93 research outputs found
Sequence effects of high-amplitude loads in the most severe flights of minitwist on fatigue crack growth in Al-alloy sheet material
No full textAerospace Engineerin
Investigation of crack-closure prediction models for fatigue in aluminum alloy sheet under flight-simulation loading
No full textAerospace Engineerin
Impact of RF Imperfections on 60 GHz Wireless Communication Systems
No full textOver the last couple of decades, wireless communication has proved to be a phenomenal success and has generated a booming industry with over 5 billion mobile handsets in use worldwide. This has on one end eased the life of its users while on the other end has introduced new challenges for wireless system designers. The varying nature of the wireless communication channel results in large differences in the instantaneous received signal strength. Since most mobile terminals are battery powered and operate in a network, simply increasing the transmission power is not an attractive solution, as it reduces the battery life and increases interference. Thus a major challenge in wireless communication is to increase the communication rate and link reliability by utilizing low power, low cost and spectrally efficient systems. Even with the advent of efficient signal processing techniques and miniaturized low power signal processing hardware, the physical bottleneck still remains the available system bandwidth. This has led to the introduction of the 60 GHz band as an attractive alternative. Among other benefits, the 60 GHz band is unlicensed and can provide system bandwidths up to 7 GHz, which is ideally suited for short range indoor wireless services such as wireless local area networks. There are, however, certain challenges that need to be overcome before full potential of 60 GHz band can be harnessed. These challenges include the design of hardware components such as antennas, amplifier and mixers, identification and utilization of suitable base band processing algorithms and efficient communication protocols for wireless networks operating in the 60 GHz domain. This dissertation deals with the design and development of baseband processing techniques for communication devices operating at a carrier frequency around 60 GHz. Firstly, two practical candidates for baseband implementation are identified. The performance of these two alternatives namely single-carrier and multi-carrier is analyzed under various radio frequency circuit imperfections such as phase noise and amplifier non-linearity because low cost radio frequency circuits operating in the 60 GHz band are expected to have less than ideal performance. For both schemes, the performance degradation in terms of operating parameters such as the required number of bits in digital-to-analog converter/analog-to-digital converter and input back-off requirements for the power amplifier as a function of bit error probability, is determined. It is shown that the single-carrier schemes suffer a lower degradation in system performance for a given set of circuit parameters. The single-carrier scheme is therefore, identified as a suitable candidate for 60 GHz baseband implementation. Secondly, we investigate the possibility of using low cost and complexity RF level diversity combining schemes to boost the system performance. Three low complexity diversity combining schemes namely equal gain combining, selection combining and switched combining are considered. An analytical framework for system performance evaluation of different diversity combining schemes by using low complexity RF level quantized phase combining is developed. Analytical expressions for the bit and symbol error rate of multi-level phase shift keying modulated symbols over Rayleigh fading channels are derived. The derived expressions are then utilized to compare the performance with non-coherent schemes under diversity reception. It is shown that the number of quantization levels required to achieve near ideal performance are dependent on the number of the receive antennas and the modulation level. The analysis is also utilized to investigate the impact of phase quantization on the switching threshold for switched combining schemes. It is shown that the switching threshold is not severely affected by phase quantization. The ability to perform various system level trade-offs is also demonstrated. Lastly, a low cost audio demonstrator is proposed. The acoustic channels investigated in this thesis are seen to provide a multi-path rich environment typical of 60 GHz channels. This offers a practical way of verifying the performance of various baseband processing algorithms in a cost effective manner.TelecommunicatieElectrical Engineering, Mathematics and Computer Scienc
Fatigue crack growth prediction study based on the ONERA model for constant-amplitude and simplified flight-simulation loading
No full textAerospace Engineerin
Prediction of fatigue crack growth under flight-simulation loading with the modified Corpus model
No full textAerospace Engineerin
Application of timber groynes in coastal engineering
No full textTimber groynes have been used for centuries to retain and control beaches. They are found throughout Europe but little information is available about the design or detailing of the structures. During recent years alternatives such as beach renourishment, detached breakwaters and rock groynes have been used increasingly, however timber groynes can still offer advantages in terms of sustainability, cost and appearance. These include the relative ease with which the level and profile of the groyne may be adapted (by adding or removing planks) or maintained. Their appearance and small footprint are particularly advantageous on amenity beaches. Beaches constantly change as they respond to natural processes including waves, currents and the wind. These processes can result in material being transported from the beach, which if not replaced by material from adjacent areas, will result in erosion. Groynes are constructed more or less perpendicular to the shoreline to restrict the movement of sediment along the shore. They usually work in two ways, by providing a physical barrier to the movement of the beach material, which enables the beach to re-orientate approximately perpendicular to the incident wave direction, and by diverting longshore currents (which may be caused by tides or waves) away from the beach. In the past, groyne design was often limited to the slightly improved replacement of existing structures. As most local authorities in the United Kingdom are responsible for their own coastal protection, groyne design differs largely along the coastline. The performance and durability of timber groynes is highly dependent on the design and detailing of the structure. By comparing several schemes, various advantages and disadvantages of groyne design have been identified. Keeping a structure and its connections as simple as possible will benefit the ease of construction and maintenance. Design details such as attaching softwood or recycled timber rubbing pieces to the piles at critical levels, thus protecting them from abrasion, can considerably increase the lifetime of a groyne. In order to assure the sustainable use of timber, certified timber should be specified. Additionally, reuse and recycling of timber can substantially reduce the need for new timber, and should be incorporated in the design and maintenance of structures. If designed properly, timber groynes can be an effective and sustainable solution to retain a beach where the main erosion problem is caused by longshore sediment transport.Civil Engineering and Geoscience
Antenna Beamforming for a 60 GHz Transceiver System
No full textThe main target of a 60 GHz transceiver system is to obtain data rates close to gigabits per second (Gbps) over short distances. The 60 GHz suffers from severe pathloss, inter-symbol interference (ISI) and a limited link budget. In order to improve the link budget, beamforming techniques are utilized. Antenna beamforming, i.e., combining signals from multiple receive antennas is one of the crucial aspects of the 60 GHz transceiver system. Adaptive antenna arrays are considered for the beamforming. A single carrier with frequency domain equalization (SC-FDE) is used for the modulation. In order to suppress the ISI, a cyclic prefix (CP) is used in SC-FDE. The effects of the physical parameters of antenna arrays on the RMS delay spread and BER have been investigated in LOS/NLOS condition. An algorithm for radio frequency (RF) level beamforming is proposed. The effects of perfect channel and non-perfect channel on the BER have been investigated using the proposed beamforming algorithm. The effects of the antenna array physical parameters on the BER using the proposed beamforming lgorithm have also been investigated. It was seen that the BER improves after the implementation of the new beamforming algorithm. The 60 GHz band shows severe ISI which is improved by using the proposed beamforming algorithm.TelecommunicationsElectrical Engineering, Mathematics and Computer Scienc
- …
