Composite raft frame and design method thereof

Abstract

The invention discloses a composite raft frame and a design method thereof, and relates to the technical field of vibration reduction. The design method of the composite raft frame comprises the following steps: determining a target frequency band of a phononic crystal unit cell; determining the number of cycles of photonic crystal unit cells according to the target frequency band; determining the target size of the phononic crystal unit cells according to the period number of the phononic crystal unit cells; and determining the radius of the acoustic black hole according to the target frequency band of the phononic crystal unit cell. According to the design method of the composite raft frame, design of the composite raft frame, the photonic crystal unit cells in the composite raft frame and the acoustic black holes can be achieved, vibration reduction of a specific low-frequency band of the composite raft frame is achieved by combining the photonic crystal unit cells and the acoustic black holes, and broadband vibration reduction of the composite raft frame from the low-frequency band to the high-frequency band is achieved.

Description

Technical Field

[0001] The present application relates to the technical field of vibration reduction, and in particular to a composite raft frame and a design method thereof. Background Art

[0002] Floating raft vibration isolation technology can effectively suppress the transmission of elastic waves generated by mechanical equipment vibration to the hull, and is considered to be an effective technical means to achieve submarine acoustic stealth. Submarines mostly sail at medium and low speeds during navigation, and mainly generate low-frequency vibrations during this process. Since low-frequency vibrations can be transmitted over long distances, they will cause the submarine to lose its stealth, so vibration reduction design is needed.

[0003] The existing methods of adding passive or active vibration isolators often have the defects of narrow vibration reduction frequency band or complex structure. As the main component of the floating raft vibration isolation platform, the vibration reduction and isolation performance of the raft frame has not been effectively developed. Therefore, it is still necessary to propose a new design method to improve the traditional raft frame to achieve the effect of low-frequency vibration reduction.

[0004] The existing design scheme that combines metamaterials with floating raft frame design to achieve low-frequency vibration cannot suppress vibration in specific low-frequency bands, and has no obvious vibration reduction effect on high-bandwidth, cannot achieve broadband vibration control, cannot suppress vibration in specific frequency bands, and embedding an acoustic black hole structure will lead to a reduction in structural strength. Summary of the invention

[0005] Purpose of the invention: An embodiment of the present application provides a design method for a composite raft frame, aiming to overcome the technical problem that the prior art is unable to reduce vibration in a specific frequency band; another purpose of an embodiment of the present application is to provide a composite raft frame.

[0006] Technical solution: A design method of a composite raft frame described in an embodiment of the present application, the composite raft frame comprises an upper bottom plate, a lower bottom plate, a phononic crystal unit cell embedded in the upper bottom plate and arranged periodically, and an acoustic black hole embedded in the lower bottom plate;

[0007] The method comprises:

[0008] determining a target frequency band of the phononic crystal unit cell;

[0009] Determining the number of periods of the phononic crystal unit cell according to the target frequency band;

[0010] Determining a target size of the phononic crystal unit cell according to the number of periods of the phononic crystal unit cell;

[0011] The radius of the acoustic black hole is determined according to the target frequency band of the phononic crystal unit cell.

[0012] In some embodiments, determining the number of periods of the phononic crystal unit cell according to the target frequency band includes:

[0013] Determining the wave velocity in the phononic crystal unit cell according to the target frequency band;

[0014] The number of periods of the phononic crystal unit cell is determined according to the target frequency band and the wave velocity in the phononic crystal unit cell.

[0015] In some embodiments, the phononic crystal unit cell includes a rubber block; the calculation formula for the number of periods of the phononic crystal unit cell is:

[0016]

[0017] Wherein, x is the number of periods of the phononic crystal unit cell; a2 is the second radius of the connection between the rubber block 6 and the upper base plate 1; v is the wave velocity in the phononic crystal unit cell; and f is the target frequency band of the phononic crystal unit cell.

[0018] In some embodiments, determining a target size of the phononic crystal unit cell according to the number of periods of the phononic crystal unit cell comprises:

[0019] Dividing the upper base plate into a plurality of preselected areas according to the number of periods of the phononic crystal unit cell;

[0020] The target size of the phononic crystal unit cell is determined according to the preselected area.

[0021] In some embodiments, the preselected area is rectangular or circular in shape.

[0022] In some embodiments, the phononic crystal unit cell further comprises a lead block; the lead block comprises a lead block body and a first pin; the rubber block comprises a rubber block body and a second pin; wherein the lead block body is a cylinder, and the radius of the lead block body is greater than the radius of the first pin; the rubber block body is a truncated cone with a pin hole at the center; the truncated cone comprises a fifth face and a sixth face; the first radius of the fifth face is less than the second radius of the sixth face; the third radius of the lead block body is the same as the first radius; the second pin is disposed on the sixth face and is located at the center; the lead block is connected to the pin hole through the first pin;

[0023] The target size includes: the first radius, the second radius, and the third radius.

[0024] In some embodiments, determining the radius of the acoustic black hole according to the target frequency band of the phononic crystal unit cell includes:

[0025] The radius of the acoustic black hole is calculated according to the upper frequency limit of the target frequency band.

[0026] In some embodiments, after determining the target size of the phononic crystal unit cell, the method further includes:

[0027] Determining whether the target size of the phononic crystal unit cell needs to be adjusted according to the preset simulation software;

[0028] After determining the radius of the acoustic black hole, the method further comprises:

[0029] Establishing a first finite element model of the lower base plate in which the acoustic black hole is embedded, and verifying according to the first finite element model;

[0030] A second finite element model of a composite raft based on phononic crystal-acoustic black hole is established, and the composite raft is verified according to the second finite element model.

[0031] Correspondingly, a composite raft frame described in an embodiment of the present application includes an upper base plate, a lower base plate, phononic crystal unit cells embedded in the upper base plate and periodically arranged, and an acoustic black hole embedded in the lower base plate; the composite raft frame is designed using the design method described above.

[0032] In some embodiments, the composite raft frame also includes ribs and a damping layer; wherein the upper base plate includes a first surface and a second surface; the lower base plate includes a third surface and a fourth surface; a cavity is formed between the ribs and the second surface; nested holes are periodically arranged on the second surface; each of the phononic crystal unit cells is located in the cavity and is partially embedded in the second surface through the nested holes; the acoustic black hole is embedded in the fourth surface; and each of the acoustic black holes is pasted with the damping layer at a position opposite to the third surface.

[0033] In some embodiments, the phononic crystal unit cell is composed of a rubber block and a lead block; the lead block is composed of a lead block body and a first pin; the rubber block is composed of a rubber block body and a second pin; wherein the lead block body is a cylinder, and the radius of the lead block body is greater than the radius of the first pin; the rubber block body is a truncated cone with a pin hole in the center; the truncated cone includes a fifth face and a sixth face; the first radius of the fifth face is less than the second radius of the sixth face; the third radius of the lead block body is the same as the first radius; the second pin is arranged on the sixth face and is located at the center; the lead block is connected to the pin hole through the first pin; the rubber block is connected to the nested hole through the second pin.

[0034] In some embodiments, the first pin is connected to the pin hole by a vulcanization process.

[0035] In some embodiments, the lower base plate and the rib plate are manufactured in an integrated manner; the upper base plate, the rib plate and the lower base plate are made of fiberglass.

[0036] In some embodiments, the damping layer is adhered to the fourth surface by an adhesive; the adhesive comprises at least one of hot melt adhesive, epoxy resin adhesive, styrene-butadiene rubber adhesive, and cyanoacrylate adhesive.

[0037] Beneficial effects: Compared with the prior art, the composite raft frame and the design method thereof of the embodiment of the present application, the design method of the composite raft frame includes: determining the target frequency band of the phononic crystal unit cell; determining the number of periods of the phononic crystal unit cell according to the target frequency band; determining the target size of the phononic crystal unit cell according to the number of periods of the phononic crystal unit cell; determining the radius of the acoustic black hole according to the target frequency band of the phononic crystal unit cell. The design method of the composite raft frame of the present application can realize the design of the composite raft frame, the phononic crystal unit cell in the composite raft frame, and the acoustic black hole, and by combining the phononic crystal unit cell and the acoustic black hole, it can realize both the vibration reduction of the specific low-frequency band of the composite raft frame and the broadband vibration reduction of the composite raft frame from the low-frequency band to the high-frequency band. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0039] Figure 1 It is a structural schematic diagram of a composite raft frame provided in an embodiment of the present application;

[0040] Figure 2 is a bottom view of the upper base plate provided in an embodiment of the present application;

[0041] Figure 3 is a cross-sectional view of a nested hole provided in an embodiment of the present application;

[0042] Figure 4 is a top view of the lower base plate provided in an embodiment of the present application;

[0043] Figure 5 is a bottom view of the lower base plate provided in an embodiment of the present application;

[0044] Figure 6 It is a schematic diagram of the structure in which the phononic crystal unit cell provided in the embodiment of the present application is arranged on a composite raft frame;

[0045] Figure 7 is a schematic diagram of the axis of the rib plate provided in the embodiment of the present application;

[0046] Figure 8 is a front view of a rib plate provided in an embodiment of the present application;

[0047] Fig. 9 is a top view of a rib plate provided in an embodiment of the present application;

[0048] Fig.10 is a schematic structural diagram of a phononic crystal unit cell provided in an embodiment of the present application;

[0049] Fig.11 is a schematic diagram of the structure of the lead block provided in the embodiment of the present application;

[0050] Fig.12 is a schematic diagram of the structure of the lead block provided in the embodiment of the present application;

[0051] Fig.13 is a schematic diagram of the structure of the rubber block provided in the embodiment of the present application;

[0052] Fig.14 is a top view of a rubber block provided in an embodiment of the present application;

[0053] Fig.15 is a right side view of the rubber block provided in the embodiment of the present application;

[0054] Fig.16 is a flow chart of a design method of a composite raft provided in an embodiment of the present application;

[0055] Fig.17 It is a vibration reduction test effect diagram of the low-frequency target frequency band provided in the embodiment of the present application;

[0056] Fig.18 It is a full-band vibration reduction test effect diagram provided in the embodiment of the present application.

[0057] Reference numerals:

[0058] 1-upper base plate; 11-nested holes; 12-cavity; 121-first sub-cavity; 122-second sub-cavity; 123-third sub-cavity; 124-fourth sub-cavity; 101-first surface; 102-second surface; 103-third surface; 104-fourth surface; 105-fifth surface; 106-sixth surface; 2-rib plate; 21-rib plate support block; 22-first baffle plate; 23-second baffle plate; 3-lower base plate; 31-acoustic black hole; 32-damping layer; 33-lower base plate pad; 4-phononic crystal unit cell; 5-lead block; 51-first column pin; 52-lead block body; 6-rubber block; 61-second column pin; 62-column pin hole; 63-rubber block body. DETAILED DESCRIPTION

[0059] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application.

[0060] It should be understood that although the terms first, second, etc. may be used herein to describe various components, these components should not be limited by these terms. These terms are used to distinguish one component from another component. Therefore, the first component discussed below can be referred to as the second component without departing from the teachings of the concepts of the present application. As used herein, the term "and / or" includes any one of the associated listed items and all combinations of one or more.

[0061] Those skilled in the art will appreciate that the drawings are only schematic diagrams of example embodiments and may not be to scale. The modules or processes in the drawings are not necessarily required to implement the present application and therefore cannot be used to limit the scope of protection of the present application.

[0062] Floating raft vibration isolation technology can effectively suppress the transmission of elastic waves generated by mechanical equipment vibration to the hull, and is considered to be an effective technical means to achieve submarine acoustic stealth. Submarines mostly sail at medium and low speeds during navigation, and mainly generate low-frequency vibrations during this process. Since low-frequency vibrations can be transmitted over long distances, they will cause the submarine to lose its stealth, so vibration reduction design is needed.

[0063] In the related art, the method of adding passive or active vibration isolators often has the defects of narrow vibration reduction frequency band or complex structure. As the main component of the floating raft vibration isolation platform, the vibration reduction and isolation performance of the raft frame has not been effectively developed. Therefore, it is still necessary to propose a new design method to improve the traditional raft frame to achieve the effect of low-frequency vibration reduction.

[0064] Local resonance acoustic metamaterials have local resonance units. When the frequency of the elastic wave is close to the natural frequency of the local resonance unit, the energy of the elastic wave is consumed by the local resonance unit, thereby generating a local resonance band gap, within which the elastic wave can be effectively suppressed. Metamaterial technology that can achieve elastic wave suppression is considered to be a new technology for achieving low-frequency vibration reduction. Currently, it has been explored for applications in the aerospace and shipbuilding fields. Combining this design method with the design of the floating raft frame is expected to achieve low-frequency vibration suppression of the floating raft frame.

[0065] The Chinese invention patent with application number "202311371823" discloses a superstructure floating plate raft with low-frequency vibration reduction performance and its preparation method. The superstructure floating raft plate raft includes: a resonance unit composed of cylindrical rubber and cylindrical metal mass blocks, a vertical rod, an upper panel with periodic circular holes, and a lower panel with orthogonal short beams attached after the holes are opened; the superstructure floating raft plate raft has a local resonance band gap, which can effectively suppress the propagation of low-frequency elastic waves, and can achieve vibration suppression in a specific frequency band through a specific design; in addition, this bar lattice sandwich structure has excellent bearing capacity, so that the structure of the present invention integrates high bearing capacity and low-frequency vibration suppression performance. However, the invention cannot suppress vibration in a specific low-frequency band, and has no obvious vibration reduction effect on high-bandwidth, and cannot achieve broadband vibration control.

[0066] The Chinese invention patent with application number "202110538300.5" discloses a vibration reduction and noise reduction enhancement structure that is a mixture of heterogeneous / heterogeneous acoustic black holes and phononic crystals. This invention achieves vibration reduction and noise reduction for low-bandwidth bands by mixing and arranging heterogeneous acoustic black holes and phononic crystals, making the structure lighter and reducing costs. However, this invention does not design the phononic crystal and acoustic black hole structures, and cannot suppress vibrations in specific frequency bands. In addition, embedding the acoustic black hole structure will reduce the structural strength.

[0067] In view of this, an embodiment of the present application provides a composite raft frame and a design method thereof, so as to design a composite raft frame capable of reducing vibration in a specific frequency band.

[0068] Figure 1 is a schematic structural diagram of a composite raft provided in an embodiment of the present application, Figure 2 is a bottom view of the upper base plate provided in the embodiment of the present application, Figure 3 is a cross-sectional view of a nested hole provided in an embodiment of the present application, Figure 4 is a top view of the lower base plate provided in the embodiment of the present application, Figure 5 is a bottom view of the lower base plate provided in the embodiment of the present application, Figure 6 Schematic diagram of the structure of the phononic crystal unit cell arranged on the composite raft provided in the embodiment of the present application. Figures 1 to 6 The composite raft frame includes an upper bottom plate 1, a rib plate 2, a lower bottom plate 3, a phononic crystal unit cell 4, an acoustic black hole 31 and a damping layer 32; wherein the upper bottom plate 1 includes a first surface 101 and a second surface 102; the lower bottom plate 3 includes a third surface 103 and a fourth surface 104; a cavity 12 is formed between the rib plate 2 and the second surface 102; nested holes 11 are periodically arranged on the second surface 102; each phononic crystal unit cell is located in the cavity 12 and is partially embedded in the second surface 102 through the nested holes 11; the acoustic black hole 31 is embedded in the fourth surface 104; and each acoustic black hole 31 is pasted with a damping layer 32 at a position opposite to the third surface 103.

[0069] There are a plurality of nested holes 11 periodically arranged on the second surface 102 of the upper base plate 1. The nested holes 11 are blind holes, and the depth of the holes can be set according to actual conditions, and no specific limitation is made here.

[0070] There are multiple phononic crystal cells 4 arranged periodically in the cavity 12. The number of phononic crystal cells is the same as the number of nested holes 11, and the arrangement on the second surface 102 is the same. Each phononic crystal cell is partially embedded on the second surface 102 of the upper base plate 1 through a nested hole 11. For example, see Figure 2 A plurality of nested holes 11 are periodically arranged on the second surface 102 of the upper base plate 1. Thus, by periodically arranging phononic crystal unit cells on the upper base plate 1 of the composite raft frame, vibration reduction of a low-frequency specific frequency band below 1000 Hz of the composite raft frame can be achieved.

[0071] The damping layer 32 is attached to the third surface 103 of the lower bottom plate 3, and the acoustic black hole 31 is embedded in the fourth surface 104 of the lower bottom plate 3. The damping layer 32 and the acoustic black hole 31 are provided in the same number and are provided at positions opposite to the third surface 103 and the fourth surface 104. Figure 4 and Figure 5 , four damping layers 32 are evenly pasted on the third surface 103, and an acoustic black hole 31 (such as Figure 5 4 acoustic black holes as shown). Thus, by embedding the acoustic black hole 31 in the bottom plate 3 of the composite raft frame, the raft frame can be damped in a higher wideband above the acoustic black hole cutoff frequency. The acoustic black hole cutoff frequency is the frequency at which the acoustic black hole structure takes effect, which is the upper limit of the target low-frequency specific frequency band. The acoustic black hole structure has a good broadband vibration reduction effect on the frequency band above the cutoff frequency.

[0072] In summary, by periodically arranging phononic crystal unit cells 4 on the upper bottom plate 1 of the composite raft frame, vibration reduction of the low-frequency specific frequency band of the composite raft frame is achieved, and by embedding the acoustic black hole 31 on the lower bottom plate 3 of the composite raft frame, with the low-frequency specific frequency band as the cutoff frequency, vibration reduction of the raft frame with a higher wideband is achieved. Therefore, by combining the two, vibration reduction of the specific low-frequency band of the composite raft frame is achieved, and broadband vibration reduction of the composite raft frame from the low-frequency band to the high-frequency band is achieved.

[0073] Among them, the thickness of the upper bottom plate 1, the rib plate 2 and the lower bottom plate 3 are all the same, which is beneficial to the structural processing design, and the rib plate with the same thickness as the bottom plate can strengthen the strength of the composite raft frame. Exemplarily, in the technical method of the embodiment of the present application, the thickness of the upper bottom plate 1, the rib plate 2 and the lower bottom plate 3 is 20mm.

[0074] The damping layer 32 is adhered to the third surface 103 by means of an adhesive.

[0075] For example, see Figure 5 , lower base pads 33 are also provided at the four corners of the fourth surface 104 of the lower base plate 3. The lower base pads 33 and the lower base plate 3 are both provided with threaded holes and are aligned, and the upper base plate 1 is installed and connected with the lower base plate 3 and the lower base pads 33 by aligning the lower base plate bolt holes with bolts.

[0076] Figure 7 is a schematic diagram of the axis of the rib plate provided in the embodiment of the present application, Figure 8 is a front view of a rib plate provided in an embodiment of the present application, Fig. 9 is a top view of the rib plate provided in the embodiment of the present application. For example, please refer to Figures 7 to 9 The first baffle 22 and the second baffle 23 are arranged in the rib plate 2, and the first baffle 22 and the second baffle 23 are arranged crosswise, so as to divide the cavity 12 into a first sub-cavity 121, a second sub-cavity 122, a third sub-cavity 123 and a fourth sub-cavity 124. Each phononic crystal unit cell is accommodated in the corresponding first sub-cavity 121, the second sub-cavity 122, the third sub-cavity 123 and the fourth sub-cavity 124.

[0077] The rib plate 2 is also provided with a plurality of rib plate support blocks 21. The upper bottom plate 1 and the rib plate support blocks 21 are respectively provided with corresponding bolt holes, and the upper bottom plate 1 and the rib plate support blocks 21 are connected by bolts.

[0078] Fig.10 is a schematic diagram of the structure of a phononic crystal unit cell provided in an embodiment of the present application, Fig.11 is a schematic diagram of the structure of the lead block provided in the embodiment of the present application, Fig.12 is a schematic diagram of the structure of the lead block provided in the embodiment of the present application, Fig.13 is a schematic diagram of the structure of the rubber block provided in the embodiment of the present application, Fig.14 is a top view of a rubber block provided in an embodiment of the present application, Fig.15 is a right side view of the rubber block provided in the embodiment of the present application. Figure 6 , Figures 10 to 15The phononic crystal unit cell 4 is composed of a rubber block 6 and a lead block 5; the lead block 5 is composed of a lead block body 52 and a first pin 51; the rubber block 6 is composed of a rubber block body 63 and a second pin 61; wherein the lead block body 52 is a cylinder, and the radius of the lead block body 52 is greater than the radius of the first pin 51; the rubber block body 63 is a truncated cone with a pin hole 62 at the center; the truncated cone includes a fifth surface 105 and a sixth surface 106; the first radius a1 of the fifth surface 105 is less than the second radius a2 of the sixth surface 106; the third radius a3 of the lead block body 52 is the same as the first radius a1; the second pin 61 is arranged on the sixth surface 106 and is located at the center; the lead block 5 is connected to the pin hole 62 through the first pin 51; the rubber block 6 is connected to the nesting hole 11 through the second pin 61.

[0079] The phononic crystal unit cell 4 is composed of an upper rubber block 6 and a lower lead block 5. The lead block 5 is composed of a cylindrical lead block body 52 and a cylindrical first pin 51 protruding from the upper part of the cylindrical lead block body 52. ​​A pin hole 62 is provided at the lower part of the rubber block 6, and a nested pin (i.e., a second pin 61) is provided at the upper part. The first pin 51 protruding from the upper part of the lead block 5 is inserted into the pin hole 62 at the lower part of the rubber block 6 for connection, and an adhesive is used to strengthen the connection at the connection part. The phononic crystal unit cell 4 is embedded in the periodically arranged nested holes 11 of the upper base plate 1 through the second pin 61 at the upper part of the rubber block 6.

[0080] The thickness d2 of the lead block 5 is twice the thickness d1 of the rubber block 6. The rubber block 6 is truncated cone-shaped, with a first radius a1 being the same as the third radius a3 of the lead block 5, and a second radius a2 of the connection with the upper base plate 1 being twice the third radius a3 of the lead block 5.

[0081] In some embodiments, the first pin 51 and the pin hole 62 are connected by a vulcanization process.

[0082] In some embodiments, the lower bottom plate 3 and the rib plate 2 are manufactured in an integrated manner; the material of the upper bottom plate 1, the rib plate 2 and the lower bottom plate 3 is glass fiber reinforced plastic.

[0083] Among them, fiberglass is used as the material for the upper and lower bottom plates and ribs of the composite raft. Compared with traditional homogeneous metal materials, it has higher structural strength, lighter weight, higher loss factor, and better wave-damping and vibration reduction effects.

[0084] In some embodiments, the damping layer 32 is adhered to the fourth surface 104 by an adhesive; the adhesive includes at least one of hot melt adhesive, epoxy resin adhesive, styrene-butadiene rubber adhesive, and cyanoacrylate adhesive.

[0085] It should be noted that the selection of adhesive can be set according to actual conditions and is not specifically limited here.

[0086] Fig.16is a flow chart of a composite raft design method provided in an embodiment of the present application. The method is applicable to the case of designing a composite raft that can be used to reduce vibration in a specific frequency band in submarine vibration reduction design. Fig.16 The design method of the composite raft comprises the following steps:

[0087] Step 110: Determine the target frequency band of the phononic crystal unit cell.

[0088] The target frequency band f can determine the bandwidth range of the target frequency band according to the target frequency upper limit f1 and the target frequency lower limit f2. max - f min .

[0089] For example, when vibration reduction is required for a specific low frequency band, the upper and lower limits of the target frequency band are the upper and lower limits of the specific low frequency band. The upper and lower limits of the frequency can be determined according to the actual application requirement frequency, and no specific limitation is made here.

[0090] Exemplarily, in the technical solution of the embodiment of the present application, the target frequency band ranges from 164 to 175 Hz.

[0091] Step 120: Determine the number of periods of the phononic crystal unit cell according to the target frequency band.

[0092] In some embodiments, determining the number of periods of a phononic crystal unit cell according to a target frequency band includes: determining a wave velocity in the phononic crystal unit cell according to the target frequency band; and determining the number of periods of the phononic crystal unit cell according to the target frequency band and the wave velocity in the phononic crystal unit cell.

[0093] Among them, the calculation formula for determining the wave velocity v in the phononic crystal unit cell according to the target frequency band is:

[0094]

[0095] Where E is the Young's modulus of the lead block and ρ is the density of the rubber block.

[0096] Calculate the number of periods of the phononic crystal unit cell based on the calculated wave velocity v and the target frequency band f:

[0097]

[0098] Wherein, x is the period number of the phononic crystal unit cell; a2 is the second radius of the connection between the rubber block 6 and the upper base plate 1; and f is the target frequency band of the phononic crystal unit cell.

[0099] Step 130: Determine the target size of the phononic crystal unit cell according to the number of periods of the phononic crystal unit cell.

[0100] In some embodiments, the target size of the phononic crystal unit cell is determined according to the number of periods of the phononic crystal unit cell, including: dividing a plurality of preselected areas on the upper base plate according to the number of periods of the phononic crystal unit cell; determining the target size of the phononic crystal unit cell according to the preselected areas, the phononic crystal unit cell size.

[0101] The pre-selected area may be a rectangular area, a circular area, etc., and may be set according to actual conditions, and no specific limitation is made here.

[0102] In some embodiments, the phononic crystal unit cell further comprises a rubber block; the lead block comprises a lead block body and a first pin; the rubber block comprises a rubber block body and a second pin; wherein the lead block body is a cylinder, and the radius of the lead block body is greater than the radius of the first pin; the rubber block body is a truncated cone with a pin hole at the center; the truncated cone comprises a fifth face and a sixth face; the first radius of the fifth face is less than the second radius of the sixth face; the third radius of the lead block body is the same as the first radius; the second pin is disposed on the sixth face and is located at the center; the lead block is connected to the pin hole through the first pin;

[0103] The target sizes include: a first radius, a second radius, and a third radius.

[0104] Specifically, the upper bottom plate is divided into different rectangular partitions according to the period number x of the phononic crystal unit cell, and the size of the second radius a2 of the rubber block is determined according to the width of the rectangular area, and the second radius a2 is smaller than the minimum width of the rectangular area. The first radius a1 of the rubber block and the third radius a3 of the lead block are determined according to the second radius a2.

[0105] Step 140: Determine the radius of the acoustic black hole according to the target frequency band of the phononic crystal unit cell.

[0106] In some embodiments, determining the radius of the acoustic black hole according to the target frequency band of the phononic crystal unit cell includes: calculating the radius of the acoustic black hole according to the upper frequency limit of the target frequency band.

[0107] The specific process of calculating the radius of the acoustic black hole according to the upper frequency limit of the target frequency band is as follows: the upper frequency limit f of the target band gap (i.e., the target frequency band) f of the phononic crystal unit cell is max As the cutoff frequency of the acoustic black hole, the radius R of the acoustic black hole is calculated according to the cutoff frequency formula of the acoustic black hole. The calculation formula of the radius is as follows:

[0108]

[0109] Wherein, h is the thickness of the lower plate; ρ is the density of the lower plate; E is the equivalent elastic modulus of the lower plate; υ is the equivalent Poisson's ratio.

[0110] Among them, the power rate curve of the acoustic black hole region conforms to the following law:

[0111]

[0112] in, are polynomial coefficients, determined by the thickness of the lower plate h and the radius of the acoustic black hole R, r is the radius of the cutoff platform; h0 is the cutoff thickness.

[0113] In the technical solution of the embodiment of the present application, the working principle of the design method of the composite raft is as follows: Fig.16 First, determine the target frequency band of the phononic crystal unit cell. Then, determine the number of periods of the phononic crystal unit cell according to the target frequency band. Secondly, determine the target size of the phononic crystal unit cell according to the number of periods of the phononic crystal unit cell. Finally, determine the radius of the acoustic black hole according to the target frequency band of the phononic crystal unit cell. Thus, this method can realize the design of the composite raft, the phononic crystal unit cell in the composite raft, and the acoustic black hole, and by combining the phononic crystal unit cell and the acoustic black hole, it can realize both the vibration reduction of the specific low-frequency band of the composite raft and the broadband vibration reduction of the composite raft from the low-frequency band to the high-frequency band.

[0114] Fig.17 This is a vibration reduction test effect diagram of the low-frequency target frequency band provided in the embodiment of the present application. For example, according to the target size determination method provided in the embodiment of the present application, the third radius a3 of the lead block in the phononic crystal unit cell is 15 mm, the thickness d2 of the lead block is 30 mm, the first radius a1 of the rubber block is 15 mm, the second radius a2 of the rubber block is 30 mm, and the thickness d1 of the rubber block is 15 mm. Please refer to Fig.17 , curve L1 is the vibration excitation point curve, and curve L2 is the vibration response point curve. Comparing L1 and L2, it can be found that the frequency spectrum vibration response of the response point and the vibration response of the excitation point have a significant difference at the design band gap of 164Hz and 181Hz. The vibration acceleration level of the two differs by about 35dB in the frequency band of 164Hz and 181Hz, and the vibration response of the response point is significantly suppressed.

[0115] Fig.18 : is a full-band vibration reduction test effect diagram provided in the embodiment of the present application. For example, according to the determination method of the acoustic black hole radius provided in the present application, the acoustic black hole radius can be obtained to be 80 mm. Fig.18 After adding ABH (Acoustic Black Hole), under the action of the band gap of the phononic crystal cell, the low frequency band below 200Hz still maintains a good vibration suppression effect. Fig.18 From the medium excitation spectrum, the vibration response spectrum without acoustic black hole and the vibration response spectrum after adding acoustic black hole, it can be found that after adding ABH, the amplitude of vibration acceleration level in the frequency band above 400Hz is further reduced, which further verifies that ABH has a significant inhibitory effect on high-frequency vibration of the structure.

[0116] After adding ABH, the hybrid phononic crystal raft structure still maintains a relatively stable band gap structure at low frequencies. Fig.18 It can be seen that after adding ABH, the acceleration level amplitude at the response point after 400 Hz is suppressed to a certain extent, which verifies that ABH has the effect of further suppressing the vibration of the phononic crystal raft structure under actual load.

[0117] In some embodiments, after determining the target size of the phononic crystal unit cell, it also includes: judging whether the target size of the phononic crystal unit cell needs to be adjusted according to preset simulation software; after determining the radius of the acoustic black hole, it also includes: establishing a first finite element model of the lower base plate embedded with the acoustic black hole, and verifying it according to the first finite element model; establishing a second finite element model of a composite raft based on the phononic crystal-acoustic black hole, and verifying the composite raft according to the second finite element model.

[0118] The target band gap (i.e., target frequency band) of the phononic crystal unit cell is calculated by the commercial software Comsol. If the calculated band gap does not meet the design requirements, the geometric dimensions of the phononic crystal unit cell are adjusted and analyzed again.

[0119] Among them, a finite element model of the lower base plate embedded with an acoustic black hole (i.e., the first finite element model) is established to verify the high-bandwidth vibration reduction effect of the acoustic black hole on the frequency band above the upper limit of the band gap frequency f of the phononic crystal unit cell.

[0120] Among them, a finite element model of the phononic crystal-acoustic black hole broadband vibration reduction composite raft (i.e., the second finite element model) was established through simulation software, and a finite element simulation verification was carried out on the phononic crystal-acoustic black hole broadband vibration reduction composite raft.

[0121] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0122] The composite raft frame and its design method provided in the embodiments of the present application are introduced in detail above, and the principles and implementation methods of the present application are explained by using specific examples. The description of the above embodiments is only used to help understand the technical solution and core idea of ​​the present application; ordinary technicians in this field should understand that: they can still modify the technical solutions recorded in the aforementioned embodiments, or replace some of the technical features therein with equivalents; and these modifications or replacements do not make the essence of the corresponding technical solution deviate from the scope of the technical solution of the embodiments of the present application.

Claims

1. A design method for a composite raft, characterized in that: The composite raft frame comprises an upper bottom plate, a lower bottom plate, phononic crystal unit cells embedded in the upper bottom plate and arranged periodically, and an acoustic black hole embedded in the lower bottom plate; The method comprises: determining a target frequency band of the phononic crystal unit cell; Determining the number of periods of the phononic crystal unit cell according to the target frequency band; Determining a target size of the phononic crystal unit cell according to the number of periods of the phononic crystal unit cell; The radius of the acoustic black hole is determined according to the target frequency band of the phononic crystal unit cell.

2. The design method of the composite raft according to claim 1, characterized in that: The step of determining the number of periods of the phononic crystal unit cell according to the target frequency band includes: Determining the wave velocity in the phononic crystal unit cell according to the target frequency band; The number of periods of the phononic crystal unit cell is determined according to the target frequency band and the wave velocity in the phononic crystal unit cell.

3. The design method of the composite raft according to claim 2, characterized in that: The phononic crystal unit cell includes a rubber block; The calculation formula for the number of periods of the phononic crystal unit cell is: Wherein, x is the number of periods of the phononic crystal unit cell; a2 is the second radius of the connection between the rubber block 6 and the upper base plate 1; v is the wave velocity in the phononic crystal unit cell; and f is the target frequency band of the phononic crystal unit cell.

4. The design method of a composite raft according to claim 1, characterized in that: Determining a target size of the phononic crystal unit cell according to the number of periods of the phononic crystal unit cell comprises: Dividing the upper base plate into a plurality of preselected regions according to the number of periods of the phononic crystal unit cell; The target size of the phononic crystal unit cell is determined according to the preselected area.

5. The design method of the composite raft according to claim 4, characterized in that: The shape of the pre-selected area is rectangular or circular.

6. The design method of a composite raft according to claim 3, characterized in that: The phononic crystal unit cell also includes a lead block; the lead block is composed of a lead block body and a first pin; the rubber block is composed of a rubber block body and a second pin; wherein the lead block body is a cylinder, and the radius of the lead block body is greater than the radius of the first pin; the rubber block body is a truncated cone with a pin hole at the center; the truncated cone includes a fifth face and a sixth face; the first radius of the fifth face is less than the second radius of the sixth face; the third radius of the lead block body is the same as the first radius; the second pin is arranged on the sixth face and is located at the center; the lead block is connected to the pin hole through the first pin; The target size includes: the first radius, the second radius, and the third radius.

7. The design method of a composite raft according to claim 1, characterized in that: The step of determining the radius of the acoustic black hole according to the target frequency band of the phononic crystal unit cell comprises: The radius of the acoustic black hole is calculated according to the upper frequency limit of the target frequency band.

8. The design method of a composite raft according to claim 1, characterized in that: After determining the target size of the phononic crystal unit cell, the method further includes: Determining whether the target size of the phononic crystal unit cell needs to be adjusted according to the preset simulation software; After determining the radius of the acoustic black hole, the method further comprises: Establishing a first finite element model of the lower base plate in which the acoustic black hole is embedded, and verifying according to the first finite element model; A second finite element model of a composite raft based on phononic crystal-acoustic black hole is established, and the composite raft is verified according to the second finite element model.

9. A composite raft, characterized in that: It comprises an upper base plate, a lower base plate, phononic crystal unit cells embedded in the upper base plate and arranged periodically, and an acoustic black hole embedded in the lower base plate; the composite raft frame is designed by the design method described in any one of claims 1-8.

10. The composite raft according to claim 9, characterized in that: It also includes ribs and a damping layer; wherein the upper base plate includes a first surface and a second surface; the lower base plate includes a third surface and a fourth surface; a cavity is formed between the ribs and the second surface; nested holes are periodically arranged on the second surface; each of the phononic crystal unit cells is located in the cavity and is partially embedded in the second surface through the nested holes; the acoustic black hole is embedded in the fourth surface; and each of the acoustic black holes is pasted with the damping layer at a position opposite to the third surface.

11. The composite raft according to claim 10, characterized in that: The phononic crystal unit cell is composed of a rubber block and a lead block; the lead block is composed of a lead block body and a first pin; the rubber block is composed of a rubber block body and a second pin; wherein the lead block body is a cylinder, and the radius of the lead block body is greater than the radius of the first pin; the rubber block body is a truncated cone with a pin hole at the center; the truncated cone includes a fifth face and a sixth face; the first radius of the fifth face is less than the second radius of the sixth face; the third radius of the lead block body is the same as the first radius; the second pin is arranged on the sixth face and is located at the center; the lead block is connected to the pin hole through the first pin; and the rubber block is connected to the nested hole through the second pin.

12. The composite raft according to claim 11, characterized in that: The first pin and the pin hole are connected by using a vulcanization process.

13. The composite raft according to claim 10, characterized in that: The lower bottom plate and the rib plate are manufactured in an integrated manner; the upper bottom plate, the rib plate and the lower bottom plate are made of glass fiber reinforced plastic.

14. The composite raft according to claim 10, characterized in that: The damping layer is adhered to the fourth surface by an adhesive; the adhesive comprises at least one of hot melt adhesive, epoxy resin adhesive, styrene-butadiene rubber adhesive and cyanoacrylate adhesive.

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