Hybrid frequency–time domain models for dynamic response analysis of marine structures

Time-domain models of marine structures based on frequency domain data are usually built upon the Cummins equation. This type of model is a vector integro-differential equation which involves convolution terms. These convolution terms are not convenient for analysis and design of motion control systems. In addition, these models are not efficient with respect to simulation time, and ease of implementation in standard simulation packages. For these reasons, different methods have been proposed in the literature as approximate alternative representations of the convolutions. Because the convolution is a linear operation, different approaches can be followed to obtain an approximately equivalent linear system in the form of either transfer function or state-space models. This process involves the use of system identification, and several options are available depending on how the identification problem is posed. This raises the question whether one method is better than the others. This paper therefore has three objectives. The first objective is to revisit some of the methods for replacing the convolutions, which have been reported in different areas of analysis of marine systems: hydrodynamics, wave energy conversion, and motion control systems. The second objective is to compare the different methods in terms of complexity and performance. For this purpose, a model for the response in the vertical plane of a modern containership is considered. The third objective is to describe the implementation of the resulting model in the standard simulation environment Matlab/Simulink.     

Mineral equilibria constraints on open‐system melting in metamafic compositions

The recent development of activity–composition relations for mineral and melt phases in high‐grade metamafic rocks allows mineral equilibria tools to be used to further aid our understanding of partial melting and the mineralogical consequences of melt segregation in these rocks. We show that bulk compositional data from natural amphibolites cover a wide compositional range, with particular variability in the content and ratios of Ca, Na and K indicating that low‐grade metasomatic alteration can substantially alter the igneous protolith chemistry and potentially affect the volume and composition of melt generated. Mineral equilibria calculations for five samples that span the compositional variability in our data set indicate that melting occurs primarily via the fluid‐absent breakdown of amphibole+quartz to produce a pressure‐sensitive peritectic assemblage of augite, orthopyroxene and/or garnet. The introduction of orthopyroxene at the onset of the amphibolite‐to‐granulite‐facies transition at lower pressure results in an increased rate of melt production until quartz is typically exhausted, and this is similarly seen for the introduction of garnet at higher pressure. Calculated melt compositions are dependent on the protolith composition, but initial solidus melting and biotite breakdown produce 1–3 mol.% of K‐rich granitic melts. As hornblende melting proceeds, 15–20 vol.% of either more granodioritic‐to‐tonalitic or granodioritic‐to‐trondhjemitic melt is produced. Once quartz is exhausted, intermediate to mafic melt compositions are produced at ultrahigh‐temperature conditions. Quartz‐rich lithologies with high Ca coupled to low Na and K are the most fertile under orogenic conditions, yielding up to 25 mol.% of sub‐alkalic granitic melt by 850°C. Such rocks did not experience significant subsolidus alteration. Altered compositions with low Ca and elevated Na and K are not as fertile, yielding less than 15 mol.% of alkalic granitic melt by 850°C. These melt volumes are enough to be segregated, and can make a contribution to granite magmatism and intracrustal differentiation that should not be overlooked.     

High-resolution analysis of submarine lobes deposits: Seismic-scale outcrops of the Lauzanier area (SE Alps, France)

The Lauzanier area represents the northernmost extension of the Annot Sandstone series and contains deposits between 650 and 900 m-thick. This basin was active from upper Bartonian or lower Priabonian to early Rupelian. It is composed of two superposed units separated by a major unconformity. The sediment supply is due to channelled flows coming from the south. Flow processes include mass flow to turbidity currents. The size of the particles and the absence of fine-grained sediment suggest a transport over a short distance. The Lower Unit is made of coarse-grained tabular beds interpreted as non-channelled lobe deposits. The Upper Unit is made of massive conglomerates interpreted as the channelled part of lobes. These lobe deposits settle in a tectonically confined basin according to topographic compensation that occurs from bed scale to unit scale. The abrupt progradation between the lower and the upper unit seems related to a major tectonic uplift in the area. This uplift is also suggested by a change in the petrographic nature of the source and an abrupt coarsening of the transported clasts.This field example allows providing high resolution analysis for depositional sedimentary sequences of terminal lobe deposits in a coarse-grained turbidite system. The outcrop analysis shows the lateral evolution of deposits and the system progradation allows a longitudinal analysis of facies evolution by superposing on the same outcrops the channelled lobe system and the non-channelled lobe system. These results of high-resolution outcrop analysis can be extrapolated to results obtained on sedimentary lobes in recent deep-sea turbidite system that are either restricted to cores, or with a lesser resolution (seismic).     

Practical aspects of frequency-domain identification of dynamic models of marine structures from hydrodynamic data

The motion response of marine structures in waves can be studied using finite-dimensional linear-time-invariant approximating models. These models, obtained using system identification with data computed by hydrodynamic codes, find application in offshore training simulators, hardware-in-the-loop simulators for positioning control testing, and also in initial designs of wave-energy conversion devices. Different proposals have appeared in the literature to address the identification problem in both time and frequency domains, and recent work has highlighted the superiority of the frequency-domain methods. This paper summarises practical frequency-domain estimation algorithms that use constraints on model structure and parameters to refine the search of approximating parametric models. Practical issues associated with the identification are discussed, including the influence of radiation model accuracy in force-to-motion models, which are usually the ultimate modelling objective. The illustration examples in the paper are obtained using a freely available MATLAB toolbox developed by the authors, which implements the estimation algorithms described.     

The 2011 expedition to the El'gygytgyn impact structure,Northeast Russia: Toward a new geological map for the crater area

El'gygytgyn is a 3.6 Ma, 18 km diameter, impact crater formed in an approximately 88 Ma old volcanic target in Northeast Siberia. The structure has been the subject of a recent ICDP drilling project. In parallel to those efforts, a Russian‐German expedition was undertaken in summer 2011 to investigate the permafrost soil, lake terraces, and the volcanic rocks of the southern and eastern crater rim. This provided the unique opportunity for mapping and sampling of the volcanic target rocks around a large part of this complex impact structure. Samples from 43 outcrops were collected and analyzed petrographically and geochemically. The results were combined with earlier mapping outcomes to create a new geological map of this impact structure and its immediate environs, at the scale of 1:50,000. Compositions of our rock suites are compared with the lithologies of the 2009 ICDP drill core. The ignimbrite described as lower bedrock in the ICDP drill core shows petrographically and chemically strong similarities to the rhyolitic and rhyodacitic ignimbrites observed on surface. The suevite sequence exposed in the ICDP drill core is a mixture of all observed target rocks at their respective proportions in the area. In contrast to previous studies, the calculated average target composition of El'gygytgyn takes the contribution of the basic target rocks into consideration: mafic and intermediate rocks approximately 7.5%, and felsic rocks approximately 92.5%.     

Climate change policy responses for Canada's Inuit population: The importance of and opportunities for adaptation

We identify and examine how policy intervention can help Canada's Inuit population adapt to climate change. The policy responses are based on an understanding of the determinants of vulnerability identified in research conducted with 15 Inuit communities. A consistent approach was used in each case study where vulnerability is conceptualized as a function of exposure-sensitivity to climatic risks and adaptive capacity to deal with those risks. This conceptualization focuses on the biophysical and human determinants of vulnerability and how they are influenced by processes and conditions operating at multiple spatial-temporal scales. Case studies involved close collaboration with community members and policy makers to identify conditions to which each community is currently vulnerable, characterize the factors that shape vulnerability and how they have changed over time, identify opportunities for adaptation policy, and examine how adaptation can be mainstreamed. Fieldwork, conducted between 2006 and 2009, included 443 semi-structured interviews, 20 focus groups/community workshops, and 65 interviews with policy makers at local, regional, and national levels. Synthesizing findings consistent across the case studies we document significant vulnerabilities, a function of socio-economic stresses and change, continuing and pervasive inequality, and magnitude of climate change. Nevertheless, adaptations are available, feasible, and Inuit have considerable adaptive capacity. Realizing this adaptive capacity and overcoming adaptation barriers requires policy intervention to: (i) support the teaching and transmission of environmental knowledge and land skills, (ii) enhance and review emergency management capability, (iii) ensure the flexibility of resource management regimes, (iv) provide economic support to facilitate adaptation for groups with limited household income, (v) increase research effort to identify short and long term risk factors and adaptive response options, (vi) protect key infrastructure, and (vii) promote awareness of climate change impacts and adaptation among policy makers.     

Some medium-path infrared observations of atmospheric boundary-layer structure during light wind

Variations in water-vapour absorption were measured using a recently constructed field spectrophotometer, operated at a wavelength of 1.38 gm and with path lengths of 15 and 20 m. Observations were made 1 m above the ground near sunset, dawn, and during the morning destruction of nocturnal atmospheric stability. A diurnally consistent evolution of water-vapour turbulence regimes was observed. The presence of ordered events was revealed. These fluctuations indicate changes of vapour pressure, spatially averaged over the base-line, as large as about +7 mb in 4 s. Classification of light-wind observing conditions by using six classes of distinct non-random events appears possible. Such a classification system may reduce some of the characteristic scatter of micrometeorological results which arises during stable observing conditions or during comparison of real-world observing sites.On sabbatical leave (1975) at the Royal Military College of Science, Shrivenham, Wilts., England.     

Spatial and Temporal Validation of In-Situ and Satellite Weather Data for the South West Agricultural Region of Australia

Seasonal variations in weather have significant impacts on crop yields. The accuracy of weather data is an import-ant consideration for crop yield models. This ...