Optical fiber preform drawing process simulation method

Abstract

The present invention relates to the field of optical fiber preforms, and more specifically to a method for simulating an optical fiber preform drawing process, comprising: gridding a two-dimensional cylindrical coordinate system; clustering the grid to obtain a plurality of clusters, and performing segmentation and filling; obtaining a new axial length and similarly a new radial length, adjusting a first region based on the new axial and radial lengths to obtain a second region, using a region composed of all second regions as a third region, and calculating the importance of axial and radial heat conduction in the third region; obtaining a temperature field, constructing a viscosity field and a velocity field based on the temperature field, and completing process simulation. The technical solution of the present invention can improve the accuracy of simulation results.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber preforms, and more particularly to a method for simulating an optical fiber preform drawing process. Background Art

[0002] Optical fiber preforms are the core material for optical fiber manufacturing. Their quality directly impacts the performance of optical fibers, and in turn, determines the transmission efficiency and reliability of optical fibers in industries such as communications, healthcare, and sensing. The manufacturing process for optical fiber preforms typically includes a stretching process, which is crucial for the shape and dimensional accuracy of the preforms, as well as the subsequent stretching of the optical fiber. The preform stretching process is typically performed under high-temperature conditions. After heating the preform to a certain temperature, it is stretched into a slender optical fiber. The core goal of the stretching process is to ensure the high quality of the final optical fiber by precisely controlling the deformation of the preform during heating.

[0003] The existing technology only constructs a steady-state temperature field for simulation through axial temperature differences, ignoring the viscosity changes and deformation caused by the radial temperature heat conduction differences in different areas of the preform rod, resulting in a large central temperature deviation of the constructed temperature field and eccentric melting. Summary of the Invention

[0004] In order to solve the technical problem that the simulation results are inaccurate when the steady-state temperature field is constructed only by the axial temperature difference, the present invention provides a method for simulating the stretching process of an optical fiber preform. The method includes: constructing a two-dimensional cylindrical coordinate system of the preform rod, gridding the two-dimensional cylindrical coordinate system to obtain a plurality of grids; calculating the axial temperature gradient and radial temperature gradient of two adjacent grids along the positive direction of the two-dimensional cylindrical coordinate system to calculate the global average axial gradient and the global average radial gradient; clustering the grids to obtain a plurality of cluster clusters, one cluster cluster corresponds to a first region, and any first region is divided and filled; adaptively adjusting the axial length of the grid of the first region based on the axial temperature gradient and the global average axial gradient to obtain a new axial length, similarly obtaining a new radial length, adjusting the first region according to the new axial length and the new radial length to obtain a second region, taking the region composed of all the second regions as the third region, calculating the importance of axial heat conduction and the importance of radial heat conduction in the third region; using the importance of axial heat conduction as a weight to correct the axial thermal conductivity of the law of conservation of energy, using the importance of radial heat conduction as a weight to correct the radial thermal conductivity of the law of conservation of energy, obtaining a temperature field, constructing a viscosity field and a velocity field based on the temperature field, and completing the process simulation.

[0005] Preferably, the calculation of the global average axial gradient and the global average radial gradient includes: taking the average of the axial temperature gradients of all grids as the global average axial gradient; taking the average of the radial temperature gradients of all grids as the global average radial gradient.

[0006] Preferably, obtaining a plurality of clusters includes: calculating a first distance of the temperature gradient between any two grid center points, and calculating a second distance between the positions of any two grid center points, and taking the sum of the first distance and the second distance as the characteristic distance of the any two grids; and clustering all grids using DBSCAN according to the characteristic distance to obtain a plurality of clusters.

[0007] Preferably, the new axial length satisfies the relationship:

[0008] , represents the new axial length, Indicates the axial length, represents the global average axial gradient, Representation Grid The axial temperature gradient, represents the maximum axial temperature gradient in the world, represents the number of grids in the first region, Indicates the axial direction, Represents the exponential function.

[0009] Preferably, the calculating the importance of axial heat conduction and radial heat conduction in the third region includes: calculating the global average axial gradient and the global average radial gradient in the third region; the importance of axial heat conduction satisfies the relationship: , Indicates the importance of axial heat conduction, represents the global average axial gradient of the third region, represents the global average radial gradient of the third region; the importance of radial heat conduction is obtained in the same way as the calculation method of the importance of axial heat conduction.

[0010] Beneficial effects of the present invention:

[0011] Through gridding and cluster analysis, this method can identify differences in heat conduction across different regions, adaptively adjusting axial and radial dimensions based on the local temperature field, ensuring uniform heat conduction and improving overall process efficiency. Furthermore, precise calculation of the importance of axial and radial heat conduction in each region allows for reasonable corrections to the law of conservation of energy under varying heat flow conditions, providing a more reliable physical basis for the simulation of temperature, viscosity, and velocity fields. This method can significantly improve the accuracy and controllability of the optical fiber drawing process and reduce production defect rates. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a flow chart of a method for simulating an optical fiber preform drawing process according to an embodiment of the present invention. DETAILED DESCRIPTION

[0013] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, but not all of the embodiments.

[0014] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0015] Reference Figure 1 The optical fiber preform drawing process simulation method includes steps S1 to S5, which are specifically as follows:

[0016] S1: Construct a two-dimensional cylindrical coordinate system of the preform rod, and perform grid division on the two-dimensional cylindrical coordinate system to obtain a plurality of grids.

[0017] In one embodiment, since the optical fiber preform is a relatively regular axisymmetric cylinder as a whole, in order to reduce the simulation time, the process problem originally a three-dimensional model can be simplified into a two-dimensional axisymmetric problem, thereby constructing a two-dimensional cylindrical coordinate system of the preform. The two-dimensional cylindrical coordinate system is meshed to obtain a number of grids. These grids provide a basis for subsequent numerical simulations and can more accurately approximate the geometric structure and physical properties of the preform.

[0018] S2: Calculate the axial temperature gradient and radial temperature gradient of two adjacent grids along the positive direction of the two-dimensional cylindrical coordinate system to calculate the global average axial gradient and the global average radial gradient.

[0019] It should be noted that during the heating process of the optical fiber preform, heat is transmitted radially from the furnace wall into the rod body, resulting in a temperature difference between the center and the edge. In addition, the uneven heat sources at different positions cause different temperature gradients in different directions at different parts of the optical fiber preform, resulting in uneven viscosity deformation.

[0020] In one embodiment, the temperature value at the center of any grid is obtained, and the axial and radial temperature gradients of two adjacent grids are calculated along the positive direction of the two-dimensional cylindrical coordinate system. The temperature gradient calculation method is well known to those skilled in the art and will not be described in detail here. The average of the axial temperature gradients of all grids is taken as the global average axial gradient; the average of the radial temperature gradients of all grids is taken as the global average radial gradient.

[0021] S3: Clustering the grids to obtain a number of clusters, where one cluster corresponds to one first region, and performing segmentation and filling on any first region.

[0022] In one embodiment, a first distance of the temperature gradient between any two grid center points is calculated, and a second distance between any two grid center points is calculated. The sum of the first and second distances is used as the characteristic distance between the two grids. Based on the characteristic distances, DBSCAN is used to cluster all grids to obtain a number of clusters. Furthermore, the first non-rectangular region is segmented and filled.

[0023] This method is effective in identifying groups of meshes with similar physical properties or behaviors, particularly in scenarios involving heat conduction or uneven temperature distribution. Using the DBSCAN clustering algorithm, these meshes can be automatically divided into clusters based on feature distances, making the meshes within each cluster more consistent in physical properties (such as temperature variation) and spatial location.

[0024] S4: Based on the axial temperature gradient and the global average axial gradient, the axial length of the grid in the first region is adaptively adjusted to obtain a new axial length. Similarly, a new radial length is obtained. The first region is adjusted according to the new axial length and the new radial length to obtain a second region. The region composed of all the second regions is used as the third region. The importance of axial heat conduction and the importance of radial heat conduction in the third region are calculated.

[0025] In one embodiment, the axial length of the grid in the first region is adaptively adjusted based on the axial temperature gradient and the global average axial gradient to obtain a new axial length, and the new axial length satisfies the relationship:

[0026] , represents the new axial length, Indicates the axial length, represents the global average axial gradient, Representation Grid The axial temperature gradient, represents the maximum axial temperature gradient in the world, represents the number of grids in the first region, Indicates the axial direction, Represents the exponential function.

[0027] when When it is less than 0, it means that the first region belongs to a high-gradient region. The grid is too coarse to capture the rapidly changing temperature gradient, resulting in distorted results. A tighter grid should be used to improve the credibility of the temperature field simulation and reduce the cumulative error caused by spatial discretization.

[0028] This adaptive adjustment method can use a tighter grid in high-gradient areas to accurately capture local temperature mutations and avoid distortion, and use a sparse grid in stable areas to avoid excessive calculation and overfitting. It also avoids the shortcoming that the global fixed grid cannot capture the temperature gradient in rapidly changing areas. Through grid adaptation, it can better fit the actual physical field distribution, reduce error diffusion and error accumulation, and make the modeling of complex boundary fields such as furnace mouths and cooling nozzles more reliable.

[0029] The new radial length is obtained in the same way as the calculation method of the new axial length, specifically satisfying the following relationship:

[0030] , represents the new radial length, represents the radial length, represents the global average radial gradient, Representation Grid The radial temperature gradient, represents the maximum global radial temperature gradient, represents the number of grids in the first region, Indicates radial direction, Represents the exponential function.

[0031] At this point, the first region can be adjusted through the new axial length and the new radial length to obtain the second region, and several second regions can be traversed to obtain the region composed of all the second regions as the third region. The size of the third region is the same as the size of the preform rod in the two-dimensional cylindrical coordinate system that divides the grid, but the grid size within the third region is different.

[0032] Calculate the global average axial gradient and the global average radial gradient of the third region.

[0033] The importance of axial heat conduction satisfies the relationship:

[0034] , Indicates the importance of axial heat conduction, represents the global average axial gradient of the third region, represents the global average radial gradient of the third region.

[0035] The importance of radial heat conduction can be obtained by the same calculation method based on the importance of axial heat conduction, which satisfies the following relationship:

[0036] , Indicates the importance of radial heat conduction, represents the global average radial gradient of the third region, represents the global average radial gradient of the third region.

[0037] In the law of conservation of energy, the heat flux of two-dimensional heat transfer is calculated independently in each direction and then added together, so weighted averaging cannot be used. The importance of this method is to strengthen heat conduction in the direction of high change and weaken heat conduction in the direction of low change without violating the law of conservation of energy, thereby emphasizing the dominant direction of heat conduction.

[0038] S5: The importance of axial heat conduction is used as a weight to modify the axial thermal conductivity of the energy conservation law. The importance of radial heat conduction is used as a weight to modify the radial thermal conductivity of the energy conservation law to obtain the temperature field. The viscosity field and velocity field are constructed based on the temperature field to complete the process simulation.

[0039] It should be noted that temperature changes during the optical fiber preform drawing process affect the viscosity of the preform, and the speed of preform drawing is affected by viscosity. Radial temperature differences in the preform lead to radial deformation viscosity differences and the thickness of the optical fiber drawn, while axial temperature differences lead to speed fluctuations in the axial drawing of the preform. Existing technologies construct temperature fields based on axial temperature differences, which fail to reflect rod deformation, resulting in large deviations and low accuracy in the constructed viscosity and velocity fields. For example, ignoring radial temperature differences can lead to low viscosity, misprediction of fiber diameter, and errors in thermoforming control. Therefore, the present invention adjusts the thermal conductivity based on the importance of axial and radial heat conduction. Using the adjusted thermal conductivity, the axial and radial heat conduction are calculated separately to construct a two-dimensional unsteady-state temperature field control equation. Based on the established temperature field, the viscosity and velocity fields are obtained and the optical fiber radius is predicted. Conventional temperature fields are based on axial temperature, where only the viscosity and velocity fields are affected.

[0040] In one embodiment, the importance of axial heat conduction is used as a weight to multiply the axial thermal conductivity in the law of conservation of energy, and the importance of radial heat conduction is used as a weight to multiply the radial thermal conductivity in the law of conservation of energy, thereby correcting the axial thermal conductivity and radial thermal conductivity in the law of conservation of energy.

[0041] This calculation method can improve the heat conduction efficiency in the dominant direction of heat conduction and identify the heat conduction path, reduce the heat conduction efficiency in the non-dominant direction, and consider the differences in heat conduction capabilities in different directions to improve the accuracy of temperature field simulation.

[0042] The existing law of conservation of energy only includes the axial heat conduction term, which is applicable to the steady-state temperature field under an ideal environment. The present invention combines axial heat conduction and radial heat conduction to achieve the precise construction of the non-steady-state temperature field, which conforms to the actual stretching scenario and avoids the center temperature error.

[0043] Based on the temperature field, the viscosity field and velocity field are constructed. The three simulated physical fields are coupled and predicted to complete the process simulation using COMSOL. The three simulated physical fields solved using COMSOL are well known to those skilled in the art and will not be described in detail.

[0044] It should be noted that those skilled in the art may make various modifications and improvements without departing from the scope of the present invention, and these modifications and improvements fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be based on the appended claims.

Claims

1. A method for simulating an optical fiber preform drawing process, characterized in that: include: Constructing a two-dimensional cylindrical coordinate system of the preform, and performing grid division on the two-dimensional cylindrical coordinate system to obtain a plurality of grids; Calculate the axial temperature gradient and radial temperature gradient of two adjacent grids along the positive direction of the two-dimensional cylindrical coordinate system to calculate the global average axial gradient and the global average radial gradient; Clustering the grids to obtain a plurality of clusters, where one cluster corresponds to one first region, and performing segmentation and filling on any first region; Adaptively adjust the axial length of the grid in the first region based on the axial temperature gradient and the global average axial gradient to obtain a new axial length. Similarly, obtain a new radial length. Adjust the first region based on the new axial length and the new radial length to obtain a second region. Calculate the importance of axial heat conduction and radial heat conduction in the third region based on the new axial length and the new radial length. The importance of axial heat conduction is used as the weight to modify the axial thermal conductivity of the energy conservation law. The importance of radial heat conduction is used as the weight to modify the radial thermal conductivity of the energy conservation law to obtain the temperature field. The viscosity field and velocity field are constructed based on the temperature field to complete the process simulation.

2. The optical fiber preform drawing process simulation method according to claim 1, characterized in that: Calculating the global average axial gradient and the global average radial gradient comprises: The average of the axial temperature gradients of all grids is taken as the global average axial gradient; the average of the radial temperature gradients of all grids is taken as the global average radial gradient.

3. The optical fiber preform drawing process simulation method according to claim 1, characterized in that: The obtaining of a plurality of clusters comprises: Calculating a first distance of the temperature gradient between any two grid center points, and calculating a second distance between any two grid center points, and taking the sum of the first distance and the second distance as the characteristic distance of the any two grids; All grids are clustered using DBSCAN according to feature distance to obtain several clusters.

4. The optical fiber preform drawing process simulation method according to claim 1, characterized in that: The new axial length satisfies the relationship: , represents the new axial length, Indicates the axial length, represents the global average axial gradient, Representation Grid The axial temperature gradient, represents the maximum axial temperature gradient in the world, represents the number of grids in the first region, Indicates the axial direction, Represents the exponential function.

5. The optical fiber preform drawing process simulation method according to claim 1, characterized in that: The calculating of the importance of axial heat conduction and radial heat conduction in the third region includes: calculating a global average axial gradient and a global average radial gradient of the third region; The importance of axial heat conduction satisfies the relationship: , Indicates the importance of axial heat conduction, represents the global average axial gradient of the third region, represents the global average radial gradient of the third region; The importance of radial heat conduction can be obtained in the same way as the calculation method of the importance of axial heat conduction.

Images