SYSTEM FOR RESTRICTING USER MOVEMENTS IN AN AQUATIC MEDIUM

Abstract

A system for restricting user movements in an aquatic medium relates to swimming systems and may be used for virtual reality (VR) simulation systems. By using the system, a swimmer returning force may be produced in response to the swimmer movement in any direction, the effect of presence in a VR may be increased, and requirements to the supporting portion and to the surface area of a zone utilized in a swimming pool may be reduced. The system comprises a flexibly resilient member retaining a swimmer (directly or via an intermediary) and anchored by means of a system of supports. The swimmer movements cause the resilient member to move in its entirety, without being deformed, such that its end elevation varies. The system responds by the resilient member flexing to the swimmer displacement in a horizontal direction. To provide for a vertical freedom, the resilient member is mounted on supports configured to rotate. Alternatively, the resilient member is configured to move translationally. The resilient member may be connected to a swimmer via a module secured on the swimmer's body or hand-held by the swimmer. The resilient member may have a curved shape to prevent it from colliding with the user.

Claims

1. A system for restricting user movements in an aquatic medium, the system comprising a flexibly resilient member, having a first end designed to be connected to a user and a second end designed to be anchored by means of a system of supports such: as to allow the resilient member to move in its entirety, without being deformed, in such a manner that elevation of the resilient member end, designed to be connected to the user, varies within a natural variation range of the user position depth when swimming along the water surface; that any substantial displacement of the user in any horizontal direction causes the resilient member to flex.

2. The system of claim 1, wherein the system of supports is disposed to rotationally move about an approximately horizontal axis distant from a swimming zone center.

3. The system of claim 2, wherein the resilient member end, designed to be anchored by means of the system of supports, is fixedly connected to the ends of two inclined supports, the supports having their opposite ends anchored at spaced apart points distant from the swimming zone center, such that the supports and the resilient member are rotatable relative to a straight line passing through the support anchoring points.

4. The system of claim 1, wherein the resilient member is disposed to translationally move along an approximately vertical axis.

5. The system of claim 4, wherein the resilient member is slidingly coupled to a system of at least two supports resting on distinct points distant from the swimming zone center.

6. The system of claim 1, wherein the resilient member is designed to be connected to the user via a module secured on the user's body or hand-held by the user.

7. The system of claim 6, wherein the module is designed to be hand-held by the user, and the resilient member is curved away from the user head at an area corresponding to the user head level and is freely rotatable about an approximately vertical axis.

8. The system of claim 1, wherein the resilient member is connected to the user via an intermediary element providing for the user rotational mobility about the resilient member.

9. The system of claim 1, wherein the system is used for virtual reality simulation systems.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] FIGS. 1 to 4 show a first embodiment, comprising a hingedly attached support:

[0039] FIG. 1 shows a version of the system comprising a single support;

[0040] FIG. 2 shows dynamic behavior of the system when a swimmer is moving upwards (hereinafter, the thicker arrows indicate departure directions of the system components in response to the user actions);

[0041] FIG. 3 shows the system behavior when the swimmer is moving towards a side-board of a swimming pool;

[0042] FIG. 4 shows the system behavior when the swimmer is moving away from the swimming pool side-board;

[0043] FIG. 5 shows a preferred implementation of the system according to the first embodiment, comprising two spaced apart supports;

[0044] FIGS. 6 to 9 show a second embodiment of the system:

[0045] FIG. 6 shows a fixedly anchored support with a sufficient bearing base;

[0046] FIG. 7 shows two supports fixedly anchored opposite each other, wherein the resilient member is translationally movable in response to horizontal movement of a swimmer;

[0047] FIG. 8 shows two supports fixedly anchored opposite each other, wherein the resilient member is translationally movable in response to vertical movement of a swimmer;

[0048] FIG. 9 shows a preferred implementation utilizing three arcuate structures secured at side-boards of a circular framed swimming pool;

[0049] FIG. 10 shows a swimmer anchored to a swimming pool bottom;

[0050] FIGS. 11 to 12 show a curved carrier utilized as a resilient member:

[0051] FIG. 11 shows a resilient member in the form of a C-shaped carrier;

[0052] FIG. 12 shows a trapezoidal resilient member;

[0053] FIG. 13 shows forces acting on a user secured by the resilient member;

[0054] FIG. 14 shows forces acting on a user secured by a suspension device (tether) for comparison.

DESCRIPTION OF EMBODIMENTS

[0055] A movement restriction system allows retaining a user (in particular, a swimmer) within a certain area of an aquatic space (a swimming zone, a simulation area) by means of a flexibly resilient member 1. Herein, the term swimming should be understood to mean any activity of the user in the aquatic medium, wherein the user applies efforts that may cause him/her to move.

[0056] The resilient member 1, at its first end (a retaining end 2), is connected to the user, and, at its second end (a retained end 3), is anchored at a system of supports (ref. to FIG. 1), for example, above or under the water surface. A system comprised by a single supporting member 4 or several supporting members 4, interconnected and anchored at a bearing surface 5, and the bearing surface as such, i.e. a swimming pool side-board, bottom or ceiling, may be utilized as the system of supports for the resilient member 1.

[0057] The retained end 3 must be anchored such that any substantial displacement of the swimmer in any horizontal direction would cause the resilient member 1 to flex. That is, for any retaining end 2 position depth, there is a region in a horizontal plane at its position depth, the region being disposed such that any exit of the retaining end 2 beyond that region causes the resilient member 1 to flex. Thus, the resilient member 1 responds to a horizontal displacement of the swimmer by flexing, rather than by stretching. In contrast to a system utilizing a tether, no force dragging the swimmer out of the water or to under the water is produced in response to a departure from an equilibrium position.

[0058] For any retaining system, an area may be defined, which a user should not exit; however, a certain displacement of the user within that area is normally allowable. In many cases, the swimming zone dimensions and shape are determined by the swimming pool dimensions and shape; moreover, there may be physical obstacles outside that area, such as a side-board of the swimming pool, and the user should be prevented from contacting them. As such, in response to a displacement of the user (and the point at which the system is secured on his/her body), which may lead to the user contacting the physical obstacles or any portion of the user body (in most cases, an outstretched arm of the user) exiting the designated swimming zone, the anchoring system should produce a returning force preventing any further displacement. Any departure causing a risk of the user exiting the swimming zone is herein referred to as a substantial departure from the swimming zone center. Indeed, in case of a substantial displacement, a returning force must be produced for the system to perform its retaining function. It should be noted that, in practice, where the swimming zone is defined for a wide range of users of different heights, arm lengths and physical qualities, the system should normally produce a sufficient returning force before the user displacement becomes substantial.

[0059] The resilient member 1 may be connected to the swimmer such as to allow him/her (the swimmer) rotate about a vertical axis separately or together with the resilient member 1. The connection to the swimmer may be of a hinged or a flexible type and may include using a short flexible intermediary element (for example, made of a rope or rubber) or other prior art joint providing for rotational mobility of the swimmer at the resilient member 1 attachment point within a range sufficient for the swimmer to freely swim.

[0060] The system is arranged such as to allow the resilient member 1 to move in its entirety without being deformed (for example, stretched). Such movement causes the retaining end 2 elevation to vary relative a selected horizontal surface, for example, the swimming pool bottom, i.e. the retaining end is displacing in a vertical direction. The displacement occurs at least within a natural range of variation of the depth at which the swimmer is positioned when swimming along the water surface. However, the retaining end 2 should not move or should move only to a minor extent in a horizontal direction in response to a depth variation. Otherwise, in case of a depth variation, the user would sense, from the retaining end 2, a horizontal pressure not associated with the user swimming activity; furthermore, the swimming zone center will have different horizontal coordinates at different depth, which is pointless for swimming pools having vertical walls.

[0061] Given the resilient member 1 vertical freedom, the system's bearing points are not required to bear the swimmer weight; moreover, in an implementation where the supports are rotatable about a horizontal axis, they are not required to bear the major portion of the overall system weight, since it bears upon the water, the swimmer, and a buoyancy member. In this way, requirements to the system anchoring at a bank may be significantly reduced. It is sufficient to restrict the system movement at the bank and to restrict movements of the ends caused by small forces. Since the system is unresponsive to the swimmer weight, it does not produce any destructive effect on the system; the swimmer weight action is not transmitted to the system, thus further reducing the requirements to the system supports.

[0062] For virtual reality systems, a minimum restriction of the swimmer activity is preferable. The claimed system acts on a swimmer in a more uniform manner; it does not prevent him/her from diving, does not drag him/her from the water or to under the water, thus not producing any excessive effect not reinforced, visually or otherwise, in the virtual reality, thanks to a reduced disadvantageous effect of the force's vertical component.

[0063] In the systems utilizing tethers, the vertical component of the force, exerted on a swimmer by the system, increases with an increasing swimmer departure from the swimming zone center. Said disadvantageous effect is associated with the vertical component heterogeneity. In systems where a user is fixedly anchored at a certain depth, when the system is rapidly dampening the vertical component of the forces (in particular, sharp forces) of the user movements, such vertical effect produces a sensation of a restriction being imposed.

[0064] When swimming naturally, in response to outward forces produced by the user legs, arms and trunk, to a displacement of the center of mass due to arm and leg movements, and to buoyancy variations due to breathing, a vertical force component is inevitable produced. That is why, in the absence of restrictions, even when swimming along the water surface (without intentionally diving down), the position depth of any point on the user body varies within a certain range, herein referred to as the point's natural swimming position depth variation. Specifically, a user body point at which the retaining system is attached tends to vary its position depth.

[0065] Furthermore, by acting against such depth variation, the retaining system destroys the sensation of natural swimming, produces a fixed stop sensation, and prevents the body from taking a posture relative to the water surface, which it would have taken, if swimming naturally.

[0066] The claimed system eliminates said disadvantageous effect by minimizing the vertical component of the force produced by the retaining system, for example, by providing a vertical freedom of movement of the point of the system attachment to the user body at least within the range of its position depth variation when the user is natural swimming along the water surface. The range of this point natural displacement in natural swimming is referred to herein as the range of the natural user position depth variation.

[0067] Tests of claimed system, in combination with virtual reality simulation systems, have demonstrated that, in contrast to the devices utilizing tethers (ropes, cables or other elements that respond by stretching to a movement), the swimmer sensations become more homogenous and more as expected, thus increasing the effect of presence in a virtual reality. Where tethers are used as a retaining member, the user feels the tether tension, feels that his/her spatial movements are restricted, that it is impossible, for example, to reach the swimming pool side-board. Users of the claimed system report that they do not feel any restriction, such that they no longer understand the real distance to the swimming pool side-board.

[0068] The resilient member 1 is the main component providing a smooth return of a swimmer to the swimming zone center. It may be a rod of a necessary length. The resilient member 1 is made of material allowing it to recover its original shape following flexural deformation in conditions of horizontal mobility under a force expected from a user. Owing to its resiliency, the member 1 provides the system restoration to a central position of equilibrium upon release of the swimming forces. The resilient member 1 may be made, for example, of fiberglass, carbon fiber reinforced plastic, metal.

[0069] Resiliency of the member 1 may be selected based on the swimming pool dimensions (a desired swimming zone surface area) and the nature of the swimmer efforts. In cases of smaller dimensions and/or more athletic style of swimming, said member may be more rigid. In cases of large swimming pools and/or relaxed swimming, the rigidity may be lowered. Such adjustment may also be done through increasing or reducing the resilient member 1 effective length by varying the position of the point where the resilient member 1 is connected to the supporting members 4. By increasing the resilient member 1 length or by reducing its rigidity, loads on the swimmer body attachment point may be mitigated due to a large radius of the swimming zone; conversely, by reducing the resilient member 1 length or by increasing its rigidity, the horizontal coordinates of the body position in the swimming pool may be made almost completely fixed, thus significantly reducing the size of the zone sufficient for swimming, which is relevant, for example, in cases where the system is installed in small framed swimming pools having a radius of 3 to 4 m.

[0070] The resilient member 1 retaining end 2 vertical mobility may be obtained by providing for the resilient member 1 translational mobility along an approximately vertical axis in response to a swimmer motion.

[0071] Furthermore, to provide for the vertical mobility, the supporting member 4 may be installed to rotationally move about an approximately horizontal axis distant from the swimming zone center. In this way, load is removed from the system supporting portion (the system attachment points at the bearing surface), they do not have to bear their own weight, which is important in cases of long, heavy and bulky supports.

[0072] The term distant from the swimming zone center with reference to the system members, points or axes should be understood to mean that they are disposed at a certain distance from the point of equilibrium corresponding to the swimmer position when the resilient member is not deformed. Where an aquatic space is used in an optimal manner, said distance is usually comparable with the swimming zone radius, so the support anchoring points, being positioned outside the swimming zone, do not create any obstacles for a user. The anchoring points may be disposed near the swimming pool along its perimeter, i.e. in the vicinity of the water boundary, of the waterbank/swimming pool side-board interface area, or, if used in an outdoor body of water, at other mobile or stationary object (a pier, a motor boat, etc.). For example, at the swimming pool handrails, side-boards, floor, walls, etc. Furthermore, they may be disposed at various elevations: above the water level or below the swimming pool floor level; that is, where reference is made to a position near, it may indicate either a vertical, or a horizontal displacement relative to the water surface.

[0073] The terms approximately vertical axis or approximately horizontal axis should be understood to mean that a member may be disposed either on the respective, i.e. horizontal or vertical, axis, or on an oblique axis close to it. Furthermore, it is preferably disposed closer to said axis or on it, while any deviation is only allowable as long as a sufficient uniformity of the produced load is provided for.

[0074] A rigid or a hard elastic supporting member 4 may be used as the support. In that case, at least one supporting member 4 is connected, at its first end, to the bearing surface 5 and, at its second end, to the resilient retaining member 1. The connection may be rigid or may allow the resilient member 1 to rotate and/or shift along an approximately vertical axis.

[0075] The supporting member 4 must be strong and rigid enough to prevent substantial horizontal displacement of the point, where the supporting member 4 is connected to the resilient member 1, under the action of the swimming forces produced by the swimmer, wherein the displacement is substantial in comparison with the swimmer horizontal displacement. The supporting member 4 may be resilient to a certain extent. However, the rigidity of a single supporting member 4, for example, attached to a swimming pool side-board, bottom or ceiling, must be much higher than that of the resilient member 1. Where two supporting members 4 are utilized, for example, those resting upon the same side-board of the swimming pool such as to form a triangular structure, their rigidity may be lower in view of a higher rigidity of the structure. Even less rigid supporting members 4 may be used in case where three or more supporting members 4 form a pyramid- or a dome-like structure, for example, resting upon distinct sides of the swimming pool. The supporting members 4 may be comprised of, for example, tubes made of an aluminum alloy, fiberglass or carbon fiber reinforced plastic. For ease of storage and transportation, the supporting members 4 may be constructed from assemblable shorter elbows.

[0076] The system's geometry is such that its components do not prevent free swimming in any direction. Specifically, where the system is anchored above the water surface, elevation of the supporting members 4 above the surface must be sufficient for a snorkel tube to freely pass below them when a swimmer is making turns. Where disposed under water, the supporting members 4 must be disposed in an area in which they would not be touched by the swimmer's legs.

[0077] The system may be implemented in various ways.

[0078] In a first embodiment, a connection between the supporting member 4 and the bearing surface 5 is selected such as to allow it to rotate about a horizontal axis passing through a point/points of connection to the bearing surface 5. For example, the supporting member 4 may be anchored via a hinged connection. Since the system is not intended to restrain the swimmer movement in a vertical direction, there is no need to provide a support in that direction. The opposite end of the hinged supporting member 4 is movable in a vertical plane and may, together with the resilient member 1 and the swimmer, freely move in a vertical plane around a large-radius circumference determined by the supporting member 4 length, thus allowing the swimmer position depth to freely vary in response to any departure of the swimmer from the zone center. The larger the distance between the swimming (simulation) zone center and the horizontal axis (the longer the support), the larger the circumference radius and the closer to vertical is the movement of the resilient member 1 retaining end 2. In this case, the vertical load exerted on the swimmer belt by the carrier (supporting member 4) is determined by the supporting member 4 weight and is essentially independent of the magnitude of swimmer departure from the equilibrium position.

[0079] The support (supporting member 4) weight may be offset by providing additional buoyancy, for example, by arranging buoyancy elements at the swimmer belt or at the supporting member 4 end.

[0080] One way of implementing the system according to the first embodiment is shown in FIG. 1. Herein, a supporting member 4 (a carrier) is anchored via an axial hinge at a bank (at a swimming pool side-board). The carrier is shaped such as to allow a swimmer to freely swim below it without striking a snorkel against it, while the retaining member 1 resiliency allows returning the swimmer into an initial central position in the swimming pool, if the swimmer departures from it. Furthermore, the system allows the swimmer to move in a vertical direction (FIG. 2) and remains operable when the swimmer turns backwards (FIG. 3, FIG. 4).

[0081] A preferred way of implementing the system according to the first embodiment is shown in FIG. 5. The system comprises two inclined supporting members 4, installed at a bearing surface 5 spaced apart from each other and fixedly connected to a resilient member 1 to form a triangular pyramid. Furthermore, the member 4 bearing points are distant from the swimming zone center, and the members 1 and 4 are rotatable around a straight line passing through them. The rigid triangle comprised by the supporting members 4 is rotatable about the bank anchoring axis. The supporting members 4 are disposed relative to each other so as to enhance stability of the structure in the main horizontal operating direction. As a result, a lightweight, quick-detachable and stable structure is produced. Herein, any two attachment points, for example, the swimming pool handrails or side-board, may act as the bearing surfaces. Suction cups may be used for securing the bearing surface 5. To install such structure, only one swimming pool side-board may be utilized, while no other walls or projections are needed; as such, the structure is suitable for large and outdoor swimming pools.

[0082] In a second embodiment, vertical mobility of a swimmer is provided by a resilient member 1 translationally movable, in response to a swimmer motion, relative to an immovable supporting member 4 (or a system of supporting members 4) at their connection point in an approximately vertical direction. Herein, immobility of the supports at the resilient member 1 anchoring point is provided in various ways. For example, a rigid supporting member/carrier 4 is fixedly anchored and has a sufficient bearing base at the bearing surface 5 (ref. to FIG. 6), the latter may be a swimming pool side-board or bottom (FIG. 10), or an indoor space wall or ceiling. The immobility may also be provided by producing a rigid structure comprised by several supporting members 4 resting upon spaced apart points (for example, at opposite side-boards of the swimming pool) and having their ends connected above the swimming zone center. Such implementation is efficient in cases where it is possible to create, by means of the supporting members, an immovable or substantially immovable point directly above or below the movement zone center.

[0083] This embodiment may be implemented with the maximum efficiency by using supporting members 4 installed at opposing side-boards (banks) (ref. to FIG. 7, FIG. 8). The supporting members 4 are connected to each other above the water surface to form a dome, at the apex of which a resilient member 1 is installed in such a manner that it can translationally move. Such implementation reduces the requirements to the rigidity of supporting member 4 anchoring at the bearing surface 5 and to restriction of their mobility, as they are prevented from rotating by being secured to each other. For small framed swimming pools, it is most preferable to use a system of three or more supporting members 4 (FIG. 9) connected to each other and resting upon distinct points of the swimming pool perimeter, and slidingly connected to the resilient member 1 to provide for the resilient member 1 translation movement in response to the swimmer motions.

[0084] The supporting member 4 may be connected to the swimmer directly or via an intermediary element.

[0085] The resilient member 1 may be coupled to the swimmer via a module 6 hand-held by the swimmer or secured on the swimmer's body, for example, disposed on a vest. The module 6 may be equipped with hand grips for the swimmer to hold it in two hands in front of him-/herself (ref. to FIG. 11, FIG. 12), thus obviating the need for a swimmer belt or harness. In this way, the process of swimmer preparation for swimming with the use of the system may be simplified. Here, the module may be used as a game controller to simulate, in a virtual reality, the actions of various tools held with both hands (a weapon, a photo camera), thus providing a wider range of gaming scenarios without making the system more complex or adding new monitored devices. Where the module 6 is hand-held, it may be provided with more vertical displacement freedom (as compared with other implementations of the claimed system) to make the module freely movable in front of the user.

[0086] The shape and method of the supporting member 4, resilient member 1 and module 6 connection may be selected such as to provide for the best possible swimmer mobility with a minimum risk of the swimmer colliding with the system components. For example, FIG. 11, FIG. 12 show an implementation of the system, wherein, with a curved shape of the resilient member 1, the swimmer may prevent his/her head and snorkel collision when holding the module 6 in his/her hands. To this end, the resilient member is curved away from the user head at the resilient member 1 portion where the user head could come into contact with the resilient member 1. The resilient member must be freely rotatable about an approximately vertical axis, such that its curvature position be consistent with the user swimming direction. For example, the resilient member 1 may be configured as a C-shaped carrier (FIG. 11) or be trapezoidal (FIG. 12).

[0087] Operation of the claimed system will now be described in comparison with the prior art systems utilizing tethers as a member retaining a swimmer and producing a returning force.

[0088] When a body secured by means of a flexibly resilient member departs from an equilibrium position, such member produces centrally directed returning forces, the forces increasing with an increase in the departure.

[0089] FIG. 13 shows the forces exerted on a swimmer, who is retained in a central zone by a resilient member in the form of a resilient curved rod, at the time of the maximum swimmer departure from an equilibrium position in response to applying a maximum swimming force F.sub.max in a horizontal direction. Where the resilient member is long enough, as compared with the swimmer displacement, its elastic force tending to return the swimmer to the equilibrium position at this time may be approximately calculated as follows: k.Math.x.sub.max, where x.sub.max is the swimmer displacement relative to the equilibrium point with the maximum force applied, k is the elastic coefficient of the rod. In the above position, the swimmer is stationary, so his/her acceleration is equal to zero, and Newton's second law, projected onto a horizontal axis of displacement, will be written as:

F.sub.max=k.Math.x.sub.max[Mathematical Formula 1]

[0090] from which:

x.sub.max=F.sub.max/k[Mathematical Formula 2]

[0091] Since the F.sub.max value is bounded from above by human physical capabilities, then, by increasing the coefficient k by selecting a more rigid resilient member, an indefinitely small maximum allowable displacement x.sub.max may be obtained, thus limiting the minimum allowable size of the zone necessary for swimming.

[0092] By way of comparison, FIG. 14 shows the forces acting on a swimmer in response to the swimmer maximum departure from the equilibrium position, when the swimmer is retained by a suspension device (tether). The swimmer also applies the force F.sub.max in a horizontal direction. The tether T tension force T is directed towards the tether anchoring point, which is anchored at elevation h departing from the vertical line by an angle .sub.max. Let the swimmer negative buoyancy value at the point of maximum departure be equal to P. Then Newton's second law, projected onto the horizontal and vertical axes, will be written as:

[00001]$\begin{array}{cc}.Math.F_{\max }.Math.=.Math.T_x.Math.& \left[\mathrm{Mathematical}\mathrm{Formula}3\right]\end{array}$$\begin{array}{cc}.Math.P.Math.=.Math.T_x.Math.& \left[\mathrm{Mathematical}\mathrm{Formula}4\right]\end{array}$

[0093] Hence,

[00002]$\begin{array}{cc}\mathrm{tg}\left({}_{\max }\right)=\frac{.Math.x_{\max }.Math.}{.Math.h.Math.}=\frac{.Math.T_x.Math.}{.Math.T_y.Math.}=\frac{.Math.F_{\max }.Math.}{.Math.P.Math.}& \left[\mathrm{Mathematical}\mathrm{Formula}5\right]\end{array}$

[0094] From which

[00003]$\begin{array}{cc}.Math.x_{\max }.Math.=.Math.h.Math..Math.\frac{.Math.F_{\max }.Math.}{.Math.P.Math.}& \left[\mathrm{Mathematical}\mathrm{Formula}6\right]\end{array}$

[0095] Thus, x.sub.max at a given elevation of the tether (suspension device) anchoring point and the maximum swimmer force F.sub.max may only be reduced by increasing his/her negative buoyancy value (by adding more weight), which is significantly disadvantageous in various ways. First, a large additional weight is disadvantageous in that it increases the load on and the requirements to the tether (suspension device) anchoring point. Second, negative buoyancy increases the risk of accidents in the event of tether breakage. Third, such added mass will add to inertia during the swimmer movements, either translational, or rotational. As such, in practice, it is reasonable to provide anchoring by means of an overhead tether, in case where the user buoyancy is close to neutral. In this event, buoyancy only starts to decrease when the user departs in such a manner that he/she is partially lifted from the water (then, if the weight is unchanged, the Archimedes force starts to decrease). Otherwise, until an angle is reached, at which the tether starts lifting the user out of the water, no forces are exerted on the user by the tether in a horizontal direction, thus resulting in the above-described jerking effect in response to a load applied to the tether.

[0096] In this way, by using a resilient retaining member, the necessary water body surface area, specifically, that of a simulation zone, may be reduced, and a more uniform distribution of forces may be obtained.