Method for determining equivalent design wave of ship wave load under six-level sea condition

Abstract

The invention discloses a ship wave load equivalent design wave determination method under a six-level sea condition, and relates to the field of ship structure safety, and the method comprises the following steps: regarding a ship body as a variable cross-section beam, for a ship with a certain navigational speed, calculating a wave load transfer function at the section of the ship body beam under different wave conditions, the wave conditions comprise different wave direction angles and different circular frequencies of incident waves; based on the wave load transfer function at the section of the ship body beam, calculating wave load short-term forecast extreme values under different wave direction angles and different zero-crossing periods within a sex-level sea condition sense wave height range; a maximum value is selected from all the short-term forecast extreme values of the wave loads, equivalent design wave parameters of the wave loads under the six-level sea condition are determined on the basis of the maximum value, the equivalent design waves are sine regular waves, and the parameters comprise the wave amplitude, the circular frequency and the wave direction. The research on the load suffered by the ship body under the random wave is converted into the research on the ship body load under the regular wave, so that the method has important significance on follow-up research on the ship body load level and structural safety.

Description

Technical Field

[0001] The invention relates to the field of ship structure safety, in particular to a method for determining an equivalent design wave of a ship wave load under level six sea conditions. Background Art

[0002] The significant wave height range of level 6 sea conditions is 4m to 6m, which belongs to the medium wave level and is a sea condition with a relatively high frequency in the ocean. The structural safety of the hull when sailing under medium and high wave levels is a problem that ship designers are more concerned about. According to the first principle, when evaluating the safety of the hull structure, it is necessary to clarify the environmental external loads suffered by the hull. The wave load, that is, the water pressure of the waves on the outer plate of the hull, is the main external load suffered by the hull. It is natural to clarify the wave external loads suffered by the hull under level 6 sea conditions and then carry out the safety analysis of the hull structure.

[0003] However, the current hull structure design specifications do not provide for the wave loads that the hull is subject to under sea conditions level VI. The hull structure design specifications generally stipulate the hull wave design load value in the chapter on total longitudinal strength, but this design load corresponds to the load that the ship is subject to throughout its entire service life cycle and is not applicable to a specific sea condition encountered by the ship (such as sea conditions level VI). The characteristic wave loads that the hull is subject to under sea conditions level VI are significantly smaller than the design loads in the specifications, so it is inappropriate to use the design loads in the specifications when evaluating the safety of the hull structure under sea conditions level VI, which will significantly overestimate the hull structure response. Therefore, in order to accurately evaluate the hull structure response under sea conditions level VI, it is necessary to clarify the characteristic values ​​and calculation methods of the hull wave loads under sea conditions level VI. Summary of the invention

[0004] In view of the above problems and technical requirements, the inventors have proposed a method for determining the equivalent design wave of ship wave loads under level 6 sea conditions. The technical solution of the present invention is as follows:

[0005] A method for determining an equivalent design wave of a ship wave load under level 6 sea conditions comprises the following steps:

[0006] The hull is regarded as a variable cross-section beam. For a ship with a certain speed, the wave load transfer function at the hull beam section under different wave conditions is calculated. The wave conditions include different wave angles and different circular frequencies of the incident wave.

[0007] Based on the wave load transfer function at the hull beam section, the short-term forecast extreme values ​​of wave loads at different wave angles and different zero-crossing periods within the significant wave height range of the sixth sea state are calculated;

[0008] A maximum value is selected from all the short-term forecast extreme values ​​of wave loads, and the equivalent design wave parameters of wave loads under level 6 sea conditions are determined based on the maximum value, where the equivalent design wave is a regular sine wave, and the parameters include amplitude, circular frequency and wave direction.

[0009] A further technical solution is to calculate the wave load transfer function at the hull girder section under different wave conditions, including:

[0010] The hull beam is cut into sections using an imaginary section, and the cut hull beam sections are balanced under the action of gravity / gravity moment, wave force / wave moment, inertia force / inertia moment and wave load at the hull beam section. The wave load at the hull beam section includes forces and moments in three directions along the xyz coordinate axes;

[0011] Under each wave condition, the wave force and wave moment caused by seawater pressure on the hull beam section are calculated, as well as the inertia force and inertia moment caused by the mass of the hull beam section. The inertia force and inertia moment are substituted into the force / moment balance formula together with the gravity and gravity moment of the hull beam section to obtain the wave load at the hull beam section under different wave conditions.

[0012] The wave loads per unit wave amplitude are calculated as the wave load transfer function at the hull girder section.

[0013] A further technical solution is to calculate the wave force and wave moment caused by seawater pressure on the hull beam sections, including:

[0014] The wet surface of the hull is discretized into grids to obtain the velocity potential at the center of each grid unit on the wet surface of the hull;

[0015] Substituting the velocity potential into the Bernoulli equation, the seawater pressure at the center of each grid cell is obtained;

[0016] Then the force and moment of seawater pressure on the hull beam section are:

[0017]

[0018] Among them, F and M are the wave force and wave moment caused by seawater pressure, S is the wet surface of the hull, n is the normal vector of the surface element of the hull wet surface, p is the seawater pressure at the center of each grid on the wet surface of the hull, and r is the bending moment vector.

[0019] A further technical solution is to calculate the inertia force and inertia moment caused by the mass of the hull beam segment, including:

[0020] Assuming the hull beam is a rigid body, use Newton's second law to establish the equation of motion:

[0021]

[0022] Where m is the hull beam segment mass matrix, are the segment center of mass velocity and displacement, respectively, and I is the segment moment of inertia of the hull beam;

[0023] The wave force caused by the calculated seawater pressure on the hull beam section With wave moment Substituting into the equation of motion, we can find the linear acceleration of the segmented center of mass: and angular acceleration

[0024] The hull beam segment mass and segment centroid linear acceleration Multiply the inertia force caused by the mass of the hull beam segment by the inertia moment of the hull beam segment and the angular acceleration of the segment center of mass Multiplying them together gives the moment of inertia caused by the mass of the hull beam section.

[0025] A further technical solution is to obtain the velocity potential at the center of each grid unit on the wet surface of the hull, including:

[0026] The velocity potential at the center of each grid unit on the wet surface of the hull is the incident velocity potential φ II , diffraction velocity potential φ D and the radiation velocity potential φ R sum;

[0027] Among them, the incident velocity potential φ I The expression is:

[0028]

[0029] Where g is the acceleration of gravity, A is the incident wave amplitude, (x, y, z) is the field point coordinates, H is the sea depth, ω is the incident wave circular frequency, β is the incident wave angle, and k is the wave number;

[0030] Radiation velocity potential φ R Decomposed into components on 6 degrees of freedom:

[0031]

[0032] In the formula, ξ j Represents the linear displacement along the three coordinate axes xyz, and the angular displacement around the three coordinate axes; φ j represents the radiation velocity potential per unit displacement;

[0033] Set the radiation velocity potential and diffraction velocity potential φ under unit displacement respectively D The boundary conditions satisfied are used to solve the diffraction velocity potential φ at the center of each grid cell on the wet surface of the hull D and the radiation velocity potential φ R .

[0034] A further technical solution is that when calculating the wave load at the hull beam section:

[0035] The cutting position is in the middle of the hull beam. Under each wave condition, the y-axis component of the wave moment caused by the sea water pressure on the hull beam section is calculated, as is the y-axis component of the inertia moment caused by the mass of the hull beam section. These are substituted into the moment balance formula together with the y-axis component of the gravity moment of the hull beam section to obtain the vertical moment at the middle section of the hull beam under different wave conditions as the wave load.

[0036] Its further technical solution is to calculate the short-term forecast extreme value of wave load at different wave angles and different zero-crossing periods within the significant wave height range of level 6 sea conditions based on the wave load transfer function at the hull beam section, including:

[0037] Based on the wave load transfer function at the hull beam section, the wave load response spectrum under different wave direction angles and different zero-crossing periods within the significant wave height range of the sixth sea state is calculated:

[0038] S response =RAO 2 ·S wave

[0039] In the formula, S response is the wave load response spectral density at the hull girder section, RAO is the wave load transfer function at the hull girder section, S wave is the significant wave height H in the specified sea state level 6 s and zero-crossing period T z Wave spectral density under wave action;

[0040] The short-term forecast extreme value of wave load under level 6 sea conditions is calculated based on the wave load response spectrum.

[0041] Its further technical solution is to calculate the short-term forecast extreme value of wave load under level 6 sea conditions based on the wave load response spectrum, including:

[0042] The wave load in the short-term sixth-order sea state follows the Rayleigh distribution, so the wave load at the hull beam section has a significant value M of one-third. sig The expression is:

[0043]

[0044] Where m0 is the 0th order moment of the wave load response spectrum, expressed as:

[0045]

[0046] Where ω is the incident wave circular frequency; then the short-term forecast extreme value of wave load under level 6 sea condition M max for:

[0047] M max =2.12M sig .

[0048] Its further technical solution is that the wave spectrum density selects the dual-parameter PM spectrum, which is expressed as:

[0049]

[0050] Where ω is the incident wave circular frequency.

[0051] A further technical solution is to determine the equivalent design wave parameters of the wave load under the sixth level sea condition based on the maximum value, including:

[0052] The wave direction angle corresponding to the maximum value is the equivalent design wave direction;

[0053] The circular frequency at the peak of the wave load transfer function corresponding to the maximum value is the equivalent design wave circular frequency;

[0054] The ratio of the maximum value to the corresponding peak value of the wave load transfer function is the equivalent design wave amplitude.

[0055] The beneficial technical effects of the present invention are:

[0056] In this method, the wave load transfer function at the hull beam section under different wave conditions is first calculated, so as to calculate the short-term forecast extreme values ​​of wave loads at different wave direction angles and different zero-crossing periods within the significant wave height range of level 6 sea conditions, and select a maximum value from them to determine the equivalent design wave parameters under level 6 sea conditions. This application uses a regular wave model to describe the waves. Regular waves are simple sinusoidal waves that can be defined by parameters such as amplitude, circular frequency, wave direction, and phase. By constructing a regular wave to simulate the most unfavorable state suffered by the hull, the study of the load problem suffered by the hull under random waves is converted into the study of the hull load problem under regular waves, which can not only simplify the calculation, but also has important significance for the subsequent research on the hull load level and structural safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 This is a flow chart of a method for determining the equivalent design wave of a ship wave load under level 6 sea conditions provided by this application.

[0058] Figure 2 It is a schematic diagram of hull girder section force and moment provided in this application.

[0059] Figure 3 It is the vertical moment M of the midship section at a hull speed of 7.6 m / s and a wave direction of 180° provided by this application. y Transfer function diagram of .

[0060] Figure 4 is the significant wave height H provided by this application s =6m, zero crossing period T z = Wave spectrum density diagram under 10s.

[0061] Figure 5 is the significant wave height H provided by this application s =6m, zero crossing period T z = Vertical moment M of midship section at 10s y Response spectrum of . DETAILED DESCRIPTION

[0062] The specific implementation of the present invention will be further described below in conjunction with the accompanying drawings.

[0063] The waves in the actual sea are often irregular, and an irregular wave model should be used to simulate the waves. In order to simplify the calculation, this application provides an equivalent design wave method, which is of great significance to define a simple sine regular wave to describe the wave load suffered by the hull under the irregular waves in the sixth level sea condition. Please refer to Figure 1 As shown, an embodiment of the present application provides a method for determining the equivalent design wave of a ship wave load under level 6 sea conditions, which specifically includes the following contents:

[0064] Step 1: Consider the hull as a variable cross-section beam. For a ship with a certain speed, calculate the wave load transfer function at the hull beam section under different wave conditions. The specific calculation method includes: using an imaginary section to divide the hull beam, and the divided hull beam sections are balanced under the action of gravity / gravity moment, wave force / wave moment, inertia force / inertia moment and wave load at the hull beam section (D'Alembert principle):

[0065] F fluid +F grav +F secLoad +F I =0 (1)

[0066] M fluid +M grav +M secLoad +M I =0 (2)

[0067] Among them: F fluid 、M fluid are the wave force and wave moment caused by seawater pressure on the hull beam segment; F grav 、M grav are the hull beam segment gravity and gravity moment respectively; F secLoad 、M secLoad The wave load on the hull girder section caused by another part of the hull girder segment includes the force F in three directions along the xyz coordinate axis. x 、F y and F z and moment (bending moment) M x 、M y and Mz , 6 section forces and bending moments, called hull girder section loads or wave loads, such as Figure 2 As shown; F I 、M I are the inertia force and inertia moment caused by the mass of the hull beam segment respectively.

[0068] Under each wave condition, calculate the wave force F caused by sea water pressure on the hull beam section fluid and wave moment M fluid , including: firstly, the wet surface of the hull is discretized into grids to obtain the velocity potential at the center of each grid unit on the wet surface of the hull, which is the incident velocity potential φ I , diffraction velocity potential φ D and the radiation velocity potential φ R When the incident wave is an Airy wave (sine regular wave), the incident velocity potential φ I The expression is:

[0069]

[0070] Where g is the acceleration of gravity, in units of meters per second squared (m / s^2), A is the incident wave amplitude, in units of meters (m); (x, y, z) are the field point coordinates, H is the sea depth, in units of meters (m), ω is the incident wave circular frequency, in units of radians per second (rad / s), β is the incident wave angle, k is the wave number, and when the sea is of infinite depth, the relationship between the wave number k and the wave circular frequency ω is:

[0071] Diffraction velocity potential φ D The boundary conditions satisfied are:

[0072]

[0073] Where n represents the normal direction of the wet surface of the hull (the surface below the waterline of the hull), represents the partial derivative along the normal direction of the hull wet surface, S body represents the wetted surface of the hull, S bottom represents the seabed boundary condition, R represents the infinite radiation control surface, represents the radial partial derivative along the control surface.

[0074] Radiation velocity potential φ R Decomposed into components on 6 degrees of freedom:

[0075]

[0076] In the formula, ξ jIt represents the linear displacement along the three coordinate axes xyz (j=1~3) and the angular displacement around the three coordinate axes (j=4~6). j represents the radiation velocity potential under unit displacement, and the boundary conditions it satisfies are:

[0077]

[0078] The diffraction velocity potential φ at the center of each grid D and the radiation velocity potential φ under unit displacement j All satisfy equations (4) and (6), with φ D and φ j As an unknown number, the equation can be established to solve the diffraction velocity potential φ at the center of each grid unit on the wet surface of the hull D and the radiation velocity potential φ R . The incident velocity potential φ I It is related to factors such as the location of the field point and the amplitude of the incident wave, which are known, so the total velocity potential at the center of each grid on the wet surface of the hull can be obtained.

[0079] Substitute the total velocity potential Φ into the Bernoulli equation to obtain the seawater pressure at the center point of each grid unit on the wet surface of the hull:

[0080]

[0081] Where ρ is the density of seawater.

[0082] Then the force and moment of seawater pressure on the hull beam section are:

[0083]

[0084] Among them, F and M are the wave force and wave moment caused by sea water pressure, S is the wet surface of the hull, n is the surface element normal vector of the hull wet surface, and r is the bending moment vector.

[0085] Next, under each wave condition, the inertial force F caused by the mass of the hull beam section needs to be calculated. I and the moment of inertia M I , including: Assuming the hull beam is a rigid body, use Newton's second law to establish the equation of motion:

[0086]

[0087] Where m is the hull beam segment mass matrix, are the velocity and displacement of the segment center of mass, and I is the segment moment of inertia of the hull beam. The wave force caused by the calculated seawater pressure on the hull beam segment With wave moment Substituting into the equation of motion (9), we can find the linear acceleration of the segmented center of mass: and angular acceleration

[0088] The hull beam segment mass and segment centroid linear acceleration Multiply them to get the inertial force F caused by the mass of the hull beam segment I , the moment of inertia of the hull beam segment and the angular acceleration of the segment center of mass rotation Multiply them to get the inertia moment M caused by the mass of the hull beam segment I The wave force F calculated according to formula (8) is fluid and wave moment M fluid , inertial force F I and the moment of inertia M I , and the hull girder segment gravity F grav and gravity moment M grav Substituting them into the force / moment equilibrium equation (1) / (2), we can obtain the wave load F at the hull beam section under different wave conditions. secLoad With M secLoad Finally, the wave load under unit wave amplitude is calculated as the wave load transfer function at the hull beam section, with the force F at the hull beam section secLoad For example, its transfer function RAO is expressed as:

[0089]

[0090] When a ship is actually sailing, the incident wave angle β, incident wave circular frequency ω, incident wave amplitude A, and ship sailing speed V will affect the hull beam section load. At the same time, along the length of the ship, from the bow to the stern, the hull beam section load at different sections is also different. For a conventional hull, the vertical moment M at the middle section of the hull is y It is particularly important for the safety of the hull structure and is the most concerned by the hull structure designer. Therefore, the vertical moment M at the middle section of the hull beam is generally y In this embodiment, the above method is used to calculate the y-axis component of the wave moment caused by the seawater pressure on the hull beam section under each wave condition. And calculate the y-axis component of the inertia moment caused by the mass of the hull beam segment The y-axis component of the girder segment gravity moment Substituting them into the moment equilibrium equation (2), we can obtain the vertical moment M at the middle section of the hull beam under different wave conditions. y As wave load. For a ship with a certain speed, multiple incident wave directions (multiple wave directions β from 0° to 180°), multiple incident wave frequencies ω, and the vertical moment M at the middle section of the hull beam are carried out. y The hull beam load transfer function is calculated. This embodiment gives the vertical moment M when the hull speed is 7.6 m / s and the wave direction is 180°.y The transfer function diagram is as follows Figure 3 As shown in the figure, the horizontal axis is the incident wave circular frequency ω (unit: rad / s), and the vertical axis is the vertical moment M at the middle section of the hull beam. y Transfer function RAO.

[0091] Step 2: Based on the wave load transfer function at the hull beam section, calculate the short-term forecast extreme value of wave load at different wave direction angles (0°~180°) and different zero-crossing periods within the range of significant wave height of level 6 sea conditions. The specific calculation method includes: firstly, based on the wave load transfer function at the hull beam section, calculate the wave load response spectrum under different wave direction angles and different zero-crossing periods within the range of significant wave height of level 6 sea conditions:

[0092] S response =RAO 2 ·S wave (11)

[0093] In the formula, S response is the wave load at the middle section of the hull girder (vertical moment M y ) response spectrum density, RAO is the vertical moment M at the middle section of the hull beam y Transfer function. S wave is the significant wave height H in the specified sea state level 6 s and zero-crossing period T z The wave spectrum density under the action of waves, in this embodiment, S wave Select the two-parameter PM spectrum, expressed as:

[0094]

[0095] The significant wave height range of irregular waves in the sixth sea condition is 4m to 6m. In order to ensure the safety of the calculation results, the upper limit of the significant wave height of the sixth sea condition is 6m, and the zero crossing period range is 5s to 18s. The wave combination of the sixth sea condition is shown in Table 1. s =6m, zero crossing period T z = The wave spectrum density diagram under the action of 10s wave is as follows Figure 4 As shown in the figure, the vertical moment M in the ship corresponding to the wave spectrum density is y The response spectrum density plot is as follows Figure 5 shown.

[0096] Table 1 Wave combinations for level 6 sea conditions

[0097]

[0098] Secondly, the short-term forecast extreme value of wave load under level 6 sea condition is calculated based on the wave load response spectrum, including: the wave load under level 6 sea condition in the short term is generally considered to obey Rayleigh distribution, then the wave load at the hull beam section (vertical moment M y ) has a value of M sig (Single amplitude) expression is:

[0099]

[0100] Where m0 is the wave load (vertical moment M y ) The zero-order moment of the response spectrum is expressed as:

[0101]

[0102] Then the wave load (vertical moment M) under the sixth sea condition is y ) Short-term forecast extreme value M max M sig 2.12 times:

[0103] M max =2.12M sig (15)

[0104] Therefore, the ship is sailing at a specified speed of 7.6 m / s in the sixth sea state, and the vertical moment M in the ship under different wave directions (0°~180° selected at a certain interval) is calculated. y Transfer function RAO. Select dual parameter PM spectrum, significant wave height H s The vertical moment M in the ship under different wave directions and different zero-crossing periods is calculated. y Short-term extreme value M max , as shown in Table 2:

[0105] Table 2 Significant wave height H at speed 7.6 m / s and sea state level 6 s = Vertical moment M corresponding to different wave directions and zero-crossing periods under 6m y Short-term forecast extremes

[0106]

[0107]

[0108] Step 3: Select a maximum value from all short-term forecast extreme values ​​of wave loads, and determine the equivalent design wave parameters under level 6 sea conditions based on the maximum value, where the equivalent design wave is a regular sine wave, and the parameters include amplitude, circular frequency and wave direction.

[0109] From Table 2, we can see that when the wave direction is 180 degrees and the zero crossing period is 7s, the short-term extreme value of the vertical moment M maxThe maximum is 1.15E+07N.m. The wave direction angle corresponding to this maximum value is the equivalent design wave direction, so the wave direction of 180° is the dangerous wave direction of vertical moment. The wave load corresponding to this maximum value (vertical moment M y ) The circular frequency ω at the peak of the transfer function is the equivalent design wave circular frequency, such as Figure 3 As shown, the vertical moment M y The response is maximum when the wave direction is 180° and the incident wave circular frequency is 1.1rad / s, and the maximum RAO value is 2.66E+06N.m. The ratio of this maximum value to the corresponding peak value of the wave load transfer function is the equivalent design wave amplitude:

[0110]

[0111] Where A is the equivalent design wave amplitude, M max H s =6m, zero crossing period T z The vertical moment M when the wave direction is 180 degrees and the wave direction is 7s y Short-term extremes, RAO max is the downward vertical moment M of the dangerous wave y The peak value of the transfer function response.

[0112] The vertical moment M in the ship under the sixth sea condition is y The equivalent design wave parameters are shown in Table 3:

[0113] Table 3 Vertical moment M in the ship y Equivalent design wave parameters

[0114]

[0115] The above is only a preferred embodiment of the present application, and the present invention is not limited to the above embodiments. It is understood that other improvements and changes directly derived or associated by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included in the protection scope of the present invention.

Claims

1. A method for determining the equivalent design wave of ship wave load under level 6 sea conditions, characterized in that: The method comprises: The hull is regarded as a variable cross-section beam. For a ship with a certain speed, the wave load transfer function at the hull beam section under different wave conditions is calculated. The wave conditions include different wave angles and different circular frequencies of the incident wave. Based on the wave load transfer function at the hull beam section, the short-term forecast extreme values ​​of wave loads at different wave direction angles and different zero-crossing periods within the significant wave height range of level 6 sea conditions are calculated; A maximum value is selected from all extreme values ​​of short-term wave load forecasts, and the equivalent design wave parameters of the wave load under level 6 sea conditions are determined based on the maximum value, wherein the equivalent design wave is a regular sine wave, and the parameters include wave amplitude, circular frequency and wave direction.

2. The method for determining the equivalent design wave of ship wave load under level 6 sea conditions according to claim 1 is characterized in that: The calculation of the wave load transfer function at the hull girder section under different wave conditions includes: The hull beam is cut into sections using an imaginary section, and the cut hull beam sections are balanced under the action of gravity / gravity moment, wave force / wave moment, inertia force / inertia moment and wave load at the hull beam section, wherein the wave load at the hull beam section includes forces and moments in three directions along the xyz coordinate axes; Under each wave condition, the wave force and wave moment caused by seawater pressure on the hull beam section are calculated, as well as the inertia force and inertia moment caused by the mass of the hull beam section. The inertia force and inertia moment are substituted into the force / moment balance formula together with the gravity and gravity moment of the hull beam section to obtain the wave load at the hull beam section under different wave conditions. The wave loads per unit wave amplitude are calculated as the wave load transfer function at the hull girder section.

3. The method for determining the equivalent design wave of ship wave load under level 6 sea conditions according to claim 2 is characterized in that: The calculation of wave forces and wave moments caused by seawater pressure on the hull beam sections includes: The wet surface of the hull is discretized into grids to obtain the velocity potential at the center of each grid unit on the wet surface of the hull; Substituting the velocity potential into the Bernoulli equation, the seawater pressure at the center point of each grid cell is obtained; Then the force and moment of seawater pressure on the hull beam section are: Among them, F and M are the wave force and wave moment caused by the seawater pressure, S is the wet surface of the hull, n is the normal vector of the surface element of the hull wet surface, p is the seawater pressure at the center of each grid on the wet surface of the hull, and r is the bending moment vector.

4. The method for determining the equivalent design wave of ship wave load under level 6 sea conditions according to claim 2 is characterized in that: The calculation of the inertia force and inertia moment caused by the mass of the hull beam sections includes: Assuming the hull beam is a rigid body, use Newton's second law to establish the equation of motion: Where m is the hull beam segment mass matrix, are the segment center of mass velocity and displacement, respectively, and I is the segment moment of inertia of the hull beam; The wave force caused by the calculated seawater pressure on the hull beam section With wave moment Substituting into the equation of motion, we can find the linear acceleration of the segmented center of mass: and angular acceleration The mass of the hull beam segment and the linear acceleration of the segment center of mass The inertial force caused by the mass of the hull beam segment is obtained by multiplying the inertial force of the hull beam segment and the angular acceleration of the segment center of mass rotation. Multiplying them together gives the moment of inertia caused by the mass of the hull beam section.

5. The method for determining the equivalent design wave of ship wave load under level 6 sea conditions according to claim 3 is characterized in that: The step of obtaining the velocity potential at the center of each grid unit on the wet surface of the hull comprises: The velocity potential at the center of each grid unit on the wet surface of the hull is the incident velocity potential φ II , diffraction velocity potential φ D and the radiation velocity potential φ R sum; Wherein, the incident velocity potential φ I The expression is: Where g is the acceleration of gravity, A is the incident wave amplitude, (x, y, z) is the field point coordinates, H is the sea depth, ω is the incident wave circular frequency, β is the incident wave angle, and k is the wave number; The radiation velocity potential φ R Decomposed into components on 6 degrees of freedom: In the formula, ξ j Represents the linear displacement along the three coordinate axes xyz, and the angular displacement around the three coordinate axes; φ j represents the radiation velocity potential per unit displacement; Set the radiation velocity potential and the diffraction velocity potential φ under the unit displacement respectively D The boundary conditions satisfied are used to solve the diffraction velocity potential φ at the center of each grid cell on the wet surface of the hull D and the radiation velocity potential φ R .

6. The method for determining the equivalent design wave of ship wave load under level 6 sea conditions according to claim 2 is characterized in that: When calculating the wave loads at the hull girder section: The cutting position is in the middle of the hull beam. Under each wave condition, the y-axis component of the wave moment caused by the sea water pressure on the hull beam section is calculated, as is the y-axis component of the inertia moment caused by the mass of the hull beam section. These are substituted into the moment balance formula together with the y-axis component of the gravity moment of the hull beam section to obtain the vertical moment at the middle section of the hull beam under different wave conditions as the wave load.

7. The method for determining the equivalent design wave of ship wave load under level 6 sea conditions according to claim 1 is characterized in that: Based on the wave load transfer function at the hull beam section, the short-term forecast extreme values ​​of wave loads at different wave direction angles and different zero-crossing periods within the significant wave height range of level 6 sea conditions are calculated, including: Based on the wave load transfer function at the hull beam section, the wave load response spectrum under different wave direction angles and different zero-crossing periods within the significant wave height range of level 6 sea conditions is calculated: S response =RAO 2 ·S wave In the formula, S response is the wave load response spectral density at the hull girder section, RAO is the wave load transfer function at the hull girder section, S wave is the significant wave height H in the specified sea state level 6 s and zero-crossing period T z Wave spectral density under wave action; The short-term forecast extreme value of the wave load under the sixth level sea condition is calculated based on the wave load response spectrum.

8. The method for determining the equivalent design wave of ship wave load under level 6 sea conditions according to claim 7 is characterized in that: The short-term forecast extreme value of the wave load under the sixth level sea condition is calculated based on the wave load response spectrum, including: The wave load in the short-term sixth-order sea state follows the Rayleigh distribution, so the wave load at the hull beam section has a significant value M of one-third. sig The expression is: Where m0 is the 0th order moment of the wave load response spectrum, expressed as: Where ω is the incident wave circular frequency; then the short-term forecast extreme value of wave load under level 6 sea condition M max for: M max =2.12M sig 。 9. The ship hull inertia load testing method based on model test according to claim 7, characterized in that: The wave spectrum density selects the dual-parameter PM spectrum, which is expressed as: Where ω is the incident wave circular frequency.

10. The method for determining the equivalent design wave of ship wave load under level 6 sea conditions according to claim 1, characterized in that: The equivalent design wave parameters of the wave load under the sixth sea state are determined based on the maximum value, including: The wave direction angle corresponding to the maximum value is the equivalent design wave direction; The circular frequency at the peak of the wave load transfer function corresponding to the maximum value is the equivalent design wave circular frequency; The ratio of the maximum value to the corresponding peak value of the wave load transfer function is the equivalent design wave amplitude.

Images