<p> Air-cushion vehicles (ACV) are defined as surface vehicles that utilize air pressure for partial-or total support over the operational surface. An outline of the history of the five widely known ACV concepts and an analysis of the mode of operation of each is given, with their advantages and disadvantages.</p> <p> A sixth type, called the thrust-cushion vehicle (TCV), is a promising but unknown concept which, as yet, has not received much study or recognition. A preliminary theoretical analysis for design purposes is made, and the test results of a static model and a model running on a radial tether are given to establish a research and design basis for future work.</p> / Thesis / Master of Engineering (MEngr)

Diploma thesis deals with the developement of hovercraft prototype. Hovercraft is generally included into the category of light appliances. It is considered as a appliance for vacation or experimental utilisation. Interior is customised for 5 member crew or else up to 600 kg of loading. Diploma thesis is focused on the exterior of the hovercraf, hence there are mentioned solutions of selected node points in interior with a view to the ergonomic features. There is an outcome of original design combined with modern technological solutions and materials in this diploma thesis project.

The Diploma thesis is dedicated to design of a hovercraft. The concept of design is a small hovercraft for personal use. The hovercraft is styled into a sports category. The interior is designed for 4 persons and personal luggage. Main part of the work is the exterior of the hovercraft. But it contains also a basic vision of interior solution with basic dimensions according to antropometric measures and other ergonomical criteria. So the result is original hovercraft, which is solved in area of design with regards for ergonomics and technological limitations, which hovercraft brings.

The work presented herein describes the production of hot strip with special attention to the runout table. Because of its high capital and operating costs, a new principle in conveying the strip using an air cushion and a new cooling system for strip cooling have been proposed. Information given here is nearly all from available literature and the author's own experience with Hot Strip Mill production problems. To support the idea of using an air cushion for strip conveying, experimental equipment was designed and built which confirmed the feasibility of the method. A new cooling system was also proposed to meet the ever increasing requirements for better mechanical properties of hot strip. Runout table design application may serve as a guideline in designing new Hot Strip Mill runout table. / Thesis / Master of Engineering (ME)

A system of ordinary differential equations (ODE) is constructed for an air cushion vehicle (ACV). The system is simplified to an equation for the balance of the vertical forces and the equation for the adiabatic compression of the air in the cushion. Air pressure is constantly supplied into the system, but can leak out from underneath the edges of the cushion. A series of regular waves encounters the air cushion, causing a change in volume. Additionally, a computational analysis of the seakeeping of a Surface Effect Ship (SES) is performed using the commercial software WAMIT, which uses low-order, linear potential panel method. The model of the T-Craft consists of catamaran hulls, rigid end skirts, and the interface between the air cushion and the water surface. Beyond the six rigid body degrees of freedom of the T-Craft, additional modes are added for the motion of the interface panels. To verify the method used, the model is benchmarked using computational data for a small-scale barge model and experimental data for a T-Craft model. A comparison is performed for the T-Craft with and without its cushion. The solution for the nonlinear time-domain system is found numerically, and the stability of the system is studied by observing bifurcations with the incoming wave amplitude as the bifurcation parameter. The system experiences a period-doubling bifurcation, from a periodic orbit, to a subharmonic orbit, to a solution with multiple periods. Further increasing the wave amplitude increases the period doubling, eventually leading to chaotic behavior. As a result of the linear-potential simulations, significant differences are found in the seakeeping of the T-Craft when on and off the cushion. These differences are caused by the direct and indirect effects of the cushion (added aerodynamics and a decreased draft). The RAO's of the craft experience changes in amplitude and phase, which will affect the multi-body relative motions. The time-domain model shows very chaotic behaviour that is presented visually in a bifurcation diagram. These linear potential and time-domain methods illustrate the complexity and importance of modelling air-cushion effects.

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

Air cushion vehicle flexible seals operate in a complex and chaotic environment dominated by fluid-structure interaction. An efficient means to explore interdependencies between various governing parameters that affect performance is through high fidelity numerical simulation. As previous numerical efforts have employed separate iterative partitioned solvers, or have implemented simplified physics, the approaches have been complex, computationally expensive, or of limited utility. This research effort performs numerical simulations to verify and validate the commercial multi-physics tool STAR-CCM+ as a stand-alone partitioned approach for fluid-structure interaction problems with or without a free surface. A dimensional analysis is first conducted to identify potential non-dimensional forms of parameters related to seal resistance. Then, an implicit, Reynolds-averaged Navier-Stokes finite volume fluid solver is coupled to an implicit, nonlinear finite element structural solver to successfully replicate benchmark results for an elastic beam in unsteady laminar flow. To validate the implementation as a seal parameter exploratory tool, a planer bow seal model is developed and results are obtained for various cushion pressures and inflow speeds. Previous numerical and experimental results for deflection and resistance are compared, showing good agreement. An uncertainty analysis for inflow velocity reveals an inversely proportional resistance dependency. Using Abaqus/Explicit, methodologies are also developed for a two-way, loosely coupled explicit approach to large deformation fluid-structure interaction problems, with and without a free surface. Following numerous verification and validation problems, Abaqus is ultimately abandoned due to the inability to converge the fluid pressure field and achieve steady state. This work is a stepping stone for future researchers having interests in ACV seal design and other large deformation, fluid-structure interaction problems. By modeling all necessary physics within a verified and validated stand-alone approach, a designer's ability to comprehensively investigate seal geometries and interactions has never been more promising. / Ph. D. / Air cushion vehicles are specialized marine craft that utilize flexible seals to enable improved performance and fully amphibious operation. An efficient means to explore interdependencies between various seal design parameters that affect performance is through computer modeling of the fluid-structure interaction between the seal and the sea. This research effort performs numerical simulations to verify and validate the commercial multi-physics tool STAR-CCM+ as a single computer program for fluid-structure interaction problems occurring on the water surface. A dimensional analysis is first conducted to identify parameters related to seal resistance. Then, a fluid model is coupled to a structural model to successfully replicate benchmark results for a flexible beam in an oscillating fluid flow. To validate the implementation as a seal parameter exploratory tool, a model of an ACV bow seal is developed and results are obtained for various operational conditions and inflow speeds. Previous numerical and experimental results for seal deflection and seal resistance are compared, showing good agreement. This work is a stepping stone for future researchers having interests in ACV seal design and other large deformation, fluid-structure interaction problems. By modeling all necessary physics within a verified and validated stand-alone computer program, a designer’s ability to comprehensively investigate seal geometries and interactions has never been more promising.

Thesis (M.S.)--Air Force Institute of Technology, 2005. / "September 2005" Also available as a PDF file on the Air Force Institute of Technlogy website.

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.

Ce mémoire décrit la conception, la modélisation et la commande d’un manipulateur pneumatique,fondé sur un principe de traction aérodynamique original. De puissants jets d’air verticauxpermettent de créer un flux d’air horizontal pour manipuler des objets sans contact. Les objetssont maintenus en constante lévitation sur la surface grâce à un coussin d’air, et peuvent positionnés selon trois degrés de libert´ du plan, grâce à la combinaison adéquate et distribuéede jets d’air verticaux. Nous détaillons la conception d’un prototype original de manipulateurexploitant ce principe fluidique. Ce prototype a été intégré dans une plate-forme expérimentaleafin de valider le principe de manipulation : le système permet de déplacer des objets à unevitesse atteignant 180 mm/s. Nous avons modélisé le fonctionnement de la surface selon plusieursméthodes. Un premier modèle comportemental, fond´e sur des données expérimentales, aété établi. Il permet de simuler l’´evolution de la position d’un objet sur la surface, selon un degréde liberté . Deux modèles de connaissance, fond´es sur une étude aérodynamique fondamentale,donnent l’´evolution de la position de l’objet selon respectivement deux et trois degrés de libertédu plan. Chacun des modèles a été validé expérimentalement. Nous avons synthétisé différentscontrˆoleurs afin d’asservir la position de l’objet : un premier, de type PID, et un second, de typerobuste (méthode H1). La commande de un, puis deux degrés de liberté du système, a permisd’atteindre de bonnes performances : temps de réponse d’environ 2 s et dépassement souventinférieur à 5%. Nous avons également étudié un micro-manipulateur pneumatique permettant ded´eplacer des objets de taille millimétrique selon deux directions, grâce à des jets d’air inclinés.Ces objets peuvent atteindre des vitesses de 123 mm/s. La résolution du positionnement estinférieure à 0.4 μm. / This thesis presents the design, the modeling and the control of a pneumatic manipulatorbased on an original aerodynamic traction principle. An horizontal air flow is induced by strongvertical air jets in order to manipulate objects without contact. The objects are maintained inconstant levitation on an air cushion. Three degrees of freedom positioning of the objects canbe realized thanks to the right combination of distributed air jets. The design of an originalmanipulator using this aerodynamic principle is detailed. The device has been integrated in anexperimental setup in order to validate the manipulation principle : objects can reach velocityof 180 mm/s. Several models of the system have been established. A first model, based on experimentaldata, gives the evolution of the 1 DOF-position of an object on the device. Twoother models, based on a fundamental aerodynamic study, respectively give the evolution of the2- and 3-DOF position of the objet. The three models have been validated experimentally. Inorder to control the position of the object, different controllers have been designed : a PID oneand a robust H1 one. The control of one and two degrees of freedom of the device gives goodperformances : settling time of around 2 s and overshoot less than 5% in most of the cases. Wehave also studied a micro-manipulator that is able to position millimetric sized objects, in twodirections, thanks to inclined air jets. Objects can reach velocity of 123 mm/s, and the resolutionof the positioning is less than 0.4 μm.