Engineering: Theses and Dissertationshttp://hdl.handle.net/10092/8402017-04-25T02:35:43Z2017-04-25T02:35:43ZPhase manipulation of speech using FIR digital filtersStephen, R. D. C.http://hdl.handle.net/10092/133722017-04-11T22:01:22Z1987-01-01T00:00:00ZPhase manipulation of speech using FIR digital filters
Stephen, R. D. C.
Three related investigations involving the fields of FIR digital filters, phase manipulation of speech, and speech coding via bandwidth compression are reported.
The first investigation is aimed at providing a means of generating the impulse response coefficients of a non-linear phase FIR digital filter. Existing methods of designing linear-phase filters are discussed and compared from a defined common comparison base.
The methods available for designing non-linear phase filters are examined. An existing linear phase design method is extended to the non-linear phase case and shown to be useful. The required impulse response length in the presence of non-linear phase is studied. Particular emphasis is placed on "random phase" filters and their generation because they are required by the second investigation.
The second investigation examines in detail the ramifications of phase randomising a speech signal. The analytic zero representation of speech which forms the underlying base on which the discussion, and answers, are based is elucidated. The technique of using a non-linear phase FIR filter is shown to be feasible and as a minimum, offers at least the same level of performance as a very early reported technique. Significant differences in the behaviour of male and female speech is demonstrated.
The third and final investigation reports some early and incomplete experiments on a radically different approach to achieving band width compression and expansion of a signal. The technique is referred to as "phase unwrapping". It is based on the application of a linear phase FIR digital filter in an adaptation of the traditional convolution relation. The motivation and validity of the basic idea is outlined and justified via application of the procedure to simple sinusoids and one experiment using real speech. The fundamental problem to be overcome is identified and the basis of a possible means of solution indicated.
1987-01-01T00:00:00ZEstimating leaf area index from airborne laser scanning.Pearse, Grant Dennishttp://hdl.handle.net/10092/133312017-04-10T22:32:17Z2017-01-01T00:00:00ZEstimating leaf area index from airborne laser scanning.
Pearse, Grant Dennis
Leaf area index (LAI) quantifies the amount of leaf surface area per unit ground area. LAI in forest ecosystems regulates the upper limit of possible light interception, atmospheric gas exchange, and primary production. These properties make LAI one of the most important ecophysiological variables with a wide range of potential applications. In the context of forests managed for production, knowledge of LAI offers the potential to align management activities with fundamental biophysical properties. For example, LAI offers the potential to precisely target and monitor management activities such as fertiliser application or disease control. Despite the potential benefits knowledge of LAI offers, usage is seldom seen outside of research applications. A key reason for this is the difficulty in obtaining LAI measurements over large areas, with field based optical methods largely constrained to use under uniform, diffuse sky conditions. Remote sensing of LAI offers one potential solution to obtain large-scale estimates of LAI. However, promising spectral-based approaches have been shown to have limited usefulness for forests with high LAI such as intensively managed coniferous plantations. Airborne laser scanning (ALS) data (lidar) offers enhanced ability to estimate LAI in a range of forest types with a high degree of accuracy, but the optimum methods for estimating LAI from lidar are not well established.
This thesis aims to develop and demonstrate a method for estimating LAI from lidar in New Zealand’s intensively managed Pinus radiata D. Don forests. To accomplish this, two distinct areas of research are addressed. First, this thesis addresses the need for acquiring a large number of LAI field measurements covering a range of stand conditions in order to calibrate ALS-LAI models. This was accomplished by validating the use of the newly developed LAI-2200C (LI-COR Biosciences Inc., Lincoln, NE, USA). This instrument allows measurement of LAI under clear sky conditions through the application of a model to correct for the impact of scattered light on gap fraction estimates. This thesis presents the first in situ comparison of LAI measurements acquired under diffuse and clear sky conditions in a coniferous forest. These results were obtained by repeatedly measuring LAI in plots of pure P. radiata in New Zealand. In addition, the thesis presents the first assessment of the importance of acquiring accurate needle spectra to parameterise the scattering correction model. These values were acquired using newly developed methods that allow accurate spectra to be acquired from needle-leaved species via spectroradiometer. The thesis also addresses the stability of needle optical properties with respect to position in the canopy, abaxial and adaxial measurements, and variability between individual trees.
The second part of this thesis used a large number of LAI measurements made possible by the new instrumentation to address key questions on the topic of estimating LAI from lidar.
To date, most ALS-LAI research has been divided between establishing empirical or physical links between lidar metrics and LAI. This has resulted in a proliferation of proposed methods and lidar metrics for estimating LAI, and few studies have compared these approaches. In addition, factors known to impact ALS-LAI estimation such as the choice of plot parameters have gone relatively unexplored, as has the use of new statistical learning approaches. This thesis attempts to offer the first simultaneous assessment of the optimum combination of lidar metrics, plot parameters, and modelling approaches for estimating LAI from ALS lidar data in P. radiata forests.
Results from the instrument validation suggest that the scattering correction model performs well in coniferous forests. Overall, clear sky LAI measurements were higher on average than diffuse sky measurements. However, there was evidence that this difference resulted from a reduction in erroneous readings obtained from the largest outer sensor ring under diffuse sky conditions. Traditionally, data from this part of the instrument have been error-prone and there was some evidence that clear sky LAI measurements offer increased accuracy by reducing scattering induced error across the range of zenith angles observed by the instrument. The method used to obtain spectroradiometer measurements from needle-leaved specimens was well suited to collecting accurate needle reflectance and transmittance for use in the scattering correction model. Use of these values improved agreement between clear and diffuse sky LAI measurements and reduced the magnitude of the largest differences at the extremes of the range. The results demonstrated that P. radiata spectra did not differ significantly with canopy position and were reasonably stable between trees. Measured P. radiata needle spectra are presented as part of this thesis and values are suggested for future users of the LAI-2200C scattering correction model in this forest type. Overall, use of measured spectra in combination with masking of outer ring data allowed LAI to be measured under both clear and diffuse sky conditions; however, clear sky conditions offered considerable reductions in the maximum potential measurement error resulting from changes in sky condition over time and between sensor locations.
Results presented in the second part of this thesis demonstrate that LAI can be accurately estimated from lidar data in P. radiata forests. A key finding from this work was that use of standard approaches developed for use in other forest types produced some of the worst models of all those trialled, indicating that successful ALS-LAI estimation in P. radiate depends on careful selection of lidar metrics, plot parameters, and modelling approach. Specifically, results showed that (1) metrics that form a proxy for gap fraction by computing the ratio of returns above and below a chosen height threshold (ratio metrics) were key predictors of LAI; (2) choice of height threshold for ratio metrics strongly impacted model performance and P. radiata appeared to require higher thresholds than other forest types; (3) the concept of a variable height threshold was beneficial in accommodating differences in tree height across plots and led to improved estimates of LAI; (4) a larger fixed plot radius generally improved model performance; (5) use of a variable plot radius linked to instrument view distance was better than any fixed radius trialled; (6) metrics linking lidar penetration to the Beer-Lambert law were only marginally less accurate than empirical models and showed strong predictive ability. This approach may offer a means of estimating LAI without calibration by inverting the Poisson model using gap fraction from lidar and an empirical projection coefficient. Finally, the research found a high level of correlation present between lidar metrics, strongly emphasising the need for modelling approaches robust to these effects. Regularised regression via the elastic net was found to be a useful method for providing both variable and model selection in high-dimensional space while accounting for the presence of high correlation between metrics. Results from models produced by the random forests algorithm were similar to results from elastic net but provided some useful insights into variable importance.
2017-01-01T00:00:00ZNumerical modelling of groundwater - surface water interactions with the Double-Averaged Navier-Stokes Equations.Dark, A. L.http://hdl.handle.net/10092/133262017-04-23T22:15:02Z2017-01-01T00:00:00ZNumerical modelling of groundwater - surface water interactions with the Double-Averaged Navier-Stokes Equations.
Dark, A. L.
The ability to model groundwater and surface water flows as two interacting components of a single resource is highly important for robust catchment management.
Existing methods for spatially-distributed numerical modelling of flow in connected river-aquifer systems treat rivers and aquifers as separate sub-domains, with different governing equations for the flow in each. Mass-fluxes exchanged between the sub-domains are modelled using one of several coupling methods, which do not accurately represent the physics of the flow across the interface between the surface and subsurface flows. This can be problematic for model stability and mass conservation.
This thesis investigates the feasibility of modelling interacting surface water and groundwater flows in a single domain, using a single system of equations.
It is shown that the governing equations in existing numerical models for river and aquifer flow can be derived from the Navier-Stokes Equations. A time- and space-averaged form of Navier-Stokes Equations, the Double-Averaged Navier-Stokes (DANS) Equations, can be used to model both groundwater and surface water flows. The volume- averaging process allows the porous medium to be represented as a continuum.
A novel two-dimensional numerical model is developed from the DANS Equations to simulate flows in connected groundwater and surface water systems. The DANS equations are solved using the finite-volume method. The model simulates two-dimensional flow in a vertical slice.
This allows the horizontal and vertical velocity components and pressure to be modelled over the depth of a stream and the underlying aquifer or hyporheic zone. The model does not require the location of the interface between surface and subsurface flows to be specified explicitly: this is determined by the spatial distribution of hydraulic properties (permeability and porosity).
The numerical model handles the transition between laminar and turbulent flows using an adaptive damping approach to modify the terms in a single-equation turbulence model, based on a locally-defined porous Reynolds number, Rep. This approach removes the need to specify a priori whether flows in any part of the domain are laminar or turbu lent. Turbulent porous media flows can be simulated.
The model is verified for porous-media and clear-fluid flows separately, before being used to simulate coupled groundwater - surface water flow scenarios.
For porous-media flows with low Rep the numerical model results agree exactly with Darcy’s Law. The value of Rep at which the model results begin to deviate from Darcy’s Law is consistent with published values.
For turbulent clear-fluid flows the time-averaged velocity and turbu lent kinetic energy (TKE) results from the numerical model are ver ified against a RANS model and published data. A good match is achieved for both velocity and TKE.
Energy grade-line slopes for free-surface flows simulated in the numerical model are a reasonably good match to equivalent results to the one-dimensional hydraulic model HEC-RAS.
Idealised river-aquifer interaction experiments are conducted in a lab- oratory flume to provide verification data for the numerical model. An innovative combination of optical flow measurement and refractive- index-matched transparent soil is used to measure two-dimensional velocities and turbulent statistics in laboratory flow scenarios that
simulate flow in both losing and gaining streams, and the underlying connected porous layer.
The “gaining stream” laboratory scenario is replicated using the numerical model. The model simulates the key features of the mean flow well. Turbulent statistics deviate substantially from the laboratory results where vertical velocities across the surface-subsurface interface are high, but are a better match elsewhere.
The “losing stream” laboratory results are unable to be reproduced with the numerical model. Results for a similar scenario with lower outflow velocities are presented. These results are qualitatively consistent with the laboratory results.
The numerical model is expected to perform better in simulations of field-like conditions that involve less extreme gradients than the laboratory scenarios.
2017-01-01T00:00:00ZSeismic resistant design of base isolated multistorey structuresAndriono, Takimhttp://hdl.handle.net/10092/133182017-03-24T14:01:12Z1989-01-01T00:00:00ZSeismic resistant design of base isolated multistorey structures
Andriono, Takim
The Base Isolation technique and its benefits in reducing the transmitted earthquake energy into
a structure has gained increasing recognition during the last two decades. This recognition is
indicated by the application of Base Isolation systems to a large number of bridges, several
multistorey buildings and some power plants in countries which have high seismic risk.
Unfortunately, the currently available design procedures, especially for multistorey structures,
seem inadequate and too restrictive and as a result present practice still relies upon a series of
deterministic time history analyses which are not only impractical for design purposes but
appear unable to give the designer a clear insight into the seismic behaviour of the multistory
structure.
This research is carried out to investigate in more detail the effects of various structural
parameters and ground motion characteristics on the seismic response of Base Isolated
multistorey structures. It also reviews the shortcomings of the current design methods. The results
are then used to develop two simplified analysis methods for practical design.
The first method which is called the Code-Type approach can be used to accurately estimate the
inertia forces, not only at the level of the isolation devices but throughout the height of the
multistorey structure. It is recommended for use as a preliminary design tool or even a final design
tool for simple Base Isolated multistorey structures. The second procedure which is based on the
Component Mode Synthesis method is suggested for final design purposes of more complex Base
Isolated multistorey structures. This method enables the designer to evaluate the effects of the
isolation devices on the contribution of each mode of vibration to the total response of the
structure.
1989-01-01T00:00:00Z