Abstract The paper presents a comparison between empirical and numerical quadratic transfer functions (QTFs) of the horizontal wave drift loads on the INO WINDMOOR floating wind turbine. The empirical QTFs are determined from cross bi-spectral analysis of model test data obtained in an ocean basin. Validation of the identified QTF is provided by comparing low frequency motions reconstructed from the empirical QTF with measurements. The numerical QTFs are calculated by a panel code that solves the wave-structure potential flow problem up to the second order. Systematic comparisons between numerical and empirical QTFs allows identification of tendencies of empirical QTFs and limitations of the second order potential flow predictions. The study is limited to hydrodynamic loads from waves only, i.e. without current. For small seastates, the results indicate that the second order potential flow predictions of the surge QTFs agree quite well with the wave drift coefficients identified empirically from the model test data. For moderate and high seastates, second order predictions underestimate the surge wave drift coefficients for all compared diagonals of the QTFs. The discrepancies between predictions and empirical coefficients are not small, especially at the lower frequency range (below around 0.10 Hz) where the potential flow wave drift forces tend to zero.
In order to assess the influence of reducing the speed limit from 50 km h-1 to 30 km h-1 in one-lane streets in local residential areas in large cities, real traffic tests for pollutant emissions and fuel consumption have been carried out in Madrid city centre. Emission concentration and car activity were simultaneously measured by a Portable Emissions Measurement System. Real life tests carried out at different times and on different days were performed with a turbo-diesel engine light vehicle equipped with an oxidizer catalyst and using different driving styles with a previously trained driver. The results show that by reducing the speed limit from 50 km h-1 to 30 km h-1, using a normal driving style, the time taken for a given trip does not increase, but fuel consumption and NOx, CO and PM emissions are clearly reduced. Therefore, the main conclusion of this work is that reducing the speed limit in some narrow streets in residential and commercial areas or in a city not only increases pedestrian safety, but also contributes to reducing the environmental impact of motor vehicles and reducing fuel consumption. In addition, there is also a reduction in the greenhouse gas emissions resulting from the combustion of the fuel.
The hydrodynamic forces and motions of floating cylinders with arbitrary cross section subjected to beam waves are studied in the time domain. The hydrodynamic radiation forces are represented by infinite frequency added masses and convolution integrals of memory functions. The exciting forces are calculated in the frequency domain. The hydrostatic forces are evaluated both around the mean equilibrium position and over the instantaneous wetted surface in order to assess the effect of the non-linearity of these forces. Results of sway, heave and roll motions are presented for cylinders with rectangular and triangular cross section shapes.
Abstract Most of the floating wind turbine (FWT) sub-structure concepts are designed with long natural periods of the vertical motions to de-tune from the wave frequency range. The consequence is that the natural frequencies of heave, roll and pitch are excited by low frequency wave and wind loads. The paper focus is on the low frequency (LF) wave drift loads and the related heave and pitch responses of a semi-submersible type of FWT (12MW INO WINDMOOR). It presents several approaches to calculate the wave drift force coefficients and related forces in irregular waves, namely mean wave drift coefficients combined with Newman’s approximation, quadratic transfer functions (QTFs) neglecting the free surface integral from the 2nd order potential flow solution and QTFs based on the full 2nd order solution. The different approximations are used to perform nonlinear time domain simulations of the FWT motions and the results compared to the model test data (the model tests were performed in the ocean basin of SINTEF at a scale of 1:40). The LF damping of heave and pitch is represented by a linear and a quadratic damping coefficient identified from decay model tests. The coupled numerical solution requires a correct representation of the surge mode of motion. In this case, the wave drift forces are represented by empirical QTFs, while the LF damping includes a contribution from the calm water damping represented by a linear and a quadratic coefficient, together with a wave drift damping coefficient. The numerical results show a good agreement with the model test data in irregular waves when full QTFs are used to calculate the wave drift forces.
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