Jv
J.W. van Gijn
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This thesis presents the design of a reusable jacket pile gripper (RJPG) concept and assesses its technical and economic feasibility. The motivation behind this is to explore the potential for innovation and cost saving for offshore wind farms (OWFs) that currently require hundreds of jacket pile grippers (JPGs) to ensure grout integrity. First, the design requirements were laid out. Through a design cycle, several potential design candidates emerged. After consideration, a single RJPG design was selected to work out into a full concept. This concept was fleshed out by designing for a reference jacket in a hypothetical OWF. The definitive concept is a design where hydraulic cylinders lay in circumferential positioned welded on the outside of the jacket leg. The hydraulic cylinders press onto the pile and secure it in place. When the grout is sufficiently cured, the cylinders retract and are automatically disconnected. Then, an offshore support vessel can come by and retrieve the RJPG by using a deck mounted crane or winch, helped by buoyancy aids. The selected lifting points in combination with hinges make sure the device clears the jacket geometry during lift-out. By carefully selecting the design wave and current, the hydraulic components could efficiently be selected. This led to a design with fewer cylinders than initially expected from a conventional JPG. When the device comes back into the yard it can be cleaned, inspected, tested and remounted on the next jacket. To gain better insight into the economics of the RJPG, an installation simulation was done. It was found that, depending on the weather and installation strategy, 10 to 16 sets of RJPGs are needed for an OWF of any size, including 2 spare sets. The simulation was also used to get estimates of the costs compared to the single-use JPG. The steelworks, hydraulic system, inspection, testing, remounting, assembly, gripper heads, vessel and other costs were estimated based on quotes, industry rules of thumb and expertise from Iv-groep. The economic analysis showed that the RJPG already edged out the single-use JPG around 25 turbines, or equivalent to 100 JPGs. These findings were further substantiated by conducting a sensitivity analysis. The potential fluctuations in four key cost drivers were analysed. They were the installation rate, the installation strategy, the steel price and the vessel day rate. This was then combined into an adverse scenario and a favourable scenario, and it showed that even in the adverse scenario, the break-even point was around 60 turbines or equivalent to 240 JPGs.
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This thesis presents the design of a reusable jacket pile gripper (RJPG) concept and assesses its technical and economic feasibility. The motivation behind this is to explore the potential for innovation and cost saving for offshore wind farms (OWFs) that currently require hundreds of jacket pile grippers (JPGs) to ensure grout integrity. First, the design requirements were laid out. Through a design cycle, several potential design candidates emerged. After consideration, a single RJPG design was selected to work out into a full concept. This concept was fleshed out by designing for a reference jacket in a hypothetical OWF. The definitive concept is a design where hydraulic cylinders lay in circumferential positioned welded on the outside of the jacket leg. The hydraulic cylinders press onto the pile and secure it in place. When the grout is sufficiently cured, the cylinders retract and are automatically disconnected. Then, an offshore support vessel can come by and retrieve the RJPG by using a deck mounted crane or winch, helped by buoyancy aids. The selected lifting points in combination with hinges make sure the device clears the jacket geometry during lift-out. By carefully selecting the design wave and current, the hydraulic components could efficiently be selected. This led to a design with fewer cylinders than initially expected from a conventional JPG. When the device comes back into the yard it can be cleaned, inspected, tested and remounted on the next jacket. To gain better insight into the economics of the RJPG, an installation simulation was done. It was found that, depending on the weather and installation strategy, 10 to 16 sets of RJPGs are needed for an OWF of any size, including 2 spare sets. The simulation was also used to get estimates of the costs compared to the single-use JPG. The steelworks, hydraulic system, inspection, testing, remounting, assembly, gripper heads, vessel and other costs were estimated based on quotes, industry rules of thumb and expertise from Iv-groep. The economic analysis showed that the RJPG already edged out the single-use JPG around 25 turbines, or equivalent to 100 JPGs. These findings were further substantiated by conducting a sensitivity analysis. The potential fluctuations in four key cost drivers were analysed. They were the installation rate, the installation strategy, the steel price and the vessel day rate. This was then combined into an adverse scenario and a favourable scenario, and it showed that even in the adverse scenario, the break-even point was around 60 turbines or equivalent to 240 JPGs.