Vascular disease numerical simulation prediction method based on bidirectional heat-fluid-solid coupling

Abstract

The invention relates to the technical field of hemodynamics numerical simulation, in particular to a vascular disease numerical simulation prediction method based on bidirectional heat-fluid-solid coupling, which comprises the following steps of: firstly, establishing a vascular three-dimensional model based on three-dimensional reconstruction software such as 3D Slicer, Geomg, Solidworks and the like according to real image data such as CT (Computed Tomography) of a patient; secondly, based on Ansys Workbench, a coupling analysis project containing Fluent, Transient Status and System Coupling is created, the model is imported into the project for mesh generation, the real blood vessel state and the blood flow pulsation state serve as input parameters for boundary condition setting, a coupling field is called by inserting an APDL command, and an external excitation temperature field is set to simulate human body / environment temperature fluctuation; creating data transmission between the outer surface of the fluid domain and the inner surface of the solid domain based on a System Coupling module; and finally, carrying out multiple times of numerical simulation based on the bidirectional heat-fluid-solid coupling analysis project. The method can better conform to the real flowing state of human blood, and the numerical simulation prediction precision of vascular diseases is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of hemodynamic numerical simulation, in particular to a blood vessel disease numerical simulation prediction method based on two-way thermal fluid-structure coupling. BACKGROUND

[0002] A large number of theoretical and experimental studies have been carried out on the analysis of hemodynamics, and some valuable research results have been obtained. However, based on the study of related research, almost no scholars consider the influence of temperature field when analyzing fluid mechanics and structural mechanics. This is because the body temperature of a normal person is relatively constant, so the fluctuation of the temperature field can be ignored. However, in some cases, the influence of temperature change cannot be ignored, such as the phenomenon of low temperature during open surgery of anesthetized patients, the fluctuation of human blood temperature caused by the injection of contrast agent, and the fever and other body temperature rise phenomenon of postoperative patients. And human blood is a typical non-Newtonian fluid, and its hemodynamic parameters such as viscosity and shear stress are closely related to temperature. Ignoring the effect of temperature field will limit the accuracy of blood vessel disease numerical simulation prediction.

[0003] Therefore, there is an urgent need for a blood vessel disease risk prediction method that takes into account the effects of human and environmental temperature, to assist doctors in predicting the risk of patients developing related cardiovascular diseases in advance, so as to choose a disease treatment plan with lower risk and reduce patient mortality. SUMMARY

[0004] To solve the above problems, the present application provides a blood vessel disease numerical simulation prediction method based on two-way thermal fluid-structure coupling, which can better conform to the real flow state of human blood and improve the accuracy of blood vessel disease numerical simulation prediction.

[0005] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0006] A blood vessel disease numerical simulation prediction method based on two-way thermal fluid-structure coupling, comprising the following steps:

[0007] Step S1, reconstructing a three-dimensional model of blood vessels;

[0008] Step S2, building a coupling calculation project;

[0009] Step S3, dividing the fluid domain and solid domain grid;

[0010] Step S4, setting initial and boundary conditions;

[0011] Step S5, creating data transmission;

[0012] Step S6, analyzing the results of numerical simulation.

[0013] Further, in step S1, the three-dimensional model of blood vessels is reconstructed as follows:

[0014] The CT data in Dicom format is imported into software such as 3D Slicer, Mimics, etc. for scanning, a suitable threshold is selected, the segmentation tool in the software is used to distinguish the vascular structure, the three-dimensional reconstruction function of the software is used, and a three-dimensional vascular model in stl format is generated according to the segmentation result;

[0015] The stl format file is imported into Geomagic, Solidworks to smooth and optimize the model surface and the vascular port, and the shell extraction function is used to add model details, and an stp format file is output to ensure that the model meets the numerical simulation requirements.

[0016] Through the above technical scheme: the CT and other real image data of the patient are imported into 3D Slicer for scanning, a suitable threshold is selected, the contrast and brightness are adjusted to better distinguish the vascular structure, the Paint, Draw, Erase and other tools in 3D Slicer are used to segment the blood vessels, remove the redundant bone and tissue parts, and the three-dimensional reconstruction function of the software is used to generate a three-dimensional model of the blood vessels according to the segmentation result, and an stl format file is output.

[0017] The stl format file is input into Geomagic, Solidworks for further optimization and repair of the model. The optimization process includes: using the Geomagic mesh doctor tool to optimize and repair the model mesh; smoothing the model using the Geomagic smoothing, sandpaper and other functions, and adding model details such as blood vessel wall thickness using the shell extraction function; using the Solidworks software "stretch cut tool" to repair the model vascular port, and outputting an stp format file to ensure that the model meets the simulation requirements.

[0018] Further, in step S2, the coupling calculation project is built as follows:

[0019] In the Analysis systems module of the ANSYS Workbench interface, select the Fluid Flow (Fluent) and Transient Structural options and the System Coupling option in the Component systems module, which can create analysis projects A (fluid), B (solid) and C (coupling calculation) in the project management area, pass the geometric data (A2) of project A to project B (B3), and pass the calculation setting data (A4) of project A and the calculation setting data (B5) of project B to project C (C2).

[0020] Further, in step S3, the grid division of the fluid domain and the solid domain is as follows:

[0021] The extracted blood vessel model file is imported into the coupling analysis project, and the fluid domain model and the solid domain model are tetrahedral meshed using the Mesh module of Fluid flow (Fluent) and Transient Structural, respectively, and the average mesh quality of both is required to be higher than 0.7, and the grid division of the fluid-structure coupling surface of the simulation model is 1.7 times the density of the outer surface of the blood vessel model.

[0022] Further, in step S4, the initial and boundary conditions are specifically set as follows:

[0023] According to the related parameters that can reflect the real pulsatile state of blood flow, the fluid flow type, velocity inlet, pressure inlet and pressure outlet are set in the Fluent module, and the fluid material properties are defined; according to the related parameters that can reflect the real structural characteristics and mechanical characteristics of the blood vessel, the solid domain material properties and the fluid-solid interface are defined in the Transient Structural module; according to the actual situation of human body temperature and the environment, the APDL command is inserted to call the temperature coupling field and set the external excitation temperature field.

[0024] Further, the APDL command inserted to set the external excitation temperature field is specifically as follows:

[0025] (1) The ET (Element Type) command is used to select the coupling field element type, and the KEYOPT (Key Options) command is used to set the key options of the element to activate the specific functions of the element;

[0026] For thermal fluid-structure coupling analysis, SOLID226 or SOLID227 coupling elements are needed to handle the coupling problem of structure and temperature field, which is specifically as follows:

[0027] For hexahedral mesh: ET, matid, SOLID226, 11

[0028] For tetrahedral mesh: ET, matid, SOLID227, 11

[0029] Wherein, matid represents the user-defined material number, SOLID226 and SOLID227 are the coupling field element types in ANSYS, 11 is the key option setting, indicating that the structure and temperature degrees of freedom are considered at the same time;

[0030] Activate structure and temperature degrees of freedom: KEYOPT, matid, 1, 11

[0031] Wherein, matid represents the user-defined material number, 1 is the key option number, and 11 is the setting value, indicating that the structure and temperature degrees of freedom are considered at the same time;

[0032] (2) Set the initial temperature of the blood vessel model using the TUNIF command:

[0033] TUNIF, T

[0034] where T is the initial temperature of the blood vessel model;

[0035] (3) Define the convective boundary condition using the SF command based on the actual temperature of the external environment and the human body, as well as the heat exchange conditions:

[0036] SF, A1, CONV, h, Tinf

[0037] where A1 is the naming selection of the blood vessel surface, h is the convective heat transfer coefficient, and Tinf is the environmental temperature.

[0038] By adopting the above technical solution: first, use the ET (Element Type) and KEYOPT (Key Options) commands to call the temperature coupled field. For the tetrahedral mesh division used in the present application, the following commands can be used:

[0039] ET, 1, 227

[0040] !*

[0041] KEYOPT, 1, 1, 11

[0042] KEYOPT, 1, 2, 0

[0043] KEYOPT, 1, 4, 0

[0044] KEYOPT, 1, 5, 0

[0045] KEYOPT, 1, 7, 0

[0046] KEYOPT, 1, 9, 1

[0047] KEYOPT, 1, 10, 1

[0048] KEYOPT, 1, 15, 0

[0049] This APDL command defines a PLANE182 element and sets the relevant key options, enabling the element to be used for thermal analysis, including temperature degrees of freedom, thermal expansion, heat flux, and heat generation, while turning off some other options such as large strain, stress, and strain degrees of freedom. These settings enable the element to handle various physical phenomena in thermal analysis while avoiding unnecessary calculations.

[0050] ET,1,227, where ET,1,227 command is used to define the element type, 1 is the real constant number, indicating that this element type will use the real constant number 1, 227 is the element number, indicating that it is using the ANSYS predefined element type number 227, which usually refers to the PLANE182 element, which is a four-node plane stress element for thermal analysis.

[0051] KEYOPT,1,1,11, where KEYOPT,1,1,11 command is used to set the key options of the element, the first 1 is the real constant number of the element type, which corresponds to the real constant number in the ET command, the second 1 is the key number, indicating that this is the first key option, 11 is the key value, for the PLANE182 element, the value 11 of the key 1 usually indicates that the element contains the temperature degree of freedom (TEMP) and thermal expansion (EXPD).

[0052] KEYOPT,1,2,0, where KEYOPT,1,2,0 is to set the second key option of the element to 0. For the PLANE182 element, KEYOPT(2) set to 0 usually indicates that the large strain option is not used.

[0053] KEYOPT,1,4,0, where KEYOPT,1,4,0 is to set the fourth key option of the element to 0. For the PLANE182 element, KEYOPT(4) set to 0 usually indicates that the stress degree of freedom is not used.

[0054] KEYOPT,1,5,0, where KEYOPT,1,5,0 is to set the fifth key option of the element to 0. For the PLANE182 element, KEYOPT(5) set to 0 usually indicates that the strain degree of freedom is not used.

[0055] KEYOPT,1,7,0, where KEYOPT,1,7,0 is to set the seventh key option of the element to 0. For the PLANE182 element, KEYOPT(7) set to 0 usually indicates that the high-order shape function is not used.

[0056] KEYOPT,1,9,1, where KEYOPT,1,9,1 is to set the ninth key option of the element to 1. For the PLANE182 element, KEYOPT(9) set to 1 usually indicates that the element contains the heat flux (HFLUX).

[0057] KEYOPT,1,10,1, where KEYOPT,1,10,1 is to set the tenth key option of the element to 1. For the PLANE182 element, KEYOPT(10) set to 1 usually indicates that the element contains the heat generation (GEN).

[0058] KEYOPT,1,15,0, where KEYOPT,1,15,0 is to set the fifteenth key option of the element to 0. For the PLANE182 element, KEYOPT(15) set to 0 usually indicates that the temperature-displacement coupling option is not used.

[0059] Secondly, the initial temperature of the blood vessel model is set using the TUNIF command. For example, if the initial temperature of the blood vessel model is set to 37℃, the following command can be used:

[0060] TUNIF, 37

[0061] Finally, according to the actual temperature and heat exchange of the external environment and the human body, the corresponding boundary conditions are applied, and the SF command can be used to define the convective boundary conditions. For example, if the external environment temperature is set to 20℃, the convective heat transfer coefficient between the solid outside surface (solidoutside) and the external environment is 4w / (m 2 ·℃), the following command can be used:

[0062] SF, solidoutside, CONV, 4, 20

[0063] Further, in step S5, the data transmission is created, which is specifically:

[0064] In the System Coupling interface, select the coupling interface of the fluid domain and the solid domain (for example, fluid solid interface), create Data Transfer to establish fluid-solid data link, including transmission of five kinds of data such as "pressure", "deformation", "temperature", "heat transfer coefficient", "near-wall temperature";

[0065] Among them, the five kinds of data transmission are:

[0066] (1) Transmit the pressure data from the Fluent (fluid analysis) module to the Transient Structural (solid analysis) module, the pressure exerted by the outer surface of the fluid domain (blood) on the inner surface of the solid domain (blood vessel wall) as a load for the calculation of external force in the solid structure analysis;

[0067] (2) Transmit the heat transfer coefficient data from the Fluent module to the Transient Structural module for calculating the inner surface convective heat transfer coefficient of the solid domain;

[0068] (3) Transmit the near-wall temperature data from the Fluent module to the Transient Structural module for calculating the inner surface convective reference temperature of the solid domain. The convective reference temperature will affect the calculation result of the convective heat transfer coefficient, and further affect the analysis of the heat transfer process;

[0069] (4) Transmit the incremental displacement data from the Transient Structural module to the Fluent module. The deformation data of the solid structure will affect the boundary conditions of the fluid domain. For example, if the solid structure is displaced, the boundary of the fluid domain will also be adjusted accordingly;

[0070] (5) Transfer temperature data from the Transient Structural module to the Fluent module. The boundary conditions of the fluid domain, temperature variation within the fluid domain, and thermal physical properties of the fluid will be adjusted according to the temperature data of the solid module.

[0071] Further, the data transmission process is specifically:

[0072] According to the fluid inlet and outlet boundary conditions, the initial temperature of the fluid, and the physical properties, the control equation of the fluid domain is solved and calculated to obtain the fluid velocity, pressure, and temperature. Through the mechanical conservation relationship of the fluid-structure interface, the calculated near-wall fluid force is transmitted to the solid inner wall, which is then used as a boundary condition to the control equation of the solid region for calculation and solving to obtain the stress, strain, and displacement of the solid region. Through the displacement conservation relationship of the fluid-structure interface, the displacement of the solid inner wall is transmitted to the near-wall fluid, and the displacement is used as a boundary condition to the control equation of the blood for calculation and solving, forming the coupling iteration between the flow field of the fluid domain and the stress field of the solid domain. Based on the energy conservation equation, the temperature field of the fluid domain is solved, and the solved temperature changes the flow field according to the non-Newtonian relationship of the blood, forming the coupling iteration between the flow field and the temperature field of the fluid domain. The near-wall fluid temperature is substituted into the heat conservation relationship of the fluid-structure interface to solve the temperature distribution of the solid inner wall. The solid temperature calculation result is used as a boundary condition to the geometric equation to solve the solid strain and stress, and according to the heat conduction differential equation, the solid strain changes the temperature field of the solid domain again, forming the coupling iteration between the stress field and the temperature field of the solid domain. According to the inner wall temperature obtained by the iteration of the solid domain, the near-wall fluid temperature is solved by substituting the temperature into the heat conservation relationship of the fluid-structure interface, forming the coupling iteration between the temperature of the fluid domain and the temperature of the solid domain.

[0073] Further, the control equations of the fluid domain, the solid domain, and the coupling interface are specifically:

[0074] (1) Blood fluid domain control equation:

[0075] In the entire blood flow field, the motion of the fluid follows the law of conservation of mass, which can be mathematically represented by the continuity equation. For an incompressible fluid, the fluid density does not change with time, so the continuity equation can be expressed as:

[0076]

[0077] wherein, are the x, y, and z direction velocity components (unit: m / s);

[0078] The blood motion process also follows the law of conservation of momentum, and the Navier-Stokes equation is commonly used to describe the momentum conservation of an incompressible fluid, which is expressed as:

[0079]

[0080]

[0081]

[0082] wherein, are the velocity components in x, y, z directions (unit: m / s), is the time (unit: s), is the unit mass fluid body force (unit: N), is the viscosity (unit: Pa·s), is the pressure (unit: Pa), is the fluid density (unit: kg / m 3 );

[0083] The energy increase in the fluid microelement is equal to the net heat flow into the fluid and the work done by the body force and surface force on the fluid microelement, and its expression is:

[0084]

[0085] wherein, is the fluid density (unit: kg / m 3 ), is the specific heat capacity of the liquid (unit: J / (kg·K), is the temperature (unit: K), is the fluid velocity vector (unit: m / s), is the thermal conductivity of the fluid (unit: W / (m K);

[0086] (2) Vessel wall solid domain control equation:

[0087] Assuming that the solid domain blood vessel is a single-layer, isotropic linear elastic material, for linear elastic material, it satisfies the three basic laws of elasticity mechanics: deformation continuity law, stress-strain relationship and motion law; Considering the influence of temperature field, therefore, there is a heat exchange process between the fluid area inside and outside the blood vessel and the solid area, the heat conduction of the solid structure needs to be considered, so the heat conduction differential equation is introduced;

[0088] The force balance equation is that the object in equilibrium state, any part of the object obeys Newton's third law, and its expression is:

[0089]

[0090]

[0091]

[0092] wherein, is stress (unit: Pa), is force (unit: N);

[0093] The stress-strain constitutive equation is expressed as the deformation of solid materials under the action of external force. Different materials will have different deformations under the same force, so the corresponding physical relationship is also different, and its expression is:

[0094]

[0095] wherein, is stress (unit: Pa), is Young's modulus (unit: N / m 2 ), is Poisson's ratio, is strain, is the first strain invariant, is the Kronecker function;

[0096] The geometric equation is expressed as the material itself is continuous, and after deformation under the action of external force, it is also continuous, and its expression is:

[0097]

[0098] wherein, is strain, is the Kronecker function, is displacement vector (unit: m), is the thermal expansion coefficient (unit: 1 / K);

[0099] The heat conduction differential equation is expressed as:

[0100]

[0101] wherein, is the solid density (unit: kg / m 3 ), is the specific heat capacity of solid (unit: J / (kg·K), is the solid thermal conductivity (unit: W / (m·K);

[0102] (3) Coupling interface control equation:

[0103] The two-way heat fluid-solid coupling meets the thermodynamic condition and the dynamic condition at the coupling boundary, and the model established in the application does not consider radiation, evaporation and other processes at the interface between the fluid and the solid. According to the energy conservation, at the fluid-solid coupling interface, the heat conduction amount of the blood vessel should be equal to the convective heat transfer amount of the blood, so the thermodynamic condition that should be met at the fluid-solid coupling interface is that the heat conduction amount of the blood vessel wall surface should be equal to the convective heat transfer amount of the blood near the wall surface:

[0104]

[0105] wherein, is the heat flux (unit: W / m 2 ), is the temperature (unit: K), is the fluid thermal conductivity (unit: W / (m·K), is the solid thermal conductivity (unit: W / (m·K), is the normal unit vector of the fluid structure interface;

[0106] In the problem of interaction between the fluid domain and the solid domain, the fluid impacts the solid structure, so that the solid is deformed, thereby changing the flow pattern of the fluid, so the dynamic condition that should be met at the fluid-solid coupling interface is that the displacement and the force are equal:

[0107]

[0108]

[0109] wherein, is the displacement vector (unit: m), is the normal unit vector of the fluid structure interface, is the stress (unit: Pa);

[0110] Further, in step S6, the numerical simulation result analysis is specifically:

[0111] Obtaining the quantitative relationship between the wall shear stress, the oscillatory shear index, the equivalent stress and the clinical characteristics of the disease, defining the corresponding risk coefficient for different blood vessel diseases to quantitatively evaluate the disease risk;

[0112] According to the pulsation characteristics of human blood and the structural characteristics of blood vessels, the high-risk point of blood vessel disease and the periodic change of the high-risk point are quantitatively analyzed from the aspects of the cardiac cycle and the characteristic points.

[0113] Compared with the prior art, the present application has the following beneficial effects:

[0114] 1. The present application is based on the real medical image data of the existing clinical equipment, reconstructs the three-dimensional structure of the blood supply system corresponding to the specific disease, and reproduces the complex trend of the three-dimensional blood vessels to assist the doctors in understanding the disease.

[0115] 2、The present application is directed to the whole blood circulation system of the human body, including atherosclerosis, thrombosis, intracranial aneurysm, etc., and has a wide range of applications.

[0116] 3、The present application innovatively proposes a two-way thermal fluid-structure coupling method, establishes a multi-field two-way coupling parameterized model of the blood vessel wall stress field, blood flow field and external excitation temperature field, further considers the influence of the environment temperature of the blood vessel on the basis of fluid-structure two-way coupling, and is more in line with the actual situation of human blood transport, and truly reproduces the blood state change of the human blood supply system, thereby providing a more optimized idea for blood flow dynamics simulation.

[0117] 4、The numerical simulation part of the present application can set the initial conditions and boundary conditions of the model according to the real clinical data such as blood pressure and blood flow rate of the patient, so as to realize personalized risk assessment of vascular diseases for different patients.

[0118] 5、The present application combines the mapping relationship between engineering numerical parameters and clinical symptoms and the treatment experience of doctors, and finally formulates the best treatment scheme and intervenes in the treatment, thereby reducing the mortality rate of patients.

[0119] 6、The present application can combine modern imaging technology (such as MRI, CT, etc.) for non-invasive monitoring, real-time acquisition of the flow state and wall stress in the blood vessel, reduction of the invasive operation on the patient, and improvement of the safety and convenience of clinical application. BRIEF DESCRIPTION OF DRAWINGS

[0120] Figure 1 is the flow chart of the method of the present application;

[0121] Figure 2 is the implementation flow chart of the present application;

[0122] Figure 3 is the coupling calculation and analysis project chart of the present application;

[0123] Figure 4 is the multi-field coupling relationship chart of fluid-thermal of the present application;

[0124] Figure 5 is the corresponding relationship chart of blood flow dynamics parameters and clinical characteristics of the present application;

[0125] Figure 6 is the vascular disease risk assessment flow chart of the embodiment of the present application;

[0126] Figure 7 is the vascular disease risk assessment result chart of the embodiment of the present application. DETAILED DESCRIPTION

[0127] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions of the embodiments of the present application will be described clearly and completely below with reference to the drawings of the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the described embodiments of the present application, all other embodiments obtained by those skilled in the art belong to the scope of protection of the present application.

[0128] Embodiment: Aortic valve stenosis complication risk assessment

[0129] A blood vessel disease risk assessment method based on a two-way thermal fluid-structure coupling, the flow chart of the blood vessel disease risk assessment method of the embodiment is as shown in Figure 6 The blood vessel disease risk assessment method comprises the following steps:

[0130] In the blood vessel disease risk assessment method, step S1, reconstruction of a three-dimensional model of a blood vessel, specifically comprises: extracting a three-dimensional model of an aorta according to real image data (CT) of a patient through 3D Slicer scanning; and optimizing the three-dimensional model of the blood vessel by using Geomagic and Solidworks.

[0131] The process of reconstructing the three-dimensional model of the blood vessel is described below:

[0132] Step S1-1, extracting a three-dimensional model of an aorta according to real image data (CT) of a patient through 3D Slicer scanning: importing CT and other real image data of an aortic valve stenosis patient into 3D Slicer for scanning, selecting a suitable threshold, adjusting contrast and brightness to display clear blood vessel structure, using Paint, Draw, Erase and other tools in 3D Slicer to segment the blood vessel, removing excess bone and tissue parts, using the three-dimensional reconstruction function of the software to generate a three-dimensional model of the blood vessel according to the segmentation result, and outputting an stl format file.

[0133] Step S1-2, optimizing the three-dimensional model of the blood vessel by using Geomagic and Solidworks: inputting the stl format model file into Geomagic software, optimizing and repairing the model grid by using the Geomagic grid doctor tool, smoothing the model by using the Geomagic smoothing, sandpaper and other functions, adding model details by using the shell extraction function, adding the thickness of the blood vessel wall, and outputting an stp format model file. Inputting the stp format file into Solidworks software, repairing the model blood vessel port by using the "stretch cut tool", and ensuring that the model meets the simulation simulation requirements.

[0134] In the blood vessel disease risk assessment method, step S2, coupling calculation project building specifically comprises: module selection; and module connection.

[0135] Step S2-1, module selection: double-click Fluid Flow (Fluent) and Transient Structural options in the Analysis systems module and System Coupling option in the Component systems module in Toolbox in the ANSYS Workbench interface, create analysis projects A (fluid), B (solid) and C (coupling calculation) in the project management area.

[0136] Step S2-2, module connection: pass the geometry data Geometry (A2) of project A (Fluent) to the Geometry (B3) module of project B (Transient Structural), and pass the calculation setup data Setup (A4) of project A (Fluent) and the calculation setup data Setup (B5) of project B (Transient Structural) to the calculation setup Setup (C2) module of project C (System Coupling).

[0137] The step S3 of the blood vessel disease risk assessment method includes: fluid domain meshing; solid domain meshing.

[0138] Step S3-1, fluid domain meshing: enter the "Mesh" module of Fluid Flow (Fluent), suppress the solid domain of the blood vessel wall, select tetrahedrons as the main division method for the fluid domain, and set the element size to 5.0mm, apply local mesh control in the key area of the fluid domain (such as the fluid inlet / outlet area), click "Generate Mesh" to generate the overall mesh, and use the "Mesh Metrics" tool to check the mesh quality, ensure that there are no negative volume elements or high twist elements, to meet the accuracy requirements of subsequent fluid domain simulation calculation.

[0139] Step S3-2, solid domain meshing: enter the "Mesh" module of Transient Structural, suppress the blood fluid domain, select tetrahedrons as the main division method for the solid domain, and set the element size to 0.8mm, apply local mesh control in the key area of the solid domain (such as the boundary layer of the blood vessel wall), click "Generate Mesh" to generate the overall mesh, and use the "Mesh Metrics" tool to check the mesh quality, ensure that there are no negative volume elements or high twist elements, to meet the accuracy requirements of subsequent solid domain simulation calculation.

[0140] Step S4, initial and boundary condition settings, in the vascular disease risk assessment method specifically includes: setting the initial and boundary conditions for the fluid domain and solid domain; inserting APDL commands to set the external excitation temperature field.

[0141] Step S4-1: Set the initial and boundary conditions for the fluid domain and solid domain:

[0142] (1) Setting initial and boundary conditions for the fluid domain:

[0143] This embodiment uses an extension of the Carreau-Yasuda viscosity model, which better reflects the rheological properties of human blood, and also considers the relationship between viscosity and temperature and shear rate. The functional relationship expression is as follows:

[0144]

[0145]

[0146] In the formula Shear rate describes the rate at which the fluid velocity changes relative to the radius of the circular flow channel. Relaxation time (unit: s). , In the Carreau-Yasuda model, the non-Newtonian properties of blood are represented by hematocrit. Related, , Hematocrit represents the percentage of blood cells in the blood volume. In adult males, hematocrit is 40%-50%. In this specific embodiment, hematocrit is 45% for viscosity calculation. It is a temperature-related blood viscosity obtained by fitting experimental data.

[0147] This specific embodiment assumes that the blood is a homogeneous, isotropic, incompressible, non-Newtonian fluid, and that the blood density is set to 1050 kg / m³. 3 With a thermal conductivity of 0.56 W / (m·K), a specific heat of 3600 J / (kg·K), and an initial inlet temperature of 37℃, the boundary conditions for the blood inlet velocity are expressed as follows:

[0148]

[0149] (2) Setting initial and boundary conditions for solid domain

[0150] This specific embodiment assumes that the aortic vessel wall is an isotropic linear elastic material, and sets the vessel wall density to 1060 kg / m³. 3The thermal conductivity is 0.42 w / (m·k), the specific heat is 3689 J / (kg·k), the Poisson's ratio is 0.45, and the Young's modulus is 2.7 MPa. The outlet section of the solid domain of the specific embodiment is provided with a fixed support condition.

[0151] Step S4-2, insert the APDL command to set the external excitation temperature field:

[0152] (1) Use the ET (Element Type) and KEYOPT (Key Options) commands to call the temperature coupled field. For the tetrahedral mesh division used in this specific embodiment, the following commands can be used:

[0153] ET, 1, 227

[0154] !*

[0155] KEYOPT, 1, 1, 11

[0156] KEYOPT, 1, 2, 0

[0157] KEYOPT, 1, 4, 0

[0158] KEYOPT, 1, 5, 0

[0159] KEYOPT, 1, 7, 0

[0160] KEYOPT, 1, 9, 1

[0161] KEYOPT, 1, 10, 1

[0162] KEYOPT, 1, 15, 0

[0163] (2) Use the TUNIF command to set the initial temperature of the blood vessel model to 36℃, and the specific command is as follows:

[0164] TUNIF, 37

[0165] (3) Use the SF command to define the convection boundary condition, set the external environment temperature to 20℃, and the blood vessel outer surface (solidoutside) and the external environment convection heat transfer coefficient to 4 w / (m 2 ·℃), and the specific command is as follows:

[0166] SF, solidoutside, CONV, 4, 20

[0167] In the blood vessel disease risk assessment method, step S5 of creating data transmission specifically includes: setting the data transmission source area and the target area; configuring data transmission parameters.

[0168] Step S5-1, setting data transmission source area, target area: double-click the "System Coupling" cell, enter the system coupling setting interface, in the "System Coupling" interface, confirm that the "Fluent" and "TransientStructural" analysis systems have been correctly loaded and displayed in the "Participants" list, in the "Source" option, select "Fluent" as the source analysis system, in the "Source Region" drop-down menu, select the named fluid domain outside surface (fluidoutside) as the data transmission source area. In the "Target" option, select "TransientStructural" as the target analysis system, and in the "Target Region" drop-down menu, select the named solid domain inside surface (solidinside) as the data transmission target area.

[0169] Step S5-2, configure data transmission parameters: in the "Data Transfer" setting, select the data transmission method as "Conservative Interface Flux" (conservative interpolation) to ensure the accuracy and energy conservation of data transfer, in the "Coupling Analysis Settings", set the coupling time step to 0.001 seconds, and set the maximum coupling iteration number to 5 times to ensure the stability and convergence of data transfer.

[0170] The step S6 of the blood vessel disease risk assessment method specifically includes: determining the correspondence between the hemodynamic parameters and the clinical characteristics, and defining the blood vessel disease risk assessment coefficient; quantitatively evaluating the risk of aortic valve stenosis complications.

[0171] Step S6-1, determine the correspondence between the hemodynamic parameters and the clinical characteristics, and define the blood vessel disease risk assessment coefficient: wall shear stress (WSS) is the force caused by friction on the arterial wall during blood flow. Unstable WSS can cause endothelial cell dysfunction. Studies have shown that changes in WSS levels are closely related to diseases such as atherosclerosis and thrombosis. The WSS value in a healthy artery is in the range of 1 Pa-7 Pa, when WSS is less than 1 Pa, it will promote the development of atherosclerosis, and when WSS is higher than the normal range, it may cause thrombosis. Therefore, this embodiment defines the thrombosis risk coefficient I 血栓 and the atherosclerosis risk coefficient I 粥样硬化 to respectively quantify the risk of aortic thrombosis and atherosclerosis, and the definitions are as follows:

[0172]

[0173]

[0174] When I is greater than 1, the aorta is prone to thrombosis and atherosclerotic complications, and the greater I is, the greater the risk of disease.

[0175] Step S6-2, quantitative evaluation of aortic valve stenosis complication risk: refer to the attached Figure 7 According to the morphological characteristics of the aorta, 14 monitoring points are selected on the aortic root, ascending aorta, aortic arch, descending aorta and branch arteries. According to the risk coefficient defined in step S6-1, the risk of concurrent atherosclerosis and thrombosis at each point is quantitatively evaluated, and high-risk points are selected to provide data guidance for preventing concurrent atherosclerosis and thrombosis in patients with aortic valve stenosis in clinical practice.

[0176] In summary, the present application can be more in line with the real flow state of human blood, and improve the numerical simulation prediction accuracy of vascular diseases.

[0177] The above is only a preferred embodiment of the present application, of course, cannot be limited to the scope of the present application, it should be noted that, for those skilled in the art, without departing from the principles of the present application, can make a number of improvements and changes, these improvements and changes are also considered to be within the scope of the present application.

Claims

1. A blood vessel disease numerical simulation prediction method based on bidirectional heat fluid-structure coupling, characterized in that, Comprise the following steps: Step S1, blood vessel three-dimensional model reconstruction; Step S2, coupling calculation project building; Step S3, fluid domain, solid domain meshing; Step S4, initial and boundary condition setting; Step S5, create data transmission; Step S6, numerical simulation result analysis.

2. The blood vessel disease numerical simulation and prediction method based on two-way thermal fluid-structure coupling according to claim 1, characterized in that, In step S1, blood vessel three-dimensional model reconstruction is specifically: Dicom format CT data is imported into 3D Slicer, Mimics software for scanning, selecting appropriate threshold, using the segmentation tool in the software to distinguish the blood vessel structure, using the three-dimensional reconstruction function of the software, according to the segmentation result to generate stl format blood vessel three-dimensional model; The stl format file is imported into Geomagic, Solidworks to smooth the model surface and blood vessel mouth optimization, and use the shell function to add model details, output stp format file, ensure that the model meets the needs of numerical simulation. 3.The blood vessel disease numerical simulation prediction method based on two-way heat fluid-structure coupling according to claim 1, characterized in that, In step S2, the coupling calculation project building is specifically: In the Analysis systems module of ANSYS Workbench interface, select Fluid Flow and TransientStructural options and System Coupling option in Component systems module, that is, create analysis project A fluid, project B solid and project C coupling calculation in project management area, pass the geometric data of project A to project B, pass the calculation setting data of project A and the calculation setting data of project B to project C.

4. The blood vessel disease numerical simulation and prediction method based on two-way thermal fluid-structure coupling according to claim 1, characterized in that, In step S3, the fluid domain, solid domain meshing is specifically: The extracted blood vessel model file is imported into the above coupling analysis project, and the Mesh module of Fluid flow and TransientStructural is used to mesh the fluid domain model and solid domain model respectively.

5. The blood vessel disease numerical simulation and prediction method based on two-way thermal fluid-structure coupling according to claim 1, characterized in that, In step S4, the initial and boundary condition setting is specifically: According to the related parameters that can reflect the real pulsatile state of blood flow, set the fluid flow type, velocity inlet, pressure inlet and pressure outlet in Fluent module, define the fluid material properties; According to the related parameters that can reflect the real structure characteristics and mechanical properties of blood vessel, define the solid domain material properties and fluid-solid coupling interface in Transient Structural module; According to the actual situation of human body temperature and environment, insert APDL command to call temperature coupling field and set external excitation temperature field.

6. The blood vessel disease numerical simulation and prediction method based on two-way thermal fluid-structure coupling according to claim 5, characterized in that, The insertion of APDL command to set external excitation temperature field is specifically: (1) use ET command to select coupling field unit type, use KEYOPT command to set key options of unit, to activate specific functions of unit; For thermal fluid-solid coupling analysis, SOLID226 or SOLID227 coupling unit is needed to handle the coupling problem of structure and temperature field, as follows: For hexahedral mesh: ET, matid, SOLID226, 11 For tetrahedral mesh: ET, matid, SOLID227, 11 Wherein, matid represents the user-defined material number, OLID226 and SOLID227 are coupled field element types in ANSYS, 11 is the key option setting, indicating that the structural and temperature degrees of freedom are considered simultaneously; Activate structural and temperature degrees of freedom: KEYOPT, matid, 1, 11 Wherein, matid represents the user-defined material number, 1 is the key option number, and 11 is the setting value, indicating that the structural and temperature degrees of freedom are considered simultaneously; (2) Set the initial temperature of the blood vessel model using the TUNIF command: TUNIF, T Where T is the initial temperature of the blood vessel model; (3) According to the actual temperature and heat exchange of the external environment and human body, define the convection boundary condition using the SF command: SF, A1, CONV, h, Tinf Where A1 is the naming selection of the blood vessel surface, h is the convective heat transfer coefficient, and Tinf is the environmental temperature.

7. The blood vessel disease numerical simulation and prediction method based on two-way thermal fluid-structure coupling according to claim 1, characterized in that, In step S5, the data transmission is specifically: In the System Coupling interface, select the coupling interface of the fluid domain and the solid domain, and create Data Transfer to establish fluid-solid data linkage, including the transmission of five kinds of data: pressure, deformation, temperature, heat transfer coefficient and near-wall temperature; Among them, the five kinds of data transmission are specifically: (1) Transmit the pressure data from the Fluent module to the Transient Structural module, and the pressure applied by the outer surface of the fluid domain to the inner surface of the solid domain is used as the load for the external force calculation in the solid structure analysis; (2) Transmit the heat transfer coefficient data from the Fluent module to the Transient Structural module, which is used to calculate the convective heat transfer coefficient of the inner surface of the solid domain; (3) Transmit the near-wall temperature data from the Fluent module to the Transient Structural module, which is used to calculate the convective reference temperature of the inner surface of the solid domain. The convective reference temperature will affect the calculation result of the convective heat transfer coefficient, and then affect the analysis of the heat transfer process; (4) Transmit the incremental displacement data from the Transient Structural module to the Fluent module. The deformation data of the solid structure affects the boundary conditions of the fluid domain. For example, if the solid structure displaces, the boundary of the fluid domain will also be adjusted accordingly; (5) Transmit the temperature data from the Transient Structural module to the Fluent module. The boundary conditions of the fluid domain, the temperature change in the fluid domain, and the thermal physical properties of the fluid will be adjusted according to the temperature data of the solid module.

8. The blood vessel disease numerical simulation and prediction method based on two-way thermal fluid-structure coupling according to claim 7, characterized in that, The data transmission process is specifically: According to the fluid inlet and outlet boundary conditions, the initial temperature of the fluid, and the physical characteristics, the fluid domain control equation is solved to obtain the fluid velocity, pressure, and temperature; the near-wall fluid force calculated is transmitted to the solid inner wall through the mechanical conservation relationship of the fluid-solid interface, and then it is taken as the boundary condition to the control equation of the solid region for calculation and solving to obtain the stress, strain, and displacement of the solid region; through the displacement conservation relationship of the fluid-solid interface, the displacement of the solid inner wall is transmitted to the near-wall fluid, and the displacement is taken as the boundary condition to the control equation of the blood for calculation and solving, forming the coupling iteration between the fluid field and the stress field of the solid domain; the temperature of the near-wall fluid is taken into the heat conservation relationship of the fluid-solid interface to solve the temperature distribution of the solid inner wall; The temperature calculation result of the solid is taken as the boundary condition to the geometric equation to solve the stress and strain of the solid, and according to the heat conduction differential equation, the stress of the solid will change the temperature field of the solid domain again, forming the coupling iteration of the stress field and the temperature field of the solid domain; according to the inner wall temperature obtained by the iteration of the solid domain, the temperature of the near-wall fluid is solved by taking the temperature into the heat conservation relationship of the fluid-solid interface, forming the coupling iteration of the temperature of the fluid domain and the temperature of the solid domain.

9. The blood vessel disease numerical simulation and prediction method based on two-way thermal fluid-structure coupling according to claim 8, characterized in that, The control equations of the fluid domain, the solid domain, and the coupling interface are specifically as follows: (1) Blood fluid domain control equation: In the entire blood flow field, the motion of the fluid follows the law of conservation of mass, which is mathematically represented by the continuity equation. For an incompressible fluid, the fluid density does not change with time, so the continuity equation is expressed as: wherein, are the x, y, z direction velocity components, respectively; The blood movement process also follows the law of conservation of momentum, and the Navier-Stokes equation is used to describe the momentum conservation of an incompressible fluid, which is expressed as: wherein, are the x, y, z direction velocity components, respectively, is time, is the volumetric force per unit mass of the fluid, is the viscosity, is the pressure, is the fluid density; The energy increase in the fluid microelement is equal to the net heat flow into the fluid and the work done by the volume force and surface force on the fluid microelement, which is expressed as: wherein, is the fluid density, is the liquid specific heat capacity, is the temperature, is the fluid velocity vector, is the fluid thermal conductivity; (2) Blood vessel wall solid domain control equation: Assuming that the solid domain blood vessel is a single-layer, isotropic, linear elastic material, for linear elastic materials, the three basic laws of elasticity mechanics are satisfied: deformation continuity law, stress-strain relationship, and motion law; considering the influence of the temperature field, therefore, there is a heat exchange process between the fluid region inside and outside the blood vessel and the solid region, and the heat conduction of the solid structure needs to be considered, so the heat conduction differential equation is introduced; The force balance equation is expressed as an object in equilibrium state, and the external force on any part of the object obeys Newton's third law, which is expressed as: wherein, is stress, is force; The stress-strain constitutive equation is expressed as the deformation of the solid material under the action of external force, and different materials have different deformations under the same force, so the corresponding physical relationship is also different, which is expressed as: wherein, is the stress, is the Young's modulus, is the Poisson's ratio, is the strain, is the first strain invariant, is the Kronecker function; The geometric equation is expressed as the material itself being continuous, and it is also continuous after being deformed under the action of external force, which is expressed as: wherein is the strain, is the Kronecker delta, is the displacement vector, is the thermal expansion coefficient; The heat conduction differential equation is expressed as: wherein, is the solid density, is the solid specific heat capacity, is the solid thermal conductivity; (3) Coupling interface control equation: According to the energy conservation, the heat conduction of the blood vessel should be equal to the heat convection of the blood at the fluid-structure coupling interface, so the thermodynamic condition that should be met at the fluid-structure coupling interface is that the heat conduction of the blood vessel wall surface should be equal to the heat convection of the blood near the wall surface: wherein, is the heat flux density, is the temperature, is the fluid thermal conductivity, is the solid thermal conductivity, is the fluid-structure interface normal unit vector; In the problem of interaction between fluid and solid domains, the fluid impacts on the solid structure, causing the deformation of the solid, and thus the flow pattern of the fluid changes, so the dynamic condition that should be met at the fluid-structure coupling interface is that the displacement and force are equal: wherein, is the displacement vector, is the fluid structure interface normal unit vector, is the stress.

10. The blood vessel disease numerical simulation and prediction method based on two-way thermal fluid-structure coupling according to claim 1, characterized in that, In step S6, the numerical simulation result analysis is specifically: Obtain the quantitative relationship between the wall shear stress, oscillatory shear index, equivalent stress and the clinical characteristics of the disease, and define the corresponding risk coefficient for different vascular diseases to quantitatively evaluate the risk of disease occurrence; According to the pulsatile characteristics of human blood and the structural characteristics of blood vessels, the high-risk point and the periodic change of the high-risk point of the blood vessel disease are quantitatively analyzed from the aspects of the cardiac cycle and the characteristic points.

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