NON-CONTACT SYSTEM FOR MONITORING A METALLIC MAGNETIC STRUCTURE UNDER DYNAMIC LOAD

Abstract

The present invention is in the field of a non-contact system for monitoring a metallic magnetic structure under dynamic load for detecting an impact induced propagating stress wave, and a method of determining strain in a metallic magnetic structure under dynamic load, such as a tube-like structure, such as a monopile for a wind turbine.

Claims

1. A non-contact system to monitor a metallic magnetic structure, comprising a load providing portion to exert a dynamic load to the structure so as to induce in said structure a propagating stress wave, and further comprising at least one array of sensors, including at least one magneto-resistive sensor, the sensors being substantially at a same first height, wherein the sensors are operated at a sampling rate of >10 kHz, and wherein the array of sensors is spaced around the structure.

2. The non-contact system according to claim 1, wherein the system is configured to exert said dynamic load to obtain a magnetic equilibrium status of the structure.

3. The non-contact system according to claim 1, wherein the sensors are evenly spaced around the structure; wherein at least one sensor is an analogue sensor; and wherein the array is spaced in a circular manner.

4. (canceled)

5. (canceled)

6. The non-contact system according to claim 1, wherein sensors in the array are synchronized in time and are in communication with a high-speed data acquisition unit.

7. The non-contact system according to claim 1, wherein each sensor is located at a distance of 1-100 cm from the structure.

8. The non-contact system according to claim 1, wherein at least one further anisotropic magneto resistive sensor is provided at a second height, which second height is 10-100 cm above or below the first height.

9. The non-contact system according to claim 1, wherein each array comprises each individually more than 2 sensors.

10. The non-contact system according to claim 1, wherein each array comprises a support on which sensors are attached.

11. The non-contact system according to claim 1, comprising a feedback loop, wherein the feedback loop is adapted to increase or decrease a subsequent dynamic load, and is adapted to increase or decrease a frequency of subsequent dynamic loads.

12. A method of non-contact monitoring of a metallic magnetic structure, comprising providing the system according to claim 1, providing a dynamic load to the structure so as to induce in said structure a propagating stress wave; determining a magnetic stray field around the structure, and calculating at least one of plastic strain, and rigid body motion of the structure.

13. The method according to claim 10, wherein the metallic structure is tube-like structure.

14. The method according to claim 10, further comprising determining a geometry of the structure.

15. The method according to claim 10, further comprising establishing a magnetic equilibrium status of the structure.

16. The method according to claim 10, comprising providing a calibration.

17. The method according to claim 10, wherein the metallic magnetic structure comprises a material selected from ferromagnetic material, anti-ferromagnetic material, ferrimagnetic material, and combinations thereof.

18. The method according to claim 10, wherein a downward moving stress wave is measured, and wherein a reflected stress wave is measured.

19. The method according to claim 10, wherein an axial displacement of the structure is measured.

20. The method according to claim 10, wherein a vertical tangential and axial deformation is measured.

21. The method according to claim 10, wherein a sampling rate is 10-250 kHz.

22. The method according to claim 10, wherein the feedback loop increases or decreases a subsequent dynamic load, and increases or decreases a frequency (#/min, or interval between) of subsequent dynamic loads, and maintains dynamic load and frequency.

Description

SUMMARY OF THE FIGURES

[0032] FIGS. 1, 2a-c, and 3a-e show some experimental details.

DETAILED DESCRIPTION OF FIGURES

[0033] FIG. 1 shows schematics of the measurements. An array of a number of AMR magnetometers surrounding a pile provided measurement input. Using a high-speed data acquisition system, and having information on the geometry of the pile, which can be obtained or determined in advance, processing software provides information of strain, rigid body motion, and plastic deformation. For calculation a one-dimensional wave propagation model with Rayleigh-Love correction can be used. For the magneto mechanical model Jiles's law of approach can be used.

[0034] FIG. 2a shows and experimental set-up with the AMR indicated with a solid arrow, and the contact strain sensor with a dashed arrow. The contact monitor is attached to the pile, and the AMR at a distance of about 40 cm. FIG. 2b shows the same set-up and gives an indication of actual sizes. FIG. 2c shows an image, obtained with a camera, of plastic deformation in the pile upon applying a load, indicated with the arrow.

[0035] In an example inventors studied the results of dynamic loads. In FIGS. 3a and 3b a series of loads, starting at about 40 seconds, and ending at about 70 seconds was applied and the magnetic field Br [μT] and Bz [μT] were measured. FIGS. 3c and 3d show a blow-up part of the measurements. Further in these figures it can be seen that the results of the non-contact determination and contact-monitoring overlap well. A distance of about 20 cm of the AMR sensor was found appropriate. The lefthand column of FIG. 3 graphs are measured given the axial strain ez), measured in the prior-art way, so with a glued strain gauge. The right column focuses on the axial component of the magnetic field (Bz) measured at 20 cm from the pole. The first row (FIG. 3a) is the full signal; the second row (FIG. 3b) shows an enlargement of every hammer blow; row three (FIG. 3c) shows the deviation of the signal on top of the spot field, so now both signals start at about 0; In row four (FIG. 3d), both signals are normalized by dividing each signal by the peak value. The bottom row (FIG. 3e) combines both normalized signals to show that with the correct scaling (ratio max (ez)/max (Bz)) the signals correspond, and therefore that the elongation can be measured by magnetism.

[0036] Experiments have been performed which support the figures and advantageous effects mentioned in the description.

[0037] The research on which this patent application is based on research that has been made possible by a grant from NWO in the EUROS (Excellence in Uncertainty Reduction of Offshore wind Systems) program from NWO (#2014/13216/STW).