Browsing by Author "Johnson, Jessica"
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- Decision framework for the design and construction of autonomous artificial reefsPublication . Johnson, Jessica; Duarte, DuarteThis thesis focused on the testing and design of an innovative Artificial Reef geometry, as part of the decision framework for the planning, design, construction, placement and subsequent monitoring of a Modular Artificial Reef (MAR). The MAR will be installed off the west coast of Portugal to promote fish biodiversity, increase biomass and to serve as a SCUBA diving point of interest for tourists. Through physical hydraulic flume testing, the Prototype Modular Artificial Reef (PMAR) underwent environmental scenarios to evaluate the current design. These environmental scenarios were designed to imitate both constant flow and wave energy environments. An Acoustic Doppler Velocimeter (ADV) was used to measure flow velocities both upstream and downstream the PMAR to quantify the impact of the PMAR on water flow. After testing, digital photographs were used to create Digital Elevation Models which were overlaid on the original photographs to create an Orthomosaic image. This orthomosaic illustrated the sediment transportation changes in and around the PMAR throughout various testing scenarios. By studying areas of scour and erosion, it was possible to see the impact of the PMAR on sediment transportation. Through testing, sediment was transported along the water flow direction. Overall erosion and scoring increased when wave energy was added to the system. In general, there was erosion around the front end of the PMAR and deposition around the back end. This led to a sinking effect of the entire PMAR with a slight rotation in the same direction as the water flow. It is recommended that a baseplate be added to the design to ensure stability, minimize sinking and prevent the PMAR from overturning in high energy wave conditions. In addition, further testing with multiple modular pieces linked together is required to ensure that the modular design can withstand these environmental strains.
- Numerical analysis of the flow field and cross section design implications in a multifunctional artificial reefPublication . Maslov, Dmytro; Pereira, Eduardo; Duarte, Duarte; Miranda, Tiago; Ferreira, Vasco; Tieppo, Marcos; Cruz, Fábio; Johnson, JessicaNowadays, multifunctional artificial reefs are integrated in coastal areas all around the world. The design of such structures is currently complex and subjective. In this context, it is essential to improve overall design approaches to more effectively relate artificial reef geometry, function and optimal performance to specific deployment sites. Part of the solution to this challenge may lie in the use of in situ data to study the hydrodynamic performance of prospective artificial reefs. This research addresses this issue by performing a numerical investigation of the flow transformation of two similar artificial reef geometries, and the analysis of performance indicators based on (i) artificial reef assembly cross section, (ii) upwelling and (iii) wake regions evaluation, (iv) efficiency indices and (v) streamlines particles. Based on typical data related to wave action, a velocity inlet boundary condition was defined adopting the non-uniform velocity distribution, aimed at simulating the most realistic boundary con-dition at the chosen deployment location. The results showed that the multifunctional artificial reef assembly with the droplet shape cross section exhibited enhanced function performance when compared to a circular shape cross section by providing significantly higher values of the upwelling velocity, wake region and associated efficiency indices. In addition, the procedure presented in this study, which considers oceanographic data at the deployment site, the geometry of the artificial reef, in situ flow characteristics and boundary conditions, as well as the devised fluid flow performance indicators, can be used for the design of artificial reefs during the concept stage in an objective manner to consider the local design requirements.