A nonlinear analysis method of anchor hole strength based on real marine environment

Abstract

The present invention discloses a nonlinear analysis method of anchor hole strength based on real marine environment, which relates to the field of digital analysis and simulation of ships, and includes the following steps: establishing a three-dimensional hydrodynamic model of the whole ship; determining the stiffness, breaking force and mooring tension angle of the anchor chain of the mooring system; determining the real environmental conditions of the anchoring sea area; solving the hydrodynamic problems of the ship and the mooring system; outputting the ship motion response and the tension response of the mooring system; establishing a three-dimensional finite element model of the bow anchor hole; adding boundary conditions to the three-dimensional finite element model of the bow anchor hole based on the ship motion response; adding contact loads to the three-dimensional finite element model of the bow anchor hole; solving the stress response of the bow anchor hole structure by a nonlinear analysis module, and evaluating its safety. It combines the ship hydrodynamic analysis with the local structure finite element analysis, takes into account the influence of the real sea environment conditions and the mooring system, and achieves a more real and effective effect of analyzing and evaluating the strength of the anchor hole.

Description

Technical Field

[0001] The invention relates to the field of digital analysis and simulation of ships, and in particular to a nonlinear analysis method of anchor hole strength based on a real marine environment. Background Art

[0002] The anchor hole is an important part of the ship's anchor system. It is a niche-shaped structure located on the side outer plates of the bow of the ship for storing anchors. Its top plate is connected to the anchor chain barrel, and the side plate is connected to the hull structure. With the large-scale ships, especially the design and construction of ultra-large container ships and ultra-large ore carriers, the mooring system is becoming more and more complex and larger in size. The conventional beam system calculation method is difficult to accurately analyze this complex structure. Due to its special structural construction and force characteristics, it is easy to produce stress concentration, causing damage to the anchor hole itself and the hull structure, thereby reducing the service life of the ship. Therefore, it is particularly important to find a method that can accurately calculate the strength of the anchor hole. Summary of the invention

[0003] The purpose of the present invention is to provide a nonlinear analysis method for anchor hole strength based on a real marine environment, which combines ship hydrodynamic analysis with local structure finite element analysis, takes into account the influence of real sea environment conditions and mooring system, is more in line with the actual situation, and the analysis and evaluation of anchor hole strength is more real and effective.

[0004] The above technical objectives of the present invention are achieved through the following technical solutions:

[0005] A nonlinear analysis method of anchor hole strength based on real marine environment includes the following steps:

[0006] Step S1, including establishing a three-dimensional hydrodynamic model of the entire ship;

[0007] Step S2, comprising determining the stiffness, breaking force and mooring tension angle of the anchor chain of the mooring system;

[0008] Step S3, including determining the actual environmental conditions of the anchoring sea area;

[0009] Step S4, including solving the hydrodynamic problem of the ship and the mooring system;

[0010] Step S5, including outputting the ship motion response and the tension response of the mooring system;

[0011] Step S6, including establishing a three-dimensional finite element model of the bow anchor hole;

[0012] Step S7, comprising, based on the ship motion response in step S5, adding boundary conditions to the bow anchor hole three-dimensional finite element model in step S6;

[0013] Step S8, comprising, based on the mooring tension angle in step S2 and the mooring system tension response in step S5, adding a contact load to the bow anchor hole three-dimensional finite element model in step S6;

[0014] Step S9 includes solving the stress response of the bow anchor hole structure based on the nonlinear analysis module of FEMAP software to evaluate its safety.

[0015] Furthermore, the three-dimensional hydrodynamic model of the entire ship established in step S1 includes a complete hull structure.

[0016] Furthermore, in step S2, the mooring tension angle of the anchor chain of the mooring system is 0°~360°, and is selected at intervals of 30°.

[0017] Furthermore, the actual environmental conditions of the anchoring sea area in step S3 are obtained based on the actual wave scatter diagram of the anchoring sea area, including seawater density, operating water depth, wave incident angle and wave frequency.

[0018] Furthermore, the hydrodynamic problem of the ship and the mooring system in step S4 is realized by means of simulation coupling analysis based on the wave force motion theory in the frequency domain and time domain through the hydrodynamic software AQWA.

[0019] Furthermore, in step S6, the established bow anchor hole three-dimensional finite element model only includes a part of the bow structure of the hull, which includes a complete anchor chain barrel, anchor hole structure and surrounding hull support structure, and the grids of the anchor chain barrel, anchor hole and the hull structure connected thereto are divided more finely.

[0020] Furthermore, the step of adding the contact load in step S8 includes:

[0021] Step S8.1, determining the chain-out angle of the anchor chain of the mooring system according to the mooring tension angle selected in step S2 and the three-dimensional structural characteristics of the bow anchor hole in step S6;

[0022] Step S8.2, establishing an anchor chain model, wherein the anchor chain close to the anchor chain barrel and anchor hole structure is modeled with body elements, and the rest of the anchor chain is modeled with line elements, and the two are transitioned through multi-point constraint elements. One end of the anchor chain is connected to the hull structure, and the other end is fixed by simulating the anchor claw;

[0023] Step S8.3, setting the anchor chain barrel and the anchor chain, the lower end opening of the anchor hole and the adjacent anchor chain in contact connection;

[0024] Step S8.4, applying mooring tension to the anchor chain according to the tension response of the mooring system output in step S5.

[0025] Furthermore, the contact connection setting in step S8.3 includes,

[0026] Step S8.3.1, setting contact pairs, there are two contact pairs: one is the contact between the anchor chain inside the anchor chain barrel and the barrel wall, the other is the contact between the anchor chain within 1 meter from the lower end opening of the anchor hole and the lower end opening of the anchor hole;

[0027] Step S8.3.2, setting the contact properties, where the friction coefficient is taken as 0.2, the maximum contact search distance is set to 20 mm, and the initial penetration condition and damping condition are selected.

[0028] Furthermore, step S9 also includes setting nonlinear parameters for the nonlinear analysis module of the FEMAP software, including: setting the calculation time step to 20 steps, setting the initial time step coefficient to 0.001, setting the convergence criteria from three aspects: displacement, load and energy, and selecting an asymmetric solver to help convergence.

[0029] In summary, the present invention has the following beneficial effects:

[0030] Compared with the existing technology, this method not only takes into account the movement of the ship itself when evaluating the anchor hole strength, but also the tension of the mooring system is closer to reality. It also truly simulates the anchor hole and the surrounding hull structure, ensuring the authenticity of the anchor hole strength assessment and the safety of the anchor hole and the connected hull structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a logic flow chart of a nonlinear analysis method of anchor hole strength based on a real marine environment of the present invention;

[0032] Figure 2 It is a schematic diagram of ship anchoring in a nonlinear analysis method of anchor hole strength based on a real marine environment of the present invention;

[0033] Figure 3 It is a schematic diagram of a three-dimensional hydrodynamic model of the whole ship in a nonlinear analysis method of anchor hole strength based on a real ocean environment of the present invention;

[0034] Figure 4 It is a schematic diagram of the mooring tension angle of the mooring system in a nonlinear analysis method of anchor hole strength based on a real marine environment of the present invention;

[0035] Figure 5 It is a schematic diagram of the six-degree-of-freedom motion response of a ship in a nonlinear analysis method of anchor hole strength based on a real marine environment of the present invention;

[0036] Figure 6 It is a schematic diagram of a three-dimensional finite element model of a bow anchor hole in a nonlinear analysis method of anchor hole strength based on a real marine environment of the present invention;

[0037] Figure 7It is a schematic diagram of finer grid division at the anchor hole and anchor chain barrel in a nonlinear analysis method of anchor hole strength based on a real marine environment of the present invention. DETAILED DESCRIPTION

[0038] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings, and this embodiment does not constitute a limitation of the present invention. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0039] A nonlinear analysis method of anchor hole strength based on real marine environment, such as Figure 1 As shown, the strength of the anchor hole structure and its surrounding hull structure is evaluated, including the following steps:

[0040] Step S1, including establishing a three-dimensional hydrodynamic model of the entire ship;

[0041] The ship anchoring diagram is as follows: Figure 2 As shown in Figure 2, the three-dimensional hydrodynamic model of the entire ship is as follows: Figure 3 As shown, the established three-dimensional hydrodynamic model of the entire ship includes a complete hull structure.

[0042] Step S2, comprising determining the stiffness, breaking force and mooring tension angle of the anchor chain of the mooring system;

[0043] Among them, Figure 4 As shown, the mooring tension angle of the anchor chain of the mooring system is 0°~360°, selected at intervals of 30°.

[0044] Step S3, including determining the actual environmental conditions of the anchoring sea area;

[0045] The actual environmental conditions of the anchoring sea area in step S3 are obtained based on the actual wave scatter diagram of the anchoring sea area, including seawater density, operating water depth, wave incident angle and wave frequency.

[0046] Step S4, including solving the hydrodynamic problem of the ship and the mooring system based on AQWA software;

[0047] The hydrodynamic problems of the ship and mooring system are solved based on the wave force frequency domain and time domain motion theory, and are solved by simulation coupling analysis using the hydrodynamic software AQWA. The specific solution process includes:

[0048] The RAO value of the structure is obtained by calculating the motion under unit amplitude wave excitation in the frequency domain. The equation of motion is:

[0049] ;

[0050] ;

[0051] Where: A is the wave amplitude; Ms is the structural mass; Ma is the additional mass; B is the damping coefficient; K is the hydrostatic stiffness; and F is the wave force.

[0052] The equation of motion in the time domain:

[0053] ;

[0054] Where: F(t) is the force condition of the floating structure, including diffraction force, radiation force, cable tension, drift force, etc.; is the acceleration. Using the impulse response method, the convolution integral form is:

[0055] ;

[0056] Where: h(t) is the acceleration iteration integral matrix.

[0057] The damping coefficient

[0058] ;

[0059] The near-field solution of the second-order wave excitation force can be written as:

[0060] ;

[0061] If the sum frequency part is ignored, the above formula can be transformed into:

[0062] ;

[0063] Newman approximation states:

[0064] ;

[0065] Based on the above equation, then:

[0066] ;

[0067] The above approximation is applicable to deep water conditions and is used to evaluate the second-order difference frequency wave force, while ignoring the wave drift damping.

[0068] Step S5 includes outputting the ship motion response and the tension response of the mooring system, such as Figure 5 The schematic diagram of the six-degree-of-freedom motion response of the ship is shown;

[0069] Step S6, comprising: establishing a three-dimensional finite element model of the bow anchor hole based on FEMAP software;

[0070] like Figure 6As shown in FIG. 1 , in step S6, the three-dimensional finite element model of the bow anchor hole established based on the FEMAP software only includes a part of the bow structure of the hull, which includes a complete anchor chain barrel, an anchor hole structure and a surrounding hull support structure, and as shown in FIG. Figure 7 As shown in the figure, the grids of the anchor chain barrel, anchor hole and the hull structure connected to it are divided more finely, with a grid size of about 50mm×50mm, in order to accurately express the local structural characteristics of the anchor hole; and the material properties are set, including material density, elastic modulus and Poisson's ratio.

[0071] Step S7: comprising, based on the ship motion response in step S5, adding boundary conditions to the bow anchor hole three-dimensional finite element model in step S6;

[0072] Step S8, comprising, based on the mooring tension angle in step S2 and the mooring system tension response in step S5, adding a contact load to the bow anchor hole three-dimensional finite element model in step S6;

[0073] The steps for adding contact loads include:

[0074] Step S8.1: Determine the chain-out angle of the anchor chain of the mooring system based on the mooring tension angle selected in step S2 and the three-dimensional structural characteristics of the bow anchor hole in step S6;

[0075] Step S8.2: An anchor chain model is established based on FEMAP software, wherein the anchor chain close to the anchor chain barrel and anchor hole structure is modeled with solid elements, and the anchor chain farther away is modeled with line elements. The two are transitioned through multi-point constraint elements. One end of the anchor chain is connected to the hull structure, and the other end simulates the anchor claw fixation;

[0076] Step S8.3: To consider the contact nonlinearity of load transfer, the anchor chain barrel and the anchor chain, and the lower end opening of the anchor hole and the adjacent anchor chain are set to be in contact connection;

[0077] The contact connection setting specifically includes:

[0078] Step S8.3.1: setting contact pairs, where there are two contact pairs: one is the contact between the anchor chain inside the anchor chain barrel and the barrel wall, and the other is the contact between the anchor chain within 1 meter from the lower end opening of the anchor hole and the lower end opening of the anchor hole;

[0079] Step S8.3.2: setting contact properties, where the friction coefficient is set to 0.2, the maximum contact search distance is set to 20 mm, and the initial penetration condition and damping condition are selected;

[0080] Step S8.4: Apply mooring tension to the anchor chain according to the tension response of the mooring system output in step S5.

[0081] Step S9, including solving the stress response of the bow anchor hole structure based on the nonlinear analysis module of FEMAP software and evaluating its safety;

[0082] The nonlinear analysis module of the FEMAP software requires some nonlinear parameter settings, including: the calculation time step is set to 20 steps, to ensure the convergence of the first step calculation, the initial time step coefficient is set to 0.001, the convergence criteria are set from three aspects: displacement, load and energy, and an asymmetric solver is selected to help convergence.

[0083] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art may make various modifications or equivalent substitutions to the present invention within the essence and protection scope of the present invention, and such modifications or equivalent substitutions should also be deemed to fall within the protection scope of the technical solution of the present invention.

Claims

1. A nonlinear analysis method for anchor hole strength based on real marine environment, characterized by: The following steps are included: Step S1, including establishing a three-dimensional hydrodynamic model of the entire ship; Step S2, comprising determining the stiffness, breaking force and mooring tension angle of the anchor chain of the mooring system; Step S3, including determining the actual environmental conditions of the anchoring sea area; Step S4, including solving the hydrodynamic problem of the ship and the mooring system; Step S5, including outputting the ship motion response and the tension response of the mooring system; Step S6, including establishing a three-dimensional finite element model of the bow anchor hole; Step S7, comprising, based on the ship motion response in step S5, adding boundary conditions to the bow anchor hole three-dimensional finite element model in step S6; Step S8, comprising, based on the mooring tension angle in step S2 and the mooring system tension response in step S5, adding a contact load to the bow anchor hole three-dimensional finite element model in step S6; The steps of adding contact loads include: Step S8.1, determining the chain-out angle of the anchor chain of the mooring system according to the mooring tension angle selected in step S2 and the three-dimensional structural characteristics of the bow anchor hole in step S6; Step S8.2, establishing an anchor chain model, wherein the anchor chain close to the anchor chain barrel and anchor hole structure is modeled with body elements, and the rest of the anchor chain is modeled with line elements, and the two are transitioned through multi-point constraint elements. One end of the anchor chain is connected to the hull structure, and the other end is fixed by simulating the anchor claw; Step S8.3, setting the anchor chain tube and the anchor chain, the lower end opening of the anchor hole and the adjacent anchor chain to be in contact connection; the contact connection setting includes: Step S8.3.1, setting contact pairs, there are two contact pairs: one is the contact between the anchor chain inside the anchor chain barrel and the barrel wall, the other is the contact between the anchor chain within 1 meter from the lower end opening of the anchor hole and the lower end opening of the anchor hole; Step S8.3.2, setting contact properties, where the friction coefficient is set to 0.2, the maximum contact search distance is set to 20 mm, and the initial penetration condition and damping condition are selected; Step S8.4, applying mooring tension to the anchor chain according to the tension response of the mooring system output in step S5; Step S9 includes solving the stress response of the bow anchor hole structure based on the nonlinear analysis module of FEMAP software to evaluate its safety.

2. The nonlinear analysis method of anchor hole strength based on real marine environment according to claim 1 is characterized by: The three-dimensional hydrodynamic model of the entire ship established in step S1 includes a complete hull structure.

3. The nonlinear analysis method of anchor hole strength based on real marine environment according to claim 1 is characterized by: In step S2, the mooring tension angle of the anchor chain of the mooring system is 0°~360°, and is selected at intervals of 30°.

4. The nonlinear analysis method of anchor hole strength based on real ocean environment according to claim 1 is characterized by: The actual environmental conditions of the anchoring sea area in step S3 are obtained based on the actual wave scatter diagram of the anchoring sea area, including seawater density, operating water depth, wave incident angle and wave frequency.

5. The nonlinear analysis method of anchor hole strength based on real ocean environment according to claim 1 is characterized by: The hydrodynamic problem of the ship and the mooring system in step S4 is realized by simulation coupling analysis based on the wave force frequency domain and time domain motion theory through the hydrodynamic software AQWA.

6. The nonlinear analysis method of anchor hole strength based on real ocean environment according to claim 1 is characterized by: In step S6, the established bow anchor hole three-dimensional finite element model only includes a part of the bow structure of the hull, which includes a complete anchor chain barrel, anchor hole structure and surrounding hull support structure, and the grids of the anchor chain barrel, anchor hole and the hull structure connected thereto are divided more finely.

7. The anchor hole strength nonlinear analysis method based on a real ocean environment according to claim 1 is characterized by: Step S9 also includes setting nonlinear parameters for the nonlinear analysis module of the FEMAP software, including: setting the calculation time step to 20 steps, setting the initial time step coefficient to 0.001, setting the convergence criteria from three aspects: displacement, load and energy, and selecting an asymmetric solver to help convergence.

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