water movements which are very similar to that encountered in reef biotopes. Since an oscillating movement is imparted to the volume of water in the aquarium, it is possible to set up even high waves with little energy input. 
   If a wave generator  16  is provided with a large storage container  22 , it is also possible to simulate an ebb and flow by keeping water pumped out for longer times. In such a case, the delivery pieces  30  of the delivery pump  32  will preferably be provided with a large-area plate-magnet valve, by which the water pumped from the interior of the aquarium  10  into the storage container  20  can be held there for a longer length of time, even if the delivery pump  32  is then turned off.