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Wu W.,Peking University | Ruan J.,Peking University | Ding S.,Peking University | Zhao L.,Peking University | And 5 more authors.
Marine Chemistry | Year: 2014

To assess the source of glycerol dialkyl glycerol tetraethers (GDGTs) and their usefulness as proxies for terrestrial organic matter inputs and temperature in the Yellow River-dominated margin, we measured isoprenoid and branched GDGT concentrations in surface sediments along a lower Yellow River-estuary-coast transect. Branched GDGTs dominated over isoprenoid GDGTs in the riverbed sediments and had similar compositions from river to coast. In contrast, isoprenoid GDGTs displayed an increasing abundance and a decreasing GDGT-0 to crenarchaeol ratio (1.6 to 0.6) toward the sea. Such distribution patterns of GDGTs, combined with the result from a principal component analysis (PCA), confirmed the different origin of branched and isoprenoid GDGTs with branched GDGTs being primarily from soil erosion of the Chinese loess plateau (CLP) whereas, in addition to allochthonous terrestrial inputs, aquatic Thaumarchaeota partially contributes to the isoprenoid GDGT pool in estuarine and coastal areas. The branched GDGT-derived temperature (avg. 11°C) is consistent with the annual mean air temperature (MAT) of the CLP in the middle river basin, a major source region for the Yellow River sediments, whereas the isoprenoid-derived temperature (12.7 to 28.4°C) deviated widely from the annual mean temperature in the study region. Application of a binary mixing model based on δ13C, the branched and isoprenoid tetraether (BIT) index and branched GDGT concentrations showed consistent decreases in the relative amount of terrestrial organic carbon toward the sea, but estimates from the latter two proxies were lower than those from the δ13C. © 2013 Elsevier B.V.

Lin X.,Ocean University of China | Lin X.,Marine Innovation and Technology | Lin X.,Woods Hole Oceanographic Institution | Yin Y.,Ocean University of China | Yang J.,Woods Hole Oceanographic Institution
Journal of Geophysical Research: Oceans | Year: 2014

Previous studies have shown that the power spectrum of satellite-observed sea surface height (SSH) variability peaks at a certain frequency (or a wave number) band at a given latitude. Lin et al. (2008) attributed this latitudinal dependence to the critical frequency of the first baroclinic mode Rossby waves in the tropical and subtropical oceans. Their study was based on the linear Rossby wave theory and focused on SSH variability in the tropical and subtropical oceans since the altimetry data do not adequately resolve lengths of baroclinic Rossby waves at and near the critical frequency in high latitudes. In this study, we expand their analysis to high-latitude oceanic basins and to include nonlinear eddy effects, by using a linear wave model and a high-resolution model output from the OGCM for the Earth Simulator (OFES). It is found that the linear wave mechanism by and large remains valid in the tropical and subtropical oceans. In higher latitudes as well as in some regions in the western tropical and subtropical oceans, other mechanisms, like nonlinear eddy, play more important role in determining the SSH variability. Key Points SSH peaks at a certain frequency at each latitudinal band The linear wave near critical frequency causes the SSH peaks in low latitudes Eddies play a more important role in SSH variability in high latitudes © 2014. American Geophysical Union. All Rights Reserved.

Roddier D.,Principle Power Inc. | Cermelli C.,Marine Innovation and Technology | Aubault A.,Marine Innovation and Technology | Weinstein A.,Principle Power Inc.
Journal of Renewable and Sustainable Energy | Year: 2010

This manuscript summarizes the feasibility study conducted for the WindFloat technology. The WindFloat is a three-legged floating foundation for multimegawatt offshore wind turbines. It is designed to accommodate a wind turbine, 5 MW or larger, on one of the columns of the hull with minimal modifications to the nacelle and rotor. Potential redesign of the tower and of the turbine control software can be expected. Technologies for floating foundations for offshore wind turbines are evolving. It is agreed by most experts that the offshore wind industry will see a significant increase in activity in the near future. Fixed offshore turbines are limited in water depth to ∼30-50 m. Market transition to deeper waters is inevitable, provided that suitable technologies can be developed. Despite the increase in complexity, a floating foundation offers the following distinct advantages: Flexibility in site location; access to superior wind resources further offshore; ability to locate in coastal regions with limited shallow continental shelf; ability to locate further offshore to eliminate visual impacts; an integrated hull, without a need to redesign the transition piece between the tower and the submerged structure for every project; simplified offshore installation procedures. Anchors are significantly cheaper to install than fixed foundations and large diameter towers. This paper focuses first on the design basis for wind turbine floating foundations and explores the requirements that must be addressed by design teams in this new field. It shows that the design of the hull for a large wind turbine must draw on the synergies with oil and gas offshore platform technology, while accounting for the different design requirements and functionality of the wind turbine. This paper describes next the hydrodynamic analysis of the hull, as well as ongoing work consisting of coupling hull hydrodynamics with wind turbine aerodynamic forces. Three main approaches are presented: The numerical hydrodynamic model of the platform and its mooring system; wave tank testing of a scale model of the platform with simplified aerodynamic simulation of the wind turbine; FAST, an aeroservoelastic software package for wind turbine analysis with the ability to be coupled to the hydrodynamic model. Finally, this paper focuses on the structural engineering that was performed as part of the feasibility study conducted for qualification of the technology. Specifically, the preliminary scantling is described and the strength and fatigue analysis methodologies are explained, focusing on the following aspects: The coupling between the wind turbine and the hull and the interface between the hydrodynamic loading and the structural response. © 2010 American Institute of Physics.

Cermelli C.A.,Marine Innovation and Technology | Roddier D.G.,Principle Power Inc. | Weinstein A.,Principle Power Inc.
Offshore Technology Conference, Proceedings | Year: 2012

A discussion covers the implementation of a 2 Mw floating wind turbine prototype installed offshore Portugal in October 2011; synergies with offshore oil and gas platforms; project management strategy developed to implement the project on a fast-track and with local content requirements; operation results; and prototype testing and expansion into pre-commercial and commercial activities. This is an abstract of a paper presented at the Offshore Technology Conference 2012 (Houston, TX 4/30/2012-5/3/2012).

Lu W.,Marine Innovation and Technology | Lu W.,Norwegian University of Science and Technology | Lubbad R.,Marine Innovation and Technology | Lubbad R.,Norwegian University of Science and Technology | And 2 more authors.
Cold Regions Science and Technology | Year: 2015

Out-of-plane failure of an ice floe has been studied extensively over the past several decades for different application purposes (e.g., an ice cover's bearing capacity for transportation; bending failure of level ice interacting with a sloping structure). Notably, most of the previous studies have idealised the considered ice floe as an infinite or semi-infinite thin plate resting on a Winkler-type elastic foundation. However, a typical ice field in the Arctic is far from continuous. Furthermore, recent Arctic offshore structures have usually been designed with support from ice management; i.e., these sloping structures are most often operating in a broken ice field and are interacting with ice floes of finite sizes. Bearing this loading environment in mind, this paper starts with the question 'What are the physical processes behind the failure of a finite size ice floe interacting with a sloping structure, and what will the failure pattern look like?' Based on an in-depth literature review in relation to out-of-plane failures of infinite and semi-infinite ice floes, depending on the floe sizes, we propose a conservative classification of an ice floe's out-of-plane failures under an edge load, i.e., 1) finite size ice floes that are broken at radial crack initiation and 2) a semi-infinite ice floe that is broken by sequentially forming radial and circumferential cracks. Between these two scenarios, we focused our study on 'radial-crack-initiation-controlled fracture' of a finite size ice floe. Specifically, we are trying to answer the following question: 'how small/large should an ice floe be to be treated as a finite size/semi-infinite ice floe?' Based on a series of assumptions, radial crack initiation and propagation within a square ice floe were theoretically formulated and numerically studied. The respective loads to initiate and propagate a radial crack have been extracted and compared to quantify the required size smaller than which an ice floe would fail at radial crack initiation. For typical ice material properties, it is theoretically illustrated that a nearly square shaped ice floe can fail at crack initiation if its physical size is smaller than approximately 27×(ice thickness)3/4. On the theoretical side, this paper contributes to the derivation of non-dimensional formulae to study radial crack initiation and propagation. Additionally, simplified yet effective numerical models to study radial crack initiation and propagation within an ice floe were proposed and validated. On the practical side, the research methodologies and conclusions presented herein shed light on the possibility of a more economic design for an Arctic offshore structure whose major operating environment is filled with finite size ice floes. In addition, because the 'radial-crack-initiation-controlled fracture' of an ice floe means a much smaller ice load (i.e., compared with continuous circumferential type bending failure within a level ice environment) on a sloping structure, it is recommended, from a mechanically preferred point of view, that floes with sizes smaller than 27×(ice thickness)3/4 should be produced in the downstream of an ice management operation. © 2015 Elsevier B.V.

Liu S.M.,Ocean University of China | Liu S.M.,Marine Innovation and Technology
Journal of Marine Systems | Year: 2014

Nutrient transport patterns in the Huanghe (Yellow River) were investigated using biogeochemical observations carried out during 2001-2011 to examine how nutrient transports were affected by water-sediment regulation events and their potential effects on the adjacent Bohai ecosystem. The concentrations and composition of nutrients in the Huanghe had an obvious change during the water-sediment regulation events, which increased dissolved nutrient transports with a similar amplitude like freshwater discharge, while amplified particulate nutrient transports. Dissolved inorganic nitrogen was the predominant species of total dissolved nitrogen. Particulate phosphorus was the major form of phosphorus affected by high content of suspended particulate matter. Phosphate represented 68% of total dissolved phosphorus. The BSi was 20% of the sum of BSi and dissolved silicate. Nutrient transport patterns highly depend on freshwater discharge. The regulation events have shifted the seasonal patterns of water and nutrient transports with high flow condition occurring at least two months prior to the normal peak flow. Abundant nutrients were transported to the coastal water and nutrient imbalance was aggravated, most likely resulting in strong impacts on the adjacent Bohai ecosystem. © 2014 Elsevier B.V. All rights reserved.

Nolte J.D.,University of Hawaii at Manoa | Nolte J.D.,Marine Innovation and Technology | Ertekin R.C.,University of Hawaii at Manoa
Journal of Renewable and Sustainable Energy | Year: 2014

We present the numerical modeling of a heaving, point-source wave energy conversion (WEC) device, previously tested by the University of Hawaii at Manoa. The WEC device converts the vertical heave displacements into a rotational motion to generate electrical power; the heave displacements converted are from the WEC system rising with the incoming waves relative to an anchoring system. Two anchoring methods of the WEC device are referred to as the single-body case (moored system) and double-body case (drogue anchored system). The numerical model performs hydrodynamic analysis in the time domain in irregular seas for the single-body or double-body case. We then compare the predictions with the available in-ocean experiments. The computer program written for this purpose solves for the individual body motion and predicts the WEC device's power production over the time series. Moreover, we present the results of the study that shows the effect of the device-damping characteristics and the size and the depth of operation of the drogue on wave-power predictions. © 2014 AIP Publishing LLC.

Forristall G.Z.,Forristall Ocean Eng. Inc. | Aubault A.,Marine Innovation and Technology
Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE | Year: 2014

Many measurements of hurricane waves have been made from deep water production facilities in the Gulf of Mexico. Measurements made on different sides of the platforms differ from one another and the incident wave field because the platforms diffract and radiate waves. For many purposes, we would like to know the incident wave field. Forristall and Aubault (OMAE2013-10860) used WAMIT diffraction calculations to successfully invert wave spectra measured under a TLP model in the Marin offshore basin. We have now used similar techniques to invert spectra measured at offshore platforms during Hurricanes Gustav and Ike. We do not have any measurements of the undisturbed wave spectra for testing the results. The tests were made by checking whether inverse calculations on all the gauges deployed at different locations on the platforms could produce the same undisturbed wave field. Wave directions are needed for the diffraction calculations. Information from the wave gauges can be used to find the directions by optimizing the agreement among the inverted power spectra. To perform the optimization, we varied both the mean direction and spreading at each spectral frequency. The rms difference between the inverted probe spectral densities was minimized at each spectral frequency. When spectra from four gauges on a platform are inverted, they agree reasonably well with each other. The average of the inverted significant wave heights is slightly lower than the average of the measured significant wave heights. But when spectra from pairs of the four probes are inverted, the results differ depending on which pair is used. This result implies that our inversion method cannot be used on data from platforms with two probes, and casts doubt on the accuracy of four probe inversions. Copyright © 2014 by ASME.

Aubault A.,Marine Innovation and Technology | Yeung R.W.,University of California at Berkeley
Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE | Year: 2012

As high-speed ferry traffic is growing in near-shore areas, fuel efficiency of vessel operating in finite-depth waters becomes more critical. This can be achieved by introducing multi-hulls and minimizing the wave resistance by a proper configuration of the hulls. The wave resistance of thin-hulled vessels can be computed within Michell's theory. Based on this principle, Yeung et al. (2004) introduced a formulation of the interference wave resistance on multi-hull vessels in deep water, after linearization of the boundary conditions. The method is generalized to any water-depth in this paper. Havelock(1921) derived the wave resistance of a single-hull vessel in finite-depth water. An expression of the interaction resistance between two hulls in finite-depth waters is derived, using a distribution of Havelock sources on the hulls. It is shown that the interference resistance may be defined as a function of geometric variables and a length-based Froude number and depth-based Froude number. The effect of sub-criticality, criticality and supercriticality of depth-based Froude number on the interference resistance is explored. The computation of the total wave resistance of two hulls is extended to vessels with any number of hulls. The application of this solution method is demonstrated. With the use of the formulation, multi-hull designs are optimized with respect to the geometric distribution of hulls as well as forward speed and water depth. The design of multi-hull vessels illustrates how an optimized design is quickly obtained. Design decisions early in the design process can therefore be facilitated by this procedure. Copyright © 2012 by ASME.

Roddier D.,Marine Innovation and Technology
Mechanical Engineering | Year: 2010

StatoilHydro, the developer of the HyWind project, and Principle Power, which is working on the WindFloat concept, are partnered with existing commercial offshore wind turbine manufacturers and are designing their floating foundations to be compatible with many kinds of turbines. This reduces the technical and financial risks significantly, since the hulls are designed according to offshore oil and gas rules, supporting the knowledge base of an industry with decades of experience in building floating structures. The design of floating structures usually involves hydrodynamics tools such as WAMIT Inc.'s software for studying wave interactions with vessels and platforms, or Principia's DIODORE, to predict the hydrodynamic quantities, such as added mass, damping and wave exciting forces, which are used as a kernel in the time domain simulations. There are currently no commercial numerical design tools on the market capable of calculating the complete response of a floating wind turbine and substructure fully coupled.

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