wake measurements behind An array of Two Model Wind Turbines (mechanical project)

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http://www.4shared.com/office/60og6CU1/FULLTEXT01.html


http://www.4shared.com/office/60og6CU1/FULLTEXT01.html

During the last decades the exploitation of energy from the wind has become one of the most promising renewable energy technologies. The main strive in today’s development of wind turbines is to increase the efficiency of the turbine and to build bigger rotors that are able to extract more power out of the wind.

When it comes to the planning and designing of a wind park, also the aerodynamic interactions between the single turbines must be taken into account. The flow in the wake of the first row turbines is characterized by a significant deficit in wind velocity and by increased levels of turbulence. Consequently, the downstream turbines in a wind farm cannot extract as much power from the wind anymore. Furthermore, the additional turbulence in the wake could be a reason for increased material fatigue through flow-induced vibrations at the downstream rotor.

The main focus of this experimental study is to investigate the local velocity deficit and the turbulence intensities in the wake behind an array of two model wind turbines. For two different turbine separation distances, the wake is scanned at three different downstream positions. The experiments are performed at the wind tunnel (1.9m x 2.7m cross section) at NTNU Trondheim using two model wind turbines with a rotor diameter of 0.9m. A hot wire probe is used to scan the wake behind the model turbines in defined positions.

Moving axially downstream the velocity deficit in the wake gradually recovers and the turbulence intensity levels slowly decrease. Furthermore, a gentle expansion of the wake can be observed. The wake profiles measured in close distances behind the rotor are characterized by evident asymmetries. Further downstream in the wake turbulent diffusion mechanisms cause a more uniform and more symmetrical flow field. Moreover, the turbulence intensity behind the second wind turbine is found to be significantly higher than behind one unobstructed turbine.

Also, considerably higher velocity deficits are found in the near wake behind the second turbine compared to the wake behind one unobstructed turbine. However, the velocity profile at five rotor diameters downstream in the wake behind the second turbine is already very similar to the velocity distribution behind the first turbine. Furthermore, the velocity field and turbulence intensity distribution in the wake behind the second turbine is more symmetrical and more uniform than behind the first turbine.

Chaos-based Random Number Generator in Finite Precision Environment (ECE/EEE Project)

Yet having a very long history, how to generating good random number sequences still remains as a technical challenge. Although some mechanical ways, such as tossing a coin or rolling a dice, are commonly accepted as good random sources, they are obviously not been able to fulfill the requirements of most of the real-world applications, in which high throughput and good quality are generally required.

For more than half century, different random number generators have been proposed. Recently, we have witnessed an active involvement of another branch of sciences in this topic, in particularly, aiming for cryptographical applications. Due to the distinct properties of chaos, including random-like dynamics, continuous broadband frequency spectrum, high sensitivity on initial conditions and system parameters, etc, the use of chaos in random number generation and cryptographical applications has aroused tremendous interests.

However, the actual realization environment is usually ignored in most of the chaos-based designs, for which an infinite precision is commonly assumed. As pointed out by some researchers, if a chaotic system is to be implemented in finite precision, its dynamics will be greatly deviated from its original one, and hence some nice properties will be vanished.

In this thesis, the use of chaotic maps or chaotic systems for the generation of random number under a finite precision environment is to be studied. Firstly, the adverse effects on the characteristics of the chaotic maps and chaos-based random number generators are investigated in details, when quantization errors occur through the evolution of the associated chaotic maps. In order to tackle with these effects, a novel high-dimensional chaos-based post-processing function is designed. With such data post-processing, the statistical quality of the generated random sequence can be greatly improved and can fulfill the up-to-date standards. From the experiments, it shows that the newly designed technique outperforms all the other existing post-processing methods, both in terms of performance and speed.

Finally, two practical designs of chaos-based random number generators are suggested for 32-bit and 8-bit precision environments. With a simple cascade structure of a chaotic map and the chaos-based post-processing function, a fast and simple chaos-based random number generator is designed in a 32-bit machine. An UDP secure chatting system is then developed, in which an effective encryption scheme is designed based on the 32-bit chaos-based random number generator. For the 8-bit environment, a chaotic circuit together with the proposed post-processing function is used. Good random number sequences can be generated and its quality is confirmed by statistical tests. This provides a unique solution for such a low precision system environment, which is still commonly found in industrial and consumer markets.

Neraj p mani

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