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Abstract:Monopile foundations have been commonly used to support offshore wind turbine generators (WTGs), but this type of foundation encounters economic and technical limitations for larger WTGs in water depths exceeding 30m. Offshore wind farm projects are increasingly turning to alternative multipod foundations (for example tetrapod, jacket and tripods) supported on shallow foundations to reduce the environmental effects of piling noise. However the characteristics of these foundations under dynamic loading or long term cyclic wind turbine loading are not fully understood. This paper summarises the results from a series of small scaled tests (1:100, 1:150 and 1:200) of a complete NREL (National Renewable Energy Laboratory) wind turbine model on three types of foundations: monopiles, symmetric tetrapod and asymmetric tripod. The test bed used consists of either kaolin clay or sand and up to 1.4 million loading cycles were applied. The results showed that the multipod foundations (symmetric or asymmetric) exhibit two closely spaced natural frequencies corresponding to the rocking modes of vibration in two principle axes. Furthermore, the corresponding two spectral peaks change with repeated cycles of loading and they converge for symmetric tetrapods but not for asymmetric tripods. From the fatigue design point of view, the two spectral peaks for multipod foundations broaden the range of frequencies that can be excited by the broadband nature of the environmental loading (wind and wave) thereby impacting the extent of motions. Thus the system lifespan (number of cycles to failure) may effectively increase for symmetric foundations as the two peaks will tend to converge. However, for asymmetric foundations the system life may continue to be affected adversely as the two peaks will not converge. In this sense, designers should prefer symmetric foundations to asymmetric foundations.

Offshore wind turbines are currently considered as a reliable source of renewable energy in the UK. These structures, owing to their slender nature, are dynamically sensitive at low frequencies, the first modal frequency of the system (less than 1 Hz) being very close to that of the excitation frequencies. The majority of operational offshore wind turbines situated in UK waters are founded on monopiles in water depths up to 30 m. For future development rounds where water depths are up to 70 m, alternative foundation arrangements are needed. To date there have been no long-term observations of the performance of these relatively novel structures. Monitoring of a limited number of offshore wind turbines has indicated a departure of the system dynamics from the design requirements. This paper summarises the results from a series of 1:100 scale tests of a V120 Vestas turbine supported on two types of foundation: monopiles and tetrapod suction caissons. The test bed used consisted of kaolin clay and sand. Up to 1 . 25 million loading cycles were applied to the scaled model, and the dynamic properties of the system were monitored. The results provide an insight into the long-term performance. Some interesting dynamic soil-structure interaction issues are identified and discussed.

Aim:The hypothesis is that the production of leukocyte and platelet-rich fibrin (L-PRF) is easy in horses without modifying human protocol, thus allowing better standardization of human protocol. In this study, the aim is to standardize the production of L-PRF in horses to direct it to human production. Methods: The authors took 9 mL of blood from the jugular vein of 6 horses to produce L-PRF membranes at a temperature > 21 °C by measuring the size of the membranes (height, length, thickness, weight, surface) and clot. Therefore we analyzed their microbiological characteristics. Results: The production of leukocyte and platelet-rich fibrin (L-PRF) is easy in horses without modifying human protocol, thus allowing better standardization of human protocol. The parameters found in the horse are clearly similar to the parameters found in humans. In optical microscopy, most of the cellular bodies were found and concentrated in the proximal portion of each membrane, with the last 1/4 observed in the center; the distal part only had residual traces of cellular bodies. The L-PRF is composed constantly when the production process below described is strictly respected. The success of L-PRF depends entirely on blood collection, on the quick transfer to a centrifuge (within 1 min) and on centrifugation and squeezing temperatures (between 21 and 30 °C) of the clot. Conclusion:The experiments on horses for the standardization of L-PRF production will improve our understanding about wound healing, particularly in the regenerative therapy of chronic skin lesions in humans. The data collected show that the best preparation method is the 2 min compression of the clot after 0 min of blood sampling, using the 9 mL vacutainer system and not a 9 mL syringe. Key words:Autologous, buffy coat, growth factor level, platelet-rich fibrin, thrombocyte concentrate ABSTRACTArticle history:

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