Session: 06-01-01 Product And Process Design

Paper Number: 90109

90109 - Non-Linear Analysis of Beam-Reinforced Thin Plates for Modeling Rectangular Duct Systems 

This paper investigates the deformation of rectangular duct systems when subjected to internal pressure by modeling them as thin-walled structures. Current design practices attempt to model rectangular duct systems as individual plates to predict maximum deflections and set stress limitations. However, these existing models are found to make inaccurate behavior predictions, and demand designs that are too costly. This paper describes a beam-reinforced plate (BRP) finite element model that can accurately predict the deformation behavior of a rectangular duct system under positive gauge pressure. The model not only accounts for the deformation of the stiffeners, but also the geometric non-linearity of the plates when the duct is subjected to a uniform internal pressure. Furthermore the BRP model considers the effects that side panels have on predicted top/bottom plate deformation. A commercial finite element software was used to generate and analyze models of rectangular duct systems, and to compare the predicted deflections from the BRP model to those from existing plate models. Parametric case studies were performed to understand how geometric variables affect the deflections of duct panels. The current study focuses on the advantages and limitations of the proposed plate model compared to the existing industry standards. Understanding the effects of changes in geometry allows the limitations of the BRP model to be defined. While the BRP model did not accurately predict the behavior of duct models with reinforcement spacings of 60 inches, it generally provided improved predictions of duct deformation compared to those generated using current design approaches. It was observed that a complete finite element duct model deflected far more than each plate model, meaning that the flexibility of duct system reinforcements needs to be taken into consideration. This investigation provided insight to adjustments that can be made to existing modeling approaches to improve their accuracy. While the BRP model did not accurately predict the behavior of duct models with spacings of 60 inches, it had more accuracy than the SMACNA Mode A and literature models, and provided insight to adjustments that can be made it improve accuracy. It was observed that the duct model deflected far more than each plate model, meaning that the flexibility of the duct system needs to be taken into consideration. Future research suggestions also include investigating plate models that can accurately predict the behavior of duct models with spacings greater than 48 inches. Future research suggestions also include investigating plate models that can accurately predict the behavior of rectangular duct systems with reinforcement spacings greater than 48 inches. Another research suggestion is to perform future case studies using non-dimensionalized parameters to remove variables from the analyses. Research on duct and plate models subjected to gravity is also recommended, as well as models subjected to negative pressures. Based on these observations, further research is recommended to continue the development of plate models that can thoroughly predict the behavior of complicated duct systems.

Presenting Author: Stephen Idem Tennessee Tech Univ

Presenting Author Biography: Dr. Stephen Idem is a professor in the Department of Mechanical Engineering at Tennessee Tech University. He received his Ph.D. in Mechanical Engineering from Purdue University. He has more than 34 years of experience in the areas of fluid flow measurement, scale model testing, and thermal modeling. He participated in many studies related to the measurement of air flow and pressure loss characteristics of typical residential and commercial duct systems. He has created a numerical model of downdraft evaporative cooling tower performance, which was verified experimentally. He has extensive experience performing flow and pressure measurements on scale models of primary and secondary air supply ducts, windboxes, and exhaust stacks of coal-fired power plants in order to improve their thermal performance. He has developed an on-line cleanliness factor model of the convection passes in coal-fired power plants, and has likewise created numerical models of steady and transient heat exchanger performance. Currently he is developing a real-time coal-fired power plant heat rate monitoring protocol.

Authors:

Matthew Crispi Tower Engineering Professionals
Jane Liu Tennessee Tech University
John Peddieson Tennessee Tech University
Stephen Idem Tennessee Tech Univ