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Wave Ship Interaction in Transforming Seas
Title
Wave Ship Interaction in Transforming Seas.
Creator
Gong, Fuxian, Dhanak, Manhar R., Florida Atlantic University, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
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...
Show moreIn 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.
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Date Issued
2017
PURL
http://purl.flvc.org/fau/fd/FA00004916, http://purl.flvc.org/fau/fd/FA00004916
Subject Headings
Hydrodynamics--Mathematical models., Fluid dynamics--Mathematical models., Ocean waves--Measurement., Water waves--Measurement., Coastal engineering.
Format
Document (PDF)
Dynamic analysis of single- and multi-module platforms in waves
Title
Dynamic analysis of single- and multi-module platforms in waves.
Creator
Kling, Kaylie Ann., Florida Atlantic University, Ananthakrishnan, Palaniswamy, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
The response of single- and multi-module floating platforms to surface waves is investigated theoretically. Wave exciting forces are computed using methods based on the Morrison equation and Froude-Krylov hypothesis. The radiation forces are obtained from experimental results of Vugt and where possible diffraction forces using the Haskind reciprocity relation. Heave and pitch response of a one-module platform and hinge-connected two-module platform are determined by integrating the...
Show moreThe response of single- and multi-module floating platforms to surface waves is investigated theoretically. Wave exciting forces are computed using methods based on the Morrison equation and Froude-Krylov hypothesis. The radiation forces are obtained from experimental results of Vugt and where possible diffraction forces using the Haskind reciprocity relation. Heave and pitch response of a one-module platform and hinge-connected two-module platform are determined by integrating the corresponding equations of rigid-body motion. A structural dynamic analysis is also carried out using the Green's function method to determine the elastic flexural response of the platform to waves. The results are compared with the experimental and numerical findings of others. The thesis contributes to a better understanding of rigid-body and elastic response of large ocean platforms subject to wave forces. The methodology is computationally less intensive and therefore can be effectively used for the design of platforms and the validation of numerical algorithms.
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Date Issued
2006
PURL
http://purl.flvc.org/fcla/dt/13399
Subject Headings
Ocean engineering, Wave motion, Theory of, Water waves--Mathematical models, Drilling platforms, Extreme value theory
Format
Document (PDF)
Design and analysis of hybrid titanium-composite hull structures under extreme wave and slamming loads
Title
Design and analysis of hybrid titanium-composite hull structures under extreme wave and slamming loads.
Creator
Rahman, Md Hafizur, Mahfuz, Hassan, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
A finite element tool has been developed to design and investigate a multi-hull composite ship structure, and a hybrid hull of identical length and beam. Hybrid hull structure is assembled by Titanium alloy (Ti-6Al-4V) frame and sandwich composite panels. Wave loads and slamming loads acting on both hull structures have been calculated according to ABS rules at sea state 5 with a ship velocity of 40 knots. Comparisons of deformations and stresses between two sets of loadings demonstrate that...
Show moreA finite element tool has been developed to design and investigate a multi-hull composite ship structure, and a hybrid hull of identical length and beam. Hybrid hull structure is assembled by Titanium alloy (Ti-6Al-4V) frame and sandwich composite panels. Wave loads and slamming loads acting on both hull structures have been calculated according to ABS rules at sea state 5 with a ship velocity of 40 knots. Comparisons of deformations and stresses between two sets of loadings demonstrate that slamming loads have more detrimental effects on ship structure. Deformation under slamming is almost one order higher than that caused by wave loads. Also, Titanium frame in hybrid hull significantly reduces both deformation and stresses when compared to composite hull due to enhancement of in plane strength and stiffness of the hull. A 73m long hybrid hull has also been investigated under wave and slamming loads in time domain for dynamic analysis.
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Date Issued
2013
PURL
http://purl.flvc.org/fau/fd/FA0004048
Subject Headings
Hulls (Naval architecture) -- Design and construction, Ships -- United States -- Design and construction, Structural dynamics, Water waves -- Mathematical models
Format
Document (PDF)