Dissertations / Theses on the topic 'Non linear hydrodynamic'

Dans cette thèse, on cherche à quantifier l’impact des effets d’origine visqueuse sur la dynamique et la production d’énergie des systèmes houlomoteurs. A l’heure actuelle, l’état de l’art pour évaluer la production d’énergie des houlomoteurs repose sur des approches en théorie linéarisée des écoulements potentiels (codes BEM) car la CFD (Computational Fluid Dynamics) est encore trop coûteuse en terme de temps de calcul. Cependant, l’approche potentielle est limité par les hypothèses de linéarité sur laquelle elle repose. Ces limitations doivent être comprises et des améliorations apportées. En particulier, une piste d’amélioration est l’ajout de correction visqueuse via l’ajout de terme quadratique à la Morison dans l’équation du mouvement. Cette correction dépend d’un coefficient de trainée qui doit être estimé avant de pouvoir réaliser la simulation. Une possibilité est d’interpoler la valeur de ce coefficient à partir des données expérimentales que l’on peut trouver dans la littérature, ou bien utiliser la CFD. Dans ce travail, on s’est intéressé à la faisabilité de cette seconde approche. Deux houlomoteurs académiques ont été modélisés. Le premier est une bouée pilonnante de forme cylindrique, à bouchains vifs. Le second est un volet oscillant en cavalement. Des calculs CFD des efforts exercés sur ces géométries ont été réalisés dans un écoulement oscillant. L’effort mesuré est lissé conformément à la formule de Morison en utilisant la méthode des moindres carrés pour déterminer les coefficients de trainée et de masse d’eau ajoutée. Ensuite, le coefficient de trainée est implémentée dans l’équation du mouvement du houlomoteur correspondant. L’absorption d’énergie avec et sans la prise en compte des effets visqueux est alors évaluée, qui met en évidence l’importance de leur prise en compte
The impact of the viscous and vortex forces in the context of floating wave energy devices has been studied in this work. At present the state of the art tools to assess the efficiency of the WECs (Wave Energy Converters) comprise the BEM (boundary element method) codes based on the potential linear approach whereas CFD (computational fluid dynamics) is still considered to be computationally expensive. However the former has its limits regarding linearity restrictions and hence needs further inspections and improvements. A possibility for improvement is to account for viscous damping via additional Morison-like quadratic damping term. The intensity of this additional damping term depends on a coefficient which needs to be estimated prior to the calculations. One can interpolate this coefficient from the many previously published experimental results or imagine using CFD. In this study, the applicability of the latter option is investigated for WEC application. Two generic devices such as a heaving cylinder with sharp corners and a surging flap type WEC are considered. CFD computations of the forces on the buoy in an oscillatory flow are performed. This CFD-force is then fitted by the Morison’s equation using least square approach, which gives estimation of the viscous damping coefficient. This coefficient is implemented in the equation of motion of the WEC. The energy absorption with and without taking into account the viscous damping is then derived, which shows the importance of its appropriate modelling

The SEAL Carrier is a marine hybrid craft with capacity to travel both on the surface and completely submerged with main objective to transport a group of divers. The craft is developed for transporting a unit of combat divers in and out the of area of operation where the high speed at surface and low signature when submerged are key features. In order to reduce the workload for the pilots during longer transports in submerged mode the manufacturer James Fisher Defence (JFD) has instigated two master theses with the aim to develop an automated depth control.This thesis concerns the ÿrst part in this project and describes the development of a hydrodynamic model of the craft. The main purpose of the model is to re°ect the behavior of the craft with focus on depth maneuvers so it can be used as a tool for the development of such a controller.Initially the fundamental theory that this mathematical model is established from is presented and explained. From how positions and motion of an underwater craft is expressed with well established methods the six equa-tions of motion necessary to fully describe these are derived. For estimating the external forces acting on the craft a semi-empirical approach is presented in order to obtain expressions and estimations of these. With these results a platform for the model have been established in the programming environment MATLAB/SIMULINK. With this platform as basis a procedure for manipulating the external forces in order to achieve a better repre-sentation of the real craft is presented.The developed model experiences some di˝culties to capture the motion of the real craft during maneuvers in depth. The cause for this is considered to be because of the methods used for expressing the hydrodynamic forces developed by the hull. The function of the model to serve as a tool for the development of a depth controller is still to be veriÿed and tests are planned. The developed model has a modular design that enables simple modiÿcations of the implemented theory as well as structural modiÿcations for future development and improvements.
SEAL Carrier är en marin hybridfarkost med kapacitet att färdas i både yt- och undervattensläge. Farkosten är utvecklad för att transportera en grupp attackdykare till och från arbetsområden då farkostens hastighet på ytan och låga signatur vid undervattensläge utnyttjas. För att minska arbetsbördan för piloterna vid längre transporter i undervattensläge har tillverkaren James Fisher Defence (JFD) utlyst två examensarbeten med huvudsakligt syfte att ta fram en automatiserad djuphållare.Denna avhandling berör den första delen i detta projekt och beskriver utvecklingen av en hydrodynamisk modell av farkosten. Det huvudsakliga syftet med modellen är att lyckas representera farkostens beteende så att denna modell kan användas som verktyg vid utvecklingen av en sådan djuphållare.Inledningsvis beskrivs den fundamentala teori som denna matematiska modell är etablerad utifrån. Med ut-gångspunkt i hur position och rörelser beskrivs enligt etablerade metoder för en undervattensfarkost härleds de sex rörelseekvationerna som är nödvändiga för att fullständigt uttrycka dessa. För uppskattning av de externa krafterna som verkar på farkosten beskrivs hur semi-empiriska metoder utnyttjats för att på ett e˛ektivt sätt erhålla uttryck och uppskattningar av dessa. Utifrån dessa resultat beskrivs hur en plattform för modellen ut-vecklats i programmeringsmiljön MATLAB/SIMULINK. Vidare presenteras en metod för att justera de externa krafterna för att fånga farkostens rörelsemönster i modellen.Den utvecklade modellen uppvisar vissa svårigheter att efterlikna den riktiga farkostens rörelsemönster vid djupmanövrar. Orsaken till detta anses vara metoden som utnyttjas för att modellera de hydrodynamiska skrov-krafterna. Modellens funktion som verktyg för utvecklingen av den tilltänkta djuphållaren återstår att veriÿera och tester är planerade. Den utvecklade modellen har en modulär design vilket på ett e˛ektivt sätt möjliggör enkla förändringar av den implementerade teorin samt strukturella förändringar för vidare utveckling och för-bättring.

Includes abstract.
Includes bibliographical references (leaves 106-112).
The Orr-Sommerfeld equation describes the growth of infinitesimal disturbances to laminar solutions of the Newtonaian Navier-Stokes equations. In this dissertation we consides in part idealised flows between two parallel planes of infinite extent and a finite distance apart. They are referred to as closed channel flows.

Será explorada a versão hidrodinâmica da equação de Schrödinger não-linear e não-local, descrevendo condensados de Bose-Einstein com auto-interações de longo alcance. Tais sistemas têm despertado interesse tendo em vista a busca da realização da condensação de Bose-Einstein sem necessidade de um potencial externo confinante e nos quais as interações atômicas locais não são suficientes. Para obter a descrição hidrodinâmica, a transformação de Madelung para a função de onda será utilizada, reduzindo o problema a uma equação da continuidade e a uma equação de transporte de momentum. Esta última é similar à equação de Euler em fluidos ideais, porém contendo um potencial quântico efetivo e um termo não local, o qual advém da interação atômica. Tais equações de fluido traduzem, respectivamente, a conservação da probabilidade e do momentum total. O método hidrodinâmico permitirá o estudo de excitações elementares, entre os quais os modos de Bogoliubov, segundo uma abordagem macroscópica.
The hydrodynamic version of the Schrödinger equation nonlinear and nonlocal will be explored, describing Bose-Einstein condensates with long-range self-interactions. Such systems have aroused interest with a view to pursuing the realization of Bose-Einstein condensation without an external confining potential and in which local atomic interactions are not enough. For the hydrodynamic description, the eikonal decomposition of the wave function is used, reducing the problem to one equation of continuity and to a transport of momentum equation. The latter is similar to the Euler equation in ideal fluid but containing an effective quantum potential and a nonlocal term, which comes from the atomic interaction. Such fluid equations translate, respectively, conservation of probability and total momentum. The hydrodynamic method will allow the study of elementary excitations, including Bogoliubov modes according to a macroscopic approach.

Ce travail est une contribution à l'étude du comportement des joints en translation. Un modèle numérique, basé sur la théorie inverse, est développé pour en prédire les performances. La principale contribution consiste dans le traitement des effets hydrodynamiques liés à la région d'entrée du contact. Les résultats numériques sont ensuite validés par comparaison avec lesmesures expérimentales. Ces dernières sont obtenues sur un dispositif original, conçu et réalisé au laboratoire INOE 2000 IHP de Bucarest. Ce banc reproduit les conditions réelles de fonctionnement d'un joint hydraulique et permet de mesurer la force de frottement à pression et vitesse constantes. La comparaison des résultats numériques et expérimentaux a été effectuéepour un joint de tige en forme de "U" à des pressions de service comprises entre 4 MPa et 20 MPa et pour deux vitesses de translation. Dans un premier temps, on a idéalisé le problème en considérant que les surfaces en contact tige-joint sont lisses. Si l'épaisseur du film est supérieure à la rugosité de la tige, les résultats numériques qu'on a obtenus sont en bonne corrélation avecles résultats expérimentaux. Dans le cas contraire, le modèle doit être amélioré. Cette amélioration a été entreprise de manière originale. En effet, la théorie inverse est appliquée à la distribution de pression statique du contact obtenue à partir de la simulation par éléments finis de l'assemblage d'un joint rugueux et d'un arbre lisse. La rugosité moyenne (Ra) de la surface dujoint en contact avec la tige a été choisie égale à la rugosité moyenne mesurée du joint étudié. Les résultats ainsi obtenus améliorent sensiblement la corrélation avec les mesures e
This work is a contribution to the study of reciprocating seals behavior. A numerical model, based on the inverse hydrodynamic lubrication theory, is developed to predict their performances. The main contribution consists in the treatment of the hydrodynamic effects in the entry region of contact. The numerical results are validated by comparison with experimentalones, obtained on an original experimental device, design and conceived in the laboratory INOE 2000 IHP of Bucharest. This bench reproduces actual operating conditions of a hydraulic seal and measures the friction force at constant pressure and speed. The comparison of experimental and numerical results was carried out for a "U" type rod seal at different operating pressuresvarying from 4 MPa up to 20 MPa and for two reciprocating speeds. Initially, we idealized the problem by assuming that the surfaces in contact are smooth. The numerical results obtained are in good correlation with experimental ones if the film thickness is greater than the rod roughness. Otherwise, the model must be improved. This improvement was undertaken in an original way. The inverse lubrication theory is applied to the dry frictionless contact pressure distribution, obtained from a FEM simulation of a rough seal and a smooth rod assembly. The average roughness (Ra) of the seal surface in contact with the rod is chosen equal to the measured average roughness of the studied seal. The results obtained significantly improve the correlationwith experimental measurements. The roughness distribution on the entry region of contact appears to have an important influence on the numerical results

In the present work the investigations of non linear effects, in the context of potential flow theory, are investigated. These effects are caused by three main reasons, namely: the changes of the wetted geometry of the floating body, the water line dynamics and the fully non linear nature of the free surface boundary conditions. In order to understand the importance of tackling the non linear effects, a three dimensional frequency study of the S175 conteinership is carried out, at different Froude numbers, using linear frequency domain methods and a partly non linear time domain method. A time domain analysis, with the aid of an unstructured mixed Eulerian Lagrangian (MEL) description of the fluid flow, is implemented aiming in exploring potential low non linear effects. In this framework, the mixed boundary value problem of the Eulerian phase of the MEL scheme is tackled by means of a Boundary Element Method using constant elements (or a direct Rankine panel method). At given time step, on Neumann boundaries the impervious boundary condition is specified whereas, on Dirichlet boundaries, the potential on the free surface is prescribed. The solution of the Boundary Value problem yields the potential on the Neumann boundaries and its normal derivative on Dirichlet boundaries. In the Lagrangian phase, the free surface boundary conditions are then integrated in time. This method was used to solve the linear time domain radiation, i.e by applying linearized free surface boundary conditions on the exact free surface and solving the mixed boundary value problem on the mean undisturbed free surface, for the case of forced motions of a hemisphere and a Wigley hull. In addition, the linear time domain method is also extended to the unified hydroelastic analysis in time domain for the cases of 2 and 3 nodes bending. Results are presented for the the Wigley hull, undergoing prescribed forced oscillations for both rigid and exible mode shapes. The extension of the MEL scheme to a numerical tool capable of addressing several degrees of non linearities (from body nonlinear to fully nonlinear) is also discussed. In this context, two numerical formulations to calculate the time derivative of the velocity potential are implemented, namely: a backward finite scheme and an exact calculation based in the time harmonic property of the velocity potential. In latter case, a second boundary value problem is constructed and solved for the time derivative of the potential on Neumann boundaries and for the normal acceleration on Dirichlet boundaries. Results of both approaches are compared for the case of a sphere undergoing force oscillations in heave are compared to results obtained by other time domain methods. Moreover, after the boundary value problem is solved, a radial basis function representation of the velocity potential and free surface elevation is constructed, this approach allows for the estimation of the gradient of the velocity potential (body nonlinear and fully nonlinear simulations) and free surface steepness (fully nonlinear simulations). The results of the body non linear analysis, for large amplitude of oscillation in heave, are presented for the both the sphere and Wigley hull. For the latter, body non linear results of the coupling between heave into the first distortion mode (2-node) are also presented. The results of the fully non linear simulations are presented for the case of a sphere. An investigation of the suitability of two unstructured meshing libraries is also performed in the context of the MEL simulation scheme. Practical issues related to (re)meshing at each time step, the representation of ship like geometries, free surface evolution and numerical stability are highlighted for both libraries.

Les écoulements fluides jouent un rôle important dans de nombreux phénomènes naturels ainsi que dans de nombreux secteurs industriels. On s’intéresse dans cette thèse aux écoulements instationnaires oscillants provenant d’une bifurcation de Hopf.L’écoulement affleurant une cavité carrée ouverte présente deux cycles limites séparés par un état quasi-périodique instable. Nous avons décrit en détail ce scénario au moyen de simulations numériques directes, de l’analyse de stabilité linéaire et de l’analyse de Floquet. La bifurcation de Hopf dans la geometry de Taylor-Couette donne naissance à deux solutions, les spirals (ondes progressives) et les rubans (ondes stationnaires dans la direction axiale). Nous avons découvert que la branche des rubans est suivie de deux cycles hétéroclines consécutifs avec deux états axisymétriques comme point d’ancrage.L’analyse de stabilité linéaire autour des solutions stationnaires permet d’obtenir le seuil de bifurcation. Une autre approche, est la linéarisation autour du champ moyen. Cette approche permet d’obtenir des fréquences très proches des fréquences non linéaires et montre dans la plupart des cas un taux de croissance proche de zéro. Nous avons montré que les spirales, les rubans, la cavité entrainée ainsi que l’écoulement autour d’un objet prismatique vérifient cette propriété.Dans la convection thermosolutal, la linéarisation autour du champ moyen des ondes stationnaires ne permet pas d’obtenir les fréquences non linéaires et le taux de croissance est loin d’être zéro, par contre pour les ondes progressives cette propriété est pleinement satisfaite. Nous avons étudié la validité d’un modèle auto-cohérent dans le cas de ces ondes progressives. En effet, si l’écoulement vérifie la propriété du champ moyen, ce modèle est supposé calculer le champ moyen, la fréquence nonlinear ainsi que l’amplitude. Ce modèle est constitué de l’équation gouvernant le champ moyen couplé avec l’équation linéarisé au travers le mode le plus instable et des contraintes de Reynolds. Nous avons montré que dans le cas des ondes progressives ce modèle permet de prédire la fréquence non linéaire seulement très proche du seuil. La prédiction est améliorée significativement en considérant les ordres supérieurs dans le terme des contraintes de Reynolds
Fluid flows play an important role in many natural phenomena as well as in many industrial applications. In this thesis, we are interested in oscillating flows origins from a Hopf bifurcation.The open shear-driven square cavity has two limit cycles separated by an unsteady quasi-periodic state. We have described this scenario in detail by using direct numerical simulations, linear stability analysis, and Floquet analysis. The Hopf bifurcation in Taylor-Couette flow gives rise to two solutions, spirals (traveling waves) and ribbons (standing waves in the axial direction). We discovered that the ribbons branch is followed by two consecutive heteroclinic cycles connecting two pairs of axisymmetric vortices. We studied in detail these two heteroclinic cycles.The linear stability analysis about the stationary solution is used to compute the threshold of the bifurcations. Another approach is the linearization about the mean field. This approach gives frequencies very close to that of the nonlinear system and shows in most cases a nearly zero growth rate. We have shown that spirals, ribbons, the lid-driven cavity and the flow around a prismatic object verify this property.In the thermosolutal convection, the frequencies obtained by the linearization about the mean field of the standing waves do not match the nonlinear frequencies and the growth rate is far from zero, on the other hand for the traveling waves this property is fully satisfied. We studied the validity of a self-consistent model in the case of the traveling waves. The self-consistent model consists of the mean field governing equation coupled with the linearized Navier-Stokes equation through the most unstable mode and the Reynolds stress term. This model calculates the mean field, the nonlinear frequency, and the amplitude without time integration. The self-consistent model is assumed to be valid for flows that satisfy the property of the mean field. We have shown that in this case, this model predicts the nonlinear frequency only very close to the threshold. We have improved significantly the predictions by considering higher orders in the Reynolds stress term

The age of the easy accessible hydrocarbon goes towards the end and new more challenging fields is the future of the oil industry. This is often synonymous with large depths where sea bed mounted platforms are highly uneconomical options. Floating platforms are therefore commonly chosen solutions.In this thesis two types of deep foating platforms are investigated; The spar buoy, a well known, well documented concept and the Octabuoy, a newly developed concept. Both platforms are analysed in two DNV programs, Wasim and Waqum. Wasim is a non linear time domain hydrodynamic program and Waqum is an impulse response function operator with the possibility of adding non linear eects. The spar bouy concept is used as a pilot test in the softwares. A recreation of the experimental results from H.A. Haslum's doctoral thesis from 2000 is attempted. The impact of non linear effects and mooring on both platforms is discussed. The subject of viscous damping is also approached.As has previously been confirmed by many researchers, the spar buoy is susceptible to non linear eects. The triggering of the Mathieu effect is shown in the Wasim analyses. Discussion is also made as to whether the spar might also be susceptible to large excitations due to second order difference frequency interactions between surface waves and body motions. Both these effects happen at low frequencies where radiation damping is low. Viscous damping is therefore of importance. From previous research mooring is found to be important to avoid the Mathieu effect by increasing the damping and moving pitch periods out of the danger zones.After analysing the spar buoy, the Octabuoy's motion characteristics are tested in mild to severe sea states in both softwares. Non linear effects are found to be significant in the vertical rotational degrees of freedom. The heave motion however seems relatively unaffected by non linear effects. Since Wasim models the free surface linearly, what makes the pitch/roll motion affected by non linearities is found to be either non linear hydro statics or non linear Froude-Krylov forces. The Octabuoy is designed to avoid the variation on hydrostatic stiffness. However, the deadrise angle is 10 degrees larger than the ideal angle. Whether this is what leads to non linear pitch/roll motion is not known at this stage.Two softwares are used in the thesis. Wasim has very long CPU time but calculates accurately and detailed information is easily accessed with for instance the Wasim application ForceInspector. Waqum is very quick, with CPU time in the order of minutes. The program requires an experienced user who knows what must be included for a complete analysis. There are uncertainties about the results from Waqum analysis and more verication is needed for the author to feel confident about the software.To conclude, the programs might work well together. Much can be tested quickly in Waqum, and then final configurations can be run more thoroughly in Wasim. It is the experience of the author that at least until the new version of HydroD is finished, running time domain analysis in Wasim should be done through scripting. This gives a larger control over the actual input and might decrease the chance for error.Keywords: Octabuoy, Spar Buoy, Non Linear Effects, Mooring, Wasim, Waqum.

Cette thèse porte sur la physique des ondes, dans le but de contrôler leur propagation. Nous cherchons à mettre en évidence des phénomènes communs à toutes les ondes grâce à un système expérimental modèle utilisant les ondes à la surface d’un liquide. Plus précisément, nous choisissons de travailler avec des ondes hydroélastiques en couvrant la surface du liquide avec un film élastique. Les déformations élastiques de cette membrane sont couplées aux mouvements du fluide, de sorte qu’en modifiant les propriétés de la membrane nous pouvons agir sur la propagation des ondes. Ainsi, en changeant localement l’épaisseur du film élastique nous montrons qu’il est possible de dévier, réfléchir ou encore focaliser les ondes. Ensuite, en structurant périodiquement la membrane nous mettons en évidence des effets liés à la périodicité et/ou à la nature des objets formant le réseau régulier. Nous utilisons des perforations circulaires dont nous varions le diamètre, l’espacement et l’arrangement dans l’espace, ce qui nous permet de contrôler très finement le comportement des ondes dans le cristal artificiel ainsi formé. Nous mettons notamment en évidence l’existence de bandes interdites de propagation. Enfin, nous re-visitons l’instabilité de Faraday, connue en hydrodynamique, en vibrant verticalement un bain liquide recouvert d’une membrane élastique, et nous montrons que cette instabilité existe également pour les ondes hydroélastiques
This thesis deals with waves at the surface of a liquid, and aims at controlling their propagation. We want to show universal results, valid for all waves, using model experiments. We work with hydroelastic waves, obtained with an elastic membrane that covers the liquid surface. The elastic deformation of this membrane couples with the motion of the fluid, so that we can change the propagation of the waves by modifying the properties of the elastic cover. We show that if we locally change the thickness of the elastic cover, we can deviate, reflect or focus the waves. We then periodically structure the membrane and thus unveil effects due to he periodicity and/or the nature of the objects that form the regular array. We use an ensemble of circular perforations of which we vary the diameter, the spacing and the pattern, in order to accurately control the propagation of the waves in this artificial crystal. In particular, we show that there exist band gaps for the waves. Lastly, we re-visit the Faraday instability, known in hydrodynamics, by vertically vibrating a fluid layer covered with an elastic membrane, and we show that this instability also exist for hydroelastic waves

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.

У дисертаційній роботі виконано уточнення математичної моделі шпаринного ущільнення з урахуванням спірального руху робочої рідини, обумовленого як обертанням валу так і полем тиску рідини в шпарині. Розроблено аналітичний метод розрахунку в лінійній постановці складових радіальної сили. Проведено аналіз нелінійності гідростатичної сили, обумовленої радіальним зміщенням валу. Отримано, що дана сила має м’яку характеристику жорсткості. Проведений фізичний експеримент, який дав змогу оцінити вплив окружних перетоків рідини на величину гідростатичної сили. У відносно довгих шпаринах експериментально отримано явище самозбудження коливань необертового ротора. На модельному та натурному роторах проведено аналіз впливу шпаринних ущільнень на динамічні характеристики ротора.
В диссертационной работе предложена уточненная модель щелевого уплотнения с учетом спирального движения рабочей жидкости (модель щелевого уплотнения конечной длины), на основе которой разработан аналитический метод расчета возникающей в щелевом уплотнении радиальной силы. Проанализировано влияние окружных перетоков рабочей жидкости, обусловленных полем давления жидкости в щели, на величину составляющих радиальной силы в зависимости от геометрических размеров уплотнения. Построены диаграммы для безразмерных коэффициентов линеаризованных составляющих радиальной силы, которые дают возможность анализировать влияние геометрии щели на радиальную силу без дополнительных расчетов. В работе исследована нелинейность гидростатической силы, обусловленная радиальным смещением вала в щели. Показано, что данная сила имеет мягкую характеристику жесткости, что ухудшает динамические характеристики ротора. Проведены экспериментальные исследования гидростатической силы у относительно длинных щелевых уплотнениях. Сопоставление данных эксперимента и расчетов свидетельствует о хорошем совпадении результатов. Проведен анализ влияния щелевых уплотнений на критические частоты ротора центробежного насоса типа ПЭ. Расчеты показывают, насколько велико влияние щелевых уплотнений на критические частоты ротора и насколько существенно они снижаются из-за окружных перетоков рабочей жидкости в щели и угловой жесткости гидростатической силы в относительно длинном щелевом уплотнении, которым является цилиндрическая щель системы авторазгрузки.
The dissertation Project offers advanced model of the clearance seal with spiral movement of the fluid. Based on that model, author demonstrates new method to calculate radial force that arises in the seal. The work contains diagrams for dimensionless coefficients of linearized components of the radial force, which allow to analyze an influence of the geometrical shape on the radial force without additional calculus. Next, non linear hydrostatic force analysis is presented. Such forces appear due to radial dislocation of the rotor in the seal, and it is shown that such forces have low hardness’s characteristics, thus lowering dynamic characteristics of the rotor. The work presents experimental results of the nonlinear resilience force in relatively long clearance seals. Comparison of the theoretical and experimental parts proves the consistence of the model.

Etude de l'intermittence, un type de transition vers la turbulence rencontre en convection et dans la réaction de Belousov-Zhabotinsky. La mesure invariante dépend continument du paramètre de bifurcation. Etude d'un modèle de couplage résonnant d'ondes de dérivé dans une limite de dissipation forte par des méthodes perturbatives et l'utilisation du théorème de la variété stable. Etude de la génération périodique de solitons dans l'équation de Schrödinger cubique avec source. Travail de synthèse sur les méthodes de moyennisation et les théorèmes adiabatiques.

The thesis is divided in two main parts. In the first part is presented a model based on a numerical integration of a new conservative form of the Fully Non-linear Boussinesq Equations (FNBE) in a contravariant formulation. As known coastal regions are characterized by a very complex morphology: presence of anthropic structures, river mouth or shoreline with articulated geometry. The use of orthogonal grid, as Cartesian coordinate, requests a huge number of calculus points that may be prohibitive. To solve this issue, a well known strategy is to integrate the motion equations on generalized curvilinear boundary conforming grid. In the second part it is presented an original fully non-hydrostatic three-dimensional model based on the numerical integration of Navier-Stokes Equations in time dependent coordinate system. The use of time dependent coordinate system allows to assign, without any approximations, bottom and free surface kinematic conditions and zero pressure condition at the upper boundary of the domain. Unlike the depth averaged model, this model is able to simulate the three-dimensionality of hydrodynamic phenomena related to the wave motion of unsteady flows. The proposed model belongs to the group of the so-called “free surface fully non-hydrostatic three-dimensional models”. These models are often used to analyze local phenomena, to evaluate flow-structure interaction, for sediment transport analysis and to study turbulences phenomena related with them. In general the free surface fully non-hydrostatic three-dimensional models are used for all engineering problems for which is necessary to know the vertical distribution of hydrodynamic quantities.

Bibliography: leaves 140-142
iv, 142 leaves : ill ; 30 cm.
Title page, contents and abstract only. The complete thesis in print form is available from the University Library.
Thesis (Ph.D.)--University of Adelaide, 1987