Frequency-domain and stochastic model for an articulated wave power device

To have the first look into device performance, analytical and numerical tools must be used. Assuming that the wave power system hydrodynamics has a linear behaviour, diffraction and radiation coefficients can be computed. If the power take-off equipment may be, for the first approach, regarded as holding a linear behaviour then overall (i.e. hydrodynamic plus mechanical) device performance can be studied for regular waves. In this study a frequency-domain model describes the articulated system behaviour for regular waves. For this paper a stochastic model is found for an articulated wave power device, and probability density functions are defined for the relevant parameters that characterize the wave power system behaviour. For these parameters and for different sea states the probability density functions are found. The articulated system is characterized by these probability density functions. Also, average values for capture width are obtained for these sea state conditions

Stochastics, Time Domain Models and Pontryagin Maximum Priciple for a Two Body Wave Power Device

In this study a stochastic model to describe the behaviour of an articulated system is developed.Optimal mechanical damping and spring coefficients are computed. Probability density functions are defined for the relevant parameters that characterize the device behaviour. For these parameters and for different sea state conditions the probability density functions are found and the articulated system is characterized in terms of these functions. Average values for useful power and capture width are also obtained for these sea state conditions. Time domain models allow the computation of time series for the variables that chracterize the wave power system behaviour. In this study a time domain model is also developed for the articulated wave power device. Results are obtained for regular and irregular waves. Pontryagin Maximum Principle is presented as an algorithm for the control of the device

Melting temperature of screened Wigner crystal on helium films by molecular dynamics

Using molecular dynamics (MD) simulation, we have calculated the melting temperature of two-dimensional electron systems on $240$\AA-$500$\AA helium films supported by substrates of dielectric constants $\epsilon_{s}=2.2-11.9$ at areal densities $n$ varying from $3\times 10^{9}$ cm$^{-2}$ to $1.3\times 10^{10}$ cm$^{-2}$. Our results are in good agreement with the available theoretical and experimental results.Comment: 4 pages and 4 figure

Frequency and Stochastic Domain Models for Two Geometries of the IPS Wave Power Buoy

Frequency-domain analysis is applied to a geometry of the original IPS buoy device concept. The analysis is particularly useful in the early development stages to establish the response of power take-off mechanism characteristic parameters to different frequencies of the wave spectrum. Optimal mechanical damping and spring coefficients are computed for some parameters restrictions. Absorbed power, capture width and other variables, such as relative displacement,are computed for regular waves and these optimal mechanical coefficients. A stochastic model is developed in order to evaluate the IPS buoy behaviour for irregular waves’ conditions. This allows defining probability density functions for parameters that characterize the device’s behaviour. Assuming that the overall system behaviour is linear and that the surface elevation for irregular waves may be regarded as a stochastic process with a Gaussian probability density function, the variables that define the system behaviour, such as bodies’ displacements and velocities, will also hold a Gaussian probability density function. The average power extraction is computed for different sea state conditions.Aiming to enhance the device’s hydrodynamic performance, a new non-axisymmetric IPS geometry is conceived. Using the stochastic modelling approach, the device’s behaviour is studied for several wave directions and compared to the axisymmetric configuration’s behaviour

Um modelo.

Volume especial, 1900, p. 62-63

Abade de Tagilde.

30 Jan.-Dez. 1913, p. 7-18

Transverse Myelitis

Os autores apresentam três casos de mielite transversa de instalação aguda em doentes jovens, salientando a possível gravidade do quadro neurológico, a necessidade de excluir uma causa potencialmente tratável e a controvérsia da terapêutica com corticosteroides

A method to consider the nonlinear behaviour of reinforced concrete in flexible earth-retaining walls: preliminary results

This paper presents a numerical methodology to incorporate in finite element analyses of deep excavations the nonlinear behaviour of reinforced concrete walls. This method is based on the interaction between two well validated numerical models: one used for incremental analysis of geotechnical works (but assuming concrete as linear elastic) and the other used for nonlinear analysis of reinforced concrete structures taking into account the characteristics of the concrete and the steel reinforcement at each structural section. The analysis of an excavation in clay supported by a single propped diaphragm wall is presented as an example of application. It is shown how the consideration of the nonlinear behaviour of reinforced concrete influences the global performance of the retaining structure

Firm preparation for ISO 9001 certification: the case of the hotel industry in Portugal

The purpose of this study is to assess whether companies conduct preparations, such as managing culture, before starting to implement an ISO 9001 Quality Management System (QMS). Based on a literature review, the paper develops a model of firm preparation for ISO 9001 certification and several research hypotheses. The survey research method adopted consists of data collection through questionnaires – sent to hotels of four and five stars, in Portugal, in two different moments (2012 and 2014) – and of a longitudinal data analysis based on non-parametric statistical tests. Results show that the majority of companies conduct preparations before starting to implement an ISO 9001 QMS. However, most companies do not assess their initial situation, nor do they plan for the preparations. One of the significant implications from this research is that a more coherent and integrated approach in ISO 9001 preparation is required. Other implications for practice and for research are also noted. This is the first study, as far as the authors are aware of, that addresses the topic of planning for the preparations that a company can make before starting to implement an ISO 9001 QMS.Fundação para a Ciência e a Tecnologia (grant UID/ECO/04007/2013) e FEDER/COMPETE (POCI-01-0145- FEDER-007659)info:eu-repo/semantics/publishedVersio