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The major component of environmental loadings on offshore structures is the wave-induced loads. The time-domain analysis has been commonly preferred to assess offshore structures because it provides considerable benefits to the practicing engineer without losing accuracy. However, such assessments are high computational demands and time costs due to complex numerical procedures in completing the hydrodynamic loadings on the offshore structures. Moreover, a huge number of simulations is required to increase the accuracy, leading to a long processing time. Hence, a simplified analysis-based time domain is introduced by applying direct calculation procedures to overcome this issue. It refers to an efficient time simulation regression method called the ETS-RegSE model. The result of the Monte Carlo Time Simulation (MCTS) will be used to compare the performance of the ETS-RegSE model's output. Provided with reasonable accuracy, the ETS-RegSE model offered a more efficient approach to optimal and costeffective structural analysis. [ABSTRACT FROM AUTHOR]

For offshore structural design, the load due to wind-generated random waves is usually the most important source of loading. The most accurate method that is commonly used to evaluate the offshore structural response on the subjected load is the Monte Carlo time simulation which can account for all sorts of nonlinearities without introducing any approximations. However, it is computationally very demanding due to its complex procedure. A simple method using finite-memory nonlinear system (FMNS) has been introduced. The method is, however, only applicable based on the linear wave analysis. Hence, by taking advantage on the efficiency of FMNS method, a new model needs to be developed by apply the FMNS method with a nonlinear wave analysis for a more reliable result. The most appropriate model can then be used to determine the probability distribution of response extreme values with great efficiency and accuracy. [ABSTRACT FROM AUTHOR]

An offshore structure is operated in an ocean wave environment that is stochastic in nature. Essential knowledge of ocean wave mechanics is practically important when it comes to the reliability of the structure. This paper summarised the numerical formulation involved in representing the ocean wave which will provide interaction effect in the design load of offshore structural response. Mechanism of wave load involved the formulation of wave spectra, ocean wave theory, water particles kinematics above sea water level, and the evaluation of wave force. Several formulations introduced by previous researchers for each process of wave load mechanism are discussed. At the end of this study, a good understanding of the estimated wave loads-induced responses will be discovered in terms of the selected ocean wave modelling. In application perspective, the calculated offshore structural responses would be utilised as the design load (structural responses) in structural reliability analysis of offshore platforms. [ABSTRACT FROM AUTHOR]

The least square error (LSE) method is frequently used in determination of Morison's coefficients from the analysis of measured wave forces on circular cylinders. It will be proved in this paper that Morison's coefficients determined from the LSE method always lead to predicted forces which have smaller variances (2nd-order statistical moments) than those of the measured forces. In other words, it is proved that predicted forces from this method are of lower intensity compared to the measured forces, and hence can be unconservative. A new method, termed the maximum correlation (MC) method, has been introduced. This method has all the advantages of the LSE method, but leads to predicted forces whose variances are equal to those of the measured forces.

Offshore structures are exposed to random wave loading in the ocean environment and hence the probability distribution of the extreme values of their response to wave loading is required for their safe and economical design. To this end, the conventional (Monte Carlo) time simulation technique (CTS) is frequently used for predicting the probability distribution of the extreme values of response. However, this technique suffers from excessive sampling variability and hence a large number of simulated extreme responses (hundreds of simulated response records) are required to reduce the sampling variability to acceptable levels. A more efficient version of the time simulation technique (ETS) was recently introduced which takes advantage of the correlation between the extreme surface elevations and their corresponding extreme responses by dividing the simulated extreme responses into a number of groups based on the magnitude of their associated extreme surface elevations. The probability distribution of response extreme values for each group is then calculated individually based on a relatively small number of simulations, and then the total probability theorem is used to derive the probability distribution of response extreme values. The ETS procedure is found to be many times more efficient than the CTS method. However, its efficiency and accuracy reduces for sea states of lower intensity. In this paper, a more efficient version of the ETS technique is introduced which takes advantage of the correlation between extreme values of the nonlinear response and their corresponding linear response extreme values (both quasi-static and dynamic linear responses are considered)). The three different versions of the ETS technique are compared by exposing a test structure to sea states of different intensity. It is demonstrated that the extreme linear response versions of the ETS technique are more accurate and efficient than the version based on surface elevation extreme values. [ABSTRACT FROM PUBLISHER]

In offshore engineering, the main forces that are loaded onto ocean structures come from wind-generated random waves. The prediction of wave forces that are applied onto slender cylindrical members is usually based on the Morison's equation, in which the wave force at any section of a member is expressed directly in terms of wave kinematics. It is essential to be able to estimate sensible kinematics at all levels of a structure to determine accurate prediction of wave forces and corresponding responses of these structures in a random wave field. Linear random wave theory (LRWT) is the simplest and most often used to simulate water particle kinematics at different nodes of an offshore structure from a reference surface elevation record. However, water particle kinematics calculated from LRWT grossly overpredicts the kinematics above the mean water level (MWL). Methods have been introduced to overcome this problem of high kinematics above the MWL, which consists of using linear wave theory (such as Wheeler, vertical stretching, effective node elevation and effective water depth methods) to provide a more realistic representation of near-surface wave kinematics. This is promising as there is some evidence that the water particle kinematics from the Wheeler method are underestimated and that those from the vertical stretching method are somewhat exaggerated. In this paper, the comparisons of the probability distributions of extreme values from different methods of simulation wave kinematics are investigated by using conventional time simulation procedure. [ABSTRACT FROM AUTHOR]