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Title: A particle based method for flow simulations in hydrodynamics and hydroelasticity
Author: Ramli, Muhammad Zahir Bin
ISNI:       0000 0004 6347 5345
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2016
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Seakeeping analysis involving violent flows is still quite challenging because the conventional Reynolds Averaged Navier-Stokes (RANS) approaches are not effective for such flow simulations. Different techniques and numerical tools are required to obtain approximate solutions. This research aims to apply Smoothed Particle Hydrodynamics (SPH), a fully Lagrangian meshless method to investigate the behaviour of ships in realistic waves. SPH has been used in a wide variety of hydrodynamic problems overcoming the limitation of finite volume or element type methods. This makes it a suitable alternative for simulating a range of hydrodynamic problems, especially those involving severe flow discontinuities, such as deformable boundary, wave breaking and fluid fragmentation, around complex hull shapes. The main goal of this research is to investigate the possibility of implementing SPH in 3-dimensional problems for the seakeeping analysis of ships treated as rigid and flexible bodies operating in reasonably rough seas. The outcomes of the research will focus on predicting wave-induced motions, distortions and loads with particular references to response in waves of reasonably large amplitude. The initial work deals with modifying standard Incompressible SPH (ISPH) formulation in generating free surface waves. It was observed that the kernel summation of standard ISPH formulation is not sufficiently accurate in obtaining the velocity and pressure fields. Therefore, a range of solutions were proposed to improve the prediction and the following were considered: i) employing collision control, ii) shifting technique to maintain uniform particle distribution, iii) improving the accuracy of gradient estimations up to 2nd order with kernel renormalization technique, iv) applying an artificial free surface viscosity and v) adapting new arc method for accurate free surface recognition. In addition, the weakly compressible SPH (WCSPH) from DualSPHysics was also applied to similar problems. It was found that WCSPH performed better in accuracy and was then adopted further in the analysis of hydrodynamic and hydroelasticity. The research studies were extended to investigate 2-D problems of radiation, diffraction and wave-induced motion. Comparisons were made with available potential flow solutions, numerical results and experimental data. Overall, a satisfactory agreement has been achieved in determining i) added mass and damping coefficients and ii) responses of fixed and floating body in waves. Convergence studies were carried out for particle density influences, as well as sensitivity and stability of implemented parameters. In the extension of the model to 3-D framework, both cases of floating rigid and flexible barges in regular waves were modelled. For this particular case, vertical bending moment (VBM) was obtained using the one-way coupling approach. Comparisons to two other numerical methods and experimental data in the prediction of RAOs, motion responses and vertical bending moments have shown consistent performance of WCSPH. Finally, the success of WCSPH was highlighted by solving the hydrodynamic coefficients for a 3-D flexible structure oscillating in rigid body motions of heave and pitch, as well as 2-node and 3-node of distortion modes.
Supervisor: Tan, Mingyi Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available