Reliable soil resistance estimates are essential for the safe and efficient design and installation of offshore monopile foundations. These are currently obtained by feeding Pile Driving Analyser (PDA) data into a signal matching model, but installing a PDA offshore requires sensors to be bolted onto the pile and later removed, a slow and costly process. This thesis investigates a non-contact alternative: using the change in magnetic flux around a steel monopile during driving as a substitute for the PDA's force signal. CAPWAP was selected as the basis for the model, since it produces a full soil resistance distribution rather than a single capacity value. Several CAPWAP driving configurations were tested with magnetic flux, including the standard wave separation formulation and a "Pulse" approach, in which the flux signal drives the model only during the initial hammer impact, after which the model matches purely on velocity. The Pulse approach proved substantially more tolerant of the flux signal's deviation from true force than wave separation, which produced unreliable estimates when driven by flux. Using Pulse, both the radial and axial flux signals produced shaft resistance and soil resistance distribution estimates in close agreement with the force-driven Pulse model and the wave separation approach. The main remaining discrepancy is in toe resistance, attributed to the Pulse model's reliance on velocity alone, which is more sensitive to the errors present in the available velocity signal. Repeating each model's optimisation from many independent starting points further showed that the shaft and toe resistance, and most other parameters under the Pulse formulation, converge consistently to well defined, unique solutions. These results show that magnetic field data can be used to estimate soil resistance parameters to a meaningful extent, closely comparable to a conventional PDA-based model. The flux signal must still be scaled to a measured force peak, so the approach is not yet fully non-contact; removing this dependency, along with closing the toe resistance gap, depends primarily on obtaining more accurate velocity measurements. A preliminary comparison against Laser Doppler Vibrometer data showed a promising alignment between the measured and impedance-based velocity peak, though the velocity signal could not yet be fully validated beyond this initial peak. A genuinely non-contact alternative to conventional PDA-based pile driving analysis therefore appears within reach. ... Read more

In this thesis, the friction performance of polyurethane tensioner pads used in offshore pipe-laying was investigated. Tensioner pads are used in pipe-lay to create tension in a pipe. The need to understand the pads better is because of the increased use of pipe coatings and pipe lay in deeper waters. Deep water leads to more pipe tension, and polymeric coating reduces friction.

A literature review was conducted on the friction of polyurethane. From the literature review, a few variables that influence polyurethane friction behaviour were summarised into the following research question: What is the influence of normal force on the pads, pad hardness, pad geometry, and pad temperature on the friction performance of polyurethane tensioner pads?

Experiments were performed at a full-scale setup. Polyurethane has a nonlinear coefficient of friction, making it difficult to upscale results from laboratory testing. In the full-scale setup, existing pads can be tested to find the influence of the different variables from the research question. The test setup was found to be flawed. Not only did it deform due to the massive forces, but the data gathered from the hydraulic pressures was not robust and accurate enough to estimate the static coefficient of friction, which is important in tensioners. Therefore, only trends in the pad behaviour were observed.

Increased normal force on the pads was found to increase the coefficient of friction. This contradicted the literature but was likely due to the geometry of flat pads versus round pipes, where the contact surface increased when the pads were loaded. Softer pads were found to yield higher friction than pads made from harder grades of polyurethane. This effect was also found in the literature. The influence of temperature was difficult to test. Since the pads could only be heated externally before testing, temperatures were inconsistent, and test results were inaccurate. The temperature did affect the friction significantly, though, so some newly produced pads were fitted with internal heating.

Next to the experiments, different pad geometries were tested in finite element analysis. A new pad shape was found that decreased stresses, leading to higher friction.

Next to the variables of the polyurethane itself, the relative humidity was recorded. The relative humidity changed significantly during the different tests, and it was found to affect friction more than anticipated.

Three sets of new pads were produced for future testing to validate the influence of geometry and further investigate the influence of the pad temperature. Moreover, a new test setup was designed to test the coefficient of friction more accurately.
... Read more