IFMASS10

225

DYNAMIC CHARACTERISTICS MODIFICATION IN THE

MECHANICAL STRUCTURES REANALYSIS

Nataša Trišović

University of Belgrade, Faculty of Mechanical Engineering, Belgrade, Serbia

1. INTRODUCTION

Dynamic response of mechanical systems depends of structural parameters. In

mechanical structures reanalysis objective is to evaluate the structural response for

successive modifications in the design avoiding the difficult solution of the modified

equations. The structural modifications may be required by external factors or by the

designer in order to improve the characteristics of structure response (eigenvalues and

eigenvectors). Modification of dynamic characteristics means change of corresponding

design variables to get desired dynamic behaviour of a structure. The design variables

depend on the type of optimization problem. In the design of structural components, such

as stiffened panels and cylinders, the design parameters represent the size and shape of

stiffeners and their spacing, and the plates or shell thickness. The thickness of plates,

cross-section areas of bars, and areas, moments of inertia, and torsion constants of beams

represent the values which should be considered for modification. Joints and members

could be eventually added or exuded during reanalysis process, modifying in this way the

geometry of the structures. A simple scheme of dynamic modification during reanalysis is

presented in Fig. 1.

Figure 1: A simplified scheme of dynamic modification

Reanalysis methods might include following activities:

(a) Modification in the geometry, with no further change in the number of degrees of

freedom.

(b) Modification of design variables (mass, damping and stiffness).

supporting system, and addition or deletion of joints and members.

(d) Selection of new material for critical components, if possible.

Reanalysis methods mostly cannot involve the last two modifications, because they

imply a change in the dimension of the system due to addition or deletion of degrees of