895 research outputs found
A New Systematic Series of Foil Sections with Parallel Sides
Parallel-sided foil sections are used for centerboards and rudders in sailing dinghy classes and also for struts placed in a fluid flow. The objective of this work is to create a systematic series of parallel-sided sections to be used under different conditions, with an emphasis on the sailing dinghies 470, 420 and Optimist. The loss, and surprisingly the gain, in performance relative to 4-digit NACA sections are also investigated. A 2D Reynolds-averaged Navier–Stokes solver is used with the k-! SST turbulence model and the gamma transition criterion. A verification study is carried out based on four grids of systematically varied density, and results compared with experimental data on a NACA 64-006 section. The parallel-sided sections are modeled with rational B\ue9zier curves whose geometrical parameters permit to link the shape of the profile to physical variables, which are systematically varied. Three Reynolds numbers and two angles of attack are investigated. Systematic plots show the influence of the trailing edge angle and nose radius for the different section families, and the optimum combination is presented in a table. Physical explanations of the trends, and of the exceptions, are given in the paper, using flow visualizations as well as pressure and friction plots
Parametric Hull Design with Rational BĂ©zier Curves and Estimation of Performances
In this paper, a tool able to support the sailing yacht designer during the early stage of the
design process has been developed. Cubic Rational BĂ©zier curves have been selected to describe the
main curves defining the hull of a sailing yacht. The adopted approach is based upon the definition of
a set of parameters, say the length of waterline, the beam of the waterline, canoe body draft and some
dimensionless coefficients according to the traditional way of the yacht designer. Some geometrical
constraints imposed on the curves (e.g., continuity, endpoint angles, curvature) have been conceived
aimed to avoid unreasonable shapes. These curves can be imported into any commercial Computer
Aided Design (CAD) software and used as a frame to fit with a surface. The resistance of the hull can
be calculated and plotted in order to have a real time estimation of the performances. The algorithm
and the related Graphical User Interface (GUI) have been written in Visual Basic for Excel. To test the
usability and the precision of the tool, two existing sailboats with different characteristics have been
successfully replicated and a new design, taking advantages of both the hulls, has been developed.
The new design shows good performances in terms of resistance values in a wide range of Froude
numbers with respect to the original hulls
A machine learning approach for forecasting hierarchical time series
In this paper, we propose a machine learning approach for forecasting
hierarchical time series. When dealing with hierarchical time series, apart
from generating accurate forecasts, one needs to select a suitable method for
producing reconciled forecasts. Forecast reconciliation is the process of
adjusting forecasts to make them coherent across the hierarchy. In literature,
coherence is often enforced by using a post-processing technique on the base
forecasts produced by suitable time series forecasting methods. On the
contrary, our idea is to use a deep neural network to directly produce accurate
and reconciled forecasts. We exploit the ability of a deep neural network to
extract information capturing the structure of the hierarchy. We impose the
reconciliation at training time by minimizing a customized loss function. In
many practical applications, besides time series data, hierarchical time series
include explanatory variables that are beneficial for increasing the
forecasting accuracy. Exploiting this further information, our approach links
the relationship between time series features extracted at any level of the
hierarchy and the explanatory variables into an end-to-end neural network
providing accurate and reconciled point forecasts. The effectiveness of the
approach is validated on three real-world datasets, where our method
outperforms state-of-the-art competitors in hierarchical forecasting
Further evidence of the contribution of the ear canal to directional hearing: design of a compensating filter
It has been proven, and it is well documented in literature, that the directional response in HRTFs comes largely from the effect of the pinnae. However, few studies have analysed the contribution given by the remaining part of the external ear, particularly the ear canal. This work investigates the directionally dependent response of the modelled ear canal of a dummy head, assuming that the behaviour of the external ear is sufficiently linear to be approximated by an LTI system. In order to extract the ear canal\u27s transfer function, two critical microphone placements (at the eardrum and at the beginning of the cavum conchae) have been used. The system has been evaluated in several positions, along the azimuth plane and at different degrees of elevation. The results point out a non-negligible directional dependence that is well within the normal hearing range; based on these findings, physical models of the ear canal have been analysed and evaluated. We have also considered the practical application to binaural listening, and the colouration originated by the superimposition of the contribution of two ear canals (the listener\u27s and the dummy head\u27s). A compensating FIR filter with arbitrary frequency response is discussed as a possible fix
A Measurement-based Analysis of the Energy Consumption of Data Center Servers
Energy consumption is a growing issue in data centers, impacting their
economic viability and their public image. In this work we empirically
characterize the power and energy consumed by different types of servers. In
particular, in order to understand the behavior of their energy and power
consumption, we perform measurements in different servers. In each of them, we
exhaustively measure the power consumed by the CPU, the disk, and the network
interface under different configurations, identifying the optimal operational
levels. One interesting conclusion of our study is that the curve that defines
the minimal CPU power as a function of the load is neither linear nor purely
convex as has been previously assumed. Moreover, we find that the efficiency of
the various server components can be maximized by tuning the CPU frequency and
the number of active cores as a function of the system and network load, while
the block size of I/O operations should be always maximized by applications. We
also show how to estimate the energy consumed by an application as a function
of some simple parameters, like the CPU load, and the disk and network
activity. We validate the proposed approach by accurately estimating the energy
of a map-reduce computation in a Hadoop platform
The assessment of hemineglect syndrome with cancellation tasks. A comparison between the bells test and the Apples test
Unilateral spatial neglect (USN) is a frequent consequence of acquired brain injury, especially following right hemisphere damage. Traditionally, unilateral spatial neglect is assessed with cancellation tests such as the Bells test. Recently, a new cancellation test, the Apples test, has been proposed. The present study aims at comparing the accuracy of these two tests in detecting hemispatial neglect, on a sample of 56 right hemisphere stroke patients with a diagnosis of USN. In order to evaluate the agreement between the Apples and Bells tests, Cohen's kappa and McNemar's test were used to assess differences between the two methods of evaluation. Poor agreement and statistically significant differences emerged between the Apples and Bells tests. Overall, the Apples test was significantly more sensitive than the Bells test in detecting USN. Based on these results, the use of the Apples test for peripersonal neglect assessment is therefore highly recommende
Topology Optimization Design of Internal Reinforcements in a Sailing Dinghy
AbstractIn this paper, a novel approach has been followed based on FEM simulation and Topology Optimization tools to locate and model the reinforcements inside the hull of a sailing dinghy. This process assumes that the inner volume included between the hull and the deck is, at the beginning of the simulation, filled with material; then a portion of this inner volume is eroded until a final free form shape of the reinforcements is obtained. A key point of this procedure is the definition of the optimization constrains because the final shape of the reinforcements must fulfill several requirements such as weight, stiffness and stress. At the end of the optimization procedure, the final shape of internal reinforcements consists of a truss-like web frame with a final weight equal to the 18% of the initial full body
Parametric Hull Design with Rational BĂ©zier Curves
AbstractIn this paper, a tool able to support the sailing yacht designer during the early stage of the design process has been developed. Quadratic and cubic Rational BĂ©zier curves have been selected to describe the main curves defining the hull of a sailing yacht. The adopted approach is based upon the definition of a set of parameters, say the length of water line, the beam of the waterline, canoe body draft and some dimensionless coefficients according to the traditional way of the yacht designer. Some geometrical constraints imposed on the curves (e.g. continuity, endpoint angles) have been conceived aimed to avoid unreasonable shapes. These curves can be imported in any commercial CAD software and used as a frame to fit with a surface. The algorithm and the related Graphical User Interface (GUI) have been written in Visual Basic for Excel. To test the usability and the precision of the tool, two sailboats with different characteristics have been replicated. The rebuilt version of the hulls is very close to the original ones both in terms of shape and dimensionless coefficients
Improving the Downwind Sail Design Process by Means of a Novel FSI Approach
The process of designing a sail can be a challenging task because of the difficulties in
predicting the real aerodynamic performance. This is especially true in the case of downwind sails,
where the evaluation of the real shapes and aerodynamic forces can be very complex because of
turbulent and detached flows and the high-deformable behavior of structures. Of course, numerical
methods are very useful and reliable tools to investigate sail performances, and their use, also as a
result of the exponential growth of computational resources at a very low cost, is spreading more
and more, even in not highly competitive fields. This paper presents a new methodology to support
sail designers in evaluating and optimizing downwind sail performance and manufacturing. A new
weakly coupled fluid–structure interaction (FSI) procedure has been developed to study downwind
sails. The proposed method is parametric and automated and allows for investigating multiple
kinds of sails under different sailing conditions. The study of a gennaker of a small sailing yacht is
presented as a case study. Based on the numerical results obtained, an analytical formulation for
calculating the sail corner loads has been also proposed. The novel proposed methodology could
represent a promising approach to allow for the widespread and effective use of numerical methods
in the design and manufacturing of yacht sails
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