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Using 3D SPH to Model the Interactions of Rogue Waves and Floating Tethered Bodies
thesis
posted on 2017-10-16, 01:33 authored by DAVID FRANCIS GUNNThis research
explored the efficacy of using a Smoothed Particle Hydrodynamics (SPH) model as
a technique for predicting the motion of a floating tethered body when
interacting with a number of wave types, including a rogue wave.
First, a preliminary study established the parameter values required for the SPH model to accurately represent fluid boundaries. This was done by exploring the optimal fluid boundary representations using SPH near a free surface and an object boundary. This was followed by an investigation on the use of a forcing region to generate surface waves.
These preliminary studies were then used to address the following research questions:
• Can SPH accurately model the interaction between surface waves and a floating tethered body, and what is the order of magnitude of the errors?
• How accurately can SPH model a rogue wave?
• What are the physical consequences of a rogue wave impact on a floating tethered body?
The findings of the preliminary studies revealed that an SPH model yielded a high level of agreement between its simulated results with actual experimental measurements, when a sufficient resolution for particle spacing was used.
After confidence in the SPH model was obtained, it was used to model the impact of a large- scale rogue wave on a tethered floating object (in this study, a moored ship). The mass of the ship and the stiffness of the cables were varied to determine what effect these have on the response of the ship to a rogue wave. Pressure sensors were placed on the ship to determine the magnitude of the impact forces at various locations. In additional simulations, it was found that increasing the mass of the ship also increased the risk of green water on the ship’s deck. It was also found that the tethering cable’s stiffness had little influence in an impact since the tension forces were an order of magnitude smaller than the buoyancy forces. Finally, the wavelength and height of the rogue wave was varied to investigate the effect these had on the moored ship. It was found that the ship could respond adequately to both of these changed conditions without significant green water on the deck. These simulations indicated that SPH modelling is a viable technique for assisting in the design of offshore vessels, with a high level of accuracy.
First, a preliminary study established the parameter values required for the SPH model to accurately represent fluid boundaries. This was done by exploring the optimal fluid boundary representations using SPH near a free surface and an object boundary. This was followed by an investigation on the use of a forcing region to generate surface waves.
These preliminary studies were then used to address the following research questions:
• Can SPH accurately model the interaction between surface waves and a floating tethered body, and what is the order of magnitude of the errors?
• How accurately can SPH model a rogue wave?
• What are the physical consequences of a rogue wave impact on a floating tethered body?
The findings of the preliminary studies revealed that an SPH model yielded a high level of agreement between its simulated results with actual experimental measurements, when a sufficient resolution for particle spacing was used.
After confidence in the SPH model was obtained, it was used to model the impact of a large- scale rogue wave on a tethered floating object (in this study, a moored ship). The mass of the ship and the stiffness of the cables were varied to determine what effect these have on the response of the ship to a rogue wave. Pressure sensors were placed on the ship to determine the magnitude of the impact forces at various locations. In additional simulations, it was found that increasing the mass of the ship also increased the risk of green water on the ship’s deck. It was also found that the tethering cable’s stiffness had little influence in an impact since the tension forces were an order of magnitude smaller than the buoyancy forces. Finally, the wavelength and height of the rogue wave was varied to investigate the effect these had on the moored ship. It was found that the ship could respond adequately to both of these changed conditions without significant green water on the deck. These simulations indicated that SPH modelling is a viable technique for assisting in the design of offshore vessels, with a high level of accuracy.
