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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

The motion and stability of spin stabilized spacecraft with hinged appendages

The dynamics and stability of a spin stabilized spacecraft with a hinged appendage system are treated analytically and numerically. The hinged system consists of a central hub with masses attached to massless booms of fixed length whose orientation relative to the main part can change. The equations of motion for the hinged system, with viscous damping at both hinge points, are linearized about the nominal equilibrium position where the booms are orthogonal to the nominal spin axis. Analytic stability criteria indicate that hinge damping must be present and that for limiting cases, where the spin axis is an axis of symmetry, certain conditions relating the hinge point offset coordinates to the moment of inertia ratio and end masses must be satisfied. The hinge damping is always required for the nominal deployment of hinge members.

Sellappan, R.↗
NASA NTRS1979

A throat-bypass stability-bleed system using relief valves to increase the transient stability of a mixed-compression inlet

A stability-bleed system was installed in a YF-12 flight inlet that was subjected to internal and external airflow disturbances in the NASA Lewis 10 by 10 foot supersonic wind tunnel. The purpose of the system is to allow higher inlet performance while maintaining a substantial tolerance (without unstart) to internal and external disturbances. At Mach numbers of 2.47 and 2.76, the inlet tolerance to decreases in diffuser-exit corrected airflow was increased by approximately 10 percent of the operating-point airflow. The stability-bleed system complemented the terminal-shock-control system of the inlet and did not show interaction problems. For disturbances which caused a combined decrease in Mach number and increase in angle of attack, the system with valves operative kept the inlet started 4 to 28 times longer than with the valves inoperative. Hence, the stability system provides additional time for the inlet control system to react and prevent unstart. This was observed for initial Mach numbers of 2.55 and 2.68. For slow increase in angle of attack at Mach 2.47 and 2.76, the system kept the inlet started beyond the steady-state unstart angle. However, the maximum transient angles of attack without unstart could not be determined because wind-tunnel mechanical-stop limits for angle of attack were reached.

Neiner, G. H.↗
NASA NTRS1991

Compressible stability of growing boundary layers using parabolized stability equations

The parabolized stability equation (PSE) approach is employed to study linear and nonlinear compressible stability with an eye to providing a capability for boundary-layer transition prediction in both 'quiet' and 'disturbed' environments. The governing compressible stability equations are solved by a rational parabolizing approximation in the streamwise direction. Nonparallel flow effects are studied for both the first- and second-mode disturbances. For oblique waves of the first-mode type, the departure from the parallel results is more pronounced as compared to that for the two-dimensional waves. Results for the Mach 4.5 case show that flow nonparallelism has more influence on the first mode than on the second. The disturbance growth rate is shown to be a strong function of the wall-normal distance due to either flow nonparallelism or nonlinear interactions. The subharmonic and fundamental types of breakdown are found to be similar to the ones in incompressible boundary layers.

Chang, Chau-Lyan↗
NASA NTRS1953

The Effects on Dynamic Lateral Stability and Control of Large Artificial Variations in the Rotary Stability Derivatives

This report presents the results of an investigation conducted in the Langley free-flight tunnel to determine the effects of large artificial variations of several rotary lateral-stability derivatives on the dynamic lateral stability and control characteristics of a 45 degree sweptback-wing airplane model. Calculations of the period and damping of the lateral motions and of the response to roll and yaw disturbances were made for correlation with the experimental results. The calculated results were in qualitative agreement with the experimental results in predicting the general trends in flight characteristics produced by large changes in the stability derivatives, but in some cases the theory with the assumption of zero lag was not in good quantitative agreement with the experimental results.

Schade, Robert O↗
NASA NTRS1961

Static Longitudinal Stability of a Rocket Vehicle Having a Rear-Facing Step Ahead of the Stabilizing Fins

Tests were conducted at Mach numbers of 3.96 and 4.65 in the Langley Unitary Plan wind tunnel to determine the static longitudinal stability characteristics of a fin-stabilized rocket-vehicle configuration which had a rearward facing step located upstream of the fins. Two fin sizes and planforms, a delta and a clipped delta, were tested. The angle of attack was varied from 6 deg to -6 deg and the Reynolds number based on model 6 length was about 10 x 10. The configuration with the larger fins (clipped delta) had a center of pressure slightly rearward of and an initial normal-force-curve slope slightly higher than that of the configuration with the smaller fins (delta) as would be expected. Calculations of the stability parameters gave a slightly lower initial slope of the normal-force curve than measured data, probably because of boundary-layer separation ahead of the step. The calculated center of pressure agreed well with the measured data. Measured and calculated increments in the initial slope of the normal-force curve and in the center of pressure, due to changing fins, were in excellent agreement indicating that separated flow downstream of the step did not influence flow over the fins. This result was consistent with data from schlieren photographs.

Keynton, Robert J.↗
NASA NTRS1999

On the Stability of Three-Dimensional Boundary Layers: Linear and Nonlinear Stability - Part 1

The primary stability of incompressible three-dimensional boundary layers is investigated using the Parabolized Stability Equations (PSE). We compute the evolution of stationary and traveling disturbances in the linear and nonlinear region prior to transition. As model problems, we choose Swept Hiemenz Flow and the DLR Transition Experiment. The primary stability results for Swept Hiemenz Flow agree very well with computations by Malik et al. For the DLR Experiment, the mean flow profiles are obtained by solving the boundary layer equations for the measured pressure distribution. Both linear and nonlinear results show very good agreement with the experiment.

Janke, Erik↗
NASA NTRS1961

Flight Investigation using Variable-Stability Airplanes of Minimum Stability Requirements for High-Speed, High-Altitude Vehicles

The pilot opinion of the flying qualities of vehicles covering a wide range of longitudinal dynamic characteristics has been determined by the use of a variable-stability airplane. Particular emphasis has been placed on determining the minimum level of stability and control characteristics that the pilot can cope with. There was considerable pilot learning associated with operation in the regions of poor stability characteristics. In the statically stable region the maximum acceptable value of time to damp to half amplitude of the longitudinal mode for normal operation was about 1 second. For emergency conditions the damping could be reduced to zero over most of the frequency range. The extreme lim it of controllability corresponded to a time to double amplitude of the oscillation of about 1 - 1/2 seconds. In the statically unstable region somewhat shorter times to double amplitude were acceptable to the pilots. The boundary for emergency operation corresponded roughly to time to double amplitude of about 2/3 second and the limit of controllability of about l/3 second.

McFadden, Norman M.↗
NASA NTRS1947

Flight-Test Evaluation of the Longitudinal Stability and Control Characteristics of 0.5-Scale Models of the Fairchild Lark Pilotless-Aircraft Configuration. Static Longitudinal Stability of Models with Wing Flap Deflections of 0 Deg and 15 Deg, TED No. NACA 2387

From flight tests of 0.5-scale models of the Fairchild Lark pilotless aircraft conducted at the flight test station of the Pilotless Aircraft Research Division at Wallops Island, Va., some evaluations of the static longitudinal stability were obtained by analysis of the short-period oscillations induced by the abrupt movement of the rudder elevators. The analysis shows that for the Lark configuration with wing flap deflections of 0 degrees and 15 degrees the static longitudinal stability decreases slightly up to the critical Mach number and than as the Mach number increases further the stability increases greatly.

Stone, David G.↗
NASA NTRS2006

Matlab Stability and Control Toolbox: Trim and Static Stability Module

This paper presents the technical background of the Trim and Static module of the Matlab Stability and Control Toolbox. This module performs a low-fidelity stability and control assessment of an aircraft model for a set of flight critical conditions. This is attained by determining if the control authority available for trim is sufficient and if the static stability characteristics are adequate. These conditions can be selected from a prescribed set or can be specified to meet particular requirements. The prescribed set of conditions includes horizontal flight, take-off rotation, landing flare, steady roll, steady turn and pull-up/ push-over flight, for which several operating conditions can be specified. A mathematical model was developed allowing for six-dimensional trim, adjustable inertial properties, asymmetric vehicle layouts, arbitrary number of engines, multi-axial thrust vectoring, engine(s)-out conditions, crosswind and gyroscopic effects.

Crespo, Luis G.↗
NASA NTRS2013

Estimation of Aerodynamic Stability Derivatives for Space Launch System and Impact on Stability Margins

This paper describes the techniques involved in determining the aerodynamic stability derivatives for the frequency domain analysis of the Space Launch System (SLS) vehicle. Generally for launch vehicles, determination of the derivatives is fairly straightforward since the aerodynamic data is usually linear through a moderate range of angle of attack. However, if the wind tunnel data lacks proper corrections then nonlinearities and asymmetric behavior may appear in the aerodynamic database coefficients. In this case, computing the derivatives becomes a non-trivial task. Errors in computing the nominal derivatives could lead to improper interpretation regarding the natural stability of the system and tuning of the controller parameters, which would impact both stability and performance. The aerodynamic derivatives are also provided at off nominal operating conditions used for dispersed frequency domain Monte Carlo analysis. Finally, results are shown to illustrate that the effects of aerodynamic cross axis coupling can be neglected for the SLS configuration studied

Pei, Jing↗
DOE OSTI2021

Stabilizing Anionic Redox Chemistry in a Mn-Based Layered Oxide Cathode Constructed by Li-Deficient Pristine State

Li-rich cathode materials are of significant interest for coupling anionic redox with cationic redox chemistry to achieve high-energy-density batteries. However, lattice oxygen loss and derived structure distortion would induce serious capacity loss and voltage decay, further hindering its practical application. Herein, a novel Li-rich cathode material, O3-type Li 0.6 [Li 0.2 Mn 0.8 ]O 2 , is developed with the pristine state displaying both a Li excess in the transition metal layer and a deficiency in the alkali metal layer. Benefiting from stable structure evolution and Li migration processes, not only can high reversible capacity (≈329 mAh g -1 ) be harvested but also irreversible/reversible anionic/cationic redox reactions are comprehensively assigned via the combination of in/ex situ spectroscopies. Furthermore, irreversible lattice oxygen loss and structure distortion are effectively restrained, resulting in long-term cycle stability (capacity drop of 0.045% per cycle, 500 cycles). Altogether, tuning the Li state in the alkali metal layer presents a promising way for modification of high-capacity Li-rich cathode candidates.

anionic redox reactions↗
DOE OSTI2021

Analysis of the SBP-SAT Stabilization for Finite Element Methods Part II: Entropy Stability

In the hyperbolic research community, there exists the strong belief that a continuous Galerkin scheme is notoriously unstable and additional stabilization terms have to be added to guarantee stability. In the first part of the series, the application of simultaneous approximation terms for linear problems is investigated where the boundary conditions are imposed weakly. By applying this technique, the authors demonstrate that a pure continuous Galerkin scheme is indeed linearly stable if the boundary conditions are imposed in the correct way. In this work, we extend this investigation to the nonlinear case and focus on entropy conservation. Here, by switching to entropy variables, we provide an estimation of the boundary operators also for nonlinear problems, that guarantee conservation. In numerical simulations, we verify our theoretical analysis.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2016

Stabilized FE simulation of prototype thermal-hydraulics problems with integrated adjoint-based capabilities

A critical aspect of applying modern computational solution methods to complex multiphysics systems of relevance to nuclear reactor modeling, is the assessment of the predictive capability of specific proposed mathematical models. In this respect the understanding of numerical error, the sensitivity of the solution to parameters associated with input data, boundary condition uncertainty, and mathematical models is critical. Additionally, the ability to evaluate and or approximate the model efficiently, to allow development of a reasonable level of statistical diagnostics of the mathematical model and the physical system, is of central importance. In this study we report on initial efforts to apply integrated adjoint-based computational analysis and automatic differentiation tools to begin to address these issues. The study is carried out in the context of a Reynolds averaged Navier–Stokes approximation to turbulent fluid flow and heat transfer using a particular spatial discretization based on implicit fully-coupled stabilized FE methods. Initial results are presented that show the promise of these computational techniques in the context of nuclear reactor relevant prototype thermal-hydraulics problems.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

First-principles study of the surface properties of y-LiAlO2: Stability and tritium adsorption

y-LiAlO2 enriched with 6Li isotope exhibits excellent performance under neutron radiation and is used in tritium-producing burnable absorber rods (TPBARs) to produce tritium (T, 3H) in pressurized water reactor (PWR). To better understand the 3H formation and diffusion on the surfaces, the first-principles calculations are performed to study the stability of y-LiAlO2 surface and the 3H adsorption on the surface. By considering all possible symmetrical stoichiometric and nonstoichiometric low-index surfaces, two most stable surfaces, one stoichiometric (100) and one nonstoichiometric (101), were identified. The 3H adsorption and diffusion on the most stable (100) surface were further explored, and the obtained results show that there are four stable sites (three O and one Al atop) for 3H adsorption. The calculated Bader charges of atoms reflect that 3H adsorption on the top of O site is a reduction process, while on the top of Al site is an oxidation one. Under low adsorption coverage of 1/4 per surface unit cell, 3H atoms are adsorbed on the most stable OA atop site. With increasing 3H diffused from bulk to surface, the AlG site is the second choice for 3H adsorption, and then the OB site. The coverage of 2/4 is the most favorable 3H adsorption state due to the counteracted charge transfer. When the coverage is up to 4/4, the interaction between 3H atoms leads to partial formation of T2 molecule that desorbs from surface. Therefore, T2 molecule should be the main product from the perfect surface of y-LiAlO2 at high 3H coverage.

Stability of y-LiAlO2 surface, Tritium-producing b↗