USE OF ARTIFICIAL DAMPING FOR ACCURATE EVALUATION OF RESPONSE UNDER PERIODIC-WAVE LOADING

The primary purpose of the paper is to present two options of a freque ncy-domain method for the accurate multi-harmonic analysis of SDOF sys tems with drag nonlinearity. The fluid loading due to waves and curren t is taken as periodic and the desired number of displacement harmonic s are found by the Newton-Raphson method. The first option, called the multi-diagonal Jacobian method (MDJM), uses essentially the full Jaco bian. The second option, termed the artificial damping method (ADM), u ses only the main diagonal of the Jacobian. Both the alternatives have been found to have excellent convergence properties and allow iterati ons to start either with a null vector or with one based on the linear ized solution. With the same computational parameters the two options provide almost identical solutions in about the same number of iterati ons. However, the computational effort per iteration required by the A DM is only a fraction of that for the MDJM, which makes it the method of choice. The methods have been validated against the results of the Runge-Kutta-Nystrom time integration and also by monitoring the residu al load. The use of the ADM to the analysis of MDOF systems in physica l coordinates has also been outlined. (C) 1997 Elsevier Science Limite d.