A method for simulating coupling between ship motion and tank sloshing by using SPH

Abstract

This invention discloses a wave dynamics (SPH) simulation method for the coupling of liquid cargo ship motion and tank sloshing, comprising the following steps: S1, building a numerical wave tank model and setting boundaries; S2, establishing a hull model and a tank wall model, and setting the position of the tank walls inside the hull; S3, merging the imported hull model and tank wall model to generate a ship model containing the tank walls; S4, setting the ship model parameters and motion state; S5, filling and setting the properties of fluid particles in the tank; S6, setting the wave generation mode, wave damping, and typical parameters; S7, running the program to solve and outputting the calculation results. This invention uses a numerical wave tank simulation technique for liquid cargo ships with internal tanks to simulate the coupled response of ship motion and tank sloshing under wave action, achieving a two-way feedback between ship motion causing tank motion and the sloshing load of the fluid inside the tank affecting the ship motion.

Description

Technical Field

[0001] This invention belongs to the field of liquid cargo ship motion prediction technology, specifically relating to a SPH simulation method that couples the motion of a liquid cargo ship with the sloshing of the liquid tank. Background Technology

[0002] Liquid cargo ships are the primary carriers for transporting marine oil and gas resources. With the increasing global demand for oil and gas energy, the construction of liquid cargo ships is trending towards larger sizes. When a liquid cargo ship moves in waves, it induces fluid sloshing within the tanks. The forces or moments generated by this sloshing then react on the hull, thus creating a coupled effect on the ship's motion. Therefore, research on the coupling between hull motion and tank sloshing under wave action is essential. Currently, research on the hydrodynamic problems of liquid cargo ships is divided into two independent aspects: hull motion and tank sloshing. However, research on the coupled simulation of liquid cargo ship motion in waves and tank sloshing is relatively limited.

[0003] In recent years, CFD technology has been widely used in the study of ship seakeeping performance. However, gridded CFD methods based on RANS have some shortcomings in simulating problems such as slamming waves, tank sloshing, and fluid breakage. The SPH method is a meshless method based on the Lagrangian algorithm, which uses free-flowing particles to simulate motion. It avoids the mesh distortion problem that occurs in mesh generation methods and can effectively simulate large deformations and fluid breakage, especially suitable for simulating violent motions such as tank sloshing. Summary of the Invention

[0004] The main objective of this invention is to overcome the shortcomings and deficiencies of the prior art and to propose a SPH simulation method that couples the motion of liquid cargo ships with the sloshing of liquid tanks.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A SPH simulation method coupling liquid cargo ship motion and tank sloshing includes the following steps:

[0007] S1. Construct the numerical water tank model and set its boundaries; the numerical water tank model includes the spatial confinement domain, the numerical water tank domain, the numerical water tank fluid particle filling domain, and the wave generator.

[0008] S2. Create the hull model and liquid tank bulkhead model, and set the position of the liquid tank bulkhead inside the hull.

[0009] S3. Merge the hull model and the liquid tank bulkhead model to generate a ship model that includes the liquid tank bulkhead;

[0010] S4. Set the ship model parameters and motion status;

[0011] S5, Liquid Tank Fluid Particle Filling and Attribute Setting: Fills and generates water particles in the fluid particle filling domain within the liquid tank.

[0012] S6. Set the wave generation mode, wave damping and typical parameters;

[0013] S7. Program execution, solution, and output of calculation results.

[0014] Furthermore, steps S1 to S2 are implemented using FreeCAD, and steps S3 to S7 are implemented using DesignSPHysics.

[0015] Furthermore, step S1 specifically includes:

[0016] In FreeCAD, a cuboid cavity domain is created as the spatial constraint domain of the numerical water tank. The spatial constraint domain consists of six faces.

[0017] A cuboid cavity domain is established as a 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.

[0018] Establish a solid cuboid model and set it as a rectangular wave-generating plate. The wave-generating plate is located inside the numerical water tank domain. The bottom edge of the wave-generating plate is located on the bottom boundary surface of the restricted domain, the top edge is located between the top boundary surface of the numerical water tank domain and the top boundary surface of the restricted domain, and the two sides are located on the boundary surfaces of the two side walls of the numerical water tank domain, respectively.

[0019] Establish the fluid particle filling domain of the numerical water tank, and perform the filling and generation of fluid particles in the numerical water tank;

[0020] Set the six boundary surfaces of the numerical water pool domain as wall boundaries and the generation mode as the surface of a cavity hexahedron; set the wave-generating plate type as wall boundary and the generation mode as solid; set the fluid particle filling domain type as fluid and the generation mode as solid.

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

[0022] Furthermore, step S2 specifically includes:

[0023] S21. Establish the ship hull model, specifically:

[0024] The three-dimensional geometric model of the hull was drawn using FreeCAD software based on the hull lines drawing and the data in the form value table; the geometric scale ratio of the ship model was determined according to the simulation accuracy requirements, scale effect and computational efficiency.

[0025] S22. Establish a model of the liquid tank wall, specifically as follows:

[0026] The tank wall model was created using FreeCAD software;

[0027] S23. Set the position of the liquid tank bulkhead inside the hull model.

[0028] Furthermore, step S3 specifically includes:

[0029] The hull model and the liquid tank bulkhead model are combined into a ship model that includes the liquid tank bulkhead.

[0030] Based on the established hull and tank bulkhead model, select the scaling factor for the imported model to adjust the ship to the model scale;

[0031] Set the spatial position of the ship model in the numerical tank;

[0032] Add the ship model to the simulation calculation, set the ship type to wall boundary, and the generation mode to surface.

[0033] Furthermore, step S4 specifically involves:

[0034] Set the initial state of the ship and set the hull's floating state to be floatable;

[0035] The initial setting of the ship's heading angle is achieved by rotating the hull in the horizontal plane;

[0036] Set the ship's mass and motion parameters:

[0037] Set the ship's mass, center of gravity coordinates, and moments of inertia about the three coordinate axes; set the initial linear velocities of the hull in the three directions and the initial angular velocities about the three coordinate axes; set the ship's translational degrees of freedom in the three directions and rotational degrees of freedom about the three coordinate axes.

[0038] Furthermore, step S5 specifically involves:

[0039] In the software, a fluid particle filling domain is created inside the liquid tank, and the size and position of the fluid particle filling domain inside the liquid tank are set.

[0040] The filling and generation of water particles in the fluid particle filling domain of the liquid tank.

[0041] Furthermore, step S6 specifically involves:

[0042] In the software, the wave generation mode is set to the push-plate wave generation method, and the motion properties of the wave generation plate are set to simulate waves.

[0043] Set the target rule wave type, period, wave height, and propagation direction;

[0044] Determine the location of the wave-damping region, set wave-damping on the three sides of the numerical water tank other than the wave-generating plate, and set the Limit Min(x,y,z), Limit Max(x,y,z), Overlimit and Redumax damping parameters within the damping region;

[0045] Set the gravitational acceleration, fluid density, viscosity type, viscosity coefficient, simulation time, step size, and particle spacing.

[0046] Furthermore, step S7 specifically includes:

[0047] Before the program calculates, confirm the total number of particles in the numerical simulation;

[0048] View the imported ship model and the numerical water tank modeling effect diagram of the liquid tank;

[0049] The software program performs numerical simulation and solution;

[0050] After the program finishes running and solving, view the data, including:

[0051] Set the target of the solution as the ship hull, and output the displacement and velocity data of the ship hull's six degrees of freedom motion;

[0052] Set the solution target to the surface of the hull or liquid tank wall, and output the fluid pressure data on the surface of the hull or liquid tank wall.

[0053] Set the solution target as a fluid particle, and output the displacement, velocity, acceleration, density, pressure, mass, volume, and vorticity data of a point in the flow field.

[0054] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0055] 1. The SPH method used in this invention is a pure Lagrange method, which can avoid the interface problem between the Euler mesh and the structural material in the Euler description. Therefore, compared with the CFD / RANS method based on the finite volume method (FVM) and the potential flow theory based on the boundary element method (BEM), the SPH method is more suitable for solving highly nonlinear fluid-structure interaction dynamics problems such as high-speed fluid collision, free surface breakage and splashing in the sloshing flow process inside the liquid tank.

[0056] 2. This invention overcomes the shortcomings of current mainstream SPH-based methods, which can only simulate ship motion or tank sloshing technology individually. By establishing a numerical wave pool simulation technology for the internal tanks of liquid cargo ships, it simulates the coupled response of ship motion and tank sloshing under wave action, realizing bidirectional feedback of ship motion causing tank motion and internal fluid sloshing load affecting ship motion.

[0057] 3. In the method of this invention, all modeling and calculation work in the numerical simulation process of the coupling of ship motion and liquid tank sloshing is completed using 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

[0058] Figure 1 This is a flowchart of the method of the present invention;

[0059] Figure 2 This is a schematic diagram of a numerical water tank model;

[0060] Figure 3 It is a geometric model of the ship's hull and bulkheads;

[0061] Figure 4 This is a diagram illustrating the effect of fluid particle filling in a numerical water tank and a liquid tank of a ship model.

[0062] Figure 5 It is a three-dimensional view of the particle distribution of the wave field around the hull and the flow field inside the liquid tank;

[0063] Figure 6 It is a mid-longitudinal cross-sectional view of the particle distribution of the wave field around the hull and the flow field inside the liquid tank.

[0064] Figure 7 It is the time-history curve of the ship's heave motion;

[0065] Figure 8 It is the time-history curve of the ship's pitching motion;

[0066] Figure 9 This is a front view showing the locations of pressure monitoring points on the front and rear walls of the liquid tank;

[0067] Figure 10 These are the fluid sloshing impact load time-history curves at typical locations on the front and rear surfaces of the bulkhead;

[0068] Figure 11 It is the wave surface elevation time-history curve at a point 5m directly in front of the ship's center of gravity in the numerical water tank;

[0069] Figure 12 It is the time-history curve of the liquid level elevation at the center point inside the rectangular liquid tank;

[0070] The following are the symbols in the attached figures: 1-Spatial confinement domain; 2-Numerical pool domain; 3-Numerical pool fluid particle filling domain; 4-Wavemaker; 5-Hull; 6-Liquid tank bulkhead; 7-Numerical pool boundary surface; 8-Fluid particles in the numerical pool; 9-Fluid particles in the hull liquid tank. Detailed Implementation

[0071] 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.

[0072] Example

[0073] In this embodiment, the open-source software FreeCAD is used to build the geometric models of the numerical water tank and the liquid cargo ship, and the open-source software DesignSPHysics is used to generate fluid particles and perform numerical calculations. 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.

[0074] like Figure 1 As shown, this invention provides a SPH simulation method coupling the motion of a liquid cargo ship with the sloshing of its tanks, comprising the following steps:

[0075] S1. Establish the geometric model and boundary settings of the numerical water tank; the numerical water tank model includes the spatial confinement domain, the numerical water tank domain, the numerical water tank fluid particle filling domain, and the wave generator; specifically including:

[0076] S11. Open the DesignSPHysic plugin in FreeCAD, then create a new case file named New Case under Pre-processing in the plugin and name it Sloshing Case. Use FreeCAD to create the geometric model of the numerical water tank case under the new case file Sloshing Case.

[0077] S12. In the Case Limits (3D) model under the root directory of the new case file Sloshing Case, set a cuboid cavity domain as the spatial constraint domain of the numerical water tank. The spatial constraint domain consists of six faces. The size of the constraint domain must be larger than all geometric models. The geometric models for subsequent modeling and calculation need to be constrained within the spatial constraint domain. Therefore, in this embodiment, the scales of the spatial constraint domain in the OX, OY, and OZ directions are 20000mm, 10000mm, and 10000mm, respectively. The coordinates of the source point O of the spatial constraint domain are (0, 0, 0).

[0078] S13. Create a new model named Tank in the root directory of the new case file Sloshing Case, and set it as a cuboid cavity domain as a 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, and the boundary surfaces of the numerical water tank domain are all located inside the spatially confined domain.

[0079] In this embodiment, the dimensions of the numerical water tank domain in the OX, OY, and OZ directions are 15000mm, 6000mm, and 6000mm, respectively; the bottom boundary surface (15000mm×6000mm) coincides with the bottom boundary surface of the spatial confinement domain; and one of the side boundary surfaces (6000mm×6000mm) coincides with the wave-generating plate.

[0080] S14. Create a solid cuboid model named Piston in the root directory of the new Sloshing Case file and set it as a rectangular wave generator. The wave generator is located inside the numerical pool domain. The wave generator is positioned near one side wall boundary and parallel to the side wall boundary of the numerical pool (6000mm × 6000mm). The bottom edge of the wave generator is located on the bottom boundary of the confinement domain, the top edge is located between the top boundary of the numerical pool domain and the top boundary of the confinement domain, and the two sides are located on the two side wall boundaries of the numerical pool domain. The wave generator is a solid element with a certain thickness, and its width (OY direction), height (OZ direction), and thickness (OX direction) are 6000mm, 6000mm, and 700mm, respectively.

[0081] The numerical water tank model established in this embodiment is as follows: Figure 2 As shown, the parameters of each component are shown in Table 1 below.

[0082] name Base point coordinates X-direction range / mm Y-direction range / mm Z-direction range / mm type Spatial confinement domain (0,0,0) 20000 10000 10000 cuboid cavity region Numerical pool domain (0,0,0) 15000 6000 6000 cuboid cavity region Wave board (0,0,0) 700 6000 6000 solid board

[0083] Table 1

[0084] S15. Fluid particle filling in the numerical water tank, specifically including the following settings:

[0085] Use the DesignSPHysics module to fill the fluid particles in the numerical water tank. Click the fillbox and create a new folder named FillTank1 in the root directory of the new case file, Sloshing Case.

[0086] Click on the FillLimit model in the FillTank1 folder to set the fluid particle filling domain of the numerical water tank. The dimensions of the fluid particle filling domain in the OX, OY, and OZ directions are 14300mm, 6000mm, and 2000mm, respectively. The fluid particle filling 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 of the water tank. One side surface (6000mm × 2000mm) coincides with one surface of the wave-generating plate, and the other two side surfaces (14300mm × 2000mm) coincide with the sidewall boundary surface of the numerical water tank domain.

[0087] The filling source point is set at 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.

[0088] S16. Boundary conditions and fill mode settings:

[0089] Add the numerical pool domain to the simulation calculation, define the 6 boundary surfaces of the numerical pool domain as Bound (wall boundary), and set the generation mode to Face (surface of the cavity hexahedron);

[0090] Add the wave generator to the simulation calculation, set the wave generator type to Bound (wall boundary), and set the generation mode to Full (solid);

[0091] The type of the fluid particle filling domain in the numerical water tank is set to fluid; the boundary type of the fluid particle filling domain is set to Fluid, and the generation mode is set to Full. Table 2 below shows the boundary conditions of each structural element of the numerical water tank model.

[0092]

[0093]

[0094] Table 2

[0095] S2. Create the hull model and liquid tank bulkhead model, and determine the position of the liquid tank bulkheads inside the hull; including:

[0096] S21. Establish the ship hull model:

[0097] In this embodiment, the standard S175 type container ship is selected as an example. The actual ship has a waterline length of 175m, a beam of 25.4m, a depth of 19.5m, a draft of 9.5m, and a displacement of 23711t. The three-dimensional geometric model of the hull is drawn using FreeCAD software based on the hull line drawings and shape value tables.

[0098] Taking into account factors such as simulation accuracy requirements, scale effects, and computational efficiency, the geometric scale ratio of the ship model was determined to be 1:40. The main parameters of the scaled-down ship model are shown in Table 3 below.

[0099] ship model parameter captain 4.375m Width 0.635m drinking water 0.238m Discharge 386.59kg

[0100] Table 3

[0101] S22. Establish a model of the liquid tank bulkhead:

[0102] A rectangular liquid tank wall model was created using FreeCAD. In this embodiment, the length, width, and height of the rectangular liquid tank are 1600mm, 500mm, and 320mm, respectively.

[0103] The rectangular liquid tank bulkhead model was imported into the 3D geometric model of the ship's hull, and the position of the bulkhead inside the hull was adjusted. The top surface of the liquid tank coincides with the deck surface of the hull, the mid-longitudinal section of the liquid tank coincides with the mid-longitudinal section of the hull, the two side bulkheads of the liquid tank are 67.5 mm from the side plates of the hull, and the forward bulkhead of the liquid tank is 1240 mm from the bow. The main parameters of the liquid tank at the model scale are shown in Table 4 below.

[0104] Liquid tank parameter tank length 1.6m tank width 0.5m tank depth 0.32m Liquid carrying capacity 70％

[0105] Table 4

[0106] S3. Merge the imported hull model and liquid tank bulkhead model to generate a ship model containing liquid tank bulkheads; specifically including:

[0107] S31. Merge the hull model and the tank bulkhead model into a single unit; click on the S175 hull model file and the tank model file 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 tank and hull is as follows. Figure 3 As shown.

[0108] S32. In the root directory of the new case file Sloshing Case, import the created 3D geometric model of the hull and liquid tanks, name it ImportedS175, and select the scaling factor of the imported model to adjust the ship to the model size.

[0109] S33. Click on the ImportedS175 model and set the center of gravity coordinates of the ship model to (7, 3, 1.975), so that the model is located in the middle area of ​​the pool.

[0110] S34. Add the ship model (including bulkheads) to the simulation calculation, set the ship model (including bulkheads) type to wall boundary, and the generation mode to surface. Add the ship model to the simulation calculation, set the hull model (including tank walls) type to Bound (wall boundary), and the generation mode to Face (surface of a cavity hull).

[0111] S4. Set hull parameters and motion status; specifically including:

[0112] S41. Select the existing hull model file and set the hull's floating state to True (floating). Select the existing liquid tank model file and set the rectangular liquid tank's floating state to True (floating).

[0113] S42. The heading angle of the ship model is initialized by rotating the hull in the horizontal plane.

[0114] S43. Set the hull's mass parameters and motion characteristics. In the Floating properties window, set the hull's mass, center of gravity, moment of inertia, initial velocity, and degrees of freedom. In this embodiment, the corresponding hull model's mass is 386.59 kg, and the center of gravity's coordinates are (7, 3, 1.975), in meters (m). The moment of inertia of the hull model about the three coordinate axes ox, oy, and oz of the ship's coordinate system is (21.519, 410.034, 410.034), in kg·m³. The initial linear velocities of the 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 degrees of freedom of the hull model, and constrain the yaw, sway, and pitch degrees of freedom. Therefore, restrict the translational displacement in the ox and oy directions, and 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.

[0115] S5, Liquid Tank Fluid Particle Filling and Property Settings, including:

[0116] S51. Fluid particle filling in the ship's hull liquid tanks, specifically including the following settings:

[0117] Use the DesignSPHysics module to fill the fluid particles inside the ship's hull tanks. Click fillbox, and create a new folder named FillTank2 in the root directory of the new case file, Sloshing Case.

[0118] Click on the FillLimit001 model in the FillTank2 folder and set the fluid particle filling domain for the liquid tank. The dimensions of the particle filling domain in the OX, OY, and OZ directions are 1600mm, 500mm, and 224mm, respectively. The particle filling domain is a cuboid space domain located inside the hull model domain. The fluid filling rate of the liquid tank is 70%, meaning that the liquid depth in an empty tank with a height of 320mm is 224mm.

[0119] Click on the FillPoint001 model in the FillTank2 folder, and set the fill source point to any point within the fluid particle filling domain of the liquid tank. In this embodiment, it is set to point (7, 3, 2) to fill and generate water particles within the fluid particle filling domain of the ship's liquid tank. The effect of fluid particle filling in the numerical water tank and ship model liquid tank is as follows. Figure 4 As shown.

[0120] S52. Set the type of the fluid particle filling domain in the liquid tank to Fluid. Click the existing FillBox001 folder option to select the particle filling domain of the hull liquid tank, set the type of the particle filling domain to Fluid, and the generation mode to Full.

[0121] S6. Set the wave generation mode, wave suppression damping, and typical parameters; specifically including:

[0122] S61. Set the motion type of the wave-generating plate to True (movable); select the wave-generating mode and use the push-plate wave-generating method to simulate regular waves.

[0123] S62. Set the target wave type, period, wave height, propagation direction, etc. In this embodiment, a 2nd Order (second-order Stokes wave) is selected, the underwater depth of the pusher plate is set to 2m, the wave propagation direction corresponding to the wave generator plate is (1,0,0), that is, the wave propagates along the OX direction, the wave height is 0.12m, and the wave period is 1.6s.

[0124] S63. Select the Damping Zone and set damping parameters such as Limit Min(x, y, z), Limit Max(x, y, z), Overlimit, and Redumax to provide wave-damping for the three side walls inside the pool, excluding those used as wave-generating plates. The specific parameters for the three wave-damping zones in this embodiment are as follows:

[0125] In the first Damping Zone, Limit Min (12, 0, 0), Limit Max (15, 0, 0), Overlimit are set to 1m and Redumax is set to 10;

[0126] In the second Damping Zone001, Limit Min (0, 0.5, 0), Limit Max (0, 0, 0), Overlimit are set to 1m and Redumax is set to 10;

[0127] In the third Damping Zone002, Limit Min (0, 5.5, 0), Limit Max (0, 6, 0), Overlimit are set to 1m, and Redumax is set to 10.

[0128] S64. Set the gravitational acceleration, fluid density, viscosity type, viscosity coefficient, simulation time, step size, and particle spacing, including the following settings:

[0129] In the DesignSPHysics module, parameters such as gravitational acceleration and fluid density are defined. 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.

[0130] In the DesignSPHysics module, define the viscosity type, viscosity coefficient, simulation time, step size, etc. In this embodiment, double precision is selected for calculation accuracy, Symplectic algorithm is selected for time integration, Wendland is selected for the interactive kernel function, Artificial is selected for the viscosity formula, damping coefficient is set to 0.01, viscosity factor is set to 1, simulation calculation time is 15 seconds, and calculation step size is 0.05 seconds, etc.

[0131] In the DesignSPHysics module, the particle spacing is defined as 0.05m.

[0132] S7. Program execution, solution, and output of calculation results; specifically including:

[0133] 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 1,560,392 particles were generated.

[0134] S72. View the imported ship model and liquid tank numerical water tank software modeling effect diagram;

[0135] S73. Start numerical simulation calculations in the DesignSPHysics module.

[0136] like Figure 5 The image shows a three-dimensional view of the particle distribution in the wave field around the ship and the flow field inside the liquid tank at time t = 2s. Figure 6 The figure shows a mid-longitudinal cross-sectional view of the particle distribution of the wave field around the hull and the flow field inside the liquid tank at time t = 2s.

[0137] S74. After the program finishes solving, select Post-prossessing in the DesignSPHysics module to view and output data such as wavefront elevation curves, hull motion, hull tank wall stress, and fluid particle information; specifically including:

[0138] Set the target of the solution as the ship hull, output the displacement and velocity data of the ship's six degrees of freedom, and view and export the displacement and velocity data of the ship's six degrees of freedom. For example... Figure 7 and Figure 8 The figures show the time-history curves of the ship model's heave (translation along the oz axis) and pitch (rotational speed around the oy axis) motion in the waves under this working condition.

[0139] The objective is set as the ship hull, and the data of the sloshing load impact pressure on the walls of the internal liquid tanks is output. Two typical locations on the fore and aft walls of the liquid tanks are selected to monitor and output the impact pressure of the sloshing 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 front view of the pressure monitoring points on the fore and aft walls of the liquid tanks is shown below. Figure 9 As shown in the figure. The time-history curve of the impact pressure of the liquid tank sloshing under this operating condition is as follows. Figure 10 As shown.

[0140] Set the target of the solution as a fluid particle, and output the wavefront elevation, displacement, velocity, acceleration, density, pressure, mass, volume, and vorticity data in the flow field. Input the coordinates of the monitoring point, and wait for the measured wavefront elevation, displacement, velocity, acceleration, density, pressure, mass, volume, and vorticity of the monitoring point to be completed. Figure 11 The figure shows the wave surface elevation time-history curve of the wave field monitored at the front of the ship (5m from the ship's center of gravity) in the numerical water tank. Figure 12 As shown, this is the time-history curve of the liquid level elevation at the center point of the rectangular liquid tank inside the ship's hull.

[0141] 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.

[0142] 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 SPH simulation method coupling liquid cargo ship motion and tank sloshing, characterized in that, Includes the following steps: S1. Construct the numerical water tank model and set its boundaries; the numerical water tank model includes the spatial confinement domain, the numerical water tank domain, the numerical water tank fluid particle filling domain, and the wave generator. S2. Create the hull model and liquid tank bulkhead model, and set the position of the liquid tank bulkhead inside the hull. S3. Merge the hull model and the liquid tank bulkhead model to generate a ship model that includes the liquid tank bulkhead; S4. Set the ship model parameters and motion status; S5, Liquid Tank Fluid Particle Filling and Attribute Setting: Fills and generates water particles in the fluid particle filling domain within the liquid tank. S6. Set the wave generation mode, wave damping and typical parameters; S7. Program execution, solution, and output of calculation results; Steps S1 to S2 were implemented using FreeCAD, and steps S3 to S7 were implemented using DesignSPHysics. Step S2 specifically includes: S21. Establish the ship hull model, specifically: The three-dimensional geometric model of the hull was drawn using FreeCAD software based on the hull lines drawing and the data in the form value table; the geometric scale ratio of the ship model was determined according to the simulation accuracy requirements, scale effect and computational efficiency. S22. Establish a model of the liquid tank wall, specifically as follows: The tank wall model was created using FreeCAD software; S23. Set the position of the liquid tank bulkhead inside the hull model; Step S3 is as follows: The hull model and the liquid tank bulkhead model are combined into a ship model that includes the liquid tank bulkhead. Based on the established hull and tank bulkhead model, select the scaling factor for the imported model to adjust the ship to the model scale; Set the spatial position of the ship model in the numerical tank; Add the ship model to the simulation calculation, set the ship type to wall boundary, and the generation mode to surface; Step S4 is as follows: Set the initial state of the ship and set the hull's floating state to be floatable; The initial setting of the ship's heading angle is achieved by rotating the hull in the horizontal plane; Set the ship's mass and motion parameters: Set the ship's mass, center of gravity coordinates, and moments of inertia about the three coordinate axes; set the initial linear velocities of the hull in the three directions and the initial angular velocities about the three coordinate axes; set the ship's translational degrees of freedom in the three directions and rotational degrees of freedom about the three coordinate axes. Step S5 is as follows: In the software, a fluid particle filling domain is created inside the liquid tank, and the size and position of the fluid particle filling domain inside the liquid tank are set. The filling and generation of water particles in the fluid particle filling domain within the liquid tank; Step S6 is as follows: In the software, the wave generation mode is set to the push-plate wave generation method, and the motion properties of the wave generation plate are set to simulate waves. Set the target rule wave type, period, wave height, and propagation direction; Determine the location of the wave-damping region, set wave-damping on the three sides of the numerical water tank other than the wave-generating plate, and set the Limit Min (x, y, z), Limit Max (x, y, z), Overlimit and Redumax damping parameters within the damping region; Set the gravitational acceleration, fluid density, viscosity type, viscosity coefficient, simulation time, step size, and particle spacing.

2. The SPH simulation method for coupling the motion of a liquid cargo ship with the sloshing of its tanks, as described in claim 1, is characterized in that... Step S1 is as follows: In FreeCAD, a cuboid cavity domain is created as the spatial constraint domain of the numerical water tank. The spatial constraint domain consists of six faces. A cuboid cavity domain is established as a 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 water tank domain. The bottom edge of the wave-generating plate is located on the bottom boundary surface of the restricted domain, the top edge is located between the top boundary surface of the numerical water tank domain and the top boundary surface of the restricted domain, and the two sides are located on the boundary surfaces of the two side walls of the numerical water tank domain, respectively. Establish the fluid particle filling domain of the numerical water tank, and perform the filling and generation of fluid particles in the numerical water tank; Set the six boundary surfaces of the numerical water pool domain as wall boundaries and the generation mode as the surface of a cavity hexahedron; set the wave-generating plate type as wall boundary and the generation mode as solid; set the fluid particle filling domain type as fluid and the generation mode as solid.

3. The SPH simulation method for coupling the motion of a liquid cargo ship with the sloshing of its tanks, as described in claim 2, is characterized in that... The wave-generating plate is a solid unit with a certain thickness.

4. The SPH simulation method for coupling the motion of a liquid cargo ship with the sloshing of its tanks, as described in claim 1, is characterized in that... Step S7 is as follows: Before the program calculates, confirm the total number of particles in the numerical simulation; View the imported ship model and the numerical water tank modeling effect diagram of the liquid tank; The software program performs numerical simulation and solution; After the program finishes running and solving, view the data, including: Set the target of the solution as the ship hull, and output the displacement and velocity data of the ship hull's six degrees of freedom motion; Set the solution target to the surface of the hull or liquid tank wall, and output the fluid pressure data on the surface of the hull or liquid tank wall. Set the solution target as a fluid particle, and output the displacement, velocity, acceleration, density, pressure, mass, volume, and vorticity data of a point in the flow field.

Images