Department of Mechanical Engineering (Fredericton)

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3D transient modeling of thin-film coated surfaces to predict the temperature and ablated areas during laser processing
3D transient modeling of thin-film coated surfaces to predict the temperature and ablated areas during laser processing
by Babak Baradaran Naghshine, Increasing the biocompatibility of biomaterials is a hot topic in biomedical engineering. Introducing new surface modification methods, that can just slightly enhance the biocompatibility can directly improve the quality of lives of thousands or millions of people all around the globe. The main goal of this thesis is to study laser processed thin film multilayer structures which can be potentially used for biomedical applications. In this thesis, the laser treatment process is numerically modeled to predict the temperature field and surface profile for each set of laser parameters including the average power, repetition rate and scanning speed. The model is successfully verified with experimental measurements. The same model was modified for laser processing of thin film coated metals. The results show that applying a thin film on the surface can completely change the temperature field and make the heat affected zone smaller or larger. A new surface modification method is introduced by combining laser processing and electrospinning technique. In this method, the surface is processed by laser beam and then it is coated with an electrospun thin layer. This method has potential applications in bone implant fabrication. The implant can benefit from excellent biocompatibility of the electrospun layer in short-term, before the fibers are degraded, as well as long-term biocompatibility of the laser treated surface. In vitro tests showed that, this method can improve the biocompatibility, especially when the laser processed surface is coated with nanoscale fibers. Furthermore, it is shown that, by applying the electrospun layer on the surface, the thermal conductivity of the surface is closer to human body’s conductivity. It makes it an attractive method for modification of dental implants, where the cells can be damaged while drinking a hot beverage. Additionally, antibacterial agents (e.g. silver and ampicillin) were added to the fibers as an antibacterial agent, to prevent implant infection.
A new computationally efficient formulation of non-linear predictive controller for dynamically rapid industrial applications
A new computationally efficient formulation of non-linear predictive controller for dynamically rapid industrial applications
by Jacob Mark Wilson, As the computational power available in the control loop increases, the use of model predictive controllers are becoming more cost effective. This has allowed them to be used in industrial facilities but only on certain systems. Systems with fast, non-linear dynamics remain out of reach due to the computational requirements every control cycle. Through leveraging the seminal dynamic matrix model predictive control scheme along with discrete time modeling techniques, an alternative formulation has been developed. Through investigation of the premise that a model predictive controller could be reduced the theory for a stateless discrete predictive controller is derived. Through a series of simulation and experiments the performance of this new controller structure was evaluated. This allowed the theoretical framework of the controllers to be validated in practice. As designed into the controller, the most significant improvement is in the computational time required each control cycle. In addition, the theoretical formulations demonstrated that the computational time can be dynamically fixed irrespective of changing controller parameters. This feature in itself is advantageous as it allows unusually long prediction horizons to improve stability, which was not previously possible. The stateless discrete predictive controller also has the advantage of being stateless, in the sense that it does not base its current prediction on any previous predictions. This allows the controller to adjust quickly to model mismatch or disturbances the system encounters. The discrete formulation of this predictive controller allows for the stateless prediction to be performed without compromising computational time. The simulation and practical results demonstrated the superior control performance in comparison to standard predictive control.
A study on measuring designers' cognitive processes
A study on measuring designers' cognitive processes
by Ganyun Sun, Design cognition, human information processing in design, has been studied for decades in order to understand creative behavior and improve the creativity of design outcomes. Comparing designers’ performance during different design tasks is challenging since data obtained from sketches and verbal protocols are unstructured. Furthermore, there is no established method to evaluate directly the effectiveness and efficiency of the transition from novice to expert designer. This study argued that designers’ cognitive load had an effect on designers’ performance, and therefore designers’ cognitive demands during design tasks should be considered in the evaluation of design outcomes. The concept of cognitive efficiency, describing the relationship between design outcomes and designers’ cognitive demands, was proposed and found to be related to expertise levels and design strategies. Designers’ cognitive processes were described quantitatively using information-based approaches from three different perspectives: the process of problem structuring, the complexity of cognitive actions, and the connections between design ideas. The quantitative measures were found to relate to cognitive efficiency and designers’ expertise levels. The quantitative measures make it possible to highlight where and when cognitive resources should be focused and which design behaviors should be encouraged to improve cognitive efficiency. Effective design strategies related to high cognitive efficiency were also identified. Explicit decomposition and the breadth-first control strategy were found to benefit problem structuring. Generating early design conjectures was related to high cognitive efficiency. The application of the systematic design method helped the designers to organize their design processes and effectively revisit and improve previous design ideas. These design strategies can be used for design education and design method comparison.
Acoustic emissions and response for detection and monitoring of flow-accelerated corrosion
Acoustic emissions and response for detection and monitoring of flow-accelerated corrosion
by Alex Martin, The viability of using acoustic emission or response of a pipe under fluid load as a means of detecting and monitoring flow-accelerated corrosion (FAC) was assessed. A system that used PZT piezoelectric elements was designed, built and tested using a straight resistance probe for on-line measurement of FAC within a circulating water loop. Both passive and active measurement techniques were employed to correlate changes in the system’s frequency response to the FAC rate calculated using the measured electrical resistance of the probe. Two probes of identical geometry and one with a larger inner diameter were constructed and tested. The system was studied at neutral water chemistry at conditions where the FAC was stifled and where it was maximized. The probe was exposed to flow rates between 1.3-4.0 L/min. Temperature was maintained at 140 °C to maximize FAC. The experimental results provided evidence to support the proof of concept for the active system to detect and monitor FAC. Suggestions for future work to develop a numerical correlation for FAC monitoring building on the present work were also provided.
Active vibration control of flexible two-link manipulator
Active vibration control of flexible two-link manipulator
by Jason R. Elliott, A finite element based model predictive controller (FEMPC) is implemented for attenuating vibrations of a two flexible link planar manipulator. This manipulator consists of two revolute joints driven by DC motors. Due to the flexibility of the links, both links are susceptible to vibrations, hence, reducing the accuracy in tracking of the end effector. As such piezoelectric plates are use as actuators to apply corrective action to suppress vibrations. The FEMPC control structure, determining these actions, is based on the structure used in dynamic matrix control (DMC), with the exception that a finite element (FE) model replaces how the predictions are formulated. This FE model is developed from and utilized to described the dynamics of each individual link. The FE predictor uses the measured strain and control actions sent to the setup to simulate the response of each link. Results show that using model predictive control has advantages in vibration control over simple conventional control, in particular proportional control. Furthermore, improvements on the model used in predicting the vibrational response will further improve on the attenuation of vibrations.
An Eulerian model of droplet dispersion in turbulent flow
An Eulerian model of droplet dispersion in turbulent flow
by Sydney David Ryan, Industrial sprays are common in many operations where liquid application to surfaces is required. Simulation of spray characteristics and surrounding flow conditions is crucial for maximizing spray efficacy. Traditionally, droplet modelling has been performed using a Lagrangian approach which requires tracking a sufficient number of droplets to form statistical estimates of droplet deposition. Alternatively, an Eulerian-based flow and droplet transport model using the Direct Quadrature Method of Moments (DQMOM) is applied to spray modeling. This model is coupled with the Reynolds Averaged N avier Stokes (RANS) equations and Shear Stress Transport (SST) turbulence model. The method described uses a novel turbulent diffusion coefficient model based on a full parametric study using Lagrangian particle tracking in a uniform, homogeneous and isotropic turbulent flow field. The model results are compared to: 1) Lagrangian tracking predictions of a log-normal particle size distribution injected into a homogeneous, isotropic turbulent flow field, and 2) full-scale experimental wind tunnel measurements in the anisotropic, non-homogeneous wake of a hollow cone hydraulic nozzle.
An evaluation of force estimation models for axisymmetric hull and sail configurations in translation at drift
An evaluation of force estimation models for axisymmetric hull and sail configurations in translation at drift
by Meghan Carson, An evaluation of current in-plane and out-of-plane force and moment models was performed for a generic submarine model at drift. Computational solutions were developed for an axisymmetric hull and sail configuration at small to moderate drift angles, and the results were validated through comparison with experimental results. Existing research provides either qualitative explanations of the flow patterns created, or quantitative results for the overall forces and moments on the full submarine configuration. Using Computational Fluid Dynamics (CFD) fills a gap in the current literature by providing force and vorticity distributions on the body. The existing algorithm was found to adequately predict the in-plane sideforce and rolling moment coefficients at all drift angles, while the yawing moment coefficient is overestimated. The out-of-plane force and moment coefficients for downforce and pitching moment are accurately estimated for angles of drift at or below 10°. At higher angles, these coefficients are significantly over-predicted, mainly due to particular model assumptions. This study has found that the interference effects of the sail on the hull forces, the downforce ahead of the sail trailing edge, and the interaction of individual vortex structures have a significant effect on the total forces experienced by the submarine. By incorporating these results in the existing force model, the maneuverability of submarines with sails could be better predicted, contributing to the safe operation of these underwater vehicles.
Analysis of a cycloidal wave energy converter using unsteady Reynolds averaged Navier-Stokes simulation
Analysis of a cycloidal wave energy converter using unsteady Reynolds averaged Navier-Stokes simulation
A computational fluid dynamic study was completed to investigate the two-dimensional wave generation and cancellation characteristics of the Atargis Cycloidal Wave Energy Converter (CycWEC). The numerical modeling was based on the unsteady Reynolds average Navier Stokes (URANS) equations and determined the free surface fluctuations using the volume of fluid method. A specialized hybrid grid design was required to accurately resolve the complex viscous flow field resulting from one or more hydrofoils rotating beneath the free surface at a constant angular velocity. The research progressed incrementally from single and two-hydrofoil wave generation concluded with two-hydrofoil wave cancellation. Unlike previous inviscid simulations, the URANS simulations were able to model nonlinear free surface interactions and viscous effects, allowing shaft torques to be numerically predicted for first time. It also provided complete velocity and pressure fields which previous experimental work could not. A grid refinement and time step sensitivity study are completed to increase simulation accuracy and computational efficiency. Fluctuations of wave height, surface pressure distribution, hydrodynamic force, and device efficiency from generated and cancelled wave fields are examined in detail for various hydrofoil pitch angles. For two-hydrofoil wave generation with large pitch angles URANS simulations predicted 94% of the required shaft power is transferred directly to the generated wave field. When operated as an energy extraction device the URANS simulations predicted that up to 92% of the incident wave field was cancelled and 82.7% of the average incident wave power was converted to useful shaft power., Electronic Only. (UNB thesis number) Thesis 9453. (OCoLC)956653838, by Christopher J. Caskey, M.Sc.E. University of New Brunswick, Department of Mechanical Engineering, 2014.
Bioactivity enhancement of titanium by laser micro/nano surface texturing
Bioactivity enhancement of titanium by laser micro/nano surface texturing
by Mitra Radmanesh, The main objective of this thesis is to introduce laser treatment for enhancing the surface bioactivity of titanium for bone and tissue implant fabrication. Improvement to the implant performance could immensely benefit the human patient. Bioactivity enhancement of materials is currently an essential challenge in implant engineering. Micro/nano laser surface texturing of materials offers a simple, accurate method to increase the biocompatibility of materials in one single step. In this thesis, the effects of laser power, scanning parameters, and frequency on surface structure and topographic properties are studied. Through bioactivity assessment of treated titanium substrates, it was found that an increase in power and frequency increases the bioactivity of titanium, while a decrease in scanning speed of the laser could lead to an increase in the cell adhesion ability of titanium. Furthermore, cell adhesion proved to be strongest in areas with higher surface irregularities and titanium oxide concentrations.
Biocompatibility enhancement of crystalline silicon
induced by nanosecond laser pulses for biomedical
device fabrication
Biocompatibility enhancement of crystalline silicon induced by nanosecond laser pulses for biomedical device fabrication
by Candace Colpitts, This thesis study aims to introduce nanosecond laser processing for the enhancement of biocompatibility of pure silicon for biomedical technologies. These results have the potential to contribute to the design of manufacturing processes of innovative biomedical devices and improve the quality of life. This research investigates the trends of various laser parameters including three scanning parameters (line spacing, overlap number, and scanning speed), pulse frequency, and laser power. Biocompatible in vitro assessment was conducted through the use of Simulated Body Fluid (SBF) and cell culturing with NIH 3T3 fibroblasts. The samples with smaller line spacing and higher overlap numbers showed more generation of SiO2 nanofibres, which were shown to be biocompatible under SBF assessment. Scanning speed samples also showed an increase in biocompatibility at lower scanning speeds. Biocompatibility increased with frequency due to the hybrid amorphous SiO2 being more prominent on high frequency samples and providing a favourable site for fibroblast cell proliferation. Fibroblasts also showed preference to higher powers. However, the heat affected zone immediately outside the ablated areas showed a mismatch of crystal orientations causing residual stress. These stress zones were avoided by cells, which lead to promising results for the potential in cell programming and manipulation.

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