Slamming of marine planing craft is expected to arise due to the high speed nature of their operating conditions. High hydrodynamic forces are inevitably induced causing the shell plating to deflect, which in turn can influence the flow physics surrounding the hull. In order to study the hull’s hydroelastic response due to a slamming event, wedge drop experiments were performed with an aluminum wedge of 57 inches in length, 47 inches in breadth, and 20 degree deadrise with 1/4 in. thick unstiffened bottom panels. The elastic behavior of the hull plating was measured via two methods. The first method uses strain gages to analyze the wedge’s deadrise panel deflections, and the second method is a Stereoscopic- Digital Image Correlation (S-DIC) technique. In the present investigation, an S-DIC code has been developed and utilized to study the deflections and to advance the capabilities of future research. Comparisons are made between the methods and also with theoretical studies. The deflections measured are approximately 0.1 in. on a panel spanning 24.5 inches, and the predictions made using S-DIC and strain gages differ by approximately 23%.

The forced water entry and exit of two-dimensional bodies through a free surface is computed for various 2D bodies (symmetric wedges, asymmetric wedges, truncated wedges and boxes). These bodies enter or exit water with constant velocity or constant acceleration. The calculations are based on the fully non-linear timestepping complex-variable method of Vinje and Brevig. The model was formulated as an initial boundary-value problem with boundary conditions specified on the boundaries (dynamic and kinematic free-surface boundary conditions) and initial conditions at time zero (initial velocity and position of the body and free-surface particles). The formulated problem was solved by means of a boundary-element method using collocation points on the boundary of the domain and solutions at each time were calculated using time stepping (Runge-Kutta and Hamming predictor corrector) methods. Numerical results for the deformed free-surface profile, the speed of the point at the intersection of the body and free surface, the pressure along the wetted region of the bodies and force experienced by the bodies, are given for the entry and exit. To verify the results, various tests such as convergence checks, self-similarity for entry (gravity-free solutions) and Froude number effect for constant velocity entry and exit (half-wedge angles 5 up to 55 degrees) are investigated. The numerical results are compared with Mackie's analytical theory for water entry and exit with constant velocities, and the analytical added mass force computed for water entry and exit of symmetric wedges and boxes with constant acceleration and velocity using conformal mapping. Finally, numerical results showing the effect of finite depth are investigated for entry and exit.

The diverse applications of advanced marine craft ascribed to their high speed and technological advancements has led to the use of stronger and lighter metals in such crafts. High speed, in effect also increases slamming loads as higher speed increases frequency of wave encounter while operating in waves. The present study is limited to wedge impact models. Fundamentally, the study is thus about two-dimensional (2D) wedge impact in water. In an attempt to predict the structural response to impact hydrodynamic force, a beam element based finite element (FE) computer program is written and the results of the code are presented in the thesis. A computational tool is developed to predict the transient elastic response of a 2D wedge under impact force using two different numerical methods. Both explicit and implicit numerical schemes have also been studied in order to apply to the present work. Explicit forth order Runge-Kutta (RK4) method and implicit Newmark-b (NB) method have been used in the present work. Coupling effects between excitation and response are ignored in the present numerical computations. Both the numerical schemes are validated using simple static solution and also modal expansion technique.

The pressures and impact forces acting on a hull while experiencing bow wave slamming is analyzed using Vorus' Impact Theory. The theory extends the hydrodynamic analysis of planing hulls from simple wedges to irregular shapes using a Boundary Element Method. A Fortran-based code developed by the Author is used to analyze hullforms. Linear strip theory is used to extend the analysis over a three dimensional hull. Post-processing of output data gives hull pressure distributions at different time steps and is visually presentable. Impact pressure, Impact force, Planing, Wave slamming, Bow impact, Vorus' theory, Boundary Element Method, Linear strip theory

The present research develops a numerical fluid-structure interaction (FSI) code based on CFDShip-Iowa version 4, a general-purpose URANS/DES overset fluid solver. Linear and nonlinear FSI methods are developed to compute structural responses on surface ships or marine structures. The modal superposition transient analysis and the nonlinear FEM structure solver are used for small and large deformation FSI problems, respectively. The gluing method is applied to transfer the forces and displacements on non-matching grids for fluid and structure domains. The linear FEM solver is applied to deform the boundary layer grid with large deformation in the fluid domain, while the deformation is ignored in small deformation problems. Deformation of an interior point in the boundary layer grid is obtained using linear interpolation in both linear and nonlinear deformation problems. The S175 containership is studied in regular waves as an application example for the linear problem. Heave and pitch responses are compared with the experiments, showing good agreement. Time histories of vertical bending moment (VBM) are calculated using rigid model, one-way coupling, and two-way coupling approaches. The elastic models are able to capture the ringing of the VBM induced by slamming, while the rigid model shows a peak at the moment of slamming without further fluctuations. The two-way coupling method shows the effects of hull deformation on the amplitude and phase of VBM as well as the accelerations of heave and pitch. For the nonlinear deformation problem three sloshing tanks with an elastic bar clamped to its bottom or top are simulated and compared with the experiments and other numerical simulation results. The present simulation results show reasonable agreement with the experiments for bar deformation and free surface elevation. A secondary wave on the free surface is creadted by the vorticity generated from the free surface. The effect of the bar on the sloshing impact is studied comparing dynamic pressure acting on the tank wall without bar, with an elatic bar, and with a rigid bar.

This thesis is an attempt to create a computer based tool that can be used academically and later industrially by naval architects in analysis and development of efficient planing hull forms. The work contained here is based on the theory created by Vorus (1996) which falls between empirical asymptotic solutions and intractable non-linear boundary value problem in the time-domain. The computer code developed predicts pressures on the bottom of high-speed planing craft during slamming events. The code is validated with available numerical data as a benchmark case. An aluminum wedge is dropped from various heights resulting in unsteady pressure distributions with high peak over the bottom plate. These pressure distributions are compared to the numerically predicted pressures by the code and presented in this thesis. The predicted flow velocities are within 8% difference of experimental data. The graphs depicts similar trends in experimental and numerical data. The predicted peak pressures deviate within 4% to 20% from experimental data. The analysis and comparison illustrate efficacy of the code.

[pt] Estruturas submarinas utilizadas nos sistemas de produção de óleo e gás offshore são normalmente projetadas para permanecerem no leito marinho por décadas. Para a grande maioria dessas estruturas a instalação é uma etapa crítica que pode requerer recursos dispendiosos e significativos esforços de engenharia. A descida de estruturas submarinas em regiões de ondas marinhas é uma operação complexa, uma vez que envolve acelerações desses corpos induzidas pelos movimentos das embarcações que, associados com os deslocamentos da superfície do mar, podem levar a significativas cargas de impacto nessas estruturas durante a entrada na água. O estágio inicial do impacto durante a entrada na água tem sido tema de muita pesquisa no último século, desde os trabalhos pioneiros de von Kármán e Wagner sobre a hidrodinâmica do pouso de hidroaviões. O cenário do impacto da proa de navios na superfície do mar também tem sido objeto de estudo, uma vez que pode levar a danos localizados ou mesmo catastróficos ao casco. Diferentes métodos numéricos têm sido aplicados para análise desse problema. A principal contribuição desse trabalho é a utilização do método numérico Smoothed Particle Hydrodynamics (SPH) para estimar as cargas de slamming em corpos rígidos durante a entrada na água considerando superfícies em repouso e sob o efeito de ondas. Inicialmente é introduzida a fundamentação teórica básica sobre o impacto hidrodinâmico, seguida da descrição do método SPH. Aplicações do SPH para simular a entrada na água de corpos rígidos são apresentadas considerando casos em queda livre e com velocidade constante e os resultados são comparados com experimentos e simulações numéricas obtidos na literatura. A presença de ondas regulares durante a entrada na água com velocidade constante também é considerada. Os resultados numéricos obtidos neste trabalho demonstram a viabilidade da abordagem proposta para estimar as cargas de slamming em estruturas submarinas durante a entrada na água. / [en] Subsea structures employed on offshore oil and gas production systems are commonly designed to be laid on seafloor for decades. For most of these structures the installation is a critical stage and may require costly resources and significant engineering effort. Lowering subsea structures through the wave zone is a complex operation as it involves accelerations of these bodies induced by the vessel motion which, associated to the sea surface displacements, may lead to significant impact loads on these structures during water entry. The initial stage of impact during water entry has been a subject of many researches over the past century since the pioneering work of von Kármán and Wagner on the hydrodynamics of an alighting sea plane. The scenario of impact of the forebody of a ship on the sea surface has also been subject of studies, as it may cause localized and eventually catastrophic damage to the hull. Different numerical methods have been applied to the analysis of this problem. The main contribution of this work is the use of the Smoothed Particle Hydrodynamics (SPH) method to estimate slamming loads on rigid bodies during water entry considering both calm and wavy surfaces. A basic theoretical background on hydrodynamic impact load is firstly introduced, followed by the description of the SPH method. Applications of SPH to simulate water entry of rigid bodies considering both free fall and constant velocity cases are presented and results are compared with experiments and numerical simulations from the literature. The presence of regular waves during constant velocity water entry is also considered. The numerical results obtained here demonstrate the effectiveness of the proposed approach to estimate slamming loads on subsea structures during water entry.

We have developed a third-order shear and normal deformable plate/shell theory (TSNDT) incorporating all geometric nonlinearities and used it to analyze, by the finite element method (FEM), transient finite deformations of a sandwich beam with two face sheets and the core made of St. Venant-Kirchhoff materials.  A triangular cohesive zone model with stress based criterion for delamination initiation and energy based relation for complete separation is used to analyze delamination failure in a beam under mixed-mode loading. We have studied transient post-buckling deformations and delamination progression in an axially compressed and initially delaminated clamped-clamped sandwich beam.  The buckling load for transient deformations exceeds that for static deformations and the increase depends upon the loading rate.  This FE software for analyzing deformations of sandwich beam is coupled with that based on the boundary element method (BEM) for studying time-dependent deformations of water and the coupled software is used to analyze deformations of flexible curved hulls due to water slamming loads.  The water is assumed to be inviscid and incompressible and undergo irrotational deformations.  The Laplace equation for the velocity potential is numerically solved by the BEM with normal velocity and pressure assumed to be continuous across the interface between the hull and the water.  Challenging issues resolved in this work include finding the wetted surface of the hull, nonlinear deformations of the fluid due to convective part of acceleration, effects of geometric nonlinearities on hull\'s deformations, resolution of the jet tip, as well as the initiation and propagation of delamination between the face sheets and the core.  It is found that both delamination and geometric nonlinearities significantly affect the hydrodynamic pressure acting on the hull, and transverse shear deformations contribute more to the strain energy absorbed by the core than its transverse normal deformations.  <br />We have used the discontinuous basis functions to derive the Galerkin formulation of a nonlinear problem involving simple shearing deformations of a homogeneous and isotropic thermo-elasto-visco-plastic body with uniform deformations perturbed to simulate the effect of a defect.  The resulting coupled nonlinear ordinary differential equations are integrated with respect to time by using the package, LSODE (Livermore Solver for Ordinary Differential Equations).  Computed results showing localization of deformations into narrow regions are found to agree well with those found by the FEM, and spatial variations of the shear stress are smoother than those obtained by the FEM.<br /><br /> / Ph. D.

Using scantling codes such as DNV or ISO for designing high speed craft has been a routine for many constructors. However, the validity of these design methods are to be questioned, especially when dealing with modern material concepts and structural layouts, since they are based on data from ships designed in the 1960ies and 1970ies using semi-empirical methods containing substantial uncertainties and limitations. For direct assessment of loading conditions, modern methods such as CFD are appreciated. But they consume lots of time and resources in the design stage, which makes efficiency worse. A simulation approach making detailed assessment of loading conditions and structural behavior for high speed craft in waves has been developed at KTH Royal Institute of Technology in Sweden, with parts of the method still in need of further validation. In the here presented project an experimental setup has been developed for detailed validation of simulated local structural responses for high-speed craft in waves. The experimental setup consists of a model structure instrumented with strain gauges and pressure sensors that is integrated into a high speed craft model. Experimental data has been generated through experiments in regular and irregular waves in the towing tank at University of Naples “Federico II”. The model structure and generated data are concluded to be feasible for the intended validation.

Arch-shaped microelectromechanical systems (MEMS) have been used as mechanical memories, micro-sensors, micro-actuators, and micro-valves. A bi-stable structure, such as an arch, is characterized by a multivalued load deflection curve. Here we study the symmetry breaking, the snap-through instability, and the pull-in instability of bi-stable arch shaped MEMS under steady and transient electric loads. We analyze transient finite electroelastodynamic deformations of perfect electrically conducting clamped-clamped beams and arches suspended over a flat rigid semi-infinite perfect conductor. The coupled nonlinear partial differential equations (PDEs) for mechanical deformations are solved numerically by the finite element method (FEM) and those for the electrical problem by the boundary element method. The coupled nonlinear PDE governing transient deformations of the arch based on the Euler-Bernoulli beam theory is solved numerically using the Galerkin method, mode shapes for a beam as basis functions, and integrated numerically with respect to time. For the static problem, the displacement control and the pseudo-arc length continuation (PALC) methods are used to obtain the bifurcation curve of arch's deflection versus the electric potential. The displacement control method fails to compute arch's asymmetric deformations that are found by the PALC method. For the dynamic problem, two distinct mechanisms of the snap-through instability are found. It is shown that critical loads and geometric parameters for instabilities of an arch with and without the consideration of mechanical inertia effects are quite different. A phase diagram between a critical load parameter and the arch height is constructed to delineate different regions of instabilities. The local water slamming refers to the impact of a part of a ship hull on stationary water for a short duration during which high local pressures occur. We simulate slamming impact of rigid and deformable hull bottom panels by using the coupled Lagrangian and Eulerian formulation in the commercial FE software LS-DYNA. The Lagrangian formulation is used to describe planestrain deformations of the wedge and the Eulerian description of motion for deformations of the water. A penalty contact algorithm couples the wedge with the water surface. Damage and delamination induced, respectively, in a fiber reinforced composite panel and a sandwich composite panel and due to hydroelastic pressure are studied. / Ph. D.