Search

CN-121997815-A - Fluid-solid coupling calculation method for predicting vortex-induced motion response of underwater single-anchor system

CN121997815ACN 121997815 ACN121997815 ACN 121997815ACN-121997815-A

Abstract

The invention discloses a fluid-solid coupling calculation method for predicting vortex-induced motion response of an underwater single anchor system, which is characterized in that a flow field calculation domain is divided based on a multi-region overlapped grid technology, data transmission is realized through boundary point interpolation, an anchor chain discrete dynamics model is established by adopting a centralized mass method, anchor chain morphology and tension distribution are solved in an iterative mode, a six-degree-of-freedom rigid body dynamics model of a mooring body is established by adopting a Newton-Euler method, constraint conditions such as hydrodynamic force and anchor chain tension are synthesized, the flow field is solved by adopting a computational fluid dynamics method, and bidirectional data exchange of fluid load, anchor chain tension and structural motion is realized by utilizing a custom function. The invention has the advantages that the large-displacement motion simulation problem of the mooring system is effectively solved through the multi-region overlapped grid and cross-platform cooperative framework, the six-degree-of-freedom vortex-induced motion response of the mooring body can be predicted with high precision, and the whole process visualization of the dynamic change of the flow field is realized.

Inventors

  • WANG WEI
  • HU YUYANG
  • MAO ZHAOYONG
  • TIAN WENLONG

Assignees

  • 西北工业大学

Dates

Publication Date
20260508
Application Date
20260109

Claims (10)

  1. 1. A fluid-solid coupling calculation method for predicting vortex-induced motion response of an underwater single-anchor system is characterized by comprising the following steps: Step 1, establishing a multi-region overlapped grid model, and respectively dividing grids of each region; the complex large-scale motion simulation of the model in the space is realized by adopting a multi-region high-precision overlapped grid method, and region communication is realized through interpolation of boundary points and data transmission; step 2, establishing an anchor chain dynamics model based on a centralized mass method; In the centralized mass method, the anchor chain is equivalently replaced by a discrete series of mass points connected by a virtual spring without mass, all forces act on the mass points, and a normal differential equation set of the system is built once for solving; step 3, establishing a rigid body dynamics model of the underwater mooring body based on Newton's Euler method; Step 4, establishing a flow field calculation model based on a computational fluid dynamics method; the computing medium is incompressible viscous fluid, and temperature change is not considered, so that the method belongs to the unsteady flow problem; and 5, iteratively calculating until the appointed time.
  2. 2. The fluid-solid coupling calculation method for predicting vortex-induced motion response of an underwater single-anchor system according to claim 1, wherein the generating step of the multi-region overlapped grid model is as follows: (1) Digging holes, namely digging overlapped grid cells by using a Cartesian grid method, a vector intersection method or a surface normal vector method; (2) Establishing communication between different grid domains; (3) Interpolation operation is carried out between grid domains, so that data transfer between different grid domains is realized.
  3. 3. The fluid-solid coupling calculation method for predicting vortex-induced motion response of an underwater single-anchor system according to claim 2, wherein in the step 1, two sets of grids are needed during grid division, one set of component grids containing a moving body and one set of background grids, a Overset model is used during numerical calculation, and meanwhile, the interface between the two sets of grids is set to overset _interface.
  4. 4. The fluid-solid coupling calculation method for predicting vortex-induced motion response of an underwater single-anchor system according to claim 3, wherein the calculation step of the anchor chain dynamics model is that an anchor chain is firstly discretized into a plurality of mass points, and then the anchor chain morphology and tension distribution are determined through iterative calculation.
  5. 5. The fluid-solid coupling calculation method for predicting vortex-induced motion response of an underwater single-anchor system according to claim 4, wherein in the step 2, the anchor chain is discretized into N segments, namely n+1 nodes, from the lower end fixed point to the upper end mooring point, the upper mooring point is made to be an i=1 node and corresponds to the anchor chain length s=0, the lower end fixed point is the i=n+1 node and corresponds to the anchor chain length s=l, and the cable lengths corresponding to the nodes satisfy the following basic relationship: Wherein, the Representing the length differential of the i-th node, Indicating the total length of the anchor chain.
  6. 6. The fluid-solid coupling calculation method for predicting vortex-induced motion response of an underwater single-anchor system according to claim 5, wherein in the step 2, the anchor chain dynamics control equation of the i-th node is: in the formula, Is a mass matrix comprising inertial masses of anchor chain nodes And its additional mass in water Wherein, l is the unit length of the anchor chain, Representing the line density of the anchor chain, subscript i-1/2 representing the physical quantity between nodes i-1 and i, subscript i+1/2 representing the physical quantity between nodes i and i+1, l i+1/2 being the length of the anchor chain between nodes i and i+1, Representing the anchor chain line density between node i and node i +1, And (3) with F i is all external forces acting on node i; Representing the identity matrix; The acceleration vector is represented as such, Representing an additional mass matrix of the underwater cable unit between the i-1 th section and the i th section in the ground coordinate system, Representing an additional mass matrix of the underwater cable unit between the ith section and the (i+1) th section under the ground coordinate system; Carrying out stress analysis on a certain node i of the anchor chain, and establishing an equation, wherein the external force F i applied to the node i of the anchor chain comprises basic cable tension Buoyancy force Gravity force Resistance to fluid flow The method comprises the following steps: In the formula, the calculation formula of the anchor chain tension is as follows: wherein E is Young's modulus; representing the tension between the i-th segment and the i+1-th segment; representing the tension between the i-1 th section and the i th section; Represents the cross-sectional area of the anchor chain; representing the strain between the i-th and i+1th segments; representing the x-direction coordinate of the ith section; Representing the x-direction coordinate of the (i+1) th segment; representing the y-direction coordinates of the ith section; Representing the y-direction coordinate of the (i+1) th segment; the calculation formula of buoyancy and gravity is as follows: Wherein, the Representing the density of the fluid; representing gravitational acceleration; Represents the cross-sectional area between the i-th segment and the i+1-th segment; represents the cross-sectional area between the i-1 th and i-th sections; The fluid resistance is calculated as: wherein d is the diameter of the anchor chain, 、 The normal and tangential drag coefficients of the anchor chain, 、 The normal speed and tangential speed of the anchor chain node i relative to the water flow are respectively; represents the normal resistance of the anchor chain; Represents the tangential resistance of the anchor chain; representing the anchor chain diameter between the i segment and the i+1 segment; Representing the anchor chain diameter between the i-1 th section and the i th section; the anchor chain node i meets the kinematic condition when moving underwater: Wherein, the Representing the z-direction coordinates of the ith segment.
  7. 7. The fluid-solid coupling calculation method for predicting vortex-induced MOTION response of an underwater single-anchor system according to claim 6, wherein in the step 3, macro files of a custom function UDF include a default_cg_ MTION (name, dt, vel, omege, time, dtime) and a default_zon_motion (name, omega, axis, origin, vel, time, dtime); "name" is a macro name used for custom, dt "is a pointer for storing a moving grid attribute, time and dtime" respectively represent current time and time step sizes, and "vel" and "omega" are arrays of translational speed and rotational angular speed respectively, and are represented in x, y and z directions, and in the custom function UDF, a structural MOTION state at time t+1 is solved according to the structural MOTION state at time t+1, and then the structural MOTION state at time t+1 is transferred to a flow field by using a macro for updating at the next time.
  8. 8. The fluid-solid coupling calculation method for predicting vortex-induced motion response of an underwater single-anchor system according to claim 7, wherein in the step 4, anchor chain force, hydrodynamic force and displacement information are obtained by using a custom macro function UDF.
  9. 9. The fluid-solid coupling calculation method for predicting vortex-induced motion response of an underwater single-anchor system according to claim 8, wherein a rigid body dynamics differential equation set is established in the custom macro function UDF in the step 4, and speed information of the next time step is solved based on force and motion constraint conditions.
  10. 10. The fluid-solid coupling calculation method for predicting vortex-induced motion response of an underwater single-anchor system according to claim 9, wherein the turbulence model calculated by the flow field in the step 4 is an SST k- ω model.

Description

Fluid-solid coupling calculation method for predicting vortex-induced motion response of underwater single-anchor system Technical Field The invention belongs to the technical field of fluid-solid coupling numerical calculation, and particularly relates to a fluid-solid coupling calculation method for predicting vortex-induced motion response of an underwater single-anchor system. Background As the demand for deep-sea resource development increases, numerous marine facilities are developed, including, in addition to conventional vessels, marine floating platforms, seafloor observation platforms, deep-sea detection nodes, underwater intelligent vehicles, and the like. In order to enable these marine development equipment to perform long-term stable operation in a certain sea area, mooring and positioning are performed, so that a mooring system is a system which is more common in the field of marine engineering. In order to improve the working stability of the underwater mooring platform, the response characteristics of the underwater mooring platform to the flow induced motion influenced by the ocean complex hydrodynamic environment need to be studied. When the conventional numerical simulation method is used for solving the problems, fluid and a structure are often simplified or decoupled, and strong nonlinear interaction between six-degree-of-freedom motion of the mooring body and a complex flow field is difficult to accurately capture. In addition, for multi-body systems comprising flexible anchor chains and rigid mooring bodies, the existing methods have limitations in handling large displacement motions and dynamic coupling effects between parts of the system, resulting in insufficient prediction accuracy. Disclosure of Invention The invention provides a fluid-solid coupling calculation method for predicting vortex-induced motion response of an underwater single-anchor system, which aims to overcome the defects of the prior art and comprises the steps of dividing a flow field calculation domain based on a multi-domain overlapped grid technology, realizing data transmission through boundary point interpolation, establishing an anchor chain discrete dynamics model by adopting a centralized mass method, iteratively solving anchor chain morphology and tension distribution, establishing a six-degree-of-freedom rigid body dynamics model of a mooring body by adopting a Newton-Euler method, synthesizing constraint conditions such as hydrodynamic force, anchor chain tension and the like, solving the flow field by adopting a computational fluid dynamics method, and realizing bidirectional data exchange of fluid load, anchor chain tension and structural motion by utilizing a custom function. The invention has the advantages that the large-displacement motion simulation problem of the mooring system is effectively solved through the multi-region overlapped grid and cross-platform cooperative framework, the six-degree-of-freedom vortex-induced motion response of the mooring body can be predicted with high precision, and the whole process visualization of the dynamic change of the flow field is realized. The technical scheme adopted for solving the technical problems is as follows: Step 1, establishing a multi-region overlapped grid model, and respectively dividing grids of each region; the complex large-scale motion simulation of the model in the space is realized by adopting a multi-region high-precision overlapped grid method, and region communication is realized through interpolation of boundary points and data transmission; step 2, establishing an anchor chain dynamics model based on a centralized mass method; In the centralized mass method, the anchor chain is equivalently replaced by a discrete series of mass points connected by a virtual spring without mass, all forces act on the mass points, and a normal differential equation set of the system is built once for solving; step 3, establishing a rigid body dynamics model of the underwater mooring body based on Newton's Euler method; Step 4, establishing a flow field calculation model based on a computational fluid dynamics method; the computing medium is incompressible viscous fluid, and temperature change is not considered, so that the method belongs to the unsteady flow problem; and 5, iteratively calculating until the appointed time. Preferably, the generating step of the multi-region overlapped grid model includes: (1) Digging holes, namely digging overlapped grid cells by using a Cartesian grid method, a vector intersection method or a surface normal vector method; (2) Establishing communication between different grid domains; (3) Interpolation operation is carried out between grid domains, so that data transfer between different grid domains is realized. Preferably, in the step 1, two sets of grids are needed for grid division, one set of component grids containing the moving body and one set of background grids, a Overset model is used for numerical calc