A Computational Method for Generating the Free-Surface Neck-Down Profile for Glass Flow in Optical Fiber Drawing

Choudhury, Sudip

doi:10.1080/104077899275344

Cited by 42 publications

(17 citation statements)

References 3 publications

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“…2) An alternative approach is to determine the free surface of the neck-down profile through numerical solution of the governing fluid mechanics and heat transfer with assumed and iteratively refined fiber radii at several discrete locations along the fiber axis until the force balance is achieved at the chosen discrete locations. This approach is hugely computationally intensive and was presented by Choudhury et al [3]. It is evident that an effective and computationally efficient approach to predicting the neck-down profiles in a generalized manner applicable to all processing conditions is necessary for a modelbased process design.…”

Section: Introductionmentioning

confidence: 98%

Optical Fiber Drawing Process Model Using an Analytical Neck-Down Profile

Mawardi

Pitchumani

2010

IEEE Photonics J.

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Numerical models play an important role in the design of the optical fiber drawing process for tailored mechanical properties and optical transmission characteristics. The rigorous part of a numerical fiber drawing model is the determination of the neck-down profile, which is calculated based on a force balance along the fiber axis, requiring intensive numerical iterations for solution. An alternative approach has been the use of an empirical neck-down profile based on experimental results; however, this approach is restricted to the simulation of the particular drawing conditions used in the experiments. This paper presents an approach to numerical simulations of an optical fiber drawing process where an analytical hyperbolic tangent function is used to describe the neck-down shape in a generalized manner, and the parameters of the function are determined based on a force balance for the drawing conditions. The physical model is based on a 2-D numerical analysis of the flow, heat, and mass transfer phenomena involved in the drawing and cooling processes during the manufacturing of optical glass fibers. The effects of fiber draw speed, maximum furnace temperature, and the furnace length on the neck-down profile are investigated and discussed in terms of the final fiber radius and the draw tension. The approach provides for computationally efficient process simulations without the need to fit the neck-down profile to experimental data.

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Section: Introductionmentioning

confidence: 98%

Optical Fiber Drawing Process Model Using an Analytical Neck-Down Profile

Mawardi

Pitchumani

2010

IEEE Photonics J.

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“…Diameter rate changes up to 1.8 mm/s have been reported on the present tower (Law et al, 2004), such rates being far too fast for compensation by feedback control. It has been noted that such rapid rate changes can significantly degrade the tensile strength of the finished product (Dianov et al, 1988;Choudhury and Jaluria, 1998;Choudhury et al, 1999). Typically both the furnace temperature and the argon flow (and its distribution via the upper and lower ports) are set at empirically determined levels for a particular draw tower and left unadjusted during the course of a fibre draw.…”

Section: Introductionmentioning

confidence: 98%

The interpretation of online measurements of optical fibre diameter

Law

Barton

Phan

et al. 2005

Transactions of the Institute of Measurement and Control

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The requirements for optical fibre diameter measurement for feedback control during drawing and for quality assurance in precision applications are different. The signal from a 1000-Hz scanning laser gauge measuring 125-mm nominal diameter fibre was examined to see if this instrument could service both applications. Static measurements showed that sensor noise was largely unaffected by the measurement position of the fibre, the sampling rate or external electrical/acoustic noise. In each case the sensor noise was essentially normally distributed with a standard deviation of 0.13 mm. Offline fibre measurements (using a video grey-scale analyser) showed significant diameter variations on a 40-mm length scale. The distribution of this diameter variation was consistent with that from the online laser gauge. It was concluded that the current default option (scanning at 1000 Hz and using window-based averaging to give an effective sampling rate of 8 Hz) is adequate if the objective is to ensure a nominal average diameter on a long-length scale via feedback control. However, such an approach will prove inadequate for quality assurance in emerging precision applications. The latter objective will require a combination of a faster scanning rate with more sophisticated signal filtering to provide a means for monitoring short-scale diameter variations while simultaneously providing a signal for use by a controller more responsive than simple feedback. Such monitoring is also a necessary prerequisite for quantifying the extent of flow instabilities in the vicinity of the drawing fibre as a function of furnace design.

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“…They also reported difficulties to ensure convergence (that is sensitive to the deformation mesh) as the number of radiative macro surfaces increases. Choudhury et al [14] used a 1-D axial velocity and force balance equations to compute the neck-down profile while solving for the temperature using the 2-D heat transfer and fluid flow. Small-diameter (1.25-cm) preforms drawn at 3 m/s was considered in their simulations.…”

Section: Introductionmentioning

confidence: 99%

Computational thermal fluid models for design of a modern fiber draw process

Lee

Wei

Hong

2006

IEEE Trans. Automat. Sci. Eng.

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Many manufacturing processes require time-consuming setups before automation can begin. This paper investigates the applications of distributed-parameter computational thermal-fluid models for automating the design of a continuous manufacturing system, which aims at reducing process setup time. A generic draw process is used as an example throughout this paper, which involves practically all modes of heat transfer. Two physically accurate distributed-parameter models (semi-two-dimensional (2-D) and quaisi-one-dimensional (1-D) are derived and experimentally validated. In deriving these models, we relax a number of assumptions commonly made in modeling draw processes, and extend the models to allow for 2-D static/dynamic response predictions. The semi-2-D model provides a means to accurately predict the free surface geometry and the location at which the glass solidifies into a fiber, which also serves as a basis to derive the quais-1-D model. The quasi-1-D model that explicitly solves for the controlled variables is attractive for control system design and implementation. These results are particularly important in the optical-fiber industry because the difficulties in making precise in situ measurements in the harsh environment of the draw process have posed a significant challenge in the control of fiber diameter uniformity. Additionally, these numerically computed and experimentally measured neck-down profiles obtained in an industry setting can be used as benchmark data for future comparisons. The modeling approaches presented here are applicable to a variety of thermal-fluid systems, such as thermal processing of semiconductor wafer and food. Despite the emphasis in this paper on the faster draw of large-diameter glass that is a participating media in radiation, the technique for predicting the 2-D temperature distribution and the streamlines describing the fluid flow is equally applicable to processes involving nonparticipating media, such as composite, polymer, or synthetic fibers.Note to Practitioners-This paper is motivated by a problem in the fiber draw industry because of the progressive difficultly in maintaining the diameter uniformity resulting from the ever-increasing preform (or glass rod) diameter and draw speed. The larger diameter a preform is, the longer the fiber can be drawn in the furnace from a single preform and in much less time by drawing at a higher speed. The number of setups to initiate the draw can thus be drastically lowered. The tradeoff, however, is that the glass takes a longer distance to cool into a fiber after leaving the furnace, for which an insulated post-chamber is added to gradually cool the fiber to solidification in order to reduce Manuscript

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A Computational Method for Generating the Free-Surface Neck-Down Profile for Glass Flow in Optical Fiber Drawing

Cited by 42 publications

References 3 publications

Optical Fiber Drawing Process Model Using an Analytical Neck-Down Profile

Optical Fiber Drawing Process Model Using an Analytical Neck-Down Profile

The interpretation of online measurements of optical fibre diameter

Computational thermal fluid models for design of a modern fiber draw process

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