Alzahabi B.

In cylindrical shells, the lowest natural frequency is not necessarily associated with the lowest wave index. In fact, the natural frequencies do not fall in ascending order of the wave index either. Solution of the vibration problem of cylindrical shells also indicates repeated natural frequencies. These modes are referred to as double peak frequencies. Mode shapes associated with each one of the natural frequencies are usually a combination of (i) Radial (flexural), (ii) Longitudinal (axial), and (iii) Circumferential (torsional) modes. During the optimization process of cylindrical shells, one is faced with a set of very unique challenges. Unlike that of simpler structures such as beams or plates, the modal spectrum of cylindrical shell exhibits very unique characteristics. Mode crossing, uniqueness modal spectrum, and redundancy of modal constraints are just a few of the unique attributes faced during the optimization process. In this paper, an extensive work of cylindrical shells optimization using MSC.Nastram is summarized. The non-uniqueness in optimum design of cylindrical shells subject to modal constraints is presented, and its implications are discussed. Related issues such as the new mode sequence, mode crossing, repeated natural frequencies and stationary modes are also discussed. The frequency responses of the resulting optimum designs are compared. A frequency response optimization is also discussed.