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Results for “Simulation optimization”

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 901 records · Page 50

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NASA NTRS1988

Conceptual designs and computer models of imaging radiometers for earth observations

An analytical model is developed based on engineering principles which can be used to predict the performance of spaceborne electro-optical remote sensors. Computer simulations and trade-off studies can be performed with this model to determine optimal sensor performance and design parameters. Computer algorithms were developed from which LOTUS spreadsheet macros were written. Computer simulations were performed to determine the performance characteristics and design parameters for the Moderate Resolution Imaging Spectrometer Nadir (MODIS-N) currently under development at NASA/Goddard Space Flight Center.

Montgomery, Harry E.↗

NASA NTRS1991

Concurrent tailoring of fabrication process and interphase layer to reduce residual stresses in metal matrix composites

A methodology is presented to reduce the residual matrix stresses in continuous fiber metal matrix composites (MMC) by optimizing the fabrication process and interphase layer characteristics. The response of the fabricated MMC was simulated based on nonlinear micromechanics. Application cases include fabrication tailoring, interphase tailoring, and concurrent fabrication-interphase optimization. Two composite systems, silicon carbide/titanium and graphite/copper, are considered. Results illustrate the merits of each approach, indicate that concurrent fabrication/interphase optimization produces significant reductions in the matrix residual stresses and demonstrate the strong coupling between fabrication and interphase tailoring.

Saravanos, D. A.↗

NASA NTRS1966

Analysis of cryogenic propellant logistics.

Large launch vehicle cryogenic propellant logistics including storage and production capacity optimization, cost and heat loss analyses by computer simulation

PROPELLANT STORAGE↗

NASA NTRS1972

A feedback control model for network flow with multiple pure time delays

A control model describing a network flow hindered by multiple pure time (or transport) delays is formulated. Feedbacks connect each desired output with a single control sector situated at the origin. The dynamic formulation invokes the use of differential difference equations. This causes the characteristic equation of the model to consist of transcendental functions instead of a common algebraic polynomial. A general graphical criterion is developed to evaluate the stability of such a problem. A digital computer simulation confirms the validity of such criterion. An optimal decision making process with multiple delays is presented.

Press, J.↗

NASA NTRS1972

Design of a celestial Thomson-scattering X-ray polarimeter.

A general discussion of the scientific importance and status of stellar X-ray polarimetry is presented. A stellar X-ray polarimeter designed to fit into the bottom half of the NASA OSO-1 wheel compartment or other similar spacecraft is described. In this design, the linear polarization is obtained as a function of energy. The sensitivity of the polarimeter in the 4-24 keV energy range was optimized with the aid of a Monte Carlo simulation computer program and is given for several important celestial X-ray sources. Estimates of sensitivity thresholds for a much larger polarimeter, suitable for flight in the NASA High-Energy Astronomy Observatory (HEAO), are also given. The minimum detectable polarization for several X-ray sources is given.

Landecker, P. B.↗

NASA NTRS1981

A model for the submarine depthkeeping team

The most difficult task the depthkeeping team must face occurs during periscope-depth operations during which they may be required to maintain a submarine several hundred feet long within a foot of ordered depth and within one-half degree of ordered pitch. The difficulty is compounded by the facts that wave generated forces are extremely high, depth and pitch signals are very noisy and submarine speed is such that overall dynamics are slow. A mathematical simulation of the depthkeeping team based on the optimal control models is described. A solution of the optimal team control problem with an output control restriction (limited display to each controller) is presented.

Ware, J. R.↗

NASA NTRS1985

Superlattices and multilayer structures for high efficiency solar cells

Possible applications of superlattices to photovoltaic structures are discussed. A new concept based on doping superstructures (NIPI) can be exploited to significantly reduce recombination losses in III-V compound solar cells. A novel multijunction structure with lateral current transport is proposed. A computer simulation has been performed which shows that by optimizing the multilayer structure, short circuit current is substantially increased with minimum drop in open circuit voltage. An additional advantage of the structure is enhanced radiation tolerance. It is anticipated that this multilayer structure can be incorporated in multibandgap cells to achieve high efficiencies.

Wagner, M.↗

NASA NTRS1990

Assignment Of Finite Elements To Parallel Processors

Elements assigned approximately optimally to subdomains. Mapping algorithm based on simulated-annealing concept used to minimize approximate time required to perform finite-element computation on hypercube computer or other network of parallel data processors. Mapping algorithm needed when shape of domain complicated or otherwise not obvious what allocation of elements to subdomains minimizes cost of computation.

Salama, Moktar A.↗

NASA NTRS1989

A control approach for robots with flexible links and rigid end-effectors

Multiarm flexible robots with dexterous end effectors are currently being considered in such tasks as satellite retrieval, servicing and repair where a two phase problem can be identified: Phase 1, robot positioning in space; Phase 2, object retrieval. Some issues in Phase 1 regarding modelling and control strategies for a robotic system comprised of along flexible arm and a rigid three-link end effector are presented. The control objective is to maintain the last (rigid) link stationary in space in the presence of an additive disturbance caused by the flexible energy in the first link after a positioning maneuver has been accomplished. Several configuration strategies can be considered, and optimal decentralized servocompensators can be designed. Preliminary computer simulations are included for a simple proportional controller to illustrate the approach.

Barbieri, Enrique↗

NASA NTRS1990

Ascent guidance algorithm using lidar wind measurements

The formulation of a general nonlinear programming guidance algorithm that incorporates wind measurements in the computation of ascent guidance steering commands is discussed. A nonlinear programming (NLP) algorithm that is designed to solve a very general problem has the potential to address the diversity demanded by future launch systems. Using B-splines for the command functional form allows the NLP algorithm to adjust the shape of the command profile to achieve optimal performance. The algorithm flexibility is demonstrated by simulation of ascent with dynamic loading constraints through a set of random wind profiles with and without wind sensing capability.

Cramer, Evin J.↗

NASA NTRS1993

Design efficiency evaluation for transonic airfoil optimization - A case for Navier-Stokes design

A constrained-optimization design method which improves the aerodynamic performance of transonic airfoils is evaluated from a design-quality and design-efficiency viewpoint. Design efficiency is a measure of the performance improvement and the design time (CPU time). Total-airfoil design and upper-surface design are performed using the Euler and Navier-Stokes equations with several grids, and are evaluated using the Navier-Stokes equations to determine the anticipated physical design response. Even though the cost of the Euler design is lower than Navier-Stokes design, the Navier-Stokes evaluation indicates that the Euler design does not necessarily improve the aerodynamic performance. Therefore, the design optimization should be based on an accurate flow simulation to achieve an actual performance improvement, and the design time is a secondary concern.

Hager, J. O.↗

NASA NTRS1993

Measuring human performance on NASA's microgravity aircraft

Measuring human performance in a microgravity environment will aid in identifying the design requirements, human capabilities, safety, and productivity of future astronauts. The preliminary understanding of the microgravity effects on human performance can be achieved through evaluations conducted onboard NASA's KC-135 aircraft. These evaluations can be performed in relation to hardware performance, human-hardware interface, and hardware integration. Measuring human performance in the KC-135 simulated environment will contribute to the efforts of optimizing the human-machine interfaces for future and existing space vehicles. However, there are limitations, such as limited number of qualified subjects, unexpected hardware problems, and miscellaneous plane movements which must be taken into consideration. Examples for these evaluations, the results, and their implications are discussed in the paper.

Morris, Randy B.↗

NASA NTRS1995

A concept for adaptive performance optimization on commercial transport aircraft

An adaptive control method is presented for the minimization of drag during flight for transport aircraft. The minimization of drag is achieved by taking advantage of the redundant control capability available in the pitch axis, with the horizontal tail used as the primary surface and symmetric deflection of the ailerons and cruise flaps used as additional controls. The additional control surfaces are excited with sinusoidal signals, while the altitude and velocity loops are closed with guidance and control laws. A model of the throttle response as a function of the additional control surfaces is formulated and the parameters in the model are estimated from the sensor measurements using a least squares estimation method. The estimated model is used to determine the minimum drag positions of the control surfaces. The method is presented for the optimization of one and two additional control surfaces. The adaptive control method is extended to optimize rate of climb with the throttle fixed. Simulations that include realistic disturbances are presented, as well as the results of a Monte Carlo simulation analysis that shows the effects of changing the disturbance environment and the excitation signal parameters.

Jackson, Michael R.↗

NASA NTRS2008

Toward Optimal Transport Networks

Strictly evolutionary approaches to improving the air transport system a highly complex network of interacting systems no longer suffice in the face of demand that is projected to double or triple in the near future. Thus evolutionary approaches should be augmented with active design methods. The ability to actively design, optimize and control a system presupposes the existence of predictive modeling and reasonably well-defined functional dependences between the controllable variables of the system and objective and constraint functions for optimization. Following recent advances in the studies of the effects of network topology structure on dynamics, we investigate the performance of dynamic processes on transport networks as a function of the first nontrivial eigenvalue of the network's Laplacian, which, in turn, is a function of the network s connectivity and modularity. The last two characteristics can be controlled and tuned via optimization. We consider design optimization problem formulations. We have developed a flexible simulation of network topology coupled with flows on the network for use as a platform for computational experiments.

Alexandrov, Natalia↗

NASA NTRS2008

The Limits of Coding with Joint Constraints on Detected and Undetected Error Rates

We develop a remarkably tight upper bound on the performance of a parameterized family of bounded angle maximum-likelihood (BA-ML) incomplete decoders. The new bound for this class of incomplete decoders is calculated from the code's weight enumerator, and is an extension of Poltyrev-type bounds developed for complete ML decoders. This bound can also be applied to bound the average performance of random code ensembles in terms of an ensemble average weight enumerator. We also formulate conditions defining a parameterized family of optimal incomplete decoders, defined to minimize both the total codeword error probability and the undetected error probability for any fixed capability of the decoder to detect errors. We illustrate the gap between optimal and BA-ML incomplete decoding via simulation of a small code.

Undetected Error Rate↗

NASA NTRS2011

A Model-Based Study of On-Board Data Processing Architecture for Balloon-Borne Aurora Observation

This paper discusses an application of ISAAC design methodology to a balloon-borne payload electronic system for aurora observation. The methodology is composed of two phases, high level design and low level implementation, the focus of this paper is on the high level design. This paper puts the system architecture in the context of a balloon based application but it can be generalized to any airborne/space-borne application. The system architecture includes a front-end detector, its corresponding data processing unit, and a controller. VisualSim has been used to perform modeling and simulations to explore the entire design space, finding optimal solutions that meet system requirements.

modeling↗

NASA NTRS2012

JELC-LITE: Unconventional Instructional Design for Special Operations Training

Current special operations staff training is based on the Joint Event Life Cycle (JELC). It addresses operational level tasks in multi-week, live military exercises which are planned over a 12 to 18 month timeframe. As the military experiences changing global mission sets, shorter training events using distributed technologies will increasingly be needed to augment traditional training. JELC-Lite is a new approach for providing relevant training between large scale exercises. This new streamlined, responsive training model uses distributed and virtualized training technologies to establish simulated scenarios. It keeps proficiency levels closer to optimal levels -- thereby reducing the performance degradation inherent in periodic training. It can be delivered to military as well as under-reached interagency groups to facilitate agile, repetitive training events. JELC-Lite is described by four phases paralleling the JELC, differing mostly in scope and scale. It has been successfully used with a Theater Special Operations Command and fits well within the current environment of reduced personnel and financial resources.

Friedman, Mark↗

NASA NTRS2015

Enhanced Engine Performance During Emergency Operation Using a Model-Based Engine Control Architecture

This paper discusses the design and application of model-based engine control (MBEC) for use during emergency operation of the aircraft. The MBEC methodology is applied to the Commercial Modular Aero-Propulsion System Simulation 40,000 (CMAPSS40,000) and features an optimal tuner Kalman Filter (OTKF) to estimate unmeasured engine parameters, which can then be used for control. During an emergency scenario, normally-conservative engine operating limits may be relaxed to increase the performance of the engine and overall survivability of the aircraft; this comes at the cost of additional risk of an engine failure. The MBEC architecture offers the advantage of estimating key engine parameters that are not directly measureable. Estimating the unknown parameters allows for tighter control over these parameters, and on the level of risk the engine will operate at. This will allow the engine to achieve better performance than possible when operating to more conservative limits on a related, measurable parameter.

control theory↗