DE102013009876A1 - Determining the intrinsic speed of a speed sensor device in a body of water for correcting the measurement signal - Google Patents

Abstract

The invention relates to a method for determining a relative speed between a reference point (1) and a water flow in a measuring direction (x), with a relative speed between a sensor device (8) in a body of water and the water flow in the measuring direction (x) through the sensor device (8) is measured, an intrinsic speed of the sensor device (8) relative to the reference point (1) is determined by the sensor device (8), the relative speed between the sensor device (8) and the water flow is corrected by the intrinsic speed to derive the relative speed between the reference point (1) and the water flow in the measuring direction (x).

Description

The present invention relates to a method for determining a relative speed between a reference point and a water flow and to a sensor device for its implementation.

State of the art

For the conversion of energy from water movements in water into usable energy a number of different devices are known. An overview of this can be found, 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, for. B. hydrodynamic lift profiles, are used. Such a system is in the DE 10 2011 105 177 A1 disclosed. 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. In the context of this application, high-energy scenarios are, for example, understood as meaning waves with an unusually high speed, amplitude or a specific frequency pattern stressing the systems.

In addition, a wave energy converter with knowledge of the expected Wellenbeaufschlagung adapted to be operated on this, for example, to maximize the energy yield of the wave energy converter.

Wave movements can be detected by means of Doppler measurements, for example by ultrasound. Sensors for measuring water currents, especially water currents based on ultrasound, can be located on moving objects, e.g. As ships or buoys. These sensors are placed below the water surface and use the Doppler effect, which measures the relative radial velocity (seen in the cylindrical coordinate system) between the sensor device and backscatter elements (eg, sediments or plankton). Obviously, however, the speed of the object to which the sensor device is attached falsifies the measurement results.

It is therefore desirable to have sensors available that can compensate for this movement autonomously and are not dependent on information from outside.

Disclosure of the invention

According to the invention, a method for determining a relative speed between a reference point and a water flow, in particular a sea current, and a sensor device for carrying it out with the features of the independent patent claims are proposed. Advantageous embodiments are the subject of the dependent claims and the following description.

Advantages of the invention

The invention makes it possible to correct the measured velocity of water flows, in particular by means of a Doppler effect, by the intrinsic speed of the sensor device arranged in the water. The compensation is carried out by determining the airspeed and direction and deduction of the measured relative velocity between the sensor device and water flow. Thus, the measurement accuracy of the water flow is increased relative to a fixed reference point.

By autonomous compensation of the sensor speed, the sensor device can provide accurate flow measurement data without complex signal processing after acquisition of the measurement data. The compensation is autonomous, without having to communicate with external sensors. In particular, the invention also functions in underwater applications where measuring velocity based on the Doppler effect over the life of an ultrasonic echo from the seabed is not expedient, e.g. B. due to a very large water depth, which leads to high measurement errors due to water currents, temperature and pressure dependence of the speed of sound. In addition to the main task of measuring water flows, the sensor device also provides information about its own speed.

The invention makes use of essentially two steps. On the one hand, a usual measurement of the relative speed between the sensor device and the water flow is carried out, in particular based on the Doppler effect, for example, using ultrasound. On the other hand, an acceleration and rotation of the sensor device is carried out by means of inertial sensors (acceleration and rotation sensors) attached to the sensor device. Inertial measurement units typically comprise three orthogonally arranged acceleration sensors (also referred to as translation sensors) which detect the linear acceleration in the x, y or z axis, from which the translatory motion can be calculated, and three orthogonally arranged angular rate sensors ( also called gyroscopic sensors) which measure the angular velocity about the x, y, and z axes, respectively, from which the rotational motion can be calculated. Suitable inertial sensors are, for example, so-called MEMS sensors (microelectromechanical systems). In order to improve the accuracy or to correct a drift of the above-mentioned sensors, additional magnetic field sensors (compass sensors) can be used.

By means of the inertial sensors, the current speed and direction of the sensor device can be determined and used to correct the measured relative speed between sensor device and water flow. In this way, the relative velocity between the water flow and a reference point, which is expediently the system, can be determined very easily.

In order to determine the speed and direction from the measured data, u. a. a temporal integration of the acceleration data needed. However, the longer the considered period lasts, the larger possible errors become. In the context of the invention is therefore advantageously exploited that located in a wave-like waters sensors are subjected mainly to periodic movements.

With a periodic acceleration, the speed can be easily calculated by means of Fourier decomposition of the measured acceleration a (t) without having to integrate the acceleration signal. A mean-harmonic acceleration can be represented as follows:

This gives for the speed:

This is a significant advantage over integrating sensor signals over a long period of time.

Transient processes (non-harmonic form) and non-periodic accelerations of the sensor device can be taken into account with a short-term integration of the acceleration signal. Since it is a short-term integration (in the range of a few seconds), an integration error is relatively small and does not lead to significant distortions.

The processes described so far allow the compensation of harmonic movements (in the mathematical sense) as well as misorientation of the sensor device.

The compensation of movements of the sensor device at a constant speed can be done especially according to the extension of the method described below. Such movements are not subject to acceleration and therefore can not be detected by means of an acceleration measurement. The preferred compensation for movements with constant speed is based on the measured relative speed between the sensor device and water flow, more precisely the scattering centers moved by the water flow. At sea waves, the velocity of the scattering centers has harmonic components that correspond to the harmonic components of the wave. The frequency of these harmonic components is not affected by the intrinsic speed of the sensor device.

Wave propagation models (eg, linear wave theory) are known which establish a relationship between frequencies, wavenumber, phase and group velocity of the wave. This relationship is known as a dispersion equation and is used as the basis for the compensation of constant velocity components. Further details can be found in this "Water Wave Mechanics for Engineers &Scientists", Robert G. Dean, Robert A. Dalrymple , From the distance covered by a location of a specific phase position in a certain time and the phase velocity, the intrinsic speed of the sensor device in the measuring direction can be determined.

η:

z-Koordinate der Wasseroberfläche

u:

Horizontalgeschwindigkeit

w:

Vertikalgeschwindigkeit

k:

Wellenzahl (2π/L)

h:

Wassertiefe

z:

z-Koordinate, Ruhewasserspiegel z = 0, Sohle z = –h

x:

x-Koordinate, Ausbreitungsrichtung

The dispersion equation is significantly influenced by the wave steepness (quotient of wave height H and wavelength L). Therefore, this method can be advantageously combined with a device for measuring the wave height, such as a buoy. Alternatively, a relationship between flow velocity and wave height can be determined from the wave models so that a coarse (uncompensated measurement) of the flow rate is sufficient to select the dispersion equation appropriate for the prevailing flow conditions. η = H / 2 × cos (k × - ω × t) u = H / 2 · ω · cosh (k · (h + z)) / sinh (k · h) · cos (k · x -ω · t) w = H / 2 · ω · sinh (k · (h + z)) / sinh (k · h) · sin (k · x -ω · t) With:

η:

z-coordinate of the water surface

u:

Horizontal speed

w:

vertical speed

k:

Wave number (2π / L)

H:

water depth

z:

z-coordinate, water level z = 0, sole z = -h

x:

x-coordinate, direction of propagation

The measurement of the sensor speed in the depth direction (z-direction, ie vertical) can be done by a pressure measurement. Namely, when the sensor device sinks, the static pressure p _stat at the location of the sensor device increases. If the wave height is known, for example by the above determination, a change in the wave height influencing the measured depth can also be compensated. The derivation of the pressure after the time and the consideration of the wave height enables the calculation of the velocity in the z-direction. The compensation of the dynamic pressure can z. B. can be achieved by using multiple pressure sensors.

mit:

ρ:

Dichte

g:

Erdbeschleunigung

It is true that:

With:

ρ:

density

G:

acceleration of gravity

A sensor device according to the invention is, in particular programmatically, adapted to carry out a method according to the invention.

Also, the implementation of the invention in the form of software is advantageous because this allows very low cost, especially if an executing processing unit is still used for other tasks and therefore already exists. Suitable data carriers for the provision of the computer program are in particular floppy disks, hard disks, flash memories, EEPROMs, CD-ROMs, DVDs and the like. a. m. 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

1 shows a wave energy converter and a sensor device which can be operated according to the invention, in partial perspective view.

Detailed description of the drawing

In 1 is a preferred, but still purely exemplary wave energy converter shown that can make use of a wave orbital motion of a wavy body of water, especially a sea. The wave energy converter is in total with 1 designated. He has a rotor 2 . 3 . 4 with a rotor base 2 on, on the over rotor or lever arms 4 elongated lift profiles 3 are attached. The lift profiles 3 are with one end with the lever arms 4 connected and, for example via adjusting 5 at an angle (so-called pitch angle) about its longitudinal axis rotatable. The adjusting devices 5 can positioners 6 be assigned.

The lift profiles 3 are relative to the axis of the rotor 2 . 3 . 4 , offset at an angle of 180 ° to each other. Preferably, the lift profiles are 3 near their pressure point with the lever arms 4 connected to the operation occurring rotational moments on the lift profiles 3 and thus to reduce the requirements for the holder and / or the adjustment. 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 more 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 is the rotor base 2 rotatable in a generator housing 7 stored. The rotor base 2 forms the rotor of the generator, the generator housing 7 its stator. The required electrical equipment such as coils and cables are not shown. In this way can be induced by the wave orbital motion rotational movement of the rotor base 2 with these on the lever arms 4 attached lift profiles 3 be converted directly into electrical energy.

Removed from the wave energy converter 1 , For example, attached to a diving buoy, is a sensor device 8th arranged in the 2 is shown very schematically. The sensor device 8th has an Acoustic Doppler Current Profiler (ADCP). The ultrasonic Doppler flow meter is oriented in a measuring direction x, which is a flow direction of the wave energy converter 1 equivalent.

An ADCP is an active sonar that uses the Doppler frequency shift of the reverberation of scattered bodies in the water (predominantly plankton) to determine the local flow velocity. The instrument is equipped with three or four independent transducers, the opposite ones forming pairs. In each case a pair of oscillators measures the horizontal movement in one direction, the vertical movement is measured by both in parallel. For this purpose, the devices emit sound pulses in the range of 500 kHz-10 MHz at fixed time intervals. Between the pulses, the backscattered signals are received again. These allow an allocation to the relative distance to the signal generator (transducer) over their running time. Depending on the design and configuration, the devices can measure the three-dimensional water velocity in different depth horizons.

In the case of a purely horizontal measurement orientation (also referred to as H-ADCP), the flow can be continuously monitored in a defined depth layer (that is to say for measurement sites located on a measurement surface oriented essentially parallel to the water level of the water body).

In the context of the invention, the sensor device is now 8th further equipped with one or more inertial and / or compass sensors or with an inertial measuring unit. The ADCP 8th is set up to determine its own motion and to use it to correct the measured flow velocity. He also has a control unit on which runs a corresponding computer program.

The sensor device 8th is adapted to measure by means of ultrasonic Doppler measurement, the relative speed between the sensor device and water flow in the x-direction and to obtain a measurement signal v _x (t). For the operation of the wave energy converter 1 However, the relative speed between wave energy converter and water flow is relevant, so that the measurement by the relative speed between the sensor device 8th and wave energy converter adopted as a fixed reference point.

The sensor device 8th is therefore also adapted to detect its own acceleration, preferably in all three spatial directions, a _x (t), a _y (t), a _z (t), over time by means of the inertial measuring unit.

Periodic portions of the acceleration can be easily determined by Fourier analysis and used to correct the measured velocity. A corrected velocity v _x * (t) results in:

Transient processes (non-harmonic form) and non-periodic accelerations of the sensor device can be taken into account with a short-term integration of the acceleration signal.

The preferred compensation of movements with constant speed v _S is based on the measured relative speed between sensor device and water flow, v _x (t).

As part of the compensation, a phase of the flow along a measuring direction, which preferably runs horizontally, is measured at a first time t ₁ and at a later second time t ₂ . It is simplified here assumed that the sea state, ie also the flow component, has only one harmonic component. This makes it easy to determine at which point x ₁ the maximum of the flow component is at time t ₁ . This is repeated at the second time t ₂ , resulting in the location x ₂ . The Distance d = x ₂ -x _{1 of} these two locations corresponds to the product of the duration (t ₂ -t ₁ ) between the two measurement times and the sum (v _P + v _S ) from the phase velocity v _P and the intrinsic velocity of the sensor device v _S in measuring direction. It is assumed that v _P and v _S do not change between t ₁ and t ₂ .

gegeben, so dass der konstante Anteil v_x,S der Eigengeschwindigkeit der Sensoreinrichtung 8 in Messrichtung x berechnet werden kann. Die Messung der Sensorgeschwindigkeit in Querrichtung y, welche senkrecht zu der Messrichtung ist und horizontal verläuft, ist mit diesem Messverfahren nicht möglich. Es kann nur auf die relative Geschwindigkeit zwischen Strömung und Sensoreinrichtung geschlossen werden, aber nicht auf die Eigengeschwindigkeit.The phase velocity is through the dispersion equation

given, so that the constant portion v _{x, S of} the intrinsic speed of the sensor device 8th can be calculated in the measuring direction x. The measurement of the sensor speed in the transverse direction y, which is perpendicular to the measuring direction and runs horizontally, is not possible with this measuring method. It can only be concluded on the relative speed between flow and sensor device, but not on the airspeed.

Furthermore, the sensor device 8th equipped with at least one pressure sensor which measures the total pressure with which the sensor device 8th is charged. By means of a pressure measurement, the depth in the z-direction, as explained above, can be determined.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102011105177 A1 [0003]

Cited non-patent literature

• G. Boyle, "Renewable Energy", 2nd Ed., Oxford University Press, Oxford 2004 [0002]
• "Water Wave Mechanics for Engineers &Scientists", Robert G. Dean, Robert A. Dalrymple [0020]

Claims (12)

Method for determining a relative speed between a reference point ( 1 ) and a water flow in a measuring direction (x), wherein a relative velocity between a located in a water sensor device ( 8th ) and the water flow in the measuring direction (x) through the sensor device ( 8th ), an intrinsic velocity of the sensor device ( 8th ) relative to the reference point ( 1 ) by the sensor device ( 8th ), the relative speed between the sensor device ( 8th ) and the water flow is corrected by the airspeed in order to calculate the relative velocity between the reference point ( 1 ) and the water flow in the measuring direction (x). Method according to claim 1, wherein the intrinsic speed of the sensor device ( 8th ) relative to a reference point ( 1 ) from an intrinsic acceleration of the sensor device ( 8th ) relative to the reference point ( 1 ) is determined. Method according to claim 2, wherein at least one periodic proportion of the self-acceleration of the sensor device ( 8th ) relative to the reference point ( 1 ) is determined and from the periodic portion of the self-acceleration, a periodic proportion of the intrinsic speed of the sensor device ( 8th ) relative to the reference point ( 1 ) is determined. Method according to claim 2 or 3, wherein at least one non-periodic proportion of the self-acceleration of the sensor device ( 8th ) relative to the reference point ( 1 ) is determined and from the non-periodic proportion of the self-acceleration, a non-periodic proportion of the intrinsic speed of the sensor device ( 8th ) relative to the reference point ( 1 ) is determined. Method according to one of the preceding claims, wherein a constant proportion of the intrinsic speed of the sensor device ( 8th ) relative to the reference point ( 1 ) in the measuring direction (x) by means of a phase analysis of the determined relative speed between the sensor device ( 8th ) and the water flow is determined. Method according to one of the preceding claims, wherein an intrinsic speed of the sensor device ( 8th ) relative to the reference point ( 1 ) in the vertical direction (z) from a pressure measurement of a on the sensor device ( 8th ) acting water pressure is determined. A computer program that causes a computing unit to perform a method according to any one of claims 1 to 6 when executed on the computing unit. Machine-readable storage medium with a computer program stored thereon according to claim 7. Sensor device ( 8th ), which is adapted to determine a relative velocity between itself and a water flow in a measuring direction (x), an airspeed relative to a reference point ( 1 ) to correct the relative velocity between itself and the water flow around the airspeed in order to obtain a relative velocity between the reference point ( 1 ) and the water flow in the measuring direction (x). Sensor device ( 8th ) according to claim 9, comprising an ultrasonic Doppler flow meter and at least one inertial sensor. Sensor device ( 8th ) according to claim 9 or 10, comprising a pressure sensor. Sensor device ( 8th ) according to claim 9, 10 or 11, adapted to carry out a method according to any one of claims 2 to 6.

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