1,720,954 research outputs found
Experimental study into the effect of wind-ice misalignment on the development of ice-induced vibrations of offshore wind turbines
No full textThe effect of misalignment between wind- and ice loading direction on the development of ice-induced vibrations of offshore wind turbines has been investigated experimentally. In the experiments a hybrid test setup was used to study the structural response to combined loading from physical model ice and numerically applied wind. The motivation for this study was the high uncertainty in the design of offshore wind turbine support structures in cold regions, caused by scarcity of full-scale and model-scale data on ice-structure interaction. Test results revealed that misaligned scenarios result in the development of sustained ice-induced vibrations in the ice load direction. The test results also showed that ice-induced vibrations can develop up to higher ice drift speeds for misaligned scenarios than for aligned scenarios. Both observations are considered to be related to low total damping in the ice drift direction for a misaligned scenario. Further comparison between a 90°-misaligned operational and an aligned idling scenario revealed that wind-induced structural displacements perpendicular to the ice drift direction do not cause the ice to fail. On the contrary, it was shown that the ice constrains the wind-induced motion for low relative velocities between ice and structure. For high relative velocities, wind-induced displacements approach those in open water as the ice fails in rapid succession at the sides of the structure during crushing. The analysis of a misaligned scenario with a smaller misalignment angle revealed that vibrations occur perpendicular to the ice drift direction and are characterized by relatively low amplitude and high frequency. The ice, being in contact with the structure, neither prevented those vibrations nor failed.</p
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
On the dependency of the development of frequency lock-in on the mode shape amplitude for higher structural modes
No full textDrifting sea ice failing in crushing against vertically-sided offshore structures can cause ice-induced vibrations. Offshore structures are typically founded on slender structures to minimize the load effect of waves and currents. In combination with large top masses, those offshore structures often provide sufficient compliance for ice-induced vibrations to develop. Although modern offshore structures can be expected to experience ice-induced vibrations in higher structural modes, this phenomenon is rarely considered during experiments and numerical analysis of dynamic ice-structure interaction. Inspired by this challenge, we investigated experimentally how the sole change of mode shape amplitude relation between higher structural modes at the water level of a multi-degree-of-freedom structure influences the development of frequency lock-in. Experiments of four different multi-degree-of-freedom structures in cold model ice have been performed in Aalto Ice and Wave Tank. To allow full control over the eigensystem during testing, modal representations of structures wereimplemented in the numerical domain of a hybrid test setup. When changing the mode shape amplitude, the total structural stiffness at the ice action point and modal damping as a fraction of critical were kept constant between the four structures. We found that the structureexperienced sustained frequency lock-in vibrations in a frequency corresponding to the mode shape amplitude of artificially high magnitude. When mode shape amplitudes of two eigenmodes were equalized, the structure experienced oscillations in the frequency of the mode with lower frequency or lower damping mainly. It was found that ice-induced vibrations of multi-degree-of-freedom structures are highly dependent on the relative velocity between the ice and structure and thus on the superposition of higher mode oscillations with lower mode oscillations.Offshore Engineerin
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Dynamic ice-structure interaction for jacket substructures
No full textWith a growing global demand of clean renewable energy, offshore wind activities will extend to more harsh environments, including sub-arctic areas like the Baltic Sea. Sea ice can occur here which needs to be taken into consideration in the design of substructures, i.e. jacket substructures, of offshore wind turbines. Several ice mitigating measures exist for jacket substructures, of which one is disregarding braces crossing the waterline. In this way, ice cannot induce loads to the relatively slender braces in the jacket. However, disregarding these braces has disadvantages in terms of structural integrity in comparison to a jacket including these braces.In Part I of this thesis, two types of jackets, one without (Type 1) and one with (Type 2) waterline crossing braces, are implemented in a numerical model and subjected to ice loading in order to conclude whether the use of a Type 1 jacket design can be justified or whether a Type 2 jacket design is also suitable in sub-arctic areas. Since over the past years the modelling techniques regarding ice-structure interaction have been updated and improved significantly, assessing the loads at the jacket braces can be done more accurately, allowing to give a more thorough conclusion on whether to use braces crossing the waterline on jackets in sub-arctic areas. As a result, a design including these braces could become feasible, whereas in the past it would be disregarded.Two types of ice failure are considered in this research, being ice bending failure and ice crushing failure. First, a model is developed to quantify the ice actions occurring at a jacket substructure as function of the approach angle of the ice direction relative to the structure and as function of an introduced 'threshold angle'. It was found that ice failing in bending is equally significantly present as ice failing in crushing. Subsequently, numerical models are introduced that describe the failure behaviour of bending and crushing ice and the force that both ice failure types will induce to the structure. The structure is represented by a 5 [MW] offshore reference turbine supported by a jacket substructure. Using these models, dynamic simulations are performed in order to investigate the local susceptibility to ice induced vibrations (IIV), as well as assessing the Ultimate Limit State (ULS) load at the braces. As a result, local brace IIV regimes could be recognised, however sustained frequency lock-in could not be observed. Furthermore, it was found that a Type 2 jacket could be suitable to use in sub-arctic areas considering the ULS load effects due to ice loading, but care should be taken for the ULS brace load, as that is of great importance for the design.In Part II of this thesis, it is assessed whether coupled dynamic ice-structure interaction can be modelled using a dynamic substructuring modelling technique, also known as Craig-Bampton method, since it is industry practice to use such a method when jackets are involved. This method is based on a model order reduction of the full finite element model representing the structure, resulting in improved computational time and allowing assembly of multiple (reduced) substructures. The method is successfully implemented allowing to solve coupled ice-structure interaction problems and a framework to do so is provided. It is shown that excluding the loaded degrees of freedom (DoFs) in the jacket from the reduction leads to more accurate results and is considered convenient since few DoFs are loaded by ice, maintaining the effectiveness of the reduction method. As a result, IIV can be investigated using this reduction method, however challenges related to the accumulation of numerical accuracy errors arise with truncation of more higher frequency modes and require further development to be resolved.Offshore and Dredging Engineerin
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