| Sheet Metal and Air Conditioning Contractor's National Association (SMACNA) is a leading provider of sheet metal ducts for the air conditioning industry. A duct system is an assembly whose primary function is to convey air between specified points. In fulfilling the function of moving air, the duct assembly must satisfy certain fundamental performance criteria. Elements of the assembly are sheets, reinforcements, seams, and joints. Theoretical and/or practical limit must be considered for the duct assembly and its element. One such important criterion is dimensional stability (shape deformation and strength). A duct system may contain ducts under positive and negative pressure. Generally speaking, duct strength, deflection, and leakage are more functions of pressure than of velocity.; During turbulent airflow, the duct sheet walls undergo excessive deflections. Since space is a limiting factor, sheet deflections for ducts are to be limited and meet preexisting standards. This thesis is an attempt to perform large deflection analysis of sheet metal ducts under internal/external pressure loading, and to determine the adequacy of finite element method in predicting its non-linear behavior in terms of deflection.; Since the deflections occurring are large, geometric non-linear finite element method and CAE program by SDRC I-DEAS is employed for the analysis. The scope of this thesis is limited to large deflection analysis and does not address any duct design optimization methods. Deflection results obtained from physical tests in a laboratory setup have been validated with FEA results with maximum relative error of 20--30%. |
