CN113237618A - Underwater shell modal test method considering internal flow field and pressure influence thereof - Google Patents
Underwater shell modal test method considering internal flow field and pressure influence thereof Download PDFInfo
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- CN113237618A CN113237618A CN202110375775.7A CN202110375775A CN113237618A CN 113237618 A CN113237618 A CN 113237618A CN 202110375775 A CN202110375775 A CN 202110375775A CN 113237618 A CN113237618 A CN 113237618A
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- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M7/00—Vibration-testing of structures; Shock-testing of structures
- G01M7/02—Vibration-testing by means of a shake table
- G01M7/025—Measuring arrangements
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D21/00—Measuring or testing not otherwise provided for
- G01D21/02—Measuring two or more variables by means not covered by a single other subclass
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M10/00—Hydrodynamic testing; Arrangements in or on ship-testing tanks or water tunnels
Abstract
The invention provides a method for testing underwater shell modal by considering the influence of an internal flow field and pressure thereof, wherein a strain gauge is adhered to the outer circumference of a test body and is connected with a digital acquisition instrument through a cable; the test body is suspended in a pressure box by a spring pull rod, and a non-contact type excitation device is arranged at the bottom of the pressure box; discharging gas in the pressure tank and injecting high-pressure water; and starting the vibration excitation device to apply vibration with preset frequency to the test body, and acquiring the strain data of each strain gauge and the vibration excitation force data of the vibration excitation device by the data acquisition instrument, and then sending the strain data and the vibration excitation force data to the analysis system to output the stress and the strain result of the test body. The device simulates the flow field and the pressure action of the test body in a real environment, and performs modal test on the test body on the basis, so that the test simulation of the circumferential modal of the test body can be quickly and efficiently realized through each step, the process is easy to operate, the data is more accurate and reliable, the test period is short, and the economy is high.
Description
Technical Field
The invention relates to the field of vibration testing of underwater structures, in particular to a method for performing modal testing on an underwater shell in a non-contact excitation mode while considering the influence of an internal flow field and pressure thereof.
Background
The hollow shell structure is a typical engineering component, and compared with most of solid structures, the shell structure has lighter weight on the premise of ensuring certain strength and rigidity, so that the hollow shell structure is widely applied to design and construction of ocean engineering structures such as underwater vehicles, platform buoyancy tanks and underwater pipelines.
In practical engineering, the influence of external fluid on the vibration of the underwater shell is not negligible, under the coupling action of water pressure and a flow field medium, the vibration of the fluid medium around the underwater shell is caused when the underwater shell is excited to vibrate, and the vibration characteristic of the shell is influenced by the change of the external flow field, so that the complexity of the vibration problem of the underwater shell is caused.
At present, the problems of structural damage and oil leakage caused by vibration deformation of an underwater pipeline structure become important factors threatening the normal operation of the underwater pipeline, and the structure needs high pressure of internal fluid due to the flow guarantee and also needs to consider the influence of the internal fluid and the high pressure thereof on the structure vibration. Therefore, the method has very important practical significance for modal test analysis of the underwater shell considering the influence of the internal flow field pressure.
The defects of the existing research on the shell modal analysis tests at home and abroad are mainly as follows:
1. the existing underwater shell modal test device mainly considers the influence of an external flow field, and simultaneously considers less influence of an internal flow field and an external flow field, so that the test related to internal pressure is rare research;
2. the existing modal test mainly obtains strain data by means of a displacement sensor or an acceleration sensor, the two types of sensors have certain mass and shape, water tight treatment is required, and the vibration modes of an external flow field and a structure are easily influenced.
3. The existing modal test mostly adopts a force hammer or a vibration exciter to excite a test piece to vibrate, the phenomena of double-click, discontinuous vibration mode and the like easily occur in the excitation of the force hammer, the excitation of the vibration exciter can increase additional rigidity and additional mass for the test piece, and the vibration characteristics and the test result of the original test piece can be influenced by the two excitation modes.
Aiming at the defects, the invention provides the underwater shell modal test method which simultaneously considers the influence of the internal and external flow fields and is based on strain modal analysis so as to realize the accurate research on the modal vibration characteristics of the underwater shell.
Disclosure of Invention
The invention aims to provide a method for performing modal test on an underwater shell in a non-contact excitation mode while considering the influence of an internal flow field and the pressure thereof.
Specifically, the invention relates to an underwater shell modal test method considering the influence of an internal flow field and the pressure thereof, which comprises the following steps:
The device simulates the flow field and the pressure action of the test body in a real environment, and performs modal test on the test body on the basis, thereby filling the blank of test research in the field. The selected strain gauge sensor and the strain mode analysis mode have small influence on the test body and the outer flow field, and can remove the error caused by displacement to the strain calculation process, so that the test structure is more accurate. The non-contact electromagnetic excitation device designed according to the electromagnetic induction law can effectively avoid the influence of the additional mass and the additional rigidity of the vibration exciter on the dynamic characteristics of the structure in the conventional modal test and the phenomena of continuous impact and concentrated stress and the like caused by a hammering method, and has higher test precision. The test simulation of the circumferential mode of the test body can be rapidly and efficiently realized through each step, the process is easy to operate, the data is more accurate and reliable, the test period is short, and the economy is high.
Drawings
FIG. 1 is a schematic flow chart of the method steps of one embodiment of the present invention;
FIG. 2 is a schematic diagram of the external structure of a test platform according to an embodiment of the present invention;
FIG. 3 is a schematic view of a strain gage mounted on the circumference of a test body in accordance with one embodiment of the present invention;
FIG. 4 is a schematic view of the axial mounting of a strain gage on a test body according to an embodiment of the present invention;
FIG. 5 is an axial schematic view of a vibration excitation device in accordance with an embodiment of the present invention;
fig. 6 is a schematic view of the magnetic field state of the excitation device according to an embodiment of the present invention.
Detailed Description
The detailed structure and implementation process of the present solution are described in detail below with reference to specific embodiments and the accompanying drawings.
As shown in fig. 1 and 2, in one embodiment of the present invention, an underwater shell modal testing method considering the influence of an internal flow field and the pressure thereof is disclosed, which comprises the following steps:
wherein, the pressure box 2 can be made of transparent material with an open top, such as glass fiber reinforced plastic, so as to facilitate the observation of the test process from the outside, a cross beam 21 which is in the same direction as the test body 1 is arranged at the open position of the pressure box 2, and the cross beam 21 can be used as a suspension supporting point of the spring pull rod 4.
The water depth in the pressure tank 2 is at least 8 times the radius of the test body 1. The test body 1 is cylindrical and the length of the test body is at least 5-20 times of the outer diameter of the test body, so that the circumferential mode of the test body can be effectively excited, and a part of a deep sea conveying pipeline can be generally directly intercepted to serve as the test body 1. The water injection in the pressure tank 2 can simulate the underwater pressure around the test body 1, and when the water depth in the pressure tank 2 is set to be 8 times of the depth of the radius of the shell, the influence of boundary conditions such as a free liquid level and a solid wall on the test body in the test process can be ignored.
The strain gauges 32 can be arranged in a row along the axial direction of the test body 1, and can also be arranged in a circle along the outer circumference of the middle part of the test body 1, and can be specifically determined according to different vibration experiment requirements. In the present embodiment, 12 strain gauges 32 may be provided at equal intervals in the circumferential direction of the test body 1, and the strain gauges 32 need to be measured using an ohmmeter after being attached to remove a failure.
The test body 1 is adhered with the strain gauge 32, the test point position is polished by sand paper in advance, a 45-degree crossed polishing mode is adopted until the test point has no oxide film and is bright, the strain gauge 32 is adhered to the test point by glue, no gap or air bubble can be left during adhesion, and then a waterproof silica gel protective film is coated on the outer surface of the strain gauge 32 so as to completely seal the strain gauge 32 and the test point.
The digital acquisition instrument 33 is connected with each strain gauge 32 through a cable and is arranged outside the pressure box 2, and the digital acquisition instrument 33 is connected with an analysis system provided with DSAP-SMA modal analysis software. The joints of the cables also need to be wrapped by insulating sleeves to realize water sealing.
two spring pull rods 4 are arranged, one end of each spring pull rod is respectively connected with the cross beam 21, and the other end of each spring pull rod is respectively connected with two ends of the test body 1 so as to suspend the test body 1 in the pressure tank 2; each spring pull rod 4 comprises a fixing support 41 fixed on the cross beam 21 and a connecting rod 43 connecting the fixing support 41 and the test body 1, the fixing support 41 is fixed on the cross beam 21 through a bolt, and two ends of the connecting rod 43 are respectively connected with the fixing support 41 and the test body 1 through springs 42.
As shown in fig. 5, the excitation device 3 is used for simulating underwater vibration, and includes a base 36 fixedly connected to the bottom of the pressure tank 2, an adjusting bracket 37 fixed to the upper surface of the base 36, a U-shaped fixing bracket 371 installed at the top end of the adjusting bracket 37 and having an upward opening, two permanent magnets 38 having opposite special-shaped magnetic poles and installed at the top of the U-shaped side of the fixing bracket 371, and an eddy current sensor 39 installed at the middle of the bottom of the fixing bracket 371 and having a coil 391 wound on the outer surface; the suspended test body 1 is axially located between the two permanent magnets 38 and is close to the eddy current induction head 39 at the bottom.
The adjusting bracket 37 can adjust the height of the fixing frame 371 according to the position of the test body 1, and further adjust the relative height of the permanent magnet 38 and the eddy current induction head 39 so as to enable the permanent magnet to be close to the test body 1 as much as possible without contacting; the adjusting bracket 37 can be any length-adjusting structure in the prior art, for example, two pipes are inserted into each other, and a fixing bolt is screwed on the outer pipe, so that after the positions of the two pipes are fixed, the inner pipe is pressed against the current position by tightening the fixing bolt.
The coil 391 of the eddy current head 39 is connected to an external power supply via a cable. The opposite poles of the two permanent magnets 38 are shaped such that if one of the permanent magnets has an N-pole with respect to the other permanent magnet, the opposite pole of the other permanent magnet has an S-pole. The strain gauge 32 attached to the outer surface of the test body 1 can measure the exciting force of the exciting device, and then transmit the measured exciting force to the digital acquisition instrument 33.
As shown in fig. 6, when the test device works, the coil 391 is externally connected with an alternating power supply to force the internal eddy current induction head 39 to generate alternating magnetic flux, the alternating magnetic flux vertically passes through the test body 1 and induces the corresponding position of the test body 1 to generate an induced eddy current field 61 which has the same frequency change with the alternating magnetic flux, according to the ampere law, the current-carrying test body 1 is acted by ampere force in the constant magnetic field 62 generated by the permanent magnet 38, and the test body 1 at the corresponding position is made to continuously vibrate along the radial direction, and when the frequency adjusted to the alternating power supply is the same as the natural frequency of the test body 1, the test body 1 can be induced to resonate, so that non.
The high-pressure water supply device 5 comprises a water supply pipe 52 connected with a water source 53, a high-pressure pump 51 arranged on the water supply pipe 52, a high-pressure pipeline 54 and a pressure relief pipeline 56 respectively arranged at two opposite ends of the test body 1, and a high-pressure valve 55 and a pressure relief valve 57 respectively controlling the high-pressure pipeline 54 and the pressure relief pipeline 56 to be switched on and off, wherein the high-pressure pipeline 54 is communicated with the high-pressure pump 51.
before the experiment of the test body 1, water injection and pressure test are needed. First, one end of the test piece 1 is connected to a high-pressure pump 51 through a high-pressure pipe 54, a water injection pipe 52 is connected to a water source 53 and the high-pressure pump 51, respectively, and a gasket is used at each connection to seal the connection. Then, the high-pressure pump 51 is turned on to inject water into the test object 1 through the high-pressure pipe 54, and when there is continuous water flow and no bubble in the pressure relief pipe 56 at the other end, it is proved that there is no gas and water in the test object 1, and in this process, the test object 1 can be tilted properly, for example, at 15 degrees, to facilitate the discharge of the gas inside. Then, the relief valve 57 is closed to achieve sealing, and the water is required to be kept still for a certain time after being filled with water, so that the relief valve 57 is closed after bubbles are eliminated. The high-pressure pump 51 is utilized again to pressurize the inside of the test body 1, different internal pressure values can be set during the test, a shockproof pressure gauge can be installed on the test body 1 so as to conveniently obtain the pressure value inside the test body 1 at any time, and after the pointer of the shockproof pressure gauge reaches the expected pressure value, the high-pressure pump 51 is closed and the high-pressure valve 55 is screwed to maintain the pressure of the test body 1.
The excitation force provided by the non-contact excitation device can be obtained through numerical calculation.
The induced current generating region in the test body 1 is an elongated region as shown in fig. 6, the bending of the cylindrical test body 1 can be basically ignored in the small part region, the induced current generating region can be approximately regarded as a rectangular metal plate, the current field can be approximately processed by a binary function, and a control equation can be obtained according to an eddy current equation in the flat plate:
in the formula, the magnetic flux B is assumed to be a simple harmonic function
And B0Is the effective value; f is the frequency of the alternating power supply; induced eddy current and flow function
Is also a simple harmonic function, and u is the effective value of the flow function; ρ is the resistivity.
The length of the rectangle of the induced current area is set as A, the width of the rectangle is set as B, the A can be divided into n sections and the B can be divided into m sections during numerical calculation, so that the distance between every two sections is h, namely:
then the differential form of the second derivative in the x, y directions at any point in the slab can be expressed as:
substituting into the control equation can obtain:
namely:
in the boundary conditions, the value of u is 0 along the boundary of the rectangular outer plate (x is 0, x is a, y is 0, and y is B), and the numerical solution can be obtained by iterative solution of the equation after the above formula is substituted.
The eddy currents induced in the region by the alternating magnetic field are subjected to an electromagnetic force F in the constant magnetic field B. If two current lines with a distance db and a length dl are taken as a micro element body, according to the prior art, the electromagnetic force dF applied to the micro element body is as follows:
dF＝0.102×10-7Jδdb·Bdl
therefore, the excitation force per unit area is:
the total excitation force in the induced current region is:
the operation of the present embodiment will be described in detail below with specific configuration and method procedures.
Before the test, the vibration excitation device 3 is fixed at the bottom in the pressure box 2, then the test body 1 is hung at the designated position of the pressure box 2 by using the spring pull rod 4, the designated position is generally based on the central axis of the test body 1, the distances between the central axis and the peripheral side wall of the pressure box 2 and the distance between the central axis and the water surface after water injection are all larger than 4 times of the radius of the shell, the influence of boundary conditions such as free liquid level and side wall can be ignored at the set position, and the permanent magnet 38 and the eddy current induction head 30 are ensured to be in non-contact with the test body 1, but the gap is as small as possible so as to reduce energy loss and obtain better vibration excitation effect. Then connect water injection pipe 52, with a plurality of foil gauges 32 attached to the assigned position of the test body 1 according to the experimental requirement, rethread cable 35 is connected with the outside digital acquisition instrument 33 of pressure tank 2, and this process needs to be accomplished before the test body 1 is placed in the pressure tank, need make foil gauges 32 and cable 35 waterproof before placing. And then injecting water into the pressure tank 2, wherein the water depth in the pressure tank 2 is not less than 8 times of the radius of the test body 1, and the water depth can meet the condition that the influence of boundary conditions such as free liquid level, side wall and the like is neglected in the test process of the test body 1.
Inject water into the test body 1 through high-pressure pump 51, in to test body 1 water injection process, need to arrange the inside air of test body 1 to the greatest extent, can install pressure release pipeline 56 on test body 1, install relief valve 57 on pressure release pipeline 56 simultaneously, pressure release pipeline 56 can be used to discharge the inside air of test body 1, can also discharge inside water after experimental completion simultaneously, and pressure release valve 57 can close pressure release pipeline 56 in order to keep the inside pressure of test body 1. In order to conveniently adjust the pressure in the test body 1, a high-pressure pipeline 54 is arranged at the other end of the test body 1 opposite to the pressure relief pipeline 56, a high-pressure valve 55 is arranged on the high-pressure pipeline 54, the high-pressure pipeline 54 is connected with a high-pressure pump 51, and the high-pressure valve 51 can adjust the pressure according to the pressure requirement in the test body 1; in addition, in order to conveniently obtain the pressure in the test body 1, a shockproof pressure gauge can be arranged on the test body 1, and the shockproof pressure gauge can be used for avoiding the vibration influence of the vibration exciter 31 during working.
When the test body 1 is exhausted, the test body can be obliquely placed, then water is injected from one side of the high-pressure pipeline 54 until water is discharged from one side of the pressure relief pipeline 56, and the test body 1 can be considered to be filled with water; in addition, in order to avoid the residual bubbles in the test body 1, the test body can be kept still for a period of time after the water is discharged from the pressure relief pipeline 56 until the internal gas is completely exhausted. After the air discharge is completed, the test piece 1 needs to be restored to the horizontal state.
After the working process, the non-contact type vibration excitation device 3 can be started to apply vibration with a preset frequency to the test body, the alternating current frequency is gradually adjusted to reach the vibration frequency of the test body to realize resonance, and the frequency of the vibration excitation device 3 is generally greater than the frequency to be measured of the test body 1. Because the test body 1 is elastically suspended in the water through the spring pull rod 4, the spring pull rod 4 does not vibrate synchronously with the test body 1 and the test effect is influenced. The strain gauge 32 transmits vibration signals borne by the test body 1 to the digital acquisition instrument 33 through the cable 35, and the digital acquisition instrument 33 transmits the collected data to the analysis system, so that the vibration characteristics of the test body 1 under the current test conditions are obtained.
As shown in fig. 3 and 4, the strain gauges 32 may be arranged in a row along the axial direction of the test body 1 or in a circle along the outer circumference of the middle portion of the test body 1 according to the test requirements, so as to obtain the vibration characteristics of the test body 1 at different positions under the same vibration conditions. When the strain gauges are arranged circumferentially, the spacing angle between the strain gauges 32 is pi/6, and the arrangement mode can measure the vibration frequency of different parts of the circumference of the test body 1 during vibration excitation, so that the acquired data are more accurate.
The embodiment simulates the flow field and the pressure action of the test body in the real environment through the device, and performs modal test on the test body on the basis, thereby filling the blank of the test research in the field. The selected strain gauge sensor and the strain mode analysis mode have small influence on the test body and the outer flow field, and can remove the error caused by displacement to the strain calculation process, so that the test structure is more accurate. The non-contact excitation mode can effectively avoid the influence of the additional mass and the additional rigidity of the excitation device on the structure dynamic characteristics in the conventional modal test and the phenomena of continuous impact and stress concentration and the like caused by a hammering method, and the test precision is higher. The test simulation of the circumferential mode of the test body can be rapidly and efficiently realized through each step, the process is easy to operate, the data is more accurate and reliable, the test period is short, and the economy is high.
The springs 42 at the two ends of the spring pull rod 4 can prevent rigid vibration from being transmitted to the cross beam 21 of the pressure box 2, and meanwhile, after the vibration frequencies of the springs 42 at the two ends are switched through the connecting rod 43, synchronous vibration cannot be generated, so that vibration transmitted by the test body 1 can be eliminated quickly, and influence is reduced.
In this embodiment, in order to obtain a good excitation effect, the number of turns of the coil 391 is set as large as possible, and the gap between the eddy current sensor 39 and the test body 1 is made as small as possible, and the permanent magnet 38 may be made of a rare earth material, such as a strong permanent magnet of samarium cobalt (SmCo) permanent magnet and neodymium iron boron (NdFeB) permanent magnet. In order to ensure that the excitation device 3 can still work underwater, the outer surfaces of the coil, the lead and the like need to be covered with non-conductive and waterproof fiber composite materials. The natural frequency of the test body is up to several kilohertz and the modes are in multiple stages, and in order to achieve the resonance state and measure the multiple-stage modes, an alternating power supply with a large frequency response range is selected to meet the test requirement.
The analysis system in this embodiment is provided with strain mode analysis software, and can record and comprehensively analyze multiple paths of strain data acquired by the data acquisition instrument 33, so as to obtain excitation simulation results at different measurement points. When the strain gauge 32 is arranged, the node of the mode shape on the test body 1 needs to be avoided, and the number and the position of the specific arrangement can be determined according to the modal frequency and the mode shape to be measured.
In one embodiment of the present invention, the two ends of the test body 1 are sealed by welding flat plates of the same material and the same thickness, the high pressure pipe 54 and the pressure relief pipe 56 are respectively welded in the passages at the centers of the two flat plates, and a shock absorbing layer, such as a plastic foam material, may be installed on the high pressure pipe 54 and the pressure relief pipe 56 to form a structure around the same. The flat plate forms the boundary condition of the simple support at the two ends of the test body 1, and can be extended to the simple support structure under other complex conditions according to the installation mode.
Thus, it should be appreciated by those skilled in the art that while a number of exemplary embodiments of the invention have been illustrated and described in detail herein, many other variations or modifications consistent with the principles of the invention may be directly determined or derived from the disclosure of the present invention without departing from the spirit and scope of the invention. Accordingly, the scope of the invention should be understood and interpreted to cover all such other variations or modifications.
Claims (10)
1. An underwater shell modal test method considering internal flow field and pressure influence thereof is characterized by comprising the following steps:
step 100, preparing a pressure tank for containing water according to experimental conditions, cutting off a part of an actually used pipeline, sealing two ends of the pressure tank to form a test body, sticking a strain gauge on the outer circumference of the test body according to test requirements, and connecting the strain gauge with a digital acquisition instrument through a cable;
step 200, mounting a non-contact type vibration excitation device at the bottom of a pressure box, suspending a test body in the pressure box by using a spring pull rod and connecting the test body with a high-pressure water supply device, wherein the suspended bottom of the test body is close to but not in contact with the vibration excitation device, and simultaneously the condition that the distances between the central axis of the test body and the peripheral side walls of the pressure box and the upper surface of water are respectively 4 times of the radius of the test body is met;
step 300, controlling the inclination of the test body through a spring pull rod, injecting water into the test body through a high-pressure water supply device to discharge internal gas, keeping the test body horizontal after the gas is discharged, and continuously injecting high-pressure water until the internal pressure of the test body reaches a preset value;
step 400, starting an excitation device to apply vibration with a preset frequency to a test body, gradually adjusting the alternating current frequency to reach the vibration frequency of the test body to realize resonance, acquiring strain data of each strain gauge and excitation force data of the excitation device by a data acquisition instrument, then sending the strain data and the excitation force data to an analysis system, calculating the excitation force of the excitation device by the analysis system according to the modal parameters which are acquired in real time and expressed by variables, then establishing a modal model for strain response calculation, and further outputting the stress and strain results of the test body.
2. The underwater housing modal test method of claim 1,
the pressure box is made of transparent material with an open top, and a cross beam for connecting the spring pull rod is arranged at the open position.
3. The underwater shell modal test method of claim 2, wherein the water depth within the pressure tank is at least 8 times the radius of the test body.
4. The underwater housing modal test method of claim 1, wherein the test body is cylindrical and has a length of 5 to 20 times its outer diameter.
5. The underwater housing modal test method of claim 1,
and polishing the measuring point of the strain gauge adhered to the test body by using sand paper, and adopting a 45-degree crossed polishing mode until the measuring point is free from an oxide film and bright, adhering the strain gauge to the measuring point by using glue, and finally coating a waterproof silica gel protective film on the outer surface of the strain gauge so as to completely seal the strain gauge and the measuring point.
6. The underwater housing modal test method of claim 5,
the strain gauges are arranged in a row along the axial direction of the test body, or are arranged in a circle along the outer circumference of the middle part of the test body.
7. The underwater housing modal test method of claim 2,
the two spring pull rods are arranged, one end of each spring pull rod is connected with the cross beam, and the other end of each spring pull rod is connected with the two ends of the test body; each spring pull rod comprises a fixed support fixed on the cross beam and a connecting rod, and the connecting rod is connected with the fixed support and the test body through springs at two ends respectively.
8. The underwater housing modal test method of claim 1,
the excitation device comprises a base fixedly connected with the bottom of the pressure tank, an adjusting bracket fixed on the upper surface of the base, a U-shaped fixing frame which is installed at the top end of the adjusting bracket and has an upward opening, two permanent magnets with opposite special-shaped magnetic poles are respectively installed at the tops of the U-shaped side edges of the fixing frame, and an eddy current induction head which is installed in the middle of the bottom of the fixing frame and has a coil wound on the outer surface; the test body is positioned between the two permanent magnets, and the bottom of the test body is close to the eddy current induction head.
9. The underwater housing modal test method of claim 1,
the high-pressure water supply device comprises a water supply pipe connected with a water source, a high-pressure pump arranged on the water supply pipe, a high-pressure pipeline and a pressure relief pipeline which are respectively arranged at two opposite ends of the test body, and a high-pressure valve and a pressure relief valve which are respectively used for controlling the high-pressure pipeline and the pressure relief pipeline to be switched on and off, wherein the high-pressure pipeline is communicated with the high-pressure pump.
10. The underwater housing modal test method of claim 1,
the process of calculating the exciting force of the exciting device by the analysis system is as follows:
firstly, setting the area of the test body generating the induced current as a rectangle, and obtaining a control equation according to a rectangular eddy current equation:
in the formula, the magnetic flux B is assumed to be a simple harmonic function
And B0Is the effective value; f is the frequency of the alternating power supply; induced eddy current and flow function
Again a simple harmonic function, and u is the effective value of the flow function; ρ is the resistivity;
then, setting the length of a rectangle of the induction current area as A and the width as B, dividing A into n sections and B into m sections during calculation, so that the distance between each section is h, and obtaining:
then the differential form of the second derivative in the x, y directions at any point in the region is expressed as:
substituting into the control equation can obtain:
in the boundary conditions, the value of u is 0 along the boundary of the region (x is 0; x is A; y is 0; y is B), and the value solution is obtained by iterative solution after the u is substituted into the formula;
the eddy current induced by the alternating magnetic field in the region is acted by an electromagnetic force F in a constant magnetic field B, two current lines which are db apart and dl in length are taken to form a microcell, and the electromagnetic force dF borne by the microcell is as follows:
dF＝0.102×10-7Jδdb·Bdl
the exciting force per unit area is obtained as follows:
the total exciting force in the final induced current region is:
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