The vibro-acoustic modelling and analysis of damage mechanisms in paper

This thesis investigates the use of the acoustic emission (AE) monitoring technique for use in identifying the damage mechanisms present in paper associated with its production process. The microscopic structure of paper consists of a random mesh of paper fibres connected by hydrogen bonds. This implies the existence of the two damage mechanisms of interest, the failure of a fibre/fibre bond and the failure of a fibre. The majority of this work focuses on the development of a novel hybrid mathematical model which couples the mechanics of the mass/spring model to the acoustic wave propagation model for use in generating the acoustic signal emitted by complex structures of paper fibres under strain. A discussion of the coupling method is presented and the model is then analysed using a simple plucked fibre as a test case with a comparison between the numerical and experimental results. The hybrid mathematical model is then used to simulate small fibre networks aimed at providing information on the acoustic response of each damage mechanism. To do this the mass/spring model must successfully simulate the response of the fibre structure when undergoing a fibre/fibre bond failure or a fibre failure. This can be achieved by dynamically manipulating the mass and spring elements of the fibre structure. The simulated AEs from the two damage mechanisms are then analysed using a Continuous Wavelet Transform (CWT) to provide a two dimensional time/frequency representation of the signal. From the CWT certain features of the AEs can be attributed to each damage mechanism and as such a criteria for the time and frequency properties of each damage mechanism can be formulated. This criterion provides the basis for identifying the damage mechanisms present in the experimental data. The final contribution of this thesis is the investigation of training an intelligent classifier which can dynamically identify the AEs from the two damage mechanisms. This is achieved by converting the time and frequency criteria for each damage mechanisms into a set of features for the training of a Self-Organising Map (SOM). The significant step in this analysis is the method for the extraction of the features from the CWT of the AE. This work successfully combines four different scientific areas, paper physics, acoustic emission technology, data analysis and computational modelling to provide an insight into the micro-mechanics of paper. The most significant contribution of this work is the development of the hybrid model which has the ability to generate the acoustic response of a paper fibre structure undergoing two different damage processes. This alone has provided a significant insight into the micro-mechanics of paper to allow for the identification of the two damage mechanisms when the AEs are analysed with the CWT. Other contributions include the method used for the extraction of relevant features from the CWT to enable the training of a SOM for identifying the type of damage mechanism the AE originated from

A metric-based scientific data model for knowledge discovery

Scientific data, which include multimedia (e.g., images, audio, and video) and non-standard data (e.g., finger prints and DNA sequences), is characterized by rich and complex inter-instance relationships in addition to the inter-entity relationships found in traditional data. Conventional data models are insufficient for modeling such inter-instance relationships. This thesis proposes a metric-based scientific data model from the notions of data-as-functions and pseudo-quasimetrics, which are used to model inter-entity and inter-instance relationships respectively. Compared to other scientific data models, the metric-based conceptual model can be applied to many data sets where geometric views might not otherwise be available. A detailed approach is outlined for exploring and deriving pseudo-quasimetrics to represent inter-instance relationships in a wide variety of data. In particular, we introduce the notion of observable properties and show how it can be applied with ideas from point set topology to systematically derive metrics from nonmetric data components such as categorical data. We also demonstrate the use of continuity as a mathematically precise tool to validate metrics derived through the proposed approach. In order to support the metric-based model at the physical level, we developed two simple mechanisms, the multipolar mapping, for transforming a pseudo-metric space into a multidimensional space, and the median transformation, for deriving a pseudo-metric from a pseudo-quasimetric. After application of multipolar mapping and (possibly) median transformation, it is easy to use existing point spatial data structures such as quadtree or octree for metric data storage and access. The results of our performance analysis demonstrate that the multipolar approach is robust and stable over a wide range of data parameters for data sets with intrinsic dimensionality of 10 or less. While it is still unclear whether the multipolar approach offers significant performance advantage on proximity queries for data sets of very high dimensionality, preliminary results for 100 dimensional data still show excellent performance on nearest neighbor queries

Determination of Sediment Filtration Efficiency of Grass Media

Vegetative filters serve the purpose of retarding flow. As a result the sediment carrying power of flowing water in a vegetated channel is greatly reduced and silting takes place along the section where the vegetation is planted. The mechanism of the filtering action of real or artificial vegetation can be described by a simplified principle, in that a gross reduction of turbulent fluctuation of the fluid is involved. This in turn allows the sediment particles to settle under the force of gravity more readily. In the case of nonsubrnerged flow, solid particles may settle out even faster due to the lengthening of the path the particles travel as they move with the fluid around the vegetation blades and the creation of zero velocity regions in front and behind the vegetation sterns. In order to determine the actual sediment trapping efficiency, a series of experimental tests were conducted under various flow conditions in a channel with continuous and discrete vegetative covers. The research results will be presented in three parts: (1) sediment filtration efficiency of continuous grass media; (2) bedload behavior in continuous and discrete vegetative filters; and (3) trapping of suspended solids by discrete vegetative filters. This research report addressed the effectiveness of the vegetative filter in trapping suspended solids when the filter is arranged in a continuous manner

Self-Flushing Piston Assembly for Slurry Pump

A slurry pump is provided having a self-flushing piston assembly mounted in a mating cylinder. The piston assembly includes a first piston having a peripheral sealing member and a reciprocating piston rod for driving the first piston for pumping action. A second piston mounted adjacent to the first piston includes a sealing member and forms an enclosed chamber with the first piston. A lost motion coupler connects the pistons together and varies the size of the chamber. On the return stroke of the piston assembly, flushing liquid on the non-slurry side is sucked into the chamber as the chamber expands. On the power stroke, the flushing liquid is forced past the second sealing member to remove slurry particles and prevent wear of the cylinder. The disc on the first piston has sufficient flexibility to allow filling of the chamber and an accumulator is provided to control the back pressure after the chamber has been filled on the return stroke. The flexible sealing discs are mounted by retainer plates and the lost motion coupler includes a hollow carrier mating with a shoulder on the rod for limited reciprocating movement

Self-Flushing Fluid Seal Assembly

A self-flushing fluid seal assembly is provided to prevent particle intrusion into the main seal around a slurry pump shaft. The assembly includes an annular tube concentrically disposed about the pump shaft and forming a chamber. The volume of the chamber is made variable by a plunger comprising an enlarged diameter portion of the pump shaft movable relative to the chamber during the power and return stroke of the pump. Flushing liquid is delivered to the chamber by means of a feed line extending through the shaft. A check valve provided in the feed line opens to allow the inward flow of flushing fluid from the feed line to the chamber as the chamber expands. Conversely, the check valve closes and a secondary shaft seal is provided to prevent the reverse flow of flushing fluid as the chamber contracts on the return stroke. Thus, during chamber contraction the flushing fluid is forced from the chamber through a passage around the tube and through the main seal to prevent particle intrusion into the seal during pumping, thereby reducing wear

Hydropower Turbine System

There is disclosed a new cavitation free hydraulic turbine system which fully utilizes well-established hydrodynamic theories useful for low-head hydroelectric applications. The hydropower turbine system of the present invention makes use of a fixed blade propeller turbine with reverse blade angle and an upward flow passage. To eliminate the complex flow control adjustable vane system and elaborate tube design and construction of the prior art, the new turbine system is provided with a vertical needle valve and a near zero absolute velocity free exit flow design

Software Aids Visualization of Computed Unsteady Flow

Unsteady Flow Analysis Toolkit (UFAT) is a computer program that synthesizes motions of time-dependent flows represented by very large sets of data generated in computational fluid dynamics simulations. Prior to the development of UFAT, it was necessary to rely on static, single-snapshot depictions of time-dependent flows generated by flow-visualization software designed for steady flows. Whereas it typically takes weeks to analyze the results of a largescale unsteady-flow simulation by use of steady-flow visualization software, the analysis time is reduced to hours when UFAT is used. UFAT can be used to generate graphical objects of flow visualization results using multi-block curvilinear grids in the format of a previously developed NASA data-visualization program, PLOT3D. These graphical objects can be rendered using FAST, another popular flow visualization software developed at NASA. Flow-visualization techniques that can be exploited by use of UFAT include time-dependent tracking of particles, detection of vortex cores, extractions of stream ribbons and surfaces, and tetrahedral decomposition for optimal particle tracking. Unique computational features of UFAT include capabilities for automatic (batch) processing, restart, memory mapping, and parallel processing. These capabilities significantly reduce analysis time and storage requirements, relative to those of prior flow-visualization software. UFAT can be executed on a variety of supercomputers