The floating offshore wind industry is growing rapidly, with increased capacity goals and expanding commercial project opportunities in the coming years. An important marine operation related to floating offshore wind is towing. The safety and cost of a tow operation are highly dependent on the choice of a suitable tug and tow speed, as well as the forces expected to act on the towing system. In the presence of waves, significant dynamic towline tensions can be experienced that may cause the towline to break. Therefore, predicting the tensions in the towline is important for efficient design and planning of the towing system. The present paper describes a methodology for towing dynamics predictions and is implemented into MATLAB as a toolbox for planning future tow operations. The proposed methodology is able to (a) estimate the bollard pull requirements and static towing forces crucial for planning the tow operation; as well as (b) predict the mean and dynamic towline tensions in the presence of a given sea state. Two separate analyses are performed. In the first analysis, the towline tension predictions from the toolbox are validated against measured towline tension data from the University of Maine’s VolturnUS 1:8 deployment together with the results from a time domain model developed in OrcaFlex. In the second analysis, a parametric study is performed using the toolbox. The results of the study show the toolbox was able to closely predict the measured static and dynamic towline tensions. In addition, the effect of propeller race interactions with the towed floating offshore wind turbine was shown to significantly impact the predicted towline tension.
Bio-based lightweight materials are promising replacements for petroleum-based foams in building and packaging applications. In this work, we developed a surfactant-assisted foam-forming method to manufacture lightweight materials based on lignocellulosic fibers (thermomechanical pulp (TMP), refined wood fibers (RWF) and pine flour (PF)) enabled by cellulose nanofibrils (CNFs). Sodium dodecyl sulfate (SDS) or cetyltrimethylammonium bromide (CTAB) at 1 g/L concentration was mixed with different concentrations of CNFs in a blender followed by the addition of a pre-determined amount of TMP, RWF or PF. The preparation of hybrid foams using TMP/PF, TMP/RWF, and TMP/PF/RWF at different weight fractions was also investigated. Results showed that among the three tested natural fibers, TMP was the best for the preparation of low-density foamed materials, with densities ranging from 11 to 45 kg/m3 in the case of foams made with SDS and 16–90 kg/km3 for those made with CTAB. Thermal conductivity of the prepared foams was between 0.031 W/m.K and 0.055 W/m.K depending on the density and the porosity of the foams. Foams made with high solids content (4–6 wt%) exhibited excellent sound absorption coefficients (0.96–1 at 3500 Hz). Water stability and mechanical properties of the resulting bio-foams were significantly improved when increasing CNF and solids contents. All foams exhibited antifungal properties against Trametes versicolor. Additionally, the hybrid foams exhibited good and competitive properties. These low-density foams enabled by the excellent bonding capability of CNFs could thus be potentially used to provide antifungal resistance as well as acoustic and thermal insulation.
Wood flour (WF) at 10 wt.% and 20 wt.% loadings was used as a reinforcing filler to enhance the applicability of polypropylene (PP) for 3D printing. After performing printability tests of PP wood plastic composites (WPCs), the mechanical properties of both injection-molded and 3D-printed PP WPC specimens were explored. Test specimens were prepared from 3D printed hexagons for analyzing the mechanical properties. Adding WF to neat PP increased the storage modulus and the glass transition temperature while decreasing the degree of crystallinity and the coefficient of thermal expansion, while enhancing the printability of neat PP. The tensile strength, tensile modulus of elasticity, flexural strength, and flexural modulus of elasticity of injection-molded neat PP improved by up to 21%, 59%, 30%, and 56%, respectively, with 20 wt.% WF. However, the impact strength of injection-molded neat PP decreased by 85%, with 20 wt.% WF. After 3D printing, the tensile strength and tensile modulus of elasticity of printed neat PP increased by up to 84% and 60%, respectively, with 20 wt.% WF. The flexural strength and flexural modulus of elasticity of neat printed PP remained unchanged compared to those of PP filled with 20 wt.% WF, while the impact strength decreased by 87%.
Advanced Structures & Composites Center