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- Lau, Chun-Yu, et al.
(författare)
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A novel CFD approach for the prediction of ride control system response on wave-piercing catamaran in calm water
- 2023
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Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018 .- 1873-5258. ; 286, s. 115494-115494
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Tidskriftsartikel (refereegranskat)abstract
- Ride Control Systems (RCS) on high-speed vessels help improve passenger comfort and mitigate dynamic structural loads. Incat Tasmania Wave-Piercing Catamarans (WPC) use RCS consisting of a central T-foil, and a stern tab on each deli-hull. Previous towing tank studies on a 2.5 m model of a 112 m WPC have demonstrated significant reductions in motions with the use of a T-foil and stern tabs. To extend this work, this study examines the use of Computational Fluid Dynamics (CFD) to predict the ship's response with RCS implemented. The model-scale WPC was simulated in calm water conditions, traveling at 2.89 m/s (Fr∼0.6), with step responses applied at the T-foil and stern tabs, to determine the trim and sinkage. The T-foil was implemented in CFD using two methods: 1) Overset mesh; 2) Forcing function. By replacing the geometric mesh with a lift force coefficient and forcing function, the setup difficulty and computational cost were reduced. Only about 7% difference was observed between CFD and experiments, but no significant difference was found between the methods of overset mesh and forcing function. This has proven the ability of CFD to predict vessel responses to RCS step changes in calm water, and the simplified forcing function method is recommended.
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| 2. |
- Lau, Chun-Yu, et al.
(författare)
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High-speed catamaran response with ride control system in regular waves by Forcing Function Method in CFD
- 2024
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Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018 .- 1873-5258. ; 297
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Tidskriftsartikel (refereegranskat)abstract
- An innovative Computational Fluid Dynamics (CFD) approach, defined as the Forcing Function Method (FFM), is used to simulate Ride Control Systems (RCS) on an Incat Tasmania Wave-Piercing Catamaran vessel in analysis conducted at model scale. This study examines the FFM's capabilities in head sea regular waves using CFD, and considers three ride control scenarios: Bare Hull (BH), Pitch Control (PC), and Non-Linear Pitch Control (NL PC). CFD-predicted vessel motion is compared to experimental data from a 2.5 m Incat Tasmania Wave-Piercing Catamaran model at 2.89 m/s (Fr∼0.6), showing good agreement. Modification in FFM to account for emergence of control surfaces from the water, and time series of lift forces produced by FFM are also discussed. The frequency domain analysis using heave and pitch Response Amplitude Operators (RAOs) showed a good of agreement in motion reduction trends between CFD and experiments, providing a high level of confidence in the FFM predictions. Dimensionless vertical accelerations are calculated along the length of hull using the various control algorithms, showing a considerable reduction in acceleration, especially at the bow. These outcomes demonstrate the novel CFD approach, FFM, that can be used by ship designers for predicting high-speed vessel motion reductions from deployment of RCS, and thereby improving passenger comfort.
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| 3. |
- Reithmaier, Gloria M.S., et al.
(författare)
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Rainfall drives rapid shifts in carbon and nutrient source-sink dynamics of an urbanised, mangrove-fringed estuary
- 2021
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Ingår i: Estuarine, Coastal and Shelf Science. - : Elsevier BV. - 0272-7714. ; 249
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Tidskriftsartikel (refereegranskat)abstract
- © 2020 Elsevier Ltd Estuaries provide valuable ecosystem services, such as carbon storage and nutrient retention, which may be affected by episodic rainfall events. This study aimed to investigate the short-term effect of episodic rainfall on alkalinity, dissolved carbon and nutrient biogeochemistry in a small, urbanised and mangrove-fringed estuary. High temporal resolution sampling (1.5-h interval) at upper and lower estuary sites, as well as groundwater sampling, were conducted over two weeks to assess estuarine source/sink dynamics of total alkalinity (TAlk), organic alkalinity (OAlk), dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), nitrate, nitrite, ammonium and phosphate. Rapid, short-term changes in estuarine biogeochemistry and mixing were triggered by two episodic rainfall events, which delivered 26 mm over 2 h and 39 mm over 21 h. The estuary was a source for TAlk and DIC exporting 2.2 ± 1.9 and 2.2 ± 1.5 mmol/m2 catchment/d, respectively, to the coastal ocean during the observation period. On average, OAlk accounted for 8% of TAlk at the upstream and 3% at the downstream site. Unlike pristine mangrove systems, the estuary was a net sink for DOC, equivalent to ~23% of the DIC source. Rainfall increased catchment nutrient inputs into the estuary, which was a source for ammonium, but a sink for nitrate and nitrite (NOx) throughout the study period. In contrast, phosphate dynamics were less clear. Estuarine biogeochemical transformations affected the exchange with the coastal ocean, driving net TAlk export and by acting as a sink for catchment-derived nutrients. Our high-temporal resolution results suggest that rainfall events rapidly modify estuarine biogeochemistry and mixing, altering the net fluxes of TAlk, dissolved carbon and nutrients to the coastal ocean.
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