In near-shore transforming seas, as waves approach the shoreline, wave shoaling
and sometimes wave breaking take place due to the decreasing water depth. When
a ship advances through the transforming seas, the ship body and waves interact with
each other substantially and can lead to unknown motions of the ship hull. The physical
process of how the wave transforms in the surf zone and how the vehicle actually
behaves when it passes through the transforming seas is a complicated issue that
triggers considerable research interest.
The goal of my research is to characterize the dynamics of a high-speed surface
ship model in transforming seas through a parametric numerical study of the shipwave
interactions. In this study, the vehicle of interest is a surface effect ship (SES)
and we aim to contribute to developing a methodology for simulating the transforming
wave environment, including wave breaking, and its interactions with the SES.
The thesis work uses a commercial software package ANSYS Fluent to generate
numerical waves and model the interface between water and air using the volume
of fluid (VoF) method. A ship motion solver and the dynamic mesh are used to
enable the modeled ship to perform three degree-of-freedom (DoF) motion and the
near-region of the ship hull to deform as well as re-mesh. Non-conformal meshes with hybrid compositions of different cell types and various grid sizes are used in the
simulations for different purposes. Five user-defined functions (UDFs) are dynamically
linked with the flow solver to incorporates ship/grid motions, wave damping
and output of the numerical results. A series of steps were taken sequentially: 1)
validation for ship motions including simulation of a static Wigley hull under steady
flows to compare against previous experimental results by other researchers, and the
comparison between the static SES model under steady flows and the moving SES
model advancing in the calm water; 2) study of the ship with 3 DoF advancing in
calm water of both constant depth and varying depth; 3) validation for numerical
waves, including predictions of numerically progressive waves in both a regular tank
and a tank with a sloped fringing reef to compare with theoretical and experimental
results, respectively; 4) investigation of the transforming characteristics of the wave
traveling over the sloped fringing reef, which mimics the near-shore wave environment
and a study of the dynamics of the SES through transforming waves.
We find that the flow solver used in this study reliably models the wave profiles
along the ship hull. The comparison between a static SES in a current and a moving
SES in calm water at the same Froude number shows that although the velocity fields
around the vehicle are significantly different, the wave profiles inside and outside the
rigid cushion of the vehicle are similar and the resistance force experienced by the
vehicle in the two scenarios agree well over time. We conducted five numerical simulations
of the vehicle traveling from shallow water to deep water across the transition
zone for different Froude numbers. From the results, we find that as the Froude number
increases, the wave resistance force on the vehicle becomes larger in both shallow
water and deep water. In addition, the overall mean resistance force experienced by
the vehicle over the whole trip increases with the Froude number. Statistical analysis
of the wave motions suggests that the energy flux decreases dramatically in the
onshore direction as the waves break. The more severe the wave-breaking process, the greater the decrease in energy flux. Both the increase of Froude number and the
wave steepness apparently increase the resistance force on the vehicle in the shallow
water.
This thesis work captures the impact of the transforming characteristics of
the waves and closely replicates the behavior of how waves interact with a ship in
transforming seas through numerical modeling and simulation. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2017. / FAU Electronic Theses and Dissertations Collection
| Identifer | oai:union.ndltd.org:fau.edu/oai:fau.digital.flvc.org:fau_38018 |
| Contributors | Gong, Fuxian (author), Dhanak, Manhar R. (Thesis advisor), Florida Atlantic University (Degree grantor), College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering |
| Publisher | Florida Atlantic University |
| Source Sets | Florida Atlantic University |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation, Text |
| Format | 142 p., application/pdf |
| Rights | Copyright © is held by the author, with permission granted to Florida Atlantic University to digitize, archive and distribute this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder., http://rightsstatements.org/vocab/InC/1.0/ |
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