Method for direct prediction of wave loads on crane vessel klinga

Abstract

The application discloses a kind of for clinker crane ship wave load direct prediction method, it includes the following steps: establishing hydrodynamic grid model, establishing mass model with the weight distribution of whole ship, by analysis calculation, under regular wave, the velocity potential is obtained;The virtual mass inertia moment of the weight on the clinker crane is obtained by using the offset mass method;Rewrite mass matrix equation;Obtain inertial internal load by calculating hydrodynamic force, and the wave bending moment and wave shear force of the front section of mass section are calculated, and the frequency response function of ship movement and load;By setting short-term sea state and wave spectrum, response spectrum is obtained, and short-term prediction is carried out on response spectrum using spectral analysis method;According to the probability distribution of each short-term sea state in long service life, the long-term load extreme value prediction of ship structure is obtained.The correct wave load of clinker crane ship is successfully obtained;Similarly, the wave load prediction problem of the clinker crane ship with multiple clinker cranes can be solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of ship technology, in particular to a wave load direct prediction method for a crane ship. BACKGROUND

[0002] With the development of offshore oil and gas development and coastal and port engineering, the application of large crane ships is paid more and more attention. The single rotating support of the crane ship is connected with the ship body, and the influence of the cargo and the wave load needs to be considered during the hoisting process. Due to the arrangement characteristics and functions of the crane ship itself, the stress state of the structure of the crane ship is quite different from that of the conventional ship, and it is not reasonable to use the load formula of the ship classification society to calculate and check the structural strength of the crane ship. Therefore, the water dynamic method must be used to predict the motion response and structural load of the crane ship, so as to accurately analyze the structural strength of the crane ship.

[0003] The existing general wave load direct prediction method is based on three-dimensional potential flow theory and uses the three-dimensional panel method for water dynamic analysis. The purpose of water dynamic analysis is to study the stress and motion of the ship in the wave and evaluate the dynamic performance of the ship in the wave. Through water dynamic analysis, the pressure distribution of the wet surface of the ship body can be obtained, the motion of the ship in the wave and the wave load at any section can be obtained, and so on.

[0004] Current problems of water dynamic analysis:

[0005] 1. When the crane ship hoists the heavy object, the crane arm and the heavy object extend out of the ship body, and the mass matrix of the general water dynamic method for predicting the wave load of the ship body is cut off at the length of the ship body, and the mass outside the ship body is not considered to exist;

[0006] 2. The crane ship has a large mass outside the ship body, which cannot be ignored. If it is ignored, the overall mass matrix is incorrect, the ship motion solution is incorrect, and the subsequent wave load solution is meaningless;

[0007] 3. If the overall mass matrix includes the mass outside the ship body, the ship motion and the dynamic pressure of the wet surface of the ship body can be correctly solved. The general water dynamic method cannot take the sectional mass outside the ship length, and a large part of the inertial load is lost. In the calculation of the wave bending moment and shear force, the final result is that the seawater external load and the inertial force cannot be balanced, which leads to the result that the tail bending moment prediction result at the bow (tail) is obviously not zero, and the result is obviously incorrect.

[0008] 4. The frequency response function (RAO) result of the ship motion and load is incorrect, which also leads to the subsequent long-term and short-term prediction results being incorrect. SUMMARY

[0009] The technical problem solved by the present application is to overcome the above-mentioned defects existing in the prior art, and provide a method for directly predicting wave load of a crane ship.

[0010] The present application solves the above technical problems by the following technical solutions:

[0011] A method for directly predicting wave load of a crane ship, comprising the following steps:

[0012] Step 1, establishing a hydrodynamic grid model, establishing a mass model with full-ship weight distribution, and obtaining a velocity potential under regular waves through analysis and calculation;

[0013] Step 2, obtaining virtual mass inertia moment of the weight on the crane by using the offset mass method;

[0014] Step 3, rewriting the mass matrix equation; first, removing the weight distribution beyond the ship length range, and adding the virtual weight of the weight at the single-point base connected with the ship body; the mass matrix at a certain section within the ship length range can be written as:

[0015]

[0016] wherein,

[0017]

[0018] Ma i is the point mass distributed within the ship length range, M is the virtual mass point, and m is the number of mass points distributed within the ship length range;

[0019] X ref =X pou -X G , wherein X pou is the X coordinate of the mass at a certain point of the section, and X G is the X coordinate of the center of gravity of the full ship;

[0020] Y ref =Y pou -Y G , wherein: Y pou is the Y coordinate of the mass at a certain point of the section, and Y G is the Y coordinate of the center of gravity of the full ship;

[0021] Z ref =Z pou -Z G , wherein: Z pou is the Z coordinate of the mass at a certain point of the section, and Z G is the Z coordinate of the center of gravity of the full ship;

[0022] wherein, I'45, I'56 and I'46 are small and can be ignored as 0;

[0023]

[0024]

[0025]

[0026] wherein: R' x is the distance from the center of gravity of the weight to the x-axis of the center of gravity of the whole ship, R' y is the distance from the center of gravity of the weight to the y-axis of the center of gravity of the whole ship, R' z is the distance from the center of gravity of the weight to the z-axis of the center of gravity of the whole ship;

[0027] Step 4, according to the rewritten mass matrix equation, the inertial internal load is obtained by calculating the hydrodynamic force, and the wave bending moment and wave shear force of the front section of the mass section and the frequency response function of the ship motion and load are calculated;

[0028] Step 5, according to the obtained frequency response function of the ship motion and load, the wave bending moment and the wave shear force, the response spectrum is obtained by setting the short-term sea state and the wave spectrum, and the spectrum analysis method is used to make short-term prediction on the response spectrum; and according to the probability distribution of each short-term sea state in the long service life, the long-term load extreme value prediction of the ship structure is obtained.

[0029] In step 1, the calculation formula of regular wave is:

[0030] ζ=ζ a cos(kx-ωt);

[0031] wherein: ζ is the wave surface elevation; ζ a is the wave amplitude; k is the wave number; ω is the circular frequency.

[0032] In step 1, the velocity potential of regular wave is:

[0033]

[0034] wherein: g is the gravity acceleration, and z is the vertical position.

[0035] In step 2, the offset mass method is specifically: the weight of the weight on the Klien crane located outside the ship side is offset to the single-point base connected with the ship body of the Klien crane, so that the weight is located within the ship length range; the virtual mass inertia moment of the weight to the center of gravity axis of the ship body is calculated according to the static balance method as MR' 2 ; wherein M is the weight mass, and R' is the distance from the center of gravity of the weight to the center of gravity axis of the whole ship.

[0036] In step 3, if the mass section does not contain the base fulcrum, the mass inertia moment of the mass section is not included in the mass inertia moment of the virtual mass point.

[0037] In Step 3, if the crane barge has multiple cranes, the mass matrix is rewritten according to the mass offset method, and then the wave load calculation is performed.

[0038] In Step 4, the hydrodynamic calculation uses the ship motion equation, and the formula of the ship motion equation is:

[0039]

[0040] Wherein:

[0041] M jk is the generalized mass matrix term, and the mass matrix is obtained in Step 2;

[0042] A jk ,B jk ,C jk are the added mass coefficient, damping coefficient, and restoring force coefficient of the jth degree of freedom caused by the motion of the kth degree of freedom, collectively referred to as hydrodynamic coefficients;

[0043] F j is the wave force on the hull in the jth degree of freedom;

[0044] η k , are the displacement, velocity, and acceleration of the kth degree of freedom motion, respectively.

[0045] In Step 4, the method for calculating the frequency response function of ship motion and load is as follows: within the complete frequency range of wave encounter frequency, 20-30 frequencies are taken, and several wave directions are selected within the entire wave direction range. For each wave direction and frequency combination, regular wave motion response calculation is performed, and the frequency response function of ship motion and load can be obtained.

[0046] In Step 4, the wave bending moment and wave shear force of the front section of the mass section can be obtained through the inertial force and fluid dynamics acting on the hull.

[0047] In Step 5, the relationship between the response spectrum S R (ω) and the wave spectrum S ζ (ω) is:

[0048] S R (ω) = RAO(ω) 2 · S ζ (ω).

[0049] The beneficial effect of the present application is that the method of the present application, by establishing a hydrodynamic grid model, a mass model with full ship weight distribution, through three-dimensional diffraction, radiation analysis and calculation, the velocity potential is obtained under regular waves; the wave bending moment and shear force are obtained by solving the motion equation and dynamic balance equation. The important innovation of the method of the present application is that the offset mass method is adopted, the mass matrix equation is rewritten, and the dynamic balance calculation is solved. The present application simulates the weight of the hoisted heavy object at the single-point support of the crane, simulates the full ship mass matrix along the ship length after distribution, and ensures the balance between the seawater external load and the inertial force internal load when calculating the wave bending moment and shear force. The present application adopts the mass offset method, which offsets the ship weight within the ship length range, rewrites the segmented mass matrix along the ship length of the general hydrodynamic method, unifies the total mass matrix and the segmented mass matrix, overcomes the limitation that the general hydrodynamic program cannot be applied to the wave load prediction of the crane ship, and has great application and promotion value. The present application solves the problem that the existing hydrodynamic method cannot obtain the correct wave load of the crane ship, and successfully obtains the correct wave load of the crane ship. The present application can also solve the wave load prediction problem of the crane ship with multiple cranes. BRIEF DESCRIPTION OF DRAWINGS

[0050] Figure 1 A crane ship hoisting heavy object schematic diagram of a preferred embodiment of the present application.

[0051] Figure 2 A crane ship hoisting heavy object mass offset diagram of a preferred embodiment of the present application. DETAILED DESCRIPTION

[0052] The following preferred embodiment is described in detail below, and the present application is more clearly and completely illustrated in combination with the drawings.

[0053] A method for directly predicting the wave load of a crane ship, comprising the following steps.

[0054] Step 1, a hydrodynamic grid model is established, a mass model with full ship weight distribution is established, and the velocity potential is obtained under regular waves through analysis and calculation.

[0055] In step 1, the calculation formula of regular wave is:

[0056] ζ = ζ a cos(kx-ωt);

[0057] Wherein: ζ is the wave elevation; ζ a is the wave amplitude; k is the wave number; ω is the circular frequency.

[0058] In step 1, the velocity potential of regular wave is:

[0059]

[0060] wherein: g is the acceleration of gravity, z is the vertical position.

[0061] Step 2, the virtual mass inertia moment of the weight on the crane is obtained by the offset mass method.

[0062] In step 2, the offset mass method is specifically: the weight of the weight on the crane outside the ship side is offset to the single-point base where the crane is connected to the ship body, so that the weight is located within the ship length range; the virtual mass inertia moment of the weight on the ship center of gravity axis is calculated according to the static balance method, and is MR’. 2 wherein: M is the weight mass, R’ is the distance from the weight center of gravity to the ship center of gravity axis.

[0063] As shown in Figure 1 and Figure 2 , the ship body 10 of the crane ship is provided with a crane 20, the crane 20 is connected to the ship body 10, and the weight 30 is outside the ship side. Since the weight M and the mass inertia moment of the weight 30 located outside the ship body need to be taken into account, first, the weight M of the weight 30 must be offset to the single-point base 11 where the crane is connected to the ship body, to form a weight 40, so that it is located within the ship length range, and the decomposition mass point height is consistent with the ship center of gravity height.

[0064] It should be noted that, Figure 1 and Figure 2 , the weight 40 at the single-point base 11 does not exist in the actual object, and only the weight 30 exists in the actual object. In order to show that the weight 30 is moved to the single-point base 11 in theory, the weight 30 and the weight 40 are shown in Figure 1 and Figure 2 .

[0065] Figure 2 In , M is the weight mass, R’ is the distance from the weight center of gravity to the ship center of gravity axis, R is the vertical distance from the weight center of gravity to the ship center of gravity axis, and r is the force arm from the base to the ship center of gravity.

[0066] Step 3, rewrite the mass matrix equation. Because the virtual mass is added to the weight distribution of the whole ship, the weight distribution of the whole ship is rewritten. First, remove the weight distribution outside the ship length range, and add the virtual weight of the weight at the single-point base connected to the ship body; the mass matrix at a certain section within the ship length range can be written as:

[0067]

[0068] wherein,

[0069]

[0070] Ma iM is the virtual mass point, m is the number of mass points distributed along the length of the ship;

[0071] X ref = X pou - X G , wherein X pou is the X coordinate of the mass point of the section, X G is the X coordinate of the center of gravity of the whole ship;

[0072] Y ref = Y pou - Y G , wherein Y pou is the Y coordinate of the mass point of the section, Y G is the Y coordinate of the center of gravity of the whole ship;

[0073] Z ref = Z pou - Z G , wherein Z pou is the Z coordinate of the mass point of the section, Z G is the Z coordinate of the center of gravity of the whole ship;

[0074] wherein I'45, I'56 and I'46 are small and can be ignored as 0;

[0075] The actual hoisted weight generates a mass inertia moment I'55 for the center of gravity of the whole ship, which should be MR ’2 The decomposition mass inertia moment generated by the general hydrodynamic software is Mr 2 Therefore, if the mass offset method is applied, the mass moment matrix generated by the general hydrodynamic software is inconsistent with the mass inertia moment generated by the actual weight, which is wrong and must be modified I'44, I'55 and I'66. For example, the vertical wave bending moment, which we are most concerned about, needs to modify I'55, directly modify the increase of the mass inertia moment of the virtual mass point section to MR'2, from the stern to the bow, and keep the total mass inertia moment generated by the weight outside the ship and the mass inertia moment generated by the virtual decomposition mass equal at the last integrated bow section position.

[0076] Therefore, the mass inertia moment along a mass section of the length of the ship (such as containing the base support point) should be:

[0077]

[0078]

[0079]

[0080] wherein R' x is the distance from the center of gravity of the weight to the x-axis of the center of gravity of the whole ship, R' yR' is the distance from the center of gravity of the weight to the y-axis of the center of gravity of the whole ship. z R" is the distance from the center of gravity of the weight to the z-axis of the center of gravity of the whole ship.

[0081] If the mass section does not contain the base fulcrum, the mass moment of inertia of the mass section is not included in the mass moment of inertia of the virtual mass point.

[0082] If the crane ship has multiple crane hoists, the mass matrix is rewritten according to the mass offset method, and then the wave load calculation is performed.

[0083]

[0084]

[0085]

[0086]

[0087] wherein: Mi is a virtual mass point, n is the number of crane hoists. The mass and mass moment of inertia of the virtual mass point are included according to the range where the mass section is located.

[0088] Step 4, according to the rewritten mass matrix equation, the inertial internal load is obtained by calculating the hydrodynamic force, and the 6-degree-of-freedom balance equation is obtained together with the external load of the sea water dynamic pressure, and the wave bending moment and wave shear force of the front section of the mass section and the frequency response function of the ship motion and load are calculated.

[0089] In step 4, the ship motion equation is used for hydrodynamic force calculation, and the formula of the ship motion equation is:

[0090]

[0091] wherein:

[0092] M jk is a generalized mass matrix term, and M is the mass matrix obtained in step 2;

[0093] A jk ,B jk ,C jk are respectively the additional mass coefficient, the damping coefficient and the restoring force coefficient of the jth degree of freedom caused by the motion of the kth degree of freedom, collectively referred to as hydrodynamic coefficients;

[0094] F j is the wave force on the ship body in the jth degree of freedom direction;

[0095] η k , are respectively the displacement, velocity and acceleration of the motion of the kth degree of freedom.

[0096] In step 4, the method for calculating the frequency response function of ship motion and load is as follows: 20-30 frequencies are taken in the complete frequency range of wave encounter frequency, several wave directions are selected in the whole wave direction range, for each wave direction and frequency combination, regular wave motion response calculation is carried out, and the frequency response function of ship motion and load can be obtained.

[0097] In step 4, the wave bending moment and wave shear force of the front section of the mass section can be obtained through the inertial force and fluid power acting on the ship body.

[0098] In step 5, according to the obtained frequency response function of ship motion and load, wave bending moment and wave shear force, response spectrum is obtained by setting short-term sea conditions and wave spectrum, and spectrum analysis method is used to carry out short-term prediction on the response spectrum; and according to the probability distribution of each short-term sea condition in the long service life, long-term load extreme value prediction of the ship body structure is obtained.

[0099] In step 5, the relationship between the response spectrum S R (ω) and the wave spectrum S ζ (ω) is as follows:

[0100] S R (ω) = RAO(ω) 2 · S ζ (ω).

[0101] The method of the application establishes a hydrodynamic grid model and a mass model with full ship weight distribution, obtains the velocity potential under regular waves through three-dimensional diffraction and radiation analysis calculation, and obtains the wave bending moment and shear force by solving the motion equation and dynamic balance equation.

[0102] The important innovation point of the method of the application is that the offset mass method is adopted to rewrite the mass matrix equation and solve the dynamic balance calculation.

[0103] The application simulates the weight of the lifted heavy object at the single-point support of the Kranen crane, simulates the full ship mass matrix along the ship length after distribution, and ensures the balance between the seawater external load and the inertial force internal load when calculating the wave bending moment and shear force.

[0104] The application adopts the mass offset method, which offsets the ship weight to be within the ship length range, rewrites the segmented mass matrix along the ship length of the general hydrodynamic method, unifies the total mass matrix and the segmented mass matrix, overcomes the limitation that the general hydrodynamic program cannot be applied to the wave load prediction of the crane ship, and has great application and promotion value.

[0105] The present application solves the problem that the existing hydrodynamic method cannot obtain the correct wave load of the crane ship, and successfully obtains the correct wave load of the crane ship.

[0106] Although the specific embodiments of the present application are described above, those skilled in the art should understand that this is only an example, and the protection scope of the present application is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of the present application, and these changes and modifications all fall within the protection scope of the present application.

Claims

1. A method for direct prediction of wave loads on a crane vessel, c h a r a c t e r i s e d in that, It comprises the following steps: Step 1, a hydrodynamic grid model is established, a mass model with the weight distribution of the whole ship is established, and the velocity potential is obtained under regular waves through analysis calculation; Step 2, the virtual mass inertia moment of the weight outside the length of the ship on the crane is obtained by using the mass offset method; Step 3, rewriting the mass matrix equation; first, remove the weight distribution outside the length of the ship, and add the virtual weight of the weight at the single-point base connected with the ship body; the mass matrix at a certain section within the length of the ship can be written as: Wherein, Ma i Ma is a virtual mass point, m is the number of mass points distributed in the length of the ship range; X ref = X pou - X G where X pou is the X coordinate of the mass at the point of the section, and X G is the X coordinate of the center of gravity of the ship. Y ref = Y pou - Y G where: Y pou is the Y coordinate of the mass at the point of the section, Y G is the Y coordinate of the center of gravity of the ship. Z ref = Z pou - Z G wherein: Z pou is the Z coordinate of the mass at the point of the section, Z G is the Z coordinate of the center of gravity of the ship. Wherein, I'45, I'56 and I'46 are small and can be ignored as 0; wherein: R' x is the distance of the center of gravity of the weight to the x-axis of the center of gravity of the whole ship, R' y is the distance of the center of gravity of the weight to the y-axis of the center of gravity of the whole ship, R' z is the distance of the center of gravity of the weight to the z-axis of the center of gravity of the whole ship; Step 4, according to the rewritten mass matrix equation, the inertial internal load is obtained through hydrodynamic calculation, and the wave bending moment and wave shear force at the front section of the mass section as well as the frequency response function of the ship motion and load are calculated; Step 5, according to the obtained frequency response function of the ship motion and load, the wave bending moment and the wave shear force, the response spectrum is obtained by setting the short-term sea state and the wave spectrum, the response spectrum is analyzed by using the spectrum analysis method to make short-term prediction; and according to the probability distribution of each short-term sea state in the long service life, the long-term load extreme value prediction of the ship structure is obtained.

2. The method for direct prediction of wave loads on a crane vessel according to claim 1, characterized in that, In step 1, the calculation formula of the regular wave is: ζ = ζ a cos(kx - ωt); where: ζ is the wave height; ζ a is the wave amplitude; k is the wave number; and ω is the circular frequency.

3. The method for direct prediction of wave loads on a crane vessel according to claim 2, characterized in that, In step 1, the velocity potential of the regular wave is: Wherein: g is the gravity acceleration, and z is the vertical position.

4. The method for direct prediction of wave loads on a crane vessel according to claim 1, wherein In step 2, the offset mass method is specifically: the weight of the heavy object located outside the ship length range is offset to the single-point base connected to the ship body of the crane, so that the weight of the heavy object is located within the ship length range; the virtual mass moment of inertia of the heavy object to the ship center of gravity axis is MR' calculated according to the static balance method. 2 ; wherein M is the mass of the heavy object, and R' is the distance from the center of gravity of the heavy object to the ship center of gravity axis.

5. The method for direct prediction of wave loads on a crane vessel according to claim 4, characterized in that, In step 3, if the mass section does not contain the base support point, the mass inertia moment of the virtual mass point is not included in the mass inertia moment of the virtual mass point.

6. The method for direct prediction of wave loads on a crane vessel according to claim 4, characterized in that, In step 3, if the crane ship has multiple cranes, the mass matrix is rewritten according to the mass offset method, and then the wave load calculation is performed.

7. The method for direct prediction of wave loads on a crane vessel according to claim 1, wherein In step 4, the ship motion equation is used for hydrodynamic calculation, and the formula of the ship motion equation is: Wherein: M jk For the generalized mass matrix term, M, the mass matrix obtained in Step 2 is used. A jk ,B jk ,C jk are the added mass coefficient, damping coefficient, and restoring force coefficient of the jth degree of freedom due to the motion of the kth degree of freedom, collectively referred to as hydrodynamic coefficients; F j Fw(j) is the wave force on the hull in the jth degree of freedom direction; η k , are the displacement, velocity and acceleration of the k-th degree of freedom motion, respectively.

8. A method for direct prediction of wave loads on a crane vessel according to claim 7, characterized in that, In step 4, the method for calculating the frequency response function of the ship motion and load is that 20-30 frequencies are taken in the complete frequency range of the wave encounter frequency, and several wave directions are selected in the whole wave direction range; for each wave direction and frequency combination, the regular wave motion response calculation is performed, and the frequency response function of the ship motion and load can be obtained.

9. A method for direct prediction of wave loads on a crane vessel according to claim 8, characterized in that, In step 4, the wave bending moment and the wave shear force at the front section of the mass section can be obtained through the inertial force and the fluid dynamic force acting on the ship body.

10. The method for direct prediction of wave loads on a crane vessel according to claim 1, wherein, In step 5, the response spectrum S R (ω) is related to the wave spectrum S ζ (ω) by: S R (ω) = RAO(ω) 2 ·S ζ (ω).

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