With the increasing water depths of the new offshore wind farms, the challenging soil conditions, the availability of assets, and other factors, jack-up installation vessels may no longer be suitable to complete the installation scope of work for the new wind farms. Therefore, installation methods and techniques using floating vessels must be further developed to allow safe and efficient installation of wind turbines. Due to the response of floating installation vessels, excessive motions can be transmitted to the lifted object, making the installation operation very weather sensitive. To increase workability, Heerema Marine Contractors (HMC) has developed the RNA method for wind turbine installation using a semi-submersible crane vessel. This method uses a temporary support structure on the vessel deck (installation tower) where the RNA is fully assembled with the assistance of the GREP (Guided Root End Positioning) tool to constrain the blade root to the top of the installation tower and consequently the hub. Finally, the RNA is installed in a single lift on the WTG permanent support structure. However, the GREP tool is compatible only with a specific range of wind turbine blade dimensions; therefore, for a different-size wind turbine blade a new GREP tool must be designed, fabricated, and mobilised. This project proposes an improvement to the HMC's RNA method to eliminate the necessity of the GREP tool. That is, a motion-compensated Stewart platform attached to the crane boom, where the blade is fixed to be installed in the hub on top of the installation tower. The project is developed by investigating the initial assumptions; those are crane boom stiffness, blade deflection, installation tower motions and their influence on the vessel's response, and aerodynamic loads acting on the blade during installation. The kinematics (inverse and forward) and dynamics of a Stewart platform are formulated, as well as the mechanical concept of the proposed system and the blade installation process using a Stewart platform attached to the crane boom. Furthermore, to eliminate the requirement of the GREP tool, a control system is developed to compensate for the blade root motions relative to the hub. The motion control system uses sensors to measure the hub's motions and generate the Stewart platform actuators' set points. Different possible sensor set-ups are evaluated, and a filter is designed to reduce the influence of the sensors' noise. The control system is developed on the basis of feedback PI (Proportional and Integral) and adaptive feedforward control to the actuators (hydraulic cylinders). It is concluded that it is technically feasible to use a motion- compensated Stewart platform for blade installation in the RNA method. However, the economic aspects of the proposed solution must be investigated.

The Netherlands aims for a circular economy by 2050. One of the major challenges is using waste as a resource. Midwaste, a cooperative association that manages waste streams and covers around 130 municipalities for the plastic waste dossier, is contributing in working towards a circular economy. As the client of this project, it requested looking into creating a valuable product out of the leftover mix fraction out of domestic plastic waste. Municipalities in the Netherlands are separating domestic plastic waste, PMD, from residual waste. After collection, it is separated further into mono streams to bring these back in the circle. However, not all the plastics can be separated yet, which results in 25% leftover mix fraction, consisting out of polyolefins and impurities. The composition and quality of the mix fluctuates, which makes it a challenging material to work with. Half of the mix is still burned and half of the mix is recycled into new products. However, there still is variety of possibilities and challenges for implementing the mix into products. The initial goal in this project was to develop a valuable product with the mix to show its potential value. It appeared that the mix was not processed with rotational moulding yet. By doing some tests with agglomerate, both with producing powder out of agglomerate and rotomoulding this powder, the potential of this material using rotational moulding has been proved. The characteristics of this material processed by rotomoulding are still unknown. The biggest challenge in further development is producing suitable powder out the agglomerate that is made by the recycler. The impurities are challenging, both in damaging the grinding system and constipating the sieves of the machinery. Besides the impurities, there is another challenge in finding the right additives for this material to improve the characteristics. Besides proving the potential of the leftover mix using rotomoulding, CirculEm has been developed. CirculEm is a small rain barrel, partially made out of the mix, that responds to two aspects regarding a circular economy. First, using waste as a resource, and secondly CirculEm responds to climate adaptation on a local level. The outside layer of the barrel is made out the mix that shows the expression of the recycled material. The inside layer of virgin PE provides strength and stiffness to the product. However, it is discussable to blend the mix with virgin material regarding to the end of life aspect of CirculEm. When characteristics are known, this multilayer construction could be optimised. Research showed that products made out of the mix tell a good story. Combining ‘using waste as a resource’ with creating products that respond to other aspects that work towards a circular economy, like climate adaptation and energy transition, makes this story even stronger. The municipality of Breda and Rotterdam, seem interested in CirculEm, because they are looking for solutions regarding water management on private area. CirculEm might be the missing link between municipalities and the commonality by starting the collaboration in tackling climate adaptation on private areas.