| dc.description.abstract | The offshore installation is a large process that will face several obstacles, including unpredictable ocean conditions. During the landing stage, the installation platform restricts the movement of the equipment. Furthermore, any external disturbance may impact the equipment, resulting in permanent damage to the entire structure. As a result, this impact energy can be used to reduce facility damage. Soft landing cylinders are made out of a cylinder with a piston, where water fills the cylinder automatically via immersion, resulting in controlled deceleration. When water enters the cylinder, the piston is compelled to push outwards. Damping is produced when the piston rod strokes the already established supporting framework.
The thesis was written for Subsea 7 that wants to develop a current concept of a soft landing cylinder or create a new design based on its design requirements. The Subsea 7 requirements are that the conceptual design must withstand modules wight 300 Tons, 40 Tons, 20 Tons, and 15 Tons, and the landing speed does not exceed 0.5 m/s for the high mass module at pressure 210 bar.
This thesis addresses developing or creating a conceptual design of a system that can control lowering and raising functions to ensure that pipe connection or disconnection prior to the final module position is more secure. The soft-landing system must be developed into two stages or functions, i.e., one for lowering function and the other for raising function. In addition to the number and position of soft landing cylinders in subsea modules, that is an important factor to consider, especially for modules with a large footprint and high mass. The nozzle of the soft landing cylinder plays an essential role in soft landing cylinder design, and landing speed assessment depends on nozzle outlet velocity. Therefore the thesis is focused on estimating the nozzle efficiency, nozzle outlet velocity, landing velocity, soft-landing cylinder diameters, and defining the cylinder location on the large footprint and high mass modules. The relevant theory was used to derive a relationship between pressure, energy loss, and velocity for estimating the nozzle outlet speed and nozzle efficiency, determining both the landing and raising speed, besides calculating the cylinder dimensions based on Subsea 7 requirements. Finite element analysis was utilized to identify the positions of the soft lading cylinder and computational fluid dynamic simulation to support the analytical results. The new conceptual design has two mechanisms water-based for the landing stage and hydraulic-based for the raising stage in the same cylinder. Two concepts of soft landing cylinder are created the first one is optimizing current model second one new concept both are to withstand high mass and large footprint. | |