Browsing by Issue Date, starting with "2018-12-03"
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- Multi-scale modelling of waves propagation on the Norwegian CoastPublication . Sánchez, Alonso Madrigal; Bihs, Hans; Jacob, JoséFjords coastlines are attributed to glaciers as the main agent of erosion. Thus, fjords are characterised by an irregular coastline con guration and rapid changes in their deep and steep slopes. These features generate a unique behaviour on the ocean wave propagation and on the water hydrodynamics. Norwegian coastline has environmental conditions to support diverse aquaculture developments along the coast. Therefore, aquaculture in Norway is considered a growing eld with an enormous potential especially in o shore locations. The development of numerical tools, such as wave models, will produce a huge improvement on the di erent technologies used nowadays. To achieve this huge engineering challenge a simulation of the ocean waves reaching the Norwegian fjords will be analysed using coupled numerical models. This study proposed a combined use of two di erent numerical models, cascade of wave models, to utilise the strengths of the models while reducing their disadvantages. For example, spectral wave model such as STWAVE is fast in open ocean but not able to capture the di raction phenomenon, shallow water model such as REEF3D::SFLOW is able to capture most wave transformation phenomenon but limited by water depth; Computational Fluid Dynamic (CFD) model such as REEF3D::CFD captures threedimensional details of water wave but is computationally costly. The results obtained from the large domain and coarse grid model will serve as the input to the next region with middle resolution and a re ned grid size. This is carried on until the results for the area of interest are obtained. A rst step validating the reliability of REEF3D::SFLOW was carried out through the use of a submerged bar case. During the process of testing the feasibility of the cascade of wave models methodology, di erent models were evaluated for speci c domain and topography. As a result, only two models were applied on the nal simulation: STWAVE and REEF3D::CFD. Thus, the combined methodology resulted useful to obtain a rough estimation of the wave propagation and transformation outside the fjords and its potential e ects over Flat ya sh farm development. It can be also an important input for their sh cage design.
- 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.