SYSTEM AND METHOD FOR DETERMINING THE MASS OF A SHIP MOVING IN WATER

Abstract

A system and a method which determines the mass of a ship moving in water, comprising at least two gravitational field strength sensor units that are stationary relative to the ship at a known distance from each other, and an analytical unit which determines the mass of the ship based of measurement signals acquired by the at least two GFS sensor units.

Claims

1-16. (canceled)

17. A system for determining a mass of a ship moving in water with at least two gravitational field strength (GFS) sensors, which are installed stationarily relative to the moving ship at a known distance from each other, and an analytical unit that determines the mass of the ship based on gravitational field strength the measurement signals obtained from the at least two GFS sensors.

18. A system according to claim 17, wherein: the at least two GFS sensors comprise at least one of a gravimeter and and confirmation of an acceleration sensor and at least two synchronized atomic clocks.

19. A system according to claim 18, wherein: the at least two GFS sensors are each a superconducting gravimeter.

20. A system according to claim 17, wherein: the measurement signals from the at least two GFS sensors are transmitted to the analytical unit by cable or wireless transmission.

21. The system according to claim 18, wherein: the measurement signals from the at least two GFS sensors are transmitted to the analytical unit by cable or wireless transmission.

22. The system according to claim 19, wherein: the measurement signals from the at least two GFS sensors are transmitted to the analytical unit by cable or wireless transmission.

23. The system according to claim 17, wherein: the at least two GFS sensors are located stationarily an area of a trajectory of movement of the ship so that the ship passes the at least two GFS sensors.

24. The system according to claim 17, wherein: the at least two GFS sensors are located in a region of a navigation channel or shipping route.

25. The system according to claim 24, wherein: the at least two GFS sensors are located on or in a bed of the navigation channel or shipping route so that when a ship passing through the navigation channel between the at least two GFS sensors the ship travels over the GFS sensors, or the at least two GFS sensors are arranged stationarily on a support structure over the navigation channel or shipping route in such manner that the ship passes the at least two GFS sensors when travelling through the navigation channel.

26. The system according to claim 17, wherein: the analytical unit comprises a computer which determines the mass of the ship based at least the measurement signals using an arithmetical.

27. The system according to claim 26, wherein: at least the geographical position data of the ship can be calculated using a range identification and tracking system, an automatic identification system or a universal automatic identification system.

28. A method for determining mass of a ship moving in water having a local mass influence on the Earth's gravitational field which is measured and used as a basis for determining the mass of the ship so that gravitational field strength under influence of mass of the ship is measured at each of at least two geographically defined and stationary measurement locations to obtain measurement values of gravitational field strength; and the mass of the ship is determined based on at least the measurement values.

29. The method according to claim 28, wherein obtaining the measurement values of the Earth's gravitational field is carried out while the ship is moving past the at least two measurement locations.

30. The method according to claim 28, wherein: a geographical position of the ship is determined relative to stationary measurement locations and is used as a basis for determining the mass of the ship.

31. The method according to claim 28, wherein: the determination of the mass of the ship is based on a gravitational influence Agi of a local center of mass shift k between a center of mass of the ship and a center of a mass of water displaced by the ship according to a relationship: ${\mathrm{\Delta g}}_i=\frac{m.Math.G}{x_w^2+y_{w,i}^2+z_w^2}-\frac{m.Math.G}{x_w^2+y_{w,i}^2+{\left(z_w+k\right)}^2}$ wherein: g equals gravitational acceleration m equals ship mass which equals mass of displaced water G equals gravitation constant r equals a relationship of spatial distance r.sup.2=x.sub.w.sup.2+y.sub.w.sup.2+z.sub.w.sup.2 wherein x, y and z represent spatial distances using a Cartesian coordinate system between a sensor and center of mass of the water displaced by the ship; and k equals distance between the center of mass of the ship and the center of mass of the water displaced by the ship

32. A use of the system according to claim 17, comprising: determining a mass distribution within the ship by providing at least two GFS sensors performing time-discrete measurements with a pre-determined scanning rate when a ship passes the at least two GFS sensors; and the measurement signals are obtained when the time-discrete measurements are taken while the ship which passes are used as the basis for determining the mass distribution of the ship.

33. The use according to claim 32, wherein: the at least two GFS sensors are located on ground of a navigational channel or above a passage of the ship at a known distance along the navigation channel or a shipping route, having spacing distance from each other which are smaller than a ship's length attributable to the ship.

34. The use according to claim 32, wherein: the scanning rate is at least 1 Hz.

35. The use according to claim 33, wherein; the scanning rate is at least 1 Hz.

36. The system according to claim 17, wherein: the measurement signals from the at least two GFS sensors are transmitted to the analytical unit by cable transmission or wireless transmission.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In the following text, the invention will be described for exemplary purposes without limitation of the general inventive thought using embodiments thereof and with reference to the drawing. In the drawing:

[0023] FIG. 1 represents the measurement system on the bed of a navigation channel;

[0024] FIG. 2 is a measurement diagram for acquisition of the change in gravitational field strength;

[0025] FIG. 3a, b shows an alternative system variant for installing the GFS sensor units;

[0026] FIG. 4 shows a measurement system with two atomic clocks;

[0027] FIG. 5 is representation of the underlying measurement principle, based on the difference in the positions of the centres of mass between the ship's mass and the displaced water mass; and

[0028] FIG. 6 is a diagram with synthetically generated measurement values for Δg.sub.i in [m/s.sup.2].

DETAILED DESCRIPTION OF THE DRAWINGS

[0029] FIG. 1 illustrates a side view of a navigation channel F along which a ship 3 moves on the surface of the water 1 at a preferably constant true speed v. The navigation channel F has a depth of water T, which corresponds to the distance between the water surface and the navigation channel bed 2. At least two, preferably three or more gravitational field strength (GFS) sensor units 4 are installed at locations A, B, B′ on or in the navigation channel bed 2, and in the state shown according to FIG. 1, the ship 3 travels vertically over them. For this purpose, the distances a between the GFS sensor units 4, 5 are chosen smaller than the ship's length.

[0030] The GFS sensor unit 4 is preferably embodied as a superconducting gravimeter which measures the locally prevailing gravitational field strength g with a measuring frequency of at least 1 Hz.

[0031] FIG. 2 is a measurement diagram with an x-axis as time axis t and a y-axis on which the measurement signals collected by the GFS sensor unit are plotted, each representing the temporally resolved gravitational field strength g. The local minimum represented in the measurement curve originates from the passage of the ship 3 over the GFS sensor unit, that is at the time of closest proximity between the center of mass of the ship 3 and the GFS sensor unit installed on the bed of the navigation channel 2, the gravitational field strength g decreases locally due to the ship's own gravity. The quantitative decrease of the gravitational field strength prevailing locally at the site of the GFS sensor unit is substantially proportional to the mass of the ship. Thus, a conclusion about the overall mass of the ship may be drawn on the basis of this change in measured value. The ship's mass is calculated in an analytical unit 6, to which the measurement signals of the GFS sensor unit 4 are transmitted via cable or wirelessly for analysis and determination of the ship's mass. Besides the measurement signals, the analytical unit 6 also receives, via AIS for example, the exact position data for the ship, to enable it to capture the relative position between the GFS sensor unit and the ship. The analytical unit is preferably supported from ashore and is arranged to be accessible by an oversight authority.

[0032] Ship 3 ideally moves over the GFS sensor unit 4, 5 vertically above the locations of the GFS sensor units 4, 5, which are arranged one behind the other in FIG. 3a. In this case, the mass of the ship 3 is able to counteract the Earth's gravitational force at the locations of the GFS sensor units 4, 5, so that in this case a maximum influence of the ship's mass can be measured at the locations of the GFS sensor units 4 in each case.

[0033] This constellation can be achieved if the GFS sensor units 4, 5 are arranged along a navigation channel which is sufficiently narrow, preferably less than 300 meters. Apart from the determination of the ship's mass, in this case the GFS sensor units 4, 5 also function as position detectors, so that the position of the passing ship can be detected with a sufficient degree of accuracy.

[0034] FIG. 3b illustrates the case in which the GFS sensor units 4, 5 are arranged on the bottom of a navigation channel or shipping route in such manner that the ship 3 does not pass vertically over the GFS sensor units 4, 5, but rather with a lateral offset. The weight of the ship as well as the ship's position can be determined accurately enough on the basis of the at least two GFS sensor units 4 and the measurement signals that can be calculated therewith. Additionally, information about the mass or weight distribution within the ship can be obtained by combining the two GFS sensor units 4, 5, each being operated with a measuring frequency of at least 1 Hz.

[0035] FIG. 4 illustrates a measurement system using two time-synchronized atomic clocks as GFS sensor units, of which a first atomic clock 4 is arranged on the seafloor 2, and a second atomic clock 5 is located in another position where the presence of the ship's mass does not have a measurable effect on the local gravitation field. The spatial proximity of the ship's mass of a ship 3 passing preferably vertically over the atomic clock 4 arranged on the seafloor 2 causes the gravitational field strength prevailing locally at the site of the atomic clock 4 to change due to the gravitational effect of the ship 3, which in turn causes the system time of the atomic clock 4 to run more slowly, in accordance with Einstein's principle of gravitational space-time curvature, than at the location of the second atomic clock 5, which is provided for example at the site of the analytical unit 6, at a distance of some kilometres, on land. The time lag is proportional to the change in the gravitational field, and thus also proportional to the ship's mass that causes it. This may be calculated with the aid of the analytical unit 6.

[0036] With the aid of the system according to the invention, it is possible to significantly improve safety for port operators and to enhance monitoring capabilities for customs and harbor police. An analytical method for improved tracking of the movement of goods within a harbor or in the marine region close to the harbor or coast may be established on the basis of the system according to the invention.

[0037] The measurement signals obtained with the measuring systems described in the preceding text are used for determining the mass of a ship, the ship's mass of which generally corresponds to the mass of water displaced by the ship. However, the center of mass of the ship and the center of gravity of the displaced water mass are not locationally identical. Consequently, although the gravitational effect of the ship's mass and that of the displaced water mass are identical, the locations from which these gravitational effects emanate are not the same. This locational difference forms the basis of measurement therefor for the purpose of measuring changes in local gravitational fields caused by a moving ship using gravimeters or accelerometer, and drawing conclusions about the mass of a passing ship from the measurement data obtained in this way.

[0038] In this regard, FIG. 5 shows a schematic cross-sectional representation through a shipping lane or channel, along which a ship is moving at constant speed v. It may be assumed that the ship 3 is following a travel direction orthogonal to the plane of the drawing, corresponding to the y-axis of a Cartesian coordinate system, whose x- and z-axes may are discernible in FIG. 5. Two gravitational field strength sensor units 4, 5 are installed on the seabed or the bottom of navigation channel 2 at a distance a from each other along the x-axis. The ship 3 has a center of mass Ps, the spatial position of which is at a distance k vertically above the center of mass Pw of the water displaced by the ship 3, that is it is assumed that the center of mass Pw of the water displaced is expressed in the Cartesian coordinate system used by the coordinates (xw, yw, zw), whereas the center of mass Ps of the ship is expressed by the coordinates (xw, yw, zw+k).

[0039] In principle, the following relationships apply: [0040] The gravitational acceleration exerted by a body having mass m at a distance r can be described with the following equation:

[00001]$g=\frac{\mathrm{mG}}{r^2}$ [0041] where: g=Gravitational acceleration [0042] m=Mass of the body exerting the gravitational acceleration [0043] G=Gravitational constant [0044] r=Spatial distance

[0045] Accordingly, the following apply for the gravitational effects gw of the mass of water displaced by the ship and gS of the ship's mass at the location of the gravitational field strength sensor unit 4:

[00002]$g_W=\frac{m.Math.G}{x_w^2+y_{w,i}^2+z_w^2}\mathrm{and}{g}_S=\frac{m.Math.G}{x_w^2+y_{w,i}^2+{\left(z_w+k\right)}^2}$

[0046] Accordingly, the gravitational influence of a passing ship may be formulated in simplified terms as the difference between the gravitational effect of the displaced water and that of the ship:

[00003]${\mathrm{\Delta g}}_i=\frac{m.Math.G}{x_w^2+y_{w,i}^2+z_w^2}-\frac{m.Math.G}{x_w^2+y_{w,i}^2+{\left(z_w+k\right)}^2}$ [0047] where: y.sub.w,i=i.Math.Δt.Math.v [0048] i={0, 1, 2, 3, . . . } number of a measurement while a ship is passing [0049] v=Speed of the ship [0050] Δt=Measurement interval of the sensor unit

[0051] For the purposes of the above, it was assumed that the ship only moves in the y direction when passing and the ship's speed is constant.

[0052] If the change over time of the gravitational field strength is measured preferably quasi-continuously, that is, with a scanning rate of one measurement per second while a ship is passing over, a measurement plot similar to the diagram representation of FIG. 6 is obtained for each of the gravitational field strength sensor units 4, 5. In the diagram illustrated, the values for Δg.sub.i in [m/s.sup.2] m are plotted on the y-axis, while the x-axis shows the timescale in seconds, with a ship's approach in the temporal range from −60 sec to <0 sec and a ship's departure in the in the temporal range from more than 0 sec to 60 sec. The ship passes over the gravitational field strength sensor units 4, 5 at time point 0 sec.

[0053] The equation for Δg.sub.i as stated above may be formulated for each of the measurement points represented in the diagram in FIG. 6, yielding a non-linear equation system. The synthetic data that was used to generate the measurement curve shown are: m=100,000 t, v=10 m/s, z=70 m, k=6 m and x=18 m. The zero point of the horizontal x-axis was placed in the curve maximum, which corresponds to the point in time at which the radial distance between ship and sensor becomes minimal. With regard to parameter k, which represents the spatial distance between the centers of mass relative to the ship's mass and displaced water mass, it may be assumed that k has a value of several meters for container ships.

[0054] The variables x, v and z can be solved by stochastic inversion of the equation system presented. For this, expected intervals are defined that allow a deviation of 50% from the parameters selected above. Parameter combinations for m, v, x, z and k in the equation stated above are used iteratively. The calculated curves are compared with the synthetic (measured) data in order to determine the parameter combination that best explains the data. In order to obtain usable inversion results, data must be used with different x, y and z positions for at least two sensors.

[0055] Use of the determined values for x, v and z simplifies the equation presented ab above. Now if m and k are scanned accurately enough, and the curves calculated on the basis of corresponding parameter combinations are compared with the synthetic (measured), the combination of m and k can be obtained.

[0056] The following measures are beneficial for improving the results: [0057] Inclusion of additional data sources (additional sensor units, AIS data, water levels, weather data, GPS data of onboard pilots, cameras, laser-based distance meters, . . . ) [0058] Increasing computing power (enables: more precise scanning of the parameter space for m and k, more iterations and consequently greater accuracy in the stochastic inversion method, or also multi-start methods) [0059] Under real-life conditions, it is advisable to ascertain the relationship between m and k while the ship is passing. AI-based methods are particularly helpful for this. When an appropriate function has been found, which describes the relationship between the two variables adequately, variable k may be replaced, so that it can be solved directly after m. [0060] Minimizing the noise in the data may be used to improve the determination of mass.

LIST OF REFERENCE SIGNS

[0061] 1 Surface of the sea [0062] 2 Bottom of navigation channel or seabed [0063] 3 Ship [0064] 4, 5 Gravitational field strength sensor unit [0065] 6 Analytical unit [0066] v Ship's true speed [0067] F Navigation channel [0068] T Depth of water [0069] a Distance between two gravitational field strength sensor units