Owing to the regulation of exhaust gas emissions from vessels, liquefied natural gas (LNG) has been garnering attention as an alternative eco-friendly fuel for vessels. LNG is considered as one of the most realistic alternatives to satisfy SOx and NOx regulations. Such social awareness is accelerating the development of LNGpowered vessels. It is necessary to expand the LNG bunkering infrastructure to supply LNG to vessels with LNG propulsion for their smooth operation. Relevant studies have been actively conducted both nationally and globally, and their feasibility has been reviewed. The Korea Research Institute of Ships & Ocean Engineering (KRISO) has been conducting studies on an offshore floating LNG bunkering system and has reviewed the system in terms of the design, equipment, and rules for offshore floating bunkering infrastructure. A floating LNG bunkering terminal (FLBT) unloads LNG from an LNG carrier and supplies LNG to the vessel with an LNG propulsion vessel through an LNG bunkering shuttle (LNG-BS). As the loading and off-loading operations of the FLBT are undertaken on the sea, it is essential to evaluate its operational stability in the marine environment. As 5K and 30K LNG-BSs have a relatively small displacement compared with FLBT, the work performance was observed to be degraded due to the marine environment under the operating conditions in the numerical analysis and model tests (Kim et
The flow around a curved riser exposed to the current in various directions was investigated at a Reynolds number of 100 using a numerical simulation. The present study found that the flow features of the curved riser were distinct from those of a straight riser as a result of its large radius of curvature. Namely, there were various wake patterns according to the flow's incident angle. As the incident angle increased from 0° to 90°, a two-row street of vortices that developed along the centerline of the curved riser became more apparent. However, when the incident angle approached 180° from 90°, these vortices were completely suppressed by the interaction between the wake and an axial flow induced by the curvature of the riser. To identify this feature, the sectional force coefficients were also considered, and it was found that the force coefficients could be different from those found in a sectional analysis based on the strip theory when investigating vortex-induced vibration. As a result, this kind of study would be important to realistically estimate the riser VIV (vortex-induced vibration) and fatigue life, and a new force coefficient database that includes the three-dimensional effect should be established.
In this study, the numerical code for the 3D nonlinear dynamic analysis of an SLWR (Steel Lazy Wave Riser) was developed using the lumped mass line model in a FORTRAN environment. Because the lumped mass line model is an explicit method, there is no matrix operation. Thus, the numerical algorithm is simple and fast. In the lumped mass line model, the equations of motion for the riser were derived by applying the various forces acting on each node of the line. The applied forces at the node of the riser consisted of the tension, shear force due to the bending moment, gravitational force, buoyancy force, riser/ground contact force, and hydrodynamic force based on the Morison equation. Time integration was carried out using a Runge-Kutta fourth-order method, which is known to be stable and accurate. To validate the accuracy of the developed numerical code, simulations using the commercial software OrcaFlex were carried out simultaneously and compared with the results of the developed numerical code. To understand the nonlinear dynamic characteristics of an SLWR, dynamic simulations of SLWRs excited at the hang-off point and of SLWRs in regular waves were carried out. From the results of these dynamic simulations, the displacements at the maximum bending moments at important points of the design, like the hang-off point, sagging point, hogging points, and touchdown point, were observed and analyzed.
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