A DPD-based simulation method and system for coarsening of fiber by centrifugal treatment

Abstract

The present invention provides a method and system for simulating the coarse-graining of centrifugal fibrillation based on DPD, belonging to the technical field of electrical digital data processing. The method and system for simulating the coarse-graining of centrifugal fibrillation based on DPD of the present invention do not need to obtain results based on repeated iterations based on experience, and only need to give the shear flow intensity and fiber material properties to obtain the behavior of the fiber film in the fluid, and improve the fiber stretching performance by regulating the flow field and changing the material parameters, thereby increasing the specific surface area of ​​the fibrillation and optimizing the dipping process. The present invention can simulate the behavior of the fiber in a complex flow field and the deposition process under centrifugal load, obtain the anisotropic material properties of the fiber and the influence of the centrifugal load on its swelling and stretching, provide a research basis for more complex fiber precipitation behavior, understand its dynamic behavior and precipitation mechanism, and provide a basis for optimizing the production process of aramid honeycomb core.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrical digital data processing, and relates to the use of particle-based methods, numerical simulation, force analysis and dissipative particle dynamics, and specifically to a DPD-based centrifugal coarsening simulation method and system for fiber analysis. Background Art

[0002] Aramid paper honeycomb is named for its structure similar to the honeycomb in nature. The sandwich structure made of it has excellent properties such as high specific strength, high specific stiffness, stable structure, sound insulation and heat insulation. It is widely used in aerospace, national defense, rail transportation, shipbuilding, communications and other fields. As the international situation becomes increasingly complex, the demand for the localization of aramid paper honeycomb, an aviation raw material, is extremely urgent, and researchers are paying more and more attention to and studying the manufacturing process of aramid paper.

[0003] The precipitated fibrils in aramid honeycomb paper are in the form of cilia or broom-like films. After being fully beaten, the precipitated fibrils swell and stretch. Their high specific surface area is the key to ensuring the quality of molding. The precipitated fibrils processing technology is the technical bottleneck that must be broken through first among the three core key technologies of aviation-grade aramid honeycomb paper manufacturing. The high-speed centrifugal continuous processing technology of precipitated fibrils can achieve sufficient slurrying of precipitated fibrils and increase the specific surface area of ​​precipitated fibrils. Computers can not only improve experimental efficiency and save research resources, but also predict phenomena and processes that cannot be observed in experiments. In order to study the behavior of fibers in complex flow fields, computer simulation can be used and the dissipative particle dynamics (DPD) method can be introduced. The DPD method can not only directly observe the static structure of the simulation system, but also record and track its dynamic evolution process, obtain the characteristic parameters at different stages of the simulation process, and further understand and analyze the precipitation mechanism.

[0004] Existing studies on the mesoscopic simulation of solid-liquid fluids using the DPD method focus on the phase behavior of complex systems, the orientation of non-deformed fibers, the structure and tension changes under no shear, the rotational motion of ellipsoidal particles in shear flow, etc., but lack the simulation of fiber stretching and deformation. Previous research objects were mainly aimed at spherical particle suspensions, high volume fraction suspensions, and non-spherical suspensions, while the precipitated fibers in aramid honeycomb paper are ciliary or broom-like film structures, and there is currently a lack of research on fibers of this morphology. Summary of the invention

[0005] The present invention is made to solve the above-mentioned problem, and aims to provide a DPD-based centrifugal treatment coarsening simulation method and system for fiber analysis.

[0006] The invention provides a simulation method for coarse-graining of centrifugal treatment of precipitated fibers based on DPD, which has the following characteristics and comprises the following steps: S10, establishing a mesoscopic-scale aramid paper dipping model according to a DPD algorithm; S20, replacing the DPD soft repulsive conservative potential energy in the aramid paper dipping model with a worm chain potential energy and using Lammps simulation software for parallel calculation, using mesh structure particles to simulate the physical form of aramid fibers, wherein the worm chain potential energy comprehensively considers the elastic connection between chain segments composed of two particles, the angular stiffness between the chain segments and the rotational stiffness of the chain segments between four continuous particles; S30, setting different material properties of aramid paper and corresponding aramid fibers and the shear flow strength applied thereto, performing parameter mapping with experimental data to match the real material properties, solving the behavior of the aramid fibers in a complex flow field under dimensionless time, and finally obtaining the swelling and stretching mechanism of the aramid fibers.

[0007] The DPD-based fibrillation centrifugal treatment coarsening simulation method provided by the present invention may also have the following features: wherein, in step S10, the DPD algorithm is the same as the algorithm of the molecular dynamics system based on Newton's second law: , , , Respectively represent the index The mass, position vector, and velocity vector of the particle, The action of adjacent particles on the particle The force vector on is conservative force, dissipative force , random force ,coefficient and respectively reflect the strength of dissipative force and random force, Two adjacent particles and The distance between is a unit vector, Neighboring particles and The speed difference, is a Gaussian white noise and , They represent the weight functions of dissipative force and random force respectively, and the general form is , represents the weight coefficient, Represents the cutoff radius.

[0008] The DPD-based centrifugal treatment coarsening simulation method for fibrillation provided by the present invention may also have the following features: wherein, in step S10, , is the Boltzmann constant, It's the temperature.

[0009] The DPD-based centrifugal treatment coarsening simulation method for fibrillation provided by the present invention may also have the following features: wherein, in step S10, in order to improve the calculation efficiency while ensuring a certain accuracy, within a truncation range, all neighboring particles are subjected to the following calculations: When the distance between two particles exceeds the cutoff range, the interaction between them is ignored.

[0010] The DPD-based centrifugal treatment coarse-grained fiber precipitate simulation method provided by the present invention may also have the following features: wherein, in step S20, each particle represents a node, and a network structure is formed by the constraint of the interaction potential energy between particles so as to capture the mechanical behavior of the aramid fiber, and the aramid paper dipping model is used to simulate the geometry, elasticity and flexibility of the fiber.

[0011] The DPD-based centrifugal treatment coarsening simulation method for fibrillation provided by the present invention may also have the following features: wherein, in step S20, the derivation of the worm chain potential energy includes the following sub-steps: S21, considering the elastic connection between the chain segments to prevent the chain segments from being overstretched or compressed: , Represents the finite extension nonlinear elastic potential energy, which is used to limit the extension behavior of the chain segment and ensure the overall stability and elasticity of the chain. r represents the distance between the chain segments composed of two particles, K The spring constant describes the elastic stiffness between the segments, R0 is the maximum elongation distance that defines the maximum allowable distance between the segments, and S22, considers the angular stiffness between the segments and limits the bending degree of the segments: , is the angular potential energy, which is used to control the bending stiffness between the segments. θ represents the angle between two adjacent segments. θ 0 is the ideal angle representing the equilibrium angle of the chain segment, k θ The angular stiffness coefficient is used to describe the resistance of the chain segment to bending; S23 considers the rotational stiffness of the chain segment between four consecutive particles and controls the degree of twisting of the chain: , is the dihedral potential energy, which is used to describe the rotational rigidity of the chain segment and affects the rotational stability of the chain segment. is the dihedral angle used to describe the rotation angle between the planes formed by four consecutive particles. The dihedral potential energy amplitude that describes the rotational stiffness of the chain segment is: n is the period number representing the periodicity of the dihedral potential energy, γTo control the phase offset angle of the dihedral potential energy; S24, to obtain the worm chain potential energy .

[0012] The DPD-based centrifugal treatment coarsening simulation method for fibrillation provided by the present invention may also have the following features: wherein, in step S21, K The larger the value, the less likely the chain segment is to be stretched. near When, potential energy tends to infinity, preventing the chain segments from being stretched beyond In step S22, k θ The larger the value, the greater the rigidity of the chain segment and the more difficult it is to bend. In step S23, The larger it is, the more difficult it is for the chain segment to rotate.

[0013] The DPD-based centrifugal treatment coarsening simulation method for fibrillation provided by the present invention may also have the following features: wherein, in step S20, the persistence length is used L p To describe the rigidity of the chain segment, the persistence length L p is the magnitude of the chain segment bending, , is the Boltzmann constant, It's the temperature.

[0014] The present invention also provides a DPD-based centrifugal treatment coarse-grained fiber simulation system, which has the following characteristics: it uses any of the aforementioned DPD-based centrifugal treatment coarse-grained fiber simulation methods, including: a data input part, used for the user to input the material properties of aramid paper and corresponding aramid fibers and the shear flow intensity applied to them; a simulation part, which uses mesh structure particles to simulate the physical form of aramid fibers; a parameter mapping part, which is connected to the data input part and the simulation part, and performs parameter mapping on the data input by the data input part and the experimental data to match the real material properties, solve the behavior of aramid fibers in complex flow fields under dimensionless time, and finally obtain the swelling and stretching mechanism of aramid fibers.

[0015] The beneficial effects of the present invention are:

[0016] (1) The present invention establishes a mesoscopic aramid paper impregnation model through a coarse-graining method, performs parameter mapping with experimental data to match the real material properties, and successfully simulates the swelling and stretching process of aramid fiber under high-speed centrifugal load. Compared with the traditional full macroscopic modeling method, it has higher accuracy and more detailed and intuitive behavior at the mesoscopic scale.

[0017] (2) The present invention simulates fibers with mesh-structured particles, performs reasonable coarse-grained simulation, and controls the stiffness of the entire film with potential energy. In previous DPD models, conservative forces may only consider the repulsive effect or simple interaction between particles. This design enables the model to better simulate the complex flow field and fiber behavior in the real system.

[0018] (3) The present invention controls different centrifugal loads through shear flow and controls the anisotropic fiber material properties through potential energy, thereby realizing the study of the effects of shear flow and material properties on the swelling and stretching properties of the fiber.

[0019] (4) The present invention finds that when changing the shear flow intensity and material properties, enhancing the shear flow will increase the specific surface area of ​​the precipitated fibers; the anisotropic material properties of the fibers have a significant effect on their swelling and stretching process, which can provide a basis for optimizing the production process of aramid honeycomb cores.

[0020] (5) Designers do not need to repeatedly iterate based on experience to obtain the final result. They only need to give the shear flow intensity and fiber material properties, and use the simulation method of the present invention to obtain the behavior of the fiber film in the fluid. The fiber stretch performance is improved by regulating the flow field and changing the material parameters, thereby increasing the specific surface area of ​​the precipitated fiber and optimizing the dipping process. The present invention uses dissipative particle dynamics to simulate the behavior of the fiber in a complex flow field, and intuitively demonstrates the deposition process of the fiber under high-speed centrifugal load. The effects of the anisotropic material properties of the fiber and the centrifugal load on its swelling and stretching are studied. The results obtained through these simplified models help provide a research basis for more complex fiber precipitation behavior and help further understand its dynamic behavior and precipitation mechanism. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a flowchart of a simulation method for coarsening fibrillation by centrifugal treatment based on DPD in an embodiment of the present invention.

[0022] Figure 2 It is the left and right solid wall movement model and velocity gradient distribution of the aramid paper fibrid in the test example of the present invention in a shear flow environment.

[0023] Figure 3 It is the dynamic behavior of the aramid paper fibrid film in the test example of the present invention in the shear flow at different times.

[0024] Figure 4 These are the dynamic behaviors of the aramid paper fibrillation film in the test examples of the present invention under static fluid and shear flow respectively.

[0025] Figure 5 It is the curling behavior of three different material properties of the aramid paper fibrid films in the test examples of the present invention. DETAILED DESCRIPTION

[0026] In order to make the technical means, creative features, objectives and effects of the present invention easy to understand, the following embodiments and drawings specifically describe a DPD-based centrifugal treatment coarse particle simulation method and system of the present invention.

[0027] <Example>

[0028] Figure 1 It is a flowchart of a simulation method for coarsening fibrillation by centrifugal treatment based on DPD in an embodiment of the present invention.

[0029] like Figure 1 As shown, this embodiment provides a DPD-based centrifugal treatment coarse-grained simulation method for fibrillation, comprising the following steps:

[0030] S10, establishing a mesoscopic scale aramid paper impregnation model based on the DPD algorithm.

[0031] As a discrete particle method, the DPD algorithm inherits the same algorithm as the molecular dynamics system based on Newton's second law:

[0032] .

[0033] in, , , Respectively represent the index The mass, position vector, and velocity vector of the particle, The action of adjacent particles on the particle In order to improve the computational efficiency while ensuring a certain accuracy, within a truncation range, all neighboring particles When the distance between two particles exceeds the cutoff range, the interaction between them is ignored.

[0034] The classical DPD interaction force consists of three parts: conservative force , dissipative force and random force .

[0035] Dissipative force .

[0036] Random Force .

[0037] coefficient and respectively reflect the strength of dissipative force and random force, Two adjacent particles and The distance between is a unit vector, Neighboring particles and The speed difference, is a Gaussian white noise and ,, They represent the weight functions of dissipative force and random force respectively, and the general form is , represents the weight coefficient, Represents the cutoff radius.

[0038] In order to satisfy the Fluctuation-Dissipation Theorem (FDT), two conditions must be met: and , is the Boltzmann constant, It's the temperature.

[0039] S20, the DPD soft repulsive conservative potential in the aramid paper dipping model is replaced by the worm chain potential. Each particle represents a node, and a network structure is formed through the constraint of the interaction potential between particles to capture the mechanical behavior of the fiber and simulate the geometry, elasticity and flexibility of the aramid fiber.

[0040] The Large-scale Atomic / Molecular Massively Parallel Simulator (Lammps) simulation software is used for parallel calculation, wherein the potential energy function of the worm chain is given according to the following steps S21 to S24:

[0041] S21, consider the elastic connection between the segments to prevent the segments from being overstretched or compressed:

[0042] .

[0043] in, Represents the finite extension nonlinear elastic potential energy, which is used to limit the extension behavior of the chain segment and ensure the overall stability and elasticity of the chain. r represents the distance between the chain segments composed of two particles, K is the spring constant describing the elastic stiffness between the segments, K The larger the value, the less likely the chain segment is to be stretched. R0 is the maximum elongation distance that defines the maximum allowable distance between chain segments. near When, potential energy tends to infinity, preventing the chain segments from being stretched beyond .

[0044] S22, considering the angular stiffness between the segments, limits the bending degree of the segments:

[0045] .

[0046] in, is the angular potential energy, which is used to control the bending stiffness between the segments. θ represents the angle between two adjacent segments. θ 0 is the ideal angle representing the equilibrium angle of the chain segment, k θ The angular stiffness coefficient that describes the resistance of the chain segment to bending, k θ The larger the value, the more rigid the segment is and the harder it is to bend.

[0047] S23, considers the rotational rigidity of the chain segment between four consecutive particles and controls the degree of chain twisting:

[0048] .

[0049] in, is the dihedral potential energy, which is used to describe the rotational rigidity of the chain segment and affects the rotational stability of the chain segment. is the dihedral angle used to describe the rotation angle between the planes formed by four consecutive particles. The dihedral potential energy amplitude that describes the rotational stiffness of the chain segment is: k The larger it is, the more difficult it is for the chain segment to rotate. n is the period number representing the periodicity of the dihedral potential energy, γ is the offset angle that controls the phase of the dihedral potential energy.

[0050] S24, get the worm chain potential energy:

[0051] .

[0052] Among them, the worm chain potential energy The stiffness and deformation of the aramid fiber are controlled as a whole, so that the fiber can exhibit real mechanical behavior under the external flow field and load.

[0053] In the combined potential model, the persistence length is used L p To describe the rigidity of the chain segment, the persistence length L p is the measure of the chain segment bending.

[0054] .

[0055] in, is the Boltzmann constant, It's the temperature.

[0056] S30, setting different material properties of aramid paper and corresponding aramid fiber and the shear flow intensity applied to them, performing parameter mapping with experimental data to match the real material properties, solving the behavior of aramid fiber in complex flow field under dimensionless time, and finally obtaining the swelling and stretching mechanism of aramid fiber.

[0057] The present embodiment further provides a DPD-based fibrillation centrifugal treatment coarse-graining simulation system, which uses a DPD-based fibrillation centrifugal treatment coarse-graining simulation method provided in the present embodiment.

[0058] The DPD-based fibrillation centrifugal treatment coarsening simulation system in this embodiment includes a data input part, a simulation part and a parameter mapping part.

[0059] The data input part is used for the user to input the material properties of the aramid paper and the corresponding aramid fiber and the shear flow strength applied thereto.

[0060] The simulation department uses mesh structure particles to simulate the physical form of aramid fibers.

[0061] The parameter mapping part is connected with the data input part and the simulation part, and the data input by the data input part is parameter mapped with the experimental data to match the real material properties, solve the behavior of the aramid fiber in the complex flow field under dimensionless time, and finally obtain the swelling and stretching mechanism of the aramid fiber.

[0062] <Test example>

[0063] This test example uses a DPD-based centrifugal treatment coarsening simulation method and system provided in the embodiment to perform a simulation test.

[0064] Figure 2 It is the left and right solid wall movement model and velocity gradient distribution of the aramid paper fibrid in the test example of the present invention in a shear flow environment.

[0065] like Figure 2 As shown, a fiber film with an aspect ratio of 20:1 is placed statically in a fluid, with solid walls on the left and right sides. A fixed speed is applied to the left and right walls of the fluid to move relative to each other along the z-axis to form a shear flow, and the fluid between the two plates presents a velocity gradient.

[0066] Under the action of shear flow, the fibers will flip at different speeds due to different shear rates, and it will also have the effect of slowing down the curling of the material.

[0067] Figure 3 is the dynamic behavior of the aramid paper fibrid film in the test example of the present invention in shear flow at different times; Figure 4These are the dynamic behaviors of the aramid paper fibrillation film in the test examples of the present invention under static fluid and shear flow respectively.

[0068] like Figure 3 and Figure 4 As shown, compared with the curled state at the dimensionless time t=300, the fiber material in the shear flow environment is obviously more stretched than the fiber material in the static fluid.

[0069] Figure 5 is the curling behavior of three different material properties of the aramid paper fibrillation film in the test example of the present invention. Among them, Figure 5 Part (a) shows the curling behavior of the three materials in their initial state. Figure 5 Part (b) shows the curling behavior of the three materials at dimensionless time t=485.

[0070] like Figure 5 As shown, the aramid paper fiber film is set to anisotropic properties, and the angle potential energy parameter in the length direction is α =0, 1, 200 ( α Angular potential energy The curling of the aramid paper fiber films in the three cases is obviously different. At the dimensionless time t=485, α =0 material has obviously curled up into a ball, α =1 The material is slightly curled. α =200 materials remain almost spread.

[0071] Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A DPD-based centrifugal treatment coarsening simulation method for fiber analysis, characterized in that: The following steps are involved: S10, establishing a mesoscopic scale aramid paper dipping model based on the DPD algorithm; S20, replacing the DPD soft repulsive conservative potential energy in the aramid paper dipping model with the worm chain potential energy and using Lammps simulation software for parallel calculation, using mesh structure particles to simulate the physical morphology of aramid fibers, The worm chain potential energy comprehensively considers the elastic connection between the chain segments composed of two particles, the angular stiffness between the chain segments, and the rotational stiffness of the chain segments between four consecutive particles; S30, setting different material properties of aramid paper and corresponding aramid fiber and the shear flow strength applied to them, performing parameter mapping with experimental data to match the real material properties, solving the behavior of aramid fiber in complex flow field under dimensionless time, and finally obtaining the swelling and stretching mechanism of aramid fiber. In step S20, each particle represents a node, and a mesh structure is formed by the constraint of the interaction potential energy between particles to capture the mechanical behavior of the aramid fiber. The aramid paper dipped model is used to simulate the geometry, elasticity and flexibility of the fiber. The derivation of the worm chain potential energy includes the following sub-steps: S21, consider the elastic connection between the segments to prevent the segments from being overstretched or compressed: V bond represents the finite stretch nonlinear elastic potential energy, which is used to limit the stretching behavior of the chain segment and ensure the overall stability and elasticity of the chain. r represents the distance between the two particles of the chain segment, K is the spring constant describing the elastic stiffness between the chain segments, and R0 is the maximum elongation distance that defines the maximum allowable distance between the chain segments. S22, considering the angular stiffness between the segments, limits the bending degree of the segments: V angle is the angular potential energy, which is used to control the bending stiffness between the segments. θ represents the angle between two adjacent segments. θ0 represents the ideal angle of the equilibrium angle of the segments. k θ is the angular stiffness factor describing the resistance of the chain segment to bending; S23, considers the rotational rigidity of the chain segment between four consecutive particles and controls the degree of chain twisting: V dihedral is the dihedral angle potential energy, which is used to describe the rotational rigidity of the chain segment and affects the rotational stability of the chain segment. φ is the dihedral angle used to describe the rotation angle between the planes formed by four continuous particles. k dihedral is the amplitude of the dihedral potential energy that describes the magnitude of the segment rotational stiffness, n is the number of periods that represent the periodicity of the dihedral potential energy, and γ is the offset angle that controls the phase of the dihedral potential energy; S24, get the potential energy of the worm chain 2. The DPD-based centrifugal treatment coarsening simulation method for fibrillation according to claim 1, characterized in that: in, In step S10, the DPD algorithm is the same as the algorithm of the molecular dynamics system based on Newton's second law: m i 、r i 、v i They represent the mass, position vector, and velocity vector of the particle with index i, respectively. i is the force vector exerted by the neighboring particles on particle i, is conservative force, dissipative force Random Force Coefficient γ ij and σ ij respectively reflect the strength of dissipative force and random force, r ij =|r ij |=|r i -r j | is the distance between two adjacent particles i and j, e ij =r ij / r ij is a unit vector, v ij =v i -v j is the difference in the velocities of adjacent particles i and j, ξ is a Gaussian white noise and ξ ij =ξ ji ,ω D (r ij ) and ω R (r ij ) represent the weight functions of dissipative force and random force respectively, and the general form is n represents the weight coefficient, r c Represents the cutoff radius.

3. The DPD-based centrifugal treatment coarsening simulation method for fibrillation according to claim 2, characterized in that: in, In step S10, And ω D (r ij )=[ω R (r ij )] 2 , k B is the Boltzmann constant and T is the temperature.

4. The DPD-based centrifugal treatment coarsening simulation method for fibrillation according to claim 2, characterized in that: in, In step S10, in order to improve the calculation efficiency while ensuring a certain accuracy, the F of all neighboring particles is calculated within a cutoff range. i When the distance between two particles exceeds the cutoff range, the interaction between them is ignored.

5. The DPD-based centrifugal treatment coarsening simulation method for fibrillation according to claim 1, characterized in that: in, In step S21, the larger the K, the less likely the chain segment is to be stretched. When r is close to R0, the potential energy V bond tends to infinity, preventing the chain segment from being stretched beyond R0, In step S22, k θ The larger the value, the more rigid the chain segment is and the harder it is to bend. In step S23, k dihedral The larger it is, the more difficult it is for the chain segment to rotate.

6. The DPD-based fibrillation centrifugal treatment coarsening simulation method according to claim 1 or 5, characterized in that: in, In step S20, the persistence length L is used p to describe the rigidity of the chain segment, The persistence length L p is the dimension of the segment bending, k B is the Boltzmann constant and T is the temperature.

7. A DPD-based centrifugal fiber processing coarse particle simulation system, characterized in that: The DPD-based centrifugal treatment coarsening simulation method for fibrillation according to any one of claims 1 to 6 is used, comprising: A data input unit, used for allowing a user to input material properties of the aramid paper and corresponding aramid fibers and shear flow strength applied thereto; The simulation part uses mesh structure particles to simulate the physical form of aramid fibers; The parameter mapping part is connected with the data input part and the simulation part, and performs parameter mapping between the data input by the data input part and the experimental data to match the real material properties, solve the behavior of the aramid fiber in the complex flow field under dimensionless time, and finally obtain the swelling and stretching mechanism of the aramid fiber.

Images