Mechatronics Systems Engineering - Theses, Dissertations, and other Required Graduate Degree Essays

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Metamodel-Based Global Optimization Methodologies for High Dimensional Expensive Black-box Problems

Date created: 
2014-12-04
Abstract: 

Many engineering problems involve high dimensional, computationally expensive, and black-box (HEB) functions such as complex finite element analyses or computational fluid dynamics simulations. Global optimization on HEB problems is challenging since it generally requires a large number of computationally expensive simulations. The aim of this thesis is to tackle optimization on HEB problems. Metamodels are mathematical models that are constructed to approximate black-box and expensive functions. Survey of existing techniques shows that metamodel-based optimization has potential to solve HEB optimization problems. High Dimensional Model Representation (HDMR) metamodeling is chosen from the literature, which is subsequently developed to Principal Component Analysis based HDMR in support of random non-uniform sampling. Also, an adaptively changing basis functions strategy is defined to ensure the orthogonality of basis functions with respect to existing samples in order to achieve the best approximation accuracy for Random Sampling HDMR. Variable correlations revealed through metamodeling are used for decomposing high dimensional problems into smaller sub-problems. Then, sensitivity analysis is used to quantify the intensities of the correlations. For problems in which all correlations are weak or there are a mix of weak and strong correlations, the proposed method is very effective in reducing the total number of function evaluations to achieve a similar accuracy. For problems whose correlations are all strong, the proposed method is not be advantageous. An optimization strategy based on iterative metamodel-supported decomposition is proposed in which the decomposition and optimization phases are performed simultaneously and iteratively, in contrast to a one-time decomposition-optimization process. The results show that except for the category of non-decomposable problems with all or lots of strong correlations, the proposed strategy improves the accuracy of the optimization results noticeably. The developed algorithm is applied to a practical engineering problem to test its effectiveness in real-world applications. An optimal assembly planning problem with a 100-dimensional objective function is optimized using the proposed method. Comparison with other optimization methods results and the baseline values shows significant improvement in the obtained optimum with the same number of function calls. The results represent the state-of-the-art for optimization of HEB problems.

Document type: 
Thesis
File(s): 
Supervisor(s): 
G. Gary Wang
Department: 
Applied Sciences:
Thesis type: 
(Thesis) Ph.D.

Aerofoil profile modification effects for improved performance of a vertical axis wind turbine blade

Author: 
Date created: 
2014-10-16
Abstract: 

Due to the growing need of sustainable energy technologies, wind energy is gaining more popularity day by day. For micro power generation vertical axis wind turbine (VAWT) is preferred due to its simplicity and easy to install characteristics. This study investigates the effects of profile-modification on a NACA0015 aerofoil used in VAWTs. The profile-modifications being investigated consist of a combination of inward semi-circular dimple and Gurney flap at the lower surface of the aerofoil. The study also uses a Response Surface Analysis (RSA) based fully automated optimization technique to maximize the average torque produced by the wind turbine blade. The data set used in the RSA optimization is generated using computational fluid dynamics (CFD) simulations. In order to ensure reliability, the model used in the CFD simulations is validated against previous experimental results. The optimized shape of the modified aerofoil is shown to improve in the aerodynamics of the wind turbine blade under both static and dynamic conditions.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Krishna Vijayaraghavan
Department: 
Applied Sciences:
Thesis type: 
(Thesis) M.A.Sc.

Characterization of Strongly Coupled Micro-Resonator Systems for Multi-Sensor Applications

Date created: 
2014-11-13
Abstract: 

The objective of this research is analyzing the behavior of strongly coupled micro-resonating systems. In coupled resonator arrays, the additional degrees of freedom from coupling of the resonators to each other can be employed to enhance the sensitivity and selectivity of the sensor system. In order to achieve this, the effect of coupling strength on sensitivity of the system is investigated. It is shown that sensitivity of the sensor system to perturbations can be increased significantly through proper selection of the coupling coefficient between resonators. To date, the research on coupled resonant sensors has concentrated on weakly coupled systems which mostly depend on measurement of signal amplitudes. Conversely, strongly coupled resonant sensor systems, provide a frequency output with all the advantages of resonant sensing. It is established that by moving to the strongly coupled region, the sensitivity of the coupled system to the input is increased compared to uncoupled resonator systems. Moreover, a method for processing signals from a coupled resonator array is developed which relates the perturbation ratio to the relative change in eigenvalues before and after insertion of perturbation. The method is based on analyzing the relative differences between eigenvalues of the system, which is in contrast to the commonplace methods of focusing on individual modes of a the coupled system. Besides enhanced sensitivity, this property can be employed to reduce the effect of manufacturing tolerances on the sensor system response. The proposed model is experimentally verified using coupled resonator arrays fabricated through in-house and standard micro-fabrication processes

Document type: 
Thesis
File(s): 
Supervisor(s): 
Behraad Bahreyni
Department: 
Applied Sciences:
Thesis type: 
(Thesis) Ph.D.

Development of an interactive engineering design optimization framework

Date created: 
2014-10-29
Abstract: 

Engineering optimization is often completely automated after initial problem formulation. Although purely algorithmic approaches are attractive, keeping the engineer out-of-the-loop also suffers from key drawbacks. First, problem formulation is a challenging task and a poorly formulated problem often causes extra efforts and extended optimization time. Second, stakeholders may not trust the results of an optimization algorithm when presented without context. This thesis uses information visualization to keep designer in-the-loop during design optimization formulation, modeling, optimization, and result interpretation stages. Parallel coordinates is the central representation used, accompanied by two-dimensional projections for navigation and a scatterplot matrix for overview. Methods are presented to split the design and performance spaces into meaningful regions by clustering and by interaction. A new data-mining technique is also presented to find relationships between black-box constraints to remove redundant and unimportant constraints. A software prototype is developed and successfully applied to an automotive assembly optimization problem.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Gary Wang
Department: 
Applied Sciences:
Thesis type: 
(Thesis) M.A.Sc.

Fuel Cell Diagnostics using Electrochemical Impedance Spectroscopy

Date created: 
2014-09-02
Abstract: 

When a proton exchange membrane (PEM) fuel cell runs short of hydrogen, it suffers from a reverse potential fault. This fault, driven by neighboring cells, can lead to anode catalyst degradation and, through cell reversal, to holes in the membrane due to local heat generation. As a result, hydrogen leaks through the electrically-shorted membrane-electrode assembly (MEA) without being reacted, and it recombines directly with air. This recombination results in a reduction in oxygen concentration on the cathode side of the MEA and a fuel cell voltage reduction. Such voltage reduction can be detected by using electrochemical impedance spectroscopy (EIS). In this research, in order to fully understand the effect of this oxygen reduction fault, the impedances of single and multi-cell stacks at different leak rates were measured. Then the impedance signatures were compared with the signatures of stacks having non-leaky cells at different oxygen concentrations with the same current densities. The signatures were analyzed by fitting the leaky stacks and oxygen concentrations impedance data sets with the parameters of a Randles circuit. The correlation between the parameters of the two data sets allows us to understand the change in impedance signatures with respect to a reduction of oxygen in the cathode side. Using the circuit parameters, a model that establishes a relationship between impedance and voltage was also considered. With the help of this model along with the impedance signatures, we are able to detect the reduction of oxygen concentrations at the cathode by using fuzzy logic (FL). However, resolution of detection was reduced with the reduction of leak rate and/or increases in the stack cell-count. The amount of hydrogen leak rates were quantified by simulating the resulting reduced amount of oxygen with the use of neural network (NN) method. Successful implementation of FL and NN methods in a fuel cell system can result in an on-board diagnostics system that can be used to detect and possibly prevent cell reversal failures, and to permit understanding the status of crossover or transfer leaks versus time in operation. Using such system will increase the reliability and performance of fuel cell stacks, where leaks can be detected online and appropriate mitigation criteria can be applied.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Farid Golnaraghi
Department: 
Applied Sciences:
Thesis type: 
(Thesis) Ph.D.

A New Integrated Approach for Modeling Green Passive Cooling Systems

Author: 
Date created: 
2014-08-11
Abstract: 

A new one-dimensional thermal network modeling approach is proposed that can accurately predict transient/dynamic temperature distribution of passive cooling systems. The present model has applications in a variety of electronic and power electronic systems. The main components of any passive cooling solution are heat spreaders, heat pipes, and heat sinks as well as thermal boundary conditions such as natural convection and radiation heat transfer. In the present approach, all the above-mentioned components are analyzed, analytically modeled and presented in the form of resistance and capacitance (RC) network blocks. The proposed RC model is capable of predicting the transient/dynamic as well as steady state thermal behavior of the targeted passive cooling systems with significantly less cost of modeling compared to conventional numerical simulations. Furthermore, the present method takes into account thermal inertia of the system and is capable of capturing thermal lags in various system components under all applicable operating conditions. To validate the proposed model, a number of custom-designed test-beds are also built and a comprehensive experimental study is conducted.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Majid Bahrami
Department: 
Applied Sciences: School of Mechatronic Systems Engineering
Thesis type: 
(Thesis) M.A.Sc.

Optimization of Centrifugal Slurry Pumps through Computational Fluid Dynamics

Date created: 
2014-08-22
Abstract: 

Centrifugal slurry pumps are a very unique turbomachine that must be able to handle the flow of high concentrations of solid particles which greatly accelerate wear. With Computational Fluid Dynamics (CFD), it is possible to accurately simulate the flow through such pumps to predict performance. A centrifugal slurry pump was simulated using water and results were validated with physical test results which also used water. Validation yielded good correlation where the most efficient flow rate was predicted correctly. With the confirmed CFD model, design changes were made to the pump to incorporate splitter blades which are shorter versions of the main blades. Optimization using the Adaptive Response Surface Method algorithm with an Intelligent Space Exploration Strategy was performed to find the optimum splitter configuration to minimize wear in the pump impeller. The optimum splitter configuration yielded an almost 19% decrease in the wear with a slight increase in efficiency.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Siamak Arzanpour
Gary Wang
Department: 
Applied Sciences: School of Mechatronic Systems Engineering
Thesis type: 
(Thesis) M.A.Sc.

Development of a Novel Portable Cooling Device for Inducing Mild Hypothermia

Author: 
Date created: 
2014-08-12
Abstract: 

Therapeutic hypothermia is rapidly becoming an integral part of post-resuscitative care for post-cardiac arrest patients, with cooling increasingly being initiated in the pre-hospital setting in order to improve patient outcome. However, commercially available devices are not sufficiently portable or do not provide enough cooling power. Additionally, despite the significant impact of thermoregulation on core temperature change during rapid cooling, current mathematical models for thermoregulation have not been validated for hypothermic conditions. In the present study, a novel portable cooling device using adsorption cooling has been proposed, and a prototype was developed to prove that the concept is feasible. Additionally, a geometrically accurate 3D model of an upper leg was developed in order to further understand heat transfer in the human body and to validate thermoregulation models from literature. There was good agreement between simulation results and experimental data at 18°C water immersion, however, significant discrepancy was observed at lower temperature.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Majid Bahrami
Carolyn Sparrey
Department: 
Applied Sciences: School of Mechatronic Systems Engineering
Thesis type: 
(Thesis) M.A.Sc.

Design of Interface Circuits for Capacitive Sensing Applications

Author: 
Date created: 
2014-08-08
Abstract: 

This thesis focuses on the design of integrated readout circuits for differential capacitive sensing applications. Such circuits are needed especially for interfacing with microsensors where capacitive transduction is predominantly used. The result of this research is the development of common framework for interface circuitries suitable for different sensing applications. These interface circuits were designed and fabricated in standard Complementary Metal-Oxide-Semiconductor (CMOS) processes and can be integrated into the design of various sensing systems. The proposed circuits in this work are characterized by high dynamic range, low power consumption, and adjustable sensing range. Such circuits promote easy-to-use user interfaces while having a low cost. Three different circuit designs were proposed and form the highlights of this thesis. The first interface circuit is a novel realization of a synchronous demodulation technique. The main advantage of the proposed circuit compared to state-of-the-art is that it has a high sensing dynamic range of 112dB and is capable of measuring capacitance as small as 30 aF with a total power consumption of 8mW. Low power consumption is one of the most important design criteria for portable sensing systems besides accuracy and precision. Following this requirement, low power consumption is the main criterion in the second circuit proposed in this work. This circuit uses a switch-based capacitance-to-voltage converter that is designed and fabricated in 0.35μm CMOS technology. This circuit had a low power consumption of 600μW. Its simple structure offers area and power advantages over the more complex circuits. In addition, its ratiometric sensing feature provides an adjustable sensing range which can be tuned for different applications. This circuit can detect capacitances as small as 230 aF in 1pF range of capacitance. To reduce the effect of parasitics on the circuit performance and improve the linearity, the design of the second circuit was enhanced. By using an additional block and an analog divider, the sensitivity of the circuit to parasitics was significantly reduced. On the other hand, a time based output allowed for the elimination of the analog buffers. The fabricated circuit consumed a total power of only 720μW and was fabricated in 0.35μm CMOS technology. Another advantage of this circuit over the previous designs is that the pulse-width output signal of this circuit can be more easily digitized. The proposed circuits in this thesis have been tested with different types of sensors including humidity, motion, and variable MEMS capacitors. For all of them also, the measurement results are found to be in good agreement with the analytic and simulation results. These circuits can be used as standalone chips or can be integrated into the design of larger sensing systems.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Behraad Bahreyni
Department: 
Applied Sciences: School of Mechatronic Systems Engineering
Thesis type: 
(Thesis) Ph.D.

Highly Sensitive Printed Accelerometer for Biomedical Applications

Author: 
Date created: 
2014-05-27
Abstract: 

This thesis introduces a highly sensitive single-axis printed accelerometer based on a flexible paper substrate. The accelerometer is fabricated by cost-effective silver nano ink printing technologies, and consists of a suspended parallel-plate sensing capacitor. By designing the suspension bridge and proof mass structures, the sensitivity to vertical accelerations is optimized based on simulation results. The optimized design with two long ellipse-shaped bridges exhibits a capacitive sensitivity of 20 fF/g at z-axis acceleration of 1-10 g. A wearable sensing system is proposed which composes of the light-weight flexible accelerometer integrated with a readout circuit. The bandage-type accelerometer system can be conformally attached to various positions on human body for motion detection as well as obtaining vital signs such as human pulse and respiratory rate. Thus, these features allow unobtrusive continuous monitoring of various vital signs and physical activities and acting as a multifunctional sensor in health monitoring system.

Document type: 
Thesis
File(s): 
Supervisor(s): 
Woo Soo Kim
Department: 
Applied Sciences: School of Mechatronic Systems Engineering
Thesis type: 
(Thesis) M.A.Sc.