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Research Internship on Motions of CALM Buoy in shallow water using a Numerical Wave Tank
The horizontal motions of moored offshore structures in waves are dominated by the resonance phenomena that occur at the natural frequencies of the mooring system. Therefore, the maximum excursions of the structure depend on both the exciting and damping forces of the system at its natural frequencies. At present, potential flow simulations are generally employed for predicting the wave loads and motions of offshore structures. However such diffraction codes cannot predict viscous effects or non-linear wave excitation on the motion response. Therefore, the current practice in the industry is to calibrate the potential flow based codes based on model testing. Nowadays, CFD simulations have the potential to predict the motion behaviour of moored offshore structures in waves. So CFD would offer an alternative solution to model testing and/or potential flow based codes. To obtain confidence in the accuracy of the results from CFD simulations, a proper verification and validation is essential.
The objective of the internship is to verify and validate MARIN’s CFD codes ReFRESCO and Comflow for the calculation of the hydrodynamic damping, wave loads, and motions of a CALM Buoy in shallow water. A CALM consists of a floating buoy anchored to the seabed by catenary chain legs which are secured to anchors or piles. One or more elastic mooring hawsers hold the tanker captive to a turntable which is mounted on top of the buoy by means of a slewing bearing. The CALM Buoy is the most popular and widely-used type of offshore loading terminal with more than 500 systems installed to date. CALM Buoys have been deployed worldwide for a variety of applications, water depths and vessel sizes ranging from small product carriers to Very Large Crude Carriers (VLCC).

Illustration of a CALM Buoy (Catenary Anchor Line Mooring)
The following research questions will be addressed within the proposed internship:

  • What is the accuracy of the CFD results and what is the sensitivity to numerical settings such as grid and time step resolution?
  • Which turbulence model should be used?
  • What is the effect of waves and current on the low-frequency viscous damping?
  • What is the difference between the damping coefficients obtained from decays or from forced oscillations?
  • What is the effect of the free-surface modelling on the low-frequency viscous damping?
  • What is the effect of the wave height on the mean wave loads applied on the offshore structure.

The internship is for the duration of 6-12 months. The start date and length of the internship can be determined in consultation with the supervisors.
We are looking for a motivated independent student, who is eager to learn and who is fascinated by floating structures in waves. You have an interest in the physics and mathematics behind numerical simulations for these type of problems. More specifically, we are looking for:

  • Master student in Naval Architecture, or other applied science.
  • Interest in Computational Fluid Dynamics (CFD) and hydrodynamics.

Department and supervisors
During the internship you will be connected with the R&D and Offshore department of MARIN. The supervisors for this internship, Arjen Koop and Frederick Jaouen, are working as Researcher at the R&D Department and Project Manager at the Offshore department.
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