74 research outputs found
Layout Optimisation of Wave Energy Converter Arrays
No full textThis paper proposes an optimisation strategy for the layout design of wave energy converter (WEC) arrays. Optimal layouts are sought so as to maximise the absorbed power given a minimum q-factor, the minimum distance between WECs, and an area of deployment. To guarantee an efficient optimisation, a four-parameter layout description is proposed. Three different optimisation algorithms are further compared in terms of performance and computational cost. These are the covariance matrix adaptation evolution strategy (CMA), a genetic algorithm (GA) and the glowworm swarm optimisation (GSO) algorithm. The results show slightly higher performances for the latter two algorithms; however, the first turns out to be significantly less computationally demanding
Global Fatigue Life Modelling of Steel Half-pipes Bolted Connections
No full textAbstractA steel hybrid structural solution for onshore wind turbine towers was proposed in the European project SHOWTIME. This solution is used in the lattice structure for the lower portion of the tower. Recently, a procedure for fatigue life estimation of steel half-pipes bolted connections applied in global structural models using multiaxial Smith-Watson-Topper (SWT) criteria was proposed by Öztürk et al. In this paper a procedure for design S-N curve modelling of steel half-pipes bolted connections is proposed. This procedure is based on a local approach using multiaxial fatigue criteria together with an elastoplastic analysis using the finite element method. The materials to be used in this analysis are the S355 and S690 steels. This evaluation to be performed is calibrated with experimental results of fatigue tests of the connection under consideration
Numerical modelling of flows involving submerged bodies and free surfaces
No full textKinetic energy extraction devices for ocean and river flows are often located in the
vicinity of the fluid free surface. This differs from wind turbines where the atmosphere
may be considered to extend to infinity for the purposes of numerical modelling. As
most kinetic energy extraction devices are based on lifting surfaces, a numerical model
is sought which can model both lifting and free surface flows. One such model is the
boundary element method which has been successfully applied to free surface problems
and to lifting flows as well as the combined problem.
This study seeks to develop a high order boundary element method that is capable
of modelling unsteady lifting and free surface flows in three dimensions. Although high
order formulations of boundary element methods are common for free surface problems,
providing improved accuracy and computational time, their usage for lifting flows is
less frequent. This may be due to the hypersingular boundary integral equation (HBIE)
which must be solved in order to find the velocity of the vortex wakes behind lifting
surfaces.
In previous lifting flow studies using high order boundary element methods the
wake velocities have been determined at the element centres and then interpolated to
the collocation points. Not until the paper of Gray et al. (2004b) has a method been
available for the direct solution of the HBIEs at the edges of three dimensional high
order elements with C0 continuous interfaces. The solution employs a technique known
as the Galerkin boundary element method.
This study shows, for the first time, that the Galerkin boundary element method is
applicable to the solution of the HBIE on the vortex wake of a lifting body. The
application of the technique is then demonstrated as part of the numerical model
developed herein. The model is based on the high order boundary element method
developed by Xu (1992) for non-linear free surface flows. This formulation is extended
to include steady uniform flow throughout the computational domain as well as the
presence of lifting and non-lifting bodies. Several verification cases are implemented to
test the accuracy of the model
Intervenciones afectivas al archivo materno en "La caja Topper" de Nicolás Gadano
No full textThrough the study of the autobiographical novel La caja Topper by Nicolás Gadano (2019), this article addresses the uses of the archive in the narratives of the children of victims ––in a broad sense–– of the last Argentine military dictatorship. Following the theoretical propositions of Jacques Derrida, Sara Ahmed, and Adriana Cavarero, we analyze the interventions that Gadano makes on the objects that his mother kept in a sneaker box as memorabilia of the family exile experience. First, we study the way in which the old box and the objects contained in it function as a matriarchive. Second, we analyze the operations that Gadano performs on the materiality, content, and ordering of the objects in the box, which produces a generational transfer of authority over the archive. Finally, we conclude that, through his fidelity to the maternal affective style, the author disassembles the traditional model of emotional labor division, reshaping the links between gender, generations, and memory.Com base no estudo do romance autobiográfico La caja Topper de Nicolás Gadano (2019), este artigo aborda os usos do arquivo nas narrativas dos filhos das vítimas da última ditadura militar argentina. Partindo das proposições teóricas de Jacques Derrida, Sara Ahmed e Adriana Cavarero, são analisadas as intervenções que, por meio da escrita do livro, Gadano faz sobre os objetos pertencentes à experiência familiar do exílio, que a mãe guardava em uma caixa de tênis. Em primeiro lugar, é estudado como a velha caixa e os objetos nela contidos funcionam como um matriarquivo. Em segundo lugar, são analisadas as operações que o livro realiza sobre a materialidade, o conteúdo e a ordenação dos objetos na caixa, para produzir uma transferência geracional da autoridade sobre o arquivo. Finalmente, conclui-se que, com sua fidelidade ao estilo afetivo materno, La caja Topperproduz uma desarticulação do modelo tradicional da divisão do trabalho emocional, que reconfigura os vínculos entre gênero, gerações e memória.A partir del estudio de la novela autobiográfica La caja Topper (2019) de Nicolás Gadano, este artículo aborda los usos del archivo en las narrativas de hijos de víctimas —en sentido amplio— de la última dictadura militar argentina. Desde las proposiciones teóricas de Jacques Derrida, Sara Ahmed y Adriana Cavarero se analizan las intervenciones realizadas por Gadano sobre los objetos pertenecientes a la experiencia familiar del exilio resguardados por la madre en una caja de zapatillas. En primer lugar, se estudia el modo en que la antigua caja y los objetos allí contenidos funcionan como un matriarchivo. En segundo lugar, se analizan las operaciones que Gadano realiza sobre la materialidad, el contenido y el ordenamiento de los objetos de la caja, para realizar un traspaso generacional de la autoridad sobre el archivo. Finalmente, se concluye que, con su fidelidad al estilo afectivo materno, el autor produce una desarticulación del modelo tradicional de la división del trabajo emocional, que reconfigura vínculos entre género, generaciones y memoria
Mean Stress Effect in Stress-Life for Hard Steels
No full textThe work in this thesis examines the effect of mean stress on the fatigue behaviour of very hard (Rockwell C 60) steels (AISI 8822, 8620, 9310, and cold-worked pre-stressing wire). In the mean stress tests, the minimum stress in the fatigue cycle was varied from test to test over a range from -1200 MPa to a value approaching the true fracture stress of each material. The results are not adequately explained by current theories for the effect of mean stress on fatigue behaviour in the region of compressive mean stresses. All current theories suggest that the maximum stress at the fatigue limit decreases with decreasing minimum stress. The results of this study shows that instead of continuing to decrease with decreasing minimum stress the maximum stress at the fatigue limit remains constant indicating an insensitivity to the minimum stress in the fatigue cycle for minimum stresses below the value in a fully reversed fatigue test. The theory proposed by the author corrects this error by maintaining the maximum stress at the fatigue limit constant with decreasing minimum stress in the region of negative mean stresses. The results are of interest to designers of components in which high negative residual stresses are introduced into materials hardened by, for example, carburizing, nitriding, or induction hardening to improve the fatigue strength of components. The present work allows considerably higher design stresses for operating stresses in the negative mean stress region than previous theories permit
Identifying the Frontier of Knowledge for Marine Renewable Energy Research
No full textAbstract|Verication and validation techniques canprovide a strategic framework for improving the predic-tive capability of numerical models used in the marinerenewable energy sector. In addition, it is proposed thatthe adoption of open source community models makeimplementing such strategies more straightforward. Atechnique of particular interest is the Phenomena Iden-tication and Ranking Table (PIRT). Such a table canbe used to quantify the current state of knowledge andthe subsequent requirements for improving the predic-tive capability of modelling software. After assessingand collating the current software usage trends withinthe wave and tidal numerical modelling community, anexample PIRT is presented for tidal energy converterhydrodynamics
Aerodynamic Shaping of a Propulsive Fuselage Concept: A Design Space Exploration
No full textBoundary layer ingestion is an airframe-propulsion integration technology capable of enhancing aircraft propulsive efficiency. The Propulsive Fuselage Concept, a tube-and-wing layout with an rear-fuselage-mounted propulsor in the boundary layer ingestion configuration, especially takes advantage this. However, the relation between physical shape and aerodynamic performance, resulting from the complex airframe-propulsor interaction, is not entirely understood. Also, contrary to long-haul aircraft, few studies have investigated the application of the concept on medium-haul aircraft with only 10% cruise thrust contribution coming from the boundary layer ingestion propulsor, which is a top-level requirement of the APPU project. To facilitate parametric studies regarding these research gaps, a parametric model is developed and implemented in an engineering design application that automates aerodynamic analysis to high degree. This thesis presents a methodology to numerically analyze axisymmetric propulsive fuselage concept designs; an engineering design application using the knowledge based engineering technology is presented that facilitates the implementation of complex engineering design rules in the construction of the parametric model. The application consist of three components. Firstly, a flexible geometric parameterization in 2D is developed that is proven capable of constructing well-performing designs. A translation mechanism is developed between these geometric input parameters and input parameters for class shape transformation curves, which form the mathematical basis for the geometry. Secondly, the construction of a C-shaped domain and a multi-block structured mesh are also automated in the application. The mesh density for this application was verified through a mesh convergence study, and can be adjusted to fit other mesh requirements through various mesh control capabilities. Lastly, the scripted interaction between the application and ANSYS Fluent software is automated. A fan modeling methodology was developed using boundary conditions that requires only fan pressure ratio as input, while mass flow continuity through the fan is ensured. The meshing and simulation routines are validated by comparing the results of the presented routine to that of a status-quo numerical simulation. All relevant aerodynamic output parameters show agreement in a range of 3.3%.The working of the engineering design application is demonstrated in a design space exploration based on the hypothesis that increased conicity of the rear fuselage and nacelle shape with respect to the longitudinal axis can reduce the required fan power in cruise conditions. To isolate the effect of conicity, a parameter sweep was conducted. Results show that with increasing conicity, the overall viscous dissipation was continuously reduced. Also the total pressure recovery at the fan inlet face increases up to a nacelle conical angle of 11 degrees, after which this decays due to increased wetted area. At 11 degrees conicity, the aerodynamic efficiency (defined as fan power required for a given net propulsive force) was increased by 0.81% relative to a less conical status-quo baseline design with 6 degrees conicity. The increased fuselage volume and wetted area due to increased conicity introduced the opportunity to shorten the fuselage without decreasing fuselage volume. This increased aerodynamic efficiency by 1.65% relative to the baseline. Also, as the intake diffusion functionality was redundant in this flow field, a third design was constructed with a 29% shorter intake duct, which increased aerodynamic efficiency by 1.81% compared to the baseline. Demonstrated by these unoptimized designs and the observed physical mechanisms, it is concluded that aerodynamic efficiency could benefit from the direct and indirect effects of an increase in conicity of the propulsive fuselage concept.APPU ProjectAerospace Engineerin
Identifying the Frontier of Knowledge for Marine Renewable Energy Research
No full textAbstract|Verication and validation techniques canprovide a strategic framework for improving the predic-tive capability of numerical models used in the marinerenewable energy sector. In addition, it is proposed thatthe adoption of open source community models makeimplementing such strategies more straightforward. Atechnique of particular interest is the Phenomena Iden-tication and Ranking Table (PIRT). Such a table canbe used to quantify the current state of knowledge andthe subsequent requirements for improving the predic-tive capability of modelling software. After assessingand collating the current software usage trends withinthe wave and tidal numerical modelling community, anexample PIRT is presented for tidal energy converterhydrodynamics
Acerca de algunas tradiciones orales de los amaziges del Alto Atlas marroquí.
No full text The author claims to have found still-alive traits of primitive byzantian christianism of the northern Africa in the folklore of Moroccan Imazighen, along with rests of even more ancient catastrophic myths.En el folklore de los amaziges marroquíes encuentra el autor huellas aún vivas de los ritos de un primitivo cristianismo bizantino del África del Norte, así como restos de mitos catastrofistas mucho más antiguos
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