College of Engineering
http://hdl.handle.net/10092/1
Tue, 26 Jul 2016 11:07:21 GMT2016-07-26T11:07:21ZDesign and prototyping of a High Country Electric Vehicle (HiCEV).
http://hdl.handle.net/10092/12510
Design and prototyping of a High Country Electric Vehicle (HiCEV).
Hennessy, Pierce L.
The development of a High Country Electric Vehicle has come about in response to a farmers desire to reduce the dependence on fossil fuels on his station. Electric vehicles have become more prominent in the urban commuter vehicle market over recent years, and are gaining greater acceptance as people look to be more environmentally aware. This project shows that electric vehicles also have a place in the primary sectors in an off-roading, rugged context.
The conversion vehicle of choice is the Toyota Land Cruiser 70 Series, an iconic farming vehicle renowned for its reliability in challenging operating conditions. The vehicle was stripped of components associated with the 1-HZ internal combustion engine (ICE) drivetrain, and electrical drivetrains was scoped, sourced and implemented in the vehicle.
This report investigates the systems integration aspects associated with modern electrical vehicle components. The aspects of integration covered mechanical analysis of shaft coupling, interfacing CANbus systems, high voltage system safety and low voltage wiring loom mapping. The vehicle has reached self-propulsion and validation testing against the initial vehicle modeling is underway.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10092/125102016-01-01T00:00:00ZNovel diaphragm free-piston Stirling cryocooler.
http://hdl.handle.net/10092/12506
Novel diaphragm free-piston Stirling cryocooler.
Caughley, Alan
In 2004, the author of this thesis invented a novel metal-diaphragm based pressure wave generator (DPWG) for pulse tube and Stirling cryocoolers. The invention used a connected pair of metal diaphragms to seal the cryocooler’s clean working gas from a conventionally lubricated drive mechanism at ambient pressure, and to balance the average gas forces on the working diaphragms so the drive only has to work against the pressure wave. The DPWG has since been developed and has proven to be effective and practical, driving pulse tube cryocoolers with up to 1200 W of refrigeration at 77 K. From early in the development of the DPWG, two questions have existed. The first is: Can the connected pair of diaphragms concept suspend the displacer in a free-piston Stirling cryocooler, removing displacer piston-to-cylinder sealing issues? And the second is: Can the large surface areas and radial flows offered by the diaphragms’ flat geometry be used for heat exchange, thus reducing the need for costly heat exchangers? This thesis addresses those two questions. To address the first question, a proof-of-concept prototype was designed, constructed and tested. It did not perform as well as expected but did reach cryogenic temperatures. A second prototype with smaller displacer diaphragms was then designed and constructed. Its performance was significantly better than the first prototype; it achieved a low temperature of 56 K and produced 29 W of refrigeration at 77 K. The prototypes proved that the double diaphragm concept could be used to produce a free-piston Stirling cryocooler and perform refrigeration at cryogenic temperatures. To address the second question, two computer models of the second prototype were developed. The first was with a one-dimensional Stirling machine modeller called Sage; the second with ANSYS® CFX, a commercial Computational Fluid Dynamics (CFD) code. A series of validation exercises were performed to confirm the models’ applicability to the oscillating flow and heat transfer typical of Stirling cryocooler gas spaces. The second prototype was modelled using Sage and CFX; both agreed with the macroscopic behaviour of the prototype and predicted the cooling power within an order of magnitude of the experiments. The CFD model confirmed the second question for the diaphragm on the cold side of the displacer, which was sufficient for heat exchange without a separate heat exchanger. However, it showed that the warm side of the machine needed extra area for heat rejection. The CFD model gave insights into why the second prototype was not performing as well as intended. A CFD model of a modified design, backed up with a Sage model, has predicted that it is possible to make a cryocooler with performance similar to a pulse tube with the same size pressure wave generator and with a higher efficiency.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10092/125062015-01-01T00:00:00ZImplementing finite impulse response (FIR) low pass filter(LPF) with diﬀerent number representations.
http://hdl.handle.net/10092/12503
Implementing finite impulse response (FIR) low pass filter(LPF) with diﬀerent number representations.
Li, Miao
Number representation can be used for representing the coeﬃcients of the digital ﬁlter as a means
of reducing the multiplication size and improved the computation speed. However, when each
coeﬃcient is rounded to the diﬀerent number representations, their quantization diﬀerent error
is caused. This quantization round-oﬀ error of coeﬃcients can inﬂuence the magnitude of the
stopband attenuation when implementing the ﬁnite impulse response(FIR) low pass ﬁlter(LPF).
The number representation systems here include two’s complement number representation sys
tem, canonical signed digit(CSD) number representation system and sum of power-of-two(SPT)
number representation system.
In this work, we analyze the round-oﬀ error of coeﬃcient of digital ﬁlter using diﬀerent number
representation systems and give the probability density distribution of round-oﬀ error at various
word-lengths. As the SPT number representation is also related to the Hamming weight K,
the probability density distribution changes with varies the value of the K. Then implementing
the FIR LPF ﬁlter with the diﬀerent number system to ﬁnd out the inﬂuence of coeﬃcients
quantization on the stopband attenuation.
Furthermore, a cost function is used to connect the computation size and ﬁlter performance
together to ﬁnd a FIR LPF which has acceptable performance and quicker computation. This
cost function is used to indicate the proper word-length and ﬁlter length for approximate FIR
LPF which achieved by diﬀerent number representations systems. After comparison of 1159
of approximate FIR LPF used diﬀerent number representation, we try to ﬁnd out the suitable
number representation which can make the approximate ﬁlter has better ﬁlter performance and
lowest computation size.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10092/125032016-01-01T00:00:00ZHybrid mensurational-physiological models for Pinus taeda and Eucalyptus grandis in Uruguay.
http://hdl.handle.net/10092/12500
Hybrid mensurational-physiological models for Pinus taeda and Eucalyptus grandis in Uruguay.
Rachid Casnati, Ana Cecilia
There is a consensus that prediction systems should be complex enough to predict yield, and the effect of various combinations of forest management practices on the functioning of interactive natural systems, but at the same time maintain a low level of detail in order to have low implementation costs and facilitate their use. For this reason hybrid mensurational-physiological models have gained importance and attention, and it is expected that their adoption will increase in the near future. This study aimed to explore the potential advantages of a hybrid mensurational– physiological model compared to models currently used in forest plantation management, and provide a better understanding of their capability to improve precision and explanation maintaining a certain level of simplicity as required for forest management. This work also aimed to provide updated tools for managing Pinus taeda and Eucalyptus grandis in Uruguay.
In Chapter 2, taper and volume equations were adjusted as those are essential to estimate individual volume and wood products. Emphasis was on testing compatible taper equations, since no models of this type have been developed to date for any species in Uruguay. However, variable exponent equations gave the best performance for predicting diameter at any height with the lowest prediction errors.
In Chapters 3 to 5, three systems of stand level equations comprising dominant height, basal area, maximum diameter, standard deviation of diameters, and mortality were developed using differential equations through three approaches:
i. Traditional time-based models using sigmoidal difference equations that restricted independent variables to age and parameters as functions of variables for region (base approach). ii. Augmented time-based models that had parameters as linear functions of water holding capacity and physiographical variables such as elevation, aspect and slope. iii. Hybrid physiological-mensurational models based on cumulative light sums since time of planting, with potential radiation-use calculated by modifiers accounting for influences of temperature, vapour pressure deficit (VPD), and water balance. These modified light sums replaced time in sigmoidal growth and yield difference equations.
Water holding capacity was the most significant among the surrogate variables tested in the mensurational models for both species (Chapter 3), whereas elevation was seldom significant. Sine and cosine of aspect weighted by the slope, and slope were usually included but to a greater extent to one species than the other. Gains in accuracy of the augmented approach were small compared to the base equations.
When adjusting hybrid growth models (Chapter 4), combinations of radiation modifiers were selected that yielded accurate results. It was important to determine whether or not the gains in accuracy were sufficiently high to justify dropping the least representative modifiers and lose flexibility. Differences in global radiation across terrain corresponding to a variety of slopes orientations were tested to see whether or not they significantly affected growth. Radiation-use modifiers related to water balance and vapour pressure deficit (VPD) produced the highest gains in precision; however the complete formulation (including also temperature) was preferred in order to maximize the model utility. Accounting for aspect and slope when computing radiation flux did not improve precision in any of the state variables for either species.
For fitting hybrid mortality models (Chapter 5), it was hypothesised that the light-use efficiency approach could better explain the process leading to mortality because it accounts for predisposing site characteristics, recurring perturbations, and aggregation of stress. Extended periods of low water stress and short periods of high water stress were specifically tested as predictors of the probability of mortality. Results suggested that increase in stress did not influence the probability of mortality for Pinus taeda. However, stress helped explain the probability of mortality for Eucalyptus grandis with a negative effect: the accumulation of mild water stress tended to decrease the probability of mortality.
For P. taeda, resource availability increased growth and decreased the probability of mortality and mortality rate, but for E. grandis, higher levels of resources increased growth, probability of mortality, and mortality rate. It was hypothesized that the eucalypt species is more sensitive to factors other than water, given a potentially higher tolerance to drought episodes and resilience compared to the pine species.
A comparison of the three contrasting systems in terms of precision and bias as well as their capacity to reflect growth rates changes when site conditions vary was conducted. The comparison was extended to explore possible gains in diameter structure estimates. Results showed that precision tended to increase with higher levels of information; however explanatory variables included in the components of each approach and precision gains varied with species. Any of the three systems of equations can be applied for managing forests in Uruguay, especially for projecting diameter distributions, since the three approaches provided diameter distributions of similar accuracy. Nonetheless models based on the hybrid approach were more precise, especially for E. grandis (with precision gains between 9 and 14% among state variables). Biases of the predicted variables were similar between approaches, but consistently less for estimating mortality in long intervals in the hybrid formulation. Along with precision, this approach offered higher utility.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10092/125002016-01-01T00:00:00Z