This paper presents a method of generating a strongly asymmetric wave in irregular wave train and a brief discussion of the effect of the waves on ringing response of a tension leg platform (TLP). Strongly asymmetric waves are usually generated in transient wave mode. Hence, the response data is too short for statistical analysis of the response to random seaways containing strongly asymmetric waves. To solve the above problem, we generate large numerical irregular wave elevation time series from a JONSWAP spectrum by varying the significant wave height, average wave period, vertical asymmetric factor and overshoot parameter. There, in the foregoing wave, we search for a zero down crossing period wave with the largest crest, and distort the wave to produce a strongly asymmetric wave in the physical wave train. The strongly asymmetric wave in the random wave train can produce a weak impact load on a TLP model fixed in the wave tank. The above wave loads can be used for the simulation of the ringing in TLPs.
To study the distribution of extreme ringing load of TLP tendons, we had generated a strongly asymmetric wave in an irregular wave train at the Texas A & M University (TAMU) wave tank (Zou et al, 1997, 1998). In the above works, however, details of the wave generation could not be addressed due to the tack of space. This paper is intended to detail the method of strongly asymmetric wave generation in the wave tank. In addition to the above, we will briefly discuss the wave effect on impact and the statistical criterion of ringing of a TLP. In nature, strongly asymmetric waves may be generated by the wind whose pressure is higher on the back than on the front of the crest.
