Analysis of damping ratio on the optimization of geometrically nonlinear truss structures subjected to dynamic loading

Abstract

The objective of this paper is to present the formulation for optimizing truss structures with geometric nonlinearity under dynamic loads, provide pertinent case studies and investigate the influence of damping on the final result. The type of optimization studied herein aims to determine the cross-sectional areas that will minimize the weight of a given structural system, by imposing constraints on nodal displacements and axial stresses. The analyses are carried out using Sequential Quadratic Programming (SQP), available in MATLAB’s Optimization Toolbox™. The nonlinear finite space truss element is defined with an updated Lagrangian formulation, and the geometrically nonlinear dynamic analysis performed herein combines the Newmark method with Newton-Raphson iterations. The dynamic analysis approach was validated by comparing the results obtained with solutions available in the literature as well as with numerical models developed with ANSYS^® 18.2. A number of optimization examples of planar and space trusses under dynamic loading with geometric nonlinearity are presented. Results indicate that the consideration of damping effects may lead to a significant reduction in structural weight and that such weight reduction is proportional to increases in damping ratio.