The role of structural dynamics in the design and operations of space systems: The history, the lessons, the technical challenges of the future

Structural dynamics and its auxiliary fields are the most progressive and challenging areas space system engineering design and operations face. Aerospace systems are dependent on structural dynamicists for their success. Past experiences (history) are colored with many dynamic issues, some producing ground or flight test failures. The innovation and creativity that was brought to these issues and problems are the aura from the past that lights the path to the future. Using this illumination to guide understanding of the dynamic phenomena and designing for its potential occurrence are the keys to successful space systems. Our great paradox, or challenge, is how we remain in depth specialists, yet become generalists to the degree that we make good team members and set the right priorities. This paper will deal with how we performed with acclaim in the past, the basic characteristics of structural dynamics (loads cycle, for example), and the challenges of the future

Structural interaction with control systems

A monograph which assesses the state of the art of space vehicle design and development is presented. The monograph presents criteria and recommended practices for determining the structural data and a mathematical structural model of the vehicle needed for accurate prediction of structure and control-system interaction; for design to minimize undesirable interactions between the structure and the control system; and for determining techniques to achieve the maximum desirable interactions and associated structural design benefits. All space vehicles are treated, including launch vehicles, spacecraft, and entry vehicles. Important structural characteristics which affect the structural model used for structural and control-system interaction analysis are given

Proper orthogonal decomposition, dynamic mode decomposition, wavelet and cross wavelet analysis of a sloshing flow

Internal hydrodynamics and its coupling with structural dynamics are non-negligible processes in the design phase of aerospace systems. An improved understanding of the nature of this coupling would allow for greater flexibility in modeling and design of such systems, and could lead eventually to the development of suitable active and/or passive control strategies for enhanced performances. In this manuscript we apply a number of data analysis techniques: proper orthogonal decomposition, dynamic mode decomposition and wavelet transform and their combination to time-resolved images of a liquid sloshing within an enclosure. We use these techniques to identify fluid-dynamic modes in space and time and to verify their coupling with the structural dynamics of vibrating structures. In particular we consider the transient case of a water tank mounted on a free oscillating cantilever. As the acceleration amplitude decays, we observe and quantify the transition from incoherent flow to standing waves. Our results show that the content of the images is very informative and can be used for quantitative analysis. As the main outcome, the hydrodynamic modes are identified using POD and DMD, and related to known features of sloshing flow, such as the frequency of the first symmetric free surface mode. Additionally we perform a comparison of wavelet transforms of POD time coefficients and measured acceleration signals at the tank base. Viewing the latter as the input and the former as the output of the fluid-dynamic system, we are able to correlate the enhanced damping of the cantilever oscillation to the different regimes of the hydrodynamic field

Experimental analysis of liquid vertical slosh damping at vacuum and atmospheric pressures

Experimental data are presented for a cantilevered vertically vibrating beam supporting a tank partially filled with liquid, inside a vacuum chamber where the air pressure can be reduced. Results are presented with and without the tank and contained liquid, as well as under two different gas pressures (atmospheric and vacuum). When the liquid is absent from the tank, aerodynamic damping and added mass effects are quantified. When the tank is partially filled with liquid, the damping versus tank amplitude curves indicate differences that are mainly due to aerodynamic effects, with more noticeable effects in the 50% fill case. The results support the observation that at the density ratios presented here, two-phase liquid/ gas modelling may not be needed for the evaluation of net damping due to violent sloshing flows.</p

NAS Technical Summaries, March 1993 - February 1994

NASA created the Numerical Aerodynamic Simulation (NAS) Program in 1987 to focus resources on solving critical problems in aeroscience and related disciplines by utilizing the power of the most advanced supercomputers available. The NAS Program provides scientists with the necessary computing power to solve today's most demanding computational fluid dynamics problems and serves as a pathfinder in integrating leading-edge supercomputing technologies, thus benefitting other supercomputer centers in government and industry. The 1993-94 operational year concluded with 448 high-speed processor projects and 95 parallel projects representing NASA, the Department of Defense, other government agencies, private industry, and universities. This document provides a glimpse at some of the significant scientific results for the year

Méthode des éléments finis hybride appliquée aux vibrations des coques sphériques

RÉSUMÉ L’analyse des coques sphériques remplies de fluide et soumises à un écoulement supersonique a été l’objet de peu de recherches. Un nombre limité de travaux a été consacré à l’analyse des coques sphériques remplies de fluide ou sous l’effet du flottement supersonique. Dans cette thèse, nous élaborons un modèle capable d’analyser le comportement dynamique des coques sphériques à vide, partiellement remplies de liquide ou soumises à un écoulement supersonique. La méthode développée est une combinaison de la méthode des éléments finis, de la théorie des coques minces, de la théorie potentielle du fluide et de la théorie aérodynamique du fluide. Différents paramètres seront considérés dans l’étude. Dans la première partie de l’étude, l’analyse vibratoire des coques sphériques a été menée. Le modèle structural est basé sur une combinaison de la théorie des coques minces sphériques et de la méthode des éléments finis classique. Les équations de mouvement utilisant la méthode des éléments finis hybride ont été dérivées et résolues numériquement. Les résultats ont été validés en utilisant les données numériques et théoriques disponibles dans la littérature. L’analyse a été accomplie pour des coques sphériques de différentes géométries, différentes conditions aux rives et plusieurs rapports rayon-épaisseur. La méthode des éléments finis hybride peut être utilisée efficacement pour la conception et l’analyse des coques sphériques utilisées dans les structures des aéronefs à haute vitesse. Dans la seconde partie de cette étude, une méthode des éléments finis hybride a été appliquée pour l’étude des vibrations libres des coques sphériques remplies de liquide. Le modèle structural est basé sur une combinaison de la théorie des coques minces et de la méthode des éléments finis classique. Nous supposons un fluide incompressible. Les fréquences naturelles pour différentes taux de remplissage sont obtenues et comparées aux données théoriques et expérimentales qui existent dans la littérature. Le comportement dynamique pour différentes géométries, taux de remplissage et conditions aux limites avec différents rapports rayon-épaisseur a été élucidé. Cette méthode des éléments finis hybride peut être utilisée efficacement dans l’analyse du comportement dynamique des structures aérospatiales avec un moindre effort de calcul et de meilleures précisions que les logiciels commerciaux utilisant la méthode des éléments finis classique.----------ABSTRACT The analysis of spherical shells filled with fluid and subjected to supersonic flow has been the subject of few research. Most of these studies treat the dynamic behaviour of empty shells. Few works have investigated spherical shells filled with fluid or subjected to supersonic flutter. In this thesis, we propose to develop a model to analyse the vibratory behaviour of both empty spherical shells and partially filled with fluid. This model is also applicable to study of the dynamic stability of spherical shells subjected to supersonic flow. The model developed is a combination of finite element method, thin shell theory, potential fluid theory and aerodynamic fluid theory. Different parameters are considered here in this study. In the first part of this study, free vibration analysis of spherical shell is carried out. The structural model is based on a combination of thin shell theory and the classical finite element method. Free vibration equations using the hybrid finite element formulation are derived and solved numerically. The results are validated using numerical and theoretical data available in the literature. The analysis is accomplished for spherical shells of different geometries, boundary conditions and radius to thickness ratios. This proposed hybrid finite element method can be used efficiently for design and analysis of spherical shells employed in high speed aircraft structures. In the second part of the present study, a hybrid finite element method is applied to investigate the free vibration of spherical shell filled with fluid. The structural model is based on a combination of thin shell theory and the classical finite element method. It is assumed that the fluid is incompressible and has no free-surface effect. Fluid is considered as a velocity potential variable at each node of the shell element where its motion is expressed in terms of nodal elastic displacement at the fluid-structure interface. Numerical simulation is done and vibration frequencies for different filling ratios are obtained and compared with existing experimental and theoretical results. The dynamic behavior for different shell geometries, filling ratios and boundary conditions with different radius to thickness ratios is summarized. This proposed hybrid finite element method can be used efficiently for analyzing the dynamic behavior of aerospace structures at less computational cost than other commercial FEM software

Dynamic stability of space vehicles. Volume 3 - Torsional vibration modes

Torsional model development and model calculations for cylindrical space vehicle systems and systems employing clustered tank

Design of Launch Vehicle Flight Control Augmentors and Resulting Flight Stability and Control (Center Director's Discretionary Fund Project 93-05, Part III)

This publication presents the control requirements, the details of the designed Flight Control Augmentor's (FCA's), the static stability and dynamic stability wind tunnel test programs, the static stability and control analyses, the dynamic stability characteristics of the experimental Launch Vehicle (LV) with the designed FCA's, and a consideration of the elastic vehicle. Dramatic improvements in flight stability have been realized with all the FCA designs; these ranged from 41 percent to 72 percent achieved by the blunt TE design. The control analysis showed that control increased 110 percent with only 3 degrees of FCA deflection. The dynamic stability results showed improvements with all FCA designs tested at all Mach numbers tested. The blunt TE FCA's had the best overall dynamic stability results. Since the lowest elastic vehicle frequency must be well separated from that of the control system, the significant frequencies and modes of vibration have been identified, and the response spectra compared for the experimental LV in both the conventional and the aft cg configuration. Although the dynamic response was 150 percent greater in the aft cg configuration, the lowest bending mode frequency decreased by only 2.8 percent

Dynamic stability of space vehicles. Volume 14 - Testing for booster propellant sloshing parameters

Recommended procedures for stability, control, and structural loading analysis of large liquid fueled rocket booster sloshing parameter