Steady two-dimensional natural convection in air-filled, regular and irregular inclined enclosures has been investigated numerically. The effect of various configurations of bidirectional temperature gradients on mode transition of thermal convection inside the cavity has been investigated. Numerical treatment of temperature discontinuity at the comer points of the cavity and its effect on the calculated Nusselt number has been discussed. Rayleigh numbers range between 103 and 104, aspect ratio (width/height) =1,2,4, and angle of inclination in the range between 0 and 90°. While the cavity bottom and top walls were kept at constant temperatures at Th (heated) and at Tc (cooled), respectively, thermal conditions of end walls were varied. In addition to the base case of insulated end walls, seven different configurations of thermal conditions of the two side walls have been studied. Results show that numerically predicted heat transfer rates strongly depend on the numerical treatment of temperature discontinuities at cavity comer points. Results also indicate that thermal conditions of cavity end walls have a significant effect on mode-transition of thermal convection flows; and hence, on heat transfer effectiveness inside the cavity, and on the Hysteresis phenomenon occurred as the cavity angle of inclination varied from zero (horizontal position) to 90 ° (vertical position) and back to zero. The effect of curved bottom is carried out by replacing flat bottom of the cavity with a curved one. Only insulated end walls were discussed in curved case. Results indicated that heat transfer rate and mode transition are strongly dependent on the height of curvature of the bottom wall, which offers more flexibility in controlling flow mode-transition, and hence, effectiveness of heat transfer inside the cavity. / Thesis / Master of Applied Science (MASc)

No description available.

Opportunities for enhancing the security and reliability of power supply as well as the utilization of renewable and efficient energy sources have generated major interest in Microgrids. A microgrid typically consists of interconnected loads, distributed generators (DG) and energy storages, and should be able to operate in parallel with the utility grid or as a power-island. The main focus of this thesis is on the transition between parallel and islanded operation of a microgrid. A literature review on existing microgrids was carried out. Based on the survey, a microgrid test system was implemented on PSCAD/EMTDC simulation program. The microgrid controls essential for the study and a load shedding scheme were designed and implemented. When the microgrid changes from parallel to islanded operation, its controls need to be changed. It was found that delays in microgrid control mode transition can impact the amount of load need to be shed to preserve the frequency stability and the power quality of the islanded microgrid. The importance of fast detection of islanding was therefore highlighted. The IEEE standard 1547.4-2011 recommends application of the existing DG synchronization criteria for microgrid synchronization. The adequacy of these criteria for synchronization of a microgrid with highly unbalanced loading was investigated. It was found that the required criteria can be met with the support of switched capacitors for voltage balancing, and a circuit breaker supervised by a synchro-check relay is sufficient to successfully reconnect an islanded microgrid back to the utility. In order to meet the requirement for fast detection of islanding of microgrids, new islanding detection technique was proposed. In the proposed scheme, Discrete Wavelet Transform was used to extract features from transient current and voltage signals, and then a Decision Tree classifier was employed to distinguish islanding events from other transients. Simulation based tests asserted that the proposed technique has a high reliability and fast response compared to most existing islanding detection methods. Also, the detection time of the proposed method was invariant with the power imbalance in the microgrid, and gave a zero non-detection-zone with any type of generator.

Opportunities for enhancing the security and reliability of power supply as well as the utilization of renewable and efficient energy sources have generated major interest in Microgrids. A microgrid typically consists of interconnected loads, distributed generators (DG) and energy storages, and should be able to operate in parallel with the utility grid or as a power-island. The main focus of this thesis is on the transition between parallel and islanded operation of a microgrid. A literature review on existing microgrids was carried out. Based on the survey, a microgrid test system was implemented on PSCAD/EMTDC simulation program. The microgrid controls essential for the study and a load shedding scheme were designed and implemented. When the microgrid changes from parallel to islanded operation, its controls need to be changed. It was found that delays in microgrid control mode transition can impact the amount of load need to be shed to preserve the frequency stability and the power quality of the islanded microgrid. The importance of fast detection of islanding was therefore highlighted. The IEEE standard 1547.4-2011 recommends application of the existing DG synchronization criteria for microgrid synchronization. The adequacy of these criteria for synchronization of a microgrid with highly unbalanced loading was investigated. It was found that the required criteria can be met with the support of switched capacitors for voltage balancing, and a circuit breaker supervised by a synchro-check relay is sufficient to successfully reconnect an islanded microgrid back to the utility. In order to meet the requirement for fast detection of islanding of microgrids, new islanding detection technique was proposed. In the proposed scheme, Discrete Wavelet Transform was used to extract features from transient current and voltage signals, and then a Decision Tree classifier was employed to distinguish islanding events from other transients. Simulation based tests asserted that the proposed technique has a high reliability and fast response compared to most existing islanding detection methods. Also, the detection time of the proposed method was invariant with the power imbalance in the microgrid, and gave a zero non-detection-zone with any type of generator.

Four different thermoviscoplastic relations, namely, the Litonski-Batra, the Johnson-Cook, the Bodner-Partom and the power law are used to model the thermoviscoplastic response of a material. Each one of these relations accounts for strain hardening, strain-rate hardening and thermal softening of the material. The material parameters in these relations are found by solving an initial-boundary-value problem corresponding to simple shearing deformations so that the computed effective stress vs. the effective plastic strain curves match closely with the experimental data of Marchand and Duffy who tested thin-walled HY-100 steel tubes in torsion. These four viscoplastic relations are used to analyze dynamic thermomechanical deformations of a prenotched plate impacted on the notched side by a cylindrical projectile made of the same material as the plate. The impact loading on the contact surface is simulated by prescribing the time history of the normal component of velocity and null tangential tractions. A plane strain state of deformation is assumed to prevail in the plate and its deformations are studied for different values of the impact speed. The in-house developed finite element code employs constant strain triangular elements, one point integration rule, and a lumped mass matrix. The Lagrangian description of motion is used to describe deformations of the plate. The coupled nonlinear partial differential equations are first reduced to coupled nonlinear ordinary differential equations (ODEs) by using the Galerkin approximation. The ODEs are integrated by using the stiff solver, LSODE, which adaptively adjusts the time step size and computes the solution within the prescribed accuracy. Results computed with the four constitutive relations are found to be qualitatively similar to each other and the general trends agree with the experimental observations in the sense that at low speed of impact, a brittle failure ensues at a point on the upper surface of the notch tip. However, at high impact speeds, a ductile failure in the form of a shear band initiates first from a point on the lower surface of the notch tip. The predicted speed at which the failure mode transitions from brittle to ductile is different for the four viscoplastic relations. Results have been computed using the Bodner-Partom law to study the effects of the notch tip radius and the presence of a circular hole ahead of the notch-tip. For sharp elliptic notch tips, it is found that there is no failure transition speed and the ductile failure always preceeded the brittle failure for the range of the impact speeds studied. For the hole located on the axis of the circular notch tip, the brittle failure always preceeded the ductile failure and it initiated at a point on the lower surface of the circular hole. / Ph. D.

No description available.

In this thesis, an architecture for the adaptive mode transition control of unmanned aerial vehicles (UAV) is presented. The proposed architecture consists of three levels: the highest level is occupied by mission planning routines where information about way points the vehicle must follow is processed. The middle level uses a trajectory generation component to coordinate the task execution and provides set points for low-level stabilizing controllers. The adaptive mode transitioning control algorithm resides at the lowest level of the hierarchy consisting of a mode transitioning controller and the accompanying adaptation mechanism. The mode transition controller is composed of a mode transition manager, a set of local controllers, a set of active control models, a set point filter, a state filter, an automatic trimming mechanism and a dynamic compensation filter. Local controllers operate in local modes and active control models operate in transitions between two local modes. The mode transition manager determines the actual mode of operation of the vehicle based on a set of mode membership functions and activates a local controller or an active control model accordingly. The adaptation mechanism uses an indirect adaptive control methodology to adapt the active control models. For this purpose, a set of plant models based on fuzzy neural networks is trained based on input/output information from the vehicle and used to compute sensitivity matrices providing the linearized models required by the adaptation algorithms. The effectiveness of the approach is verified through software-in-the-loop simulations, hardware-in-the-loop simulations and flight testing.

No description available.

Plane strain deformations of an elastoplastic material are studied using numerical methods. In the first chapter, a meshless formulation of the static small strain elastic-plastic problem is formulated using the meshless local Petrov-Galerkin method. The code is validated against the small strain plasticity routines in the commercial finite element code ABAQUS for two basic configurations with loading, unloading, and reloading. The results are found to agree within 5%. The validated code is then used to analyze the stress intensity factor (SIF) in a double edge-cracked plate. Deformations of the plate are studied both with and without exploiting the symmetry conditions. The penalty method is used to enforce the essential boundary condition in the former case. When analyzing the deformations of the entire plate, the diffraction method is employed in order to introduce the discontinuity in the displacement field across the crack faces. The log-log and a higher order extrapolation technique due to Dally and Berger (1996) are used to calculate the SIF. It is found that the penalty method was inadequate to enforce the essential boundary conditions in the vicinity of the crack tip and that in this region the deformations were oscillatory. Consequently, the SIF calculation using the higher order technique was not accurate. It is also found that for a small plastic zone (3% of the cracked length) the SIFs do not differ significantly from their values for the corresponding linear elastic problem. In the second chapter, a finite element formulation of the dynamic deformations of a micro-porous thermoviscoplastic solid is formulated. The heat conduction in a material is assumed to be governed by a hyperbolic heat equation; thus thermal and mechanical waves propagate with finite speeds. The formation and propagation of an adiabatic shear band (ASB) inplane strain tensile deformations is studied for eleven materials. The ASB is assumed to form when the maximum shear stress has been reduced to 80% of its peak value at a point and it is deforming plastically. The materials are ranked according their susceptibility to the formation of an ASB. A parametric study of the effect of the initial defect strength where the defect is assumed through an initially inhomogeneous distribution of porosity, the thermal conductivity, the thermal wave speed, and the applied strain-rate upon the ASB initiation and propagation is conducted. It is found that the susceptibility ranking for this configuration differs somewhat from that previously found for simple shear and torsion of thin-walled tubes. It is also found that thermal conductivity influences ASB initiation and propagation only for materials with large values of · and that for such materials an adiabatic model may not be adequate. The effects of initial defect strength and the nominal strain-rates are both found to be consistent with simple shearing studies except that the ASB propagation speed was found to decrease with increasing nominal strain-rate. It is found that the criterion employed for ASB initiation accurately predicts the onset of the collapse of the total axial load applied to the body. In the final chapter, the formulation from the previous chapter is modified to permit the formation and propagation of brittle and ductile fracture. Deformations of the impact loaded double edge-crack specimen of Kalthoff and Winkler (1987) are studied. The brittle to ductile failure mode transition with increasing impact speed was found. Previous studies have focused on identifying the transition speed and did not allow for crack propagation. In this study, crack propagation is achieved through a nodal release algorithm and interpenetration of the crack surfaces is prevented using stiff-spring contact elements. Brittle fracture is assumed to occur when the maximum tensile principal stress achieves a critical value and the ductile fracture is assumed to occur when the effective plastic strain reaches a critical value. It is found that the transition speed for 4340 steel is approximately 54 m/s. For the brittle failure, the stress field is found to be significantly modified by the propagating crack and in the vicinity of the propagating crack the field is mode-I dominant. The crack formed through brittle fracture is found to completely propagate through the plate. For the ductile failure, the distribution of effective plastic strain about the crack tip is not significantly altered by the formation of the crack. The temperature rise in the vicinity of the ductile crack is found to be approximately 45% of the melting temperature of the material. / Ph. D.

abstract: Kinetic inductance springs from the inertia of charged mobile carriers in alternating electric fields and it is fundamentally different from the magnetic inductance which is only a geometry dependent property. The magnetic inductance is proportional to the volume occupied by the electric and magnetic fields and is often limited by the number of turns of the coil. Kinetic inductance on the other hand is inversely proportional to the density of electrons or holes that exert inertia, the unit mass of the charge carriers and the momentum relaxation time of these charge carriers, all of which can be varied merely by modifying the material properties. Highly sensitive and broadband signal amplifiers often broaden the field of study in astrophysics. Quantum-noise limited travelling wave kinetic inductance parametric amplifiers offer a noise figure of around 0.5 K ± 0.3 K as compared to 20 K in HEMT signal amplifiers and can be designed to operate to cover the entire W-band (75 GHz – 115 GHz).The research cumulating to this thesis involves applying and exploiting kinetic inductance properties in designing a W-band orthogonal mode transducer, quadratic gain phase shifter with a gain of ~49 dB over a meter of microstrip transmission line. The phase shifter will help in measuring the maximum amount of phase shift ∆ϕ_max (I) that can be obtained from half a meter transmission line which helps in predicting the gain of a travelling wave parametric amplifier. In another project, a microstrip to slot line transition is designed and optimized to operate at 150 GHz and 220 GHz frequencies, that is used as a part of horn antenna coupled microwave kinetic inductance detector proposed to operate from 138 GHz to 250 GHz. In the final project, kinetic inductance in a 2D electron gas (2DEG) is explored by design, simulation, fabrication and experimentation. A transmission line model of a 2DEG proposed by Burke (1999), is simulated and verified experimentally by fabricating a capacitvely coupled 2DEG mesa structure. Low temperature experiments were done at 77 K and 10 K with photo-doping the 2DEG. A circuit model of a 2DEG coupled co-planar waveguide model is also proposed and simulated. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2016