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The growth of the nuclear power industry has provided a considerable stimulus for investigations into fluid-structure interaction problems. The safety case for nuclear reactors requires an understanding of the impact response of structures enclosing or surrounded by fluids. In many cases the structural response is in excess of that which can be predicted by elastic analyses and both material and geometrical non-linearities must be considered. The understanding of the interaction between the structure and the contained fluid poses additional problems which, in the extreme loading conditions envisaged, have received little attention. There is a lack of data relating to basic fluid-structure interaction problems involving dynamic plastic structural impact. Two sets of experiments are described which were carried out to provide some such data. The first set of experiments considered beams, both fully clamped (leading to large membrane forces) and partially clamped (preventing rotational and transverse motion while allowing the beam material to be fed in from the supports), struck centrally by a projectile. The second set of experiments considered a circular plate clamped around its periphery, sealing a volume of fluid, and struck centrally by a projectile. The shape of the plates and beams as they deformed were recorded, as were the pressure variations during the tests. In both sets of experiments the main contribution of the fluid to the beam or plate response was to localise the deformations. The early deformation of the beams was limited to the centre half span and the deformation only spread to the ends of the beams as the supporting effect of the fluid was lost due to the fluid escaping. In the plate experiments, where a good seal could be achieved, the deformation throughout was localised compared with a similar plate in air. The deformation in these cases was limited to a central disc of approximately half the plate diameter. The pressures recorded during the tests suggest that the fluid response was predominantly incompressible. A finite element program was written to model the response of beams and circular plates (axisymmetric problems). A brief history of the finite element method, the background theory and the development of the method to treat non-linear, large displacement, dynamic problems are given. The results are presented for a number of beam and plate problems, both those described above and other problems for which data was available. The finite element program was found to give good predictions of the deforming shapes of both the beams and the plates. No detailed analysis of the fluid was carried out, but two types of approximation to the effect of the fluid were investigated. Firstly a time varying pressure pulse (based on the measured pressure pulses) or a pressure loading derived from the beam velocity (acoustic and incompressible fluid approximations) were used to represent the loading on the beam due to the fluid. Secondly a mass was added to the plate mass to represent the inertia of the fluid. The applied pressure loading worked to a limited extent for the beams but no one pressure pulse shape gave good results for both end fixities. The best results for the plate problem were achieved with the added mass approach. Finally a number of areas of experimental and computational work are identified, which it is felt would benefit from further study.

Thesis (Ph.D.)--University of Iowa, 2006. / Includes separate files for thesis supplements. Supervisor: H.S. Udaykumar. Includes bibliographical references (leaves 120-125).

With the emergence of nano-devices and nano-scale research, gaining further understanding of the evolution of drag forces exerted by molecular flows, at low Knudsen numbers (-0.1-0.5), over nano-scaled objects with 20-100 nm size is a realistic expectation. The proposed research examines the fluid-structure interaction at nano-scales from first principles. It has also critically evaluated, and if necessary modified, the assumptions made during the development of a computational model. The research has provided new insights in modelling molecular interaction with continuum as well as molecular walls and calculation procedures for predicting macroscopic properties such as velocity, pressure and drag coefficients. The proposed formulation has been compared with the state of the art formulations as published in recent journals and verified on number numerical and molecular tests as experimental and analytical results are unavailable at this scale. The effect of various geometry configurations (slit pore, inclined and stepped wall) to model the pressure driven molecular flow through confined walls is studied for number of surface roughness and driving force values given by adjusting molecular accelerations. The molecular flow over diamond, circular and square shaped cylinders confined within parallel walls has also been modelled at various input conditions. It is expected that the proposed research will have impact in developing future nanoscale applications, in the field of drug delivery, surface cleaning and protein movement, where adsorption, drag resistance or, in general, understanding of the knowledge of fluid-structure interaction at 50-100nm scale is important. Some of the future research areas resulting from this research have also been identified.

The objective of this thesis is to further extend the application range of immersed computational approaches in the context of hydrodynamics and present a novel general framework for the simulation of fluid-structure interaction problems involving rigid bodies, flexible solids and multiphase flows. The proposed method aims to overcome shortcomings such as the restriction of having to deal with similar density ratios among different phases or the restriction to solve single-phase flows. The new framework will be capable of coping with large density ratios, multiphase flows and will be focussed on hydrodynamic problems. The two main challenges to be addressed are: - the representation, evolution and compatibility of the multiple fluid-solid interface - the proposition of unified framework containing multiphase flows, flexible structures and rigid bodies with possibly large density ratios First, a new variation of the original IBM is presented by rearranging the governing equations which define the behaviour of the multiple physics involved. The formulation is compatibile with the "one-fluid" equation for two phase flows and can deal with large density ratios with the help of an anisotropic Poisson solver. Second, deformable structures and fluid are modelled in a identical manner except for the deviatoric part of the Cauchy stress tensor. The challenging part is the calculation of the deviatoric part the Cauchy stress in the structure, which is expressed as a function of the deformation gradient tensor. The technique followed In this thesis is that original ISP, but re-expressed in terms of the Cauchy stress tensor. Any immersed rigid body is considered as an incompressible non-viscous continuum body with an equivalent internal force field which constrains the velocity field to satisfy the rigid body motion condition. The "rigid body" spatial velocity is evaluated by means of a linear least squares projection of the background fluid velocity, whilst the immersed force field emerges as a result of the linear momentum conversation equation. This formulation is convenient for arbitrary rigid shapes around a fixed point and the most general translation- rotation. A characteristic or indicator function, defined for each interacting continuum phase, evolves passively with the velocity field. Generally, there are two families of algorithms for the description of the interfaces, namely, Eulerian grid based methods (interface tracking). In this thesis, the interface capturing Level Set method is used to capture the fluid-fluid interface, due to its advantages to deal with possible topological changes. In addiction, an interface tracking Lagrangian based meshless technique is used for the fluid-structure interface due to its benefits at the ensuring mass preservation. From the fluid discretisation point of view, the discretisation is based on the standard Marker-and-Cell method in conjunction with a fractional step approach for the pressure/velocity decoupling. The thesis presents a wide range of applications for multiphase flows interacting with a variety of structures (i.e. rigid and deformable) Several numerical examples are presented in order to demonstrate the robustness and applicability of the new methodology.

A numerical model for the simulation of fully-coupled fluid-structure interaction is developed in this study. In modeling the fluid, the Reynolds Averaged Navier-Stokes equations are solved for an incompressible viscous fluid field and a k-ε model is employed for turbulence computations. Hydrodynamic forces obtained by the integration of the fluid pressure along the structural boundaries are applied as external excitation forces to the structural system and the dynamic response of the structural system is computed based on dynamic equilibrium. To determine the nonlinear dynamic response of the structure in the flow field, iterative procedures are developed. The numerical model is verified and validated through comparisons with several different types of experiments. The numerical model is then applied to examine the runup and rundown of the submarine landslide generated waves with various configurations. The functional relationships between the maximum runup/rundown and the geometric and material properties of landslides are obtained. The numerical model is also applied to predict the experimental moored response of a structure subjected to periodic waves. The linear and nonlinear waves, as well as the structural response, are modeled accurately. The dynamic response of the moored structure, which is modeled with nonlinear restoring forces, shows the characteristic behaviors such as subharmonic/ super-harmonic responses. General application procedures for the fluid-structure interaction model are presented. The subaerial and aerial drop of a rigid body and the influence of impact on the fluid body are examined. / Graduation date: 2005

Flow velocity field, vorticity and circulation and wall shear stresses were simulated by FSI approach under conditions of pulsatile flow in a scale model of the rabbit elastin-induced aneurysm. The flow pattern inside the aneurysm sac confirmed the in vitro experimental findings that in diastole time period the flow inside the aneurysm sac is a stable circular clock-wise flow, while in systole time period higher velocity enters into the aneurysm sac and during systole and diastole time period an anti-clock circular flow pattern emerged near the distal neck; in the 3-D aneurysm sac, the kinetic energy per point is about 0.0002 (m2/s2); while in the symmetrical plane of the aneurysm sac, the kinetic energy per point is about 0.00024 (m2/s2). In one cycle, the shape of the intraaneurysmal energy profile is in agreement with the experimental data; The shear stress near the proximal neck experienced higher shear stress (peak value 0.35 Pa) than the distal neck (peak value 0.2 Pa), while in the aneurysm dome, the shear stress is always the lowest (0.0065 Pa). The ratio of shear stresses in the proximal neck vs. distal neck is around 1.75, similar to the experimental findings that the wall shear rate ratio of proximal neck vs. distal neck is 1.5 to 2.

published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

Thesis (Ph. D.)--University of Hawaii at Manoa, 2004. / Includes bibliographical references (leaves 145-149).