Fundamental Frequency Of Structure Research Articles

Optimal Linearization of Morison‐Type Wave Loading

The linearization of Morison-type wave loading is to replace \Iu\N|\N\Iu\N|\N by \Icu\N, where \Iu\N is a zero mean, stationary Gaussian random process and \Ic\N is a constant. The coefficient \Ic\N is traditionally determined by a use of the statistical least-square error linearization; that is minimizing \IE\N[(\Iu\N|\N\Iu\N|\N-\Icu\N)²]. In this study, the optimal linearization refers to a coefficient \Ic\N, chosen in such a way that the statistics of structural response calculated from the linearized force will be identical to that calculated from the originally nonlinear force. To accomplish this, the optimal linearization must not only consider the ocean wave properties, but incorporate the structural properties. While most offshore structural engineers believe that the least-square linearization may cause significantly nonconservative error only when the fundamental structural frequency is nearly three times the peak wave frequency, this study shows that worse errors may occur for other frequency ratios.

A Free-flying Power Plant for a Manned Space Station

The 0.1 Hz fundamental structural frequency anticipated for the large solar array panels required to power manned space stations is close to the attitude control system bandwidth, and within the bandwidth of crew motion disturbances. Attention is presently given to a detachment of the solar panel system to create a free-flying powerplant for the space station, and to the control system that will maintain its attitude and position relative to the space station by means of thrusters that are supplied with space station state data by a laser/optical sensor system. Power transmission alternatives for this free-flying power system are discussed.

Increase of the first natural frequency and buckling load of plates by optimal fields of initial stresses

Departing from the common way of optimization of vibrating structures by an optimal mass distribution this paper deals with the problem of maximizing the fundamental frequency of structures by optimizing fields of initial stresses without varying the given appropriate shape of the structure. Thin elastic circular and rectangular plates are considered, which may be loaded by external inplane forces, and optimal initial membrane stress fields are calculated, which produce values of the first natural frequency of the free bending vibrations as high as possible. As a constraint, the strain energy caused by the field of initial stresses in the resting, externally unloaded plate is given. The computation leads to a max-min-problem solved numerically with the help of gradient methods. The optimal fields of initial stresses of the buckling plates are calculated as extreme cases in the same manner.