31 research outputs found
Multi-radio interference diagnosis in unlicensed bands using passive monitoring
No full textThe increasing density and data rate of unlicensed band wireless devices has led to significant inter- and intra-radio interference problems. Multiple competing standards such as the IEEE 802.11b/g, Bluetooth and ZigBee, all of which operate in the 2.4 GHz ISM band, can interfere with each other when used in typical indoor environments, potentially causing significant performance degradation. This thesis aims to characterize different types of heterogeneous interference in the 2.4 GHz unlicensed band and develop techniques to diagnose interference related problems using passive monitoring. The first
part of the thesis presents detailed experimental results (using the ORBIT radio grid testbed) to quantify the effects of such interference in representative small office and home (SOHO) environment. In particular, different topologies, traffic loads and number
of interfering devices are emulated to show the impact of multi-radio interference and to characterize each kind of interference. The second part of the thesis describes
a cross-layer, multi-radio interference diagnosis framework (called “spectrum MRI”) which aims to classify and diagnose multi-radio interference problems using heuristic and model-based methods. Validation experiments show that broad auto-classification of multi-radio interference in terms of congestion, slow links, inter AP interference and
Bluetooth interference is possible using heuristic algorithms and passive monitoring.M.S.Includes bibliographical referencesby Akash Bai
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Detection of Damage in a Composite Structure Using Guided Waves
No full textAdvanced composites are being increasingly used in state-of-the-art aircraft and aerospace structures. In spite of their many advantages composite materials are highly susceptible to hidden flaws that may occur at any time during the life of a structure and if undetected, may cause sudden and catastrophic failure of the entire structure. An example of such a structural component is the "honeycomb composite" in which thin composite skins are bonded with adhesives to the two faces of extremely lightweight and relatively thick metallic honeycombs. These components are often used in aircraft and aerospace structures due to their high strength to weight ratio. Unfortunately, the bond between the honeycomb and the skin may degrade with age and service loads can lead to separation of the load-bearing skin from the honeycomb (called "disbonds") and compromise the safety of the structure. The need for model-based studies is widely recognized in the NDE community and a great deal of work has indeed been carried out for simple, metallic structures. However the literature on composite structures is rather limited due to the enormous mathematical complexity involved in dealing with them. In this dissertation a comprehensive approach including numerical (finite element method) and analytical method is used for calculating the ultrasonic wavefield in composite structural components with and without defects. Laboratory experiments are carried out on a composite honeycomb specimen containing damage to the skin or a localized disbond at the skin-core interfaces. The skin and the honeycomb composite are considered separately in order to understand the interaction of ultrasonic waves with damage in the two structures. The waves are launched into the specimen using a broadband PZT transducer and are detected by a distributed array of identical transducers located on the surface of the specimen. The guided wave components of the signals are shown to be strongly influenced by the presence of a defect in the skin or the honeycomb composite structure. The experimentally observed results are used to develop an autonomous scheme to locate the disbonds. The calculated results from the simulations are compared with existing and new experiments to validate and improve the models. The results should be very useful in model-based understanding of ultrasonic data collected during nondestructive inspection and evaluation (NDI/NDE) of advanced aircraft and aerospace structure and in the development of reliable health monitoring systems in the structures
Advanced composite wind turbine blade design and certification based on durability and damage tolerance
No full textClosed-Form Solutions for Code Case 2286 Allowable Compressive Stresses Analogous to Vacuum Chart Method
No full textA set of nine principles for distributed-design information storing
No full textThe issues of distributed working are many, with problems relating to information access and information acquisition the most common (Crabtree et al., 1997). Keeping track of project and team information is becoming more complex as design is increasingly being carried out collaboratively by geographically dispersed design teams across different time zones. The literature notes that little prescription or guidance exists on information management for designers (Culley et al., 1999) and Hicks (2007) highlights a relative lack of overall principles for improving information management. Additionally, evidence from earlier studies by the author into ‘How information is stored in distributed design project work’ reinforces the need for guidance, particularly in a distributed context (Grierson, 2008). Distributed information collections were found to be unorganised, contained unclear information and lacked context. Storing and sharing of distributed information was often time consuming and the tools awkward to use. This can lead to poor project progress and can impact directly on the quality and success of project outcomes (Grierson et al., 2004, 2006). This paper seeks to address these issues by presenting the development, implementation and evaluation of a set of Principles and a Framework to support distributed design information storing in the context of a Global Design class. Through both quantitative and qualitative evaluation methods the Principles were found to help in a number of ways – with the easy access of information; the structuring and organising of information; the creation of an information strategy; the making of information clear and concise; the supporting of documentation during project work; and the strengthening of team work; all helping teams to work towards project outcomes
A critical review of auscultating bowel sounds
No full textAuscultation (listening for bowel sounds) is part of an abdominal physical assessment and is performed to determine whether normal bowel sounds are present. This article evaluates the technique involved in listening for bowel sounds and the significance of both normal and abnormal auscultation findings. Review of the relevant literature reveals conflicting information and a lack of available research on the topic of auscultating bowel sounds. The clinical significance of auscultation findings when there is no evidence base to support the practice of listening for bowel sounds is explored by further analysis of the literature and reflection by the author on the teaching she received and her own personal practice
Process analysis of temperature and eigenstrains in stiffening ribs printed on a multi curved structure with a robot-based extrusion process
No full textIn this study, we investigate simulations for a pellet-based extrusion process with high-performance materials for 3D printing.
The utilization of a robotic arm equipped with an extruder mounted on it has opened up new avenues for 3D printing, such as printing on curved surfaces or large overhangs without requiring additional support structures. In this research, our focus is on a doubly curved
Carbon Fiber Reinforced Polymer (CFRP) structure, which has been strengthened by adding short fiber-reinforced ribs. These ribs are printed onto the curved surface of the structure to enhance its stiffness. However, during the high-temperature printing process with highperformance materials, significant temperature gradients occur, leading to eigenstrains and deformation of the ribs. To predict the impact of these effects on the stiffness of the structure, a process simulation is conducted by using the GENOA 3DP software suite from
Alpha STAR Corp. The proposed AM process simulation takes into account AM parameters such as the toolpath (Gcode), deposition rate and extrusion temperature. The thermophysical process is modelled
by an element-by-element activation based on the toolpath so that local temperature gradients are captured. This allows the consideration of manufacturing related effects for the
prediction of process-dependent material and component properties.
The primary objectives of this study are to simulate the intricate extrusion process and to estimate the eigenstrains and deformations that occur during the process as well as to gain an
in- depth understanding of the process for further optimisation
