JPH092385A - Permanent magnetiszm removing method of ship - Google Patents

Abstract

PURPOSE: To minimize the permanent magnetic moment through the constant monitoring by calculating the permanent magnetic moment in the longitudinal direction in the process of removing the permanent magnetism of a ship having a steel hull. CONSTITUTION: In a process in which a ring of windings is fitted approximately with equal intervals around a steel hull 2 of a ship 1, and the permanent magnetism in the longitudinal direction of the ship is canceled by carrying current to the ring 3 of windings by gradually reducing the current while the polarity of the current is alternately changed to positive or negative, the magnetic field in X, Y and Z directions of the hull 2 is measured by a plurality of magnetism detector 7 installed on the sea bed, and the permanent magnetic moment in the longitudinal direction is quantitatively calculated based on the measured values by a plurality of magnetism detectors 7 to minimize the value of the permanent magnetic moment through the constant monitoring.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a permanent magnetic demagnetization method for a ship, which is capable of demagnetizing a permanent magnet generated from a magnetic material, for example, a ship having a steel hull.

[0002]

2. Description of the Related Art Conventionally, in order to erase the permanent magnetism retained by a ship having a hull made of steel, several windings are attached to the outer circumference of the hull and the polarity of the current is applied to the windings. While changing the sign to positive or negative, the size is gradually reduced to energize.In the process, the required hull is measured according to the measured value of a specific magnetic detector among the plurality of magnetic detectors installed on the seabed. The magnetic data was calculated intermittently, and the demagnetization process was carried out while the permanent magnetic component based on it was intermittently monitored, and the effect was evaluated.

[0003]

The demagnetization process of the permanent magnetism of a ship based on the above-mentioned hull magnetism measurement involves extracting and monitoring the permanent magnetism component from the measurement values of a certain specific magnetic detector (for example, two). This is a magnetic field control method, but at that time, fluctuations in water depth due to ebb and flow of the sea surface of the measurement surface and measurement errors due to displacement of the relative position between the hull and the magnetic detector, etc., greatly affect the demagnetization effect. Was there.

Moreover, the calculation of the magnetic properties of the hull, the determination of the energization amount, and the evaluation of the demagnetization effect in the above-mentioned work depended largely on the abundant experience and skilled skill of the worker.

Further, even when a large number of magnetic detectors are installed on the seabed, only the measured values of a specific magnetic detector are used to calculate the ship's magnetic specifications, and the remaining magnetic detectors are measured. There is a tendency that the value is not used effectively.
This is because, in the conventional method, it was considered that the calculation and the like would be extremely complicated if the measured values of a large number of magnetic detectors were used to calculate the magnetic properties of the ship.

The present invention has been made by paying attention to these problems, and by utilizing a computer from the measured values of a plurality of magnetic detectors installed on the seabed or the like, the entire hull is converted into a magnetic moment. An object of the present invention is to provide a permanent demagnetization method for a ship, which enables the demagnetization process to be performed while constantly calculating and calculating the value quantitatively, and enabling the system to be automated.

[0007]

In order to achieve the above object, the method of permanent magnetic demagnetization of a ship according to the present invention is such that a number of body winding wheels are attached to a hull made of a magnetic material of the ship, In the process of erasing the permanent magnetism in the direction of the bow-stern line, the magnetic field of the hull is detected by a plurality of magnetic detectors in the process of erasing the permanent magnetism in the bow-caudal direction by changing the polarity of the current to positive or negative and energizing the coil. The permanent magnetic moment in the bow and tail line direction is quantitatively calculated based on the measured values of the plurality of magnetic detectors, and the value of the permanent magnetic moment is minimized while being monitored.

[0008]

In the permanent magnetic demagnetization method for a ship according to the present invention, the ship's magnetic moment is calculated from the measured values of a plurality of magnetic detectors installed on the seabed or the like, and the bow-tail line is calculated based on the magnetic moments. It is intended to extract the permanent magnetic moment in the direction and minimize it while monitoring its value.
The calculation of the ship magnetic moments in the X, Y, and Z directions of the ship can be performed using the expansion formula of the elliptic harmonic function. The hull magnetic moment calculated from the measured value of the magnetic field of the hull made of magnetic material by the expansion formula of the ellipsoidal harmonic function is a mixture of the permanent magnetic moment and the induced magnetic moment. It is possible from the moments calculated in the state facing south. Then, the value of the permanent magnetic moment obtained by the separation is constantly monitored (monitoring every time the energizing current is turned off after the demagnetizing current is applied to the body winding wheel) to quantitatively determine the erased state of the permanent magnetism. Can be evaluated. In this case, you can effectively use all the measurement data of the magnetic detector installed on the seabed,
It is possible to reduce the measurement error and improve the demagnetization effect as compared with the conventional method in which only the measured value of a specific magnetic detector is used.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a ship permanent magnetic demagnetization method according to the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram of a ship permanent magnetic demagnetization facility used in an embodiment of the ship permanent magnetic demagnetization method according to the present invention. In the figure, reference numeral 1 denotes a ship, which has a hull 2 made of a magnetic material, such as steel, and several body winding wheels 3 are wound and mounted on the outer circumference of the hull 2. It is desirable that the winding pitches of the body winding wheel 3 be evenly spaced, but a slight gap can be allowed. In the demagnetization process, the ship 1 is connected to the mooring table 5 fixed on the seabed side by the mooring wire 4. The body winding wheel 3 is connected to a demagnetization processing power supply chamber 6 having a power supply for supplying a demagnetization current via a power cable 9.

A large number of magnetic detectors 7 are fixed to the seabed below the mooring position of the ship 1. For example, some magnetic detectors 7 are arranged in the fore-and-aft direction of the hull 2, and further several are arranged on both sides in the fore-and-aft direction. Then, each magnetic detector 7 is connected to a measuring chamber 8 having a computer for receiving those measured values. In FIG. 1, the bow-tail direction of the hull 2 is the X direction, the direction perpendicular to the X direction in the horizontal plane is the Y direction, and the vertical direction is the Z direction.

Next, a method of calculating the magnetic moment of the magnetic body of the vessel 1, for example, the vessel 2 made of steel, will be described. Assuming that the vessel exists in a spatial region that does not include conduction current, Since the magnetic field is vortex-free, the scalar potential or magnetic field of the magnetic field satisfies the Laplace equation.

As shown in FIG. 2, points c1 and c2 are placed at both ends on the geometrical center line of the hull 2 of FIG. 1, and the spheroid coordinates (η, ξ, φ) with these points as the focal points are set. Set up. An arbitrary point P (η, ξ, φ) is a spheroidal surface η (η ≧
1), rotating hyperboloid ξ (-1 ≦ ξ ≦ 1) and half plane φ (0
≦ φ ≦ 2π). If the point P exists outside the spheroidal surface circumscribing the hull, the magnetic field F there is

[Equation 1] And can be expanded by an infinite series of spherical spherical harmonics.

On the other hand, the coordinates of the spheroid of the point P (η, ξ,
φ) in Cartesian coordinates

[Equation 2] Becomes

Therefore, each expansion coefficient is based on [Equation 1] based on the data measured by each magnetic detector 7 in each north-south direction of the bow (when the bow is moored in the south direction and in the north direction). It is possible to obtain by the method of least squares by applying the above-mentioned negative derivative (the negative derivative of the magnetic potential F corresponds to the magnetic field). In specific numerical calculation, n must be selected as an appropriate value, but as a quantitative evaluation method in which the function converges, it can be obtained as a relative value of the mean square error with respect to the maximum measured magnetic field value. Where the mean square error σ _i is

(Equation 3) It is. However, H _i : a calculated value obtained by using each expansion coefficient, H _id : a measured value of each magnetic detector 7, N: a measured number, and i = X, Y, Z. The relative value P (%) of the mean square error σ _i with respect to the maximum value of the measured magnetic field is P = (σ _i / H _imax ) × 100. Where H _imax is the maximum value of the measured magnetic field. The mean square error σ _i and the relative value P are calculated based on the hull magnetic field measurement values of the magnetic detectors 7 in the X, Y and Z directions.
It can be obtained for each of the Y direction and the Z direction.

Here, each expansion coefficient obtained above is n = 1.
And

(Equation 4) Thus, each expansion coefficient corresponds to the magnetic moments M _x , M _y , and M _z of the hull in the X, Y, and Z directions.

Each expansion coefficient calculated in each of these directions contains a magnetic moment corresponding to a permanent magnetic component and an induced magnetic component due to the earth's magnetic field. The former changes due to changes in ship magnetism over time, but the latter changes. As long as they exist in the same place and in the same direction, they may be regarded as almost constant.

Therefore, if each expansion coefficient corresponding to the magnetic moment in the direction of the bow and tail is separated into the permanent magnetic component and the induced magnetic component,

(Equation 5) Becomes Here, the subscript p is the permanent magnetic component, the subscript i is the induced magnetic component, and N and S are the respective expansion coefficients calculated in the north and south directions (when moored to the north of the bow and moored to the south). is there.

As a result, the expansion coefficient corresponding to the permanent magnetic moment in the bow and tail line direction

(Equation 6) By repeating the energization to minimize, the permanent magnetism in the bow-caudal direction of the entire ship can be demagnetized.

FIG. 3 is a flow chart showing a series of procedures of the embodiment according to the present invention. First, the ship 1 of FIG. 1 is moored so that the bow faces north and south, and step # 1 of FIG. 3 is executed to measure the measured values of the magnetic detectors 7 in the measurement chamber 8
To the computer inside. Then, step # 2 is executed and each expansion coefficient is calculated from the measured values of the magnetic field under the bottom of the ship in each direction (north and south of the bow) using the spherical harmonic expansion formula.

(Equation 7) Is calculated, and in step # 3, it is separated into an inductive magnetic component in the bow and tail line direction and a permanent magnetic component.

(Equation 8) Here, it is necessary to make the induced magnetic component induced by the earth's magnetic field at that location apparently zero by energizing the body winding wheel 3 wound around the hull 2 of FIG. Therefore, step # 4 is executed. That is, in order to determine the current value for canceling the induced magnetic component, by subtracting the underfloor magnetic field under a certain current from the underfloor magnetic field under a non-energized state, The magnetomotive force can be calculated, and the current for eliminating the induced magnetic component is proportional to the magnetomotive force, so that it can be easily determined. Hereinafter, the current for erasing the induced magnetic component will be referred to as the base current.

From this state, steps # 5, # 6, #
7 and # 8 are executed. That is, the maximum energization amount, for example +
While changing the polarity to positive / negative such as 3000A, then −2800A, + 2600A, the magnitude of the current of the body winding wheel 3 is gradually reduced according to a certain attenuation rate, and the base current obtained above is used as a reference as approaching the final stage. Energizing while gradually decreasing is the same as the conventional technique, but in the process, as shown in FIG. 4, energization is turned off after each energization to calculate the permanent magnetic component (step # 6), and the value is calculated. Will be constantly monitored, and demagnetization processing will be carried out until it becomes minimum. If it is determined in step # 8 that the minimum value of the permanent magnetism has been obtained, step # 9 is executed to determine whether or not the demagnetization effect is successful, and it is determined that the demagnetization of the permanent magnetism has been performed satisfactorily (for example, If the permanent magnetic component is less than a certain value), the process ends.

The series of operations shown in FIG. 3 can be automated by utilizing a computer.

[0023]

As described above, according to the permanent magnetic demagnetization method for a ship according to the present invention, the demagnetization state is calculated as the magnetic moment of the entire hull, so that the permanent magnetic moment can be quantitatively grasped. This makes it possible to carry out an optimum demagnetization treatment and improve the demagnetization effect. Further, this demagnetization process is suitable for automation using a computer, does not require a high level of skill of an operator, and can improve the efficiency of the work by introducing the computer.

[Brief description of drawings]

FIG. 1 is a schematic view of a permanent magnetic demagnetization treatment facility for a ship used in an embodiment of a ship permanent magnetic demagnetization method according to the present invention.

FIG. 2 is an explanatory diagram showing a mathematical model for calculating a ship magnetic moment.

FIG. 3 is a flowchart of an embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a decay state of permanent magnetism in the bow-tail direction in the course of demagnetization processing of the ship.

[Explanation of symbols]

 1 Ship 2 Hull 3 Body Winding Wheel 7 Magnetic Detector

Claims (1)

[Claims] 1. A hull made of a magnetic material of a ship, to which several body winding wheels are attached, and the body winding wheel is energized by gradually reducing the magnitude of the current while changing the polarity of the current to positive or negative. Thus, in the process of erasing the permanent magnetism in the bow-tail direction, the magnetic field of the hull is measured by a plurality of magnetic detectors, and the permanent magnetic moment in the bow-tail direction is measured based on the measured values of the plurality of magnetic detectors. Is calculated quantitatively and is minimized while monitoring the value of the permanent magnetic moment.