Blood pressure, dietary fats, and antioxidants.

This report describes the development of a fast and reasonably accurate model for the prediction of energy production in offshore wind farms taking wake effects into account. The model has been implemented as a windows application called Fuga which can run in batch mode or as a graphical user interface. Fuga is briefly described. The model is based on a linearization technique which is described in some detail, and linearized, governing equations are derived and written in a standard form based on a mixed-spectral formulation. A new solution method is used to solve the equations which involves intensive use of look-up tables for storage of intermediate results. Due to the linearity of the model, multiple wakes from many turbines can be constructed from the wake of a single, solitary turbine. These are in turn constructed from Fourier components by a fast Fourier integral transform of results derived from generic look-up tables. Three different models, based on three different closures, are examined: 1) the 'simple closure' using an unperturbed eddy viscosity kucentre dotz. 2) the mixing length closure. 3) the E-epsilon closure. Model results are evaluated against offshore wind farm production data from Horns Rev I and the Nysted wind farm, and a comparison with direct wake measurements in an onshore turbine (Nibe B) is also made. A very satisfactory agreement with data is found for the simple closure. The exception is the near wake, just behind the rotor, where all three linearized models fail. The mixing length closure underestimates wake effects in all cases. The E-epsilon closure overestimates wake losses in the offshore farms while it predicts a too shallow and too wide the wake in the onshore case. The simple closure performs distinctly better than the other two. Wind speed data from the the Horns rev met masts are used to further validate Fuga results with the 'simple' closure. Finally, Roedsand 1 and 2 are used as an example to illustrate the interaction between wind farms. (Author)

https://orbit.dtu.dk/files/6354851/ris-r-1772.pdf

Linearised CFD Models for Wakes

A new highly accurate fast algorithm is proposed for computing the Fourier transform integrals of discontinuous functions (DIFFT) by employing the analytical Fourier transforms of Gauss-Chebyshev-Lobatto interpolation polynomials and the scaled fast Fourier transform. This algorithm can achieve the exponential accuracy for evaluation of Fourier spectra at the whole frequency range with a low computational complexity. Furthermore, the algorithm allows the adaptive sampling densities for different sections of a piecewise smooth function. Numerical experiments are shown for the applications in computational electromagnetics.

DIFFT: A Fast and Accurate Algorithm for Fourier Transform Integrals of Discontinuous Functions

A highly accurate, fast algorithm is proposed to evaluate the flnite Fourier transform of both continuous and discontinues functions. As the discretization is conformal to the function discontinuities, this method is called the conformal Fourier transform (CFT) method. It is applied to computational electromagnetics to calculate the Fourier transform of induced electric current densities in a volume integral equation. The spectral discrimination in the CFT method can be arbitrary and the spectral range can be as large as needed. As no discretization for the Fourier exponential kernel is needed, the CFT method is not restricted by the Nyquist sampling theorem, thus avoiding the aliasing distortions that exist in other traditional methods. The accuracy of the CFT method is greatly improved since the method is based on high order interpolation and the closed-form Fourier transforms for polynomials partly reduce the error due to discretization. Assuming Ns and N are the numbers

/pdf/a-high-accuracy-conformal-method-for-evaluating-the-1hl23ayrin.pdf

A high accuracy conformal method for evaluating the discontinuous fourier transform

Laser-Doppler velocimetry (LDV) is an established technique for noninvasive monitoring of skin blood flow. The LDV is based on the interference between the photons scattered from the moving red cells and the surrounding stationary tissue. In this work we have developed a new chopper stabilized LDV method. The light bema from the 10 mW HeNe laser was pulsed by a mechanical chopper at a frequency of 130 Hz. The light pulses backscattered from the skin were measured by a dual PIN photodiode electrometer amplifier. In the Fourier spectrum the chopper 130 Hz + harmonics peaks were dominating. The width of the peaks was diminished when measuring necrotic skin areas. The interference signal was demodulated by multiplying the measured pulsed signal by the chopper waveform. The resulting LDV spectra had a negligible amount of electrical distortion. The main advantage of the chopper stabilization is that pulse modulation concentrates the signal power near the chopper frequencies, which are free of electrical 50 Hz + harmonics pick-up.

H. Olkkonen

Papers

Fast method for computing the Fourier integral transform via Simpson's numerical integration

Dual diode transducer for laser doppler skin blood velocimeter

Running discrete cosine transform

Fast sinc interpolation of digitized signals using the Hilbert transform.