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Numerical study on the mooring force of a gravity-type fish cage under currents and waves
Published in C. Guedes Soares, T.A. Santos, Trends in Maritime Technology and Engineering Volume 2, 2022
The linear wave theory is used to model the waves and the Morison equation is used to calculate the hydrodynamic load. The velocity potential is expressed as: ϕ(x,z,t)=H1g2ωcosh(k(h+z))cosh(kh)sin(kx−ωt)
Possible Future Studies
Published in Patrick Bar-Avi, Haym Benaroya, Nonlinear Dynamics of Compliant Offshore Structures, 2017
Patrick Bar-Avi, Haym Benaroya
Refined models for the structure as well as for the external forces can be formulated;Tension Leg Platform with multiple cables, and cables with extension require future study.Risers with extension, with non-standard materials, and material nonlinearities pose significant challenges.Nonlinear wave theories that include high and steep wave heights can be used in Morison equation.Use of a different approximation for the wave forces, rather than Morison’s equation can be considered.More physically realistic vortex-shedding models will improve the understanding of the coupling between fluid and structure.
Waves and offshore engineering
Published in P. Novak, A.I.B. Moffat, C. Nalluri, R. Narayanan, Hydraulic Structures, 2017
P. Novak, A.I.B. Moffat, C. Nalluri, R. Narayanan
The Morison equation for the wave force exerted on a submerged cylinder of small diameter considers that the force is simply a sum of the drag and inertia forces. The latter arise as a consequence of the unsteady nature of the wave field. The Morison equation for the in-line force, Fi, per unit length of the cylinder is
Experimental and numerical investigation on reserve strength of jackets with single diagonal and X brace configurations
Published in Ships and Offshore Structures, 2023
A. Renugadevi, S. Nallayarasu, S. Karunanithi
The total base shear was obtained for combined effect of 100-year storm wind, wave and current. Wave and current force are computed by the Morison equation. Stokes’s 5th order wave theory was used to calculate the water particle kinematics and wave kinematic factor as per API RP 2A (2007) has been used. The drag and inertia coefficient of 0.65 and 1.6 was used for smooth cylinders while 1.05 and 1.2 was used for rough cylinders (with marine growth). The current blockage factor of 0.80 for end-on and broadside direction and 0.85 for diagonal direction has been used in the load calculation. Wind pressure is calculated using the drag formula and applied to the deck structure. The environmental data used for the load calculation are summarised in Tables 6 and 7 for Mumbai high field (South) and Heera field, respectively. These typical data are pertaining to offshore platforms located in western offshore India.
Energy-efficient control of a thruster-assisted position mooring system using neural Q-learning techniques
Published in Ships and Offshore Structures, 2021
Huacheng He, Lei Wang, Xuefeng Wang, Bo Li, Shengwen Xu
The elastic force acting on node i in the q direction can be expressed as: where q represents the global Cartesian coordinates x, y, z of the node, is the elastic energy of element j, and EA, are the axial rigidity and the original length of the element. For mooring lines suspended in water, Morison equation can be used to compute the hydrodynamic loads acting on the elements. The consequent inertia and drag forces are usually expressed separately in directions normal and tangential to the element: whereis the tangent drag coefficient,represents the normal drag coefficient,denotes the normal added mass coefficient,is the water density,is the line diameter,is the relative velocity between the line segment and the fluid,is the tangential unit vector, andis the acceleration of the fluid.
A panel method for floating offshore wind turbine simulations with fully integrated aero- and hydrodynamic modelling in time domain
Published in Ship Technology Research, 2018
Stefan Netzband, Christian W. Schulz, Ulf Göttsche, Daniel Ferreira González, Moustafa Abdel-Maksoud
The Morison equation is applied to calculate the forces acting on small slender body elements of the floating structure; these body parts are not considered in the meshed platform geometry. The Morison equation captures the forces due to the added mass, the drag and the unsteady pressure field induced by the waves (Froude–Krylov force). Irregular and regular waves are specified as wave potential. The linear potential wave theory is applied and the wave elevations as well as the actual submerged hull surface are updated in each time step. A detailed description of the application of panMARE for the simulation of floating or submerged bodies in waves can be found in Schoop-Zipfel and Abdel-Maksoud (2014) and Ferreira González et al. (2015). In the next paragraphs, the different techniques used by the hydrodynamic model are briefly summarised.