This thesis is concerned with the modelling of electrical machines for use in variable-speed drives. Even when the structure of the model of the machine is known values have to be assigned to the parameters. In addition, it is usual for only some of the state variables to be measured, any others needed being estimated using the model. The present work is a study of methods of making on-line estimates of the model parameters, using a reduced number of measured states. To offer high level dynamic torque control the non-measured state variables must be indirectly estimated to a high degree of accuracy throughout the complete range of operating conditions. The state estimator is generally classified with respect to the degree of structural complexity. At one end of the spectrum the model is constructed with a very high level of complexity in order to describe fully the system during any operating conditions. Because of this structural accuracy, the model parameters can be fixed prior to running the machine under normal conditions. However, this scheme suffers from a high computational burden in the state estimation process, and requires sophisticated commissioning strategies in order to permit the complete identification of the relatively large parameter set. The alternative is to use a simpler model structure and update the parameters with sufficient speed on-line in order to compensate for the inherently larger structural error. In this thesis the latter method is considered and preferred, as it has a greater robustness to unforeseen system behaviour and is more compatible with existing control strategies. As a consequence of the simple estimator the identification scheme has to compensate for the considerable structural errors. To this end the strategy of full parameter set identification is described. Work has also been done, and is presented, concerning on-line parameter identification using genetic optimisation techniques, which are shown to be well suited to this type of problem. The first studies of modelling and parameter extraction were concerned with dc machines, for these were thought to be simpler to model and to understand. DC machines are also different, in that the simple model includes mechanical parameters, and so represents a more complete system than the models of the ac machine studied later. A number of standard, enhanced and novel parameter identification methods are analysed and implemented on a practical machine and drive test bench. Also included were state estimators, intended to permit speed-sensorless control; however, the limitations on the experimental rig, based as it was around a commercially available drive, meant that some of the testing had to be done by running the estimator off-line, using data recorded from actual runs as the input. The thesis is primarily concerned with the induction machine and specifically the parameters required to permit field and speed sensorless rotor field orientated vector control. Sufficient work was done to allow a preliminary experimental comparison of a number of algorithms. At this stage it appears that several of these could be developed into successful drives, the precise choice depending on the specific application.

Variability of pre-main-sequence stars observed at optical wavelengths has been attributed to fluctuations in the mass accretion rate from the circumstellar disk onto the forming star. Detailed models of accretion disks suggest that young deeply em- bedded protostars should also exhibit variations in their accretion rates, and that these changes can be tracked indirectly by monitoring the response of the dust enve- lope at mid-IR to millimeter wavelengths. Interferometers such as ALMA offer the resolution and sensitivity to observe small fluctuations in brightness at the scale of the disk where episodic accretion may be driven. In this thesis, novel methods for comparing interferometric observations are presented and applied to CARMA and ALMA 1.3mm observations of deeply embedded protostars in Serpens taken 9 years apart. No brightness variation is found above the limits of the analysis of a factor of ~>50%, due to the limited sensitivity of the CARMA observations and small number of sources common to both epochs. It is further shown that follow up ALMA observa- tions with a similar sample size and sensitivity may be able to uncover variability at the level of a few percent, and the implications of this for future work are discussed. / Graduate

No description available.

Variable speed limit (VSL) systems are important active traffic management tools that are being deployed across the U.S. and indeed around the world for relieving congestion and improving safety. Oregon’s first variable advisory speed limit signs were activated along Oregon Highway 217 in the summer of 2014. The variable advisory speed system is responsive to both congestion and weather conditions. This seven-mile corridor stretches around Western Portland and has suffered from high crash rates and peak period congestion in the past. VSL systems are often deployed to address safety, mobility and sustainability related performance. This research seeks to determine whether the newly implemented variable advisory speed limit system has had measurable impacts on traffic safety and what the scale of the impact has been. The research utilizes a before-after crash analysis with three years of data prior to implementation and around 16 months after. Statistical analysis using an Empirical Bayes (EB) approach will aim to separate the direct impacts of the variable advisory speed limit signs from the long term trends on the highway. In addition, the analysis corrects for the changes in traffic volumes over the study period. Three data sources will be utilized including Washington County 911 call data, Oregon incident reports, and official Oregon Department of Transportation crash data reports. The analysis results are compared between data sources to determine the reliability of 911 call data as a proxy for crash statistics. The conclusions should be able to provide an indication of whether variable advisory speed limits can provide increased safety along high crash corridors.

The purpose of this study is to investigate the pricing of variable annuity embedded derivatives in a Lévy process setting. This is one of the practical issues that continues to face life insurers in the management of derivatives embedded within these products. It also addresses how such providers can protect themselves against adverse scenarios through a hedging framework built from the pricing framework. The aim is to comparatively consider the price differentials of a life insurer that prices its variable annuity guarantees under the more actuarially accepted regime-switching framework versus the use of a Lévy framework. The framework should address the inadequacies of conventional deterministic pricing approaches used by life insurers given the increasing complexity of the option-like products sold. The study applies finance models in the insurance context given the similarities in payoff structure of the products offered while taking into account the differences that may exist. The underlying Lévy process used in this study is the Variance-Gamma (VG) process. This process is useful in option pricing given its ability to model higher moments, skewness and kurtosis, and also incorporate stochastic volatility. The research results compare well with the regime-switching framework besides the added merit in the use of a more refined model for the underlying that captures most of the observed market dynamics. / Dissertation (MSc)--University of Pretoria, 2014. / tm2015 / Mathematics and Applied Mathematics / MSc / Unrestricted

This article describes the first development phase of a centrifugal compressor with variable geometry which is designed to match the needs of future heavy-duty engines. Requirements of truck engines are analyzed, and their impact on the properties of the compressor map is evaluated in order to identify the most suitable kind of variable geometry. Our approach utilizes the transformation of engine data into pressure ratio and mass flow coordinates that can be displayed and interpreted using compressor maps. One-dimensional and three-dimensional computational fluid dynamics fluid flow calculations are used to identify loss mechanisms and constraints of fixed geometry compressors. Linking engine goals and aerodynamic objectives yields specific recommendations on the implementation of the variable geometry compressor.

A well-known challenge in vehicle dynamics is to design a vehicle that will not only keep the occupants comfortable, but will also ensure safe and stable operation during various manoeuvres over multiple driving surfaces. A soft and compliant suspension is generally required for good ride comfort, while a stiff suspension with a low centre of mass is required for improved handling. These contradicting factors in the design process is commonly referred to as the ride comfort versus handling compromise. A newly developed semi-active hydropneumatic suspension system is proposed to reduce or negate this compromise by being able to change its characteristics according to the dynamic state of the vehicle. The unit is equipped with two proportional solenoid valves that can provide continuously variable damping. In addition, the valves are able to completely close off flow to compressible gas volumes to provide four discrete stiffness characteristics. This suspension system is based on a previously developed suspension that had only two state (open or closed) valves, which provided discrete damping characteristics. A thorough investigation of the older system proved that the system was capable of addressing the ride comfort versus handling compromise. The purpose of this study was to investigate whether the updated design could deliver improved performance and to recommend focus areas for future research initiatives. The suspension system’s characteristics were determined experimentally by actuating the unit on a test bench. Results indicated that the unit produced the desired stiffness, low damping and response time characteristics. A mathematical model of the suspension unit was developed and validated against experimental data. The model was used in single degree of freedom simulations to investigate both passive and semi-active controlled performance. Results indicated that the suspension could be semi-actively controlled for improve ride comfort. However, the magnitude of improvements with semi-active control, which includes a suitable response time, proved to be rather insignificant compared to the optimum passive suspension. / Dissertation (MEng)--University of Pretora, 2019. / Mechanical and Aeronautical Engineering / MEng (Mechanical) / Unrestricted

Bibliography: pages 155-165. / The unusual spectra of the spatially-resolved nova shells of DQ Her, T Aur and CP Pup are reviewed. Because calculations for these conditions have not been made, recombination models of HI, HeI and CNO from a neutral to a doubly ionized state were constructed. The models are described and the results presented for densities at various temperatures. A photoionization model is also described. The effects of non-uniform density distributions in nova shells have been investigated and the observational consequences discussed. A model of the CP Pup shell is described and the evolution of this plasma during the nova's constant luminosity phase traced. The properties of neon novae are summarized and compared with the features seen in the optical spectra of old classical novae. Enhanced neon abundances are used in the model of the CP Pup Shell to investigate its effect on the evolution of the shell. Finally, the results of some near-infrared observations made on the shells of CP Pup, RR Pic and T Pyx are reported.

Chainsaws have seen a constant improvement over the time of their production and are still an object of improvement by the bigger chainsaw companies. The chainsaw engine is highly developed and optimised for the assigned uses. This thesis project aims to further optimise the engine by implementing a system that allows for variable inertia on the rotational system. A high inertia is needed at higher velocity to reduce speed fluctuations but a high inertia also makes it harder for an object to accelerate, a low start inertia could help accelerate the system and then reach a higher inertia for stability at higher velocities.  The variable inertia system were developed for a Husqvarna 550 XP mk.II. Concepts were developed using the product development process and the evaluation is based on the interpreted needs of the product. The most promising concepts underwent dynamic system simulations to ensure the best performing concept is selected. The chosen concept were then further designed with an iterative process where each iteration was analysed with the finite element method to ensure structural rigidity. The developed product indicates a performance increase. The magnitude of this performance increase is mainly governed by the size constraints in the chainsaw.

Thesis advisor: Paul Cichello / Migration is becoming increasingly common in the developing world. A growing body of literature seeks to address the effects of migration on the families of migrants; namely, the effects of migration on the children of migrants. This study uses the Indonesia Family Life Survey (IFLS) panel dataset to quantify the long-term impacts of experiencing parental migration as a child (aged 5 to 18) on the income of working Indonesian adults. To address the issue of endogenous migration, the out migration rate of an individual’s birth Kabupaten (Regency) is used as an instrumental variable. The results of this study indicate that the proposed instrumental variable strongly predicts an individual’s parental migration status. However, the wide standard errors on the coefficients of interests prohibit any conclusive remarks to be made on the effects of parental migration on future income. This study illustrates how extensive panel datasets, such as the IFLS, can facilitate analyses on the long-term effects of parental migration. The author recommends further research on the topic of parental migration be performed on other outcome variables such as education, measures of health, and subjective wellbeing. / Thesis (BA) — Boston College, 2021. / Submitted to: Boston College. College of Arts and Sciences. / Discipline: Departmental Honors. / Discipline: Economics.