bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular Kinetics and Physical Gas Dynamics
Authors: Gallis Michael A.
Published: December 2010

Detailed analyses of non‐equilibrium effects in hypersonic high‐temperature and high‐altitude phenomena require a clear understanding of the concepts and methods of the kinetic theory of gases. In this chapter, the Boltzmann equation and its extensions to polyatomic gases and mixtures are presented. The most prominent analytical, numerical, and physical methods for the solution of the Boltzmann equation are outlined. It is shown that the Navier–Stokes equations of fluid mechanics can be derived from the Boltzmann equation in the limit of near‐continuum, near‐equilibrium conditions.
Hypersonic Transition and Turbulence
Authors: Schneider Steven P. , Bowersox Rodney
Published: December 2010

Laminar‐turbulent transition and the subsequent development of the turbulent boundary layer at hypersonic speeds affect heat‐transfer, skin friction, and boundary‐layer separation. Particularly at high‐speeds, much remains unknown about the main mechanisms and the area remains one of active current research. The goal of this chapter is to provide the reader with an introduction to the current state of understanding, so it can serve as a starting point for further reading. Transition is the result of a complex, difficult to predict laminar‐instability process that can be very sensitive to apparently small factors. The transition process is summarized, with emphasis on those events that are specific to high speeds, along with the instability process and some parametric effects. In the second part of the chapter, the main properties of high speed turbulence are described to provide an understanding of qualitative and quantitative trends in surface loads at large Mach numbers where high‐temperature effects become active.
Plasma Dynamics and Flow Control Applications
Authors: Adamovich Igor V.
Published: December 2010

Over the last decade, there has been considerable interest in the use of plasmas generated over high‐speed vehicles for flow control and energy management. Plasma flow control does not use moving parts, and can be turned on and off on a very short time scale. In laboratory experiments, thermal plasmas, laser‐induced breakdown, as well as various types of surface and volume‐filling electric discharge plasmas, have been widely used to modify both subsonic and supersonic flows. Potential plasma flow control applications include drag reduction, boundary layer separation and transition control, mixing enhancement, shock wave modification, wave drag reduction, and on‐board electrical power generation. Primary mechanisms of plasma flow control include magnetohydrodynamic (MHD) and electrohydrodynamic (EHD) interactions, as well as thermal methods using Joule heating of the flow. This article provides a brief overview of the main concepts and methods of plasma flow control.
Fundamentals of Heat Transfer and Thermal Physics
Authors: Klausner James F.
Published: December 2010

Thermal engineers and scientists are concerned with the transport of thermal energy or heat. The concept of heat is closely related to the thermodynamic internal energy of matter and depends on the orientation and motion (translation, rotation, and vibration) of molecules and atoms that comprise matter. Increases in temperature result in increases in the intensity and frequency of molecular and atomic motions and typically result in increased thermal or heat transport (Eckert and Drake, 1987). In the classical treatment of heat transfer, which utilizes macroscopic modeling, there exist three basic modes of transporting thermal energy: (i) conduction, (ii) convection, and (iii) radiation. This chapter will focus on the classical approach to heat transfer analysis for which a global body of engineering solutions and analyses has been developed. It is also worthwhile pointing out that there have been many recent advances in understanding thermal transport at the micro or atomic scale. Energy carriers at the microscale consist of phonons, electrons, fluid particles, and photons. For a comprehensive treatment of energy transport at the microscale, Kaviany (2008) provides an excellent treatise of the subject.
Heat Transfer Enhancement: Phase Change, Geometry, and Jets/Sprays
Authors: Kim Jungho , Chen Tailian
Published: December 2010

Many applications require higher heat transfer than can be obtained from simple geometries such as smooth tubes or flat plates using single‐phase fluids. Methods to enhance heat transfer include exploiting the latent heat of vaporization, increasing the surface area, or increasing the effectiveness of single‐phase heat transfer. Each of these methods are discussed in this chapter.
Introduction to Computational Fluid Dynamics
Authors: van Leer Bram , Powell Kenneth G.
Published: December 2010

Computational fluid dynamics (CFD) has its roots in weapons research; since World War II, it has been used to replace experiments that are expensive, difficult, dangerous, or even impossible to conduct. The development of CFD for compressible flow was dominated by weapons research and astrophysics until 1980, when aeronautical CFD caught up, took the lead, and has been in the forefront since. CFD is primarily concerned with the approximation of partial differential equations (PDEs) on computational grids; to make these approximations suitable for the simulation of fluid flow, they have to adhere to principles of consistency, stability, convergence, monotonicity, conservation, and irreversibility. Major tools in the development of CFD solvers are the Von Neumann analysis, a linear Fourier analysis used to determine numerical stability as well as analyzing the dissipative and dispersive errors in the numerical approximation, and the nonlinear monotonicity analysis, which is used to develop limiters needed to prevent numerical oscillations that may overrun the numerical simulation. When applying these tools in developing a practical flow solver, a host of practical issues relating to the physical model, the grid, the choice of implicit or explicit marching methods, and convergence acceleration, must be considered.
Direct Numerical Simulation of Turbulent Fluid Flow
Authors: Coleman Gary N. , Sandberg Richard D.
Published: December 2010

An overview is given of benefits, costs and challenges associated with direct, i.e. model‐free, numerical simulations of turbulence. The central role played by the Reynolds number, and its relationship to the computational cost, is explained. Critical numerical issues are introduced, including the rationale for the widespread use of spectral and finite‐difference methods. Practical guidelines are offered for performing this specialist subset of Computational Fluid Dynamics.
Computational Modeling of Rarefied Gas Flows
Authors: Boyd Iain D. , Agarwal Ramesh K.
Published: December 2010

Rarefied gas dynamics involves flows for which the number of collisions is too small to maintain the velocity distribution functions (VDFs) at the molecular level near the well‐known equilibrium forms. Such conditions occur at low density and for flows with very small characteristic length scales. Computational methods for the analysis of such flows are described. The approaches reviewed include extension of surface boundary conditions for use in continuum methods, extended sets of continuum flow equations, solution of the Boltzmann equation, and a Monte Carlo method. Hybrid techniques that combine continuum and non‐continuum methods are described for situations that involve a mixture of flow regimes.
Computational Combustion
Authors: Menon Suresh , Fureby Christer
Published: December 2010

Computational combustion is discussed as a field of numerical modeling and simulations using advanced large‐scale parallel systems, and offers a new avenue to understand and interpret the dynamics of acoustic‐flame‐vortex interactions that occur in most combustion systems. Some of the key modeling assumptions and numerical strategies that are being used are identified with a goal to highlight the various issues to be aware of rather than explicitly explain or justify any particular method. Validation of these methods against experimental data and their use in design process are just starting to happen and will likely to become a new strategy in the future given the rapid advances in large‐scale parallel systems, increasing cost of experimental studies and limitations of direct in‐situ data acquisition.
Lattice Boltzmann Method for Computational Fluid Dynamics
Authors: Luo Li‐Shi , Krafczyk Manfred , Shyy Wei
Published: December 2010

This article provides a concise survey of the lattice Boltzmann equation: its mathematical theory and its capabilities for applications in computational fluid dynamics (CFD). The lattice Boltzmann method stems from the Boltzmann equation, and thus differentiates from any conventional method for CFD based on direct discretizations of the Navier–Stokes equations. The lattice Boltzmann method is formulated for near incompressible flows. We will show some examples to demonstrate the state of the art and capabilities of the lattice Boltzmann method. The examples include direct numerical simulations of decaying homogeneous turbulence, large eddy simulations of flows past a sphere, suspensions in fluid, a droplet moving on a surface, and multi‐component flows through porous media. The chapter is concluded with an outlook of future work.
Flow Visualization by Direct Injection Technique
Authors: Nelson Robert C. , Babie Brian M.
Published: December 2010

The use of flow visualization often plays a defining role in the understanding of many fluid flow problems. Through the use of direct injection flow visualization, the researcher may be afforded either a global view of a complex flow field or the enhanced understanding of a critical flow feature. The current article serves to introduce the reader to several commonly practiced direct injection flow visualization techniques including smoke injection, smoke wire, chemical reactions and helium bubbles. Several considerations for the use of each of these techniques are provided along with multiple examples of the use of direct injection flow visualization.
Basic Concepts: Propulsion and Power
Authors: Rao Arvind G. , van Buijtenen Jos
Published: December 2010

The propulsion system provides the required force/power to propel forward an aircraft/rocket or any other object moving in air or space. The propelling force is the most important aspect in the design and operation of aircraft/spacecraft mission. Every major technological breakthrough in propulsion and associated system has redefined the frontiers of aerospace sciences. The urge to improve propulsion systems keeps engineers and scientist busy alike till this day and will continue to do so in the future. When the atmospheric air is used as a working medium in a propulsion system, it is often known as air‐breathing propulsion. This section explains the basics of air‐breathing propulsion through simple analogies. The evolution of various types of propulsion systems in the history of aviation is traced, with special emphasis on the jet engines. The developments and advancements in jet engines over the years, and the main challenges which aircraft propulsion will be facing in the future are also discussed. Finally, new engine concepts and their viability are presented.
Propulsion System Cycles
Authors: Dahm Werner J.A.
Published: December 2010

The most important cycles used for practical air vehicle propulsion systems are discussed and analyzed, including their relative thermal efficiencies and various other attributes that determine their suitability for specific propulsion applications. This includes the fundamental thermodynamic performance of the most widely used heat engine cycles, such as the Otto and Diesel cycles, which are widely used in reciprocating engines, the Brayton cycle, which is used in continuous‐flow systems such as gas turbines and ramjet engines, and the Humphrey cycle, which is relevant to various wave‐driven propulsion systems including pulse jets and pulse detonation engines. Classical ideal cycle results are obtained for each case, and discussion of real cycle effects shows where the performance of practical systems departs from the ideal cycles. Performance metrics for the various cycles are compared, and realistic values for modern systems are used to assess the relative merits of practical propulsion systems based on each these heat engine cycles.
Chemical Equilibrium, Kinetics, and Combustion
Authors: Driscoll James F.
Published: December 2010

The combustion of fuel and air, which occurs in jet engines and in other devices, is one example of an important set of chemical reactions. To understand and to model this complex process, the basic laws of chemical equilibrium and chemical kinetics are applied. First, the Law of Mass Action is described for a system that is in chemical equilibrium, and then the Arrhenius law is applied to unsteady systems that are changing due to chemical kinetics. Some basic information is presented about the properties of premixed flames, non‐premixed flames, and detonations.
Multiphase Dynamics and Pollutant Formation
Authors: McDonell Vincent G. , Dunn‐Rankin Derek
Published: December 2010

This chapter discusses the controlling phenomena associated with the combustion of liquid and solid fuels for aerospace applications. The key physical processes and governing factors are reviewed within the context of the fluid mechanical devices and systems that are generally utilized in aerospace power and propulsion systems. A general discussion of the role of fuels in terms of pollutant formation as well as combustion system operability is provided. Finally, some comments are made to summarize the material discussed.
A Brief History of Positive Displacement Aviation Engines
Authors: Schock Harold J.
Published: December 2010

The positive displacement internal combustion engine was the engine used for the first successful powered manned flight by the Wright Brothers in North Carolina, United States, 1903. Positive displacement engines differ from turbine engines in that their work is generally obtained by the products of combustion expanding against a sealed piston. The aircraft engine has stringent operating requirements, and these are outlined. From 1900–1950 the primary types of positive displacement engines were: in‐line, rotary radial, static radial, vee engines, opposed cylinder engines, and diesel engines. Piston engines can be turbocharged to maintain engine output at high altitudes.
Gas Turbine Engines: Turbines
Authors: Bohn Dieter , Kusterer Karsten
Published: December 2010

The working principle of the turbine in a gas turbine engine is to convert the energy from the fluid into mechanical energy of the shaft. Thus, the power derived from the shaft can be used to drive a compressor, fan, or for the electrical power supply. The chapter introduces the reader to the basic characteristics of typical turbine designs and gives an overview of the different design approaches. Furthermore, it explains major aerodynamic loss mechanisms in axial turbines. As the front stages consist typically of cooled blades, the chapter describes the different design approaches for cooled turbine blades.
Gas Turbine Engines: Turbine Cooling
Authors: Bunker Ronald S.
Published: December 2010

The advancement of gas turbine cooling has allowed engine design to greatly exceed normal material temperature limits. Cooled component design and development has consistently trended in the direction of higher heat loads, and higher through‐wall and in‐plane thermal gradients. The ultimate goals in gas turbine cooling are consistent with the thermodynamics of isentropic energy transfer in that (1) the component or some portion of it is desired to be isothermal to eliminate all internal thermal stresses, (2) the component is desired to be as hot as allowable to minimize coolant usage and inefficient energy transfers, and (3) thermal gradients from the component to the support and containment structure are desired to be minimized. In terms of the turbine system, the goal of turbine cooling is to achieve the longest component life with the least impact on engine efficiency and cost. This summary describes the means and methods, as well as the constraints, concerning the cooling of gas turbine components.
Commercial Engine Noise
Authors: Benzakein Mike J.
Published: December 2010

The source of commercial engine noise is briefly discussed for the legacy fleet, as well as for the new products being introduced into the field. While considerable progress has been done over the last fifty years, there is more to be done. Fan and jet noise are the very components requiring attention as we go forward. New regulations reflecting the public needs are putting pressure on the industry to lower the noise levels for new upcoming products. Intensive research is underway in industry, academia, and government to meet these challenges.
Solid Propellants
Authors: Thakre Piyush , Yang Vigor
Published: December 2010

Solid propellants are widely used in rocket propulsion applications. They are often tailored by specific applications such as space launchers, missiles, and guns. Solid propellants are typically classified as homogeneous or heterogeneous (composite propellants), according to their chemical composition and physical structures. The former contains fuels and oxidizers, which are chemically linked at the molecular level. The latter include fuel and oxidizers, which are mixed physically. Typical examples of homogeneous propellants are single‐base (NC and additives), double‐base (NC, NG and additives), and triple‐base (NC, NG, NQ, and additives) propellants. For composite propellants, the ingredients often used as oxidizers are AP, AN, ADN, RDX, and HMX. Some of the commonly employed binders are HTPB, CTPB, and GAP. Metal fuel additives such as aluminum particles are widely employed in propellant mixtures to enhance motor performance and stability characteristics. This section details the composition and classification of solid propellants, along with their combustion behaviors.
Solid Rocket Motor Failure
Authors: McDonald Allan J.
Published: December 2010

An overview of solid rocket motor (SRM) failures is presented in this chapter. The historical context of large rocket motor development is introduced, along with the strategic and financial motivations for the great efforts toward failure prevention. Several historically significant US and international failures, including that of the space shuttle
Challenger
, are presented in order to identify the primary modes of failure of most modern rocket systems. The overall rates of failure of liquid and solid rockets are compared. A summary of failure analysis tools and methods is given, and common sources of information used to facilitate the determination of rockets' modes of failure are identified. Recommendations are made regarding a prudent approach to post‐flight or post‐test investigations of motors exhibiting anomalous conditions. To illustrate such an approach, the response to the
Challenger
explosion is examined in detail. Evidence of
Challenger's
abnormal SRM operation is presented, and subsequent subscale and full‐scale testing and engineering analysis is described. Finally, the overarching lessons learned over many years of SRM failure analysis are summarized.
Liquid Propellants and Combustion: Fundamentals and Classifications
Authors: Chehroudi Bruce , Talley Doug , Yang Vigor
Published: December 2010

Relevant properties of propellants such as physical properties, specific impulse, specific gravity, material compatibility, and others are briefly described. Various kinds and classifications of liquid propellants are reviewed, and common ones are briefly described. The ignition properties of these propellants are divided into hypergolic and nonhypergolic classes, and methods of igniting nonhypergolic propellants are discussed. The steps and stages of the subsequent combustion process are described generally, and the problem of combustion instabilities is introduced and briefly described, along with methods for testing for them and eliminating them.
Liquid Propulsion: Propellant Feed System Design
Authors: Cannon James L.
Published: December 2010

The propellant feed system of a liquid rocket engine determines how the propellants are delivered from the tanks to the thrust chamber. They are generally classified as either pressure fed or pump fed. The pressure‐fed system is simple and relies on tank pressures to feed the propellants into the thrust chamber. This type of system is typically used for space propulsion applications and auxiliary propulsion applications requiring low system pressures and small quantities of propellants. In contrast, the pump‐fed system is used for high‐pressure, high‐performance applications. The selection of one propellant feed system over another is determined based on design trade studies at both the engine and vehicle levels. This chapter first provides a brief overview of the basic configurations of pressure‐fed systems. Pump‐fed systems are then discussed with greater detail given to the turbomachinery design. Selected design requirements and configurations are provided.
Liquid Propulsion: Systems Engineering, Design Trades, and Testing
Authors: Emdee Jeffery L.
Published: December 2010

Liquid rocket engine design, manufacturing, and testing require implementation of a robust systems engineering process to be successful. In addition to propulsion, there are multiple disciplines involved, including thermal, structures, structural dynamics, electrical engineering, and fluid dynamics. There are also significant interface challenges when integrating the engine system with the launch vehicle. The overall process requires a balance of often competing requirements, including cost, schedule, performance, and reliability. Application of the systems engineering process to liquid rocket engine system design and test evaluation is described in this chapter. Considerations for several system design requirements are covered, including human rating and reliability. After an engine is designed and manufactured, extensive testing and evaluation are required to confirm analytical model predictions and assumptions. Engine testing processes are described to provide an overview of test objectives and requirements. Development testing is used to characterize engine operation and to identify failure modes before qualification begins. Qualification test requirements and flight test demonstration goals will also be reviewed. Finally, systems engineering tools, which are available to prevent and resolve failures, are summarized with specific application to liquid rocket propulsion systems described.
Hybrid Propulsion
Authors: Chiaverini Martin J.
Published: December 2010

Hybrid rocket propulsion systems have several inherent safety and operational features that make them attractive choices for a broad range of applications, including primary propulsion for launch vehicles, upper stage propulsion, tactical and strategic missile systems, and the emerging field of commercial space transportation. Although hybrid rocket motors as we know them today have been investigated for more than six decades, their development and maturation has not been as actively pursued as that of liquid bipropellant engines or solid rocket motors. Historically, military applications have favored the storability and launch‐readiness capabilities of solid rocket motors, while high specific impulse and controllability made liquid engines the system of choice for civil applications. Nevertheless, emphasis on greater propulsion safety, reduced development and recurring costs, insensitive munitions, environmentally benign propellants, propulsion system robustness and reliability, and a high degree of operability have heightened interest in hybrid propulsion systems for commercial space applications and some military propulsion programs. In response to this, hybrid rocket research and development efforts have, within the past decade, led to significant state‐of‐the‐art advancements in hybrid rocket propulsion. The purpose of this chapter is to introduce the reader to the operating principles and characteristics of hybrid rocket motors.
Ion Thrusters
Authors: Goebel Dan M. , Foster John E.
Published: December 2010

Ion thrusters utilize high‐voltage grids to electrostatically accelerate ions to high velocity to produce thrust. Efficient ionization of the propellant carried onboard the spacecraft is achieved by optimized hollow cathode, RF or microwave discharge chambers, and electrons from an external hollow cathode are injected into the ion beam to provide charge neutralization in order to avoid spacecraft charging. The ion thruster propulsion subsystem also contains a power processor, a propellant control system and a gimbal mechanism. The high exhaust velocities produced in present flight thrusters by acceleration of the ions to energies in the range of 1–2 keV produces a specific impulse that exceeds 3000 s, and energies of over 10 keV have been demonstrated. The low thrust produced by these devices of typically a fraction of a Newton requires that thruster lifetimes measured in years are needed for most deep space prime propulsion and earth‐orbiting station‐keeping applications. Ion thrusters feature the highest efficiency (60 to < 80%) and very high specific impulse (2000 to over 10000 s) compared to other thruster types.
Pulsed Plasma Thrusters
Authors: Burton Rodney L.
Published: December 2010

Pulsed plasma thrusters comprise a large class of electric space thrusters, using an electric discharge to accelerate solid, liquid, or gaseous propellant. Each pulse provides a small velocity increment to a spacecraft. Repeating the pulses at a constant rate over 103–109pulses creates significant spacecraft velocity change and also permits highly accurate spacecraft control. The thruster propellant is accelerated either by discharge pressure heating, or by high current electromagnetic forces. The chapter discusses the basic pulsed thruster concept, the measurement of thruster propulsion performance, and describes the distinguishing features of a large number of pulsed thrusters, including those that have achieved space application and those that have experienced advanced development in the laboratory.
Electrospray Propulsion
Authors: Lozano Paulo C. , Martínez‐Sánchez Manuel , Hruby Vlad
Published: December 2010

“Electrospray thrusters” are electrostatic accelerators of charged droplets or of ions extracted directly from a liquid. The best known of these devices are those based on droplets, for which the term “colloid propulsion” has been used. Colloid propulsion development was initiated in the 1960s and 1970s, but this development was halted after reaching near flight status, due to perceived complexity and risks associated with high voltages. More recent developments include the pure ionic regime using ionic liquids, which opens up access to high specific impulses at low voltage, and the use of micro‐fabrication to build compact arrays of hundreds or thousands of emitters. A new factor favoring electrospray propulsion is the emergence of micro‐propulsion missions, especially those requiring high precision and repeatability. However, research work underway indicates that massive arraying can also open the way to practical, highly efficient, high specific impulse main propulsion. This chapter reviews the pertinent physics and the status of the technology, including examples from the older generation and from recent applications.
Power Management and Distribution
Authors: Lenertz Brian A.
Published: December 2010

The topic of Power Management and Distribution (PMAD) for spacecraft Electrical Power Systems (EPS) is presented. Various PMAD architectures are shown, followed by a discussion of the PMAD elements, and then moving into power distribution and fusing. Design requirements such as power quality and stability are covered, as well as command and telemetry, fault tolerance, and design verification.
Linear Elasticity
Authors: Mal Ajit
Published: December 2010

A brief exposition of the theory of linear elastostatics is presented in this chapter. The equations of elasticity are written in compact forms using the index notation and coordinate‐independent direct vector notation when convenient. The chapter is divided into three sections dealing with kinematics, balance laws, and constitutive relations. The concepts of displacement, strain, and stress are developed and the relationships between them are derived under the assumption of linearity. The equations of equilibrium are derived based on the application of Newton's laws to deformable solids. Solutions of a few typical linear elastostatic problems of interest in aerospace engineering applications are presented.
Plates and Shells
Authors: Birman Victor
Published: December 2010

The chapter outlines the foundations of the theory of plates and shells. The general approach employed in all versions of the relevant theories leads to particular cases including the classical (technical) theory of isotropic and composite plates and shells. Examples of solutions of linear bending and buckling problems are illustrated. The effect of large nonlinear deformations on the response of plates and shells is reviewed. The analysis of stiffened plates and shells is discussed, including the method modeling discrete reinforcements and the smeared stiffeners technique applicable to closely spaced identical stringers. It is shown that openings and cut‐outs influence the behavior and strength of plates and shells, both locally through the stress concentration as well as globally through their effect on the stiffness. The concepts of composite and sandwich plates and shells are elucidated, providing insight on the peculiarities of mechanics of these structures.
Fatigue and Fracture Mechanics in Aerospace Structures
Authors: Kardomateas George A. , Geubelle Philippe H.
Published: December 2010

The usage history of aerospace structures may include cyclic loads of either constant or varying amplitude, fluctuations in temperature, or a corrosive environment. This section deals with the effects of cyclic loads, which lead to material degradation over time, due to the initiation and growth of cracks; this degradation can eventually result in failure (fatigue). Thus, a reliable prediction of component fatigue life is critical to aircraft safety. This is even more important as the average age of the world's transport fleet continues to rise. This section provides a general overview of the approaches, based on fracture mechanics, which have been developed to arrive at an estimate of fatigue life or at an inspection interval (damage tolerance) with the goal of ensuring component safety.
Structural Stability
Authors: Simitses George J. , Hodges Dewey H.
Published: December 2010

The behavior of structures can be classified in terms of response and stability. Structural stability can, in turn, be further classified in terms of the rate at which the structure is loaded. Structures that are very slowly loaded may be analyzed with static principles; otherwise, dynamic behavior must be taken into account. In the first part of this chapter basic principles of static structural stability are discussed. The main part of the discussion is presented in the framework of analyses that are linearized about an equilibrium state, which may be governed by nonlinear equations. The discussion also distinguishes conservative from nonconservative loading; outlines the uses of classical, kinetic, and imperfection methodologies; and illustrates bifurcation buckling, finite disturbance buckling, and snap‐through. A brief buckling analysis example and a discussion of the role of experiments are presented. In the second part an overview of dynamic stability is presented. Dynamic stability analyses for structures subjected to aperiodic time‐dependent loads are distinguished from those subjected to periodic time‐dependent loads. An example analysis is presented for stability of a system subjected to a periodic force, leading to parametric resonance. Finally, an overview is given of the application of structural stability to the aerospace field.
Damping in Structural Dynamics
Authors: Lesieutre George A.
Published: December 2010

Damping is an important aspect of aerospace structural dynamics. Passive damping is caused by numerous physical mechanisms, only some of which can be exploited by design. The most effective methods of designing materials‐based passive damping into structures involve the use of: high damping viscoelastic polymers in layered damping treatments; elastomers; shunted piezoelectrics; and damped composites. To consider damping during the design process, accurate models are needed—these must capture the general effects of damping, while also enabling the detailed design of damping treatments. Strain‐based viscous damping models yield modal damping that increases monotonically with frequency, a result inconsistent with observations. More general proportional damping is best regarded as a mathematical curiosity. Complex stiffness models, although capable of accommodating frequency‐dependent damping and stiffness in frequency response analysis, cannot directly predict structural response to arbitrary loading. The combination of either the complex stiffness or the modal strain energy method with a modal damping model, however, often yields acceptable results. The need for better accuracy in some applications has motivated the development of improved time‐domain models that capture the frequency‐, temperature‐, and amplitude dependence of damping and stiffness exhibited by the high‐loss materials that are frequently used to effect significant damping.
The Evolution of Analytic and Computational Methods for Fixed‐Wing Flight Vehicle Aeroelasticity
Authors: Livne Eli
Published: December 2010

The development of analysis and computational methods used to design and certify fixed‐wing flight vehicles is presented in this chapter from the early work following World War I and up to recent development in computational fluid dynamics/finite element‐based computational aeroelasticity and from flight vehicles operating in the low subsonic flow regime to vehicles that fly transonically, supersonically, and hypersonically, representing flight vehicle technology developed over more than a hundred years of flight. The professional literature on aeroelasticity is vast, and only key references are included in the bibliography at the end of this chapter. These references contain substantial references lists of their own that can serve as appoint of departure for further searches.
Hypersonic Aeroelasticity and Aerothermoelasticity
Authors: McNamara Jack J. , Friedmann Peretz P.
Published: December 2010

Hypersonic aeroelasticity and aerothermoelasticity involves the study of mutually coupled fluid‐structure interactions that occur as a result of flexible structures operating in hypersonic flow. Starting between Mach 3.0 and Mach 5.0, the effect of flow nonlinearities and aerodynamic heating on the structural response of hypersonic vehicles becomes an important consideration. Aeroelastic phenomena in hypersonic flow is an essential consideration in the hypersonic flow regime due to the potential to lead to structural failures (e.g., flutter, fatigue, buckling, etc.) and increase the complexity of interactions between the aerodynamic, structural, control, and propulsion systems (i.e., aero‐servo‐thermo‐elastic‐propulsive interactions). This article discusses the fundamental aspects of the problem, strategies for solution, modeling approaches, and hypersonic aeroelastic and aerothermoelastic behavior as observed from previous experimental and computational investigations.
Rotary Wing Aeroelasticity
Authors: Friedmann Peretz P.
Published: December 2010

This chapter provides an introduction to rotary wing aeroelasticity (RWA). Basic rotor configurations in use currently are described. Fundamental differences between RWA and fixed wing aeroelasticity are identified. The methodology for formulation and solution of the RWA problem is given, followed by a limited number of illustrative results. These examples illustrate several key problems in RWA such as the coupled flap–lag and coupled flap–lag–torsional isolated blade stability in hover, followed by the coupled rotor–fuselage problem in hover. Comprehensive rotorcraft analysis codes are also discussed, and their application to bearingless rotor stability analysis is illustrated. Modeling of composite blades is also briefly described. The chapter describes noteworthy current activities and concludes by discussing future developments.
Error Estimation and Quality Control
Authors: Díez Pedro , Parés Núria , Huerta Antonio
Published: December 2010

This chapter provides a description of the error assessment tools available for general finite element analysis, in particular those for solid and structural mechanics. The text focuses on goal‐oriented error estimation, in terms of general quantities of interest rather than on energy norm. However, the energy norm estimates are also discussed because they are seen as basic tools that must be used for assessing the error in arbitrary functional outputs of the solution. Attention is paid to the classification of the different methodologies and their main characteristics.
Computational Methods in Buckling and Instability
Authors: de Borst René
Published: December 2010

This chapter gives a succinct overview of computational methods to identify instability and bifurcation phenomena in systems that arise after discretization of solids and structures. Next, path‐following methods are discussed, which allow for tracing the complete load‐displacement behavior of thin‐walled structures, including snap‐through and snap‐back behavior.
Computational Optimization
Authors: Maute Kurt
Published: December 2010

Aerospace systems are often subject to challenging requirements on performance and reliability. Computational design optimization is an approach assisting design engineers in meeting these requirements. It automates the design procedure, allows for predicting the performance of a system by large, high‐fidelity numerical models, and enables consideration of a large number of design constraints and optimization variables. The formulation and solution of design optimization problems can be organized around three tasks: (i) transforming an engineering design problem into a mathematical optimization problem which is then solved by numerical algorithms, (ii) selecting the features of the systems that can be altered in the optimization process and expressing these modifications as functions of the optimization variables, and (iii) predicting the performance of the system as a function of the optimization variables. Today design optimization methods are used to optimize the material composition and the geometry of aerospace structures, considering for example structural, aerodynamic, and thermodynamic performance criteria. Optimization approaches are used to determine the conceptual layout of the system and to fine‐tune a particular feature. Computational design optimization supports design engineers in efficiently developing products. However, it requires an in‐depth understanding of the numerical models and methods used in the optimization process to obtain reliable optimization results.
Static Fracture Response of Materials
Authors: Zehnder Alan T.
Published: December 2010

Attention to the fracture of aerospace materials is critical to the safety and performance of aerospace structural systems. Basic concepts of linear elastic fracture mechanics, including crack tip stress and displacement fields, stress intensity factor, energy release rate and fracture initiation, and growth criteria are reviewed. Analytical, computational, and experimental methods for calculating and measuring crack tip stress intensity factors are discussed. Several experimental methods for the measurement of fracture initiation toughness and crack propagation resistance are described as well.
Testing of Structural Joints
Authors: Smeltzer Stanley S.
Published: December 2010

Structural joints are tested primarily to determine the maximum single‐use load or continuous, time varying load spectrum a specific joint architecture can sustain prior to failure. The behavior of bolted and bonded joints is the focus of the testing described in this section. The test conditions and resulting failure mechanisms identified for each joint type are important parameters documented from the test, which help identify trends within certain joint architectures for classification purposes. Ultimately, joint test results are used to develop empirical prediction methods to predict the performance of related joints when subjected to similar applied loads.
Dynamic Response of Materials
Authors: Lambros John
Published: December 2010

The dynamic response of materials necessitates a separate study than that at quasi‐static loading rates primarily for two reasons:

the mechanics of a dynamic problem in which material inertia has to be accounted for are different than the static case because they allow for traveling discontinuities, stress waves, in the material, and

the constitutive response of many materials exhibits rate sensitivity.

This rate dependent response can manifest itself as an increase in elastic modulus with increasing strain rate (or decreasing temperature), and/or a change in yield properties such as yield strength and hardening rate. Unlike polymers, it is rare that metals exhibit a strain rate dependence of elastic modulus, but they can have a strong viscoplastic response. Various techniques have been employed to accurately measure rate dependent material response. The main challenge in these techniques is to separate the inertial (i.e., wave propagation) effects from the actual material response. The two most common high rate constitutive measurement techniques are the split‐Hopkinson, or Kolsky, bar, and the pressure shear plate impact experiment. Following a short introduction, which describes some fundamental aspects of the mechanics of wave motion in solids, these two experimental techniques are discussed in some detail, and sample results from each are presented.
Nondestructive Evaluation of Structures
Authors: Regez Brad , Krishnaswamy Sridhar
Published: December 2010

This chapter summarizes why nondestructive evaluation (NDE) is important in the aerospace industry, and then reviews both classical and emerging NDE techniques. Classical techniques presented include visual, penetrant testing, magnetic particle, eddy current, ultrasonic, and x‐ray. The emerging techniques discussed include thermal imaging, laser based optical, terahertz, microwave, millimeter‐wave, and real‐time ultrasonic imaging. The strengths, limitations, flaw detectability, and typical aerospace applications of the techniques are discussed.
Nondestructive Evaluation of Structures
Authors: Farrar Charles R. , Worden Keith , Lieven Nicholas A. J. , Park Gyuhae
Published: December 2010

The process of implementing a damage identification strategy for aerospace systems is referred to as structural health monitoring (SHM). Here, damage is defined as changes to the material and/or geometric properties of these systems, including changes to the boundary conditions and system connectivity, which adversely affect the system's current or future performance. A wide variety of highly effective local non‐destructive evaluation tools are available for such monitoring. However, the majority of SHM research conducted over the last 30 years has attempted to identify damage in structures on a more global basis and in a more autonomous manner. Recent research has begun to recognize that the SHM problem is fundamentally one of statistical pattern recognition, and a strategy to address this problem as it applies to aerospace structures is described herein. To conclude this discussion, technical challenges that must be addressed if SHM is to gain wider application in the aerospace industry are summarized.
Guided Wave Methods for Structural Health Monitoring
Authors: Giurgiutiu Victor , Soutis Constantinos
Published: December 2010

This article reviews the state of the art in guided wave (GW) methods for structural health monitoring (SHM). The GW methods permit
on‐demand
interrogation of the structure to determine its current state of structural health (“active SHM”). The enabling element for active SHM is the piezoelectric wafer active sensor (PWAS), which allows both transmission and reception of GW into the structure. The mechanisms of Lamb wave excitation and detection with PWAS transducers are first presented. It is shown that Lamb wave mode tuning can be achieved by the combination of PWAS dimensions, frequency values, and mode characteristics. The isotropic GW theory is subsequently extended to GW propagation in composites. The pitch‐catch, pulse‐echo, and phased array ultrasonic methods for damage detection are also addressed. Detection of cracks, disbonds, delaminations, and diffuse damage in metallic and composite structures are exemplified. Finally, suggestions for further work are made.
Signal Processing for Structural Health Monitoring
Authors: Staszewski Wieslaw J. , Sohn Hoon
Published: December 2010

Recent years have shown a number of new structural health monitoring (SHM) technologies that have the potential for online damage detection in aircraft structures. Signal processing will become more critical in the implementation of these technologies because automated signal processing and data interpretation are the key for the success of online SHM. Signal processing can mainly address seven different problems related to SHM:

measurements and data acquisition,

data pre‐processing,

signal feature analysis,

pattern recognition and machine learning,

reliability analysis,

uncertainties, and

data fusion.

This chapter briefly discusses all seven problems. Finally, this chapter illustrates some signal‐processing examples relevant to damage detection in aircraft structure. Four different examples related to fatigue crack in aluminum specimens and impact damage detection in a composite specimen are presented.
Structural Materials: Aluminum and Its Alloys – Properties
Authors: Dashwood Richard J. , Grimes Roger
Published: December 2010

The intention of this chapter is to introduce the reader to the range of aluminum alloys used in the aerospace industry, their key properties, and the reasons for their selection. A brief review of the history of the aluminum industry, its role within the aerospace sector, and the current and future trends for its use is presented. Aluminum alloy metallurgy and the main methods for strengthening aluminum alloys are explained paying particular attention to age hardening. The Aluminum Association alloy designation and temper system is introduced, along with the key characteristics (typical mechanical properties and aerospace applications) of the seven main wrought alloy series. Recent alloy developments, in particular aluminum lithium alloys are highlighted.
Titanium and its Alloys: Processing, Fabrication and Mechanical Performance
Authors: Jackson Martin , Boyer Rodney R.
Published: December 2010

Titanium alloys have excellent mechanical properties and corrosion resistance. However, annual global titanium is dwarfed by commodity metals. This is in part due to the current primary production method which requires a complex discontinuous reduction route in addition to several costly downstream processing steps to convert titanium sponge into usable product for aerospace and aircraft components. The processing routes from vacuum arc remelting to downstream forging and extrusion are discussed in detail for titanium alloys. Casting and powder metallurgy (PM) routes are also described for near net shape products and cost savings. A wide range of post processing fabrication routes are presented, including welding, superplastic forming/diffusion bonding, and the most costly fabrication step, machining. Emerging additive manufacturing techniques are also included in this chapter. Finally, the effects of prior processing and resultant alpha and beta morphology on the mechanical performance, including tensile strength, ductility, fatigue, fracture toughness, and creep are covered in detail.