Calculation method of ship motion response amplitude operator

Abstract

The invention provides a method for calculating a ship motion response amplitude operator, which comprises the following steps of: generating a transient wave packet based on a specified wave spectrum, carrying out a target ship type seakeeping model test by adopting the transient wave packet, and extracting a time sequence of the transient wave packet and a time sequence of ship model swaying motion; wherein the time sequence of the transient wave packet needs to be collected when no ship model exists in a water pool, a Hilbert marginal spectrum analysis model based on Hilbert-Huang transform is established, and the time sequence of the transient wave packet and the time sequence of the ship model swaying motion under the action of the transient wave packet are input into the Hilbert marginal spectrum analysis model. The method comprises the following steps of: acquiring a transient wave packet time sequence, acquiring a marginal spectrum of the transient wave packet time sequence and the ship model swaying motion time sequence, and acquiring a target ship swaying motion response amplitude operator according to a ratio of the ship model swaying motion time sequence to the marginal spectrum of the transient wave packet time sequence. And therefore, the problem that a ship motion response amplitude operator curve has a relatively large error can be solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ship and ocean engineering test research, in particular to a calculation method of ship motion response amplitude operator, namely a calculation method of ship motion response amplitude operator (RAO) in seakeeping model test. BACKGROUND

[0002] At present, seakeeping model test is usually used to predict and evaluate the performance of ship motion in waves, and the response amplitude operator (RAO) curve of ship motion is generally obtained by using regular waves or white noise irregular waves. A series of regular wave tests take a long time (about 60 minutes) and are difficult to capture the peak value of the RAO curve. White noise irregular wave takes a relatively short time (10-30 minutes), but may be affected by the pool wall reflection.

[0003] To solve the above problems, the seakeeping model test based on transient wave (focusing wave) package takes a very short time (1-2 minutes), which can significantly improve the test efficiency and avoid the influence of pool wall effect. However, when using transient wave to carry out model test, the maximum wave amplitude in the transient wave may have strong nonlinearity, and the RAO obtained by combining the traditional Fourier spectrum analysis method in the post-processing of test data may have large error. SUMMARY

[0004] The technical problem to be solved by the technical scheme of the present application is that when using transient wave to carry out model test, the maximum wave amplitude in the transient wave may have strong nonlinearity, which may result in large error of the obtained RAO.

[0005] In order to achieve the above technical purpose, the technical scheme of the present application provides a calculation method of ship motion response amplitude operator, comprising the following steps:

[0006] Simulate a transient wave package containing focusing wave and satisfying a specified wave spectrum;

[0007] Carry out seakeeping model test of the target ship type by using the transient wave package to obtain time series of the transient wave package and time series of the ship model oscillation motion;

[0008] Decompose the time series of the transient wave package and the time series of the ship model oscillation motion to obtain transient wave package eigenmode function and ship model oscillation motion eigenmode function, and process the transient wave package eigenmode function and the ship model oscillation motion eigenmode function by using transient wave package Hilbert marginal spectrum analysis model and ship model oscillation motion Hilbert marginal spectrum analysis model to obtain transient wave package Hilbert amplitude spectrum and ship model oscillation motion Hilbert amplitude spectrum;

[0009] According to the transient wave packet Hilbert amplitude spectrum and the ship model oscillation motion Hilbert amplitude spectrum, a transient wave packet Hilbert marginal spectrum and a ship model oscillation motion Hilbert marginal spectrum are obtained.

[0010] The ratio of the transient wave packet Hilbert marginal spectrum and the ship model oscillation motion Hilbert marginal spectrum is taken to obtain a ship oscillation motion response amplitude operator.

[0011] Preferably, based on the linear superposition principle, the specified wave spectrum is obtained by selecting the constituent wave frequencies at equal frequency intervals, and the specified wave spectrum is used for pool simulation to obtain the transient wave packet that focuses at a specified position and time.

[0012] Preferably, the time sequence of the ship model oscillation motion is a time history of the transient wave packet collected when there is no ship model in the pool.

[0013] Preferably, the time sequence of the transient wave packet and the time sequence of the ship model oscillation motion are decomposed by using an empirical mode decomposition method in Hilbert-Huang transformation to obtain a transient wave packet intrinsic mode function and a ship model oscillation motion intrinsic mode function, and the transient wave packet Hilbert amplitude spectrum and the ship model oscillation motion Hilbert amplitude spectrum are obtained by using a transient wave packet Hilbert marginal spectrum analysis model and a ship model oscillation motion Hilbert marginal spectrum analysis model according to the transient wave packet intrinsic mode function and the ship model oscillation motion intrinsic mode function by using Hilbert transformation in Hilbert-Huang transformation.

[0014] Preferably, the wave face elevation expression of the transient wave packet is:

[0015]

[0016] wherein N is the number of constituent waves of the focusing wave train, a ti is the amplitude of the constituent wave of the focusing wave train, k i is the wave number of the constituent wave of the focusing wave train, ω i is the frequency of the constituent wave of the focusing wave train, (x b , t b ) is the focusing position and time.

[0017] Preferably, the wave frequency ω i is as follows:

[0018] ω i = ω min + iδω

[0019] wherein ω min is the minimum frequency when the frequency spectrum is discretized.

[0020] Preferably, the wave amplitude a ti is as follows:

[0021]

[0022] delta omega = (omega max - omega min ) / N

[0023] wherein omega max is the maximum frequency of the spectrum discretization, and omega min is the minimum frequency of the spectrum discretization.

[0024] Preferably, the empirical mode decomposition method employs the following formula:

[0025]

[0026] wherein a i is the amplitude, and x(t) is the time series of the transient wave packet or the time series of the ship model oscillation motion.

[0027] Preferably, the transient wave packet Hilbert marginal spectrum and the ship model oscillation motion Hilbert marginal spectrum formula are as follows:

[0028]

[0029] wherein h(omega) is the transient wave packet Hilbert marginal spectrum or the ship model oscillation motion Hilbert marginal spectrum of the time-frequency distribution of the amplitude a i , H(omega, t) is the transient wave packet Hilbert amplitude spectrum or the ship model oscillation motion Hilbert amplitude spectrum, and T is the time span of x(t).

[0030] Preferably, the ratio of the transient wave packet Hilbert marginal spectrum and the ship model oscillation motion Hilbert marginal spectrum is processed through data smoothing.

[0031] The technical scheme of the present application proposes a calculation method of a ship motion response amplitude operator, generates a transient wave packet based on a specified wave spectrum, carries out a target ship type seakeeping model test using the transient wave packet, extracts a time series of the transient wave packet and a time series of a ship model oscillation motion, wherein the time series of the transient wave packet needs to be collected in the absence of a ship model in the pool, establishes a Hilbert marginal spectrum (MHS) analysis model based on Hilbert-Huang transform (HHT), inputs the time series of the transient wave packet and the time series of the ship model oscillation motion under the action of the transient wave packet into the MHS model, to obtain the marginal spectrum of the time series of the transient wave packet and the time series of the ship model oscillation motion, and applies the ratio of the marginal spectrum of the time series of the ship model oscillation motion and the time series of the transient wave packet to obtain the target ship oscillation motion RAO, thereby solving the problem of large error in the ship motion response amplitude operator curve caused by the strong nonlinearity of the maximum wave amplitude in the transient wave. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1A flow chart of a method for calculating a ship motion response amplitude operator provided by an embodiment of the present invention;

[0033] Figure 2 A schematic diagram of the time history of a transient Gaussian wave packet provided in an embodiment of the present invention;

[0034] Figure 3 A schematic diagram of the time history of the heave motion of a ship under the action of a transient Gaussian wave packet provided by an embodiment of the present invention;

[0035] Figure 4 A schematic diagram of the intrinsic mode function of the time history of a transient Gaussian wave packet provided by an embodiment of the present invention;

[0036] Figure 5 A schematic diagram of the eigenmode function of the time history of the heave motion of a ship under the action of a transient Gaussian wave packet provided by an embodiment of the present invention;

[0037] Figure 6 A schematic diagram comparing the Hilbert marginal spectrum and the Fourier amplitude spectrum of the time history of a transient Gaussian wave packet provided in an embodiment of the present invention;

[0038] Figure 7 A schematic diagram showing a comparison between the Hilbert marginal spectrum and the Fourier amplitude spectrum of the time history of the heave motion of a ship under the action of a transient Gaussian wave packet provided by an embodiment of the present invention;

[0039] Figure 8 Schematic diagram of the heave motion RAO obtained by using the ratio of the heave motion response and the Hilbert marginal spectrum of the transient Gaussian wave packet provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0040] Below in conjunction with specific embodiment, further set forth the present invention.Should be understood that these embodiments are only used to illustrate the present invention and are not used in limiting the scope of the present invention.In addition, should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall equally within the scope limited by the appended claims of the application.

[0041] like Figure 1 As shown, an embodiment of the present invention provides a method for calculating a ship motion response amplitude operator, which is applicable to nonlinear and non-stationary data, can reduce the error introduced by applying the fast Fourier transform (FFT) method to analyze transient waves, and can more accurately obtain the ship motion RAO result. The method is applied to the processing of ship seakeeping model test data based on transient waves, and includes the following steps:

[0042] Step 1: First, simulate the transient wave packet in the test pool based on the specified spectrum to obtain the transient wave packet that is focused at the specified position and time.

[0043] Based on the linear superposition principle, the transient wave packet containing the focusing wave and satisfying the specified wave spectrum is obtained by selecting the component wave frequency value with equal frequency interval, and the wave face elevation expression is:

[0044]

[0045] where N is the number of component waves of the focusing wave train, a ti is the amplitude of the component wave of the focusing wave train, k i is the wave number of the component wave of the focusing wave train, ω i is the circular frequency of the component wave of the focusing wave train, (x b , t b ) is the focusing position and time.

[0046] The component wave frequency is selected by the method of equal frequency interval, i.e.:

[0047] ω i = ω min + iδω

[0048] where ω min is the minimum frequency when the spectrum is discretized.

[0049] S(f) is selected as the Gaussian spectrum, and its expression is:

[0050]

[0051] ω = 2πf

[0052] where H s is the significant wave height, f is the wave frequency (Hz), f p is the spectral peak frequency, and σ is the shape factor.

[0053] For example, when H s = 0.05 m, f p = 0.714 Hz, and σ = 0.16, a transient Gaussian wave packet containing a focusing wave can be simulated in a towing tank as shown in FIG. 1. Figure 2

[0054] Step 2, the transient wave packet is used to carry out the seakeeping model test of the target ship type, and the time series of the transient wave packet and the time series of the ship model oscillation motion are obtained as the time history of the ship motion under the action of the transient wave packet. The time series of the transient wave packet is the time history of the transient wave packet collected when there is no ship model in the tank.

[0055] The amplitude of the above wave train can be determined according to a specific sea wave spectrum, and the transient wave packet is simulated in the test tank by the above method and the seakeeping model test of the ship is carried out to obtain the time history of the ship motion under the action of the transient wave packet.

[0056] ​The focused wave train consists of wave amplitude a ti The calculation formula is as follows:

[0057]

[0058] δω=(ω max -ω min ) / N

[0059] Among them, ω max is the maximum frequency when the spectrum is discrete, ω min is the minimum frequency when the spectrum is discretized.

[0060] For example, based on Figure 2 The transient Gaussian wave packet shown contains a focused wave. A model test was carried out in a towing tank under the action of the transient Gaussian wave packet, and the following results were obtained: Figure 3 The time history of the heave motion response of the ship model is shown.

[0061] Step 3: Decompose the transient wave packet history and the corresponding ship motion history using the Empirical Mode Decomposition (EMD) method within the Hilbert-Huang Transform (HHT) to obtain the Gaussian wave packet and the intrinsic mode functions of the ship motion. These intrinsic mode functions are then Hilbert transformed to obtain the Hilbert marginal spectrum (MHS) analysis model (the time-frequency distribution of the amplitude) of the transient wave packet and the ship motion. The Hilbert-Huang Transform includes both EMD and the Hilbert Transform.

[0062] Among them, empirical mode decomposition can express any time series x(t) as the sum of n intrinsic mode functions with different time scales. That is, empirical mode decomposition is used to decompose the transient wave packet or ship motion history x(t) into the sum of n intrinsic mode functions (IMFs) with different time scales. The formula is as follows:

[0063]

[0064] Among them, r(t) is the residual function of the screening process, which represents the average trend of x(t).

[0065] The analytical signal can be constructed as:

[0066] Z i (t) = C i (t)+jH[C i (t)]

[0067] in, C i Hilbert transform of (t).

[0068] Z i (t) can also be expressed as The amplitude a i, phase θ i are calculated by The instantaneous frequency is defined as

[0069]

[0070] For example, the Hilbert-Huang transform of a transient Gaussian wave packet and a ship's heave time history is performed. First, the intrinsic mode functions of the transient Gaussian wave packet, as shown in FIG. 2A, and the intrinsic mode functions of the ship's heave time history, as shown in FIG. 2B, are obtained by empirical mode decomposition. Then, the Hilbert marginal spectrum of the transient Gaussian wave packet, as shown in FIG. 2C, and the Hilbert marginal spectrum of the ship's heave time history, as shown in FIG. 2D, are obtained by Hilbert transform. Figure 4 Figure 5 Figure 6 Figure 7

[0071] Step 4, input the time series of the transient wave packet and the time series of the ship's heave motion into the Hilbert marginal spectrum (MHS) analysis model of the transient wave packet and the ship's motion.

[0072] The time-frequency distribution of the amplitude is the Hilbert amplitude spectrum H(ω, t). Using the Hilbert amplitude spectrum H(ω, t), the Hilbert marginal spectrum is defined by integrating the Hilbert amplitude spectrum:

[0073]

[0074] where the Hilbert amplitude spectrum H(ω, t) is the time-frequency distribution of the amplitude a i , the above equation can be regarded as a Fourier expansion with time-varying amplitude and frequency, and T is the time span of x(t).

[0075] Step 5, finally, the ship's heave motion RAO is obtained by using the ratio of the Hilbert marginal spectrum of the ship's motion to the Hilbert marginal spectrum of the transient wave packet. The ratio can be further processed by data smoothing.

[0076] For example, the ship's heave motion response RAO, as shown in FIG. 2E, is obtained by the ratio of the motion response marginal spectrum to the transient Gaussian wave packet marginal spectrum. Figure 8

[0077] ​​​​​​In summary, the application provides a ship motion response amplitude operator calculation method, which is applied to data processing of ship seakeeping model test based on transient wave packets, including: step S1, generating a transient wave packet based on a specified wave spectrum; step S2, carrying out a target ship type seakeeping model test by using the transient wave packet, and extracting a time sequence of the transient wave packet and a time sequence of ship model oscillation motion, wherein the time sequence of the transient wave packet is collected when there is no ship model in the pool; step S3, establishing a Hilbert marginal spectrum (MHS) analysis model based on Hilbert-Huang transform (HHT); step S4, inputting the time sequence of the transient wave packet and the time sequence of the ship model oscillation motion under the action of the transient wave packet into the MHS model to obtain the marginal spectrum of the time sequence of the transient wave packet and the time sequence of the ship model oscillation motion; and step S5, obtaining the target ship oscillation motion RAO by using the ratio of the time sequence of the ship model oscillation motion and the marginal spectrum of the time sequence of the transient wave packet.

[0078] Beneficial effects: the ship motion response amplitude operator calculation method provided by the application can process the nonlinear influence of the transient wave packet, and can be applied to the processing of seakeeping model test data based on various transient wave packets.

[0079] Through the description and the drawings, the typical embodiments of the specific structure of the specific embodiment are given, and other conversions can be made based on the spirit of the application. Although the above application proposes the existing preferred embodiment, however, these contents are not as limitations.

[0080] For those skilled in the art, after reading the above description, various changes and modifications will undoubtedly be apparent. Therefore, the appended claims should be considered as covering all changes and modifications within the true intent and scope of the application. Any and all equivalent ranges and contents within the scope of the claims should be considered as still within the intent and scope of the application.

Claims

1. A method for calculating a ship motion response amplitude operator, characterized in that: The following steps are involved: Simulate transient wave packets containing focused waves and satisfying specified wave spectra; The transient wave packet is used to carry out the seakeeping model test of the target ship type, and the time series of the transient wave packet and the time series of the ship model's swaying motion are obtained; The time series of the transient wave packet and the time series of the ship model swaying motion are decomposed to obtain the transient wave packet eigenmode function and the ship model swaying motion eigenmode function. The transient wave packet eigenmode function and the ship model swaying motion eigenmode function are processed using the transient wave packet Hilbert marginal spectrum analysis model and the ship model swaying motion Hilbert marginal spectrum analysis model to obtain the transient wave packet Hilbert amplitude spectrum and the ship model swaying motion Hilbert amplitude spectrum; According to the Hilbert amplitude spectrum of the transient wave packet and the Hilbert amplitude spectrum of the ship model swaying motion, the Hilbert marginal spectrum of the transient wave packet and the Hilbert marginal spectrum of the ship model swaying motion are obtained; The amplitude operator of the ship swaying motion response is obtained by taking the ratio of the Hilbert marginal spectrum of the transient wave packet and the Hilbert marginal spectrum of the ship model swaying motion.

2. The method for calculating the ship motion response amplitude operator according to claim 1, wherein: Based on the principle of linear superposition, the specified wave spectrum is obtained by selecting component wave frequencies at equal frequency intervals. A test water tank simulation is performed based on the specified wave spectrum to obtain the transient wave packet that is focused at the specified position and time.

3. The method for calculating the ship motion response amplitude operator according to claim 1, wherein: The time series of the ship model swaying motion is the time history of the transient wave packet collected when there is no ship model in the pool.

4. The method for calculating the ship motion response amplitude operator according to claim 1, wherein: The empirical mode decomposition method in the Hilbert-Huang transform is used to decompose the time series of the transient wave packet and the time series of the ship model swaying motion to obtain the transient wave packet eigenmode function and the ship model swaying motion eigenmode function. The Hilbert transform in the Hilbert-Huang transform is used to process the transient wave packet eigenmode function and the ship model swaying motion eigenmode function using the transient wave packet Hilbert marginal spectrum analysis model and the ship model swaying motion Hilbert marginal spectrum analysis model to obtain the transient wave packet Hilbert amplitude spectrum and the ship model swaying motion Hilbert amplitude spectrum.

5. The method for calculating the ship motion response amplitude operator according to claim 1, wherein: The wavefront rise expression of the transient wave packet is: Where N is the number of waves in the focused wave train, a ti is the amplitude of the focused wave train, k i is the wave number of the focused wave train, ω i is the wave frequency of the focused wave train, (x b ,t b ) is the focus position and time.

6. The method for calculating the ship motion response amplitude operator according to claim 5, characterized in that: The wave frequency ω i The formula is as follows: oh i =ω min +here Among them, ω min is the minimum frequency when the spectrum is discretized.

7. The method for calculating the ship motion response amplitude operator according to claim 5, characterized in that: The wave amplitude a ti The formula is as follows: here=(oh max -oh min ) / N Among them, ω max is the maximum frequency when the spectrum is discrete, ω min is the minimum frequency when the spectrum is discretized.

8. The method for calculating the ship motion response amplitude operator according to claim 1, wherein: The formula used in the empirical mode decomposition method is as follows: Among them, a i is the amplitude, and x(t) is the time series of transient wave packets or the time series of the swaying motion of the ship model.

9. The method for calculating the ship motion response amplitude operator according to claim 8, wherein: The formulas for the Hilbert marginal spectrum of the transient wave packet and the Hilbert marginal spectrum of the ship model swaying motion are as follows: Where h(ω) is the amplitude a i The time-frequency distribution of the transient wave packet Hilbert marginal spectrum or the ship model rocking motion Hilbert marginal spectrum, H(ω,t) is the transient wave packet Hilbert amplitude spectrum or the ship model rocking motion Hilbert amplitude spectrum, and T is the time span of x(t).

10. The method for calculating the ship motion response amplitude operator according to claim 1, wherein: The ratio of the Hilbert marginal spectrum of the transient wave packet to the Hilbert marginal spectrum of the ship model swaying motion is processed by data smoothing.

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