Method for forecasting response of energy-saving guide pipe structure in front of propeller in ship steering state

Abstract

The invention discloses a method for forecasting the response of an energy-saving conduit structure in front of a propeller in a ship steering state, and the method comprises the steps: obtaining a ship flow field model, simulating and obtaining the transient flow field of a target ship in different steering states based on a CFD method, and obtaining the transient pressure load distribution corresponding to a set fluid domain grid node through calling Starccm + software; obtaining structural domain grid nodes of the energy-saving conduit area in front of the ship propeller through finite element software according to a preset ship finite element model; on the basis of a nearest neighbor interpolation method and according to the node space distance, transient pressure load distribution data corresponding to the fluid domain grid nodes are mapped to the structural domain grid node with the nearest space distance, and a structure-load coupling file is obtained; and calling LS-Dyna software to obtain the structural response of the pre-oar energy-saving conduit according to the structure-load coupling file, thereby solving the problem that the structural response in the actual operation process of the conduit is difficult to reflect although a corresponding conduit efficacy load calculation method is given in a standard manner at present.

Description

Technical Field

[0001] The present invention relates to the technical field of ship engineering, and in particular to a method for predicting the structural response of an energy-saving duct in front of a propeller in a ship steering state. Background Art

[0002] With the continuous advancement of energy conservation, emission reduction, and green shipping concepts, propeller-forward energy-saving ducts, as an energy-saving device that effectively improves propeller propulsion efficiency, have been widely used in various commercial and specialized vessels. This device guides the incoming flow in front of the hull, optimizing the propeller inflow angle, thereby improving propulsion performance and reducing fuel consumption. However, during actual navigation, especially during rotational movements such as steering and turning, the ship's flow field undergoes drastic changes, resulting in significantly increased fluid loads on the energy-saving ducts and unsteady characteristics, which in turn places higher demands on their structural safety.

[0003] Because the connection area between the energy-saving duct and the hull is relatively fragile, the duct can be subjected to significant hydrodynamic loads during maneuvering, potentially causing it to detach and damage the hull structure. Current research on propeller-front energy-saving ducts has primarily focused on evaluating their static propulsion efficiency and analyzing flow characteristics under steady-state conditions. However, relatively little research has been conducted on predicting the structural response of energy-saving ducts under complex dynamic conditions, such as ship steering. In particular, during actual navigation, limited measurement conditions and environmental disturbances at sea make it difficult to obtain real-time structural stress information, making it difficult to meet engineering requirements for early warning of duct structural safety. Consequently, while current standards provide methods for calculating effective duct loads, these methods often struggle to reflect the structural response of ducts during actual operation.

[0004] Therefore, there is an urgent need for an analysis method that can quickly and effectively predict the structural response of the energy-saving duct under steering conditions by combining ship motion monitoring data. Summary of the Invention

[0005] The present invention provides a method for predicting the structural response of an energy-saving duct in front of a propeller when a ship is steering, so as to overcome the above technical problems.

[0006] In order to achieve the above object, the technical solution of the present invention is:

[0007] A method for predicting the structural response of an energy-saving duct in front of a propeller during ship steering comprises the following steps:

[0008] S1: Import the pre-established 3D model of the target ship into the Starccm+ software, and construct the calculation domain and boundary conditions of the target ship;

[0009] The calculation domain includes a background domain, a hull overlap domain and a rudder domain;

[0010] The computational domain boundary conditions include inlet boundary conditions, outlet boundary conditions, and wall boundary conditions;

[0011] The ship flow field model is obtained by coupling the computational domain based on the overlay grid technology;

[0012] S2: Based on the CFD method, the SST k-ω turbulence model and the virtual disk are combined with the computational domain boundary conditions to simulate and obtain the transient flow field of the target ship under different steering states;

[0013] The virtual disk is a virtual entity that simplifies the ship propeller into a virtual entity for providing thrust for the ship through the Starccm+ software;

[0014] The fluid domain grid is set according to the ship flow field model, and the mesh nodes of the fluid domain are the mesh nodes of the area where the energy-saving duct surface in front of the propeller of the target ship is located;

[0015] S3 builds a six-degree-of-freedom motion model of the ship and obtains the transient pressure load distribution corresponding to the fluid domain grid nodes according to the transient flow field by calling the run control component of the Starccm+ software, thereby obtaining the pressure load database of the energy-saving duct in front of the propeller;

[0016] S4: Establish a finite element model of the ship based on the ship's material properties;

[0017] The ship material properties shall at least include the elastic modulus, Poisson's ratio and material density of the ship steel;

[0018] The shell element partitioning tool Mesh in the finite element software is called to perform regional meshing on the ship finite element model to obtain the structural domain mesh nodes of the energy-saving duct area in front of the ship propeller;

[0019] S5: Obtain the spatial distance between each node of the structure domain grid and the fluid domain grid;

[0020] Based on the nearest neighbor interpolation method and the propeller front energy-saving duct pressure database, the transient pressure load distribution data corresponding to the fluid domain grid node is mapped to the structural domain grid node with the smallest spatial distance to obtain the structure-load coupling file;

[0021] The LS-Dyna software is used to obtain the structural response of the energy-saving duct in front of the propeller according to the structure-load coupling file;

[0022] The structural response includes stress / strain values of various regions of the energy-saving duct in front of the propeller;

[0023] S6: The structural response of the propeller front energy-saving duct is visualized using the LS-Prepost software, and the maximum stress / strain value of the propeller front energy-saving duct under the current steering state is extracted to predict the structural response of the propeller front energy-saving duct under different steering states of the ship.

[0024] Furthermore, the six-degree-of-freedom motion model of the target ship constructed in S3 is

[0025]

[0026] Where: m represents the mass of the hull; u, v, w represent the linear velocity of the target ship's hull in the x, y, z directions of the preset coordinate system respectively; p, q, r represent the angular velocity of the target ship's hull around the x, y, z axes respectively; X, Y, Z and K, M, N represent the force and torque acting on the target ship's hull respectively; I x ,I y ,I z Represent the moment of inertia in the x, y, and z directions relative to the center of gravity of the ship.

[0027] Furthermore, the rules for constructing the computational domain of the target ship in S1 include:

[0028] Background domain setting rules, hull overlap domain setting rules, and rudder domain setting rules;

[0029] The background domain setting rules:

[0030] The first preset distance from the bow is used as the front boundary of the background domain, and the second preset distance from the stern is used as the rear boundary of the background domain; the third preset distance from the two sides of the hull is used as the left and right boundaries of the background domain; the fourth preset distance from the upper surface of the hull is used as the upper boundary of the background domain; and the fifth preset distance from the lower surface of the hull is used as the lower boundary of the background domain, so as to obtain a first rectangular block surrounding the pre-established three-dimensional model of the target ship and define it as the background domain;

[0031] The rules for setting the hull overlap domain are as follows:

[0032] The sixth preset distance from the front boundary of the background domain is used as the front boundary of the hull overlap domain, and the seventh preset distance from the rear boundary of the background domain is used as the rear boundary of the hull overlap domain; the eighth preset distance from the left and right boundaries and the upper and lower boundaries of the background domain are used as the left and right boundaries and the upper and lower boundaries of the hull overlap domain, so as to obtain a second rectangular block surrounding the pre-established three-dimensional model of the target ship, and define it as the hull overlap domain;

[0033] The rudder domain setting rules:

[0034] The ninth preset distance from the rudder in each direction is used as the boundary of the rudder domain in each direction to obtain a third rectangular block surrounding the rudder, and the third rectangular block is defined as the rudder domain.

[0035] Furthermore, the rules for constructing the computational domain boundary conditions in S1 include:

[0036] Rules for setting inlet boundary conditions, outlet boundary conditions, and wall boundary conditions;

[0037] The inlet boundary condition setting rules are:

[0038] Define the inlet boundary where the fluid flows in and specify the velocity distribution on the inlet boundary to specify the velocity at the inlet boundary as the velocity at the boundary, which is expressed as

[0039] v=v s ·θ s

[0040] Where: v represents the inlet velocity of the computational domain; v s represents the fluid velocity; θ s Indicates the direction of fluid inflow; T s represents the static temperature of the fluid;

[0041] The static pressure at the inlet boundary is obtained based on the static pressure inside the computational domain. Its expression is:

[0042]

[0043] Where: p s represents the static pressure at the inlet boundary; represents the static pressure inside the computational domain;

[0044] The export boundary condition setting rules are as follows:

[0045] The exit boundary condition adopts the Velocity Inlet Far Field condition, which means the preset velocity component is used as the velocity field of the exit boundary.

[0046] The wall boundary condition setting rules are:

[0047] Set the outer surface of the hull as a wall boundary condition.

[0048] Furthermore, the method for obtaining the ship flow field model by coupling the computational domain based on the overlaid grid technology in S1 specifically includes the following steps:

[0049] S11: setting a first scale division grid, and gridding the background domain to obtain a background domain grid;

[0050] By calling the field function pre-programmed in the Starccm+ software, the background domain grid is driven to translate in the plane and rotate around the z-axis along with the hull overlapping domain, thus forming a first-level moving body;

[0051] S12: setting a second scale division grid, and meshing the hull overlapping domain to obtain the hull overlapping domain grid;

[0052] By calling the Overset Interface tool in the Starccm+ software, the hull overlap domain is nested in the background domain mesh as a rigid body to move, so as to couple the hull overlap domain mesh and the background domain mesh; by setting the DFBI rotation and translation, a secondary moving body is formed;

[0053] S13: setting a third scale division grid, and meshing the rudder domain to obtain a rudder domain grid;

[0054] The overlapping meshes of the rudder domain and the hull overlap domain are identified and set as a motion region that rotates independently around the rudder axis using an overlapping nesting method. Furthermore, by defining the local rotation coordinate system of the rudder domain in the Star-CCM+ software and calling a pre-programmed field function to control the rudder angle change, the overlapping meshes are given the ability to move relative to the hull overlap domain structure while maintaining coupling, thereby forming a three-level motion body.

[0055] The primary moving body, the secondary moving body and the tertiary moving body are used as the ship flow field model under the ship steering state.

[0056] Beneficial effect: The present invention provides a method for predicting the structural response of the propeller-front energy-saving duct under the steering state of a ship. The method couples the computational domain based on the overlapping grid technology to obtain a ship flow field model. Based on the CFD method, the transient flow field of the target ship under different steering states is simulated and obtained according to the SST k-ω turbulence model and the virtual disk combined with the computational domain boundary conditions, so as to obtain the transient pressure load distribution corresponding to the set fluid domain grid node by calling the run control component of the Starccm+ software; the structural domain grid nodes of the ship propeller-front energy-saving duct area are obtained according to the preset ship finite element model through the shell unit Mesh in the finite element software; based on the nearest neighbor interpolation method, the data of the transient pressure load distribution corresponding to the fluid domain grid node is mapped to the structural domain grid node with the smallest spatial distance according to the node spatial distance to obtain the load mapping data; the LS-Dyna software is called to obtain the structural response of the propeller-front energy-saving duct according to the load mapping data to obtain the maximum stress / strain value of the propeller-front energy-saving duct of the target ship in the current steering state, and then by combining the ship motion monitoring data, the structural response prediction of the energy-saving duct under different steering states can be quickly and effectively predicted. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0058] Figure 1 This is a flow chart of a method for predicting the structural response of the propeller-front energy-saving duct under the ship's steering state according to the present invention;

[0059] Figure 2 Schematic diagram of the calculation domain of the ship turning in this embodiment;

[0060] Figure 3 Schematic diagram of the overlapping grid division area of the target ship calculation domain in this embodiment;

[0061] Figure 4 Schematic diagram of the multi-level motion system of the ship computational domain grid in this embodiment;

[0062] Figure 5 The 3D mesh model of the hull computational domain in this embodiment;

[0063] Figure 6 Graph showing the forces and changing trends of the energy-saving duct in front of the propeller in different directions in this embodiment;

[0064] Figure 7 This is a schematic diagram of a finite element model of the energy-saving duct structure in front of the propeller of the ship in this embodiment;

[0065] Figure 8 is a comparison curve diagram of the load mapping data in this embodiment;

[0066] Figure 9 Graphs showing pressure distribution on both sides of the energy-saving duct in front of the propeller of the ship at different times in this embodiment;

[0067] Figure 10 : This is a pressure distribution diagram of the duct during the rotation phase of the ship at different drafts in this embodiment;

[0068] Figure 11 : This is a pressure distribution diagram of the energy-saving duct in front of the propeller at different speeds in this embodiment;

[0069] Figure 12 : This is the duct pressure distribution diagram during the ship turning phase at different rudder angles in this embodiment;

[0070] Figure 13 3 is a curve diagram showing the stress peak value of the energy-saving duct in front of the propeller changing with time in this embodiment. DETAILED DESCRIPTION

[0071] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0072] This embodiment provides a method for predicting the structural response of the propeller front energy-saving duct under the ship steering state, such as Figure 1 As shown, the following steps are included:

[0073] S1: Import the pre-established 3D model of the target ship into the Starccm+ software, and construct the calculation domain and boundary conditions of the target ship;

[0074] The calculation domain includes a background domain, a hull overlap domain and a rudder domain;

[0075] The computational domain boundary conditions include inlet boundary conditions, outlet boundary conditions, and wall boundary conditions;

[0076] In a specific embodiment, the rules for constructing the computational domain of the target ship include:

[0077] Background domain setting rules, hull overlap domain setting rules, and rudder domain setting rules;

[0078] The background domain setting rules:

[0079] The first preset distance 2Lpp from the bow is used as the front boundary of the background domain, and the second preset distance 2.5Lpp from the stern is used as the rear boundary of the background domain; the third preset distance 2ppL from both sides of the hull is used as the left and right boundaries of the background domain; the fourth preset distance 0.5Lpp from the upper surface of the hull is used as the upper boundary of the background domain; and the fifth preset distance 1Lpp from the lower surface of the hull is used as the lower boundary of the background domain, so as to obtain a first rectangular block surrounding the pre-established three-dimensional model of the target ship and define it as the background domain;

[0080] The rules for setting the hull overlap domain are as follows:

[0081] The sixth preset distance 0.2 Lpp from the front boundary of the background domain is used as the front boundary of the hull overlap domain, and the seventh preset distance 0.2 Lpp from the rear boundary of the background domain is used as the rear boundary of the hull overlap domain; the eighth preset distance 0.3B from the left and right boundaries and the upper and lower boundaries of the background domain are used as the left and right boundaries and the upper and lower boundaries of the hull overlap domain, so as to obtain a second rectangular block surrounding the pre-established three-dimensional model of the target ship, and define it as the hull overlap domain;

[0082] The rudder domain setting rules:

[0083] The ninth preset distance in each direction from the rudder is used as the boundary of the rudder domain in each direction to obtain a third rectangular block surrounding the rudder, and this is defined as the rudder domain. The ninth preset distance can be determined based on expert experience as long as it completely covers the rudder.

[0084] In this embodiment, the pre-established three-dimensional model of the target ship is imported into the Starccm+ software to define the calculation domain and the calculation domain boundary conditions. The calculation domain boundaries include the velocity inlet boundary, the pressure outlet boundary, the wall boundary and other boundaries. The calculation domain is divided into three sets. The first set is the background domain, the inlet is 2Lpp from the bow, the outlet is 2.5Lpp from the stern, the side of the ship is 2ppL from the left and right surfaces, and the upper and lower surfaces are 0.5Lpp and 1Lpp from the ship respectively; the second set is the hull overlap domain, the overlap domain size can be set to 0.2Lpp from the bow and stern to the overlap domain boundary, and the distance from the upper and lower surfaces of the ship to the overlap domain boundary is 0.3B; the third set is the rudder overlap domain, the rudder overlap domain size can completely cover the rudder body, and the propeller that provides the ship thrust is replaced by a set virtual disk to improve the calculation efficiency; the virtual disk is to simplify the ship propeller into a virtual entity for providing thrust for the ship by the Starccm+ software. The specific implementation method is an existing well-known technology and will not be described in detail here.

[0085] In a specific embodiment, since in CFD numerical simulation, the boundary is used to define the spatial range of the calculation domain and completely surround the entire flow area, and the boundary condition is a specific description of the change of the physical quantity or its derivative with time and space on the boundary of the calculation domain, it is a key factor to ensure the feasibility and accuracy of the numerical solution. The setting of the boundary condition is the basis for ensuring that the control equation is solvable. In any CFD numerical simulation, the boundary conditions must be reasonably defined. In this embodiment, the types of boundary conditions include inlet boundary conditions, outlet boundary conditions and wall boundary conditions. Since the duct structure has asymmetric characteristics, this embodiment uses the calculation domain for solution, and the boundary conditions are set as follows Figure 2 As shown in the figure, velocity inlet boundary conditions are set at the inlet, bottom, top, and near the port and starboard sides of the computational domain. The boundary at the stern is set as a pressure outlet to ensure the full development of the flow field. At the same time, a wall function is applied to the hull surface to reasonably reflect the interaction between the viscous fluid and the solid wall, thereby improving the simulation accuracy.

[0086] In this embodiment, the rules for constructing the computational domain boundary conditions include:

[0087] Rules for setting inlet boundary conditions, outlet boundary conditions, and wall boundary conditions;

[0088] In this embodiment, the ship thrust is provided by a set virtual disk. The body force propeller method is selected in the model settings, and the required data of the virtual disk (including propeller open water data, position coordinates, inner and outer radius, and thickness, etc.) are added. In the numerical calculation, the time step is set to Δt = 0.01s, and the maximum number of iterations per step is limited to 10.

[0089] The inlet boundary condition setting rules are:

[0090] In Starccm+ software, the velocity inlet boundary is usually used to define the inflow conditions of the fluid, that is, the corresponding velocity distribution is specified at each node of the inlet boundary. To ensure the accuracy of the calculation results, the outer boundary of the calculation area should be set at a position far enough away from the hull to reduce the interference of the boundary on the flow field. In addition, the pressure value on the inlet boundary is usually obtained by extrapolating the pressure field inside the area, so as to achieve a reasonable setting of the boundary pressure condition. In this embodiment, the inlet boundary conditions specifically include:

[0091] S100: Define the inlet boundary for the fluid to flow in, and specify the velocity distribution on the inlet boundary to specify the velocity of the inlet boundary as the velocity at the boundary, which is expressed as

[0092] v=v s ·θ s (1)

[0093] Where: v represents the inlet velocity of the computational domain; v s represents the fluid velocity; θ s Indicates the direction of fluid inflow; T s represents the static temperature of the fluid;

[0094] S101: Obtain the static pressure at the inlet boundary based on the static pressure inside the computational domain. The expression is:

[0095]

[0096] Where: p s represents the static pressure at the inlet boundary; represents the static pressure inside the computational domain;

[0097] The export boundary condition setting rules are as follows:

[0098] The exit boundary condition usually adopts the Velocity Inlet Far Field condition, that is, the preset velocity component is used as the velocity field of the exit boundary;

[0099] In this embodiment, when using Starccm+ software for numerical simulation, the inlet boundary usually adopts the velocity far field (Velocity Inlet Far Field) condition, and the velocity field of the outer boundary surface can be initialized by presetting the velocity component. In order to obtain a calculation result closer to the actual physical situation, the position of the outer boundary should be as far away from the hull surface as possible to reduce the impact of the boundary on the mainstream field. As for the pressure value on the inlet boundary, it can be estimated and set by extrapolating or interpolating the pressure field inside the calculation domain; the method for estimating and setting the method for extrapolating or interpolating the pressure field inside the calculation domain is an existing well-known technology and will not be described in detail here.

[0100] The wall boundary condition setting rules are:

[0101] Set the outer surface of the hull as a wall boundary condition;

[0102] In this embodiment, the wall boundary is used to represent a solid surface that is impenetrable by the fluid. In this embodiment, the outer surface of the hull is set as the wall boundary condition. Considering the viscous properties of the fluid, there is no relative sliding between the fluid particles attached to the wall and the wall, that is, their relative velocity is zero. This physical phenomenon is usually called the "no-slip condition". This condition is an important basis for the interaction between fluid and solid surface and has a key impact on the accuracy of the simulation results, namely: u wall =v wall =w wall =k wall ;

[0103] The ship flow field model is obtained by coupling the computational domain based on the overlay grid technology;

[0104] In a specific embodiment, Figures 3 and 4 As shown, this embodiment also includes four different coordinate systems, namely, a geodetic coordinate system, a hull-fixed coordinate system, a virtual disk coordinate system, and a rudder axis coordinate system. Each coordinate system is defined using a Cartesian coordinate system. The origin of the geodetic coordinate system is set at the center of gravity of the ship, the X-axis is toward the bow, the Y-axis is toward the starboard, and the Z-axis is vertically upward. The method for obtaining a ship flow field model by coupling the computational domain based on the overlaid grid technology specifically includes the following steps:

[0105] S11: setting a first scale division grid, and gridding the background domain to obtain a background domain grid;

[0106] And by calling the field function pre-programmed in Starccm+ software, namely a sin(${vy} / ${velocityin XY plane}), where vy represents the velocity component of the ship in the y-axis direction and velocity represents the total velocity of the ship in the xy plane, the background domain grid is driven to translate in the plane and rotate around the z-axis with the hull overlapping domain, thereby forming a first-level moving body;

[0107] In this embodiment, the background domain is the main part of the entire computational domain, covering the hull and a large area of surrounding waters. A coarser grid is used to ensure a larger time step and computational efficiency. The grid size is usually controlled to 1 / 100 to 1 / 200 of the ship length, and local areas can be appropriately denser. To further save computing resources, this embodiment uses a method of controlling the background domain to move with the hull using a field function. This method can effectively reduce the number of background domain grids, thereby significantly improving computational efficiency while ensuring numerical accuracy.

[0108] S12: setting a second scale division grid, and meshing the hull overlapping domain to obtain the hull overlapping domain grid;

[0109] By calling the OversetInterface tool in the Starccm+ software, the hull overlap domain is nested in the background domain mesh as a rigid body to move, so as to couple the hull overlap domain mesh and the background domain mesh; by setting the DFBI rotation and translation, a secondary moving body is formed;

[0110] In this embodiment, the hull computational domain includes the hull geometry and covers the hull. The grid is of medium density, with a focus on densification of the energy-saving duct surface. This area is nested as a rigid body in the background domain and moves. An OversetInterface is set between the background domain grid and data is transferred by interpolation. At the same time, DFBI rotation and translation are set for the hull to obtain a six-degree-of-freedom motion module to form a secondary motion body.

[0111] S13: setting a third scale division grid, and meshing the rudder domain to obtain a rudder domain grid;

[0112] The overlapping meshes of the rudder domain and the hull overlap domain are identified and set as a motion region that rotates independently around the rudder axis using an overlapping nesting method. Furthermore, by defining the local rotation coordinate system of the rudder domain in the Star-CCM+ software and calling a pre-programmed field function to control the rudder angle change, the overlapping meshes are enabled to move relative to the hull overlap domain structure while maintaining coupling, thereby forming a three-level motion body.

[0113] In this embodiment, the rudder domain contains a separate rudder body geometric area and does not intersect with the hull. By dividing the high-density local grid and using overlapping nesting, it is confirmed that there is partial overlap between this area and the hull overlapping domain grid. It is set as an independent rotation motion area around the rudder axis, and a field function that controls the change of the rudder angle, namely the rudder field function, is applied separately.

[0114] ($Time<=12)? 0:(($Time<14.1875)?0.279:0),

[0115] By defining the local rotating coordinate system of the rudder domain in Star-CCM+, the region is able to move relative to the hull structure while maintaining coupling, thus forming a three-level moving body.

[0116] The first-level moving body, the second-level moving body and the third-level moving body are used as the ship flow field model under the ship steering state, such as Figure 5 As shown;

[0117] S2: Based on the CFD method and the SST k-ω turbulence model combined with the computational domain boundary conditions, the transient flow field of the target ship under different steering states is simulated and obtained;

[0118] Specifically, in order to avoid the problem that the model is too sensitive to the inlet boundary conditions, this embodiment adopts the SST k-ω model with better robustness;

[0119] And the equation expression of the SST k-ω model is:

[0120]

[0121] in, represents the generation term of turbulent kinetic energy k caused by the average velocity; G ω represents the generation term of ω; Γ represents the diffusion term; Y represents the turbulent dissipation term; D represents the cross-diffusion term; S represents the custom source term; where the SST k-ω diffusion term is:

[0122]

[0123] Where: k and σ ω represents the Prandtl number corresponding to k and ω;

[0124] in G k and G ω It can be solved by the following formula:

[0125]

[0126] Among them, β * Indicates the correction factor.

[0127]

[0128] Where α is the turbulent viscous damping correlation coefficient;

[0129] The turbulent kinetic energy dissipation term is expressed as follows:

[0130] Y k =ρβ * kω (10)

[0131] Y ω =ρβω 2 (11)

[0132] Where β represents the correction coefficient;

[0133] The fluid domain grid is set according to the ship flow field model, and the mesh nodes of the fluid domain are the mesh nodes of the area where the energy-saving duct surface in front of the propeller of the target ship is located;

[0134] S3: Build a six-degree-of-freedom motion model of the ship, and obtain the transient pressure load distribution corresponding to the fluid domain grid node according to the transient flow field by calling the run control component of the Starccm+ software, and then obtain the pressure load database of the energy-saving duct in front of the propeller, such as Figure 6 As shown;

[0135] Specifically, the six-degree-of-freedom motion model of the target ship is constructed as follows:

[0136]

[0137] Where: m represents the mass of the hull; u, v, w represent the linear velocity of the target ship's hull in the x, y, z directions of the preset coordinate system respectively; p, q, r represent the angular velocity of the target ship's hull around the x, y, z axes respectively; X, Y, Z and K, M, N represent the force and torque acting on the target ship's hull respectively; I x ,I y ,I z Respectively represent the moment of inertia in the x, y, and z directions relative to the center of gravity of the ship;

[0138] S4: Establish a finite element model of the ship based on the ship's material properties, and set the hull as a fixed boundary;

[0139] The ship material properties shall at least include the elastic modulus, Poisson's ratio and material density of the ship steel;

[0140] The shell unit division tool Mesh in the finite element software is called to perform regional mesh division on the ship finite element model and obtain the structural domain mesh nodes of the energy-saving duct area in front of the ship propeller, such as Figure 7 As shown;

[0141] S5: Obtain the spatial distance between each node of the structure domain grid and the fluid domain grid;

[0142] Based on the nearest neighbor interpolation method and the propeller front energy-saving duct pressure database, the transient pressure load distribution data corresponding to the fluid domain grid node is mapped to the structural domain grid node with the smallest spatial distance to obtain the load mapping data, such as Figure 8 As shown;

[0143] This embodiment obtains the surface pressure data of the energy-saving duct in front of the propeller calculated based on the CFD method and the coordinates of the structural finite element model nodes in the ship finite element model; a Fortran program with pre-programmed energy consumption reads the CFD surface element coordinates and the surface pressure value of the energy-saving duct in front of the propeller, calculates the spatial distance between the fluid domain node and the current structural domain node, maps the CFD pressure to the nearest structural model node through the nearest neighbor interpolation method, and generates structure-load coupling file data supported by the structural calculation software; the programming method of the Fortran program is a well-known technology and will not be described in detail here;

[0144] The LS-Dyna software is used to obtain the structural response of the energy-saving duct in front of the propeller based on the load mapping data.

[0145] The structural response includes stress / strain values of various regions of the energy-saving duct in front of the propeller;

[0146] Specifically, in this embodiment, the known basic theoretical knowledge of obtaining the structural response of the propeller front energy-saving duct using the LS-Dyna software is as follows:

[0147] The basic governing equations for elastic small deformation dynamics include the equations of motion, geometric equations, physical equations, and boundary conditions, as follows:

[0148] Equation of motion: σ ij n j +ρf i =ρii (13);

[0149] Geometric equations:

[0150] Physics equation:

[0151] Boundary conditions:

[0152] Among them, S u +S σ =S, and and These are all known functions in advance. The boundary conditions are specifically stress boundary conditions, and there are p i =σ ij nj ;

[0153] Numerical calculation methods of elastic dynamics:

[0154] In elastic dynamics, the deformation of an object (specifically, the structure of the energy-saving duct in front of the propeller of a ship in this embodiment) is not only affected by external forces but is also closely related to changes in the object's internal forces (such as elastic forces) and displacement. Therefore, the variational principle provides an effective method for solving elastic problems. This principle can unify physical quantities such as deformation, stress, and velocity in continuous media, providing a systematic framework to help solve complex dynamic problems involving deformation and vibration of elastic objects.

[0155] The initial and final value conditions used in the Hamilton variational principle are u(x,o)=u0(x),u(x,t1)=u1(x), where u0(x) and u1(x) are given functions. The geometric equations, physical equations, and displacement boundary conditions are retained. The Hamilton variational principle is expressed as follows: In all possible states of motion, the expression for the true state that satisfies the stationary value condition is:

[0156]

[0157] Where: L represents the Lagrange function; represents the kinetic energy of the system; represents the potential energy of the system;

[0158] Substituting K and U into the expression of the stationary value condition and performing variational operations item by item, the formula after variational operation can be obtained as follows:

[0159]

[0160] Since (σ ij δu i ) ,i =σ u,j δu j +σ ij δu i,j , p i =σ ij n j , substitute the formula after variational operation and apply the divergence theorem to get

[0161]

[0162] The direct calculation of the stationary value of the universal function by applying the finite element method is to discretize the structural space and perform displacement interpolation on the discretized elements and nodes. The expression for displacement interpolation is:

[0163] u i(x,y,z,t)=N,(x,y,z)u il (t) (20)

[0164] Where: N1 represents the shape function of node 1, repeated subscripts represent summation within its value range, and it can be written in matrix form as u=NU, Similar to the finite element calculation method of elastic statics, the geometric equation and physical equation are written in matrix form: σ=Eε,ε=BU,δu=NδU, and substituted into the expression for displacement interpolation to obtain

[0165]

[0166] Let M = ∫ V N T ρNdV,K=∫ V B T EBdV,F1=∫ V ρfN T dV, Due to the arbitrariness of δU, we can rewrite the formula

[0167]

[0168] After the rewritten formula is discretized by finite element, the second-order ordinary differential equation for the structural dynamic response is obtained, which usually does not consider the influence of structural damping; generally speaking, the damping of the system can be approximated to be linearly related to the motion speed on an engineering scale, that is, c represents the viscous damping coefficient;

[0169] Introducing the damping term into the dynamic differential equation through the same derivation process as above, we can get

[0170]

[0171] In the formula, the damping matrix C is generally calculated using the proportional damping method in engineering, that is, C = α0M + α1K, and the coefficients α0 and α1 can be determined by experimental methods or experience. In LS-DYNA3D software, the keyword *DAMPING_PART_STIFFNESS can be used to define the coefficients.

[0172] Basic solution and solution process of finite element elastic dynamics:

[0173] Based on Hamilton's variational principle, the differential equations for numerical analysis of elastic dynamics are established: A variety of numerical methods can be used for vibration response analysis in elastic dynamics, depending on the specific computational problem, structural complexity, accuracy requirements of the numerical method, and difficulty of solution. Among them, the explicit central difference method has become the core solution algorithm widely used in LS-DYNA3D software due to its high computational efficiency and relatively simple implementation. The details are as follows:

[0174] Assume 0,t 1 ,t 2 ,…,t n The node displacement, velocity and acceleration at time t are all known. Now solve n+1 The structural response at time (t+Δt). The central difference method uses the central difference to replace the derivatives of acceleration and velocity, that is,

[0175]

[0176] Substituting formula (15) into formula (14), we can get

[0177]

[0178] Where, are called the effective mass-star matrix and the effective load vector, respectively. F, M, C, and K are the structural load vector, mass matrix, damping matrix, and rigid matrix, respectively.

[0179] Solving the linear equations (25) can obtain the node displacement vector U at time t+Δt: t+Δt , will U t+Δt Substituting back into the geometric equations and physical equations, the grid unit stress and grid unit strain at time t+Δt can be obtained. The form of Equation (25) is the same as the basic finite element equation F=KU of elastic statics, so it can be solved using the static finite element solution method;

[0180] S6: The structural response of the energy-saving duct in front of the propeller is visualized using LS-Prepost software, such as Figures 9 to 12 As shown, the maximum stress / strain value of the propeller front energy-saving duct of the target ship in the current steering state is extracted to realize the structural response prediction of the propeller front energy-saving duct under different steering states of the ship.

[0181] In this embodiment, the 82KBC ship is taken as an example, and a calculation experiment is conducted based on the structural response prediction method of the propeller front energy-saving duct under the ship's steering state. Figure 3 The target ship is meshed. Based on the six-degree-of-freedom module and overlapping mesh technology, the hydrodynamic load value and variation trend of the energy-saving duct in front of the target ship's propeller can be solved. Figure 6 The force and change trend of the propeller front energy-saving duct in different directions when the ship is steering; Figure 7The figure shows the construction of the finite element model of the energy-saving duct in front of the ship propeller, and the pressure data is mapped from the fluid domain to the structural domain. In order to verify the accuracy of the mapping, one of the units is selected for comparison, as shown in the figure. Figure 8 As shown in the figure, the trend is consistent, the error is small and the accuracy is high. By putting the mapped data file into the LS-Prepost software for calculation, the trend of the duct stress peak value over time is obtained. The original pressure and mapped pressure time history curves show that the mapped pressure is highly consistent with the original pressure and the change trend is consistent: the original pressure peak is 0.0645MPa, and the mapped pressure peak is 0.0647MPa, which is 3.09% higher than the original pressure peak. Since the pressure peak values are not much different and the degree of consistency is high except for the peak value, it is believed that the mapped pressure can reflect the real slamming load of the propeller front energy-saving duct, as shown in the figure. Figure 13 As shown, the method described in this embodiment can quickly and effectively predict the structural response of the energy-saving duct under different steering conditions by combining the ship motion monitoring data, greatly improving the efficiency and accuracy of the structural response prediction of the energy-saving duct in front of the propeller under different steering conditions.

[0182] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for predicting the structural response of the propeller-front energy-saving duct under ship steering conditions, characterized in that: The specific steps include: S1: Import the pre-established 3D model of the target ship into the Starccm+ software, and construct the calculation domain and boundary conditions of the target ship; The calculation domain includes a background domain, a hull overlap domain and a rudder domain; The computational domain boundary conditions include inlet boundary conditions, outlet boundary conditions, and wall boundary conditions; The ship flow field model is obtained by coupling the computational domain based on the overlay grid technology; S2: Based on the CFD method, the SST k-ω turbulence model and the virtual disk are combined with the computational domain boundary conditions to simulate and obtain the transient flow field of the target ship under different steering states; The virtual disk is a virtual entity that simplifies the ship propeller into a virtual entity for providing thrust for the ship through the Starccm+ software; The fluid domain grid is set according to the ship flow field model, and the mesh nodes of the fluid domain are the mesh nodes of the area where the energy-saving duct surface in front of the propeller of the target ship is located; S3: Build a six-degree-of-freedom motion model of the ship, and obtain the transient pressure load distribution corresponding to the fluid domain grid node according to the transient flow field by calling the run control component of the Starccm+ software, and then obtain the pressure load database of the energy-saving duct in front of the propeller; S4: Establish a finite element model of the ship based on the ship's material properties; The ship material properties shall at least include the elastic modulus, Poisson's ratio and material density of the ship steel; The shell element partitioning tool Mesh in the finite element software is called to perform regional meshing on the ship finite element model to obtain the structural domain mesh nodes of the energy-saving duct area in front of the ship propeller; S5: Obtain the spatial distance between each node of the structure domain grid and the fluid domain grid; Based on the nearest neighbor interpolation method and the propeller front energy-saving duct pressure load database, the transient pressure load distribution data corresponding to the fluid domain grid node is mapped to the structural domain grid node with the smallest spatial distance to obtain the structure-load coupling file; The LS-Dyna software is used to obtain the structural response of the energy-saving duct in front of the propeller according to the structure-load coupling file; The structural response includes stress / strain values of various regions of the energy-saving duct in front of the propeller; S6: The structural response of the propeller front energy-saving duct is visualized using the LS-Prepost software, and the maximum stress / strain value of the propeller front energy-saving duct under the current steering state is extracted to predict the structural response of the propeller front energy-saving duct under different steering states of the ship.

2. The method for predicting the structural response of the propeller-front energy-saving duct under ship steering conditions according to claim 1 is characterized in that: The six-degree-of-freedom motion model of the target ship constructed in S3 is: Where: m represents the mass of the hull; u, v, w represent the linear velocity of the target ship's hull in the x, y, z directions of the preset coordinate system respectively; p, q, r represent the angular velocity of the target ship's hull around the x, y, z axes respectively; X, Y, Z and K, M, N represent the force and torque acting on the target ship's hull respectively; I x ,I y ,I z Represent the moment of inertia in the x, y, and z directions relative to the center of gravity of the ship.

3. The method for predicting the structural response of the propeller front energy-saving duct under ship steering state according to claim 1 is characterized in that: The rules for constructing the computational domain of the target ship in S1 include: Background domain setting rules, hull overlap domain setting rules, and rudder domain setting rules; The background domain setting rules: The first preset distance from the bow is used as the front boundary of the background domain, and the second preset distance from the stern is used as the rear boundary of the background domain; the third preset distance from the two sides of the hull is used as the left and right boundaries of the background domain; the fourth preset distance from the upper surface of the hull is used as the upper boundary of the background domain; and the fifth preset distance from the lower surface of the hull is used as the lower boundary of the background domain, so as to obtain a first rectangular block surrounding the pre-established three-dimensional model of the target ship and define it as the background domain; The rules for setting the hull overlap domain are as follows: The sixth preset distance from the front boundary of the background domain is used as the front boundary of the hull overlap domain, and the seventh preset distance from the rear boundary of the background domain is used as the rear boundary of the hull overlap domain; the eighth preset distance from the left and right boundaries and the upper and lower boundaries of the background domain are used as the left and right boundaries and the upper and lower boundaries of the hull overlap domain, so as to obtain a second rectangular block surrounding the pre-established three-dimensional model of the target ship, and define it as the hull overlap domain; The rudder domain setting rules: The ninth preset distance from the rudder in each direction is used as the boundary of the rudder domain in each direction to obtain a third rectangular block surrounding the rudder, and the third rectangular block is defined as the rudder domain.

4. The method for predicting the structural response of the propeller-front energy-saving duct under ship steering conditions according to claim 3 is characterized in that: The rules for constructing the computational domain boundary conditions in S1 include: Rules for setting inlet boundary conditions, outlet boundary conditions, and wall boundary conditions; The inlet boundary condition setting rules are: Define the inlet boundary where the fluid flows in and specify the velocity distribution on the inlet boundary to specify the velocity at the inlet boundary as the velocity at the boundary, which is expressed as v=v s ·θ s Where: v represents the inlet velocity of the computational domain; v s represents the fluid velocity; θ s Indicates the direction of fluid inflow; T s represents the static temperature of the fluid; The static pressure at the inlet boundary is obtained based on the static pressure inside the computational domain. Its expression is: Where: p s represents the static pressure at the inlet boundary; represents the static pressure inside the computational domain; The export boundary condition setting rules are as follows: The exit boundary condition adopts the Velocity Inlet Far Field condition, which means the preset velocity component is used as the velocity field of the exit boundary. The wall boundary condition setting rules are: Set the outer surface of the hull as a wall boundary condition.

5. The method for predicting the structural response of the propeller-front energy-saving duct under ship steering conditions according to claim 4 is characterized in that: The method for obtaining the ship flow field model by coupling the computational domain based on the overlaid grid technology in S1 specifically includes the following steps: S11: setting a first scale division grid, and gridding the background domain to obtain a background domain grid; By calling the field function pre-programmed in the Starccm+ software, the background domain grid is driven to translate in the plane and rotate around the z-axis along with the hull overlapping domain, thereby forming a first-level moving body; S12: setting a second scale division grid, and meshing the hull overlapping domain to obtain the hull overlapping domain grid; By calling the Overset Interface tool in the Starccm+ software, the hull overlap domain is nested in the background domain mesh as a rigid body to move, so as to couple the hull overlap domain mesh and the background domain mesh; by setting the DFBI rotation and translation, a secondary moving body is formed; S13: setting a third scale division grid, and meshing the rudder domain to obtain a rudder domain grid; The overlapping meshes of the rudder domain and the hull overlap domain are identified and set as a motion region that rotates independently around the rudder axis using an overlapping nesting method. Furthermore, by defining the local rotation coordinate system of the rudder domain in the Star-CCM+ software and calling a pre-programmed field function to control the rudder angle change, the overlapping meshes are given the ability to move relative to the hull overlap domain structure while maintaining coupling, thereby forming a three-level motion body. The primary moving body, the secondary moving body and the tertiary moving body are used as the ship flow field model under the ship steering state.

Images