Dee Nition Research Articles

Aeroelasticity of Nonconventional Airplane Configurations-Past and Future

At the end of the e rst century of manned, powered e ight, it is worthwhile to look backward to understand how innovation in airplane design required developments in aeroelasticity and how aeroelasticity has played a role in shaping the e rst 100 years of aircraft design. The insights gained will help to predict how and where aeroelasticity and aeroservoelasticity will ine uence the future development of efe cient, more capable, innovative air vehicles, and dee nethe needs fortechnology and tools to enable this future. By dee nition, all new aircraft begin as unconventional to a certain extent. Designs that never see universal use remain curiosities, but still help our questforbettervehiclesandguidethedevelopmentofanalysis, design, and testing tools. Innovative, nontraditional designsaffected by aeroelasticconsiderations haveincluded obliquewing aircraft, forward-swept wing aircraft,Xwings,e ying wings, andlargejoined wings. Designsthat wereunusually innovativeat thetimeoftheirintroduction but later became widespread include the swept-back wing jet, the T-tail, and the e y-by-wire control cone gured vehicle. Control and exploitation of aeroelasticity depends on the continued development of new materials, new structuralandaerodynamicconcepts,sensors,actuators,andactivecontroltechniques.Suchdevelopmentsmustbe accompanied by properintegratedanalysis/designtools,and,most importantly, by thesamehumaninquisitiveness and creativity that has driven aircraft design for over a century. This paper uses the history of nonconventional airplane cone gurations to review some of the steps taken during the past century to establish aeroelastic effects as integrated design features that must be anticipated, controlled, and exploited. The paper goes on to discuss the potential impact of past lessons on emerging airplane cone gurations currently in various stages of study and development.

Computational Aeroelasticity: Success, Progress, Challenge

This article asserts a much broader dee nition of the term, one in whichCAEencompassesalllevelsofaeroelasticanalysis.Aeroelastic tools based on both linear unsteady aerodynamics and nonlinear CFD methods have been developed and successfully applied. We refer to both of these methodologies as components of CAE. Likewisestructuralmodelingassimpleasbeamtheorytostate-of-the-art e nite element modeling (FEM) have been incorporated into aeroelastic tools, and these techniques should also be included under the CAE heading. It is not the intention of this article to provide an exhaustive history of the development and application of CAE over the past 70 years. Rather, the subject will be examined in the context of two primary themes: 1) aeroelastic problems requiring theoretical

Numerical Simulation of Ion Beam Optics for Multiple-Grid Systems

Ahighspecie cimpulseionthrusteroperatedatavoltageof10kVhasbeen studied,andtheproblemsofdirection impingementontheacceleratinggridandcharge-exchangeionproductionand impingementhavebeen considered. These problems are addressed by considering the use of four or more grids (multiple-grid system). To evaluate these multiple grid systems, a three-dimensional particle simulation code that employs 1) an energy compensation method, 2) a simplie ed sheath dee nition method, and 3) a high-speed coding was developed. It was cone rmed that results from this simulation are obtained at a high-speed and are in good agreement with experimental data. With use of this code, several multiple-grid systems were evaluated. Nomenclature a = acceleration h = length between mesh points I = current m = mass n = number density q = charge density r, z, µ = cylindrical coordinate t = time V = voltage v = velocity x, y = Cartesian coordinate = dielectric constant A = electric potential ae = cross section Subscripts

Effects of dairy products on oral health

Dr Johansson has presented an excellent and fascinating review of the effects of milk and dairy products on oral health in Scandinavian Journal of Nutrition, issue 3, 2002 (1). Although milk is one of the more commonly eaten foods it has been the subject of remarkably little clinical research concerning its ine uence on oral disease. The composition of milk has been compared with that of saliva, and like saliva it harbours a multitude of antibacterial agents, including immunoglobulins, and possesses remarkable physical properties. There is growing evidence that the antimicrobial effects of saliva probably act in concert and that the separation of its constituents may not be the ideal way to investigate their effects; a similar situation may prevail with milk. There appears to be confusion in the minds of some paediatric dentists on the role of milk in cariogenesis. It is perhaps important to have a clear idea of some dee nitions. Cariogenic applies to any substance that promotes caries; non-cariogenic applies to agents that neither promote nor reduce the prevalence or incidence of dental caries. Cariostatic refers to substances that prevent or reduce the incidence of dental caries in the presence of a cariogenic challenge. It has been claimed that milk when given in a bottle may contribute to ‘‘nursing bottle caries’’ or early childhood caries. However, reports fail to account for the remainder of the diet that infants ingest, nor do they recognize the physical effect of the nipple, which obstructs the e ow of saliva (2‐4). All of the available evidence suggests that milk is simply non-cariogenic and may have modest cariostatic properties under well-dee ned circumstances. Desalivated rats given milk as a sole source of nutrition orally remained essentially caries free (2); these observations are consistent with the results on the pH effects of milk on dental plaque as cited by Johansson. Furthermore, caries induced by 4% lactose (the same concentration found in cow’s milk) far exceeded that observed in rats fed whole milk. It is also noteworthy that the number and extent of carious lesions induced by milk containing up to 10% added sucrose were signie cantly less than observed in rats given 10% sucrose in water (3). Under these circumstances milk exerts a cariostatic effect, i.e. it overcomes to a large extent the harmful effects of sucrose. However, if the animals are fed a normal cariogenic diet separately and offered milk to drink, a reduction in incidence of caries is not observed. Specie c constituents of milk, even in the presence of saliva, can be adsorbed on to hydroxyapatite surfaces and thereby affect pellicle formation. There is some evidence to suggest that the micelles in milk (similar to saliva) are adsorbed to salivacoated hydroxyapatite (pHA). Several constituents in milk have the capacity to adsorb to pHA, including phosphopeptides and glycosylated

The dynamics of measuring attachment

Shaver and Mikulincer’s review makes a strong case that self-reports of adult attachment are associated with attachment-related processes that are unconscious or at least that occur automatically and outside of awareness. Therefore, the common criticism that self-reports cannot meaningfully assess attachment orientations in a manner that is ree ective of dynamic processes is clearly false. The belief that interview measures are the only valid way to assess adult attachment is based in fundamental assumptions about what can and cannot be assessed in self-reports, and what needs to be assessed in determining adult attachment orientation. The AAI approach to assessing adult attachment is based on the assumption that assessment of defensive strategies, which operate at least partially outside of conscious awareness, is a necessary component in the evaluation of ‘states of mind’ with respect to attachment. Moreover, it is assumed that these strategies can be accurately scored (given appropriate training of coders) from the transcripts of interviews in which participants discuss the relationships they had with their parents in childhood. The attachment strategies identie ed in the AAI are assumed to ree ect processes that operate outside the interview setting, especially in attachment-relevant contexts such as parenting. By dee nition, individuals with particular attachment strategies deny some types of psychological experiences and/or distort their responses to questions tapping these experiences. AAI advocates would therefore tend to conclude that it makes little sense to ask individuals with insecure attachment patterns direct questions about processes that are assumed to be defensively distorted and not open to conscious access. In contrast, they would argue that interview procedures are the most appropriate way to assess adult attachment because defensive strategies can be assessed and provide important clues to underlying attachment issues. Thus, it is common in the attachment literature to see comments such as: ‘Because we are interested in differences in processing attachment-related thoughts and feelings, we deal only with e ndings linking attachment states of mind [as assessed by the AAI] with psychopathology’ (Dozier, Stovall, & Albus, 1999, p. 498). How can self-reports be useful if this is true? One possibility is that self-reports about attachment are valid assessments of dynamic processes. This seems unlikely since these reports are not designed to assess such processes. Another possibility, suggested by Hesse (1999), is that states of mind with respect to early attachment experiences are not necessarily available to conscious awareness (therefore requiring interview measures to assess), but attachment orientations in the romantic domain are (therefore allowing for self-report assessments). However, we cannot think of any good reasons why the process of recalling and reporting on childhood experiences would be qualitatively different from the process of recalling and reporting on

Advances in Data Handling Systems for Space Experiment Control

The Space Vehicles Directorate of the U.S. Air Force Research Laboratory developed a small satellite payload package containing an ensemble of microelectronics subexperiments, which was integrated and launched on the Space Test Research Vehicle-1d satellite. The scientie c payload consists of an electronics testbed, nine subexperi- ments, and a data handling system that in turn interfaces with the spacecraft onboard computer. The hardware and software architectures are described, and future extensions of the data handling system concept are discussed. memory management capability. The DHS design simplie es some of the complexities to be faced by individual subexperimenters by providing a less complex interface for operation and measurement ofadvancedelectronicsradiationperformanceintheharshSTRV-1d space environment. The DHS improves on-orbit use of individual subexperiment resources by recording experimental results, storing them locally, and then communicating those results to the space- craft for download to the ground station. The DHS reduces the risk to the spacecraft mission by providing a degree of separation be- tween the spacecraft and less-proven newtechnologies contained in each experiment and byproviding a similardegree of separation be- tween the experiments. In the process of developing the ETB DHS, a simple 12-conductor interface was employed. This interface was based on the RS-422 signaling standard, along with standardized dee nitions for supply voltage and analog inputs. This interface was developedsothatitcan beusedonfuturespacemissions.Whenvar- ious novel approaches to the design aspects and requirements are used, a high functionality was reached while preserving valuable spacecraft power and mass, which allowed additional experiments to be manifested. Moving further toward the goal of the ideal no-weight and no- powerDHS,futureETBarchitectures aredescribed inthepaperthat surpassthe efe ciencyinsize,mass,and powerofthe present design. This includes a peer-to-peer distributed ETB concept, which does not require a centralized DHS.

Direct Surface Triangulation Using Stereolithography Data

An efe cient and user-friendly approach is presented for constructing unstructured surface grids directly on three-dimensional CAD surface data. This system has the following features: 1 ) use of stereolithography data as surface dee nitions, that is, background grids for surface meshing; 2 ) automatic reconstruction of geometric features for initial front setup; 3 ) graphical user interface for easily controlling surface mesh density by inserting line sources and point sources on the surface; 4 ) adoption of an advancing-front surface triangulation method, which minimizes the necessity to divide the surface into a number of patches; and 5 ) outer boundary generation from templates in the system. The resulting system has been applied to several airplane cone gurations, and a notable reduction in turnaround time has been achieved. OMPUTATIONAL e uid dynamics (CFD) has become an indispensable design and analysis tool for many different types of geometric cone gurations and e eld regimes. The effectiveness of CFD usage in an actual design environment, however, is often limited. Most of these limitations are due to dife culties in generating the computational grid in a reasonable amount of time. The grid generation method should be automated as much aspossible. This is true for volume grid generation; it is now possible to create volume grids automatically. For the surface grid generation, however, user interventions are often required because the surface meshdirectlyaffectsthesolutionaccuraciesinCFDproblems,especiallyfortheaerodynamicevaluationofairplanes.Theaerodynamic performance is usually evaluated by surface values, such as pressure,skin friction,and so on.Thesevalues arehighlyaffected by the dee nition of sound geometric features, as well as the surface grid density. This suggests that surface grid generation methods must easily facilitate changes in grid density to obtain the best result with limited computational resources. Although controllability is often incompatible with the automation of grid generation, it is essential for surface meshing.

Comparison of Multiple Agent-Based Organizations for Satellite Constellations

A comparison is made of several autonomous software architectures for multiple satellite systems. Multiple, agent-based satellite systems are envisioned because they are capable of higher performance, lower cost, better fault tolerance, recone gurability, and upgradability. Software agents are dee ned at the spacecraft and functional levels, using a wide variety of algorithms including multivariable control, linear programming, fuzzy logic, contract net protocol, negotiation, and radar placement. The agent dee nitions allow many types of agent-based software architectures to be developed. Several novel agent-based architectures with a more traditional system for a distributed space-based radar mission are compared. Agent-based simulations of several mission scenarios show the autonomous operation of different organizations of increasing autonomy and compare the benee ts and drawbacks of each.

Functional Dyspepsia and Gastric Acid: Any Relation?

Gastric acid and upper gastrointestinal disorders are closely connected, and antacids and acid secretion inhibitors are commonly used in the treatment of such disorders. Gastro-oesophageal ree ux disease (GERD) and peptic ulcer disease are undoubtedly acid-related disorders (although Helicobacter pylori might be more important in patients with ulcer disease), but the relation between acid and functional dyspepsia (FD) (or non-ulcer dyspepsia) has been questioned for many years (1). Previous discussions have been hampered by poor dee nition of FD and different diseases in the upper gastrointestinal tract were in part mixed in. Although the different disease entities have been better dee ned with less overlap, the role of gastric acid in patients with FD remains obscure. The uncertainty is ree ected in the treatment. There are well-documented and effective treatments (medical and surgical) for patients with peptic ulcer disease and GERD, whereas the treatment for patients with FD remains controversial. Symptomatic improvement following treatment with acid secretion inhibitors indicates a relation between acid and FD. Numerous studies have evaluated the symptomatic effect of antacids, H2-receptor antagonists and proton-pump inhibitors in patients with FD, and meta-analyses sum up the results (2, 3). Bolling-Sternevald et al. present one further study in this issue of the Scandinavian Journal of Gastroenterology (4). Most reviews and meta-analyses, like the study by Bolling-Sternevald et al., conclude that acid secretion inhibitors are effective, but the therapeutic gain above placebo is small (in the range of 10%‐20%) and the clinical signie cance of the effect is poorly documented. The clinical benee t is also mentioned in the study by Bolling-Sternevald et al. (4). The e nding that mild abdominal pain/discomfort compared to moderate/severe symptoms was indicative of a favourable outcome, and that the PGWB index (quality of life) could not detect any signie cant differences between the treatment groups, questions the clinical usefulness of the treatment in all patients. Most studies indicate that the effect is restricted to a subset of patients (5). If the effect is restricted to a subgroup with an impressive effect, the therapeutic effect might be highly valuable to this group. With the exception of an effect in patients with ree ux-like symptoms (who might have GERD and not FD), it has been dife cult to characterize the responder. Accordingly, the ‘trial and error’ method has been used to tailor the optimal therapy for the individual patient. Various pathophysiological mechanisms in the oesophagus, stomach and duodenum might bring about acid-induced FD. A characteristic pattern of acid ree ux to the oesophagus might in some patients cause dyspepsia (without ree ux symptoms), which is effectively treated with acid secretion inhibitors (6). Acid in the stomach might also provoke symptoms. Direct installation of acid in the stomach and increased acid secretion after injection of pentagastrin provoke symptoms in patients with dyspepsia, and rebound hypersecretion after withdrawal of acid secretion inhibitors induces dyspepsia in healthy volunteers (7‐9). Sensitivity and motility in the upper GI tract are often altered in patients with FD, and acid affects both gastric and duodenal sensitivity and motility. HCl increases the sensitiveness of mucosal mechanoreceptors in the gastric wall, and acid suppressants delay gastric emptying in healthy volunteers (10, 11). Patients with FD, but not healthy volunteers, report nausea after infusion of acid in the duodenum (12, 13). Motility studies after infusion of acid in the duodenal bulb in the fasting period demonstrate decreased clearance of exogenous acid from the duodenal bulb and decreased duodenal motor activity in dyspeptic patients compared to controls (12‐14). Acid secretion inhibitors alter the antropyloroduodenal motor response to acid infusion (14). This variety of pathophysiological disturbances in patients with FD explains the dife culties in predicting response to acid secretion inhibitors in the individual patient and in characterizing the responder. Inall, it is likely that acid provokes symptoms in a subset of patients with FD through various mechanisms in the upper gastrointestinal tract. Non-acid related disturbance is the cause of symptoms in other patients. Further research should aim at expanding our understanding of the pathophysiology in patients with FD and improve the methods for predicting response to treatment in the individual patient.

Effect of Ambient Pressure on an Airblast Spray Injected into a Crossflow

The injection of a fuel spray into a cross stream was studied for its application in rapid fuel ‐air mixing for lean combustion processes. The fuel is injected as either a discrete stream or as a partially to fully atomized jet of droplets. Of particular interest was the penetration of the outer and inner edges of the spray of liquid fuel into the gaseous airstream. The experiment focused on exploring the effect of e ow conditions on the spray surface trajectories from the point of injection to a downstream distance of z/Dfuel = 35. Tests were conducted under ambient pressures of 1, 3, and 5 atm at atomizing air pressure drops varying from 0 to 4.8% for a jet-A fuel e ow of 0.18 g/s and a baseline crosse ow airvelocity of 38 m/s. A modie ed dee nition of the jet-to-crosse owmomentum-e ux ratioq2 wasdeveloped to accommodatea two-phasejetandwassubsequentlyused to obtaina relationshipbetween the e ow conditions and thespray surface trajectories. The effect of the degree of atomization in thespray resulting from the change in operating conditions was incorporated by implementing a pressure ratio correction factor into the correlating equation. Nomenclature Aairbl = area associated with the airblast air, assumed as the difference between Aspray and Aliquid Aliquid = area associated with the fuel injection orie ce Aspray = area associated with the spray injection orie ce Cd = orie ce discharge coefe cient cn = correlation constants, n D0;1;2;3 Dfuel = fuel injection orie ce diameter Dspray = spray injection orie ce diameter q1 = single-phase jet-to-crosse ow momentum-e ux ratio q2 = two-phase jet-to-crosse ow momentum-e ux ratio V = velocity Wecross = crosse ow-associated Weber number ΩairV 2 crossDfuel=ae x = penetration distance z = downstream distance Ω = density

Evolution of Debris Clouds to Microscopically Chaotic Motion

An evaluation is presented of the effects of orbital perturbations that arise in the early phase of debris cloud evolution. This assessment enables the dee nition of various characteristic timescales associated with the cloud evolution to a mature debris population, characterized by a “ chaotic” distribution, required for the statistical description of debris as provided by the direct simulation Monte Carlo method (DSMC). The ine uences of gravitational harmonic terms J2, J3, and J4 together with that for solar radiation pressure upon both the precession of the argument of perifocus (resulting in the familiar torus ) and regression of the line of nodes (resulting in a band structure) are presented. Dimensionless characteristic timescales indicating the rate at which the evolution in the orbital parameters, subject to each of theperturbations relativeto the orbital lifetime, are dee ned. From this modeling approach to debris studies, it is noted that the dimensionless ratio f perturbation evolutionary timescale g to f orbital lifetime g must be greater than unity. A general conclusion is that it is found that for objects of centimetric size above an altitude of approximately 350 km the DSMC methodology is appropriate. The presented analytic approach highlights the signie cant ine uence during the early phase of J3. The methodology is applied to several scenarios for the fragmentation caused by collisions and explosions. The results show clearly how the evolution to a fully chaotic debris distribution is mass specie c and scenario dependent. Debris particles ejected with forward component velocity vectorsresult with a mass spectrum, which differsfrom thoseejected with rearward velocities. Assumptions of isotropic fragmentation must therefore only be considered as approximations.

The Perception of Muslims in Bulgaria and Greece: Between the 'Self' and the 'Other'

This paper investigates the shifts in the perception of ethnic identity of Muslims in Bulgaria and Greece, focusing on ethnic Turks and Bulgarian Muslims (Pomaks) in Bulgaria, and considering the Greek case mainly for the sake of comparison. The emphasis is put on ofe cial dee nitions of the ethnic and national afe liation of Muslim populations in Bulgaria and Greece and their ‘academic’ substantiation. Related to this, the paper also considers the political consequences—as well as causes—of the various ways of perceiving Muslims in these two countries after their ‘liberation’ from Ottoman domination. Perceptions of Muslims were shifting with changes in internal policies as well as foreign relations. In terms of the ‘Self’ and the ‘Other’, Muslim populations were placed on various points of this scale at different moments of time. Pomaks and Turks were, at a specie c moment, declared the ‘Self’, after having served as the ‘Other’, against whom consolidation of the nation had been aiming. These questions are related to the problem of ethnic and national identity. The policies of both the Bulgarian and the Greek nation-states intended to ascribe a e xed ethnic identity to the whole population aiming at making the administrative border coincide with the ethnic frontier. 2 The question was whether the boundaries of the constitutive ethnic group were drawn in a way that would allow the inclusion of Muslims in the nation, or instead would facilitate their exclusion. It was the task of intellectuals, especially of historians, ethnographers and human anthropologists, to create the ‘cultural stuff’ 3 within these boundaries in order to substantiate national identity. Politicians in their turn had to implement those concepts into actual policies.

Experimental Analysis of Aerodynamic Interactions Occurring on Hypersonic Spacecraft

Experimentalinvestigationshavebeenachievedin theONERAresearch facilitiesof theChalais ‐Meudon Center in order to validate design tools used for the dee nition of a scramjet for a hypersonic spacecraft. Aerodynamic interactions occurring on such a spacecraft have been thoroughly studied, notably 1 ) the shock/shock interactions ahead of the air inlets, 2 ) the shock-wave/boundary-layer interaction and its control inside the air inlet, and 3)the e ow cone uence between an external e ow and an aerospike nozzle jet in an underexpansion condition. These studies contribute to the knowledge of the e ow physics of aerodynamic interactions that occur on hypersonic spacecraft, compensate for the lack of published detailed measurements of such e owe eld patterns, and provide well-documented test cases to validate computer codes.

Analytical-Experimental Correlation for a Stiffened Composite Panel Loaded in Axial Compression

A combined analytical and experimental study of a blade-stiffened composite panel subjected to axial compression was conducted. The study e rst examined the effects of the differences between a simple model used to design the panel and the actual experimental conditions. It was found that the large imperfection used in the design process compensated for the simplifying assumptions of the design model, and the experimental failure load was only 10% higher than the design load. Next, e nite element analyses wereperformed in order to correlateanalytical and experimental results. The buckling loads from e nite element analyses agreed well with the experimental failure loads. However, substantial differences were found in the out-of-plane displacements of the panel. Finite element simulations of nonuniform load introduction with general contact dee nitions improved correlation between the measured and predicted out-of-plane deformations.

Design of a Guided Missile Interceptor Using a Genetic Algorithm

An apportioned pareto genetic algorithm was used to manipulate a solid rocket design code, an aerodynamic designcode,andathree-loopautopilottoproduceguidedmissileinterceptordesignscapableofaccuratelyengaging a high-speed/high-altitude target. Dee nition of the optimization problem required 29 design variables, and 4 primary goals were established to assess the performance of the interceptor designs. Design goals included the following: minimize miss distance, minimize intercept time, minimize takeoff weight, and minimize maximum g loading. In 50 generations, the genetic algorithm was able to develop 2 basic types of external aerodynamic designs that performed nearlythe same, with miss distances less than 1.0ft. The solid rocket motors that propelled these external shapes shared common characteristics such as a large initial burning area and a large combustion chambervolume. Thegeneticalgorithmdid not prefermaximizing theamount offuel within therocket motorcase (high fuel volume ratio). A higher fuel volume ratiotypicallymeans higher launch weight, but does not necessarily guarantee faster intercepts given enite thermal limits. Examination of the intercept trajectories themselves shows that standard proportional navigation guidance works adequately, but could probably be improved by thrust compensation,especiallyduringthelaunchtransient.Thethree-loopautopilotperformswellevenforhigh-altitude engagements, and the analytic gain determination makes the autopilot straightforward to implement.

Probability of Collision Between Space Objects

The International Space Station is being designed to perform debris avoidance maneuvers based on certain criteria developed from the probability of collision Pc. Existing methods to determine the Pc are based on the dee nitionofacollision/conjunctionplanethatcontainsallofthepositionuncertaintyassociatedwiththeproblem.In thispaperwedevelopa directand more naturalway of obtaining probability ofcollision and presentanalternative but equivalent dee nition for Pc that leads to the same results obtained earlier. Because debris avoidance is crucial for every orbiting asset in low Earth orbit, a study of this nature helps to establish the equivalence of different methods for risk assessment and evaluation. HE International Space Station (ISS) shall continuously face the threat of collision with orbiting debris. Hence, there needs to be a comprehensive methodology that can assess the risks posed byindividualdebrisencountersand suggestmaneuverswhenneces- sary. Such a study shall not only benee t the ISS, but also any future orbital asset placed in low Earth orbits. Thus, although we refer to the ISS in the rest of our paper, the analysis presented here holds true for any other orbiting asset of size and orbit comparable with that of the upcoming ISS. Space shuttle (SS) maneuvers are commanded to avoid poten- tial collisions with cataloged space objects (maintained by the U.S. Space Command ) whenever the estimated conjunction with an ob- jectfalls within a box centered on the estimated SSposition. The di- mensionsofthisconjunctionboxare §5 kmin thein-track direction and §2kmintheradialandout-of-planedirections.Thedimensions of such a conjunction box are probably based on prior estimates of position error covariances. The determination was made that this simple criterion, or any other known deterministic criterion 1,2 when applied to the ISS, would result in too many maneuvers. 3 In addi- tion, unnecessary maneuvers waste fuel and hamper the micrograv- ity experiments onboard the ISS. Although the size of the conjunc- tion box could be decreased to decrease the manuever rate, such a step clearly increases the risk to unacceptable levels. Therefore, the ISS needs a more rigorous probability-based approach for collision avoidance. 4

Revised Interpretation of Work Potential in Thermophysical Processes

An alternative development is attempted of the concept of exergy or availability by introducing the idea that exergy represents an abstract thermodynamic metric that, essentially, quantie es the distance from the state of equilibrium with respect to a given reference value. Traditional and textbook approaches usually develop exergy asasystem’ spotentialtodoreversiblework.Usually,combiningthebalanceofenergyandentropyequationsmakes it possible to construct a corresponding balance of exergy and to use its dee nition to interpret the resulting terms. In contrast, the essential elements presented deal with the mathematical property of concavity of the entropy as the essence of the second law and how this property translates into a geometric complementarity relation between entropy and exergy. The balance of exergy equation is presented as an expression representing the corresponding convexity of the exergy, again demonstrating a mathematical property intrinsic to the second law. Nomenclature E = total energy density e = total specie c energy g = gravitational acceleration constant H = enthalpy density h = specie c enthalpy I = e ux or current of quantity k = coefe cient of thermal conductivity M = molecular mass m = mass P = thermodynamic pressure = thermal energy transfer rate (heating) R = gas constant S = entropy density s = specie c entropy T = temperature t = time U = internal energy density u = specie c internal energy V = volume = e uid velocity v = specie c volume = mechanical energy transfer rate (working) X = exergy density (also known as availability ) xk = Cartesian coordinates z = elevation level in a gravitational e eld b = thermal expansion coefe cient c = ratio of specie c heats D = total change in quantity d ij = Kronecker delta j = isothermal compressibility k = second coefe cient of viscosity l = e rst coefe cient of viscosity n = generic variable q = mass density s ij = viscous stress tensor u = specie c exergy w = specie c e ow exergy

Ride Quality of Civil Aircraft from a Probabilistic Viewpoint

A novel approach is proposed for the analysis and design of the ride quality augmentation system for a civil aircraft. In contrast to the standard problem formulation, where a mean acceleration level is minimized, the ride quality level is quantie ed in a probabilistic framework. A method is dee ned to limit the probability of exceeding a given vertical acceleration level in one or more points of the aircraft. The novelty of the proposed approach lies mainly in the dee nition of the control design in a probabilistic framework, which gives deep physical insight to the problem and more realistic results. An example is discussed to illustrate the proposed approach where the controller is obtained through an eigenstructure assignment procedure; the robustness of the controlled structure is guaranteed through a linear matrix inequality formulation.

Behavior of Two-Temperature Model in Intermediate Hypersonic Regime

Shock standoffdistancefora sphereis calculated to examine thebehavioroftheexisting two-temperature model in theintermediate hypersonic e ow regime. Calculations are carried outforthreebinary scaling parametervalues, corresponding to nearly frozen, nonequilibrium, and nearly equilibrium e ows, respectively. The obtained shock standoff distances are compared with the experimental data obtained in a ballistic range. It is shown that the two-temperature model reproduces the shock standoff distances in the intermediate hypersonic e ows fairly well but tends to lose its accuracy where vibrational excitation occurs but chemical reactions are nearly frozen. Nomenclature M = collision partner in dissociation/recombination reactions p1 = static pressure in the test section, Pa q = power on the vibrational temperature in the dee nition of Ta, 0<q <1 R = nose radius of a sphere, m T = translational temperature, K Ta = rate-controlling temperature for dissociation reactions, T 1 iq T q v , K Tv = vibrational temperature, K U1 = e ight velocity, m/s ° = specie c heat ratio Ω1 = freestream density, kg/m 3

Predictions for Cryogenic Homogeneous Two-Phase Flows in a Choked Laval Nozzle

The vapor-liquid, two-phase, inviscid, compressible e ow in a converging-diverging nozzle is computed by high accuracy total-variation-diminishing and Newton‐ Raphson schemes. A homogeneous speed of sound dee nition based on e ow quality and void fraction is presented, along with some gas dynamic relations. Analytical twophase mass-e ow expressions are also derived, and solutions are compared with those obtained from the numerical schemes.Thecomputational resultsofvoid-fraction and Mach-numberrelation obtained fortheLavalnozzlecompare favorably with both schemes. Equilibrium and nonequilibrium numerical results for cryogenic nitrogen e ow are also presented. Numerical mass e ux at both choked and unchoked throat conditions agrees with experimental data, but some discrepancy is observed in the pressure proe les at the diffusing portion of the nozzle.