Session: 02-09-01: Computational Modeling and Simulation for Advanced Manufacturing-I

Paper Number: 68684

Start Time: Tuesday, 10:15 AM

68684 - Comparison of Finite Element Modeling With Measured Deflection of Spiral Flat Oval Duct 

COMPARISON OF FINITE ELEMENT MODELING WITH MEASURED DEFLECTION OF SPIRAL FLAT OVAL DUCT

Avinash Paruchuri, Ph.D.

Lecturer, Manufacturing and Engineering Technology Department

Jane Liu, Ph.D.

Professor, Department of Civil and Environmental Engineering

Stephen Idem, Ph.D.

Professor, Mechanical Engineering Department

Tennessee Technological University

Cookeville, TN, 38505 U.S.A.

EXTENDED ABSTRACT

The use of flat oval ducts is advantageous in those applications where space limitations do not allow the installation of round ducts. However, there is a tendency for flat oval ducts to exhibit excessive deflections when exposed to substantial positive/negative static gauge pressures, particularly when large flat spans are utilized. In those instances, it may be necessary to select a thicker duct wall, or to provide some means of either internal or external reinforcement. Such reinforcements limit duct deflection, and therefore reduce the possibility of permanent damage to the ducts caused by large deformations. In order to further promote the use of flat oval ducts in HVAC applications, designers must have access to knowledge of the most economical combination of duct gauge and reinforcement for a given duct cross section, based on the expected pressure in the system. This paper describes an experimental program that was designed to measure the deformation of several unreinforced and externally reinforced galvanized steel spiral flat oval duct systems subjected to a range of positive and negative internal gauge pressures. The purpose of the study was to supply deflection data that were used to corroborate a finite element model. A brief description of the finite element model is included in this paper.  Deformation was measured as a function of internal static gauge pressure for galvanized steel spiral 12 in. ´ 43 in. (305 mm ´ 1092 mm) flat oval ducts. Both unreinforced and externally reinforced ducts were considered. Dial deflection gauges were used to measure the duct deformation at prescribed locations on the top and bottom surface of the test duct and compared to corresponding predictions generated using a non-linear finite element model that accounted for the self-weight of the duct walls. The Average Wall Thickness (AWT) method was utilized to account for the presence of a continuous spiral seam. Shell elements were employed to represent the thin-walled structure of the ducts. External trapeze reinforcements spaced 3 ft (0.91 m), 6 ft (1.83 m), and 12 ft (3.66 m) apart were modeled using beam elements. The finite element model of the duct system was found to yield realistic deformation predictions. It was concluded that finite element modeling can be used to guide decisions regarding the selection of a thicker duct wall, or inclusion of either internal or external reinforcement, if concerns exist about excessive duct or reinforcement deformation caused by high internal gauge pressures. The use of the AWT modeling approach afforded substantial simplification to the development of the finite element models needed to predict duct deformation associated with elevated internal positive or negative gauge pressures, either with or without external reinforcements.

Presenting Author: Venkata Avinash Paruchuri Tennessee Technological University

Authors:

Avinash Paruchuri Tennessee Technological University
Jane Liu Tennessee Tech University
Stephen Idem Tennessee Technological University