Conversion method of onshore to underwater vibration response of cabin structure

Abstract

The present invention relates to a method for converting the vibration response of a cabin structure from onshore to underwater, comprising: S1, testing the structural mode under onshore support state, performing modal analysis to obtain the mass, damping and stiffness matrix M+M 支 、C+C 支 , K; S2, when the equipment in the onshore structure is running, test the structural vibration response and obtain the vibration displacement response u1 of the cabin structure onshore; S3, calculate the constant excitation vector F0 inside the structure; S4, additional displacement impedance Z for the bottom support 支 , additional displacement impedance Z of adjacent structures 邻 , additional displacement impedance of water Z 水 Calculate the following: S5. Calculate the inherent mass matrix M and damping matrix C of the compartment structure in the free state; S6. Calculate the underwater vibration displacement response u2 of the compartment structure when the same equipment within the compartment is operating. The present invention modifies the onshore compartment boundary conditions based on additional impedance, eliminating the differences in bottom support, structural truncation, and water environment between the onshore and underwater compartments, thereby enabling the estimation of underwater vibration of the onshore compartment.

Description

Technical Field

[0001] The present invention belongs to the technical field of ship noise and vibration control, and in particular relates to a method for converting the vibration response of a cabin structure from onshore to underwater. Background Art

[0002] Integral testing of large structures, such as ships, places high demands on test conditions and techniques, and testing costs increase with increasing complexity. Therefore, in practical engineering, onshore scale-down and compartment tests are often used as an alternative to integral structural testing. Therefore, estimating the acoustic and vibration performance of submerged compartments based on onshore test results of truncated compartments has become a promising alternative.

[0003] Currently, there is still a lack of comprehensive technical support for the accurate assessment of cabin acoustic performance. Relevant research at home and abroad has mainly focused on the structural vibration response to mechanical excitation under the same medium environment, the theory and simulation of structural vibration sound radiation, etc. However, there is insufficient research on the differences in structural vibration response and radiated noise under different environments. As a result, during the ship development process, it is impossible to accurately estimate underwater characteristics in a timely manner during the onshore test phase, making it difficult to identify design problems and make timely rectifications and optimizations. Specifically, the main defects of the relevant technologies are manifested in the following aspects:

[0004] 1) The corresponding relationship between structural acoustic performance in different fluid environments (air and water) is not understood;

[0005] 2) The support and structural truncation of the onshore compartment are different from the boundary conditions in the water, making it difficult to accurately assess their impact on the structural acoustic performance;

[0006] 3) The impact of onshore boundary conditions on the performance of vibration isolation devices such as rafts within the compartment is still lacking in assessment and correction technology;

[0007] 4) The cabin structure acoustic simulation model has not been subjected to experimental verification and revision, and its accuracy and credibility have not been verified.

[0008] Taking into account the differences in the three boundary conditions between the onshore truncated compartment and the underwater structure, namely, bottom support, structural truncation and water environment, it is necessary to study the influence of these three boundary conditions, and to correct the test results of the onshore compartment to predict the vibration and noise results of the underwater compartment. Summary of the Invention

[0009] In response to the technical problems existing in the above-mentioned prior art, the present invention provides a method for converting the onshore to underwater vibration response of a cabin structure. The method studies the differences in three boundary conditions, namely, bottom support, structural truncation, and water environment, between a truncated cabin on land and a full cabin in water, and proposes a method for correcting the influence of onshore boundary conditions based on additional impedance. This method solves the problem of converting the vibration characteristics of a single-cabin structure supported on land to an unsupported multi-cabin underwater structure. The method can be used to correct the test results of the onshore cabin and predict its underwater vibration response results.

[0010] The technical solution adopted by the present invention to solve the above-mentioned technical problems is:

[0011] A method for converting the vibration response of a cabin structure from onshore to underwater includes the following steps:

[0012] S1. Test the structural mode under the land support state and perform modal analysis to obtain the mass, damping and stiffness matrix M+M 支 、C+C 支 , K;

[0013] S2. When the equipment in the onshore structure is in operation, the structural vibration response is tested to obtain the onshore vibration displacement response u1 of the cabin structure;

[0014] S3. Substitute the above parameters into equation (1) to calculate the constant excitation vector F0 inside the structure;

[0015] [-ω 2 (M+M 支 )+jω(C+C 支 )+K]{u1}=F0 (1)

[0016] S4. Using finite element simulation method, the additional displacement impedance Z of the bottom support is 支 Calculate and obtain M according to formula (2) 支 、C 支 ; Using the finite element simulation method, the additional displacement impedance Z of the adjacent structure 邻 Calculate and obtain M according to formula (2) 邻 、C 邻 ; The additional displacement impedance Z of water is calculated using the boundary element method 水 , and calculate M according to formula (2) 水 、C 水 ;

[0017]

[0018] S5, the matrix M+M obtained from the modal analysis in step S1 支 and C+C 支 Subtract the M obtained in step S4 from 支、C 支 , we can obtain the inherent mass matrix M and damping matrix C of the cabin structure in the free state;

[0019] S6, the parameter matrix M, C, M 水 、C 水 、M 邻 、C 邻 Substitute , K and F0 into equation (3) to calculate the vibration displacement response u2 of the cabin structure underwater when the same equipment in the cabin is running, so as to achieve the purpose of predicting the vibration response of the underwater structure through onshore testing;

[0020] [-ω 2 (M+M 水 +M 邻 )+jω(C+C 水 +C 邻 )+K]{u2}=F0 (3)

[0021] In equations (1)-(3), F0 represents the constant excitation vector inside the structure; M, C, and K are the inherent mass, damping, and stiffness of the cabin structure, respectively; Z 支 、Z 水 、Z 邻 are the additional displacement impedance of the bottom support, the additional displacement impedance of water, and the additional displacement impedance of the adjacent structure; M 支 、C 支 are the additional mass and additional damping brought to the structure by the bottom support; M 水 、C 水 are the additional mass and additional damping brought to the structure by the attached water; M 邻 、C 邻 are the additional mass and additional damping brought to the structure by the adjacent structures; u1 and u2 are the vibration displacement responses of the cabin structure on land and underwater respectively; ω is the circular frequency; j is the imaginary unit.

[0022] In the above scheme, in step S4, if it is an elastic support, the spring stiffness can be directly calculated to obtain Z 支 .

[0023] The beneficial effects of the present invention are:

[0024] The present invention provides a method for converting the onshore to underwater vibration response of a cabin structure. The method corrects the onshore boundary conditions of the cabin based on additional impedance, eliminates the differences in bottom support, structural truncation, and water environment between the onshore and underwater cabins, and enables the estimation of underwater vibration of the onshore cabin. This ensures that accurate estimation of underwater characteristics can be carried out in a timely manner during the onshore test phase of ship development, allowing design problems to be discovered as early as possible and rectified and optimized, thus providing technical support for the acoustic performance evaluation and design optimization of cabins in engineering projects.

[0025] The present invention proposes a method for converting onshore cabin structure vibration test data to its underwater vibration, which meets the urgent need of timely predicting underwater performance during the onshore test phase in engineering.

[0026] The present invention will be applied in structural acoustic status assessment, cabin structure testing, noise index control, cabin structure noise reduction system design, and mechanical equipment assessment, and will significantly promote structural acoustic status assessment and noise control research. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0028] Figure 1 This is a flow chart of the method for converting the onshore to underwater vibration response of a cabin structure according to the present invention;

[0029] Figure 2 is a mode shape cloud diagram of the land-based support compartment in an embodiment of the present invention;

[0030] Figure 3 is a vibration response cloud diagram of the land-based support cabin section in an embodiment of the present invention;

[0031] Figure 4 is the additional impedance Z of the adjacent structure in the embodiment of the present invention 邻 Finite element calculation model; among them: (4-a) is a single-cabin finite element model, (4-b) is a three-cabin finite element model;

[0032] Figure 5 This is a comparison chart of the vibration responses of two typical measuring points in water measured in an embodiment of the present invention and converted by this method;

[0033] Figure 6 3 is a comparison chart of the conversion result of this method in an embodiment of the present invention and the radial mean square velocity of the shell measured in water. DETAILED DESCRIPTION

[0034] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described in detail with reference to the accompanying drawings.

[0035] Although the differences in boundary conditions between onshore and underwater structures can be divided into three types: bottom support, structural truncation, and water environment, their influence can actually be eliminated by calculating the same dynamic equation. The present invention provides a method for converting the onshore to underwater vibration response of a cabin structure. Based on the additional impedance, the onshore boundary conditions of the cabin are corrected to eliminate the three boundary condition differences between the onshore cabin and the underwater cabin: bottom support, structural truncation, and water environment. As long as the onshore vibration mass, damping, and stiffness matrices of the cabin structure, as well as the internal excitation data of the structure, are obtained, and the additional impedance corresponding to the three boundary conditions is mastered, the influence of the boundary conditions can be corrected through the equation to obtain the predicted value of the underwater vibration response of the cabin structure.

[0036] like Figure 1 As shown, the present invention provides a method for converting the vibration response of a cabin structure from onshore to underwater, comprising the following steps:

[0037] S1. Test the structural mode under the land support state and perform modal analysis to obtain the mass, damping and stiffness matrix M+M 支 、C+C 支 , K;

[0038] S2. When the equipment in the onshore structure is in operation, the structural vibration response is tested to obtain the onshore vibration displacement response u1 of the cabin structure;

[0039] S3. Substitute the above parameters into equation (1) to calculate the constant excitation vector F0 inside the structure;

[0040] [-ω 2 (M+M 支 )+jω(C+C 支 )+K]{u1}=F0 (1)

[0041] Equation (1) is the frequency domain representation of the cabin structure dynamic equation.

[0042] S4. Using finite element simulation method, the additional displacement impedance Z of the bottom support is 支 Calculate and obtain M according to formula (2) 支 、C 支 If it is an elastic support, the impedance data can also be directly obtained by applying the spring complex stiffness calculation; the additional displacement impedance Z of the adjacent structure is calculated using the finite element simulation method. 邻 Calculate and obtain M according to formula (2) 邻 、C 邻 ; The additional displacement impedance Z of water is calculated using the boundary element method 水 , and calculate M according to formula (2) 水 、C 水 ;

[0043]

[0044] S5, the matrix M+M obtained from the modal analysis in step S1 支 and C+C 支 Subtract the M obtained in step S4 from 支 、C 支 , obtain the inherent mass matrix and damping matrix M, C of the cabin structure in the free state;

[0045] S6, the parameter matrix M, C, M 水 、C 水 、M 邻 、C 邻 , K and F0 are substituted into equation (3) to calculate the vibration displacement response u2 of the cabin structure underwater, thus achieving the purpose of predicting the vibration response of the underwater structure through onshore testing;

[0046] [-ω 2 (M+M 水 +M 邻 )+jω(C+C 水 +C 邻 )+K]{u2}=F0 (3)

[0047] In equations (1)-(3), F0 represents the constant excitation vector inside the structure; M, C, and K are the inherent mass, damping, and stiffness of the cabin structure, respectively; Z 支 、Z 水 、Z 邻 are the additional displacement impedance of the bottom support, the additional displacement impedance of water, and the additional displacement impedance of the adjacent structure; M 支 、C 支 are the additional mass and additional damping brought to the structure by the bottom support; M 水 、C 水 are the additional mass and additional damping brought to the structure by the attached water; M 邻 、C 邻 are the additional mass and additional damping brought to the structure by the adjacent structures; u1 and u2 are the vibration displacement responses of the cabin structure on land and underwater respectively; ω is the circular frequency; j is the imaginary unit.

[0048] Through the above steps, the influence of the difference between the onshore and underwater boundary conditions on the structural vibration response can be eliminated and corrections can be made, thereby realizing the conversion of the onshore to underwater vibration characteristics of the cabin.

[0049] The following uses a cylindrical shell model as an example to illustrate the specific implementation of this patent:

[0050] S1. Place the structure on elastic vibration isolators and conduct onshore vibration modal testing. The modal data obtained from the test analysis are shown in Table 1. Examples of typical modal vibration shape cloud diagrams are shown in Figure 2 , a total of 29 modes below 400 Hz are obtained, and the modal matrix is 168 rows and 29 columns.

[0051] Table 1 Modal test results of the onshore support compartment (normalized by mass)

[0052]

[0053] S2. Start the mechanical equipment inside the shell structure to stimulate the shell and test the vibration response of each measuring point of the structure. The measured structural vibration distribution cloud diagram is shown in the following example. Figure 3 .

[0054] S3. The mass, damping and stiffness matrices M+M obtained from these test analyses 支 、C+C 支 , K, and the vibration displacement response u1 of the cabin structure on land are substituted into equation (1) to calculate the constant excitation vector F0 inside the structure.

[0055] S4. Directly apply the spring complex stiffness data to calculate the additional impedance Z of the bottom support 支 , and calculate M according to formula (2) 支 、C 支 ;like Figure 4 -b shows the additional impedance Z of the adjacent structure using finite element simulation. 邻 Calculate and obtain M according to formula (2) 邻 、C 邻 ; Use boundary element method to calculate the additional impedance Z of water 水 , and calculate M according to formula (2) 水 、C 水 .

[0056] S5. Perform additional impedance correction on the elements in the matrix affected by the land support to obtain the inherent mass matrix and damping matrix M and C of the shell structure in the free state.

[0057] S6, the known parameter arrays M, C, M 水 、C 水 、M 邻 、C 邻 Substituting , K and F0 into equation (3), the vibration displacement response u2 of the structure in the underwater state under the same internal excitation can be calculated, and the underwater vibration response of the structure can be predicted based on the onshore test data.

[0058] The comparison between the calculation results of the method of the present invention and the measured data of underwater vibration of the shell structure is shown in Figure 5 、 Figure 6 ,in Figure 5 The following are comparison curves of the vibration responses of two typical measuring points measured in water and converted by this method. Figure 6The figure shows a comparison curve between the calculated average vibration response of the entire cylindrical shell (radial mean square velocity) and the measured data. The results of this example show that the error of this method is less than 5dB in the frequency range of 0 to 400Hz.

[0059] Therefore, the proposed method can eliminate and correct the effects of differences in onshore and underwater boundary conditions on the structural vibration response, enabling conversion of onshore to underwater vibration characteristics of the cabin structure. Subsequently, the well-established structural vibration acoustic radiation method can be used to calculate the underwater radiated noise of the structure.

[0060] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are protected by the present invention.

Claims

1. A method for converting the vibration response of a cabin structure from onshore to underwater, characterized in that: The following steps are involved: S1. Test the structural mode under the land support state and perform modal analysis to obtain the mass, damping and stiffness matrix M+M 支 、C+C 支 , K; S2. When the equipment in the onshore structure is in operation, the structural vibration response is tested to obtain the onshore vibration displacement response u1 of the cabin structure; S3. Substitute the above parameters into equation (1) to calculate the constant excitation vector F0 inside the structure; [-ω 2 (M+M 支 )+jω(C+C 支 )+K]{u1}=F0 (1) S4. Using finite element simulation method, the additional displacement impedance Z of the bottom support is 支 Calculate and obtain M according to formula (2) 支 、C 支 ; Using the finite element simulation method, the additional displacement impedance Z of the adjacent structure 邻 Calculate and obtain M according to formula (2) 邻 、C 邻 ; The additional displacement impedance Z of water is calculated using the boundary element method 水 , and calculate M according to formula (2) 水 、C 水 ; S5, the matrix M+M obtained from the modal analysis in step S1 支 and C+C 支 Subtract the M obtained in step S4 from 支 、C 支 , we can obtain the inherent mass matrix M and damping matrix C of the cabin structure in the free state; S6, the parameter matrix M, C, M 水 、C 水 、M 邻 、C 邻 Substitute , K and F0 into equation (3) to calculate the vibration displacement response u2 of the cabin structure underwater when the same equipment in the cabin is running, so as to achieve the purpose of predicting the vibration response of the underwater structure through onshore testing; [-ω 2 (M+M 水 +M 邻 )+jω(C+C 水 +C 邻 )+K]{u2}=F0 (3) In equations (1)-(3), F0 represents the constant excitation vector inside the structure; M, C, and K are the inherent mass, damping, and stiffness of the cabin structure, respectively; Z 支 、Z 水 、Z 邻 are the additional displacement impedance of the bottom support, the additional displacement impedance of water, and the additional displacement impedance of the adjacent structure; M 支 、C 支 are the additional mass and additional damping brought to the structure by the bottom support; M 水 、C 水 are the additional mass and additional damping brought to the structure by the attached water; M 邻 、C 邻 are the additional mass and additional damping brought to the structure by the adjacent structures; u1 and u2 are the vibration displacement responses of the cabin structure on land and underwater respectively; ω is the circular frequency; j is the imaginary unit.

2. The method for converting the onshore to underwater vibration response of a cabin structure according to claim 1 is characterized in that: In step S4, if it is an elastic support, the spring stiffness can be directly calculated to obtain Z 支 .

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