No / A novel acoustic sensor has been developed which is capable of remotely monitoring the free surface ‘fingerprint’ of shallow flows. The temporal and spatial properties of this fingerprint are shown to contain a wealth of information regarding the nature of the flow itself. The remote measurement can thereby be used to infer the bulk flow properties such as depth, velocity, and hydraulic roughness to within 8 % accuracy. The instrument is totally non-invasive and as such is low cost, low maintenance, and low power. Such a device will allow for widespread monitoring of flow conditions in drainage and river networks, informing flood models, and facilitating pro-active maintenance and real time control.

A novel acoustic sensor has been developed, capable of remotely monitoring the free surface ‘fingerprint’ of shallow flows. Temporal and spatial properties of this pattern are shown to contain information regarding the nature of the flow itself. The remote measurement can thereby be used to infer the bulk flow properties such as depth, velocity, and the hydraulic roughness of the pipe. The instrument is non-invasive and is also low cost, low maintenance, and low power. Such a device will allow for widespread monitoring of flow conditions in drainage networks, enabling pro-active maintenance and reliable real-time control.

Sensing in harsh environments is always in great need. Although many sensors and sensing systems are reported, such as optical fiber sensors and acoustic sensors, they all have drawbacks. In this dissertation, fused quartz and sapphire acoustic waveguides and sensors are developed for high temperature and heavy gamma radiation. The periodic structure, acoustic fiber Bragg grating (AFBG), is the core sensor structure in this dissertation. To better analyze the propagation of acoustic waves, the acoustic coupled more analysis is proposed. It could solve for the reflection spectrum of the AFBG with at most 2.1% error. For the waveguide, the fused quartz "suspended core" waveguide is designed. It achieved strong acoustic energy confinement so surface perturbations no longer affected the wave propagation. Single crystal sapphire fiber features low acoustic loss, and survivability under high temperature. It is also chosen as an acoustic waveguide. AFBGs are fabricated in both waveguides. The fused quartz suspended core AFBG is shown to sense temperature up to 1000 C and to have stable reading at 700 C for 14 days. The sapphire AFBG as a temperature sensor works up to 1500 C and also provides continuous stable reading at 1100 C for 12 days. Both waveguides with AFBGs are then tested under long-term gamma radiation. Despite some fluctuations from radiation-related causes, the readings of both sensors generally remain stable. Given the experimental observations, the fused quartz AFBG waveguide and the sapphire AFBG waveguide are shown to work well in high temperature and gamma radiations. / Doctor of Philosophy / Sensing in harsh environments, like high temperature, high pressure, and corrosive environment, is always in great need. Efficient and safe operation of instruments like nuclear reactors could be better secured. Although many sensors and sensing systems are reported, such as optical fiber sensors and acoustic sensors, they all have drawbacks so new designs are constantly in need. In this dissertation, silica (a glass commonly acquired by melting sand) and sapphire (used in iphone screens due to its transparency and hardness) acoustic waveguides and sensors are developed. A periodic structure known as acoustic fiber Bragg grating (AFBG) is the core sensor structure in this dissertation. A calculation method is proposed first. Acoustic wave needs a waveguide to propagate somewhere further, and a new waveguide structure is made to keep the acoustic energy within the very center of the waveguide, so any change on the outer surface does not affect the wave inside. Also, sapphire has good acoustic property and is used. The AFBGs are fabricated in both waveguides. These sensing waveguides are shown to work at >1000 C temperature and provide stable reading for more than 10 days. Long term exposure to gamma radiation for weeks or months resulted in stable performances. Therefore, it is concluded that silica and sapphire waveguide sensors are successfully developed for high temperature and nuclear radiation applications.

Sewer flooding incidents in the UK are being increasingly associated with the presence of blockages. Blockages are difficult to deal with as although there are locations where they are more likely to occur, they do occur intermittently. In order to manage sewer blockage pro-actively sewer managers need to be able to identify the location of blockages promptly. Traditional CCTV inspection technologies are slow and relatively expensive so are not well suited to the rapid inspection of a network. This is needed if managers are to be able to address sewer blockages pro-actively. This thesis reports on the development of low-cost, rapidly deployable acoustic base sensor that will be able to survey live sewer pipes. The sensor emits short coded acoustic signals which are reflected from any defects of the wall of the underground pipes and recorded for future processing. The processing algorithms are based on the temporal windowing, deconvolution, Fourier, and intensity analysis so that the response can be linked directly to the location and property of the of the pipe deformation. The sensor was tested in a full scale sewer pipe in the laboratory and in few sites in UK, Austria and Netherlands and it was shown that it is able to discriminate between blockages and structural aspects of a sewer pipe such as a manhole and lateral connection. The anticipated cost is orders of magnitude lower than any current technique.

Underwater Acoustic Sensor Networks (UW-ASNs) have the potential to enable many applications such as environmental monitoring, undersea exploration and distributed tactical surveillance. In order to realize the potential gains of these applications, it is essential that the sensor nodes can be accurately located in a three dimensional underwater sensor network topology. Although many localization protocols have been proposed recently for terrestrial sensor networks, the unique characteristics of the underwater acoustic communication channel, such as high and variable propagation delay, necessitate new localization protocols. In order to address this need, a localization protocol for UW-ASN, Three-Dimensional Underwater Localization (3DUL), is presented in this thesis. 3DUL achieves network-wide robust 3D localization by using a distributed and iterative algorithm. Importantly, 3DUL exploits only three surface buoys for localization. The sensor nodes leverage the low speed of sound to accurately determine the inter-node distances. We show through simulation experiments that the localization accuracy does not degrade significantly with an increase in the number of nodes, making 3DUL scalable.

Sonar is the traditional method of underwater target detection and tracking. However, using traditional sonar arrays may be difficult and impractical in some mission-critical scenarios as they require a ship or a submersible to be mounted on or towed by. Alternatively, Underwater Acoustic Sensor Networks (UW-ASN) offer a promising solution approach. In this thesis, a target tracking algorithm for UW-ASN, Three-Dimensional Underwater Target Tracking (3DUT) is presented. The objective of 3DUT is to collaboratively accomplish accurate tracking of underwater targets with minimum energy expenditure. Based on the time-of-arrival (ToA) of the echoes from the target after transmitting acoustic pulses from the sensors, the ranges of the nodes to the target are determined, and trilateration is used to obtain the location of the target. The location and the calculated velocity of the target are then exploited to achieve tracking. In order to realize energy-effective target tracking, 3DUT incorporates a new target movement-based duty cycle mechanism. To avoid rapid depletion of energy resources of boundary nodes due to continuous surveillance, 3DUT employs an adaptive procedure to find, designate, and activate new boundary nodes. Performance evaluation shows that 3DUT is a promising alternative to the traditional sonar based target tracking approaches especially for on-demand surveillance applications.

Thesis (MEng)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: A desire to increase the efficiency of the comminution process in mineral process systems has led to the need of determining the size distribution of ore particles at various stages in the system. The objective of this research is to investigate the feasibility of the use of an acoustic sensor for measuring particle size distribution. The acoustic signal generated when the particles impact on a cantilever bar is analysed using digital signal processing techniques. As rocks fall onto a metal bar, the bar vibrates. The vibrations contain information th a t is extracted to determine the size of particles tha t impacted on the bar. The bar is modelled as a linear system which is excited by impulses (impact of particles). The response of the bar is deconvolved from the acoustic signal to obtain an impulse whose amplitude is proportional to the energy of the impact. In order to improve size estimates, deconvolution is performed using a statistical model of the impulse sequence (Bernoulli-Gaussian) and then estimated using MAP estimation. Size estimates are not only a function of the mass of particles, but also on the exact position of impact on the bar. Since there is always a variation in the position of impact, size estimates are erroneous. It was found that the position of impact can be determined as to reduce variances dramatically. Due to physical sampling in space, the sensor has a bias towards larger particles. We show how this can be represented mathematically and removed. This project is mainly concerned with rocks in the +8-25mm (+0,7-22 gram) size range. / AFRIKAANSE OPSOMMING: Vergruising van erts in die mineraalbedryf verg groot hoeveelhede energie. Daar is ’n behoefte gei'dentifiseer orn hierdie proses meer effektief te maak. Aangesien die effektiwiteit van ’n meul ’n funksie is van die ertsgroottes wat gemaal word, kan partikel grootte inligting aangewend word om effektiwiteit te bevorder. Die doel van hierdie tesis is om die lewensvatbaarheid van ’n akoestiese sensor vir die doel van partikelgrootte estimasie, te ondersoek. Erts partikels wat val vanaf ’n vervoerband op ’n kantelbalk, veroorsaak dat die balk vibreer. Deur hierdie vibrasies te meet en verwerk, kan inligting aangaande partikel grootte verkry word. Die stelsel word gemodelleer as ’n lineere sisteem met impulse as intree. Die geobserveerde sein is die konvolusie tussen die intree impulse en die impulsweergawe van die sisteem. Deur gebruik te maak van ’n statistiese model en MAP-estimasie, word die effek van die sisteem gedekonvuleer vanaf die geobserveerde sein om ’n benadering van die intree impuls sein te verkry. Die amplitudes van die impulse word gebruik as ’n aanduiding van partikel massa. Partikelgroottes soos benader deur die stelsel, is ’n funksie van die die posisie waar die partikel die balk tref. Deur van patroonherkenning tegnieke gebruik te maak, word die posisie van impak bepaal om sodoende grootte benaderings aan te pas en die variansie van grootte verspreidings te verminder. As gevolg van die feit dat partikels gemonster word deurdat slegs ’n klein persentasie van die hele omvang van partikels ondersoek word, onstaan daar ’n oorhelling ( “bias” ) na groter partikels. Die kans dat groter partikels die balk tref is groter as vir klein partikels. ’n Wiskundige model vir hierdie verskynsel word voorgestel en gewys hoe die die oorhelling geneutraliseer kan word. Hierdie projek het te doen met ertsgroottes +8-25mm (+0,7-22 gram).

In Underwater Acoustic Sensor Networks (UWASNs), cameras have recently been deployed for enhanced monitoring. However, their use has faced several obstacles. Since video capturing and processing consume significant amounts of camera battery power, they are kept in sleep mode and activated only when ultrasonic sensors detect a target. The present study proposes a camera relocation structure in UWASNs to maximize the coverage of detected targets with the least possible vertical camera movement. This approach determines the coverage of each acoustic sensor in advance by getting the most applicable cameras in terms of orientation and frustum of camera in 3-D that are covered by such sensors. Whenever a target is exposed, this information is then used and shared with other sensors that detected the same target. Compared to a flooding-based approach, experiment results indicate that this proposed solution can quickly capture the detected targets with the least camera movement.

No description available.

Sewer flooding incidents in the UK are being increasingly associated with the presence of blockages. Blockages are difficult to deal with as although there are locations where they are more likely to occur, they do occur intermittently. In order to manage sewer blockage pro-actively sewer managers need to be able to identify the location of blockages promptly. Traditional CCTV inspection technologies are slow and relatively expensive so are not well suited to the rapid inspection of a network. This is needed if managers are to be able to address sewer blockages pro-actively. This thesis reports on the development of low-cost, rapidly deployable acoustic base sensor that will be able to survey live sewer pipes. The sensor emits short coded acoustic signals which are reflected from any defects of the wall of the underground pipes and recorded for future processing. The processing algorithms are based on the temporal windowing, deconvolution, Fourier, and intensity analysis so that the response can be linked directly to the location and property of the of the pipe deformation. The sensor was tested in a full scale sewer pipe in the laboratory and in few sites in UK, Austria and Netherlands and it was shown that it is able to discriminate between blockages and structural aspects of a sewer pipe such as a manhole and lateral connection. The anticipated cost is orders of magnitude lower than any current technique.