Este trabalho tem como objetivo desenvolver ferramenta computacional para simulação e análise do fenômeno de penetração e cravação de estacas torpedos em solo marítimo. A abordagem será baseada no método Moving Particle Semi-Implicit (MPS). Por se tratar de um método de partícula, sem malha, o mesmo apresenta grande flexibilidade na modelagem de problemas de interação fluido-sólido com fragmentação ou junção de superfície livre e grandes deslocamentos ou deformações dos sólidos, fenômenos esses presentes no impacto e cravação da estaca no solo marítimo. Para isso, dois desafios foram elencados: a modelagem dos solos como fluidos não-newtonianos e a determinação da força de arrasto viscosa na superfície de sólidos. A modelagem do fluido não-newtoniano foi feita considerando os modelos de Power Law, Bingham e Herschel-Bulkley. O cálculo da força de arrasto viscosa foi avaliado determinando-se o gradiente da velocidade do fluido na direção normal à parede com base na regressão polinomial. Por simplicidade, foi considerada a hipótese de que a variação da velocidade na direção tangencial da parede é muito menor se comparada a variação da mesma na direção do vetor normal. O método implementado, assim como o escoamento de fluidos não-newtonianos, foi validado por meio de comparação entre o resultado obtido de simulações com geometrias pré-definidas e as respostas analíticas para tais casos. Como exemplo de aplicação da ferramenta computacional desenvolvida, um caso simplificado de cravação das estacas torpedos foi simulado avaliando-se o seu deslocamento dentro do solo e os esforços cisalhantes a ela submetidas. / This work aims to develop computational tools to simulate and analysis the torpedo anchor penetration in marine soil. The approach will be based on the Moving Particle Semi-Implicit (MPS) method. Because it is a meshless method, it is extremely flexible to model fluid-solid interaction with fragmentation or junction of free surface and large displacements or deformations of solids, phenomena presented at the torpedo anchor impact. Two challenges were listed: the modeling of soils as non-Newtonian fluids and the determination of the viscous drag on the solids surface. The modeling of non-Newtonian fluid was done based on the Power Law, Bingham and Herschel-Bulkley models. The calculation of the viscous drag was evaluated by determining the velocity gradient in the normal direction of the wall based on polynomial regression considering the fluid particles near the solid wall. In this work, for sake of simplicity, the hypothesis that the velocity variation in the tangential direction of the wall is much smaller compared to its variation in the normal direction is adopted. The proposed technique, as well as the flow of non-Newtonian fluids, were validated comparing the results obtained in flow simulations with predefined geometries with the expected analytical responses. As an example of the application of the computational tools developed, a simplified case of torpedo penetration was simulated by evaluating its displacement and the shear stresses submitted to it.

Este trabalho tem como objetivo desenvolver ferramenta computacional para simulação e análise do fenômeno de penetração e cravação de estacas torpedos em solo marítimo. A abordagem será baseada no método Moving Particle Semi-Implicit (MPS). Por se tratar de um método de partícula, sem malha, o mesmo apresenta grande flexibilidade na modelagem de problemas de interação fluido-sólido com fragmentação ou junção de superfície livre e grandes deslocamentos ou deformações dos sólidos, fenômenos esses presentes no impacto e cravação da estaca no solo marítimo. Para isso, dois desafios foram elencados: a modelagem dos solos como fluidos não-newtonianos e a determinação da força de arrasto viscosa na superfície de sólidos. A modelagem do fluido não-newtoniano foi feita considerando os modelos de Power Law, Bingham e Herschel-Bulkley. O cálculo da força de arrasto viscosa foi avaliado determinando-se o gradiente da velocidade do fluido na direção normal à parede com base na regressão polinomial. Por simplicidade, foi considerada a hipótese de que a variação da velocidade na direção tangencial da parede é muito menor se comparada a variação da mesma na direção do vetor normal. O método implementado, assim como o escoamento de fluidos não-newtonianos, foi validado por meio de comparação entre o resultado obtido de simulações com geometrias pré-definidas e as respostas analíticas para tais casos. Como exemplo de aplicação da ferramenta computacional desenvolvida, um caso simplificado de cravação das estacas torpedos foi simulado avaliando-se o seu deslocamento dentro do solo e os esforços cisalhantes a ela submetidas. / This work aims to develop computational tools to simulate and analysis the torpedo anchor penetration in marine soil. The approach will be based on the Moving Particle Semi-Implicit (MPS) method. Because it is a meshless method, it is extremely flexible to model fluid-solid interaction with fragmentation or junction of free surface and large displacements or deformations of solids, phenomena presented at the torpedo anchor impact. Two challenges were listed: the modeling of soils as non-Newtonian fluids and the determination of the viscous drag on the solids surface. The modeling of non-Newtonian fluid was done based on the Power Law, Bingham and Herschel-Bulkley models. The calculation of the viscous drag was evaluated by determining the velocity gradient in the normal direction of the wall based on polynomial regression considering the fluid particles near the solid wall. In this work, for sake of simplicity, the hypothesis that the velocity variation in the tangential direction of the wall is much smaller compared to its variation in the normal direction is adopted. The proposed technique, as well as the flow of non-Newtonian fluids, were validated comparing the results obtained in flow simulations with predefined geometries with the expected analytical responses. As an example of the application of the computational tools developed, a simplified case of torpedo penetration was simulated by evaluating its displacement and the shear stresses submitted to it.

The offshore oilfield industry is continuously developing unique and break-through technologies and systems to extract hydrocarbons from ever increasing ocean depths. Due to the extreme depths being explored presently, large anchors are being utilized to secure temporary and permanent facilities over their respective drilling/production site. A vertically loaded, torpedo-style, deepwater mooring anchor developed by Delmar Systems, Inc. is one of these anchors. The OMNI-Max anchor is an efficient, cost-effective alternative for use as a mooring system anchor intended for floating facilities. The OMNI-Max is designed to free-fall towards the ocean bottom and uses its kinetic energy for self-embedment into the soil, providing a mooring system anchor point. Values such as drag coefficient and terminal velocity are vital in predicting embedment depth to obtain the mooring capacity required by the floating facility. Two scaled models of the Mark I OMNI-Max anchor were subjected to a series of tests in the Haynes Coastal Engineering Laboratory at Texas A & M University to evaluate the overall drag coefficient and penetration depth. The 1/24 scale model was tested by measuring the amount of penetration into an artificial mud mixture. The 1/15 scale model was attached to a tow carriage and towed through a water-filled tank to measure the drag forces and evaluate the drag coefficient. The anchor terminal velocity was measured using underwater cameras to track the free fall of the model anchor through 15 ft of water inside the tow tank. The 1/24 scale model penetrated the mud an average of 22 inches from the leading tip of the anchor to the mud surface, approximately 1.5 anchor lengths. The penetration depth increased as impact velocity increased, while the penetration depth decreased as the fins were retracted. The 1/15 scale anchor was towed at 6 different velocities producing a varied total drag coefficient between 0.70 and 1.12 for Reynolds number flows between 3.08E 05 and 1.17E 06. The drag coefficient increased as the fins were retracted and when the mooring rope was attached. The 1/15 scale anchor was allowed to free-fall in the tow tank and obtained an average terminal velocity of and 14.6 feet per second. The drag coefficients ranged from 0.46 to 0.83, which increased as the fins were retracted. When using the results to estimate prototype sized anchor drag coefficient, the average value was estimated to be 0.75.