Controllability of higher order linear systems.
Dynamical system with time evolution described by second order linear differential equation in complex Banach space, discussing controllability
Fattorini, H. O.↗
SEARCH · Search NASA
Results for “Complex dynamical systems”
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Synthesis of stiffness and mass matrices from experimental vibration modes.
With highly complex structures, it is sometimes desirable to derive a dynamic model of the system from experimental vibration data. This paper presents algorithms for synthesizing the mass and stiffness matrices from experimentally derived modal data in a way which preserves the physical significance of the individual mass and stiffness elements. The synthesizing procedures allow for the incorporation of other mass and stiffness data, whether empirical or based on the analyst's insight. The mass and stiffness matrices are derived for a cantilever beam example and are compared with those obtained using earlier techniques.
Ross, R. G., Jr.↗
Monitoring complex trace-gas mixtures by long-path laser absorption spectrometry
Laser-based spectrophotometric methods, which have been proposed for the detection of trace concentrations of gaseous contaminants, include Raman and passive radiometry. The paper discusses a simple long-path laser absorption method which is capable of resolving complex mixtures of closely related trace contaminants at ppm levels. A number of species were selected which are most likely to accumulate in closed environments, such as submarines or long-duration manned space flights. Absorption coefficients at CO2 laser wavelengths were measured, accurate to + 3 per cent or better, for each of these species. This data base was then used to determine the presence and concentration of the contaminants in prepared mixtures of 12 to 15 gases. Computer programs have been developed which will permit a real-time analysis of the monitored atmosphere. Minimum detectable concentrations for individual species are generally in the ppm range, and are not seriously degraded by interferences even in complex mixtures. Estimates of the dynamic range of this monitoring technique for various system configurations and comparison with other methods of analysis are discussed
Green, B. D.↗
IUE observations of the peculiar star RX Puppis
The first set of high-dispersion UV observations of RX Pup are presented. Anomalous line profile structure observed in a number of high-excitation emission lines is discussed in context with a model that includes streams and complex mass motions in the system. Anomalies in high-excitation lines suggest dynamic activity in circumstellar material that probably has the form of rings and/or gas streamers between the cool giant and the hot companion. The continuum in low dispersion is fairly flat around 1200-2000 and rises toward longer wavelengths, and cannot be due to a star earlier than A0 II. Alternatively, it may be from an accretion disk. Photoionizing radiation may be due to the presence of an unseen, hot subdwarf with most probable effective temperature 75,000-90,000 K. Alternatively, it may be due to an accretion disk around a secondary with boundary layer temperature about 100,000 K.
Kafatos, M.↗
Dynamic Identification for Control of Large Space Structures
This is a compilation of reports by the one author on one subject. It consists of the following five journal articles: (1) A Parametric Study of the Ibrahim Time Domain Modal Identification Algorithm; (2) Large Modal Survey Testing Using the Ibrahim Time Domain Identification Technique; (3) Computation of Normal Modes from Identified Complex Modes; (4) Dynamic Modeling of Structural from Measured Complex Modes; and (5) Time Domain Quasi-Linear Identification of Nonlinear Dynamic Systems.
Ibrahim, S. R.↗
Real parameter margin computation for uncertain structural dynamic systems
This paper is concerned with the problem of computing real parameter margins for stabilized, structural dynamic systems with the masses, spring constants, and damping constants as uncertain parameters. Numerical algorithms for uncertain systems with multilinear parameters are investigated. It is shown that for a certain class of structural dynamic systems with small passive damping (e.g., flexible structures in space), the computational complexity of the problem can be avoided by modeling the system as a conservative plant, without loss of any practical significance.
Wie, Bong↗
Application of Lanczos vectors to control design of flexible structures, part 2
This report covers the period of the grant from January 1991 until its expiration in June 1992. Together with an Interim Report (Ref. 9), it summarizes the research conducted under NASA Grant NAG9-357 on the topic 'Application of Lanczos Vectors to Control Design of Flexible Structures.' The research concerns various ways to obtain reduced-order mathematical models of complex structures for use in dynamics analysis and in the design of control systems for these structures. This report summarizes the research.
Craig, Roy R., Jr.↗
Multiprocessor Adaptive Control Of A Dynamic System
Architecture for fully autonomous digital electronic control system developed for use in identification and adaptive control of dynamic system. Architecture modular and hierarchical. Combines relatively simple, standardized processing units into complex parallel-processing subsystems. Although architecture based on neural-network concept, processing units themselves not neural networks; processing units implemented by programming of currently available microprocessors.
Juang, Jer-Nan↗
Stage Separation Performance Analysis Project
Stage separation process is an important phenomenon in multi-stage launch vehicle operation. The transient flowfield coupled with the multi-body systems is a challenging problem in design analysis. The thermodynamics environment with burning propellants during the upper-stage engine start in the separation processes adds to the complexity of the-entire system. Understanding the underlying flow physics and vehicle dynamics during stage separation is required in designing a multi-stage launch vehicle with good flight performance. A computational fluid dynamics model with the capability to coupling transient multi-body dynamics systems will be a useful tool for simulating the effects of transient flowfield, plume/jet heating and vehicle dynamics. A computational model using generalize mesh system will be used as the basis of this development. The multi-body dynamics system will be solved, by integrating a system of six-degree-of-freedom equations of motion with high accuracy. Multi-body mesh system and their interactions will be modeled using parallel computing algorithms. Adaptive mesh refinement method will also be employed to enhance solution accuracy in the transient process.
Chen, Yen-Sen↗
Load Balancing Strategies for Multi-Block Overset Grid Applications
The multi-block overset grid method is a powerful technique for high-fidelity computational fluid dynamics (CFD) simulations about complex aerospace configurations. The solution process uses a grid system that discretizes the problem domain by using separately generated but overlapping structured grids that periodically update and exchange boundary information through interpolation. For efficient high performance computations of large-scale realistic applications using this methodology, the individual grids must be properly partitioned among the parallel processors. Overall performance, therefore, largely depends on the quality of load balancing. In this paper, we present three different load balancing strategies far overset grids and analyze their effects on the parallel efficiency of a Navier-Stokes CFD application running on an SGI Origin2000 machine.
Djomehri, M. Jahed↗
Combustion Stability Evaluation of Artificial Disturbance Dynamic Response
General guidelines are provided in CPIA Publication 6551 for evaluation of the response due to an artificial disturbance, however the guideline also allows for ambiguous interpretation. Stability rating devices that produce an artificial disturbance are traditionally explosive bombs and pulse guns. This paper reviews a recently developed objective process that can be applied consistently in the reduction of artificial disturbance dynamic data. It also examines three methods of response evaluation. The first method examines the response of a specific mode of interest and requires data filtering encompassing that mode. The second method examines the response of a specific mode of interest and its nonlinear components and requires a more complex filtering scheme. The third method examines the response of the entire dynamic system and consists of examining a wide bandwidth consisting of multiple modes of interest. The evaluation process is described and the advantages and disadvantages of the evaluation methods are discussed. Signal processing is used as a tool in quantifying the assessment, clearly as an improvement from the subjective heritage approach consisting primarily of engineering judgement. Data for several engines and components have been compiled and evaluated using these methods. A summary of these combustion devices is provided and observations are discussed.
Casiano, M. J.↗
Proof-of-Concept for a Long-Term Health Metric to Quantify End of Mission Health Status in Astronauts
NASA has long used Probabilistic Risk Assessment (PRA) when high-stakes decisions need to be made about complex systems. For spaceflight medical risk, the Human Research Program’s Medical Extensible Dynamic Probabilistic Risk Assessment Tool (MEDPRAT) is a significant step towards robustly quantifying the risk to crew health during exploration missions. However, there remains a significant gap in the ability to comprehensively characterize and assess risk across the disparate functionalities and capabilities which comprise the entire Crew Health and Performance (CHP) system. To fill this gap, the Crew Health and Performance – Probabilistic Risk Assessment (CHP-PRA) project aims to perform risk characterization for the CHP system by assessing performance risk in addition to medical risk. This effort also includes quantifying Long-Term Health (LTH) risk in addition to in-mission risk outcomes within the CHP-PRA results. LTH risk encompasses the timeframe from immediately post-flight, through the rest of an astronaut’s career, through retirement, and until death. A proof-of-concept LTH risk metric is based on medical condition end-state, as defined by the Evidence Library, capturing the spaceflight specific medical impacts persisting into post-flight[1]. Condition outcomes in the Evidence Library progress through three Clinical Phases (CP): the diagnostic phase (CP1), the treatment/convalescent phase (CP2), and the end-state phase (CP3) which represents the detrimental effects of the condition after the crew member has recovered to the maximal extent. Each CP has an associated Task Impairment (TI), defined as the degree of crew incapacity due to experiencing the condition, and is quantified with a 0-1 range. Conditions with an associated CP3 (e.g. Sepsis, Traumatic Hypovolemic Shock, Sudden Cardiac Arrest, etc.) typically have serious consequences that can cause an astronaut to be fully or partially debilitated throughout the remainder of the mission. Consequently, the Cumulative CP3 TI End-of-Mission Health Status Metric is developed by CHP-PRA to quantify the cumulative effects of all conditions which progressed to the CP3 state throughout the entirety of the mission. Hence, this End-of-Mission Health Status Metric attempts to serve as an indicator of an astronaut’s health state at the time of landing. The severity of the lingering effects of in-mission medical events are dependent on mission activities and the level of available in-mission medical care. This allows the associated cumulative TI metric to be used in comparison with the crew’s end of mission health status for different levels of in-mission resources. This presentation provides the strategy for using CP3 as an LTH metric component, as well as a proof-of-concept demonstration of LTH risk characterization using this component.
long term health↗
POD Model Reconstruction for Gray-Box Fault Detection
Proper orthogonal decomposition (POD) is the mathematical basis of a method of constructing low-order mathematical models for the "gray-box" fault-detection algorithm that is a component of a diagnostic system known as beacon-based exception analysis for multi-missions (BEAM). POD has been successfully applied in reducing computational complexity by generating simple models that can be used for control and simulation for complex systems such as fluid flows. In the present application to BEAM, POD brings the same benefits to automated diagnosis. BEAM is a method of real-time or offline, automated diagnosis of a complex dynamic system.The gray-box approach makes it possible to utilize incomplete or approximate knowledge of the dynamics of the system that one seeks to diagnose. In the gray-box approach, a deterministic model of the system is used to filter a time series of system sensor data to remove the deterministic components of the time series from further examination. What is left after the filtering operation is a time series of residual quantities that represent the unknown (or at least unmodeled) aspects of the behavior of the system. Stochastic modeling techniques are then applied to the residual time series. The procedure for detecting abnormal behavior of the system then becomes one of looking for statistical differences between the residual time series and the predictions of the stochastic model.
Park, Han↗
Parameter estimation for distributed parameter models of complex, flexible structures
Distributed parameter modeling of structural dynamics has been limited to simple spacecraft configurations because of the difficulty of handling several distributed parameter systems linked at their boundaries. Although there is other computer software able to generate such models or complex, flexible spacecraft, unfortunately, neither is suitable for parameter estimation. Because of this limitation the computer software PDEMOD is being developed for the express purposes of modeling, control system analysis, parameter estimation and structure optimization. PDEMOD is capable of modeling complex, flexible spacecraft which consist of a three-dimensional network of flexible beams and rigid bodies. Each beam has bending (Bernoulli-Euler or Timoshenko) in two directions, torsion, and elongation degrees of freedom. The rigid bodies can be attached to the beam ends at any angle or body location. PDEMOD is also capable of performing parameter estimation based on matching experimental modal frequencies and static deflection test data. The underlying formulation and the results of using this approach for test data of the Mini-MAST truss will be discussed. The resulting accuracy of the parameter estimates when using such limited data can impact significantly the instrumentation requirements for on-orbit tests.
Taylor, Lawrence W., Jr.↗
An experimental comparison of several current viscoplastic constitutive models at elevated temperature
Four current viscoplastic models are compared experimentally for Inconel 718 at 593 C. This material system responds with apparent negative strain rate sensitivity, undergoes cyclic work softening, and is susceptible to low cycle fatigue. A series of tests were performed to create a data base from which to evaluate material constants. A method to evaluate the constants is developed which draws on common assumptions for this type of material, recent advances by other researchers, and iterative techniques. A complex history test, not used in calculating the constants, is then used to compare the predictive capabilities of the models. The combination of exponentially based inelastic strain rate equations and dynamic recovery is shown to model this material system with the greatest success. The method of constant calculation developed was successfully applied to the complex material response encountered. Backstress measuring tests were found to be invaluable and to warrant further development.
James, G. H.↗
Tethered elevator and platforms as space station facilities: Systems studies and demonstrative experiments
Several key concepts of the science and applications tethered platforms were studied. Some conclusions reached are herein listed. Tether elevator and platform could improve the space station scientific and applicative capabilities. The space elevator presents unique characteristics as microgravity facility and as a tethered platform servicing vehicle. Pointing platforms could represent a new kind of observation facility for large class of payloads. The dynamical, control and technological complexity of these concepts advised demonstrative experiments. The on-going tethered satellite system offers the opportunity to perform such experiments. And feasibility studies are in progress.
Source record↗
Interactive orbital proximity operations planning system
An interactive graphical proximity operations planning system was developed, which allows on-site design of efficient, complex, multiburn maneuvers in a dynamic multispacecraft environment. Maneuvering takes place in and out of the orbital plane. The difficulty in planning such missions results from the unusual and counterintuitive character of orbital dynamics and complex time-varying operational constraints. This difficulty is greatly overcome by visualizing the relative trajectories and the relevant constraints in an easily interpretable graphical format, which provides the operator with immediate feedback on design actions. The display shows a perspective bird's-eye view of a Space Station and co-orbiting spacecraft on the background of the Station's orbital plane. The operator has control over the two modes of operation: a viewing system mode, which enables the exporation of the spatial situation about the Space Station and thus the ability to choose and zoom in on areas of interest; and a trajectory design mode, which allows the interactive editing of a series of way points and maneuvering burns to obtain a trajectory that complies with all operational constraints. A first version of this display was completed. An experimental program is planned in which operators will carry out a series of design missions which vary in complexity and constraints.
Grunwald, Arthur J.↗
Dynamics and Clearance Analysis of NASA's Space Launch System Block-1 and Block 1B Solid Rocket Booster Separation Event
NASA’s Space Launch System (SLS) solid rocket booster separation event is an essential area of study requiring high fidelity modelling to capture the complexity of an intra-atmospheric stage separation event. The setup and analysis for this event leveraged the NASA-developed CLVTOPS multi-body dynamics toolchain to model aerodynamics at the separation event, booster thrust tailoff, and Core Stage engine throttling in addition to the separation system itself (booster separation motors (BSMs), pyrotechnic bolts and struts). The approach documented here will give a brief background on the CLVTOPS toolchain, how key input models are integrated and verified, and how results are quantified using an ordered-statistics approach. Specific areas discussed herein address the performance-to-orbit realized by adjusting the delay time between the separation cue and the actual separation event, and how the orientation of the aft BSMs was tuned to address small clearances between the aft diagonal attach struts and the Core Stage. Post-flight results from the inaugural Artemis I flight are also shown, and validation is performed between predicted vs. actual separation dynamics and clearances. Challenging night launch conditions necessitated comparisons that were more qualitative in nature, but still showed very good agreement to pre-flight predictions.
Carole J Addona↗