Determination of hydrodynamic forces acting on space-truss system members in offshore structures depending on solidity ratio

Generally, the wind-induced horizontal forces acting on a space-truss system constructed on land have been calculated by using EIA-TIA-222G standart based on solidity ratio of its sectors. In this case, the wind velocity can also be defined as steady-state flow increasing with structure height. Therefore, such velocities will cause the drag forces on structural members. When constructing similar structures in marine, it is seen that the project area will be exposed to the unsteady flow of wave movement. Horizontal wave particle velocities and accelerations due to the unsteady flow of harmonically oscillating wave cause to occur the drag forces as well as the inertia forces. In addition to this, the wave motions around vertical, lateral and braced members transform the fluctuations within structure sectors. In this case, the calculation of hydrodynamic forces on these members becomes complicated and can be only accomplished numerically. Modelling and analysis process is rather complicated with considerably long processing time. Because of this, a new approach is proposed to make ease the process for designers. In order to calculate hydrodynamic forces which include different solidity ratios and wave parameters, both ANSYS-Fluent and Artificial Neural Network (ANN) are used in modelling and solving numerically. In this study, at the beginning of solving process, the ANN model is at first used without performing ANSYS-Fluent model and then, it is founded that the equivalent hydrodynamic forces can be obtained from the ANN model processing the parameters satisfying the Second Order Stokes wave theory such as different wave heights (H), periods (T) and water depths (d) together with both constant and variable solidity ratios. Moreover, it is concluded that the hydrodynamic forces on the basis of ANN model, which provides relatively esay way, can be practically calculated in accordance with the solidity ratio of each sector for unsteady flow. In developing an accurate ANN model, these forces are firstly calculated by the ANSYS-Fluent software for the seven-different structures which have both constant and variable solidity ratio. The ANN model considers several parameters; solidity ratio of each sector (e), dimensionless numbers such as H/(gT2) and d/(gT2), sectorial dimensionless numbers (z/D), dimensionless number for unsteady flow (t/T) and project area of each sector (A) for each stucture. The forces obtained from the both models are compared and their conveniences are proved statistically. It is concluded that hydrodynamic forces calculated will be associated with their solidity ratios by evaluating the success of ANN model in predicting those of ANSYS-Fluent It has been demonstrated that it is possible to be projected more rapidly and practically by using the solidity ratio-hydrodynamic force relationship of the offshore structures, which require precise, complex and long-term operation.