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Research Internship: “Motions of a Drillship 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.
 
Internship
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 drillship. A drillship is a merchant vessel designed for use in exploratory offshore drilling of new oil and gas wells or for scientific drilling purposes. In most recent years the vessels are used in deepwater and ultra-deepwater applications, equipped with the latest and most advanced dynamic positioning systems. A few years ago, model tests were conducted on a soft-moored drillship in regular and irregular waves. In those tests, the motions and wave elevations in the rectangular shaped moonpool were measured. The model test data will be used as a validation material for this internship.


Illustration of drillship fixed in waves
 
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.

 
Duration
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.
 
Profile
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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