The use of computational fluid dynamics to investigate surface ship dynamics and characteristics has been growing during recent years. With technological advancements continuing in leaps and bounds more and more complex simulations are possible. The interests of this paper concern the numerical simulations of a surface effect ship which is a specific type of air cushion vehicle. The simulation work presented here attempts to replicate the model tests involving a generic surface effect ship and demonstrate the value of numerical simulations in understanding air cushion vehicles. The model tests consist of a surface effect ship running through a range of Froude numbers in calm seas and a variety of wave cases. The numerical simulations were developed using CD-adapcos's STAR-CCM+ to model the surface effect ship characteristics and dynamics. The pressurized air cushion and flexible, dynamic seals are of the greatest importance when modeling a surface effect ship; however, some idealizations had to be made. The air cushion fans are represented as constant momentum sources while the seals are represented as shortened and rigid. Throughout the simulations drag, pitch, and heave were constantly monitored for comparison purposes with the model tests. It was found that the rigid skirt approximation accounts for a large portion of error when comparisons were made between the numerical and analytical data. Furthermore, it would be impossible to accurately represent the surface effect ship dynamics in waves with this approximation. An alternative method to modeling the skirts was investigated which would include the use of a porosity function. It was found that the porosity skirt model would allow for cushion pressure to be maintained while limiting the interaction of the rigid skirt and the free surface. The full implementation of porous skirts on the surface effect ship is a difficult challenge as numerical instabilities arise. However, implementing the porous skirt would lead to more accurate calm water simulations and the ability to model the surface effect ship in wave cases. / Master of Science

Numerical simulations of fluid-structure interaction (FSI) problems were performed in an effort to verify and validate a commercially available FSI tool. This tool uses an iterative partitioned coupling scheme between CD-adapco's STAR-CCM+ finite volume fluid solver and Simulia's Abaqus finite element structural solver to simulate the FSI response of a system. Preliminary verification and validation work (VandV) was carried out to understand the numerical behavior of the codes individually and together as a FSI tool. Verification and Validation work that was completed included code order verification of the respective fluid and structural solvers with Couette-Pouiselle flow and Euler-Bernoulli beam theory. These results confirmed the 2nd order accuracy of the spatial discretizations used. Following that, a mixture of solution verifications and model calibrations was performed with the inclusion of the physics models implemented in the solution of the FSI problems. Solution verifications were completed for fluid and structural stand-alone models as well as for the coupled FSI solutions. These results re-confirmed the spatial order of accuracy but for more complex flows and physics models as well as the order of accuracy of the temporal discretizations. In lieu of a good material definition, model calibration is performed to reproduce the experimental results. This work used model calibration for both instances of hyperelastic materials which were presented in the literature as validation cases because these materials were defined as linear elastic. Calibrated, three dimensional models of the bow seal on the University of Michigan bow seal test platform showed the ability to reproduce the experimental results qualitatively through averaging of the forces and seal displacements. These simulations represent the only current 3D results for this case. One significant result of this study is the ability to visualize the flow around the seal and to directly measure the seal resistances at varying cushion pressures, seal immersions, forward speeds, and different seal materials. SES design analysis could greatly benefit from the inclusion of flexible seals in simulations, and this work is a positive step in that direction. In future work, the inclusion of more complex seal geometries and contact will further enhance the capability of this tool. / Ph. D.

This thesis presents the results from the computational fluid dynamics simulations of surface effect ship model tests. The model tests being simulated are of a generic T-Craft model running in calm seas through a range of Froude numbers and in two head seas cases with regular waves. Simulations were created using CD-adapco's STAR-CCM+ and feature incompressible water, compressible air, pitch and heave degrees of freedom, and the volume of fluid interface-capturing scheme. The seals are represented with rigid approximations and the air cushion fans are modeled using constant momentum sources. Drag data, cushion pressure data, and free surface elevation contours are presented for the calm seas cases while drag, pressure, heave, and roll data are presented for the head seas cases. The calm seas cases are modeled both with no viscosity and with viscosity and turbulence. All simulations returned rather accurate estimations of the free surface response, ship motions, and body forces. The largest source of error is believed to be due to the rigid seal approximations. While the wake's amplitude is smaller when viscosity is neglected, both viscous and inviscid simulations' estimations of the free surface qualitatively match video footage from the model tests. It was found that shear drag accounts for about a quarter of the total drag in the model test simulations with viscosity, which is a large source of error in inviscid simulations. Adding the shear drag calculated using the ITTC-1957 friction coefficient line to the total drag from the inviscid simulation gives the total drag from the viscous simulations within a 6% difference. / Master of Science

A Computational Fluid Dynamics (CFD) tool is developed in this thesis to solve complex fluid-structure interaction (FSI) problems. The fluid domain is based on Smoothed Particle Hydro-dynamics (SPH) and the structural domain employs large-deformation Finite Element Method (FEM). Validation tests of SPH and FEM are first performed individually. A loosely-coupled SPH-FEM model is then proposed for solving FSI problems. Validation results of two benchmark FSI problems are illustrated (Antoci et al., 2007; Souto-Iglesias et al., 2008). The first test case is flow in a sloshing tank interacting with an elastic body and the second one is dam-break flow through an elastic gate. The results obtained with the SPH-FEM model show good agreement with published results and suggest that the SPH-FEM model is a viable and effective numerical tool for FSI problems. This research is then applied to simulate a two-dimensional free-stream flow interacting with a deformable, pressurized surface, such as an ACV/SES bow seal. The dynamics of deformable surfaces such as the skirt/seal systems of the ACV/SES utilize the large-deformation FEM model. The fluid part including the air inside the chamber and water are simulated by SPH. A validation case is performed to investigate the application of SPH-FEM model in ACV/SES via comparison with experimental data (Zalek and Doctors, 2010). The thesis provides the theory of the SPH and FEM models incorporated and the derivation of the loosely-coupled SPH-FEM model. The validation results have suggested that this SPH-FEM model can be readily applied to skirt/seal dynamics of ACV/SES interacting with free-surface flow. / Ph. D.