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Recent Submissions
Experimental Characterization of Sample Tubing Dynamics for the Improvement of Droplet Microfluidic Feedback Control Systems
(University of Waterloo, 2024-11-05) Hahn, Dylan
This thesis presents the development of an experimental methodology to characterize
pressure transient dynamics across liquid sample tubing in the plant of a pressure-driven
droplet microfluidic feedback control system (PDMFCS). To progress the PDMFCS towards
being a widely adopted fluidic analysis tool for non-expert end-users in various
biochemical fields, i.e. progressing the PDMFCS towards modularity, will require utilization
of an accurate plant model to establish informed and robust control system design
procedures. Increased accuracy in the plant model can be obtained through development of
experimental methods to characterize the dynamics associated with the plant components.
Previous PDMFCS implementations have approximated the sample tubing dynamics using
a hydrodynamic equivalent circuit model (HECM), but did not experimentally validate
this model. As well, pressure transient studies performed for other fluid applications do
not model a flow scenario physically similar to that occurring through the sample tubing
during PDMFCS operation, further justifying the need for this present study.
Pressure transient dynamics across the sample tubing of the PDMFCS plant were found
to be characterized as an approximately linear first-order system with transport lag through
estimation of a transfer function (TF), with 95% confidence in uncertainty in the estimated
parameters, from an experimental frequency response obtained by simultaneously measuring
pressure waves at the inlet and outlet of the sample tubing. Decreasing the average
inlet pressure, increasing the tubing length to inner diameter ratio, or increasing the fluid
viscosity, resulted in a decrease of the corner frequency (an increase in the time constant)
of the frequency (step) response of the experimentally estimated TF. Comparing experimentally
estimated TF dynamics to those predicted by the HECM showed that, due to the
assumption of hydrodynamic steady-state flow inherent to its derivation, the HECM fails
to quantitatively approximate the pressure transient dynamics across the sample tubing.
The primary conclusion of this study is that the experimentally estimated TF should be
used, instead of the HECM, to approximate the sample tubing dynamics within the PDMFCS
plant model. Using the experimentally estimated TF to approximate the pressure
transient dynamics across the sample tubing should improve the plant model accuracy,
such that informed and robust control system design methodologies can be developed for
the PDMFCS, which will enhance the modular potential of the system.
The Feasibility and Perceived Impact of the DEmentia Lifestyle Intervention for Getting Healthy Together (DELIGHT) Program for People Living with Dementia and their Care Partners
(University of Waterloo, 2024-10-30) Tupling, Olivia
Improving supports to enhance quality of life for people living with dementia is a priority of research and practice. Multimodal lifestyle interventions that include components such as physical activity, nutrition, and social activity may help support quality of life and function for people living with dementia and their care partners. The DEmentia Lifestyle Intervention Program for Getting Healthy Together (DELIGHT) was co-designed by people with dementia, care partners, community stakeholders, and researchers with the goal of promoting ‘living well’ with dementia. The DELIGHT program incorporates exercise and shared learning on topics related to health and wellbeing (healthy eating, physical activity, social support, mental wellbeing, sleep). The aim here was to assess the feasibility and perceived impact of the 8-week in-person DELIGHT program. Feasibility was evaluated through recruitment rate (target: 6 per month), attendance (target: 75% of sessions), retention (target: 80% of participants who started the program complete post-program assessments), and program acceptability. Perceived impact and challenges and were also assessed through semi-structured interviews with participants, study leaders, and volunteers. Interview transcripts were analyzed using inductive thematic analysis to identify and describe experience with, and impact of, the DELIGHT program. A separate deductive content analysis was used to identify issues related to feasibility (challenges and recommendations). Exploratory effectiveness outcomes included quality of life, physical activity, balance confidence, exercise self-efficacy, nutrition risk, social connectedness, social isolation, balance, strength, and fitness. Quantitative and qualitative results were compared to support a richer interpretation of the programs impact on participants. Seventeen participants completed the DELIGHT program, recruited at an average of 4.25 participants/month, which was lower than our feasibility target. All participants completed the program with an average attendance of 89.7% and 16 (94%) completed post-program evaluation. All (100%) of participants (n=16) and volunteers/study personnel (n=7) described enjoying their participation in the DELIGHT program and reported that they would be interested in participating again. Four themes related to the impact of and satisfaction with the DELIGHT program were identified from interviews. Making the most of today for tomorrow describes the immediate and lasting emotional and physical benefits of the program and the empowerment participants felt over their health, inspiring lifestyle changes. These aligned with group average improvement on assessments of physical function and physical activity. Broadening perspectives and taking action describes how participants and volunteers challenged stigma, providing hope and inspiring action to continue the conversation. Connecting and caring describes the feelings of comfort and belonging among participants and volunteers, inspiring participants to engage and go outside their comfort zone. These aligned with the group average improvement of social connection and maintained low levels of loneliness. Learning together and sharing knowledge describes how participants and volunteers learned from each other’s unique knowledge and perspectives, and the paramount value of learning from experience. All themes generally suggest that DELIGHT supported participants in improving wellbeing however, quantitative measures of quality of life showed a decrease of one point in average scores. Results indicate DELIGHT is a feasible lifestyle intervention for people living with dementia and their care partners with promise for supporting wellbeing but more time may be required to recruit to the program. Further large-scale evaluation is warranted to examine the effectiveness of DELIGHT. In addition, adaptation of DELIGHT for specific ethno-cultural groups should be explored.
Antarctic basal environment shaped by high-pressure flow through a subglacial river system
(Springer Nature, 2022-10-27) Dow, Christine F.; Ross, Neil; Jeofry, Muhammad Hafeez; Siu, Kevin; Siegert, Martin J.
The stability of ice sheets and their contributions to sea level are modulated by high-pressure water that lubricates the base of the ice, facilitating rapid flow into the ocean. In Antarctica, subglacial processes are poorly characterized, limiting understanding of ice-sheet flow and its sensitivity to climate forcing. Here, using numerical modelling and geophysical data, we provide evidence of extensive, up to 460 km long, dendritically organized subglacial hydrological systems that stretch from the ice-sheet interior to the grounded margin. We show that these channels transport large fluxes (~24 m3 s−1) of freshwater at high pressure, potentially facilitating enhanced ice flow above. The water exits the ice sheet at specific locations, appearing to drive ice-shelf melting in these areas critical for ice-sheet stability. Changes in subglacial channel size can affect the water depth and pressure of the surrounding drainage system up to 100 km either side of the primary channel. Our results demonstrate the importance of incorporating catchment-scale basal hydrology in calculations of ice-sheet flow and in assessments of ice-shelf melt at grounding zones. Thus, understanding how marginal regions of Antarctica operate, and may change in the future, requires knowledge of processes acting within, and initiating from, the ice-sheet interior.
Totten Glacier subglacial hydrology determined from geophysics and modeling
(Elsevier, 2020-02-01) Dow, Christine F.; McCormack, Felicity S.; Young, Duncan A.; Greenbaum, Jamin S.; Roberts, Jason L.; Blankenship, Donald D.
Aurora Subglacial Basin (ASB), which feeds Totten Glacier, is a marine basin lying below sea level and contains up to 3.5 m of global sea level equivalent. Rates of future sea level rise from this area are primarily dependent on the stability of Totten Ice Shelf and the controls on ice flow dynamics upstream of the grounding line, both of which may be influenced by subglacial hydrology. We apply the GlaDS subglacial hydrology model to ASB to examine whether the spatial patterns of distributed and efficient drainage systems impact the dynamics of Totten Glacier. We determine the most appropriate model configuration from our series of sensitivity tests by comparing the modeled basal water pressure and water depth results with specularity content data. Those data are derived from ICECAP radar surveys over the same region and represent regions of basal water accumulation. The best match between simulated basal hydrology properties and specularity content shows a strong correspondence in regions of distributed water in the ASB troughs for both water depth and water pressure, but weak correspondence between water depth and specularity content near the grounding line. This may be due to the presence of several large channels draining over the grounding line into the head of Totten Ice Shelf, which are likely not as well represented in the specularity content data as distributed systems. These channels may have a significant impact on melt, and therefore the stability, of Totten Ice Shelf. Within ASB, regions of high water pressure and greater water accumulation correspond well with regions of faster ice flow, suggesting some control of basal hydrology on ice dynamics in this region.
Semi-Analytical Framework for Thermo-Mechanical Analysis of Energy Piles in Elastic and Elastoplastic Soils
(University of Waterloo, 2024-10-29) Paul, Abhisek
Energy piles or geothermal piles are used to reduce the energy demand of a building by helping in the heating/cooling of the building as required. The advantage of energy piles over other ground heat exchangers is that piles are an integrated part of the foundation of a building to carry the superstructure load. The same piles can be used to extract/inject heat from/to the ground and that heat can be used in the cooling/heating of the building. Thus, the energy demand of the building for heating/cooling is reduced. Energy piles are subjected to mechanical load that comes from the superstructure as well as thermal load (temperature change) caused by the heat exchange operation. The combined mechanical and thermal load changes the behavior of the pile foundation. Because the length of the pile is much higher compared to its diameter, the temperature change affects the axial behavior of the pile rather than its lateral response. The settlement of an energy pile is different than a conventional pile foundation as heating or cooling of the pile causes extension in some parts of the pile and compression in other parts of the pile. The axial response of an energy pile under mechanical and thermal loads in terms of vertical settlement, strain, and stress in the pile is calculated in the available literature where the pile-soil interaction has been considered by modeling the soil with equivalent linear and nonlinear soil springs. The representation of soil as springs does not take into account the effect of three-dimensional pile-structure interaction. Analysis of the energy pile considering the three-dimensional pile-structure interaction has been done in the literature using numerical methods which are computationally expensive. Apart from that, the thermo-mechanical behavior of soil needs to be considered in the energy pile analysis because of the temperature change of the pile and soil, and heat exchange between the pile and the soil. In this context, the thermo-mechanical soil constitutive model should satisfy the laws of thermodynamics. The analysis of the energy pile with a thermodynamically acceptable thermo-mechanical soil constitutive model is lacking in the available literature.
In this thesis, a continuum-based semi-analytical framework for the analysis of the energy pile that takes into account the three-dimensional pile-structure interaction is proposed. First, the semi-analytical framework for an energy pile that is embedded in multi-layered soil and subjected to mechanical axial load and thermal load is developed using the variational principle of mechanics by minimizing the potential energy of the pile-soil continuum where both the pile material and soil are considered to behave as a linear elastic material.
In the next part of the thesis, a semi-analytical framework for the same energy pile is developed where the soil is modeled as an elastoplastic material. The analysis framework for the energy pile in elastoplastic soil is developed from the laws of thermodynamics with the energy potential and dissipation function where the plastic behavior of soil is taken into account through the dissipation function. The derived analytical framework is used for elastoplastic soil response with the Drucker-Prager constitutive model. The results from the present analysis are verified with available results in the literature from experiments and numerical analysis. The Drucker-Prager constitutive model does not take into account the effect of temperature on the stress-strain response of the soil. So, this constitutive model is most suitable to model the thermo-mechanical behavior of sand as the effect of temperature on the thermo-mechanical response of sand is not significant. Therefore, energy piles in sand can be analyzed using the present framework with the Drucker-Prager constitutive model. Energy pile in clay needs to be represented with a soil constitutive model that can capture the effect of temperature on the thermo-mechanical response of clay. In the third part of the thesis, the present analytical framework for an energy pile in elastoplastic soil is used to analyze the pile in clay with a thermo-mechanical constitutive model that takes into account the change in the mechanical response of clay due to temperature change. The thermo-mechanical model used in the analysis was developed using the hyperplasticity formalism, which satisfies the laws of thermodynamics. The present framework in all cases predicts results with acceptable accuracy. The present analytical framework predicts the response of energy pile under different loads (mechanical and thermal) in terms of vertical displacement, stress (with <10% difference between the results from the present analysis and finite element analysis/field tests) with acceptable accuracy in less computational time. The run time for the present analysis is approximately 10 and 5 times faster than axisymmetric finite element analysis for elastic and elastoplastic cases, respectively.
In the final part of the thesis, the stresses developed in an energy pile under mechanical and thermal loads are observed for different soil properties. A parametric study is conducted on the developed stresses in an energy pile in single and two-layer soils under multiple loading conditions. A correlation between the applied mechanical and thermal load is established, and under these loading conditions, the effects of soil layering and material properties on the developed stresses are observed. The development of the tensile zone and its range in an energy pile for certain conditions are concluded from the parametric study.