A method for simulating hydrodynamic performance of multiple floating bodies during liquid cargo ship alongside operation by using SPH

Abstract

This invention discloses a SPH (Self-Pulse Hydraulic Dynamics) simulation method for multi-buoy hydrodynamics during berthing operations of liquid cargo ships, comprising the following steps: S1, establishing a geometric model of a numerical tank; S2, establishing models of a first hull, a second hull, a first liquid tank, and a second liquid tank, determining the position of the liquid tanks inside the hull, merging the liquid tanks and the hull, importing the hull into the numerical tank, and adjusting its position within the tank; S3, setting the initial states and motion characteristics of the first and second hulls; S4, filling the first and second liquid tanks with fluid particles; S5, setting boundary conditions and wave generation modes; S6, setting mooring chains, wave damping, and typical parameters; S7, running the program to solve and outputting the calculation results. This invention simulates the coupling effect of the motion of two ships and the swaying of liquid tanks during multi-buoy hydrodynamic numerical tank operations under wave action by establishing a simulation technology for the multi-buoy hydrodynamics of a liquid cargo ship and its internal liquid tanks.

Description

Technical Field

[0001] This invention belongs to the field of liquid cargo ship motion prediction technology, specifically relating to a SPH simulation method for the hydrodynamics of multiple floating bodies during alongside operations of liquid cargo ships. Background Technology

[0002] Liquefied natural gas (LNG) has attracted widespread attention as a clean, efficient, and inexpensive new energy source. For the exploration, extraction, and transportation of marine LNG, a single vessel or floating structure cannot complete the process independently; often, the coordinated operation of multiple vessels or floating structures is required. For example, LNG carriers berth alongside FLNG (floating LNG storage and regasification units) for loading and unloading oil and gas; FPSO (floating production storage and offloading unit) works in conjunction with shuttle tankers for loading, unloading, and transferring oil and gas.

[0003] The severity of sea conditions has a significant impact on vessels loading and unloading oil and gas cargo side-by-side. Waves not only cause hull rolling motion, but the movement of the cargo tanks with the hull in the waves also leads to violent sloshing of the liquid inside. The massive sloshing generated by partial cargo loading, in particular, can cause fatal damage to the hull structure and cargo tanks. Furthermore, when two liquid-carrying vessels operate side-by-side, their relative motion in the waves becomes highly complex, causing them to deviate from their original positions and creating a series of safety risks. For example, too close a distance could lead to a collision, while too large a distance could entangle oil pipelines. Therefore, accurate prediction and simulation of the coupling between the motion of the two vessels and the sloshing of the cargo tanks during multi-buoy collaborative operations under wave action is essential. Currently, relevant research mainly focuses on ship motion and hydrodynamic disturbances of multi-buoys; however, research on the coupling simulation of fluid disturbances between multi-buoys and the sloshing of cargo tanks is relatively limited.

[0004] The SPH method is a meshless method based on the Lagrange algorithm, particularly suitable for simulating violent fluid flow problems such as tank sloshing. Compared with CFD / RANS methods based on the finite volume method (FVM) and potential flow theory based on the boundary element method (BEM), the SPH method is more suitable for solving strongly nonlinear fluid-structure interaction dynamics problems such as tank sloshing, free surface breakage, and fluid splashing in liquid cargo ships. Summary of the Invention

[0005] The main objective of this invention is to overcome the shortcomings and deficiencies of the prior art and provide a SPH simulation method for the hydrodynamics of multiple floating bodies during berthing operations of liquid cargo ships. The method utilizes the open-source software DesignSPHysics based on the SPH algorithm to perform coupled simulation of the motion of the two ships and the sloshing of the liquid tanks during multi-floating body cooperative operations in waves.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for simulating the hydrodynamics of multiple floating bodies during alongside operations of a liquid cargo vessel includes the following steps:

[0008] S1. Establish a numerical water tank model; the numerical water tank model includes a spatial confinement domain, a numerical water tank domain, a numerical water tank fluid particle filling domain, and a wave generator.

[0009] S2. Establish models of the first hull, the second hull, the first liquid tank, and the second liquid tank; determine the position of the liquid tank inside the hull; merge the liquid tank and the hull; import the hull into the numerical water tank and adjust its position inside the numerical water tank.

[0010] S3. Set the initial state and motion characteristics of the first and second hulls;

[0011] S4. Fill the first and second liquid tanks with fluid particles;

[0012] S5. Set boundary conditions and wave generation mode;

[0013] S6. Set the mooring anchor chain, wave-damping damping and typical parameters;

[0014] S7. Run the program to solve and output the calculation results. Set the calculation monitoring quantities and data output. Confirm the number of particles in the numerical simulation. Perform numerical simulation calculations and output the results.

[0015] Furthermore, steps S1 to S2 are implemented using FreeCAD, and steps S3 to S7 are implemented using DesignSPHysics.

[0016] Furthermore, step S1 specifically includes:

[0017] In FreeCAD, a cuboid cavity region is set up as the spatial constraint region for numerical simulation. The spatial constraint region consists of six faces.

[0018] A cuboid cavity domain is set as the numerical water pool domain. The numerical water pool domain consists of a bottom boundary surface, a top boundary surface, and four side wall boundary surfaces. The six boundary surfaces of the numerical water pool domain are located inside the spatially confined domain.

[0019] Establish a solid cuboid model and set it as a rectangular wave-generating plate. The wave-generating plate is located inside the numerical pool domain. The bottom edge of the wave-generating plate is located on the bottom boundary surface of the spatial confinement domain, the top edge is located between the top boundary surface of the numerical pool domain and the top boundary surface of the spatial confinement domain, and the two sides are located on the boundary surfaces of the two side walls of the numerical pool domain, respectively.

[0020] Establish a fluid particle filling domain for a numerical water tank, and perform the filling and generation of fluid particles within the numerical water tank.

[0021] Furthermore, the wave-generating plate is a solid unit with a certain thickness.

[0022] Furthermore, step S2 specifically includes:

[0023] S21. Establish a model of the first hull and the first liquid tank:

[0024] The surface of the hull was drawn using FreeCAD based on the hull profile and data from the form value table, thus creating a three-dimensional geometric model of the first hull.

[0025] Establish a three-dimensional geometric model of the first liquid tank, import the first liquid tank model into the first hull model and determine the position of the first liquid tank inside the first hull, and merge the first liquid tank and the first hull into a whole;

[0026] Taking into account the simulation accuracy requirements, scale effect, and computational efficiency, the geometric scaling ratio of the ship model is determined; the scaling factor for importing the hull model is selected to achieve the scaling ratio between the ship model and the actual ship.

[0027] Set the spatial position of the first hull in the numerical pool;

[0028] S22. Establish a model of the second hull and the second liquid tank:

[0029] The curved surfaces of the hull were drawn using FreeCAD based on the hull profile and data from the form value table, thus creating a three-dimensional geometric model of the second hull.

[0030] Establish a three-dimensional geometric model of the second liquid tank, import the second liquid tank model into the second hull model and determine the position of the second liquid tank inside the second hull; merge the second liquid tank and the second hull into a whole;

[0031] Select the scaling factor for the imported hull model to achieve the scale ratio between the hull model and the actual ship.

[0032] Set the spatial position of the second hull in the numerical pool.

[0033] Furthermore, step S3 specifically includes:

[0034] S31. Set the initial state and motion characteristics of the first hull:

[0035] Set the first hull's floating state to be floatable;

[0036] The first hull is positioned in the numerical pool by translating the ship, and the heading angle of the first hull is initialized by rotating the ship in the horizontal plane.

[0037] The motion characteristics of the first hull are defined, including:

[0038] Set the mass, center of gravity coordinates, and moment of inertia about the three coordinate axes of the first hull; set the initial linear velocity and initial angular velocity about the three coordinate axes of the first hull in the three directions; set the translational degrees of freedom and rotational degrees of freedom of the first hull in the three directions.

[0039] S32. Set the initial state and motion characteristics of the second hull:

[0040] Set the second hull to a floating state;

[0041] The second hull is positioned in the numerical tank by translating the ship, and the heading angle of the second hull is initialized by rotating the ship in the horizontal plane.

[0042] The motion characteristics of the second hull are set, including:

[0043] Set the mass, center of gravity coordinates, and moments of inertia about the three coordinate axes of the second hull; set the initial linear velocities and initial angular velocities about the three coordinate axes of the second hull in the three directions; set the translational degrees of freedom and rotational degrees of freedom of the second hull in the three directions.

[0044] Furthermore, step S4 specifically includes:

[0045] S41, Fluid particle filling in the first liquid tank:

[0046] In the software, a fluid particle filling domain is established within the first liquid tank, and the size and position of the fluid particle filling domain within the first liquid tank are set.

[0047] Water particles are filled and generated in the fluid particle filling domain of the first liquid tank;

[0048] S42, Fluid particle filling in the second liquid tank:

[0049] In the software, a fluid particle filling domain is created within the second liquid tank, and the size and position of the fluid particle filling domain within the second liquid tank are set.

[0050] Water particles are filled and generated in the fluid particle filling domain of the second liquid tank.

[0051] Furthermore, step S5 specifically involves:

[0052] Add the numerical pool domain to the simulation calculation, set the 6 boundary surfaces of the numerical pool domain as wall boundaries, and set the generation mode to the surface of a cavity hexahedron.

[0053] Add the wave generator to the simulation calculation, set the wave generator type to wall boundary, and the generation mode to solid;

[0054] Add the first and second hulls to the simulation calculation, set the ship model type to wall boundary, and the generation mode to surface;

[0055] Set the fluid particle model in the first and second liquid tanks to fluid boundary and the generation mode to solid.

[0056] The wave generation mode was set to the push-plate wave generation method, and the motion properties of the wave generation plates were set to simulate waves.

[0057] Set the target rule wave type, period, wave height, and propagation direction.

[0058] Furthermore, step S6 specifically involves:

[0059] Select the hull to be moored and set the corresponding MoorDyn Parameters, and determine the anchor chain length, position, and number of anchor chain links;

[0060] Set Limit Min(x, y, z), Limit Max(x, y, z), Overlimit and Redumax damping parameters to set wave damping on the three sides of the numerical water tank other than the wave-generating plate.

[0061] Set typical parameters, including gravitational acceleration, fluid density, viscosity type, viscosity coefficient, simulation time, step size, and particle spacing.

[0062] Furthermore, step S7 specifically includes:

[0063] Before the program calculates, confirm the total number of particles in the numerical simulation;

[0064] View the renderings of the two hull models, two liquid tanks, and the mooring device;

[0065] Set the solution objective as the first hull, and output the displacement and velocity data of the first hull's six degrees of freedom;

[0066] Set the solution objective as the second hull, and output the displacement and velocity data of the second hull's six degrees of freedom;

[0067] Set the solution target as a fluid particle, and output the displacement, velocity, acceleration, density, pressure, mass, volume and vorticity data of any fluid particle in the flow field of the numerical water tank or liquid tank.

[0068] After the program completes the solution process, it outputs the fluid pressure and tensile / compressive forces on the hull and tank walls, as well as the anchor chain.

[0069] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0070] 1. Current SPH methods can generally only simulate the motion of the hull in waves, tank sloshing, and hydrodynamics of multiple floating bodies independently. They are difficult to comprehensively consider the coupling effect of the three factors of motion in waves, tank sloshing, and hydrodynamics of multiple floating bodies when two liquid cargo ships are berthed together. This invention establishes a simulation technology of a numerical hydrodynamic pool for multiple floating bodies with built-in tanks for liquid cargo ships, thereby simulating the coupling effect of the motion of two ships and tank sloshing when multiple floating bodies cooperate under wave action.

[0071] 2. In addition to analyzing the floating body of a liquid cargo ship in a free state, the method of the present invention can also consider the role and influence of the anchor chain on the motion of the ship or floating body in a moored state. It couples the mooring force of the anchor chain with the hydrodynamic forces such as wave force and liquid tank sloshing load of the ship or floating body, and can evaluate and analyze the stress and strength of the anchor chain pipeline.

[0072] 3. All modeling and calculation work involved in the method of this invention is completed using the SPH open-source software. The XML source code of the algorithm in DesignSPHysics can be directly modified and supplemented according to the simulation needs, avoiding the disadvantages of high purchase cost and inability to perform secondary development of commercial software. Attached Figure Description

[0073] Figure 1 This is a flowchart of the method of the present invention;

[0074] Figure 2 This is a modeling diagram of a numerical water tank model;

[0075] Figure 3 It is the geometric model of the first hull;

[0076] Figure 4 It is the geometric model of the second hull;

[0077] Figure 5 These are renderings of the numerical water tank, the first hull, and the second hull after modeling.

[0078] Figure 6 This is a diagram showing the effect of filling the numerical water tank, the first liquid chamber, and the second liquid chamber with fluid particles.

[0079] Figure 7 It is a flow field particle distribution diagram of the first and second hulls and the first and second liquid tanks under wave action;

[0080] Figure 8 It is the heave motion time-history curve of the first hull;

[0081] Figure 9 It is the pitching motion time history curve of the first hull;

[0082] Figure 10It is the heave motion time-history curve of the second hull;

[0083] Figure 11 It is the pitching motion time history curve of the second hull;

[0084] Figure 12 It is the wave surface elevation time-history curve at the front of the first hull in the numerical water tank;

[0085] Figure 13 It is the time-history curve of the liquid level elevation at the center point of the first liquid tank;

[0086] Figure 14 It is the time-history curve of the liquid level elevation at the center point inside the second liquid tank;

[0087] Figure 15 It is the time-history curve of fluid sloshing impact pressure at a typical location in the first liquid tank;

[0088] Figure 16 It is the time-history curve of fluid sloshing impact pressure at a typical location in the second liquid tank;

[0089] Explanation of the reference numerals: 1-Spatial confinement domain; 2-Numerical pool domain; 3-Wavemaker; 4-Numerical pool fluid particle filling domain; 5-First hull; 6-First liquid tank bulkhead; 7-Second hull; 8-Second liquid tank bulkhead; 9-Mooring anchor chain. Detailed Implementation

[0090] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0091] Example

[0092] In this embodiment, the open-source software FreeCAD is used to build a numerical water tank and a liquid cargo ship model, and the open-source software DesignSPHysics is used to generate fluid particles and perform numerical calculations, thereby simulating the hydrodynamic problem of two liquid-carrying ships operating side by side in the numerical water tank. DesignSPHysics is an open-source software module based on the SPH algorithm and the DualSPHysics solver, and its user interface is built into the general-purpose open-source software FreeCAD.

[0093] like Figure 1 As shown, this invention provides a method for simulating the hydrodynamics of multiple buoys during alongside operations of a liquid cargo ship, comprising the following steps:

[0094] S1. Establish the geometric model of the numerical water tank, including the spatial confinement domain 1, the numerical water tank domain 2, the numerical water tank fluid particle filling domain 4, and the wave-generating plate 3; specifically including:

[0095] S11. Open the DesignSPHysics plugin, create a new case file named New Case and name it FloatingsCase;

[0096] S12. In the Case Limits (3D) model under the root directory of the new case file FloatingsCase, set a cuboid cavity region as the spatial constraint region for numerical simulation. The spatial constraint region consists of six faces, and its size must be larger than all geometric models. Subsequent modeling and calculation of the geometric models must be constrained within the spatial constraint region. Therefore, in this embodiment, the dimensions of the spatial constraint region in the OX, OY, and OZ directions are 20000mm, 10000mm, and 10000mm, respectively, and the coordinates of the source point O of the spatial constraint region are (0, 0, 0).

[0097] S13. Create a new model named Tank in the root directory of the new case file Floatings Case, and set it as a cuboid cavity domain as the numerical water tank domain. The numerical water tank domain consists of a bottom boundary surface, a top boundary surface, and four side wall boundary surfaces. All six boundary surfaces of the numerical water tank domain should be inside the spatial confinement domain. Therefore, in this embodiment, the dimensions of the numerical water tank domain in the OX, OY, and OZ directions are 15000mm, 10000mm, and 10000mm, respectively. The bottom boundary surface (15000mm × 10000mm) coincides with the bottom boundary surface of the spatial confinement domain, and one of the side boundary surfaces (10000mm × 10000mm) coincides with the wave-generating plate.

[0098] S14. Create a solid cuboid model named Piston in the root directory of the new case file Floatings Case, and set it as a rectangular wave generator. The wave generator is located inside the numerical pool domain, positioned near one side wall boundary and parallel to the side wall boundary of the numerical pool (10000mm × 10000mm). The bottom edge of the wave generator is located on the bottom boundary of the spatially confined domain, the top edge is located between the top boundary of the numerical pool domain and the top boundary of the spatially confined domain, and the two sides are located on the two side wall boundaries of the numerical pool domain. The wave generator is a volume element with a certain thickness, and its width (OY direction), height (OZ direction), and thickness (OX direction) are 10000mm, 10000mm, and 300mm, respectively.

[0099] like Figure 2 The image shown is a modeling diagram of the numerical water tank model;

[0100] S15. Fill the numerical water tank with fluid particles, specifically including the following settings:

[0101] Use the DesignSPHysics module to fill fluid particles. Click fillbox, and create a new folder named FillTank in the root directory of the new case file Floatings Case;

[0102] Click on the FillLimit model in the FillTank folder to set the particle-filled domain for the numerical water tank. The dimensions of the particle-filled domain in the OX, OY, and OZ directions are 14700mm, 10000mm, and 2000mm, respectively. The particle-filled domain is a cuboid space domain located inside the numerical water tank domain. Its bottom surface coincides with the bottom boundary surface of the numerical water tank domain, and its top surface is located at a height of 2000mm from the bottom surface. One side surface (10000mm × 2000mm) coincides with one surface of the wave-generating plate, and the other two side surfaces (14700mm × 2000mm) coincide with the sidewall boundary surface of the numerical water tank domain.

[0103] Click the FillPoint model in the FillTank folder, and set the fill source point to any point within the numerical water tank fluid particle filling domain. In this embodiment, it is set to point (1, 1, 1) to fill and generate water particles in the numerical water tank fluid particle filling domain. Table 1 below shows the structural unit parameters of the numerical water tank model.

[0104] Model unit Base point coordinates X-direction range / mm Y-direction range / mm Z-direction range / mm type Spatial confinement domain (0,0,0) 18000 10000 10000 cuboid cavity region Numerical pool domain (0,0,0) 15000 10000 10000 cuboid cavity region Particle-filled domain (10,0,0) 14700 10000 2000 cuboid domain Wave board (0,0,0) 300 10000 10000 solid board

[0105] Table 1

[0106] S2. Establish models of the first hull 5, the second hull 7, the first liquid tank, and the second liquid tank; determine the positions of the liquid tanks inside the hulls; merge the liquid tanks and the hulls; import the hulls into the numerical water tank and adjust their positions within the numerical water tank; specifically including:

[0107] S21. Establish a model of the first hull and the first liquid tank:

[0108] S211. In this embodiment, the first hull is selected as an S175 type container ship. FreeCAD software is used to draw the curved surface of the hull shell according to the hull line drawing and the data of the hull value table, and to create a three-dimensional geometric model of the first hull.

[0109] S212. A new rectangular liquid tank named Tank1 is created using FreeCAD. The tank's length, width, and height are 1600mm, 500mm, and 320mm, respectively. The tank model is imported into the hull model, and its location within the hull is determined. The top surface of the tank coincides with the deck surface of the hull, as does its mid-longitudinal section. The side bulkheads of the tank are 67.5mm from the hull's side plates, and the forward bulkhead is 1240mm from the bow of the hull. The main parameters of the tank are shown in Table 2 below.

[0110] S213. Merge the first liquid tank and the first hull into a single unit. Click on the model files of the first hull and the first liquid tank respectively, and in the DSPH simulation module, set the MKbound parameter of both to the same number; in this example, it is set to 5. The overall model after merging the first hull and the first liquid tank is as follows. Figure 3 As shown.

[0111] S214. Based on comprehensive considerations such as simulation accuracy requirements, scale effect, and computational efficiency, the geometric scale ratio of the ship model is determined to be 1:40.

[0112] S215. Import the geometric model of the first hull (including the first liquid tank) that has been created into the root directory of the new case file Floatings Case (ImportedS175), and select the scaling factor of the imported model as (0.025, 0.025, 0.025), so that the scale ratio between the ship model and the real ship is 1:40. The main parameters of the scaled first hull (including the first liquid tank) are shown in Table 2 below.

[0113] S216. Click on the ImportedS175 model and set its position to (7, 3, 1.975). In this embodiment, the center of gravity of the first hull is the control point, so (7, 3, 1.975) is also the center position. The relative position of the first liquid tank and the first hull remains unchanged.

[0114] First hull parameter First liquid tank parameter captain 4.375m tank length 1.6m Width 0.635m tank width 1.0m Draft 0.238m tank depth 0.32m Discharge 386.59kg Liquid carrying capacity 70％

[0115] Table 2

[0116] S22. Establish a model of the second hull and the second liquid tank:

[0117] S221. In this embodiment, a simplified box-shaped floating body is selected as the second hull. A rectangular hexahedron is drawn using FreeCAD software to create a three-dimensional geometric model of the second hull's outer shell. A rectangular floating body with dimensions of 5m × 2m × 1m is created in the root directory of the new case file as the second hull, which is located inside the numerical water tank. The bottom and top planes of the second hull are parallel to the bottom boundary surface, and the bottom surface is located inside the water tank area at a height of 1.8m from the bottom surface of the water tank. The four sides are parallel to the four sides of the numerical water tank area.

[0118] S222. Create a new model of the second liquid tank named Tank2 using FreeCAD. The second liquid tank is located inside the second hull, and all six surfaces of the second liquid tank are parallel to the six surfaces of the second hull. The bottom surface of the second liquid tank is 0.5m away from the bottom surface of the second hull, the top surface of the second liquid tank coincides with the top surface of the second hull, the two long sides of the second liquid tank are 0.5m away from the sides of the second hull, and the two short sides of the second liquid tank are 1.0m away from the bow and stern of the second hull.

[0119] S223. Merge the second liquid tank and the second hull into a single unit. Click on the model files of the second hull and the second liquid tank respectively, and set the MKbound parameter of both to the same number in the DSPH simulation module. In this embodiment, it is set to 5. The overall model after merging the second hull and the second liquid tank is as follows. Figure 4 As shown.

[0120] S224. Import the geometric model of the second hull (including the second liquid tank) that has been created into the root directory of the new case file Floatings Case. Select the same scaling factor for the imported second hull (including the second liquid tank) model as the first hull.

[0121] S225. Click on the ImportedLNG model and set its position to (7, 6, 1.8). In this example, the center of gravity of the second hull is the control point, so (7, 6, 2.3) is its center of gravity position. The relative position of the second liquid tank and the second hull remains unchanged. The bow of the second hull is 4.2m away from the wavemaker, and the lateral distance from the side of the first hull is 0.6825m.

[0122] Table 3 below shows the main parameters of the second hull (including the second liquid tank).

[0123] Second hull parameter Second liquid tank parameter Rectangular float length 5m tank length 3m Rectangular float width 2m tank width 1m Draft 0.2m tank depth 0.5m Discharge 1100kg Liquid carrying capacity 60％

[0124] Table 3

[0125] S3. Set the initial state and motion characteristics of the first and second hulls; specifically including:

[0126] S31. Set the initial state and motion characteristics of the first hull:

[0127] S311. Set the floating state of the first hull to True (floatable); set the floating state of the first liquid tank to True (floatable).

[0128] S312. The heading angle of the ship model is initialized by rotating the first hull in the horizontal plane. In this embodiment, the wave heading angle is the wave-facing angle.

[0129] S313. Set the motion characteristics of the first hull. In the Floating properties window, set the mass, center of gravity, moment of inertia, initial velocity, and degrees of freedom of the first hull. In this embodiment, the mass of the first hull is 386.59 kg, and the coordinates of the center of gravity are (7, 3, 1.975). The moments of inertia of the first hull about the three coordinate axes ox, oy, and oz of the ship's coordinate system are (21.519, 410.034, 410.034). The initial linear velocities of the first hull in the three directions ox, oy, and oz of the ship's coordinate system, and the initial angular velocities about the three coordinate axes are all set to the default value of 0. Release the heave, pitch, and roll of the first hull, and constrain the yaw, sway, and heave. Therefore, restrict the translational displacement in the ox and oy directions, release the translational displacement in the oz direction; restrict the rotation about the oz coordinate axis, and release the rotation about the ox and oy coordinate axes.

[0130] S32. Set the initial state and motion characteristics of the second hull:

[0131] S321. Set the floating state of the second hull to True (floatable); set the floating state of the second liquid tank to True (floatable).

[0132] S322. The heading angle of the ship model is initialized by rotating the second hull in the horizontal plane. In this embodiment, the wave heading angle is the wave-facing angle.

[0133] S323. Set the motion characteristics of the second hull. In the Floating properties window, set the mass, center of gravity, initial velocity, and degrees of freedom of the second hull. In this embodiment, the mass of the second hull is 1100 kg, and the coordinates of the center of gravity are (7, 3, 2.3). The initial linear velocity of the second hull in the three directions (o-xyz) and the initial angular velocity about the three coordinate axes are all set to the default value of 0. Restrict translational displacement in the x and y directions, and release translational displacement in the z direction; restrict rotation about the z coordinate axis, and release rotation about the x and y coordinate axes.

[0134] S4. Fill the first and second liquid tanks with fluid particles; specifically including:

[0135] S41, Fluid particle filling in the first liquid tank:

[0136] S411. Use the DesignSPHysics module to fill fluid particles. Click fillbox and create a new folder named FillTank1 in the root directory of the new case file Floatings Case. Click the FillLimit001 model in the FillTank1 folder to set the fluid particle filling domain of the first liquid tank. The dimensions of the fluid particle filling domain in the OX, OY, and OZ directions of the first liquid tank are 1600mm, 500mm, and 224mm, respectively. The particle filling domain is a cuboid space domain located inside the first hull. The fluid filling rate of the first liquid tank is 70%, that is, the liquid depth in an empty tank with a height of 320mm is 224mm.

[0137] S412. Set the filling source point to any point within the fluid particle filling domain of the first liquid tank. In this embodiment, it is set to point (7, 3, 2) to fill and generate water particles in the fluid particle filling domain of the first liquid tank.

[0138] S42, Fluid particle filling in the second liquid tank:

[0139] S421. Use the DesignSPHysics module to perform fluid particle filling. Click fillbox and create a new folder named FillTank2 in the root directory of the new case file Floatings Case. Click the FillLimit002 model in the FillTank2 folder to set the fluid particle filling domain of the second liquid tank. The dimensions of the particle filling domain in the OX, OY, and OZ directions of the second liquid tank are 3000mm, 1000mm, and 500mm, respectively. The particle filling domain is a cuboid space domain located inside the second hull. The fluid filling rate of the second liquid tank is 60%, that is, the liquid depth in an empty tank with a height of 500mm is 300mm.

[0140] S422. Set the filling source point to any point within the fluid particle filling domain of the second liquid tank. In this embodiment, it is set to point (7, 6, 2, 4) to fill and generate water particles in the fluid particle filling domain of the second liquid tank.

[0141] S5. Set boundary conditions and wave generation mode; specifically including:

[0142] S51. Click on the established Tank model to select the numerical pool domain, and click the Add to DSPHSimulation option to add it to the simulation calculation. Define the six boundary surfaces of the numerical pool domain as Bound, and set the generation mode to Face (the surface of the cavity hexahedron).

[0143] S52. Click on the established Piston1 model, select the wave generator, and click the Add to DSPH Simulation option to add it to the simulation calculation. Set the wave generator type to Bound and the generation mode to Full.

[0144] S53. Click the existing ImportedS175 option to select the first hull (including the first liquid tank) model, and click the Add to DSPH Simulation option to add it to the simulation calculation. Set the type of the first hull (including the first liquid tank) model to Bound and the generation mode to Face (the surface of the cavity hull).

[0145] S54. Click the existing ImportedLNG option to select the second hull (including the second liquid tank) model, and click the Add to DSPH Simulation option to add it to the simulation calculation. Set the type of the second hull (including the second liquid tank) model to Bound and the generation mode to Face (the surface of the cavity hull).

[0146] S55. Set the type of the fluid particle filling domain in the first liquid tank to Fluid and the generation mode to Full.

[0147] S56. Set the type of the fluid particle filling domain in the second liquid tank to Fluid and the generation mode to Full.

[0148] S57. Set the wave-generating mode to push-plate wave generation method, and set the motion properties of the wave-generating plates to simulate waves. Clicking the Motion option will bring up the Motion Configuration option window. Set the motion type of the wave-generating plates to True (can move).

[0149] S58. Set the type, period, wave height, and propagation direction of the target regular wave. In the Create New dropdown menu, select Regular Wave Generator (Piston) to simulate a regular wave using the pusher plate wave generator method. Then, in the newly appearing input box, set the type, period, wave height, and propagation direction of the target wave. In this embodiment, 2ndOrder (second-order Stokes wave) is selected, the underwater depth of the pusher plate is set to 2m, the wave propagation directions corresponding to the two wave generator plates are (1,0,0), the wave height is 0.12m, and the wave period is 1.6s.

[0150] Table 4 below shows the boundary conditions of the structural units of the numerical model established in this embodiment.

[0151]

[0152] Table 4

[0153] S6. Set the mooring chain 9, wave-damping parameters, and typical parameters; specifically including:

[0154] S61. Click the Special option, select Moorings and enable (True). In this embodiment, only the second hull is moored. Set the corresponding MoorDyn Parameters and determine the anchor chain length, position, and number of anchor chain links. Check the second hull particle parameters, click Configure MoorDyn Parameters to set the water depth, free surface height, anchor chain length, anchor chain position, and number of anchor chain links. After setting, click Add a new Line to create anchor chains. In this embodiment, four anchor chains with a length of 2.3m are created and placed at the four corners of the bottom surface of the second hull (4.5, 5, 1.8), (9.5, 5, 1.8), (9.5, 7, 1.8), and (4.5, 7, 1.8), respectively. The other end of the anchor chain is located at (3.5, 4, 0), (10.5, 4, 0), (10.5, 8, 0), and (3.5, 8, 0), respectively. After completing the setup, check the "Save points (CSV)" option in the Moorings Configuration interface.

[0155] S62. Determine the damping location and set the damping parameters such as Limit Min(x, y, z), Limit Max(x, y, z), Overlimit, and Redumax within the damping zone. This will create wave-damping on the three sides of the pool other than the wave-generating plate. Click the Special option, select Damping Zone, and set the damping parameters such as Limit Min(x, y, z), Limit Max(x, y, z), Overlimit, and Redumax to create wave-damping on the three sides of the pool other than the wave-generating plate. In this embodiment, the specific parameters for setting the three wave-damping dampers are as follows: In Damping Zone, Limit Min (12, 0, 0), Limit Max (15, 0, 0), Overlimit are set to 1m and Redumax is set to 10; In Damping Zone 001, Limit Min (0, 0.5, 0), Limit Max (0, 0, 0), Overlimit are set to 1m and Redumax is set to 10; In Damping Zone 002, Limit Min (0, 9.5, 0), Limit Max (0, 10, 0), Overlimit are set to 1m and Redumax is set to 10.

[0156] S63. Set typical parameters, including gravitational acceleration, fluid density, viscosity type, viscosity coefficient, simulation time, step size, and particle spacing. In this embodiment, gravitational acceleration is defined as 9.81 m / s² downwards. 2 Fluid density 1000 kg / m³ 3 Use the system default values ​​for the remaining parameters.

[0157] In the DesignSPHysics module, select the Execution Parameters option to open the DSPHExecution Parameters window, where you can define the viscosity type, viscosity coefficient, simulation time, step size, etc. In this embodiment, double precision is selected for calculation accuracy, the Symplectic algorithm is selected for time integration, Wendland is selected for the interactive kernel function, Artificial is selected for the viscosity formula, the damping coefficient is set to 0.01, the viscosity factor is set to 1, the simulation calculation time is 15 seconds, and the calculation step size is 0.05 seconds.

[0158] In the DesignSPHysics module, define the particle spacing as 0.05m in the Inter-particle distance input box.

[0159] S7. Program execution, solution, and output of calculation results; setting calculation monitoring parameters and data output; confirming the number of particles in the numerical simulation; performing numerical simulation calculations using software program; and outputting results; specifically including:

[0160] S71. Before the program calculation, check and confirm the total number of particles in the numerical simulation in the DesignSPHysics module. In this embodiment, a total of 1,760,392 particles were generated.

[0161] S72. View the rendered images of the two imported ship models, two liquid tanks, mooring devices, and other numerical tank models created using the software. The rendered images of the numerical tank, the first hull (including the first liquid tank), and the second hull (including the second liquid tank) are shown below. Figure 5 As shown in the figure, the effect of filling the numerical water tank, the first liquid chamber, and the second liquid chamber with fluid particles is as follows. Figure 6 As shown, the particle distribution of the flow field within the two hulls and their respective liquid tanks under wave action is as follows: Figure 7 As shown.

[0162] S73. Monitor the displacement and velocity of the six degrees of freedom of the first hull. Input the calculation number of the first hull to view and export the displacement and velocity of the six degrees of freedom of the first hull. For example... Figure 8 and Figure 9 The figures show the time-history curves of the first hull's heave (translation along the oz axis) and pitch (rotational speed around the oy axis) motion in the waves under this working condition.

[0163] S74. Monitor the six degrees of freedom displacement and velocity of the second hull. Enter the calculation number of the second hull to view and export the six degrees of freedom displacement and velocity of the second hull. For example... Figure 10 and Figure 11 The figures show the time-history curves of the second hull's heave (translation along the oz axis) and pitch (rotational speed around the oy axis) motion in the waves under this working condition.

[0164] S75. Monitor the displacement, velocity, acceleration, density, pressure, mass, volume, and vorticity of any fluid particle in a flow field. Input the coordinates of the monitoring point to obtain the displacement, velocity, acceleration, density, pressure, mass, volume, and vorticity of the monitoring point. Figure 12 The figure shows the wave surface elevation time-history curve of the wave field in the numerical water tank, monitored at a location directly in front of the first hull (5m from the ship's center of gravity). Figure 13 The figure shows the time-history curve of the liquid level elevation at the center point of the first liquid tank. Figure 14 As shown, this is the time-history curve of the liquid level elevation at the center point inside the second liquid tank.

[0165] S76. After the program completes the solution, it outputs data such as the fluid pressure on the hull and tank walls, and the tensile and compressive forces on the anchor chains. The solution target is set to the first hull, and the data on the swaying load impact pressure on the first tank wall 6 inside the first hull is output.

[0166] Input the coordinates of the monitoring points to measure the force at those points. Two typical locations on the front and rear walls of the first liquid tank are selected to monitor and output the impact pressure of the swaying load. These two monitoring points are located 124 mm below the water surface, with spatial coordinates (6.2,3,2) and (7.8,3,2), respectively. The time-history curves of the impact pressure of the swaying load measured at the pressure monitoring point on the front and rear walls of the first liquid tank (the central location at a height of 0.124 m below the liquid surface) are shown below. Figure 15 As shown.

[0167] Set the target of the solution to the second hull, and output the data of the swaying load impact pressure on the bulkhead 8 of the second liquid tank inside the second hull.

[0168] Input the coordinates of the monitoring points to measure the force at those points. Two typical locations on the front and rear walls of the second liquid tank are selected to monitor and output the impact pressure of the swaying load. These two monitoring points are located 100 mm below the water surface, with spatial coordinates (5.5, 6, 2.5) and (8.5, 6, 2.5), respectively. The time-history curves of the impact pressure of the swaying load measured at the pressure monitoring point on the front and rear walls of the second liquid tank (the central location 0.10 m below the liquid surface) are shown below. Figure 16 As shown.

[0169] It should also be noted that, in this specification, terms such as "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0170] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for simulating the hydrodynamics of multiple buoys during alongside operations of a liquid cargo vessel, characterized in that, Includes the following steps: S1. Establish a numerical water tank model; the numerical water tank model includes a spatial confinement domain, a numerical water tank domain, a numerical water tank fluid particle filling domain, and a wave generator. S2. Establish models of the first hull, second hull, first liquid tank, and second liquid tank; determine the positions of the liquid tanks inside the hull; merge the liquid tanks and hull; import the hull into the numerical water tank and adjust its position inside the numerical water tank; specifically including: S21. Establish a model of the first hull and the first liquid tank: The surface of the hull was drawn using FreeCAD based on the hull profile and data from the form value table, thus creating a three-dimensional geometric model of the first hull. Establish a three-dimensional geometric model of the first liquid tank, import the first liquid tank model into the first hull model and determine the position of the first liquid tank inside the first hull, and merge the first liquid tank and the first hull into a whole; Taking into account the simulation accuracy requirements, scale effect, and computational efficiency, the geometric scaling ratio of the ship model is determined; the scaling factor for importing the hull model is selected to achieve the scaling ratio between the ship model and the actual ship. Set the spatial position of the first hull in the numerical pool; S22. Establish a model of the second hull and the second liquid tank: The curved surfaces of the hull were drawn using FreeCAD based on the hull profile and data from the form value table, thus creating a three-dimensional geometric model of the second hull. Establish a three-dimensional geometric model of the second liquid tank, import the second liquid tank model into the second hull model and determine the position of the second liquid tank inside the second hull; merge the second liquid tank and the second hull into a whole; Select the scaling factor for the imported hull model to achieve the scale ratio between the hull model and the actual ship. Set the spatial position of the second hull in the numerical pool; S3. Set the initial state and motion characteristics of the first and second hulls; S4. Fill the first and second liquid tanks with fluid particles; specifically including: S41, Fluid particle filling in the first liquid tank: In the software, a fluid particle filling domain is established within the first liquid tank, and the size and position of the fluid particle filling domain within the first liquid tank are set. Water particles are filled and generated in the fluid particle filling domain of the first liquid tank; S42, Fluid particle filling in the second liquid tank: In the software, a fluid particle filling domain is created within the second liquid tank, and the size and position of the fluid particle filling domain within the second liquid tank are set. Water particles are filled and generated in the fluid particle filling domain of the second liquid tank; S5. Set boundary conditions and wave generation mode; S6. Set the mooring anchor chain, wave-damping damping and typical parameters; S7. Program execution, solution, and output of calculation results; setting calculation monitoring parameters and data output; confirming the number of particles in the numerical simulation; performing numerical simulation calculations; and outputting the results; specifically: Before the program calculates, confirm the total number of particles in the numerical simulation; View the renderings of the two hull models, two liquid tanks, and the mooring device; Set the solution objective as the first hull, and output the displacement and velocity data of the first hull's six degrees of freedom; Set the solution objective as the second hull, and output the displacement and velocity data of the second hull's six degrees of freedom; Set the solution target as a fluid particle, and output the displacement, velocity, acceleration, density, pressure, mass, volume and vorticity data of any fluid particle in the flow field of the numerical water tank or liquid tank. After the program completes the solution process, it outputs the fluid pressure and tensile / compressive forces on the hull and tank walls, as well as the anchor chain.

2. The SPH simulation method for multi-buoy hydrodynamics during berthing operations of a liquid cargo ship according to claim 1, characterized in that, Steps S1 to S2 are implemented using FreeCAD, and steps S3 to S7 are implemented using DesignSPHysics.

3. The SPH simulation method for multi-buoy hydrodynamics during berthing operations of a liquid cargo ship according to claim 2, characterized in that, Step S1 is as follows: In FreeCAD, a cuboid cavity region is set up as the spatial constraint region for numerical simulation. The spatial constraint region consists of six faces. A cuboid cavity domain is set as the numerical water pool domain. The numerical water pool domain consists of a bottom boundary surface, a top boundary surface, and four side wall boundary surfaces. The six boundary surfaces of the numerical water pool domain are located inside the spatially confined domain. Establish a solid cuboid model and set it as a rectangular wave-generating plate. The wave-generating plate is located inside the numerical pool domain. The bottom edge of the wave-generating plate is located on the bottom boundary surface of the spatial confinement domain, the top edge is located between the top boundary surface of the numerical pool domain and the top boundary surface of the spatial confinement domain, and the two sides are located on the boundary surfaces of the two side walls of the numerical pool domain, respectively. Establish a fluid particle filling domain for a numerical water tank, and perform the filling and generation of fluid particles within the numerical water tank.

4. The SPH simulation method for multi-buoy hydrodynamics during berthing operations of a liquid cargo ship according to claim 3, characterized in that, The wave-generating plate is a solid unit with a certain thickness.

5. The SPH simulation method for multi-buoy hydrodynamics during berthing operations of a liquid cargo ship according to claim 2, characterized in that, Step S3 specifically includes: S31. Set the initial state and motion characteristics of the first hull: Set the first hull's floating state to be floatable; The first hull is positioned in the numerical pool by translating the ship, and the heading angle of the first hull is initialized by rotating the ship in the horizontal plane. The motion characteristics of the first hull are defined, including: Set the mass, center of gravity coordinates, and moment of inertia about the three coordinate axes of the first hull; set the initial linear velocity and initial angular velocity about the three coordinate axes of the first hull in the three directions; set the translational degrees of freedom and rotational degrees of freedom of the first hull in the three directions. S32. Set the initial state and motion characteristics of the second hull: Set the second hull to a floating state; The second hull is positioned in the numerical tank by translating the ship, and the heading angle of the second hull is initialized by rotating the ship in the horizontal plane. The motion characteristics of the second hull are set, including: Set the mass, center of gravity coordinates, and moments of inertia about the three coordinate axes of the second hull; set the initial linear velocities and initial angular velocities about the three coordinate axes of the second hull in the three directions; set the translational degrees of freedom and rotational degrees of freedom of the second hull in the three directions.

6. The SPH simulation method for multi-buoy hydrodynamics during berthing operations of a liquid cargo ship according to claim 3, characterized in that, Step S5 is as follows: Add the numerical pool domain to the simulation calculation, set the 6 boundary surfaces of the numerical pool domain as wall boundaries, and set the generation mode to the surface of a cavity hexahedron. Add the wave generator to the simulation calculation, set the wave generator type to wall boundary, and the generation mode to solid; Add the first and second hulls to the simulation calculation, set the ship model type to wall boundary, and the generation mode to surface; Set the fluid particle model in the first and second liquid tanks to fluid boundary and the generation mode to solid. The wave generation mode was set to the push-plate wave generation method, and the motion properties of the wave generation plates were set to simulate waves. Set the target rule wave type, period, wave height, and propagation direction.

7. The SPH simulation method for multi-buoy hydrodynamics during berthing operations of a liquid cargo ship according to claim 2, characterized in that, Step S6 is as follows: Select the hull to be moored and set the corresponding MoorDyn Parameters, and determine the anchor chain length, position, and number of anchor chain links; Set Limit Min (x, y, z), Limit Max (x, y, z), Overlimit and Redumax damping parameters to set wave damping on the three sides of the numerical water tank other than the wave-generating plate; Set typical parameters, including gravitational acceleration, fluid density, viscosity type, viscosity coefficient, simulation time, step size, and particle spacing.

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