bluuebunny/crossref_metadata_2025 huggingface dataset:
Riemann Solvers in Aerospace Engineering
Authors: Toro Eleuterio F.
Published: December 2010

The Riemann problem is first explained in the setting of finite volume methods and solution approaches are then reviewed, ending with a detailed description of a particular solver as applied to the three‐dimensional Euler equations for compressible multicomponent flow. A number of related issues are briefly discussed and key references for further study are given.
Grid Generation Techniques
Authors: Soni Bharat K. , Shih Alan M. , Ito Yasushi
Published: December 2010

The grid generation (or mesh generation) process is a critical yet challenging step in the simulations that solve numerically nonlinear partial differential equations (PDEs) representative of fluid dynamics. It is often a tedious and labor‐intensive process when complex geometries are involved. There are many techniques in the grid generation process. In this chapter, concepts, strategies, algorithms, and software tools employed in the grid generation process are described. A brief outline of the grid generation process and adaptive grid generation is presented. Structured grid systems with Cartesian and curvilinear strategies and unstructured grid systems with quadtree/octree, Delaunay triangulation, advancing front, and advancing layers methods are summarized to provide readers with a clear overview of these important approaches. Software tools and literature sources for further information on grid generation techniques and applications are stated. In the final section, future trends in grid generation and technology vision are provided. Computational examples are presented throughout this chapter to demonstrate applications of grid strategies.
High Performance Computing forCFD
Authors: Garbey Marc
Published: December 2010

This chapter describes some general aspects of high performance computing in CFD. High performance computing has been dominated by commodity clusters with large number of cheap processors. These systems provide exceptional opportunity in performance to cost but bring numerous difficulties in designing numerically efficient parallel CFD solution. We will discuss successively hardware/software solution for CFD and reemphasize the importance of algorithm and software libraries.

We will also discuss new opportunities in aerospace engineering brought by large parallel systems.
Reynolds‐Averaged Navier–Stokes Methods
Authors: Leschziner Michael A.
Published: December 2010

RANS methods constitute the overwhelmingly dominant approach to computing the broad variety of flows that are pertinent to fluid‐engineering applications. Notwithstanding recent advances in Large Eddy Simulation (LES), this is set to remain the position for many years to come, mainly because of the stubbornly high computational costs of LES, especially in flows that are sensitive to the near‐wall turbulence structure. On the other hand, the RANS framework poses formidable challenges in respect of physical fidelity and generality, because its predictive characteristics hinge critically on complex turbulence models that involve extensive approximation and much intuition. This chapter provides an introductory review to the fundamentals of the RANS approach and the major classes of turbulence models used to approximate the Reynolds stresses – the correlations of turbulent velocity fluctuations that arise upon Reynolds‐averaging of the Navier–Stokes equations. The rationale of the models is outlined, the principal equations are included, and the main properties of the alternative models are discussed relative to other model types.
Large Eddy Simulation
Authors: Sagaut Pierre , Drikakis Dimitris
Published: December 2010

This article presents the current trends in modeling and simulation of transitional and turbulent flows using the state‐of‐the‐art of large eddy simulation (LES) computational strategies. The fundamentals of both the explicit and implicit LES strategies are presented followed by indicative examples showing the applicability of these approaches. Issues relating to numerical uncertainties and validation are also discussed.
Computational Modeling for Multiphase Flows, Including Microgravity and Space Applications
Authors: Shyy Wei , Sim Jaeheon
Published: December 2010

Multiphase flows involving moving interfaces between different fluids/phases are observed in nature as well as in a wide range of engineering applications. With the recent development of high‐fidelity computational techniques, a number of challenging multiphase flow problems around complex solid geometries can now be computed. We introduce the basic notion of the main categories of multiphase flow computational techniques and address issues arising from interface evolution in time with shape/topological changes, merger and breakup of objects such as drops or bubbles, and the steep fluid property and flow variable jumps across the phase boundary. We discuss Lagrangian, Eulerian, and Eulerian–Lagrangian techniques to represent and follow interface, and sharp and continuous interface methods to model interfacial dynamics. The marker‐based adaptive Eulerian–Lagrangian method, which is one of the most popular methods, is highlighted with microgravity flows and space applications including droplet collision and spacecraft liquid fuel tank sloshing and surface stability.
Optimization Methods in Computational Fluid Dynamics
Authors: Jameson Antony , Ou Kui
Published: December 2010

This chapter discusses the role that computational fluid dynamics (CFD) plays in the design of aircraft. An overview of the design process is provided, covering some of the typical decisions that a design team addresses within a multi‐disciplinary environment. On a very regular basis, trade‐offs between disciplines have to be made where a set of conflicting requirements exist. Within an aircraft development project, we focus on the aerodynamic design problem and review how this process has been advanced, first with the improving capabilities of traditional computational fluid dynamics analyses and then with aerodynamic optimizations based on these increasingly accurate methods. We then review the formulation and application of optimization techniques based on control theory for aerodynamic shape design in both potential flow and inviscid compressible flow. The theory is applied to a system defined by the partial differential equations of the flow, with the boundary shape acting as the control. The Frechet derivative of the cost function is determined via the solution of an adjoint partial differential equation, and the boundary shape is then modified in a direction of descent. This process is repeated until an optimum solution is approached. Each design cycle requires the numerical solution of both the flow and the adjoint equations, leading to a computational cost roughly equal to the cost of two flow solutions. Several case studies are provided, which highlight the benefits of utilizing automatic aerodynamic shape optimization.
Adaptive Mesh and Overlapping Grid Methods
Authors: Henshaw William D.
Published: December 2010

Adaptive mesh refinement (AMR) is a technique used in computational fluid dynamics to add fine grid patches to regions of the flow where more resolution is needed, such as near shocks and detonations. AMR can dramatically speed up a computation and/or enable simulations with a much higher effective resolution compared to uniformly refining the grid. Overlapping grids (also known as Chimera or overset grids) are a technique for covering a complex geometry with a set of overlapping structured grids. Overlapping grids can be more easily generated than multi‐block‐structured grids. Efficient numerical schemes can be written for overlapping grids since they are composed of structured grids and Cartesian grids. They are also effective for moving geometry problems such as aircraft store separation, and rotor craft, since the grids can be rapidly regenerated at each time step.
Solution Methods and Acceleration Techniques in Computational Fluid Dynamics (
CFD
)
Authors: Dwight Richard P. , Lucas Peter , Bijl Hester
Published: December 2010

Methods for solving the discretized equations of fluid motion are discussed, with particular reference to efficient methods for solving compressible flow problems to a steady state. A spectrum of algorithms of widely varying efficiency and complexity are considered from explicit single‐stage methods, through Runge–Kutta (RK), implicit methods, defect correction, to multigrid. They are classified with respect to cost per iteration, convergence rate, and memory requirements and compared for a concrete high‐Reynolds number test‐case. Time‐resolved calculations are then considered using the dual‐time framework.
Discontinuous Galerkin Methods
Authors: Shu Chi‐Wang
Published: December 2010

In this article we describe the discontinuous Galerkin method, which is a finite element method incorporating successful shock capturing finite volume techniques such as Riemann solvers, limiters, and total‐variation‐diminishing Runge–Kutta time discretizations, suitable for solving hyperbolic conservation law systems as well as convection‐dominated convection diffusion equations such as the high Reynolds number Navier–Stokes equations.
Optical Flow Visualization
Authors: Kontis Konstantinos , Zare‐Behtash Hossein
Published: December 2010

Optical flow visualization techniques rely on the changes in flow density and hence the refractive index of the flow. Through various flow visualization techniques an image of the flow field is obtained which can be either qualitative, quantitative, or even both. The use of the appropriate visualization technique strongly depends on the flow field under investigation and the flow properties sought. The optical visualization techniques described here fall into the following categories: shadowgraphy, schlieren, moiré deflectometry, and interferometry. The optical tomography method which allows for the three‐dimensional reconstruction of the flow using two‐dimensional results is also briefly described.
Pressure and Velocity Measurements
Authors: Telionis Demetri P. , Yang Yihong , Jones Gregory S. , Rediniotis Othon K.
Published: December 2010

Multi‐hole probe (MHP) design is based on the fact that the static pressure varies over a solid surface from the maximum value equal to the stagnation pressure to low values, the order of the base pressure in the wake of the body. In this chapter we describe the basic principles of operation, the construction and the calibration methods of MHPs. A very short discussion of their uses is also given.
Thermal Anemometry: An Introduction and Special Topics
Authors: Andreopoulos Yiannis
Published: December 2010

The basic principles and practices of thermal anemometry are presented and discussed. Modes of operation include constant temperature, constant current, and constant voltage. Models of the transfer function are considered for single and multiple hot‐wire probes which include techniques to measure vorticity, rate of strain, and dissipation rate of kinetic energy in incompressible and compressible flows. The response of hot wires to pitch and yaw variations of the incoming velocity vector is also addressed. Owing to its high‐frequency response, good spatial resolution, and relatively inexpensive hardware acquisition cost, thermal anemometry techniques appear to be widely used in the measurements of time‐dependent flow velocity, mass flux, or temperature.
Laser Doppler Velocimetry
Authors: Tropea Cameron
Published: December 2010

The laser Doppler technique, most frequently referred to as a laser Doppler anemometer (LDA) or laser Doppler velocimeter (LDV), is a wide‐spread technique for point‐wise velocity measurements in a flow with fluid markers. Some decisive advantages of the technique over more conventional probe‐based techniques can be mentioned: non‐intrusiveness, directional sensitivity, high spatial and temporal resolution, and high accuracy. In this chapter the fundamental principles of laser Doppler velocimetry will be introduced, including a discussion of optical arrangements, signal generation, signal processing, and data processing. Particular attention will be given to applications in aerodynamic flows, in which the introduction of tracer particles and the velocity bandwidth of the instrument demand special attention. Also, the challenge of performing point measurements with high spatial resolution in large facilities will be addressed.
Spectroscopic and Scattering Techniques
Authors: Ötügen M. Volkan
Published: December 2010

This chapter reviews techniques that depend on the spectroscopic analysis of scattered laser light by atoms or molecules in a gas. A number of techniques are available today that can provide quantitative information about species concentration, gas density, temperature, pressure, and velocity. In most cases, the measurements are resolved in space and in time. In addition to single‐point measurements, two‐ or three‐dimensional quantitative imaging of the desired flow parameter are possible with some of the techniques. Scattering and spectroscopic methods are non‐intrusive since only the laser beam is present in the measurement environment. Hence, they are well suited for aerodynamics applications, particularly for high‐speed and reacting flows. The measurement techniques discussed here are absorption spectroscopy, Rayleigh scattering, Raman scattering, laser‐induced fluorescence (LIF), and coherent anti‐Stokes Raman scattering (CARS).
Temperature and Heat Transfer Measurements
Authors: Camci Cengiz
Published: December 2010

This chapter deals with the state‐of‐the‐art in temperature and heat transfer measurements that are frequently encountered in Aerospace Engineering. Resistive temperature transducers, thermocouples, bi‐metallic temperature sensors, semi‐conductor diode‐based temperature sensing, liquid crystal thermography, infrared thermography, and pyrometry are discussed in detail. Measurements of convective, conductive, radiative, or total heat transfer rates are often required in aerospace engineering such as atmospheric re‐entry studies, hot‐section component development for gas turbines, ramjet/scramjet development, ballistic missile nose cone development, heat exchanger development, rocket engine combustors, and nozzles. Finally, heat transfer measurements are discussed. Although many illustrations and discussions are used throughout the text, more detailed information in this area can be obtained from the many valuable references provided.
Measurement of Aerodynamic Forces and Moments in Wind Tunnels
Authors: Fan Zhaolin
Published: December 2010

Aerodynamic forces and moments are among the most important data required for flight vehicle performance simulation and design, and such data can be obtained through wind tunnel model tests among other methods. The work described here relates to wind tunnel tests based on relativity and similarity principles. Test models of the studied objects were fabricated in accordance with similarity criteria and connected to a balance and support system fixed on a motion‐controlling mechanism for changing or controlling the attitude angles of the model. This has been installed in the test section of a wind tunnel. When gas flows under test conditions through the wind tunnel section, aerodynamic forces and moments exerted on the model are transferred to the balance and converted into electrical signals. These signals are filtered and amplified by a signal‐conditioning system, sampled by a data acquisition system and then processed to obtain the aerodynamic forces and moments. Other parameters such as total and static pressures, total temperature, and model attitude angle are measured by a pressure transducer, temperature sensor, and angle sensor, respectively. After synthesizing all the measurements, the non‐dimensional aerodynamic force and moment coefficients are obtained and then used for vehicle design and simulation.
Lift, Thrust, and Flight
Authors: Hu Hui , Shyy Wei , Shih Tom I‐P.
Published: December 2010

An overview is provided on forces and motions and their generation that are relevant to flight. First, Newton's laws of motion are outlined. Next, the four types of forces that are involved in flight – weight, lift, drag, and thrust – and their interrelationships are described. This is followed by an introduction on how natural flyers/swimmers generate lift and thrust to fly/swim through flapping wings/fins. The understanding of these flight mechanisms is important to the development of micro aerial vehicles, which operate at relatively low Reynolds numbers and where lift generation typically produces unsteady flows. Afterwards, a discussion is given on how humankind achieves flight through the airplane, where the weight of the payload, the flight speed, and the range of flight can be orders of magnitudes higher than natural flyers. For the airplane, the wings generate most of the lift, and the propulsive devices generate the thrust. The propulsive devices summarized include propellers, turbojets, turbofans, ramjets, scramjets, and rockets – all of which produce thrust by ensuring that the momentum exiting the propulsive device far exceeds the momentum entering the propulsive device.
An Overview of Gas Turbine Engines
Authors: Reddy Dhanireddy R.
Published: December 2010

Gas‐turbine engines are widely used for aircraft propulsion because of their high efficiency in the power range of interest. This chapter presents an overview of gas‐turbine engines, including a discussion of the thermodynamic cycle and definitions of component and system efficiencies relevant to the performance of the engines. Also presented is how gas‐turbine engines are classified as turbojet, turbofan, turboprop, propfan, and ramjet based on how thrust is generated for propulsion. For each of these types of gas‐turbine engines, the distinguishing features are highlighted. Finally, application of supersonic combustion in a ramjet, known as a scramjet, for propulsion in hypersonic speed regime is outlined.
Internal Air and Lubrication Systems
Authors: Johnson Bruce V.
Published: December 2010

The internal air and lubrication systems of gas turbines are described. The internal air system of a gas turbine distributes the air extracted from the main gas path at several axial locations in the compressors to ventilate and cool the engine components and to provide an axial pressure balance on the rotating components to control the axial loads on the bearings. Special fluid engineering and heat transfer technologies that are required for this task are described, including transfer of air through rotating orifices, transfer of the blade cooling air from passages in the engine case to the rotating turbine disks, cooling compressor disk cavities, controlling the sealing flow in the compressor, and controlling the ingestion of combusted gases from the turbine stages into the turbine disk cavities. The lubrication system provides pressurized oil to the bearing compartments that also receive buffer air and returns the oil‐air mixtures to the oil‐air separators and the oil reservoir.
Gas Turbine Engines: Seals
Authors: Chupp Raymond E. , Hendricks Robert C. , Steinetz Bruce M.
Published: December 2010

In turbomachines, seals control clearances. Excessive clearances lead to losses in cycle efficiency, flow instabilities, and hot gas ingestion into disk cavities. Insufficient clearances limit coolant flows and cause interface rubbing, possible overheating of downstream components, and damage interfaces; thus limiting component life. Clearance control is often the most cost effective method to enhance system performance. Advanced concepts and proper material selection continue to play important roles in maintaining interface clearances to enable the system to meet design goals. This chapter presents an overview of sealing in turbomachines.
The Scramjet Engine: Basic and Combined Cycles
Authors: Segal Corin
Published: December 2010

The supersonic‐combustion ramjet (scramjet) is a cycle similar to the basic ramjet with the exception that the airflow remains, at least in certain engine regions, supersonic. The short residence time of the order of milliseconds for a full size engine, imposes severe technological requirements for fuel injection, mixing, and combustion to efficiently release heat and produce thrust. The engine is suitable for flight in excess of Mach 6 when due to the low angle of the ensuing shock waves, the engine becomes highly integrated with the vehicle. The following broadly describes the operation of the scramjet engine and the differences between this and the subsonic ramjet device. Given the range of flight speeds travelled by a hypersonic vehicle, the scramjet will operate along other cycles in a closely couple fashion; several combined cycled concepts are also described.
Emerging Air‐Breathing Propulsion Technologies
Authors: Reddy Dhanireddy R. , Blankson Isaiah
Published: December 2010

This chapter presents emerging trends in airbreathing propulsion technology development based on the technology roadmaps of leading government research organizations addressing national priorities related to engine efficiency, pollutant emissions, noise, reliability, and safety. Technologies and concepts relevant to each of the speed regimes, ranging from subsonic to hypersonic mach numbers that need to be developed and investigated to overcome existing and anticipated barriers, as well as enable commercially viable flight operations, especially at high speeds, are highlighted along with the time frames planned for these developments over the next 25 years. In addition, some of the unconventional research concepts that require sufficient time to understand and overcome engineering challenges of making these concepts practical are also presented, including a few examples such as the exoskeletal engine, the AJAX‐inspired MHD‐controlled turbojet, and the ATREX engine.
Rocket Propulsion: Basic Concepts and Introduction
Authors: Thakre Piyush
Published: December 2010

Rocket propulsion is of vital importance for space travel and for launching satellites into orbits around the earth. It is also instrumental in military applications. Rocket propulsion is a class of jet propulsion that produces thrust by ejecting burned propellant. The thrust is generated on the basis of Newton's third law of motion. Rocket propulsion systems can be broadly classified according to the type of energy source (chemical, solar, electric, or nuclear). The most commonly used rockets are solid propellant rocket motors and liquid propellant rocket engines. This chapter provides an introduction to rocket propulsion by covering the overall classification, basic concepts, and rocket equations. Different types or rocket nozzle designs, the concept of multistaging, and other issues are also presented.
Historical Overview and Solid Rocket Motor Fundamentals
Authors: Geisler Robert L. , Frederick Robert A. , Giarra Matthew
Published: December 2010

A technical and historical overview of solid rocket motors (SRMs) is presented. Typical SRM applications are identified, and the principles of SRM operation are described. Common ranges of operating conditions are described, including internal temperatures, pressures, and so on. Several major components of typical SRMs (case, grain, nozzle, and igniter) and the unique design challenges associated with each are discussed in some detail. The performance parameters used in SRM analysis are defined, and some modern analysis tools are identified and discussed. Finally, a brief history of American solid rocketry is given, including the motivations for and developments of some of the scientific and engineering milestones that have enabled the modern era of solid propulsion. The historical relevancies of several notable solid rockets are described as well.
Solid Propulsion: Motor Interior Ballistics – Modeling and Design
Authors: Jackson Thomas L. , Austin Joanna M.
Published: December 2010

Understanding the interior ballistic characteristics of solid rocket motors is a daunting task for the motor designer because of the large number of coupled performance parameters. The performance parameters depend upon the internal ballistic properties of the motor, such as propellant burn rate. The designer has two basic options for developing new motors, built‐and‐test, or using a combination of numerical simulation, empiricalism, and small‐scale testing for validation, collectively known as virtual engineering. Virtual engineering, which requires appropriate models for the propellant, chamber, nozzle, and plume regions, is rapidly becoming the standard tool for designing new motors. We highlight some modern developments of physics‐based models used in virtual engineering, and comment on current trends.
Liquid Propulsion: Historical Overview, Fundamentals, and Classifications of Liquid Rocket Engines
Authors: Kim Eun S. , Emdee Jeffery L. , Cohn Richard K.
Published: December 2010

Over the course of the history of today's rockets, liquid rocket engines have been used as primary propulsion for most space launch vehicles and early ballistic missiles. The visions of historical figures such as Tsiolkovsky, Goddard, and Oberth have become reality, resulting in humans reaching the moon and space exploration programs that stretch beyond the earth's orbit. A liquid rocket engine uses fuel and oxidizer in liquid form. Various combinations of liquid propellants have been characterized, tested, and flown. Engines are also classified according to the engine power cycle, which determines how the propellants reach the combustion chamber. Liquid rocket engines utilize numerous design power cycles and propellants depending on the application and design requirements. This chapter provides an overview of liquid rocket propulsion. Key historic achievements associated with pioneering efforts and development of large operational liquid rocket engines are first discussed. The fundamentals of liquid rocket engines are then described along with underlying design theory and practical experience. Lastly, the classifications of liquid rocket engines are provided in terms of application, engine cycle, and propellant combination.
Liquid Propulsion: Thrust Chamber Design
Authors: Cohn Richard K. , Vega John C. , Kim Eun S.
Published: December 2010

The thrust chamber serves the critical purpose of converting the chemical energy stored in the propellants into the kinetic energy required to generate thrust. When the propellants enter the thrust chamber, they undergo a complex series of physiochemical processes such as atomization, vaporization, mixing, reaction, and expansion. A gas‐generator cycle or a staged‐combustion cycle uses an auxiliary combustion device to generate the power required to operate the pump in a much lower temperature environment. This chapter deals with key elements associated with thrust chamber design and is organized as follows. A comprehensive description of the thrust chamber is first given along with the underlying design concept and its applications. Typical nozzles used with the thrust chamber are then described. Finally, auxiliary combustion devices are summarized.
Nuclear Thermal Propulsion (
NTP
)
Authors: Borowski Stanley K.
Published: December 2010

The nuclear thermal rocket (NTR) derives its energy from fissioning uranium‐235 atoms contained within fuel elements that comprise the engine's reactor core. During operation, hydrogen (H
2
) propellant is pumped through coolant channels in the fuel elements where it is superheated to high temperatures and then expanded out a supersonic nozzle to generate high thrust at twice the specific impulse (
I
sp
∼900 s) of today's best chemical rockets. This technology is not new. Twenty rocket reactors were designed, built, and ground tested during the Rover and NERVA (Nuclear Engine for Rocket Vehicle Applications) programs conducted between 1955 and 1972. These programs demonstrated: (1) a wide range of thrust; (2) high‐temperature carbide‐based nuclear fuel; (3) sustained engine operation; (4) accumulated lifetime; and (5) restart capability. Ceramic metal fuels were also evaluated as a backup. The NTR has a significant growth capability. Configured as a “bimodal” system, the NTR can generate spacecraft electrical power. Adding an “afterburner” nozzle for oxygen (O
2
) injection and supersonic combustion in the engine's hot H
2
exhaust downstream of the nozzle throat can enable a variable thrust and
I
sp
capability. For future human missions to Mars, the NTR can reduce the required launch mass by ∼400 t compared to chemical propulsion. It also has fewer mission elements, simpler space operations, and the use of clustered, lower thrust engines can help reduce development cost and overall mission risk.
Micropropulsion
Authors: Ketsdever Andrew D.
Published: December 2010

A wide range of micropropulsion systems have been proposed, designed, and developed in an effort to revolutionize space operations. Micropropulsion is generally defined as a propulsion system capable of producing a change in momentum on a microspacecraft (i.e., a spacecraft with a mass less than 100 kg). Allowing a broad definition of micropropulsion includes a wide range of propulsion systems ranging from scaled‐down versions of existing larger‐scale thrusters to specially designed thrusters that utilize advanced micro‐fabrication techniques. This section briefly summarizes design constraints, scaling laws, mission requirements, and application of micropropulsion systems. This section also summarizes the current state‐of‐the‐art in micropropulsion system development including both microchemical and micro‐plasma concepts.
Laser Propulsion
Authors: Komurasaki Kimiya , Wang Bin
Published: December 2010

“Beamed Energy Propulsion” is distinguished by its use of a collimated laser or microwave beam that enables long‐distance wireless power supply, no‐fuel airbreathing flight, high heating rates (detonation and ablation) by beam focusing, and other useful features. Remotely powered space propulsion is a potential alternative to chemical and electric propulsion. Compact onboard laser thrusters also provide unique features. This chapter presents a worldwide review of beamed energy propulsion studies, most of which have been reported at the series of International Symposium on Beamed Energy Propulsion (ISBEP).
Magnetic Plasma Sails
Authors: Winglee Robert M.
Published: December 2010

Magnetic plasma sails can augment spacecraft propulsion by the deflection of charge particles from an external source, thereby utilizing energy and momentum that is not actually carried on board the spacecraft. The external source could be the solar wind that has speeds of 350–800 km s−1, which is more than an order of magnitude faster than most plasma propulsion system presently being considered. Because of the tenuous nature of the solar wind, a mini‐magnetosphere needs to be created by the injection of low energy plasma that expands the magnetic field out to tens of kilometers. This expansion can be achieved by induced plasma currents stemming from the plasma interaction with a base dipole magnet field. An alternative use of plasma sails is the deflection of beamed plasmas. This latter application opens up a host of new applications, including raising or lowering of orbits of spacecraft around the Earth, as well as fast missions to the planets. New developments in magnetic nozzles opens up the possibility of having collimated plasma beams propagating over large distances to achieve efficient distant beamed plasma applications.
Radio‐Frequency and Microwave Thrusters
Authors: Micci Michael M.
Published: December 2010

Both radio‐frequency (RF) and microwave electromagnetic energy can be used to heat a propellant gas to plasma temperatures followed by a gasdynamic converging{‐‐}diverging nozzle expansion in an electrothermal rocket mode. RF energy can be coupled to a gas either capacitively or inductively. Capacitive coupling operates effectively only at low gas pressures that are not desired in a thruster concept due to frozen flow losses. Inductive coupling has been shown to effectively couple RF energy to gases at atmospheric and higher pressures. However, because inductively coupled plasmas fill the entire absorption chamber, heat losses to the chamber walls are severe. Microwave energy can be used in one of several modes including, resonant microwave cavity, surface wave or propagating plasma modes, to ignite and sustain plasmas that can be localized away from any walls, thus reducing heat losses from the thruster. State‐of‐the‐art microwave thrusters utilize the microwave resonant cavity mode, where a standing wave is created within a cavity with plasma formation only at regions of high electric field intensity. Microwave thrusters have been demonstrated at frequencies ranging from 915 MHz to 14.5 GHz at power levels from 10 to 11 000 W. High specific impulses have been measured for microwave thrusters for both helium and ammonia propellants.
Fusion Propulsion
Authors: Kammash Terry
Published: December 2010

Next to antimatter annihilation reactions, fusion nuclear reactions produce more energy per unit mass than other energy sources considered suitable for space propulsion. The mass converted to energy in fusion reactions is almost an order of magnitude larger than that in fission reactions, and several orders of magnitude larger than chemical reactions. The fusion fuel, which can also serve as a propellant, must, however, be heated to very high temperatures, comparable to those inside the sun, in order to achieve ignition, and for the reactions to become self sustaining. At such temperatures the fusion fuel becomes ionized consisting of unbound, freely moving charged particles, namely electrons and ions often referred to as “plasma.” In order to produce energy exceeding that required to heat it to ignition, the plasma must be confined long enough to allow the ions to undergo fusion reactions. Such confinement is generally achieved in one of two ways, “magnetic” or “inertial.” Both of these approaches have been investigated for utilization in space propulsion. In what follows, the underlying principles of the use of fusion energy in space propulsion will be examined, and some representative concepts of both confinement approaches will be addressed.
Space Power Trends
Authors: Spanjers Gregory , Roberts Thomas
Published: December 2010

Size and performance characteristic limits are discussed for government and commercial spacecraft classes. Potential future sources of space power are described. These technologies are not intended to be all‐inclusive; however, electrodynamic tethers, nuclear fission reactors, nuclear fusion, and antimatter provide a good range of the various stages of research and development encountered as technologies are matured for space flight. Historical and present‐day spacecraft power levels show an ever‐increasing rise in the maximum available power, although the use of these high power levels is limited to a small few commercial communications spacecraft. Peak power levels today, excluding the International Space Station, are 18‐‐20 kW, although this is expected to rise to the 25‐‐30 kW range in the near future. Early high‐power spacecraft relied on nuclear fission reactors for critical military missions, primarily for the Soviet government. These were retired after the 1980s due to improved photovoltaic power‐generation technology. At present the power levels used for earth‐orbiting spacecraft are spread across the 0‐‐20 kW range, with the distribution dominated by the constellations programs. Interplanetary space continues to be restricted to low power levels afforded by Radioisotope Thermoelectric Generators, until research can mature technologies such as nuclear to provide high‐power capability far from the sun.
Variational Principles in Structural Mechanics
Authors: Shaw John A. , Elliott Ryan S.
Published: December 2010

This chapter introduces the calculus of variations and associated mathematical operators on functionals, which are used to formulate boundary value problems in structural mechanics. Weak forms of equilibrium are derived in terms of the principle of virtual work and the theorem of minimum potential energy. These are used to establish the governing field equations (Euler–Lagrange differential equations) and associated geometric, natural, or mixed boundary conditions. Weak forms of kinematic compatibility are derived in terms of the principle of complementary virtual Work and the theorem of minimum complementary potential energy. Examples are provided for each.
Finite Element Methods of Structural Analysis
Authors: Hulbert Gregory M.
Published: December 2010

This chapter presents an overview of two widely used numerical methods for structural analysis. The Rayleigh–Ritz method employs a global perspective of approximation, while the finite element method (of Galerkin form), employs a local approximation basis. Both methods are introduced via a simple truss example. For the finite element method, the construction of element stiffness matrices and loading vectors are shown starting from the general differential equations for truss response, through developing a weak form of the equations, to the Galerkin approximation method and then to specific choices of assumed solutions. Finite element generation, element assembly and global solution techniques are articulated. The generality of the finite element approach is demonstrated by application to beam bending theory.
Elements of Structural Dynamics
Authors: Kosmatka J. B.
Published: December 2010

Modern aerospace vehicles have become larger, lighter, and more flexible, where the effects of dynamic loading can produce large structural oscillatory responses leading to potential catastrophic failures. It is imperative that practicing aerospace engineers are knowledgeable of the system variables that can be used to control (or limit) these large dynamic oscillations as well as understanding the analytical tools that can be used to model these systems and predict the system response. These tools range from approximate single‐ and multidegree of freedom lumped mass models to large‐scale finite element models, where to keep the problem tractable a limited number of vibration modes are used in the response predictions. In addition, closed‐form solutions provide valuable insight into the trends of this complex behavior, as well as providing benchmark cases for validating approximate solutions. In this chapter, the analytical tools are reviewed for both approximate and closed‐form approaches, where numerous results are presented that highlight techniques for controlling the system response.
Static and Dynamic Aeroelasticity
Authors: Weisshaar Terrence A.
Published: December 2010

Aeroelasticity is concerned with the consequences created by interactions among aerodynamic forces, structural deformation, and motion of aerodynamic and hydrodynamic surfaces. Aeroelasticity has four primary effects: (i) lift redistribution that changes external loads; (ii) changes in aircraft trim and dynamic response; (iii) control effectiveness, including aileron reversal, which limits maneuverability; and (iv) aircraft structural dynamic response, in particular buffeting and flutter. A simple model is used to explain some of these effects.

Aeroelastic effects have plagued aircraft from the beginning of flight, sometimes delaying technology transition. Early designs suffered from tail flutter and aileron‐wing flutter that led to in‐flight aircraft destruction. Flutter is a self‐excited structural dynamic instability that occurs when, at high speeds, wing or tail surface vibration extracts energy from the airstream. Today, aircraft development includes extensive, expensive analysis and testing to provide safe operation and prevent flutter.

Solutions to aeroelastic problems nearly always include adding structural weight. Aeroelastic structural stiffness tailoring and active aeroservoelastic control are alternative remediation and exploitation methods. These efforts have led to modern designs such as the X‐29 research aircraft and the FA‐18 Active Aeroelastic Wing. A list of standard textbooks and major references is included.
Transonic Nonlinear Aeroelasticity
Authors: Dowell Earl , Bendiksen Oddvar , Edwards John , Strganac Thomas
Published: December 2010

A review of the state of the art of transonic nonlinear aeroelasticity is presented. The discussion begins with a description of the generic nonlinear aeroelastic behavior that may occur followed by a summary of lessons learned from flight experience. Physical sources of nonlinear behavior are identified in both the aerodynamic fluid flow and the structure. Methods for the efficient computation of unsteady aerodynamic forces are summarized and then the chapter concludes with a discussion of correlation of theory and experiment for flutter boundaries in transonic flow and limit cycle oscillations (LCOs) arising from a variety of physical sources for several distinct aeroelastic configurations.
Panel Flutter
Authors: Dowell Earl H. , Bendiksen Oddvar
Published: December 2010

Panel flutter or the flutter of plates and shells differs in some important respects from the classical flutter of airfoils and wings. These include (i) streamwise bending deformations which are more important than spanwise deformations, (ii) the effects of nonlinear structural forces which typically become significant when the plate deformations are on the order of the plate thickness, and (iii) the impact of viscous boundary layer effects in the transonic flow regime.

It is also sometimes said that panel flutter only occurs at supersonic Mach numbers. And that is true if the leading and trailing edges of the panel are fixed, but not if the trailing edge is free. In the latter case the phenomenon is more analogous to the flutter of a flag and can occur in all speed regimes including subsonic flow. This recent work on transonic and subsonic panel flutter is considered here as well.

In the present chapter, the essential elements of panel flutter are described, the essence of the extant mathematical models reviewed and representative comparisons between theory and experiment cited.
Aeroservoelasticity
Authors: Mukhopadhyay Vivek , Livne Eli
Published: December 2010

The engineering field of aeroservoelasticity in flexible flight vehicles involves mathematical modeling, analysis, and control of the interaction between aerodynamics, structural, and flight dynamic systems along with wind tunnel and flight testing of the advanced active control technology. Adverse aerodynamic‐structure‐control interactions of flexible aircrafts have been a major problem throughout the history of aeronautics. If the flexible vehicle structure is not properly designed, aerodynamic‐structure interactions at high speeds may cause excessive dynamic responses leading to an instability or catastrophic structural failure. In this chapter, fundamentals of these aerodynamic‐structure interactions and optimal feedback control of the resulting flight dynamic instabilities are presented. First, a brief historical review of the evolution of aeroservoelasticity and active control of aeroelastic responses is presented. Then, basic mathematical formulation and analytical modeling techniques for a general aeroservoelastic system along with fundamentals of optimal robust feedback control law design processes are outlined. Techniques for large flexible aircraft structural deformation modal control, bending torsion flutter suppression, and gust load alleviation systems are explained. Two examples of research projects are presented that have demonstrated flutter suppression and gust load alleviation of aeroservoelastic models in wind tunnel tests. Finally, possible future directions of this exciting field of applied aerospace engineering technology and their applications to advanced aircrafts are discussed.
Aeroelastic Testing and Certification
Authors: Cooper Jonathan , Lind Rick , Wright Jan
Published: December 2010

All aircraft must be certified under airworthiness regulations in order to ensure that they are safe from any aeroelastic instability and do not exceed design loads throughout the entire desired flight envelope. The certification process is a combination of numerical simulations validated by a range of different experimental tests. This chapter describes the main analyses and tests that must be performed in order to satisfy the airworthiness regulations relating to aeroelasticity.
Fundamentals of Discretization Methods
Authors: de Borst René
Published: December 2010

This chapter gives a concise introduction into modern discretization concepts that are used for the stress analysis of structures and in fluid–structure interaction problems.

Departing from a by now classical concept, namely the finite element method, mesh‐free methods and partition‐of‐unity‐based discretization methods are introduced. Since the majority of the structural applications in aerospace engineering concern thin‐walled structures, some attention is given to shell elements. In view of the rapidly increasing use of laminated composites, interface elements are also briefly treated.

Furthermore, the growing importance of multiscale analysis as a new paradigm is discussed.
Finite Element Analysis of Composite Plates and Shells
Authors: Reddy J.N. , Arciniega Roman A. , Moleiro Filipa
Published: December 2010

In this chapter, an overview of recent developments on finite element analysis of composite plates and shells are presented. Two major developments in the last decade by the author and his colleagues have been in the formulation of (1) least–squares finite element models of plates and (2) the weak‐form Galerkin finite element formulations of first‐order and third‐order shell theories. The least–squares formulations are based on the first‐order shear deformation theory, while the weak‐form Galerkin is based on the first‐order as well as the third‐order shear deformation theories. Results using the weak‐form Galerkin finite element model based on improved 7‐parameter first‐order theory are also included for geometrically nonlinear cases. The least–squares finite element models of plates are based on mixed formulations in which displacements as well as stress resultants are treated as the unknown field variables. The weak‐form Galerkin finite element models are displacement‐based. In the latter, a family of high‐order Lagrange interpolation functions (with equally spaced nodes and Gauss–Lobatto–Legendre nodes) is used to prevent shear locking. Numerical results are presented for a number of benchmark problems involving isotropic, laminated composite, as well as functionally graded plates and shells.
Meshfree Discretization Methods for Solid Mechanics
Authors: Rabczuk Timon , Bordas Stéphane P.A. , Askes Harm
Published: December 2010

Meshfree methods are used for the spatial discretization of partial differential equations, but in contrast to finite element methods, they do not employ elements in the construction of the interpolants. Instead, a set of nodes is accompanied by a domain of influence for each node, whereby the overlap of domains of influence accounts for the interconnectivity between nodes. In this chapter, we will treat the formulation, implementation, and application to solid mechanics of meshfree methods. The focus will be on the element‐free Galerkin method but we will also provide an overview of other meshfree methods. As regards the applications, we will treat two major classes: firstly, incorporating discontinuities in meshless interpolations and secondly, exploiting the hypercontinuity of meshfree shape functions. Finally, we will discuss some urban myths surrounding meshfree methods, the relation with the new generation of node‐based finite element methods, and the future of meshfree methods.
Extended Finite Element Methods
Authors: Wells Garth N.
Published: December 2010

The extended finite element method is a powerful approach for simulating propagating cracks. It relies on the partition of unity property of finite element shape functions to introduce special functions locally, such as the singularity terms from linear elastic fracture mechanics or discontinuous functions to represent an evolving crack surface. The method is described here in the context of linear elastic fracture mechanics and cohesive crack propagation.