RU2265234C1 - Method for determining deformation of soil by emitting panel - antenna of pulse seismic source with electromagnetic drive - Google Patents

Abstract

FIELD: geophysics.

SUBSTANCE: electromagnetic drive during selection of gap is provided with energy transformation mode with permanency of formed force, at which current i_l is measured in electromagnet excitation winding during operation of seismic source on soil. Then shift of antenna panel and deformation of soil is determined from current difference i_l proportional to them and from known current i_o in excitation winding, appropriate for operation of seismic source with immobile emitting plate.

EFFECT: higher efficiency.

4 dwg

Description

The invention relates to pulsed non-explosive seismic sources with an electromagnetic drive, used during seismic surveys and, in particular, to methods for evaluating the effectiveness of a seismic source when it is used on soils with different rheological characteristics. The magnitude and rate of deformation of the soil under the antenna plate when exposed to the force developed by the electromagnetic drive determines to a large extent the dynamics and efficiency of the seismic source, the power and the amplitude-frequency characteristic of the seismic wave created by it. In this regard, the operational determination of the dependence of soil deformation on time allows us to determine the mechanical interaction of the plate with the soil both during its operation directly in the field and during bench tests of manufactured seismic sources.

The control of the seismic source is usually carried out using accelerometers placed on the load and (or) the radiating plate-antenna (Smirnov V.P. Electromagnetic sources of seismic oscillations of the Yenisei series SEM, KEM // Instruments and systems for exploration geophysics. / Quarterly official publication of the Saratov departments of the Euro-Asian Geophysical Society, No. 1 (3), 2003, pp. 21-25) [1]. Monitoring the operation of the seismic source using accelerometers is carried out as follows: during the operation of the seismic source on the ground, the signal from the accelerometer attached to the load and (or) the radiating plate-antenna is measured and the fact of the operation of the seismic source is visually recorded and its stability is evaluated.

In the described method for monitoring the operation of a seismic source, only one feature that matches the essential feature of the claimed invention can be distinguished - this is the operation of the seismic source on the ground as a condition for making measurements. Moreover, in the analogue method, the measured value is the signal of the accelerometer, and in the present method is the signal of the current sensor. Therefore, the claims are made without division into restrictive and distinctive parts.

The described method has several disadvantages. Significant phase distortions and disturbances, characteristic of accelerometers measuring short-term pulse accelerations exceeding tens of times the acceleration of gravity, do not allow an assessment of the dynamics of the seismic source and, in particular, to determine the movement of the radiating plate-antenna and the resulting soil deformation. The lack of reliability of accelerometers subjected to high dynamic loads reduces the reliability and efficiency of the seismic source.

The problem to which the invention is directed, is to increase the efficiency of the seismic source and its reliability.

The technical result is to obtain information about the deformation of the soil under the radiating plate-antenna of the seismic source during the application of the force developed by the electromagnet to it by measuring the current of the field winding of the power electromagnet of the seismic source.

This problem is solved in that the proposed method for determining soil deformation rigid radiating plate antenna seismic source with an electromagnetic actuator comprising a magnetic circuit of the electromagnet with a flat nonmagnetic gap and creates a force between prigruzami and said plate antenna, an electromagnetic actuator is provided on choosing δ gap _of mode energy conversion with the constancy of the created force. In this mode, the current i _{1 is} measured in the excitation winding of the electromagnet during the operation of the seismic source on the ground and then the displacement of the antenna plate and, obviously, the equal deformation of the soil are determined by the proportional difference between the current i ₁ and the known current i _о in the excitation winding corresponding to the operation of the seismic source with a stationary radiating plate-antenna. A change in soil deformation and its magnitude characterizes the efficiency of transferring the mechanical energy of an electromagnetic drive into the soil and creating seismic waves.

The essence of the method is illustrated by drawings.

Figure 1 - Structural diagram of a pulsed seismic source, which shows: 1 - soil; 2 - plate-antenna with racks 3; 4 - an anchor of an electromagnet; 5 - load; 6 - inductor of an electromagnet with field winding 7; 8 - a gap of δ _o between the armature 4 and the inductor 6 of the electromagnet.

Figure 2 - Schematic diagram of the pulsed power system of the excitation coil of an electromagnet, in which: 7 - field winding; 9 - storage capacitor bank; 10 - battery charger 9; 11 - switching device (thyristor); 12 - power diode; 13 - shunt for measuring current; 14 - signal from the shunt.

Figure 3 - Change in current in the excitation winding of an electromagnet during operation of the seismic source: 15 - on hard ground, in which the deformation of the soil is negligible; 16 - on softer soil; 17 - on even softer soil.

Figure 4 - Graphs of the movement of the radiating plate and the load under the action of the force of the electromagnet: 18 - change created by the electromagnet force; 19 - movement of the cargo; 20 - movement of the radiating plate in hard ground; 21 - plate movement with softer soil.

The seismic source (figure 1) contains a radiating plate-antenna 2 mounted on the ground 1 with racks 3, on which the armature 4 of the electromagnet is supported. The loading mass 5 (load) is supported on the antenna plate 2 and is located between the uprights 3. A magnetic core 6 of the inductor with the excitation winding 7 is fixed to the load 5. In the initial position, the armature 4 and the inductor 6 are separated by a gap 8 of δ _о . A characteristic feature of the structural scheme of the seismic source is the use of a power electromagnet with a flat gap of 8 of a value of δ _о , which allows it to provide it with an approach to constant values of the field induction in the gap and, consequently, the generated force, during the time that the gap is selected.

The proposed method for determining the soil deformation is to measure the field current during the operation of the seismic source on the ground in the constant force mode of the electromagnetic drive, followed by comparing the measured current with the field current corresponding to the operation of the seismic source with a stationary radiating plate. The difference between these currents is proportional to the movement of the antenna plate and the deformation of the soil under the plate.

The method is carried out at the next operation of the seismic source. At time t _o , the thyristor 11 opens at the signal from the seismic station and the capacitance 9, charged from the device 10, is discharged to the excitation winding 7 by the time t ₁ (Fig. 2). During the time from t _o to t _{1, the} change in the gap 8 compared to its value δ _{о is} insignificant and practically does not affect the change in the discharge current. At time t _{1, the} voltage across the capacitance 9 changes sign, the diode 12 automatically opens and the field winding 7 is shorted through diode 12. At t greater than t _{1, the} magnitude of the magnetic flux Φ and induction B, and therefore the force generated by the electromagnet 17, remain constant for time for selecting the entire value of δ _{about the} gap 8 of the electromagnet. Under the action of this force at t greater _than t _{1, the} load 5 with the inductor 6 (Fig. 1) moves up in accordance with the dependence 19 (Fig. 4), and the anchor 4 with the posts 3 and the antenna plate 2 moves down in accordance with the curves 20 or 21 in FIG. 4. The change in the gap of the electromagnet is determined by the sum of the displacements 19 and 20 (or 21). The change in current in the field winding can be determined from Ohm's law for the magnetic circuit of an electromagnet

where F is the magnetizing force;

w is the number of turns of the field winding;

F _m - the constant magnetic flux when t is greater than t ₁ ;

R _f is the magnetic resistance of the magnetic circuit.

The magnetic resistance of the gap 8 value δ _about taking into account its change x when moving x _about load 5 and x ₁ anchor 4 with a radiating plate-antenna 2

where S is the area of the poles of the electromagnet;

μ _about - magnetic constant.

Since the gap change

where x _about - moving 18 of the load up,

x ₁ - the movement of the anchor with the antenna plate down, equal to the deformation of the soil 20 or 21.

From (1), taking into account (2) and (3), it follows that the field current

where I _f is the magnetization current of the magnetic circuit of the electromagnet;

K is a constant depending on the number of turns w of the field winding and the maximum value of its magnetic flux Φ _m passing through the poles of the magnetic circuit of the inductor 6

For the case of a stationary radiating plate-antenna x ₁ = 0, the current i _o in the field winding corresponds to curve 15 in Fig. 3 and, taking into account (4), is determined by the dependence

The difference between the currents i _o and i ₁

The movement x _{1 of the} slab, and therefore the deformation of the soil created by it

and in proportion to the difference Δi of the currents i _o and i ₁ .

The value of the coefficient K can be determined from the experimental curves 15, 16 and 17 of the current in the excitation winding 7. Since at t = t _{1 the} currents i _{1 are} maximum, ax≈0 (x _o ≈0 and x ₁ ≈0), then from ( 4) or (6) it follows that

where I _f is the current in the winding at the time of selection of the gap δ _about (moments t ' ₂ , t ₂ or t _{2 (0)} ).

The time for choosing a gap 8 of δ _о depends on the stiffness of the soil. With very hard soil, in which the movement of the antenna plate is negligible, this time is determined by the moment t _{2 (0)} (Figs. 3, 4); with soft ground - with moment t ₂ , and with even softer - with moment t ' ₂ . The displacements 20 and 21 of the antenna plate during the time of choosing the gap to and, correspondingly equal to the time of applying the force 18 to the antenna plate are shown in Fig. 4 by solid lines, and after choosing the value of δ ₀ to the gap 8 - dotted.

From the nature of the change in curve 20, it follows that the moment t _{2 of the} end of the force 18 and, therefore, the end of the choice of δ _{about the} gap 8 occurs later than the maximum compression of the soil, when it has already begun to expand and, therefore, the soil does not receive mechanical pressure at t greater than t ₂ energy from an electromagnet. This mode of operation of the seismic source is not quite consistent with the load - soil. To obtain a more consistent mode, it is necessary either to increase the power of the electromagnet 18 by increasing the charging voltage on the capacitive storage 9, or to reduce the value of δ _{about the} gap 8 in order to reduce its selection time. Curve 21, corresponding to softer soil, characterizes a more consistent mode of operation of the seismic source with the load-soil, since the moment t ' _{2 of the} choice of the gap corresponds to the growing part of the movement of the radiating plate-antenna, when the deformation of the soil is not yet maximum.

Thus, measuring the current in the field winding with subsequent determination of soil deformation under the antenna plate during the action of the electromagnet forces on it also allows you to choose the most effective modes of the seismic source, taking into account the rheological properties of the soil and thereby increase the efficiency of seismic surveys. The current measurement of the field winding can be carried out using signal 14 from the shunt 13 or in another way, providing noise immunity and reliability of measurement during operation of the seismic source in difficult operating conditions.

The signal 14 from the shunt 13 can be transmitted by known methods to the seismic station and processed on it in accordance with the proposed method in order to obtain information about the deformation of the soil under the antenna plate, which allows you to solve several problems: to be able to quickly monitor the operation of the seismic source; take into account the features of the seismic source when processing seismic information received from the seismic receivers, and provide the seismic source with the most effective modes during its operation. In powerful seismic sources, two or more plate-antennas are used, the force on each of them is formed by one or more electromagnets containing one or two field windings. For example, in a bogey double-seismic source, in which the first and second runners are the radiating element, one or more electromagnets are installed on each run to create the necessary force (50 ÷ 100) 10 ⁴ H or more. The capacitive drive 9 of the power circuit is in this case made in the form of two separate sections connected to parallel-connected excitation windings of the electromagnets of the first and second runners, respectively. With this technical solution, sleigh runners are separate seismic emitters that can create seismic waves simultaneously, alternately, or according to another law. To measure the movements of the runners and the soil deformation created by each of them, a shunt is included in the discharge circuit of each section of the capacitive energy storage unit, through which the sum of the currents of the parallel connected excitation windings of the electromagnets of one runner passes. Signals from shunts are used to determine, according to the proposed method, the movements of skids and soil deformations under each of them.

An experimental verification of the proposed method was carried out in laboratory conditions on a sled seismic source design, the skid of which serves as a radiating antenna plate. The results obtained by measuring the displacement x ₁ runner by the rechordal sensor (CLP13) and the proposed method differ by no more than (5-7)%. With changes in the maximum value of the force developed by the electromagnetic drive P _m = (10 ÷ 25) · 10 ⁴ H the movement of the radiating plate x ₁ = (0.5 ÷ 1.5) · 10 ^-3 m.

Sourse of information

1. Smirnov V.P. Electromagnetic sources of seismic oscillations of the Yenisei series SEM, KEM // Instruments and systems for exploration geophysics. / Quarterly official publication of the Saratov branch of the Euro-Asian Geophysical Society. No. 1 (3), 2003, pp. 21-25.

Claims (1)

A method for determining soil deformation by a radiating plate-antenna of a pulsed seismic source with an electromagnetic drive containing an electromagnet magnetic circuit with a flat non-magnetic gap and creating a force between the load and said plate, which means that the electromagnetic drive is provided with an energy conversion mode for the duration of the gap selection, with the force being generated at a constant which measure the current i ₁ in the field winding of the electromagnet when the seismic source is on the ground and then determine the movement of the plate-ant The soil deformation is also proportional to the difference between the current i ₁ and the known current i _o in the excitation winding, which corresponds to the operation of the seismic source with a stationary radiating plate.

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