Ph.D., Oklahoma State University
M.S., Korea Advanced Institute of Science and Technology
B.S., Hankuk Aviation College, Korea
Acoustics and Vibrations
Fluid-Structure Interaction
Flow-Induced Vibrations
Aerodynamics in Web Handling
Elastohydrodynamic Lubrication
Aerodynamics in Web Handling - The objective of the research is to develop new aerodynamic technologies for non-contact handling of web materials such as paper and plastic films. Analytical, experimental, and computational methods are used to study the Coanda effect and the interaction between air jets and web materials. The behavior of air jets, the aerodynamic pressure on the web, and the friction drag are being investigated. A commercial software program called Fluent is used for computation.
Web Flutter - Modern paper-making machines are nearly 10 meters in width and run at speeds higher than 30 m/s. When web materials are so wide and travel so fast, violent vibration (or flutter) can occur in the web due to the aerodynamic effects. Web flutter can cause breaks in paper, especially when it is still wet, resulting in downtime of the machine. In air-flotation ovens, the air flow in the gap between a solid surface and the web can cause flutter. The research focuses on the out-of-plane dynamics of fast-moving web materials, the dynamics of slack edges subjected to air flows, and the air-web interaction in air-flotation ovens.
Elastohydrodynamic Lubrication - When web materials are wound at high speeds, excessive amounts of air can be entrapped in the wound roll resulting in defects to the roll. Similar air entrainment problems can occur at high-speed operation of heating/cooling drums because the air film between the drum and the web reduces heat transfer. The research focuses on the effects of a nip roller on the air entrainment in winding rolls and at heating/cooling drums. Computational methods are used to predict the amount of air entrainment.
Flow-Induced Vibrations - Structural vibration induced by a fluid flow can be a serious problem in nuclear reactors, heat exchangers, ocean structures, and tall buildings. Vibration of cylindrical structures induced by vortex-shedding and the fluidelastic instability of tube arrays are of main interest.
Chang, Y. B. and Moretti, P. M., 2000, "Flow-induced vibration of free edges of thin films," Flow-Induced Vibration, A.A.Balkema, Rotterdam, pp. 801-810.
Chang, Y. B. and Moretti, P. M., 2000, "Aerodynamic Characteristics of Pressure-Pad Air Bars," Trans. ASME, J. Applied Mechanics, vol. 67, no. 1, pp. 177-182.
Chang, Y. B., Cho, C. H., and Moretti, P. M., 1999, "Edge Flutter," Proc. ASME, Noise Control and Acoustics Division - 1999, NCA-Vol.26, pp. 413-423.
Chang, Y. B., Swanson, R. P., and Moretti, P. M., 1999, "Longitudinal and Out-of-Plane Stiffness of a Web in an Air-Flotation Oven," Proc. ASME, Noise Control and Acoustics Division - 1999, NCA-Vol.26, pp. 435-443.
Chang, Y. B., Swanson, R. P., and Moretti, P. M., 1999, "Resiliency of an Air-Floated Web," Proc. of the Fifth International Conference on Web Handling, Stillwater, Oklahoma, pp. 543-559.
Aravamudhan, V. R., Moretti, P. M., and Chang, Y. B., 1998, "An Experimental Study of the Coanda Effect for 90-Degree Turning of Subsonic Air Jets," ASME Fluids Engineering Summer Meeting, Washington, DC.
Moretti, P. M. and Chang, Y. B., 1997, "Web Flutter at Circular-Tube Air-Turn Bars," Proceedings of the Fourth International Conference on Web Handling, Stillwater, Oklahoma.
Chang, Y. B., Chambers, F. W., and Shelton, J. J., 1996, "Elastohydrodynamic Lubrication of Air-Lubricated Rollers," ASME Journal of Tribology, Vol. 118, No. 3, pp. 623-628.
Chang, Y. B. and Moretti, P. M., 1995, "Ground-Effect Theory and Its Application to Air Flotation Devices," Proceedings of the Third International Conference on Web Handling, Stillwater, Oklahoma, pp. 338-345.
Moretti, P. M., Chang, Y. B., and Vedula, K., 1994, "Vibration Intensity Measurement of Fluttering Webs by Laser-Doppler Sensors," SPIE Proceedings Series, Vol. 2358, Vibration Measurements by Laser Techniques: Advances and Applications, pp. 409-420.
Chang, Y. B., Cho, C. H., and Moretti, P. M., 1994, "Edge Flutter of Translating Webs Induced by Cross-Flow of Air," Proceedings of the Third International Congress on Air- and Structure-Borne Sound and Vibration, Montreal, Canada, pp. 1127-1134.
Chang, Y. B. and Moretti, P. M., 1992, "An Experimental Study on Edge Flutter in Webs," ASME AMD-Vol. 149, Web Handling, pp. 67-78.
Chang, Y. B., Fox, S. J., Lilley, D. G., and Moretti, P. M., 1991, "Aerodynamics of Moving Belts, Tapes, and Webs," ASME DE-Vol. 36, Machinery Dynamics and Element Vibrations, pp. 33-40.
Chang, Y. B. and Moretti, P. M., 1991, "Edge Flutter in Webs," Proceedings of the First International Conference on Web Handling, Stillwater, Oklahoma.
Chang, Y. B. and Moretti, P. M., 1991, "Interaction of Fluttering Webs With Surrounding Air," TAPPI Journal, Vol. 74, No. 3, pp. 231-236.
Lee, H. and Chang, Y. B., 1990, "Flow-Induced Vibration of Rod Arrays in a Jet Flow," ASME Journal of Pressure Vessel Technology, Vol. 112, No. 1, pp. 46-49.