Structural evaluation of fixed offshore platforms

Abstract

In fixed offshore structures, damage incurred below the waterline is often difficult to detect, but significant enough to be the source of a subsequent massive failure. A technique is described that can be used to detect subsurface structural failure by detecting changes in the natural frequencies of the structure. One tower aas extensively studied; the dynamic measurement and analysis techniques are described. A parallel computer model of this tower was used to simulate the effect of removal of structural members on natural frequency. The parameters which determine the level of minimum detectable damage are discussed. Experimental data correlating wind and wave height spectra to observed structure response is presented. Statistical Energy Analysis is introduced as a method for predicting the dynamic response of offshore towers to random waves. The method is superior to the classical random vibration approach, in that it does not require the calculation of the wave force spectrum from the wave height spectrum, thus eliminating the calculations and assumptions common to the frequently used Morrison wave force equation. SEA is also applicable to a broad range of fixed and floating structures.