A longitudinal wave propagation suppressor for measuring shear wave velocity of seabed sediment

Abstract

The present application relates to the technical field of measuring the shear wave speed of seabed sediment, and particularly relates to a longitudinal wave propagation inhibitor for measuring the shear wave speed of seabed sediment, which comprises a first cylindrical rod, a matching layer and a second cylindrical rod connected coaxially in sequence, and the cylindrical rod and the matching layer are made of different materials, according to the selection of materials with different parameters, when the transverse wave is excited by the transverse wave transmitting transducer, and when the transverse wave is received by the transverse wave receiving transducer, the matching layer approximately constitutes an acoustic half-wavelength sound transmission sheet for the propagation of the transverse wave, and the matching layer approximately constitutes an acoustic quarter-wavelength sound insulation sheet for the propagation of the longitudinal wave, the longitudinal wave propagation can be inhibited by the present application, so that the amplitude of the transmitted longitudinal wave is greatly attenuated, and the amplitude of the transmitted transverse wave is slightly attenuated, thereby realizing the effect of inhibiting the longitudinal wave propagation.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of measuring the shear wave velocity of seabed sediments, and particularly relates to a longitudinal wave propagation inhibitor for measuring the shear wave velocity of seabed sediments. BACKGROUND

[0002] Seabed sediments are porous media composed of sand, clay and seawater. Currently, seabed sediments are usually collected in PVC tubes with an outer diameter of about 75 mm. When seabed sediments are collected, a 2-3 meter long PVC tube is placed inside a gravity corer, and the gravity corer sends seabed sediments into the PVC tube when the gravity corer penetrates seabed sediments.

[0003] After the gravity corer is taken from the seabed to the deck of a ship, the PVC tube containing seabed sediments, i.e., a seabed sediment long sample, is taken out of the gravity corer, and is sealed and the like to reduce disturbance.

[0004] After being transported back to a laboratory, when the acoustic parameters of seabed sediments are measured, the seabed sediment long sample is usually cut into short samples with a length of about 300 mm or less, considering the large acoustic attenuation of seabed sediments.

[0005] As shown in Figure 1 and Figure 2 , when the shear wave velocity of seabed sediments needs to be measured, if a shear wave transmitting transducer and a shear wave receiving transducer are directly arranged at two ends of seabed sediments in the PVC tube containing seabed sediments (as shown in Figure 1 and Figure 2 ), this method is not feasible. Because when the shear wave transmitting transducer excites a shear wave, a longitudinal wave is also generated simultaneously; if the length of seabed sediments is not long enough, the acoustic wave waveform received by the shear wave receiving transducer will be a curve in which the shear wave waveform and the longitudinal wave waveform are superimposed together, and the travel time of the shear wave through seabed sediments cannot be determined.

[0006] According to the principle that the longitudinal wave velocity of an elastic medium is higher than the shear wave velocity, a longer seabed sediment sample can be used to make the longitudinal wave waveform and the shear wave waveform received by the shear wave receiving transducer be staggered on the time axis. However, because the acoustic attenuation of seabed sediments is large, the acoustic energy is completely attenuated before reaching the shear wave receiving transducer, and the shear wave receiving transducer will not receive an acoustic signal.

[0007] In order to reduce the influence of longitudinal waves on shear waves when the shear wave velocity of seabed sediments is measured, a feasible method is to theoretically inhibit the propagation of longitudinal waves without inhibiting the propagation of shear waves. However, there is currently no longitudinal wave propagation inhibitor for measuring the shear wave velocity of seabed sediments, and therefore there is an urgent need for a longitudinal wave propagation inhibitor that can be applied to the measurement of the shear wave velocity of seabed sediments. SUMMARY

[0008] The application aims at solving the problems in the prior art.

[0009] To solve the problems in the prior art, the application adopts the following technical scheme:

[0010] The longitudinal wave propagation inhibitor for measuring the transverse wave speed of seabed sediment comprises cylindrical rods and a matching layer with different materials.

[0011] Further, the matching layer is made of metal material, and the cylindrical rod is made of engineering plastic material.

[0012] Further, the first cylindrical rod, the matching layer and the second cylindrical rod are connected by end face coaxial connection, and the diameters of the first cylindrical rod and the second cylindrical rod are the same as that of the matching layer.

[0013] Further, the first cylindrical rod and the second cylindrical rod are made of the same elastic material, the cylindrical rod is made of the first material, and the matching layer is made of the second material; the parameters of the first material and the second material include transverse wave speed, longitudinal wave speed, acoustic characteristic impedance, transverse wave length and longitudinal wave length.

[0014] Further, the thickness of the matching layer is equal to one fourth of the longitudinal wave length of the second material.

[0015] Further, the acoustic characteristic impedance of the second material is three times greater than that of the first material.

[0016] Further, the length of the first cylindrical rod is L1, the length of the second cylindrical rod is L3, L1=L3, and the lengths of L1 and L3 are the prime number times of one fourth of the longitudinal wave length of the first material.

[0017] Further, the diameter of the cylindrical rod is smaller than the longitudinal wave half wavelength of the first material.

[0018] Further, the absolute error of the transverse wave speed of the second material and one half of the longitudinal wave speed is within ±96m / s, and the relative error is within ±5%.

[0019] Further, the transverse wave speed of the second material is one half of the longitudinal wave speed.

[0020] The application has the following advantages:

[0021] In the present application, the first cylindrical rod, the matching layer and the second cylindrical rod are coaxially connected in sequence, and the cylindrical rod and the matching layer are made of different materials. According to the selection of materials with different parameters, when the transverse wave transmitting transducer excites the transverse wave, and when the transverse wave receiving transducer receives the transverse wave, the matching layer approximately constitutes an acoustic half-wavelength sound transmission sheet for the propagation of the transverse wave, and the matching layer approximately constitutes an acoustic quarter-wavelength sound insulation sheet for the propagation of the longitudinal wave. The present application can be used to suppress the propagation of the longitudinal wave, so as to greatly attenuate the amplitude of the transmitted longitudinal wave and slightly attenuate the amplitude of the transmitted transverse wave, thereby achieving the effect of suppressing the propagation of the longitudinal wave. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 Structure diagram of the present application;

[0023] Figure 2 Structure diagram of the present application; Figure 1 Structure diagram of the present application;

[0024] Figure 3 Structure diagram of the present application;

[0025] Figure 4 Structure diagram of the present application; Figure 3 Structure diagram of the present application;

[0026] Figure 5 Structure diagram of the present application; Figure 3 Structure diagram of the present application;

[0027] BRIEF DESCRIPTION OF DRAWINGS DETAILED DESCRIPTION

[0028] In order to make the purpose, technical scheme and beneficial effects of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all.

[0029] As shown in Figures 3 to 5 A longitudinal wave propagation suppressor for measuring the transverse wave speed of seabed sediments, comprising cylindrical rods and a matching layer 7 made of different materials.

[0030] The cylindrical rods comprise a first cylindrical rod 5 and a second cylindrical rod 6, which are respectively connected to the two ends of the matching layer 7, and the first cylindrical rod 5, the second cylindrical rod 6 and the matching layer 7 are coaxially connected.

[0031] In the present application, the first cylindrical rod 5, the matching layer 7 and the second cylindrical rod 6 are coaxially connected in sequence, and the cylindrical rod and the matching layer 7 are made of different materials. According to the selection of materials with different parameters, when the transverse wave transmitting transducer 3 excites the transverse wave, and when the transverse wave receiving transducer 4 receives the transverse wave, the matching layer 7 approximately constitutes an acoustic half-wavelength sound transmission sheet for the propagation of the transverse wave, and the matching layer 7 approximately constitutes an acoustic quarter-wavelength sound insulation sheet for the propagation of the longitudinal wave. The present application can suppress the propagation of the longitudinal wave to achieve the purpose of greatly attenuating the amplitude of the transmitted longitudinal wave and slightly attenuating the amplitude of the transmitted transverse wave, thereby achieving the effect of suppressing the propagation of the longitudinal wave.

[0032] The cross section of the first cylindrical rod 5 and the second cylindrical rod 6 can be other shapes, but in order to be coaxially connected with the matching layer 7 and easy to be coaxial with the submarine sediment 2b in the PVC pipe 2a, etc., the first cylindrical rod 5 and the second cylindrical rod 6 are preferably cylindrical rods with circular cross section.

[0033] The submarine sediment 2b collected at present is usually contained in a PVC pipe 2a with an outer diameter of about 75 mm. When the submarine sediment 2b is obtained, a 2-3 meter long PVC pipe 2a is placed inside the gravity corer, and when the gravity corer penetrates the submarine sediment 2b, the gravity corer sends the submarine sediment 2b into the PVC pipe 2a.

[0034] After the gravity corer is taken from the seabed to the deck of the ship, the PVC pipe 2a containing the submarine sediment 2b, i.e. the submarine sediment long sample, is taken out of the gravity corer, and is sealed and treated to reduce disturbance.

[0035] After being transported back to the laboratory, when measuring the acoustic parameters of the submarine sediment, considering the large acoustic attenuation of the submarine sediment, the submarine sediment long sample is usually cut into a submarine sediment short sample with a length of about 300 mm or less.

[0036] When measuring, the two submarine sediment transverse wave speed measurement longitudinal wave propagation suppressors are arranged at the two ends of the submarine sediment 2b in the submarine sediment short sample 1 to be measured, and the submarine sediment speed measurement longitudinal wave propagation suppressor is arranged at the center of the end face of the submarine sediment 2b in the submarine sediment short sample 1, and the outer sides of the two submarine sediment transverse wave speed measurement longitudinal wave propagation suppressors are respectively provided with the transverse wave transmitting transducer 3 and the transverse wave receiving transducer 4.

[0037] In this way, in the present application, under the action of the submarine sediment transverse wave speed measurement longitudinal wave propagation suppressor, the wave shape received by the transverse wave receiving transducer 4 is avoided to be a curve in which the longitudinal wave and the transverse wave waveforms are superimposed together, so that the staff can interpret the travel time of the transverse wave through the submarine sediment 2b, and the problems existing in the prior art are solved.

[0038] The center frequency of the shear wave transmitting transducer 3 and the shear wave receiving transducer 4 is preferably 50 kHz-200 kHz, because if the frequency is too high, the energy of the shear wave will decay quickly; if the frequency is too low, the wavelength will be greater than 75 mm, which will cause diffraction of the acoustic wave and affect the accuracy of the measurement results. The center frequency of the shear wave transmitting transducer 3 and the shear wave receiving transducer 4 can be any value between 50 kHz and 200 kHz, such as 60 kHz or 70 kHz, etc.

[0039] In some embodiments, the diameters of the first cylindrical rod 5 and the second cylindrical rod 6 are the same as the diameter of the matching layer 7.

[0040] In some embodiments, the first cylindrical rod 5 and the second cylindrical rod 6 are made of the same elastic material; the material used for the cylindrical rod is the first material, and the material used for the matching layer 7 is the second material.

[0041] Each material includes parameters such as shear wave speed, longitudinal wave speed, acoustic characteristic impedance, shear wave wavelength, and longitudinal wave wavelength.

[0042] That is, when selecting the first material and the second material, the parameters of the materials are selected, and the acoustic parameters of different materials are as described in the prior art, and the selection conditions include: (1) the absolute error of the half of the longitudinal wave speed and the shear wave speed of the second material, i.e., the half of the longitudinal wave speed minus the shear wave speed is within ±96 m / s, and the relative error, i.e., [(the half of the longitudinal wave speed minus the shear wave speed) / the half of the longitudinal wave speed]×100%, is within ±5%; (2) the thickness of the matching layer 7 is equal to one fourth of the longitudinal wave wavelength of the second material; (3) the acoustic characteristic impedance of the second material is greater than three times the acoustic characteristic impedance of the first material; (4) the length of the first cylindrical rod 5 is L1, the length of the second cylindrical rod 6 is L3, L1=L3, and the lengths of L1 and L3 are an odd number times one fourth of the longitudinal wave wavelength of the first material; (5) the diameter of the cylindrical rod is less than the half of the longitudinal wave wavelength of the first material.

[0043] In the present application, according to the acoustic and physical parameters of the existing materials, the first material is an engineering plastic, and the second material is a metal material, which can meet the requirements of the longitudinal wave propagation suppressor for measuring the shear wave speed of the seabed sediment.

[0044] As an embodiment of the present application, the matching layer 7 is made of red copper material, and the cylindrical rod is made of organic glass material, or the matching layer 7 is made of tin material, and the cylindrical rod is made of polyethylene material, or the matching layer 7 is made of titanium material, and the cylindrical rod is made of polystyrene engineering plastic material.

[0045] As an embodiment of the present application, the matching layer 7 is made of brass, and the cylindrical rod is made of organic glass. The main acoustic and physical parameters of the present application are shown in Table 1.

[0046]

[0047] The error of the acoustic velocity of the matching layer to the half of the acoustic velocity of the longitudinal wave is shown in Table 2.

[0048]

[0049] The error of the acoustic velocity of the matching layer to the half of the acoustic velocity of the longitudinal wave is shown in Table 2.

[0050] According to the parameters shown in Table 1, when the acoustic wave frequency is 50 kHz, the main parameters of the matching layer 7 and the cylindrical rod in the longitudinal wave suppressor are shown in Table 3.

[0051]

[0052] The main parameters of the matching layer in the longitudinal wave suppressor when the acoustic wave frequency is 50 kHz are shown in Table 3.

[0053] According to the parameters shown in Tables 1 to 3, and in combination with the half-wavelength sound transmission sheet and quarter-wavelength sound insulation sheet principles of acoustic theory, the theoretical transmission coefficient of the longitudinal wave is 0.03036676, and the theoretical transmission coefficient of the transverse wave is about 1. It can be seen that the present application can well suppress the propagation of the longitudinal wave, and has little suppression on the propagation of the transverse wave.

[0054] From the above conclusions, it can be seen that the matching layer 7 in the longitudinal wave propagation suppressor for measuring the transverse wave acoustic velocity of the seabed sediment of the present application approximately constitutes an acoustic half-wavelength sound transmission sheet for the propagation of the transverse wave, and approximately constitutes an acoustic quarter-wavelength sound insulation sheet for the propagation of the longitudinal wave, thereby constituting an independent functional acoustic device with a large attenuation of the transmitted longitudinal wave amplitude and a small attenuation of the transmitted transverse wave amplitude.

[0055] In detail, according to the parameters shown in Tables 1 and 2, when the acoustic wave frequency is 50 kHz, the longitudinal wave wavelength of the matching layer 7 is 88.6 mm, the thickness of the matching layer 7 is one quarter of the longitudinal wave wavelength, i.e. 22.15 mm, which is close to one half of the transverse wave wavelength 21.2 mm.

[0056] Further, the acoustic characteristic impedance of the matching layer 7 made of brass is 3588300 Kg / (m 2 ·s), and the acoustic characteristic impedance of the first cylindrical rod 5 and the second cylindrical rod 6 made of organic glass is 315060 Kg / (m 2The ratio of the acoustic characteristic impedance of the matching layer 7 made of brass to the acoustic characteristic impedance of the cylindrical rod made of organic glass is 11.39, which is much greater than 3. In addition, the acoustic characteristic impedances of the cylindrical rod made of organic glass and the seabed sediment are relatively close, and the coupling is good.

[0057] That is, under the action of the present application, the propagation of the longitudinal wave can be inhibited, and the propagation of the transverse wave is inhibited little, and the problem of the superposition of the longitudinal wave waveform in the measurement of the transverse wave speed of the seabed sediment 2b can be solved.

[0058] Further, the connections of the first cylindrical rod 5, the matching layer 7 and the second cylindrical rod 6 are all end face coaxial connections. In use of the present application, the two ends of the seabed sediment in the seabed sediment short sample 1 are respectively provided with the transverse wave transmitting transducer 3 and the transverse wave receiving transducer 4, and the longitudinal wave propagation inhibitor for the measurement of the transverse wave speed of the seabed sediment is arranged between the seabed sediment short sample 1 and the transverse wave transmitting transducer 3 and the transverse wave receiving transducer 4, so as to realize the effect of inhibiting the propagation of the longitudinal wave and solve the problem of the superposition of the longitudinal wave waveform in the measurement of the transverse wave speed of the seabed sediment.

[0059] If the transverse wave transmitting transducer 3 excites a 50KHz transverse wave, a 50KHz longitudinal wave will also be generated. The transverse wave and the longitudinal wave are simultaneously transmitted from the A end face of the first cylindrical rod 5 into the longitudinal wave inhibitor, the amplitude of the longitudinal wave is greatly attenuated by the matching layer 7, while the amplitude of the transverse wave is little attenuated by the matching layer 7, the transmitted longitudinal wave amplitude from the B end face of the second cylindrical rod 6 is greatly attenuated, while the transmitted transverse wave amplitude is little attenuated, so as to realize the inhibition of the propagation of the longitudinal wave.

[0060] In the embodiment, the length of the first cylindrical rod 5 and the second cylindrical rod 6 is determined as 146.85mm. After the geometric dimensions of the first cylindrical rod 5 and the second cylindrical rod 6 and the matching layer 7 are determined, the right end face of the first cylindrical rod 5 and the left end face of the matching layer 7 are coaxially and tightly connected by an adhesive, and the right end face of the matching layer 7 and the left end face of the second cylindrical rod 6 are coaxially and tightly connected by an adhesive.

[0061] Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

Claims

1. A longitudinal wave propagation suppressor for use in a measurement of shear wave sound velocity of a seabed sediment, characterized by, The cylindrical rod and the matching layer are made of different materials; the cylindrical rod includes a first cylindrical rod and a second cylindrical rod, the first cylindrical rod and the second cylindrical rod are connected at two ends of the matching layer respectively, the first cylindrical rod, the second cylindrical rod and the matching layer are coaxially connected; the matching layer is made of metal material, and the cylindrical rod is made of engineering plastic material; The first cylindrical rod, the matching layer and the second cylindrical rod are all end face coaxial connection; The first cylindrical rod and the second cylindrical rod are made of the same engineering plastic, the cylindrical rod is a cylindrical rod made of a first material, and the matching layer is a matching layer made of a second material; the parameters of the first material and the second material include transverse wave speed, longitudinal wave speed, acoustic characteristic impedance, transverse wave length and longitudinal wave length; the diameter of the cylindrical rod is smaller than the longitudinal wave half wavelength of the first material; the transverse wave speed of the second material is half of the longitudinal wave speed; The thickness of the matching layer is equal to one fourth of the longitudinal wave length of the second material; the acoustic characteristic impedance of the second material is three times greater than the acoustic characteristic impedance of the first material.

2. The longitudinal wave propagation suppressor for measurement of shear sound speed in marine sediments according to claim 1, characterized in that, The diameters of the first cylindrical rod and the second cylindrical rod are the same as the diameter of the matching layer.

3. The longitudinal wave propagation suppressor for shear wave acoustic velocity measurement of seabed sediments of claim 1, wherein, The length of the first cylindrical rod is L1, the length of the second cylindrical rod is L3, L1=L3, and the lengths of L1 and L3 are an odd number times one fourth of the longitudinal wave length of the first material.

4. The longitudinal wave propagation suppressor for shear wave acoustic velocity measurement of seabed sediments of claim 1, wherein, The absolute error of the transverse wave speed of the second material and half of the longitudinal wave speed is within ±96m / s, and the relative error is within ±5%.

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