AbstractsTransportation

With the increase in size of offshore structures and the increase in costs related to the construction of these facilities, a necessity to optimize the construction of offshore facilities arises. An element that contributes greatly to these costs is the transportation and installation of the structures. Transportation costs are proportional to the distance covered and the number of transports necessary, since special vessels or tug boats are required. Installation costs are mainly proportional to time since the day rates of specialized construction vessels are extremely high. One of the most used structural members in offshore construction are steel cylindrical structural members, such as piles and pipelines. With increasing dimensions, also these members increase in size and it is often found wishful from a viewpoint of cost efficiency to transport the members on barges that are smaller in length than their cargo. Not only are standardized cargo barges more widely available then specialized equipment, their use also saves on fuel costs and pollution due to their reduced resistance compared with vessels that are greater in dimensions. Due to forces induced by the sea state the barges move and the oversized cargo undergoes a relative motion with regard to the sea surface. In certain environmental conditions this relative motion can develop in such a way that impact and/or submergence of the cargo occurs. This thesis focuses on the hydrodynamic loads involved with this interaction of oversized steel piles and the sea. The relative motions have been determined from a linearized motion analysis of an industry standard 122m long cargo barge. A radiation and diffraction analysis using potential theory software WAMIT has been performed to 1) determine the hydrodynamic coefficients of the barge, and 2) determine the effect of radiation and diffraction on the fluid pressures in the surrounding fluid field. It was found that the relative motions have a peak amplitude at wave periods that are commonly encountered in marine transport. This holds for approaches with and without taking into account the effects of wave radiation and diffraction. The analysis of the relative motions shows that for large enough wave heights water impact is possible to occur. To be able to quantify the loads an extensive literature review has been conducted on the involved hydrodynamic processes. It was found that knowledge on the governing load mechanisms is available. Water exit effects are less well covered in literature and conservative upper limit assumptions have been made to account for water exit effects. For quantification of the involved hydrodynamic loads, two approaches have been developed. First, a quasi-stationary approach is chosen to analyze the hydrodynamic loads. Four characteristics orientations have been identified which give a good representation of the maximum loading situations. The parameters for this approach are found from a spectral analysis of the relative motions, both with and without taking diffraction and radiation…