Numerical Simulation of Fluctuating Wind Effects on an Offshore Deck Structure

Abstract

The offshore structures that play a vital role in oil and gas extraction are always under complicated environmental conditions such as the random wind loads. The structural dynamic response under the harsh wind is still an important issue for the safety and reliable design of offshore structures. This study conducts an investigation to analyze the wind-induced structural response of a typical offshore deck structure. An accurate and efficient mixture simulation method is developed to simulate the fluctuating wind speed, which is then introduced as the boundary condition into numerical wind tunnel tests. Large eddy simulation (LES) is utilized to obtain the time series of wind pressures on the structural surfaces and to determine the worst working condition. Finally, the wind-induced structural responses are calculated by ANSYS Parametric Design Language (APDL). The numerically predicted wind pressures are found to be consistent with the existing experimental data, demonstrating the feasibility of the proposed methods. The wind-induced displacements have the certain periodicity and change steadily. The stresses at the top of the derrick and connections between deck and derrick are relatively larger. These methods as well as the numerical examples are expected to provide references for the wind-resistant design of the offshore structures.

Fatigue assessment on local components of a semi-submersible platform subjected to wind and wave loads

“…(7,8), respectively. This method in the present study combines the WAWS method with high numerical accuracy and the AR method with less time cost [14]. Thus, it becomes an efficient and accurate numerical simulation method for generating fluctuating wind and waves.…”

“…Step 3: apply the time series of wind and wave loads on the corresponding finite-element grid nodes of the offshore structures by the Newmark-method with ANSYS Parametric Design Language (APDL, ANSYS, Inc., USA) [14]. Calculate the structural dynamic equations and export the structural dynamic responses (e.g.…”

“…In the present study, a combined wind and waves relationship, based on the energy transferring relationship between wind and water surface, is explored to provide the corresponding wind speed, wave height and period according to the previous studies and the mechanism wind generating waves [10][11][12][13]. Secondly, provided that random wind and waves are a stationary Gaussian process, the combined wind and waves can be described by the power spectral density function (PSDF) [14]. Therefore, many numerical simulation methods are used to simulate the time series of the fluctuating wind and wave loads, such as the two classical approaches, the weighted amplitude wave superposition (WAWS) method [15] and auto-regression (AR) method [16,17].…”

“…Therefore, many numerical simulation methods are used to simulate the time series of the fluctuating wind and wave loads, such as the two classical approaches, the weighted amplitude wave superposition (WAWS) method [15] and auto-regression (AR) method [16,17]. Integrating the respective advantages of WAWS and AR methods, a mixture simulation (MS) method is applied to the present study with the aid of the wavelet method, whose efficiency and accuracy has been validated in our previous work [13,14]. Thus, a joint application of a proposed combined wind and waves relationship and an innovative proposed MS method can simulate the fluctuating wind and waves.…”

“…However, there are some limitations in the first two methods: the deterministic analysis method only considers the Design Wave, which leads to lower calculation accuracy compared to practical results; the spectral-based analysis method, as a widely-used method, only calculates stress with the narrow-band Gaussian random process, due to the limitation of the linear assumption [21]. Thus, as a relatively accurate method, the TDA method is adopted and improved in the present study, which generally requires the following three parts: structural dynamic response analysis [14,22], S-N curve approach and cumulative fatigue damage rule [20,[23][24][25], rain-flow counting method [26,27]. However, to improve the efficiency and accuracy of the TDA method further, an improved TDA (ITDA) method is provided in the present work and the improvements include three aspects.…”