Showing papers by "National Aerospace Laboratories published in 2000"

Synthesis and sintering of TiB2 and TiB2–TiC composite under high pressure

Abstract: TiB2 and TiB2x2013;TiC composite compacts with 98x2013;99% density are prepared by high-pressure sintering (HPS) of premixed powders and by high-pressure self-combustion synthesis (HPCS) from the elemental constituents. The sintering and synthesis experiments are carried out at 3 GPa in the temperature and time ranges 2250x2013;2750 K and 5x2013;300 s, respectively. A high sintering temperature (2750 K) is required to obtain dense monolithic TiB2 compacts (98% density) by HPS. Compacts with a similar density are obtained at lower sintering temperature (2250 K) when 15 mol% TiC is added to TiB2. The composite compacts have marginally better fracture toughness than that of monolithic compacts. TiB2 and TiB2x2013;TiC compacts (99% density) are also prepared by HPCS from elemental constituents. A minimum ignition temperature of 2250 K is required to make the reaction self-sustaining.The compacts prepared by HPCS have superior fracture toughness to those prepared by HPS. The microstructures and the properties of the compacts prepared by HPS and HPCS are compared. A possible sequence of reaction during the HPCS of TiB2x2013;TiC is proposed.

Multiobjective evolutionary computation for supersonic wing-shape optimization

Abstract: This paper discusses the design optimization of a wing for supersonic transport (SST) using a multiple-objective genetic algorithm (MOGA). Three objective functions are used to minimize the drag for supersonic cruise, the drag for transonic cruise, and the bending moment at the wing root for supersonic cruise. The wing shape is defined by 66 design variables. A Euler flow code is used to evaluate supersonic performance, and a potential flow code is used to evaluate transonic performance. To reduce the total computational time, flow calculations are parallelized on an NEC SX-4 computer using 32 processing elements. The detailed analysis of the resulting Pareto front suggests a renewed interest in the arrow wing planform for the supersonic wing.

Probabilistic data association avoiding track coalescence

Abstract: For the problem of tracking multiple targets, the joint probabilistic data association (JPDA) approach has shown to be very effective in handling clutter and missed detections. The JPDA, however, tends to coalesce neighboring tracks and ignores the coupling between those tracks. Fitzgerald (1990) has shown that hypothesis pruning may be an effective way to prevent track coalescence. Unfortunately, this process leads to an undesired sensitivity to clutter and missed detections, and it does not support any coupling. To improve this situation, the paper follows a novel approach to combine the advantages of JPDA coupling, and hypothesis pruning into new algorithms. First, the problem of multiple target tracking is embedded into one filtering for a linear descriptor system with stochastic coefficients. Next, for this descriptor system, the exact Bayesian and new JPDA filters are derived. Finally, through Monte Carlo simulations, it is shown that these new PDA filters are able to handle coupling and are insensitive to track coalescence, clutter, and missed detections.

The validity and reliability of the Dutch Effort-Reward Imbalance Questionnaire.

Abstract: The reliability and validity of the Effort-Reward Imbalance Questionnaire were tested in 775 blue- and white-collar workers in the Netherlands. Cronbach's alpha revealed sufficient internal consistency of all subscales except Need for Control. With exploratory probabilistic scaling (Mokken) analysis, the psychometric qualities of the Need for Control scale were improved. With confirmatory factor analysis, the factorial validity of the Extrinsic Effort and Reward subscales was confirmed. A model with 3 separate dimensions for reward (status control, esteem reward, and monetary gratification) proved adequate, emphasizing the importance of distinguishing subscales. The congruent validity of the subscales and a hypothesized relationship with an external construct, health functioning, were confirmed.

Multiobjective genetic algorithm applied to aerodynamic design of cascade airfoils

Abstract: A multiobjective genetic algorithm (GA) based on Fonseca-Fleming's Pareto-based ranking and fitness-sharing techniques has been applied to aerodynamic shape optimization of cascade airfoil design. Airfoil performance is evaluated by a Navier-Stokes code. Evaluation of GA population is parallelized on the Numerical Wind Tunnel, a parallel vector machine. The present multiobjective design seeks high pressure rise, high flow turning angle, and low total pressure loss at a low Mach number. Pareto solutions that perform better than existing control diffusion airfoils were obtained.

Development of a new in-flight simulator MuPAL-alpha

Abstract: National Aerospace laboratory of Japan has developed a new in-flight simulator named "MuPALa", with the aim of providing an experimental facility for the research and development of advanced aeronautical technologies. MuPAL-a is based on a Dornier 228-200. A fly-by-wire control system and a direct lift control system realize the variable stability and response capability, which is applicable not only to the motion simulation but also to the flight demonstration of advanced guidance and control technologies. The other features of MuPAL-a are its unique second cockpit and data acquisition system with high accuracy and extensity. The second cockpit with a head-mounted display will provide a flexible environment for the research on various pilot interfaces and the effects of visual and motion cues on pilots. In a safety aspect, MuPAL-a adopted the duplex system to improve the probability of failure detection. The auto-disengage function incorporated in the fly-by-wire control system ensures MuPAL-a from exceeding the proven operational envelope of Do228-200. This paper deals with the design requirements, the system architecture and the topics in the development phase.

Effect of natural ventilation on the boundary layer separation and near-wake vortex shedding characteristics of a sphere

Abstract: Experiments were conducted in water and wind tunnels on spheres in the Reynolds number range 6 × 103 to 6.5 × 105 to study the effect of natural ventilation on the boundary layer separation and near-wake vortex shedding characteristics. In the subcritical range of Re ( 4 × 105), ventilation caused a downstream shift in the mean locations of boundary layer separation and reattachment; these lines showed significant axisymmetry in the presence of venting. No distinct vortex shedding frequency was found. Instead, a dramatic reduction occurred in the wake unsteadiness at all frequencies. The reduction of wake unsteadiness is consistent with the reduction in total drag already reported. Based on the present results and those reported earlier, the effects of natural ventilation on the flow past a sphere can be categorized in two broad regimes, viz., weak and strong interaction regimes. In the weak interaction regime (subcritical Re), the broad features of the basic sphere are largely unaltered despite the large addition of mass in the near wake. Strong interaction is promoted by the closer proximity of the inner and outer shear layers at supercritical Re. This results in a modified and steady near-wake flow, characterized by reduced unsteadiness and small drag.

Tracking filter and multi-sensor data fusion

Abstract: In this paper factorization filtering, fusion filtering strategy and related algorithms are presented. Some results of implementation and validation using realistic data are given.

Separation control by tangential blowing inside the bubble

Abstract: Experiments have been carried out investigating the effectiveness of steady tangential blowing (inside the separation bubble) to control an axisymmetric separated flow at low speeds. Turbulent boundary separation was induced on a contoured afterbody and the separated shear layer reattached on a narrow cylindrical sting. Measurements made consisted of model surface pressures, mean velocity, turbulent shear stress and kinetic energy profiles using a 2-component LDV system. The results explicitly demonstrate that blowing downstream of the separation location, but within the bubble, can be an effective means of separation control, considering both wall and wake flow reversals.

Effect of fibre orientation on mode-i interlaminar fracture toughness of glass epoxy composites

Abstract: The mode-I interlaminar fracture toughness (IFf) property of room temperature13; (RT) cured glass-epoxy (LY556/HY95I ) composites was studied using a double cantilever13; beam (DCB) test specimen with unidirectional fiber orientations of 0xB0;, +45xB0;/-45xB0;,13; +60xB0;/-60xB0; and 90xB0; in the neighborhood of the crack zone. Three 1FT data reduction techniques.13; viz.: (l) Modified Beam Theory (MBT). (2) Compliance Calibration Theory (CC)13; and (3) Modified Compliance Calibration Theory (MCC) were verified for the DCB data13; generated for 0xB0; fiber oriented specimens. The fracture toughness property estimates were13; noted to be approximately the same for all three techniques. Only the MBT reduction procedure13; (as per ASTM) was used for other orientations. It was observed that the IFT increased as13; the fiber orientation was changed from 0xB0; to 90xB0; with reference to the direction of crack propagation.13;

Psychophysical thresholds associated with the simulation of linear acceleration

Abstract: This paper presents the range of motion stimuli that produce realistic sensations of longitudinal acceleration during a simulated take-off run in an advanced research simulator. The gain of the translational (surge) and tilt-coordination channel (pitch) were systematically varied, together with the bandwidth of the high-pass filter of the surge channel. Seven experienced pilots judged their motion perception. Based on their subjective response, psychometric curves were constructed in order to determine the minimum and maximum permissible gain settings of the washout algorithm. The results suggest that platform motion was generally overestimated relative to the visually simulated motion. It is therefore concluded that for realistic perception of linear accelerations in a flight simulator, downscaling is essential. The best simulation was obtained with a gain of 0.2 (in combination with a bandwidth of 0.73 rad/s) for the high-pass filter in the translational channel and a gain of 0.6 for the low-pass filter in the tilt-coordination channel.

On Stokes flow in a semi-infinite wedge

Abstract: Consider Stokes flow in the semi-infinite wedge bounded by the sidewalls ϕ = ±α and the endwall z = 0 Viscous fluid fills the region 0 r < ∞, 0 z < ∞ bounded by these planes; the motion of the fluid is driven by boundary data given on the endwall z = 0 A consequence of the linearity of the problem is that one can treat the velocity field q ( r , ϕ, z ) as the sum of a field q a ( r , ϕ, z ) antisymmetric in ϕ and one symmetric in it, q s ( r , ϕ, z ) It is shown in each of these cases that there exists a real vector eigenfunction sequence v n ( r , ϕ, z ) and a complex vector eigenfunction sequence u n ( r , ϕ, z ), each member of which satisfies the sidewall no-slip condition and has a z -behaviour of the form e − kz It is then shown that one can, for each case, write down a formal representation for the velocity field as an infinite integral over k of the sums of the real and complex eigenfunctions, each multiplied by unknown real and complex scalar functions b n ( k ) and a n ( k ), respectively, that have to be determined from the endwall boundary conditions A method of doing this using Laguerre functions and least squares is developed Flow fields deduced by this method for given boundary data show interesting vortical structures Assuming that the set of eigenfunctions is complete and that the relevant series are convergent and that they converge to the boundary data, it is shown that, in general, there is an infinite sequence of corner eddies in the neighbourhood of the edge r = 0 in the antisymmetric case but not in the symmetric case The same conclusion was reached earlier for the infinite wedge by Sano & Hasimoto (1980) and Moffatt & Mak (1999) A difficulty in the symmetric case when 2α = π/2, caused by the merger of two real eigenfunctions, has yet to be resolved

Models for Liquid Impact Onboard Sloshsat FLEVO

Abstract: Orbital experiments on the behavior of liquid in spacecraft are planned. The Sloshsat free-flyer is described. Preparation of the experiments, and later evaluation, are supported by models of varying complexity. The characteristics of the models are discussed. Particular attention is given to the momentum transfer between the liquid and the spacecraft, in connection with the liquid impact that may occur at the end of a reorientation maneuver of the spacecraft.

Hiding expressed using relation algebra with multi-relations-oblique lifting and lowering for unbalanced systems

Abstract: The analysis of existing software architectures may be supported by a relational approach. The approach is based on relational algebra with multi-relations extended with a theory about "lifting". Lifting transforms a relation at a certain level of the decomposition structure of a system (e.g. the module level) to a higher level (e.g. the subsystem level). The application of lifting has been reported for various industrial contexts for balanced systems (i.e. systems where the decomposition structure is a balanced tree). This paper reports upon a more liberal kind of lifting, termed "oblique lifting", which has the important advantage that it can also be used for unbalanced systems. Lowering, the opposite of lifting, can be liberalized in a similar fashion. The use of oblique lowering is illustrated by means of a typical example from the field of software architecture verification. The leading example of this paper uses the relational approach as a formal basis for a software architecture browser visualizing the module interconnection architecture of a software system. Oblique lifting is applied to hiding the decomposition structure of a module in a module interconnection diagram by choosing an appropriate mapping. After the hiding, various kinds of weights (or multiplicities) may be associated with the interconnections in the resulting diagram. Four definitions of weights are described, including the formalization of their related operations, with each weight having its own merits during architectural analysis.

Flow simulation of NAL experimental supersonic airplane/booster separation using overset unstructured grids

Abstract: The overset unstructured grid method developed for multiple-body problems is applied to a flow simulation about an experimental supersonic airplane separation from a rocket booster. An unstructured grid around the rocket booster is overset on the stationary grid around the airplane and moves with time to simulate the separation process. Detailed components of the rocket booster are faithfully reproduced by the unstructured grid. This capability of the unstructured grid reduces the number of required overset grids and significantly simplifies the overset procedure. The computed result of the airplane/booster separation clearly simulates the complex reflection patterns of shock waves between two bodies during the separation process. The computed lift and pitching moment coefficients are compared with the wind tunnel results. The computational accuracy of the aerodynamic coefficients is improved by including the detailed components of the airplane and rocket.

Thermal and toughness property studies on a polybenzimidazole-modified epoxy resin system

Abstract: The effect of polybenzimidazole (Pill) on a silica-filled epoxy resin matrix has been investigated. Polybenzimidazole (PBI) was incorporated into a difunctional epoxy resin matrix to the extent of 10%, before being cured with an anhydride hardener. The effects of Pill on the curing reaction and glass transition temperature (Tg) and on the toughness of the cured epoxy matrix have been studied using differential scanning calorimetry (OSC), thermogravimetric ctric analysis (TGA) and a universal testing machine (Instron). The results indicate that the PBI modifier enhanced not only the glass transition temperature of the difunctional epoxy m.atrix but also its toughness, by its catalytic action. Further investigations have been carried out on the fractured specimens, using scanning electron microscopy (SEM) to support the enhanced toughness property of the epoxy matrix.