WO2014121997A1

WO2014121997A1 - Method for determining a wave increasing and/or speed potential field in a body of water moved by waves

Info

Publication number: WO2014121997A1
Application number: PCT/EP2014/050890
Authority: WO
Inventors: Alexander Poddey; Nik Scharmann; Benjamin Hagemann; Jasper Behrendt
Original assignee: Robert Bosch Gmbh
Priority date: 2013-02-08
Filing date: 2014-01-17
Publication date: 2014-08-14
Also published as: DE102013002127A1

Abstract

The invention relates to a method for determining a wave increasing and/or speed potential field in a body of water moved by waves. Measurement data is ascertained at at least two measurement locations (81, 82) which are located on a measurement surface (80, 80') oriented substantially parallel to a calm water level (70) of the body of water, and the wave increasing and and/or speed potential field is determined from the measurement data. (Figure 6a)

Description

Method for determining a wave-raising and / or velocity potential field in a wave-driven body of water

description

The present invention relates to a method for determining a wave-raising and / or velocity potential field in a wave-moved body of water, as well as means for its implementation, in particular in a wave energy converter and / or a

Wave energy converter Park.

State of the art

For the conversion of energy from water movements in water into usable energy a number of different devices are known. For example, G. Boyle, "Renewable Energy," 2nd Ed., Oxford University Press, Oxford, 2004. Such devices are referred to herein as "wave energy converters."

Wave energy converters, which are arranged with their moving parts under the water surface and exploit a wave orbital motion present there, are of particular interest in the context of the present invention. The wave orbital motion can be converted into a rotational movement by means of rotors. For this purpose, rotors with coupling bodies, e.g. hydrodynamic lift profiles. Such a system is disclosed in US 2010/0150716 A1. However, the invention can be applied to all wave energy converters as well as other turbines in wave-driven waters affected by wave motion.

In such systems, it may be advantageous to determine the expected wave exposure in advance, in order to predict occurring loads in particular and to be able to put appropriate systems in a high-energy scenarios emergency mode in a protective mode. Under high energy scenarios, for example, waves with unusual in the context of this application high speed, amplitude or a certain, the systems burdening frequency pattern understood.

In addition, a wave energy converter can be operated with knowledge of the expected Wellenbeaufschla- tion adapted to this, for example, to maximize the energy yield of the wave energy converter.

Known methods for predicting the wave exposure of turbines in wave-moving waters include, for example, the generation of statistical data (spectra) of seas. This can be done for example by means of a point measurement by means of so-called waverider buoys, the evaluation of radar data or the use of Doppler signals. The latter is disclosed, for example, in US Pat. No. 7,768,874, B2.

A deficiency of the known methods is, in particular, to be regarded as the limited functionality of the aforementioned measuring methods, which either make punctual and therefore insufficient measurement data available and / or frequently do not function reliably. For example, the functionality of radar sensors is significantly limited by rain. Radar systems must also be installed far above the water surface, which in particular requires a considerable additional effort in the wave energy converters explained in the introduction.

There is therefore a need for improved methods for the deterministic, non-statistical prediction of the turbulence of turbines in wave-driven waters, in particular of wave energy converters. Disclosure of the invention

Against this background, the present invention proposes a method for determining a wave elevation and / or velocity potential field in a wave-moving body of water, as well as means for its implementation, in particular in a wave energy converter and / or a wave energy converter park, having the features of the independent patent claims. Preferred embodiments are subject of the dependent claims and the following description.

Advantages of the invention

A method according to the invention serves to predict a shaft loading of at least one installation located in a wave-moving body of water, in particular at least one shaft. energy converter. From measurement data of at least two different measurement locations located on at least one measurement surface oriented substantially parallel to a water table of the water body, a wave collection and / or velocity potential field in the wave-moved body of water can be computationally determined ("reconstructed").

For the determination of the measurement data, different methods are available, wherein in the context of the application, in particular the use of one or more acoustic Doppler flow profile as sensors is described. However, the use of pressure sensors, shaft height sensors, buoys, lidar sensors and / or radar sensors for determining the measured data is also advantageous. It should be noted that the sensor or sensors are spatially separated both at the plant itself and from it, e.g. at buoys or similar can be attached.

An essentially parallel to a water level of the water body oriented measuring surface is preferably oriented parallel to the water level of the water body or closes with this an angle of at most 10 °, preferably at most 6 °, a.

Preferably, a sensor is arranged in a water depth in which energetically particularly relevant wave frequencies can be measured in a suitably resolved manner. The use of multiple sensors located at different depths is particularly advantageous in broadband wave spectra (i.e., many wave frequencies). The respectively selected measuring depth expediently represents a compromise between the spatial range of the sensor in the wave propagation direction and the measuring accuracy. If different measuring surfaces are measured, their measured data are preferably computationally combined in order to determine the wave height and / or velocity potential field.

The sensor or sensors are preferably aligned with their measuring direction counter to the main shaft preparation direction ("flow direction"). When using a plurality of sensors, in particular for covering different main shaft preparation direction, different measuring directions can be selected, for example a grid-like (parallel or crosswise), a fan-shaped (polar) or a star-shaped (polar) arrangement of the measuring directions.

From the reconstructed wave elevation and / or velocity potential field, the wave loading of the plant can then also be predicted mathematically. As a result, the operation of the system can be significantly improved. In particular, a feedforward control can take place so that occurring control deviations are reduced. As a result, the control interventions can be reduced, the control becomes more robust. The operation becomes less reactive. For the prediction of the wave exposure (ie propagation of the wave elevation and / or velocity potential field), a spectra simulation, in particular a so-called three-dimensional high order spectral method (HOS, see, for example, Ducrozet, G., Bonnefoy, F., Le Touze, D and Ferrant, P .: 3-D HOS simulations of extreme waves in open seas, Nat. Hazards Earth Syst., Sei. 7, 2007, 109-122). Alternatively, simpler methods such as linear Airy theory can be used for reconstruction and propagation.

One aspect of the invention is the use of said acoustic Doppler flow profiler. Acoustic Doppler flow profilers are sold, for example, by the company RD Instruments under the name ADCP (Acoustic Doppler Current Profiler, ADCP). A special design of the ADCP is the horizontally measuring ADCP (also referred to as H-ADCP). Acoustic Doppler flow profilers have long been known for measuring currents in waters and are particularly suitable for determining directional components of the velocity vector field. Acoustic Doppler flow profilers measure extremely reliably, so that the results obtained are sometimes used as reference values for the validation or calibration of other flow measuring systems. In particular, owing to their cost-effectiveness, their high information density and their reliability, acoustic flow measuring systems have prevailed since the beginning of the 1990s for flow measurement in certain areas. Acoustic Doppler flow profilers can be used, for example, on ships, anchored to the ground and / or at different depths and / or with different operating frequencies. From its point of attachment, an acoustic Doppler flow profiler punctually measures a three-dimensional flow vector permanently and temporally highly resolved for different depth layers up to the water surface. When mounted horizontally or when using a horizontally-measuring acoustic Doppler flow profiler (H-ADCP), the flow can be continuously monitored in a defined depth layer (i.e., for measurement sites located on a measurement surface oriented substantially parallel to the water level of the water). The use of an acoustic Doppler flow profiler can be used, for example, on vessels for multi-dimensional flow measurement at different depths during different tidal phases. In this way, for example, flow atlases can be created for certain areas for use in coastal protection. An example of the use of a Doppler acoustic airfoil is disclosed by Cysewski, M.C .: Characterization of flow field structures measured with an Acoustic Doppler Current Profiler. Geesthacht: Helmholtz Center Geesthacht, Center for Materials and Coastal Research GmbH, 201 1.

According to one aspect of the invention, a wave energy converter is operated as a plant. The invention presents a method which includes a precontrol of the manipulated variables (in particular generator torque and / or angle of attack (pitch angle) of the coupling body) allows. The operation preferably comprises a control, wherein the controlled variable may be a phase angle between a rotational movement of a rotor of the wave energy converter and an orbital flow of the wave motion. For further details on intervention or control options for the energy conversion, reference is made to the non-prepublished DE 10 201 1 105 177, the disclosure of which is made part of the present invention. As a result, the control interventions can be reduced, the control becomes more robust. The operation of the wave energy converter is improved because less has to be responded to changes already occurred (which leads to a deterioration of energy production), and instead by means of a feedforward control of the wave energy converter is already set to expected changes (which a deterioration of energy production reduced or completely prevented). The conversion efficiency is increased. This applies in particular to multichromatic wave states which place particularly high demands on the control of wave energy converters. Furthermore, there are particularly advantageous options when it comes to protective measures.

Especially for wave energy converters, which use the hydrodynamic lift principle, a very good knowledge of the flow field is crucial, since in case of incorrect control / regulation a decoupling of the system from the local flow and thus the wave motion can occur. In this case, the efficiency of the system would decrease significantly. In addition, the mechanical load on the system would increase significantly. In the context of the invention, the flow field induced by the waves is calculated on the wave energy converter in order to enable a control of the system.

According to another aspect, the invention can also be used in areas in which a prediction of the wave motion offers advantages for the operation or safety of a marine construction. The operation may include, for example, bringing into a rest position (e.g., feathering position with coupling bodies of wave energy converters). Furthermore, offshore operations can be carried out more efficiently (e.g., transferring a load from a moving ship to an oil rig or to the seabed, crew transfer from a maintenance ship to an offshore wind turbine, dynamic positioning of a ship). In particular, however, the invention can be used in wave power plants to increase the conversion efficiency. In this context, the invention can be used particularly advantageously for concerted control of a plurality of power plants (parks). This applies in particular to the case where the absorption and / or emission characteristic of the individual power plants is known and can be described by suitable models.

Preferably, an acoustic Doppler flow profiler, in particular an H-ADCP, for measuring the incoming wave motion in spatial and temporal dimension on the below the surface occurring flow vectors used. This allows a deterministic reconstruction of the surface elevation. It is thus possible to make spatial and temporal statements about the wave survey including all flow vectors below the surface. The H-ADCP is particularly suitable for the method according to the invention if it has a particularly high sampling frequency.

In order to be able to include movements of the sensor in the calculation, additional movement measuring devices can be used. For example, accelerometers can be used. As a result, erroneous speed values that result from a horizontal translational movement of the sensor can be corrected. Furthermore, values can be determined via a rotational and vertical translatory movement of the sensor by means of corresponding movement measuring devices and used for a more accurate computational reconstruction of the wave collection and / or velocity potential field. The use of an H-ADCP is particularly suitable for use in an offshore park, for example a wave or wind energy converter park. In this case, an H-ADCP can be provided in common for a large number of corresponding systems, for example wave energy converters. It is also possible to provide a plurality of H-ADCPs, the measuring direction of which is preferably not oriented parallel or rectified, so that a wider angular range can be covered. As a result, the detection of multi-directional sea state systems is possible. In order to simulate a higher sampling rate, the sensors can also be arranged offset, so that they can measure the same wave state at different phase angles. As a result, an improved resolution, in particular of complex wave states, can be made possible. The H-ADCP can also be attached to structures separate from the system, so that a largely uninfluenced by the system measurement is possible.

Preferably, the expression of the flow vector field detected at each time point is used in order to reconstruct the wave collection and / or velocity potential field in at least a required extent by calculation. A reconstructed wave collection and / or velocity potential field can then be propagated to the individual plants with the aid of a suitable propagation process. In this way, for each individual plant, for example each wave energy converter at the location of a wave energy converter park, the expression of the flow vector field can be determined in a spatially and temporally resolved manner, as far as necessary. In particular, the propagation of the flow field entering the systems in the future is known by such propagation of the wave motion, so that the control / regulation of each individual system can access this information and determine an optimal trajectory including optimal pitch adjustment and generator torque control. Through appropriate sensor technology, the maintenance of be monitored and, if necessary, readjusted by a corresponding regulation.

Particularly suitable for the invention is such an H-ADCP as marketed by the company RD Instruments. Such an H-ADCP operates with a measurement frequency of 300 kHz. It is a narrow-beam acoustic monitoring system that measures horizontally from where it is located, detecting currents and multidirectional waves near or near the surface of the water body (or the corresponding depth). By means of this H-ADCP up to 128 individual points in a horizontal range of up to 200 m can be detected, so that from this the entire wave structure or a corresponding wave field can be reconstructed. The previous use of such sensors, however, limited to the monitoring of incoming waves to predict maximum events safely.

An arithmetic unit according to the invention, e.g. a drive unit of a system located in a wave-moving body of water, in particular a wave energy converter is, in particular programmatically, adapted to carry out a method according to the invention.

The implementation of the invention in the form of software is also advantageous, since this allows particularly low costs, in particular if an executing arithmetic unit is still used for further tasks and therefore already exists. Suitable data carriers for providing the computer program are, in particular, floppy disks, hard disks, flash memories, EEPROMs, CD-ROMs, DVDs and the like. It is also possible to download a program via computer networks (Internet, intranet, etc.). Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination indicated, but also in other combinations or in isolation, without departing from the scope of the present invention.

The invention is illustrated schematically with reference to an embodiment in the drawing and will be described in detail below with reference to the drawing. figure description

Brief description of the drawings FIG. 1 shows a schematic representation of wave orbital motions under the surface of a wavy moving body of water. Figure 2 shows a wave energy converter, which can be operated according to the invention, in a partially perspective view.

FIG. 3 shows the wave energy converter of FIG. 2 in a wave field in a more schematic representation.

Figure 4 shows a wave energy converter park, which can be operated according to the invention, in a schematic representation.

FIG. 5 illustrates a method according to an embodiment of the invention in the form of a schematic flow chart.

Figure 6 illustrates different arrangement and alignment possibilities for sensors.

In the figures, identical or equivalent elements carry identical reference numerals. A repeated explanation is omitted.

Embodiments of the invention

FIG. 1 shows a schematic representation of wave orbital motions under the surface of a wavy moving body of water. A wave on the surface of the water is designated by W. At a position A there is a wave crest, at a position C a wave trough. The wave propagates in a wave propagation direction 1 1. At positions B and D are the transitions Wellenberg / Wellental and Wellental / Wellenberg. The mean water surface is designated 12.

Due to the wave motion below the surface of the water wave orbital movements result in the form of orbital paths 13, which are only partially provided with reference numerals. Immediately below the surface of the water body, these orbital paths 13 each have radii r, which correspond to the amplitude of the wave W. The radii decrease with increasing distance to the surface of the water. In deep water, the orbital trajectories 13 are circular, in the shallow water increasingly elliptical. The local water movement is shown in FIG. 1 in each case in the form of short, bold arrows which correspond to the respective motion vectors v. Under a wave crest at position A, the entirety of the water particles moves in the direction of the wave propagation direction 1 1. Under a wave trough at position C, the entirety of the water particles moves towards the wave propagation direction 1 1. In the transition from a wave crest (position A) to a wave trough (position C) progressing in the wave propagation direction, at position B there is a situation in which the entirety of the water particles move vertically upward. Conversely, in the transition from a wave trough (position C) to a wave crest (position A), again progressing in wave propagation direction 1 1, the entirety of the water particles moves vertically downwards. Overall, results in a fixed position, a continuous change in the direction of flow, whose rotational speed corresponds to the shaft frequency. In multichromatic waves there is a temporal variability.

In particular, the present invention comprises the prediction of a wave loading of a system located in a wave-moved body of water, for example a wave energy converter, by a particularly simple and proven detection of flow characteristics of a water body. On the basis of the detected flow characteristics, a wave field in the water body is mathematically reconstructed and propagated. In Figure 2, a wave energy converter is shown, which is the wave orbital motion shown

Use can. The wave energy converter is designated overall by 1. It has a rotor 2, 3, 4 with a rotor base 2, on which over rotor or lever arms 4 elongated lift profiles 3 are mounted. The lift profiles 3 are connected at one end to the lever arms 4 and, for example, via adjusting devices 5 at an angle (so-called pitch angle) about its longitudinal axis rotatable. The adjusting devices 5 can be assigned 6 position encoder. The wave energy converter 1 may be associated with a motion measuring device 9 which is adapted to measure a movement of the wave energy converter 1 in the water body. The movement measuring device 9 may include an acceleration sensor. The buoyancy profiles 3 are, relative to the axis of the rotor 2, 3, 4, offset from one another at an angle of 180 °. The buoyancy profiles 3 are preferably connected to the lever arms 4 in the vicinity of their pressure point, in order to reduce rotational torques occurring during operation to the buoyancy profiles 3 and thus to reduce the requirements for the holder and / or the adjusting devices. The radial distance between a suspension point of a lift profile 3 and the rotor axis is, for example, 1 m to 50 m, preferably 2 m to 40 m and particularly preferably 6 m to 30 m. The chord length of the lift profiles 3 is for example 1 m to 8 m. The maximum longitudinal extent may be, for example, 6 m or more. The wave energy converter 1 has an integrated generator. Here, the rotor base 2 is rotatably mounted in a generator housing 7. The rotor base 2 forms the rotor of the generator, the generator housing 7 whose stator. The required electrical equipment such as coils and cables are not shown. In this way, a rotational movement of the rotor base 2 induced by the wave orbital motion can be directly converted into electrical energy with the lift profiles 3 attached thereto via the lever arms 4. Although a wave energy converter 1 is shown in FIG. 2, in which the lift profiles 3 are attached via their lever arms 4 to only one side of a rotor base 2, the invention can, as mentioned, also be used with wave energy converters 1 in which Both sides of the rotor base 2 lever arms 4 and 3 Auftriebsprofile are attached. A use in so-called squirrel cage runners is also possible. Also, the rotor arms 4 need not necessarily be formed as shown. For example, the lift profiles 3 can also be connected to the rotor base 2 via a disk-shaped element.

Attached to the wave energy converter 1 or removed therefrom, there is provided an acoustic double flow profiler 8, which is shown in a highly schematized manner in FIG. The acoustic Doppler flow profiler 8 is oriented in a measuring direction which corresponds to a direction of flow of the wave energy converter 1. He is trained, for example, as H-ADCP.

FIG. 3 again shows the wave energy converter 1 of FIG. 2 in plan view of the rotor base 2. The illustration of the Doppler flow profiler 8 has been omitted. A control unit is shown schematically and designated 200. The rotor 2, 3, 4 is below the water surface of a wavy moving body of water, such as an ocean, arranged. In this case, for example, deep-water conditions are to be present in which the orbital trajectories 23 (cf., FIG. 1) of the water particles are largely circular. A rotational axis of the rotor (perpendicular to the plane of the drawing) is oriented largely horizontally and largely perpendicular to the direction of propagation 21 of the waves 20 of the wavy moving body of water.

The wave energy converter 1 is impinged by the orbital flow with an onflow velocity. The flow is the orbital flow of sea waves (see FIG. 1) whose direction changes continuously with an angular velocity Ω. In so-called monochromatic waves, the direction of flow changes with the angular velocity Ω = 2 π f = const., Where f represents the frequency of the monochromatic wave. In multichromatic waves, Ω undergoes a temporal change, Ω = f (t), since the frequency f is a function of time, f = f (t). FIG. 3 thus shows a snapshot. The method according to the invention In the case of multichromatic waves, this includes corresponding (local) adaptations. The invention is particularly advantageous for the prognosis of corresponding multichromatic waves or the corresponding wave application. In the case shown, the rotation of the orbital flow is oriented in the counterclockwise direction, ie the associated wave propagates from right to left. It is envisaged that the rotor 2, 3, 4 rotates in synchronism with the orbital flow of the wave motion with an angular velocity ω, wherein the term of synchronicity in multichromatic waves is to be understood in the time average.

By the action of the flow with the AnStrömungsgeschwindigkeit ~ on the buoyancy profiles 3 are each a buoyancy (indicated in each case by the force vector F) and thereby generates a force acting on the rotor 2, 3, 4 first torque. To set the synchronicity can be applied to the rotor 2, 3, 4, a preferably variable second torque in the form of a resistor, so a braking torque, or an acceleration torque. Means for generating the second torque can be arranged between the rotor base 2 and the generator housing 7.

Between the rotor orientation, which is illustrated by a lower dashed line and which passes through the rotor axis and the center of the two adjusting devices 5, and the direction of the orbital flow, which is illustrated by an upper dashed line, and passing through one of the velocity arrows , there is a phase angle or offset Δ whose magnitude can be influenced as a parameter value by a suitable adjustment of the first and / or second torque. FIG. 4 shows a wave energy converter park which can be operated according to the invention. The wave energy converter park is denoted overall by 10 and, in the illustrated example, comprises 15 wave energy converters 1, which are only partially provided with reference symbols. The representation corresponds to a plan view, the water surface is therefore in the drawing plane in Figure 4. The wave energy converter 1 are shown greatly simplified compared to the figure 2 and 3. Support structures (mooring) and the like are not shown. In FIG. 4, a total of two acoustic Doppler flow profiles 8 are shown greatly enlarged, measuring in different directions below a water surface. The scanning direction of the Doppler flow profile 8 is oriented differently, so that a particularly large area around the wave energy converter park 10 can be scanned. The corresponding fan-shaped scanning regions are each designated 80. For example, areas 80 of 150 ° below the surface can be scanned by the acoustic Doppler flow profile 8. The acoustic Doppler flow profiler 8 are aligned substantially horizontally below the water surface. Each of the areas 80 represents a measuring area with a plurality of different measuring locations, wherein the measuring area is oriented substantially parallel to a water level of the water body. The two Doppler flow profiles 8 and thus the two regions 80 can lie in the same depths or at different depths. Although two Doppler flow profiles 8 are shown in FIG. 4, embodiments which comprise only one, a plurality of identically oriented and, if appropriate, one behind the other and / or a multiplicity of Doppler flow profilers 8 may also be advantageous.

FIG. 5 illustrates a method according to an embodiment of the invention in the form of a schematic flow chart and denotes 100 as a whole. In a first step 101, the method 100 according to the invention comprises the acquisition of sensor data as measured data. The sensor data are in this case by means of one or more sensors, such. The Doppler flow profiler 8 shown in FIG. 4, at a plurality of measuring locations 81, which lie on a measuring surface 80 oriented substantially parallel to a water level 70 of the water body, is determined (see FIG. 6a). Preferably, a plurality of measuring locations 81, 82 are measured on a plurality of measuring surfaces 80, 80 '. By means of the exemplified Doppler flow profile 8, a directional component of a velocity vector field of the water body is determined at each measuring location 81, 82. The measuring surfaces 80, 80 'close with the still water mirror 70 an angle α of at most 10 °, preferably at most 6 °.

The sensor or sensors are preferably aligned with their measuring direction counter to the main shaft preparation direction ("flow direction"). When using a plurality of sensors, in particular for covering different main shaft preparation direction, different measuring directions can be selected. In FIG. 6b, two lattice-like orientations are illustrated, with only one row 83, 84 of sensors 8 each having a parallel measuring direction (illustrated by arrows on the rectangle) in a parallel lattice and two vertical rows 83, 84 of sensors 8 in the case of a lattice grid each parallel direction of measurement are present. In Fig. 6c, a star-shaped orientation (all sensors 8) and a fan-shaped orientation (any sector of the star) are shown.

It should be noted that as an alternative or in addition to the Doppler flow profilers, pressure sensors 8 '(eg in a flat or spatial matrix arrangement, shown in plan view in FIG. 6d) for determining a plurality of pressure values ("pressure field") as measurement data in one or more in multiple levels of the fluid, or wave height sensors, such as buoys, lidar and / or radar sensors, can be used to determine several wave height values as measured data of a ("wave height field") of the water. As illustrated by 1 10, at this time, information of a movement of the sensor in the water, which are detected for example by means of a movement measuring device 9, can be evaluated and included in the following calculation.

In a step 102, based on the acquired sensor data, a wave-raising and / or speed-potential field is reconstructed, for example, according to the following method.

First, the measured data are transformed into a speed potential φ at the sensor depth at the measuring points. If the measured data are directional components of a velocity vector field (eg particle velocities u _x ), then the transformation comprises an integration according to δφ = u _x dx.

Subsequently, the speed potential obtained in this way is transformed to the level of the at-rest water level 70, as described, for example, in "Potential Theory in Gravity and Magnetic Applications", Richard J. Blakoly, Cambridge University Press.

Thereafter, a wave field (wave elevation η) is calculated from the time derivative of the velocity potential field on the basis of a linear or non-linear wave theory. For example, in the case of a linear wave theory, grj =

From the reconstructed wave field, the subsequent wave loading of the installation is determined in a step 103 by computational propagation with the aid of a suitable wave model (for example Higher Order Spectral Method).

On this basis, as illustrated at 120, corresponding signals for the control and regulation of the plant can be output.

Claims

claims

1. A method for determining a wave elevation and / or velocity potential field in a wave-moved body of water, wherein measurement data at at least two measurement locations (81, 82), which are located on a substantially parallel to a water table (70) of the water oriented measuring surface (80, 80 ') are determined, and from the measured data, the wave collection and / or speed potential field is determined.

2. The method according to claim 1, wherein the measurement data are determined at at least four measurement locations (81, 82), wherein at least two first (81) of the at least four measurement locations are based on a first measurement area oriented substantially parallel to the water table (70). 80) and wherein at least two second (82) of the at least four measuring locations are located on a second measuring surface (80 ') oriented substantially parallel to the water level of the water body (70) and different from the first one.

3. The method of claim 1 or 2, wherein the substantially parallel to Ruhewasser mirrors gel of the water oriented measuring surface (80, 80 ') with the still water level (70) forms an angle of at most 10 °, preferably at most 6 °.

4. The method according to any one of the preceding claims, wherein the measured data comprise at least one directional component of a velocity vector field of the water body.

5. The method according to any one of the preceding claims, wherein the measured data comprise at least one pressure value of the water body.

6. The method according to any one of the preceding claims, wherein the measured data comprise at least one wave height of the water.

7. The method of claim 1, wherein determining the wave-elevation and / or velocity potential field from the measurement data comprises calculating a temporal evolution of an output sea state in a predefined time window, in particular at a location different from the measurement locations (81, 82). includes.

8. The method according to any one of the preceding claims, wherein a movement of the at least one sensor (8, 8 ') detected in the water and is taken into account in determining the wave collection and / or speed potential field.

9. arithmetic unit which is adapted to perform a method according to any one of the preceding claims.

10. Computer program with program code means which cause a computer unit to perform a method according to one of claims 1 to 8, when they are executed on the arithmetic unit, in particular according to claim 9.

1 1. A machine-readable storage medium with a computer program stored thereon according to claim 10.

12. system, in particular wave energy converter (1), with a computing unit according to claim 9, wherein the arithmetic unit is further adapted to control the system (1) in dependence on the particular wave collection and / or speed potential field.

13. Plant according to claim 12, comprising at least one Doppler flow profiler (8), at least one pressure sensor (8 '), at least one wave height sensor, at least one lidar sensor and / or at least one radar sensor for determining the measured data.

14. Plant according to claim 12, which has at least two differently oriented Doppler flow profiles (8) for determining the measured data.