Creating a shallow-water experimental wave environment

This PhD concerns laboratory wavemaking in shallow and intermediate water conditions. Theoretical solutions and experimental evidence are presented to advance both our understanding of the wave generation process as well as its practical success. A comparison is made between two wave generation techniques, a first based on controlling the wavemaker displacement, and a second based on controlling the wavemaker force. In deep water, a force-based approach, which includes active wave absorption, was recently shown to offer benefits in terms of wave quality. To investigate the influence of the water depth on this type of control, a range of generation scenarios is considered, including regular, bi-chromatic, focused and random waves. The work demonstrates that force-based wave generation in shallow water suffers from similar limitations as position control. This principally concerns the contamination of the testing area due to unwanted free waves, where the present focus is placed on the superharmonic range. The main advance of the work lies in the solutions it offers to overcome this free wave contamination. The nature of the nonlinear wave solution upon which force-based generation should be based depends on the type of wave case (regular, bi-chromatic, focused or random). For each of these cases, a suitable methodology is proposed and validated. The developed methodology allows for high quality wave generation, whilst maintaining the benefit of active wave absorption. The work is timely in the sense that is responds to two recent developments. First, the majority of wavemaking facilities are now computer controlled, and active absorption has become commonplace. The work presented offers solutions highly relevant to such installations. Second, developments particularly in offshore wind, have seen many new structures placed in relatively shallow-water depth. It is essential that the model testing of such structures adequately accounts for the issues and solutions presented herein.Open Acces

Direct mining of subjectively interesting relational patterns

Data is typically complex and relational. Therefore, the development of relational data mining methods is an increasingly active topic of research. Recent work has resulted in new formalisations of patterns in relational data and in a way to quantify their interestingness in a subjective manner, taking into account the data analyst's prior beliefs about the data. Yet, a scalable algorithm to find such most interesting patterns is lacking. We introduce a new algorithm based on two notions: (1) the use of Constraint Programming, which results in a notably shorter development time, faster runtimes, and more flexibility for extensions such as branch-and-bound search, and (2), the direct search for the most interesting patterns only, instead of exhaustive enumeration of patterns before ranking them. Through empirical evaluation, we find that our novel bounds yield speedups up to several orders of magnitude, especially on dense data with a simple schema. This makes it possible to mine the most subjectively-interesting relational patterns present in databases where this was previously impractical or impossible

Analysis of cyclic prefix length effect on ISI limitation in OFDM system over a Rayleigh-fading multipath

In this work, the influence of the cyclic prefix on the performance of the OFDM system is studied. We worked out an OFDM transceiver using a 16 QAM modulation scheme, a comparison of the BER for various lengths of the cyclic prefix has been achieved, and the influence of the noise introduced in the channel has been highlighted, for both a Gaussian and Rayleigh noise. The simulation was carried out on MATLAB where the curves of the BER for various lengths of the cyclic prefix are given and compared. We also adopted as a metric the QAM constellation to show the dispersion of the carriers as a consequence of the transmission channel, the mitigation of this effect by the CP is noticeable

G-Shaped Antenna Mounted On USB Dongle Optimized For MIMO Applications Under WLAN 5.2/5.8/5.9

In this study, we used a G-shaped antenna due to its ease of integration into the overall design. The basic structure was adapted from a model proposed by W.-C. Liu. Then, we integrated it into a USB dongle, then added another antenna element to use it for MIMO applications in WLAN networks. A neutralization line is added between these two antenna elements to increase insulation

Analytical model for life time in wirless sensor networks

Numerous analytical models have been proposed to evaluate the performance of wireless sensor networks, therefore, analytical models providing a clear understanding of the fundamental limitations of different systems, as well as a convenient way to review their performance and optimize their parameters are necessary. In this paper, we propose an analytical framework model that defines the performance of a sensor network, with an emphasis on an analytic model that is based on the lifetime, the offered traffic, and the maximum number of retransmissions Kmax