Experimental Study of Tendon Failure Analysis for a TLP Floating Offshore Wind Turbine

This paper describes an experimental study conducted on a multi-column tension leg platform (TLP) floating offshore wind turbine (FOWT). A prototype model of the TLP FOWT supporting the NREL 5-MW wind turbine with a scale ratio of 1:50 is tested under various wind and wave conditions at the State Key Laboratory of Coastal and Offshore Engineering at Dalian University of Technology, China. This work has particularly focused on the tendon failure and its impact on the dynamic response of the FOWT. Free decay tests, regular wave tests, wind-wave combined tests and tendon failure tests are conducted using different environmental parameters.The results suggest that natural periods, dynamic responses of the platform, and forces in the tendons satisfy the design requirements. The analysis indicates that the impact of tendon failure on the platform surge, heave and pitch responses are found to be insignificant. When one of the tendons is broken, the adjacent tendons experience a significant increase in tensile force; and, the maximum tensile force in the remaining tendon is found to increase by about 130%. The overstepping of the minimum breaking load as recommended by the design standard DNV GL is not reached, and this indicates that the safety of the system is ensured even during the harshest failure condition

Diatom and silicoflagellate assemblages in modern surface sediments associated with human activity: A case study in Sishili Bay, China

The spatial distribution of diatom and silicoflagellate fossils deposited in modern surface sediments was studied in inshore and offshore zones of Sishili Bay, China, to explore the impact of human activity on the coastal ecosystem. The sediments from 28 sites representing a gradient in intensity of human activity from inshore to offshore were sampled. Although the nutrient parameters inshore showed far higher concentrations than the offshore area, due to sewage discharge and waste dumping in the bay, the average fossil abundance did not differ significantly between the two areas. The diatom fossil Paralia sulcata, supposed to be a eutrophic indicator dominated most sediment samples and displayed a significant and positive correlation with dissolved inorganic nitrogen and phosphorus in the upper water column, but did not show a significant difference in abundance between inshore area and offshore area. Factors such as sediment disturbance (e.g., shipping), grazing pressure (e.g., shellfish aquaculture farm) and sediment characteristics (e.g., grain size) can affect the preservation of fossil debris in the sediment and lower the precision with which human activities can be associated with the fossil abundance.The spatial distribution of diatom and silicoflagellate fossils deposited in modern surface sediments was studied in inshore and offshore zones of Sishili Bay, China, to explore the impact of human activity on the coastal ecosystem. The sediments from 28 sites representing a gradient in intensity of human activity from inshore to offshore were sampled. Although the nutrient parameters inshore showed far higher concentrations than the offshore area, due to sewage discharge and waste dumping in the bay, the average fossil abundance did not differ significantly between the two areas. The diatom fossil Paralia sulcata, supposed to be a eutrophic indicator dominated most sediment samples and displayed a significant and positive correlation with dissolved inorganic nitrogen and phosphorus in the upper water column, but did not show a significant difference in abundance between inshore area and offshore area. Factors such as sediment disturbance (e.g., shipping), grazing pressure (e.g., shellfish aquaculture farm) and sediment characteristics (e.g., grain size) can affect the preservation of fossil debris in the sediment and lower the precision with which human activities can be associated with the fossil abundance. (C) 2012 Elsevier Ltd. All rights reserved

Multi-objective optimization design for a 15 MW semisubmersible floating offshore wind turbine using evolutionary algorithm

This paper introduces a framework designed to optimize the structural design of a 15 MW floating offshore wind turbine (FOWT) with a focus on cost-efficiency. The proposed framework employs a multi-objective evolutionary algorithm, integrating frequency domain (FD) simulations with equilibrium analysis to assess the response attributes of the floating platform and its mooring system. The objective function of the optimization includes the steel structural mass of the floating platform, the pitch heel angle, and the motion response amplitude operator (RAO) peak as determined by the FD simulation. Constraints pertinent to these objective functions, alongside the safety of the mooring system and the dynamic response and parameter settings of the FOWT, are meticulously enforced. The resulting optimized designs exhibit substantial improvements in the steel structural mass and pitch heel angle when contrasted with the initial design parameters. The practicality of this optimization framework is corroborated through time domain (TD) simulations, which elucidate the effects of the pitch heel angle and motion RAO peaks on the time domain response of the optimized structures. These insights offer reference for the future optimization of floating platforms and mooring systems in the realm of offshore wind energy

The world's largest macroalgal bloom in the Yellow Sea, China: Formation and implications

The world's largest trans-regional macroalgal blooms during 2008-2012 occurred in the Yellow Sea, China. This review addresses the causes, development and future challenges in this unique case. Satellite imagery and field observations showed that the macroalgal blooms in the Yellow Sea originated from the coast of Jiangsu province and that favorable geographic and oceanographic conditions brought the green macroalgae from the coast offshore. Optimal temperature, light, nutrients and wind contributed to the formation and transport of the massive bloom north into the Yellow Sea and its deposition onshore along the coast of Shandong province. Morphological and genetic evidence demonstrated that the species involved was Ulva prolifera, a fouling green commonly found growing on structures provided by facilities of Porphyra aquaculture. Large scale Porphyra aquaculture (covering >20,000 ha) along the Jiangsu coast thus hypothetically provided a nursery bed for the original biomass of U. prolifera. Porphyra growers remove U. prolifera from the mariculture rafts, and the cleaning releases about 5000 wet weight tonnes of green algae into the water column along the coast of Jiangsu province; the biomass then is dispersed by hydrographic forcing, and takes advantage of rather high nutrient supply and suitable temperatures to grow to impressive levels. Certain biological traits of U. prolifera -efficient photosynthesis, rapid growth rates, high capacity for nutrient uptake, and diverse reproductive systems- allowed growth of the original 5000 tonnes of U. prolifera biomass into more than one million tonnes of biomass in just two months. The proliferation of U. prolifera in the Yellow Sea resulted from a complex contingency of circumstances, including human activity (eutrophication by release of nutrients from wastewater, agriculture, and aquaculture), natural geographic and hydrodynamic conditions (current, wind) and the key organism's biological attributes. Better understanding of the complex biological-chemical-physical interactions in coastal ecosystems and the development of an effective integrated coastal zone management with consideration of scientific, social and political implications are critical to solving the conflicts between human activity and nature. (c) 2013 Elsevier Ltd. All rights reserved.The world's largest trans-regional macroalgal blooms during 2008-2012 occurred in the Yellow Sea, China. This review addresses the causes, development and future challenges in this unique case. Satellite imagery and field observations showed that the macroalgal blooms in the Yellow Sea originated from the coast of Jiangsu province and that favorable geographic and oceanographic conditions brought the green macroalgae from the coast offshore. Optimal temperature, light, nutrients and wind contributed to the formation and transport of the massive bloom north into the Yellow Sea and its deposition onshore along the coast of Shandong province. Morphological and genetic evidence demonstrated that the species involved was Ulva prolifera, a fouling green commonly found growing on structures provided by facilities of Porphyra aquaculture. Large scale Porphyra aquaculture (covering >20,000 ha) along the Jiangsu coast thus hypothetically provided a nursery bed for the original biomass of U. prolifera. Porphyra growers remove U. prolifera from the mariculture rafts, and the cleaning releases about 5000 wet weight tonnes of green algae into the water column along the coast of Jiangsu province; the biomass then is dispersed by hydrographic forcing, and takes advantage of rather high nutrient supply and suitable temperatures to grow to impressive levels. Certain biological traits of U. prolifera -efficient photosynthesis, rapid growth rates, high capacity for nutrient uptake, and diverse reproductive systems- allowed growth of the original 5000 tonnes of U. prolifera biomass into more than one million tonnes of biomass in just two months. The proliferation of U. prolifera in the Yellow Sea resulted from a complex contingency of circumstances, including human activity (eutrophication by release of nutrients from wastewater, agriculture, and aquaculture), natural geographic and hydrodynamic conditions (current, wind) and the key organism's biological attributes. Better understanding of the complex biological-chemical-physical interactions in coastal ecosystems and the development of an effective integrated coastal zone management with consideration of scientific, social and political implications are critical to solving the conflicts between human activity and nature. (c) 2013 Elsevier Ltd. All rights reserved

[μ-1,2-Bis(4-pyrid­yl)ethane-κ2 N:N′]bis­[(4′-phenyl-2,2′:6′,2′′-terpyridine-κ3 N,N′,N′′)silver(I)] bis­(trifluoro­methane­sulfonate)

In the title compound, [Ag2(C12H12N2)(C21H15N3)2](CF3SO3)2, the AgI atom is coordinated by three N atoms of one 4′-phenyl-2,2′:6′,2′′-terpyridine (phtpy) ligand and one pyridyl N atom of the 1,2-bis­(4-pyrid­yl)ethane (bpe) ligand, displaying a distorted square-planar geometry. Two AgI atoms are bridged by one trans-bpe ligand, generating a dinuclear cation. The dinuclear cation is located on a centre of inversion, which is in the middle of the ethyl­ene fragment of the bpe ligand. In the crystal, the pyridyl rings of neighboring dinuclear units are stacked by π–π inter­actions with centroid–centroid distances of 3.667 (2) and 3.835 (2) Å. The F and O atoms of the CF3SO3 − anions are involved in inter­molecular C—H⋯F and C—H⋯O hydrogen-bonding inter­actions, respectively, with –CH groups from the phtpy ligands