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Recent Submissions
Numerical Study of Interactions between surface waves, currents and hydrography in extreme weather conditions
(2025-01-15) Hughes, Colin; Yes; Doctor of Philosophy; Department of Oceanography; Not Applicable; Oliver Fringer; Yes; Ian Folkins; Michael Dowd; Jinyu Sheng; William Perrie
Surface gravity waves significantly affect air-sea interactions, turbulent vertical mixing, ocean currents and hydrography in the upper ocean, particularly during extreme weather events such as hurricanes and winter storms. Currents in the upper ocean also influence surface waves via the Doppler shift, relative wind effect, refraction and advection. This thesis examines the impact of wave breaking (WB), Langmuir turbulence (LT) and conservative wave effects on the upper ocean dynamics and effects of currents on surface waves during hurricane conditions using a coupled circulation-wave model. The wave-current interactions (WCIs) are investigated numerically in two cases using (a) idealized hurricanes moving at three translational speeds and (b) Hurricane Arthur (2014) over the northwest Atlantic Ocean. Model results in the fully coupled run are examined in comparison with results in other runs in which wave effects are selectively disabled to quantify main physical processes of WCIs, with a special focus on wave-induced changes to the upper ocean turbulent kinetic energy (TKE), thermal structure and currents. For the case of idealized hurricanes, analyses of model results reveal that LT has a larger impact on upper ocean currents, temperature and TKE, compared to the other considered processes. The combined wave effects reduce the surface currents in the front two quadrants of the hurricane and enhance the cold wake and near-surface cooling, predominantly to the right of the storm track. For the case of Hurricane Arthur, both the LT and WB driven acceleration are found to be important to storm-induced changes in the upper ocean temperature and circulation. By contrast, the WB induced surface flux of TKE has a limited effect on the temperature, salinity and currents in the surface layer. Over pathways of the Gulf Stream, the large WCIs reduce the significant wave heights (SWHs) of surface waves during Hurricane Arthur, with the biggest differences occurring to the right of the storm track. SWHs on the left hand side of the storm are limited by the shorter fetch, shallower water depths and coastline.
A City Transformed? Urban Development and the Role of Canadian Railway Policy in Halifax, Nova Scotia, 1900-1920
(1992-03) Hodgins, Murray B.; Not Applicable; Master of Arts; Department of History; Not Applicable; unknown; Not Applicable; David Sutherland; Henry Roper; Michael Cross
This thesis analyzes the development of the city of Halifax in the first two decades of the twentieth century, emphasizing the themes of suburban growth, the rise of municipal boosterism, and the drive for industrial development. During this period the notions of privacy and autonomy of the traditional leadership of Halifax were challenged by Ottawa's decision to build a modern wharf and rail complex in the heart of Halifax's genteel south end. This challenge and the responses it generated within the city's business elite, civic administration, and Civic Improvement League, a group committed to the planned and orderly development of the city, provide an opportunity to explore major elements of the city building process in post Confederation Atlantic Canada.
The federal design, a massive departure from the existing course of development, was announced as a fait accompli. Fear of the project's vulnerability to political opposition compelled the booster element in the business elite to support the proposal as presented, despite the fact that the elite residential district would be destroyed. The municipal administration and the Civic Improvement League yielded to pressure and "rubber stamped" elite approval of the project. The League rose to assume the role of advocate for the city's interests, and used this position to continue its pursuit of comprehensive planning and orderly development. Its progressive goals were reduced to the enactment of protective zoning legislation for the residential area, however. The decline in national economic fortunes after 1913, and the onset of post-war economic deflation in 1921, slowed the city's growth to a halt. This decline rendered obsolete the optimistic projections behind the Ocean Terminals, and left the city of Halifax with a large, federally-controlled transportation complex in its formerly proud south end.
TREATMENT PERFORMANCE ASSESSMENT AND MODELING OF A SOIL-BASED WASTEWATER TREATMENT SYSTEM IN NORTHERN CANADA
(2025-01-14) Carvalho Boratto, Débora; Not Applicable; Master of Applied Science; Department of Civil and Resource Engineering; Not Applicable; n/a; Not Applicable; Dr. Lauren Somers; Dr. Azadeh Kermanshahi pour; Dr. Rob Jamieson; Dr. Barret Kurylyk
Wastewater treatment in northern communities is an ongoing challenging. This research focused on the performance assessment and modeling of a passive soil-based wastewater infiltration system in Fort Good Hope, Northwest Territories. A combination of year-round site-specific field data and physically-based numerical modeling of subsurface contaminant transport was used. The investigations reveal that site conditions allow satisfactory system performance despite harsh operating routines, with accumulation of nitrate in groundwater being the most prominent concern. Wintertime conditions have a significant impact on the system’s hydrodynamics and microbial community structure. Model results indicate that an improved effluent distribution system would be required to avoid system failure from excessive mounding in more restrictive scenarios. Atypical operation routines can exhibit advantages from a hydraulic perspective but decrease pollutant removal efficiency compared to conventional procedures. Ultimately, the research findings contribute to addressing knowledge gaps related to the use of soil-based wastewater treatment systems in northern regions.
Autonomous Landing of an Unmanned Aerial System on Water in an Unknown Sea State
(2025-01-12) Taylor, Connor; Not Applicable; Master of Applied Science; Department of Mechanical Engineering; Not Applicable; n/a; Not Applicable; Dr. Guy Kember; Dr. Clifton Johnston; Dr. Mae Seto; Dr. Robert Bauer
Unmanned aerial systems (UAS) are used in the marine and oceans environment for a variety of purposes. In this thesis, an approach is taken to enable safe and reliable autonomous landing of a UAS on the water's surface in an unknown sea state. With a UAS capable of landing on the water's surface under a range of sea state wave conditions, the types of mission that a UAS can undertake in marine and oceans environments will be expanded.
In this work, it is assumed the UAS has no prior information of the water surface wave characteristics at the landing spot. Therefore, algorithms were developed to enable the UAS to determine the dominant wave period, significant wave height, and mean wave propagation direction in-situ using range measurements with onboard range sensors. With the desired ocean wave characteristics identified, a method was devised to identify persistent low wave-height segments in the wave field, over a spot, using onboard range sensor measurements. These persistent low wave-height segments provide safe landing windows for the UAS. A staged landing algorithm was then developed to ensure safe and timely autonomous landing of the UAS on the water surface. In addition, an investigation was conducted to determine the efficacy of ultrasonic sensors to measure wave heights when the sensors are in motion and mounted at oblique angles on the UAS.
The contributions of this work are: a timely method to identify water surface wave characteristics in situ using range sensor measurements, a means to classify and identify low wave-height segments of a wave field using range sensor measurements, a staged landing algorithm for safe and reliable landing on the water's surface in a sea state, and the analysis of the efficacy of an ultrasonic sensor when mounted at oblique angles to measure water wave heights.
Development of a flexible electronic control unit for seamless integration of machine vision to CAN-enabled boom sprayers for spot application technology
(Elsevier B.V, 2024-12-01) Mozammel Bin Motalab; Ahmad Al-Mallahi
This research work aimed to develop an Electronic Control Unit (ECU) to establish a flexible bridge between machine vision and boom sprayer to control nozzles individually for pesticide spot application based on the Controller Area Network (CAN). The ECU consisted of two electronic entities. The first used UART protocol to parse machine vision messages, detect pest areas, and convert them into binary arrays for nozzle activation. The second received these arrays and generated nozzle controller CAN frames which were broadcast to control the sprayer nozzles on the implement bus. The ECU was tested in four scenarios involving combinations of three machine vision systems and two nozzle systems. The lab tests confirmed, assuming accurate detections, the ECU successfully sent spray commands to all targets across various camera-nozzle ratios. However, at specific ratios (1:3 and 1:6), some nozzles opened in unintended patterns. In the fourth scenario conducted in the field at a 1:2 ratio, all targets were sprayed regardless of their dimensions and distribution in the field. In this scenario, the sprayer operated at speeds of 3.22 km/h, 6.44 km/h, and 9.66 km/h, demonstrating real-time spraying with 55° angled nozzles, where the ECU sent CAN messages every 10ms and issued 400 ms spray commands upon detection, achieving a minimum spray length of 345 mm per detection.
In Memoriam: Dale Ells
(Dalhousie University, 2025)