A TPMS housing metamaterial structure for underwater sound insulation and a design method thereof

Abstract

The application discloses a TPMS shell metamaterial structure for underwater sound insulation and a design method thereof. The structure comprises a shell base body, the shell base body has an inner surface thin wall layer, an outer surface thin wall layer and a structure layer between the inner surface thin wall layer and the outer surface thin wall layer; a D-shaped TPMS periodic porous unit is arranged in the structure layer, the D-shaped TPMS periodic porous unit is periodically arranged along a shell curved surface direction, a circumferential direction or an axial direction, and a continuous curved surface wall body and a connected pore structure are formed. The shell structure has the advantages of light weight, high specific rigidity, continuous bearing, parameterizable design and complex curved surface adaptation capability, and is suitable for underwater equipment shell, underwater pipeline protective shell, ship local structure and underwater sound insulation and damping protection of hydraulic structures.

Description

Technical Field

[0001] This invention relates to the field of underwater acoustic insulation, vibration reduction and noise reduction technology, and in particular to a TPMS shell metamaterial structure for underwater acoustic insulation and its design method. Background Technology

[0002] With the development of marine engineering, underwater equipment, cross-sea transportation engineering, and underwater construction technology, underwater structures are susceptible to the combined effects of mechanical vibration, fluid excitation, equipment operating noise, and external underwater acoustic waves during service, which propagate structural noise into the surrounding waters. Because sound waves travel quickly, over long distances, and attenuate slowly in water, underwater structural noise not only affects the operating environment of equipment and the safety of structural service, but may also adversely impact the ecological environment of the surrounding waters. Therefore, developing lightweight, efficient, and designable underwater acoustic insulation shell structures is of significant engineering importance.

[0003] Existing underwater acoustic insulation structures mostly employ rubber coatings, foam sandwiches, damping coatings, traditional porous materials, or composite sandwich structures. While these structures can achieve sound insulation or vibration reduction effects within a certain frequency range, they still suffer from problems such as insufficient low-frequency sound insulation, large structural thickness, high mass, limited parameter control capabilities, and insufficient adaptability to complex curved surfaces. Especially for underwater equipment hulls, curved protective hulls, and irregularly shaped hydraulic components, traditional homogeneous or regularly porous materials struggle to simultaneously meet the requirements of lightweight design, load-bearing capacity, and broadband sound insulation.

[0004] The Tri-Period Minimal Surface Structure (TPMS) possesses continuous smooth surfaces, high interconnectivity, high specific surface area, good mechanical continuity, and parametric adjustability. When used as a shell-type acoustic insulation structure, the advantages of TPMS include: continuous curved walls maintain the continuity of force transmission within the shell, reducing stress concentration caused by traditional discrete pore or sharp-corner structures; the through-type and tortuous three-dimensional channels extend the propagation path of sound waves within the structural layers, causing reflection, scattering, and diffraction at the interfaces of the channels, curved walls, and water medium; periodic curved elements can induce local resonance and bandgap effects through adjustment of geometric period and wall thickness; and the reciprocating motion of the water medium within the channels and the vibration of the thin-walled structure generate viscous energy dissipation and structural damping energy dissipation. Therefore, TPMS shell structures are advantageous for achieving integrated design of underwater acoustic insulation, vibration reduction, and load-bearing functions under lightweight conditions.

[0005] The D-type TPMS structure, as a typical TPMS configuration, features a double-continuous diamond-shaped topology, three-dimensional interconnected channels, smooth surface transitions, and strong spatial anisotropic connectivity. Compared to ordinary straight-hole, regular grid, or homogeneous shell structures, the D-type TPMS structure can form more tortuous sound propagation paths and more sound-solid-liquid coupling interfaces within a smaller structural thickness. This facilitates the control of the sound insulation peak value and effective sound insulation frequency band through unit cell size, wall thickness, porosity, and horizontal ensemble parameters. Therefore, it is necessary to propose a D-type TPMS shell metamaterial structure for underwater acoustic insulation and its design method. Summary of the Invention

[0006] The purpose of this invention is to provide a TPMS shell metamaterial structure for underwater acoustic insulation and its design method, aiming to solve the problems of limited low-frequency sound insulation effect, large structural mass, insufficient adaptability to complex curved surfaces, and difficulty in controlling structural parameters of existing underwater acoustic insulation shell structures.

[0007] The technical solution provided by this invention is as follows:

[0008] A TPMS shell metamaterial structure for underwater acoustic insulation, the structure includes a shell substrate, the shell substrate having an inner thin-walled layer, an outer thin-walled layer, and a structural layer located between the inner and outer thin-walled layers; D-type TPMS periodic porous units are disposed within the structural layer, the D-type TPMS periodic porous units being periodically arranged along the curved surface direction, circumferential direction, or axial direction of the shell, forming a continuous curved wall and a connected pore structure.

[0009] Preferably, the D-type TPMS structure is generated by an implicit function, which is:

[0010]

[0011] Where a is the edge length of the unit cell, and c is the level set parameter that controls the porosity and solid volume fraction.

[0012] Preferably, the shell structure is made of at least one of the following materials: metal, resin, rubber, ceramic, fiber-reinforced composite, and cement-based composite.

[0013] Preferably, in the metamaterial structure, single or multiple D-type TPMS periodic porous units are provided within the structural layers.

[0014] This invention further discloses a design method for a TPMS shell metamaterial structure for underwater acoustic insulation, the method comprising the following steps:

[0015] (1) Determine the target frequency band, structural dimensions, boundary conditions, and material parameters for underwater acoustic insulation;

[0016] (2) Select the D-type TPMS structure as the basic unit cell and establish the implicit surface equation of the D-type TPMS;

[0017] (3) Arrange the D-type TPMS unit cells along the circumferential direction to form a D-type TPMS periodic porous unit;

[0018] (4) Thin-walled layers are set on the inner and outer sides of the D-type TPMS periodic porous unit to obtain a TPMS shell metamaterial structure with inner and outer thin walls;

[0019] (5) Use COMSOL Multiphysics software to establish finite element models of the water area, the TPMS shell metamaterial structure, and the acoustic-structural coupling boundary;

[0020] (6) Perform frequency domain underwater acoustic simulation in COMSOL to calculate the acoustic transmission loss of the TPMS shell metamaterial structure in the target frequency band.

[0021] This invention overcomes the shortcomings of existing technologies and provides a TPMS shell metamaterial structure for underwater acoustic insulation and its design method. Unlike traditional solutions that rely on increasing mass or laying homogeneous sound-absorbing and damping materials, this invention utilizes a D-type TPMS with tortuous interconnected channels, continuous curved walls, and multiple acoustic-structural coupling interfaces to reconstruct the propagation path of underwater acoustic energy: when incident sound waves reach the outer thin-walled layer, they are reflected due to acoustic impedance differences; sound waves entering the structural layer undergo multiple reflections and scattering between the dual continuous channels and the curved walls. Simultaneously, the elastic vibration of the curved thin walls couples with the movement of the water medium within the channels, converting some acoustic energy into structural vibration energy, which is dissipated through material damping and multi-interface coupling. The local resonance and bandgap effect generated by the periodic units further suppress sound energy transmission within the target frequency band. The inner thin-walled layer, together with the structural layer, forms a multi-level impedance mismatch, thereby increasing the sound transmission loss of the shell.

[0022] The innovation of this invention lies in combining a D-type TPMS dual-continuous topology with inner and outer thin-walled shells to form a load-bearing, sealable, and parameter-adjustable curved underwater acoustic metamaterial structure. It establishes a complete design method from determining the target frequency band, generating implicit curved surfaces, arranging unit cells conformally or periodically along the shell's circumference or axial direction, constructing inner and outer thin-walled structures, to acoustic-structure interaction finite element analysis and sound transmission loss evaluation. By changing the periodic parameters, level set parameters, unit cell size, curved surface wall thickness, porosity, number of circumferential periods, number of structural layers, and total shell thickness, the equivalent stiffness, equivalent density, acoustic impedance, resonant frequency, and effective sound insulation band can be adjusted. Furthermore, multi-layer units with different parameters can be used to construct a gradient structure to achieve synergistic design between structural quality, load-bearing capacity, and sound insulation performance.

[0023] The key technical points of this invention are: ensuring the continuous arrangement of D-type TPMS units on the curved surface of the shell and the geometrical continuity between units, structural layers and inner and outer thin-walled layers; refining the mesh based on the target highest frequency and minimum geometric features; setting an acoustic-structural coupling boundary at the interface between the water area and the shell; and using the transmission loss obtained by integrating the acoustic power on the incident and transmission sides as the basis for parameter screening and optimization, thereby obtaining a lightweight underwater acoustic insulation structure suitable for underwater equipment shells, underwater pipeline protective shells and hydraulic structures.

[0024] The beneficial effects of this invention after adopting the above technical solution are as follows:

[0025] (1) The present invention uses D-type TPMS periodic porous unit to construct shell structure. The curved wall is continuous and the pores are three-dimensionally connected, which can effectively avoid the problems of local stress concentration and acoustic change in traditional discrete porous structure.

[0026] (2) The present invention extends the propagation path of sound waves in the shell structure layer by using the double continuous curved surface channel of the D-type TPMS structure, so that the incident water sound waves are reflected, scattered and diffracted at multiple interfaces, thereby improving the water sound transmission loss.

[0027] (3) The present invention can generate local resonance, bandgap modulation and energy dissipation in a specific frequency band by using the acoustic-structural coupling effect between the D-type TPMS thin-walled curved surface, water medium and shell matrix, which is beneficial to improving the mid-low frequency sound insulation performance of the shell structure.

[0028] (4) By adjusting the unit cell size, wall thickness, porosity, horizontal set parameters, number of circumferential periods and shell thickness of the D-type TPMS, the present invention can achieve designable control of the sound insulation frequency band, sound insulation peak value and structural quality.

[0029] (5) The shell structure of the present invention is lightweight, has high specific stiffness, continuous load bearing, parametric design and complex surface adaptability, and is suitable for underwater equipment shells, underwater pipeline protective shells, ship partial structures and underwater acoustic insulation and vibration reduction protection of hydraulic structures. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the TPMS shell metamaterial structure;

[0031] Figure 2 This is a schematic diagram of the shell matrix in the TPMS shell metamaterial structure;

[0032] Figure 3 This is a schematic diagram of the D-type TPMS periodic porous unit in the TPMS shell metamaterial structure;

[0033] Figure 4This is a schematic diagram of the structure of a D-type TPMS unit cell in a D-type TPMS periodic porous unit.

[0034] Figure 5 The transmission loss curve of the underwater acoustic simulation model of the TPMS shell metamaterial structure in COMSOL Multiphysics 6.3 is shown. Detailed Implementation

[0035] The technical solution of the present invention will be further described in detail below with reference to specific embodiments, but this does not constitute any limitation on the present invention.

[0036] This invention discloses a design method for a TPMS shell metamaterial structure for underwater acoustic insulation, comprising the following steps:

[0037] (1) Determine the target frequency band, structural dimensions, boundary conditions, and material parameters for underwater acoustic insulation.

[0038] In step (1), the target frequency band to be suppressed is determined based on the actual working environment and noise spectrum of the underwater equipment, typically using the lowest target frequency f. min and the highest target frequency f max This indicates, and is based on the speed of sound in water, c w Calculate the corresponding wavelength λ=c w / f is used to determine the shell dimensions and unit cell scale. Based on the application, the shell's inner and outer contours, radius of curvature, axial length, structural layer thickness, inner and outer thin-wall layer thickness, circumferential and axial unit cell counts, and mounting interfaces are determined; simultaneously, the incident sound field type, sound wave incident direction, shell support method, and water area are determined. In the numerical model, the water area uses a pressure acoustic frequency domain interface, and the shell uses a solid mechanical interface. A sound-structure coupling boundary is set at the water-shell contact surface, a plane wave or point source is set on the incident side, and a radiation boundary or perfectly matched layer is set at the far-field boundary. The shell edges are set with free, simply supported, or fixed constraints according to actual working conditions. Material parameters include at least the density and velocity of water, as well as the density, Young's modulus, Poisson's ratio, and structural damping of the shell material; parameters should use data under the same temperature and pressure conditions. The mesh size is determined based on the shortest underwater wavelength corresponding to the highest target frequency, and local refinement is applied to TPMS surfaces, narrow channels, and thin-walled regions to ensure accurate analysis of the sound and structural fields.

[0039] (2) Select the D-type TPMS structure as the basic unit cell, such as Figure 4 As shown, the implicit surface equation of D-type TPMS is established.

[0040] In step (2), the D-type TPMS unit cell structure is generated by combining the D-type TPMS implicit function as shown in the following formula with MATLAB software.

[0041]

[0042] Where a is the edge length of the unit cell, and c is the level set parameter controlling the porosity and solid volume fraction. Different D-type TPMS unit cells with varying porosities and pore sizes can be obtained by changing a and c, such as... Figure 4 As shown.

[0043] (3) Arrange the D-type TPMS unit cells along the circumferential direction to form a D-type TPMS periodic porous unit.

[0044] In step (3), the generated D-type TPMS unit cell is translated, rotated, and periodically replicated according to the local tangential direction of the shell surface to form a continuous D-type TPMS periodic porous unit. By adjusting the number of circumferential unit cells, the number of axial unit cells, the unit cell size, and the horizontal set parameters, D-type TPMS periodic porous units with different porosities, pore tortuosity, and structural quality can be obtained, such as... Figure 3 As shown.

[0045] (4) Thin-walled layers are set on the inner and outer sides of the D-type TPMS periodic porous unit to obtain a TPMS shell metamaterial structure with inner and outer thin walls, such as Figure 1 As shown.

[0046] In step (4), the inner thin-walled layer, the D-type TPMS periodic porous unit, and the outer thin-walled layer are Boolean-unified to form a continuous shell matrix. When setting the thin-walled layer, it should be ensured that the thin-walled layer is fully connected to the TPMS curved wall, without through gaps, unexpected overlaps, or sharp geometric abrupt changes, and the minimum machinable wall thickness and pore size should be retained according to the manufacturing process, such as... Figure 2 As shown. The inner and outer thin-walled layers are used to improve the overall stiffness and structural integrity of the shell and protect the internal periodic porous elements. When using multi-layer D-type TPMS periodic porous elements, different layers can have different unit cell sizes, wall thicknesses, porosities, or level set parameters to form a gradient structure. After completion, a TPMS shell metamaterial structure for subsequent underwater acoustic finite element analysis can be obtained, such as... Figure 1 As shown.

[0047] In this embodiment of the invention, the TPMS shell metamaterial structure for underwater acoustic insulation obtained according to the above design method includes a shell substrate, which has an inner surface, an outer surface, and a structural layer located between the inner and outer surfaces. D-type TPMS periodic porous units are disposed in the structural layer. The D-type TPMS periodic porous units are periodically arranged along the curved surface direction, circumferential direction, or axial direction of the shell, forming a continuous curved wall and a connected pore structure. The D-type TPMS periodic porous units are used to reflect, scatter, resonate locally, and dissipate incident sound waves in the water medium, thereby improving the underwater acoustic insulation performance of the structure.

[0048] In this embodiment of the invention, the inner and outer surfaces of the shell substrate are configured as continuous thin-walled layers to improve the overall rigidity of the shell, enhance structural integrity, protect the internal D-type TPMS periodic porous unit, and adjust the acoustic impedance matching relationship between the shell structure and the water medium.

[0049] In metamaterial structures, single or multiple D-type TPMS periodic porous units are incorporated within the structural layers. In further implementation, when using multiple D-type TPMS periodic porous units, different D-type TPMS periodic porous unit structural layers can have different unit cell sizes, wall thicknesses, porosities, or horizontal settling parameters to form a gradient-type underwater acoustic insulation shell structure, thereby broadening the sound insulation frequency band or enhancing the sound insulation effect within a specific frequency band.

[0050] Having obtained the general structure of the TPMS shell metamaterial structure for underwater acoustic insulation described above, the design method of the present invention further includes the following steps to obtain the metamaterial structure with the desired performance:

[0051] (5) Use COMSOL Multiphysics software to establish finite element models of the water area, the TPMS shell metamaterial structure and the acoustic-structure coupling boundary.

[0052] (6) Perform frequency domain underwater acoustic simulation in COMSOL to calculate the sound transmission loss of the TPMS shell metamaterial structure in the target frequency band. The sound transmission loss can be calculated according to the following formula:

[0053] TL = 10*log 10 (W in / W out );

[0054] Among them, W in For incident side acoustic power, W out This represents the transmitted side acoustic power. W in and W out It can be obtained by integrating the acoustic power on the incident and transmission sides.

[0055] Figure 5To simulate the acoustic transmission loss of a D-type TPMS shell structure, the software-generated D-type TPMS structure was first imported into COMSOL Multiphysics 6.3. Then, a three-dimensional finite element model including the water area and the solid shell structure was established. The water area material was set to water, and the solid shell material could be set to titanium alloy. In the physics settings, the water area used the pressure acoustics frequency domain module, and the shell structure used the solid mechanics module. An acoustic-structure boundary was set at the interface between the water area and the shell structure. Through this acoustic-structure coupling boundary, the coupling calculation of the sound pressure in the water acting on the shell structure and the back-radiated sound waves from the shell vibration could be realized. A point sound source was then set at the center of the shell, and a perfectly matched layer was set at the outer boundary of the water area to reduce the influence of boundary reflection on the calculation results. The water area size was determined based on the target frequency range and the shell's external dimensions, ensuring sufficient distance between the transmission side integral surface and the shell to avoid near-field interference significantly affecting the acoustic transmission loss calculation. During mesh generation, the water area mesh was determined based on the shortest wavelength corresponding to the highest calculation frequency. After the model was established, a frequency domain study was conducted to calculate the acoustic transmission loss at different frequencies. The acoustic transmission loss can be calculated using the following formula:

[0056] TL = 10*log 10 (W in / W out )

[0057] in:

[0058] W in =intop1(abs(acpr.p_t)^2 / (2*acpr.rho*acpr.c)),

[0059] W out = intop2(abs(acpr.p_t)^2 / (2*acpr.rho*acpr.c)).

[0060] The results show that the structure has a good sound insulation effect in the mid and low frequencies, with an average sound insulation of about 20dB.

[0061] Depending on the specific engineering requirements, the TPMS shell metamaterial structure can be fabricated using methods such as integral molding, modular assembly, additive manufacturing, casting, or composite material molding. When fabricated using additive manufacturing, a three-dimensional model can be generated based on the implicit functions of the D-type TPMS, and the solid structure can be obtained through metal additive manufacturing, resin printing, or composite material printing.

[0062] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A TPMS shell metamaterial structure for underwater acoustic insulation, characterized in that, The structure includes a shell substrate, which has an inner thin-walled layer, an outer thin-walled layer, and a structural layer located between the inner and outer thin-walled layers. D-type TPMS periodic porous units are provided in the structural layer. The D-type TPMS periodic porous units are periodically arranged along the curved surface direction, circumferential direction, or axial direction of the shell, forming a continuous curved wall and a connected pore structure.

2. The metamaterial structure as described in claim 1, characterized in that, The D-type TPMS structure is generated by an implicit function, which is: ； Where a is the edge length of the unit cell, and c is the level set parameter that controls the porosity and solid volume fraction.

3. The metamaterial structure as described in claim 1, characterized in that, The shell structure is made of at least one of the following materials: metal, resin, rubber, ceramic, fiber-reinforced composite, and cement-based composite.

4. The metamaterial structure as described in claim 1, characterized in that, In the metamaterial structure, single or multiple D-type TPMS periodic porous units are arranged within the structural layers.

5. A design method for a TPMS shell metamaterial structure for underwater acoustic insulation, characterized in that, The method includes the following steps: (1) Determine the target frequency band, structural dimensions, boundary conditions, and material parameters for underwater acoustic insulation; (2) Select the D-type TPMS structure as the basic unit cell and establish the implicit surface equation of the D-type TPMS; (3) Arrange the D-type TPMS unit cells along the circumferential direction to form a D-type TPMS periodic porous unit; (4) Thin-walled layers are set on the inner and outer sides of the D-type TPMS periodic porous unit to obtain a TPMS shell metamaterial structure with inner and outer thin walls; (5) Use COMSOL Multiphysics software to establish finite element models of the water area, the TPMS shell metamaterial structure, and the acoustic-structural coupling boundary; (6) Perform frequency domain underwater acoustic simulation in COMSOL to calculate the acoustic transmission loss of the TPMS shell metamaterial structure in the target frequency band.

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