Application of the Modified Weakly Compressible SPH Method to the 3D Turbulent Wave Breaking Impact

In this paper, the mesh-less weakly compressible Smoothed Particle Hydrodynamics (SPH) method was used to solve the continuity and momentum equations with laminar viscosity and the sub-particle scale (SPS) turbulence model. To correct the pressure field and improve the accuracy of free surface, modification of the kernel and its gradient is applied to weakly compressible SPH. The modified method, namely the mSPH-T-K, was also equipped with periodic smoothing of the density using the modified kernel. To validate the modified model, the pressure field and the wave front position of the 2D dam break flow were compared with those of experimental data, the standard SPH method and the mSPH-T method, which is the turbulence SPH method without modification of the kernel and its gradients. Finally, a 3D wave impact was simulated using the mSPH-T-K method. A comparison of results with experimental data showed that this model is a powerful tool for the simulation of complicated free surface flows with large deformations and impact

Free Surface Flow Simulation Using VOF Method

Viscous flow with moving free surface is an important phenomenon in nature which has broad applications in engineering. For these flows, temporal and spatial position of this moving free surface in unsteady or non‐uniform conditions is very complicated. In this chapter, free surface simulation methods based on computational grid are presented. Volume of fluid (VOF) is a powerful and the most prevailing method for modeling two immiscible incompressible fluid‐fluid interfaces. Herein, the governing equations of fluid flow including Navier‐Stokes coupled with VOF equation are discussed and the most prominent VOF schemes hierarchically presented to the readers. Meanwhile, Compressive Interface Capturing Scheme for Arbitrary Meshes (CICSAM), Higher Resolution Artificial Compressive (HiRAC), High Resolution Interface Capturing (HRIC), Switching Technique for Advection and Capturing of Surfaces (STACS), and some other newly proposed methods are introduced, and the accuracy and time calculation of each method are evaluated. Moreover, surface tension modeling and its discretization as one of the most demanding phenomena in the nature are brought to the readers. Finally, two schemes of parametric study of interfaces are discussed

Numerical Modelling of Sloshing with VOF Method

Sloshing in tanks carrying LNG, LPG and petroleum is an important phenomenon as dynamic pressure arises from sloshing can destroy the containing tanks. So it is vital to consider this phenomenon in design stages of carriers. The governing equations in fluid flow are conservation of mass and momentum. Modeling of free surface flow in tank needs a suitable tool. One of the most powerful tools to model the free surface is VOF method. Employing additional transport equation together with conservation of mass and momentum enable us to follow the free surface changes. A computer code was developed to evaluate sloshing problem. This code could calculate dynamic pressures exerted on walls of the containers. The model was validated using experimental data

SHORT-TERM PREDICTION AND ANALYSIS OF WAVE-INDUCED MOTION AND LOAD RESPONSES OF A WAVE-PIERCING TRIMARAN

In this paper, we used a statistical short-term analysis in order to determine the wave-induced motions and loads responses of a trimaran ship with three side hull configurations including symmetric, inboard and outboard types. The calculation of these wave-induced loads was carried out using MAESTRO-Wave, a seakeeping analysis code. A rule-based design for the hull was created based on the American Bureau of Shipping (ABS) rules followed by building a global FEM model of the ship with MAESTRO to predict the wave-induced motion and load responses. In order to validate the numerical prediction, we tested a rigid segmented model of trimaran with symmetric side hull configuration in the National Iranian Marine Laboratory (NIMALA) towing tank. The numerical results revealed that transverse torsion moments and shear forces are significant in head seas. But, transverse bending moments have higher response magnitudes in oblique seas. Also, in transverse wave loads, outboard side hulls offer slightly better performance in waves in comparison to the other forms. This study offers useful information on wave-induced motion and load responses for the purpose of balancing sea-keeping performance as well as other design considerations in developing the conceptual design of a wave-piercing trimaran

On the selection of boundary conditions for top tensioned risers facing wave induced vibrations

The severe ocean environment is obviously the source of many uncertain random loads on offshore structures. This harsh environment when acting on the slender top tensioned risers with high aspect ratio (L/D) causes multimodal vibration leading to fatigue failure. Thus, a reliable stress analysis procedure should be applied in the assessment of their long-term behaviors. This research is a study on the effect of boundary conditions on the total and local response of offshore risers due to loads in different sea states. A FEM code is developed for discretization of riser’s structural model and was run for the riser of Amirkabir semisubmersible vessel for 87 sea states in the Caspian Sea and four boundary conditions. The results show that the most severe stresses in the riser don’t happen essentially in the harshest environment. The comparison of boundary conditions shows that clamped-clamped boundaries lead to lowest stress values while the riser experiences a wider band of stress in the pinned-pinned boundary type. While the riser top end boundary condition highly influences the displacements and stresses even in the lower part of riser

Wave-induced loads on cross-deck of a wave-piercing trimaran with different hull forms of outriggers

Trimaran has unique hull form with a rapidly growth in recent years due to its application as a mode of transports and naval vessels. Designing trimaran faces many technical challenges because of its complex structural outlines and high-speeds operation. This article investigates the influence of side hulls configuration (symmetric, inboard and outboard types) for wave loads on cross-deck of a trimaran ship when advancing at sea in regular waves. The computation of these hydrodynamic forces is carried out using MAESTRO-Wave 3D panel method code. This code is based on potential flow theory that uses Green’s function with the forward speed correction in the frequency domain. The results demonstrate that the outboard side hull form has the best performance on wave-induced load among three kinds of side hull forms. Furthermore, the results of this study offer more information for selecting the side hull form of the trimaran